User activity detection

Abstract

The embodiment of the invention relates to a method and device for user activity detection (UAD). A terminal device receives a configuration associated with a set of subcarriers from a network device in a radio access network, where the set of subcarriers is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicates activity information of an active terminal device set in the terminal device set; and transmitting a modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the set of subcarriers with symbols, and the modulated conjugate symmetric signal includes sparse multicarrier (MC-FTN) conjugate symmetric signaling that is faster than Nyquist. In this way, a new solution for reducing latency and measurement resource costs for UAD for large-scale access is provided.

Description

Technical Field

[0001] Various example embodiments relate to the field of telecommunications, and more particularly to methods, devices, apparatuses, and computer-readable storage media for user activity detection (UAD). Background Art

[0002] With the development of communication technologies, future society will become digital and data-driven, for example, through interconnected industries, intelligent transportation systems, smart cities, etc., thus providing greater convenience for daily life and industrial development. Machine-type communication (MTC) can support a large number of connections, thus providing a possible way to realize such a digital and data-driven society. At the same time, the further development of society will impose new and more stringent requirements on wireless connections. There is still a need to enhance MTC for UAD. Summary of the Invention

[0003] Generally, the example embodiments of the present disclosure provide a solution for performing UAD.

[0004] In a first aspect, a terminal device in a radio access network is provided. The terminal device may include at least one processor and at least one memory storing instructions. When executed by the at least one processor, the instructions cause the terminal device to at least: receive, from a network device in the radio access network, a configuration associated with a subcarrier set, where the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active terminal device set in the set of terminal devices; and transmit a modulated conjugate symmetric signal to the network device, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the subcarrier set with symbols, and the modulated conjugate symmetric signal includes faster-than-Nyquist sparse multi-carrier (MC-FTN) conjugate symmetric signaling.

[0005] In a second aspect, a network device in a radio access network is provided. The network device may include at least one processor and at least one memory storing instructions. When executed by the at least one processor, the instructions cause the terminal device to at least: transmit, to a set of terminal devices in the radio access network, a configuration associated with a set of subcarriers, where the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; receive, from the active set of terminal devices, a superimposed signal associated with the modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating, respectively, the set of subcarriers associated with the active set of terminal devices with a set of symbols corresponding to the active set of terminal devices and includes sparse MC-FTN conjugate symmetric signaling; and identify, from the set of terminal devices, the active set of terminal devices based on the received superimposed signal.

[0006] In a third aspect, a method is provided. The method may include receiving, at a terminal device, from a network device in a radio access network, a configuration associated with a set of subcarriers, where the set of subcarriers is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; and transmitting, to the network device, a modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the set of subcarriers with symbols, and the modulated conjugate symmetric signal includes sparse MC-FTN conjugate symmetric signaling.

[0007] In a fourth aspect, a method is provided. The method may include transmitting, at a network device, to a set of terminal devices in a radio access network, a configuration associated with a set of subcarriers, where the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; receiving, from the active set of terminal devices, a superimposed signal associated with the modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating, respectively, the set of subcarriers associated with the active set of terminal devices with a set of symbols corresponding to the active set of terminal devices and includes sparse MC-FTN conjugate symmetric signaling; and identifying, from the set of terminal devices, the active set of terminal devices based on the received superimposed signal.

[0008] In a fifth aspect, an apparatus is provided. The apparatus may include: means for receiving, at a terminal device, a configuration associated with a subcarrier set from a network device in a radio access network, where the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; and means for transmitting the modulated conjugate symmetric signal to the network device, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the subcarrier set with symbols, and the modulated conjugate symmetric signal includes sparse MC-FTN conjugate symmetric signaling.

[0009] In a sixth aspect, an apparatus is provided. The apparatus may include: means for transmitting, at a network device, a configuration associated with a subcarrier set to a set of terminal devices in a radio access network, where the subcarrier set is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; means for receiving, from the active set of terminal devices, a superimposed signal associated with the modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating, respectively, the subcarrier set associated with the active set of terminal devices with a symbol set corresponding to the active set of terminal devices and includes sparse MC-FTN conjugate symmetric signaling; and means for identifying, based on the received superimposed signal, the active set of terminal devices from the set of terminal devices.

[0010] In a seventh aspect, a non-transitory computer-readable medium is provided, which includes program instructions for causing an apparatus to at least execute the method according to any one of the third aspect to the fourth aspect above.

[0011] In an eighth aspect, a computer program including instructions is provided, which when executed by an apparatus causes the apparatus to at least: receive a configuration associated with a subcarrier set from a network device in a radio access network, where the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; and transmit a modulated conjugate symmetric signal to the network device, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the subcarrier set with symbols, and the modulated conjugate symmetric signal includes sparse MC-FTN conjugate symmetric signaling.

[0012] In a ninth aspect, there is provided a computer program comprising instructions which, when executed by a device, cause the device to at least: transmit to a set of terminal devices in a radio access network a configuration associated with a set of subcarriers, wherein the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; receive from the active set of terminal devices a superimposed signal associated with the modulated conjugate symmetric signal, wherein the modulated conjugate symmetric signal is generated by modulating the set of subcarriers associated with the active set of terminal devices with a set of symbols corresponding to the active set of terminal devices, respectively, and comprises sparse MC-FTN conjugate symmetric signaling; and identify the active set of terminal devices from the set of terminal devices based on the received superimposed signal.

[0013] In a tenth aspect, there is provided a terminal device in a radio access network. The terminal device may comprise: receiving circuitry configured to receive from a network device in the radio access network a configuration associated with a set of subcarriers, wherein the set of subcarriers is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; and transmitting circuitry configured to transmit to the network device a modulated conjugate symmetric signal, wherein the modulated conjugate symmetric signal is generated by modulating subcarriers from the set of subcarriers with symbols, and the modulated conjugate symmetric signal comprises sparse MC-FTN conjugate symmetric signaling.

[0014] In an eleventh aspect, there is provided a network device in a radio access network. The network device may comprise: transmitting circuitry configured to transmit to a set of terminal devices in the radio access network a configuration associated with a set of subcarriers, wherein the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; receiving circuitry configured to receive from the active set of terminal devices a superimposed signal associated with the modulated conjugate symmetric signal, wherein the modulated conjugate symmetric signal is generated by modulating the set of subcarriers associated with the active set of terminal devices with a set of symbols corresponding to the active set of terminal devices, respectively, and comprises sparse MC-FTN conjugate symmetric signaling; and identifying circuitry configured to identify the active set of terminal devices from the set of terminal devices based on the received superimposed signal.

[0015] It should be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily apparent through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Some example embodiments will now be described with reference to the drawings, in which:

[0017] Figure 1A An example communication network in which embodiments of the present disclosure can be implemented is shown;

[0018] Figure 1B A schematic diagram showing an effective uplink (UL) channel impulse response (CIR) in a random access scenario according to some embodiments of the present disclosure;

[0019] Figure 2 A schematic diagram showing a communication process according to some embodiments of the present disclosure;

[0020] Figure 3A An example diagram showing a data signal and a UAD signal in the time domain according to some embodiments of the present disclosure;

[0021] Figure 3B An example diagram showing a multiplexing structure of a data signal and a UAD signal in the frequency domain according to some embodiments of the present disclosure;

[0022] Figure 4A An example diagram showing a phase estimation error based on partial prior knowledge on a corresponding UL channel according to some embodiments of the present disclosure;

[0023] Figure 4B An example diagram showing a phase compensation factor design according to some embodiments of the present disclosure;

[0024] Figure 4C An example diagram showing a reconstruction condition of the sign of the imaginary part of a received symbol in a subcarrier according to some embodiments of the present disclosure;

[0025] Figure 5 An example diagram showing a transmission process of a modulated conjugate symmetric signal according to some embodiments of the present disclosure;

[0026] Figure 6 An example diagram showing a process of generating a discrete-time baseband conjugate symmetric signal according to some embodiments of the present disclosure;

[0027] Figure 7A An example diagram showing the transmission of a downlink (DL) beacon signal in a communication network according to some embodiments of the present disclosure;

[0028] Figure 7B An example diagram showing a pre-compensation process of a UL carrier phase offset (CPO) according to some embodiments of the present disclosure;

[0029] Figure 8An example diagram showing the receiving process of superimposed MC FTN conjugate symmetric signaling according to some embodiments of the present disclosure;

[0030] Figure 9 An example implementation of a process for a joint UAD and timing acquisition algorithm according to an embodiment of the present disclosure is shown;

[0031] Figure 10 An example implementation of a process for communication according to an embodiment of the present disclosure is shown;

[0032] Figure 11A An example implementation of MC-FTN conjugate symmetric signaling in the frequency domain according to some embodiments of the present disclosure is shown;

[0033] Figure 11B An example diagram of a traditional physical layer random access channel (PRACH) signal in the frequency domain is shown;

[0034] Figure 11C An example diagram of MC-FTN conjugate symmetric signals and traditional PRACH signals in the time domain according to some embodiments of the present disclosure is shown;

[0035] Figure 12A and Figure 12B A comparison of the joint UAD and timing acquisition performance between MC-FTN conjugate symmetric signaling and a traditional PRACH process via Zadoff-Chu (ZC) sequences under the same time-frequency resources according to some embodiments of the present disclosure is shown;

[0036] Figure 13 A flowchart of a method implemented at a terminal device according to some embodiments of the present disclosure is shown;

[0037] Figure 14 A flowchart of a method implemented at a network device according to some embodiments of the present disclosure is shown;

[0038] Figure 15 A simplified block diagram of a device suitable for implementing embodiments of the present disclosure is shown; and

[0039] Figure 16 A block diagram of an example computer-readable medium according to some embodiments of the present disclosure is shown.

[0040] Throughout the drawings, the same or similar reference numerals denote the same or similar elements. Detailed Description

[0041] The principles of the present disclosure will now be described with reference to some example embodiments. It should be understood that these embodiments are described for illustrative purposes only and help those skilled in the art to understand and implement the present disclosure, without imposing any limitation on the scope of the present disclosure. The disclosure described herein can be implemented in various ways other than those described below.

[0042] In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0043] References in this disclosure to "one embodiment", "an embodiment", "example embodiment", etc., indicate that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment must include that particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, those skilled in the art will recognize that it is within their knowledge to affect such feature, structure, or characteristic in connection with other embodiments (whether or not explicitly described).

[0044] It should be understood that although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the example embodiments, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element. As used herein, the term "and / or" includes any and all combinations of one or more of the listed terms.

[0045] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the example embodiments. As used herein, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are also intended to include the plural forms. It should also be understood that the terms "comprises", "comprising", "has", "having", "covers", and / or "covering", when used herein, specify the presence of the stated features, elements, and / or components, etc., but do not preclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. As used herein, "at least one of the following: <list of two or more elements>" and "at least one of <list of two or more elements>" and similar phrases, where the list of two or more elements is joined by "and" and "or", mean at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0046] As used in this application, the term "circuitry" may refer to one or more or all of the following:

[0047] (a) Implementations achieved only by hardware circuits (such as implementations only in analog and / or digital circuit devices), and

[0048] (b) Combinations of hardware circuits and software, such as (where applicable):

[0049] (i) Combinations of analog and / or digital hardware circuits and software / firmware, and

[0050] (ii) Any part of a hardware processor (including a digital signal processor), software, and memory with software, which work together to enable a device such as a mobile phone or a server to perform various functions), and

[0051] (c) Hardware circuits and / or processors that require software (such as firmware) to operate, such as a microprocessor or a part of a microprocessor, but the software may not exist when it is not required to operate.

[0052] This definition of circuit device applies to all uses of this term in this application, including in any claim. As a further example, as used in this application, the term circuit device also includes implementations of only hardware circuits or processors (or multiple processors) or a part of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuit device also includes, for example and if applicable to a specific claim element, a baseband integrated circuit or a processor integrated circuit for a mobile device, or a similar integrated circuit in a server, a cellular network device, or other computing or network devices.

[0053] As used herein, the term "communication network" refers to a network that follows any suitable communication standard, such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), NarrowBand Internet of Things (NB-IoT), etc. In addition, communication between a terminal device and a network device in a communication network can be performed according to any suitable generation of communication protocol, including but not limited to the third generation (3G), fourth generation (4G), 4.5G, fifth generation (5G), or further sixth generation (6G) communication protocols, and / or any other protocol known currently or to be developed in the future. Embodiments of the present disclosure can be applied to various communication systems. Considering the rapid development of communication, of course, there will also be future types of communication technologies and systems to which the present disclosure can be applied. It should not be regarded as limiting the scope of the present disclosure to the foregoing systems.

[0054] As used herein, the term "network device" refers to a node in a communication network through which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, Node B (NodeB or NB), evolved Node B (eNodeB or eNB), NR NB (also referred to as gNB), remote radio unit (RRU), radio header (RH), remote radio header (RRH), relay, low-power node (such as femto, pico, etc.), depending on the terminology and technology applied.

[0055] The term "terminal device" refers to any end device capable of wireless communication. By way of example and not limitation, the terminal device may also be referred to as a communication device, user equipment (UE), subscriber station (SS), portable subscriber station, mobile station (MS), or access terminal (AT). The terminal device may include, but is not limited to, mobile phones, cellular phones, smart phones, IP voice (VoIP) phones, wireless local loop phones, tablet computers, wearable terminal devices, personal digital assistants (PDA), portable computers, desktop computers, image capture terminal devices, such as digital cameras, game terminal devices, music storage and playback appliances, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, smart devices, wireless customer premise equipment (CPE), Internet of Things (IoT) devices, watches or other wearable devices, head-mounted displays (HMD), helmet-mounted displays (HMD), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in the context of an industrial and / or automation processing chain), consumer electronic devices, devices operating on commercial and / or industrial wireless networks, etc. In the following description, the terms "terminal device", "communication device", "terminal", "user equipment", and "UE" may be used interchangeably. In the following description, the terms "preamble", "sequence", "waveform", and "signal" may be used interchangeably.

[0056] In 5G, MTC is divided into ultra-reliable low-latency communication (URLLC) or critical MTC (cMTC) (in a controlled environment with small payloads and low data rates), and mMTC with a decentralized traffic pattern for large-scale / dense deployments. In the next decade, due to emerging industrial use cases and the verticalization of service provision, these two areas will evolve into several specialized subclasses, thus requiring multi-dimensional optimization and scalable design. With the development of communication technologies, evolving technologies are needed to serve highly diverse applications, ranging from high-data-rate holographic images and connected 360XR (augmented / virtual / mixed reality) to the large-scale access of various types of IoT devices. It is proposed that one category in the MTC service category for 6G be classified as scalable critical MTC (cMTC), which refers to supporting large-scale connections with high reliability and low latency, such as critical medical monitoring and factory automation. Scale and flexibility will continue to be important metrics for measuring 6G performance. 6G communication is expected to support a high connection density of 10 million devices per square kilometer.

[0057] In contrast to human-centric communication, machine-centric communication (e.g., scalable cMTC) typically has two distinct characteristics. On the one hand, the entire system needs to support large-scale connectivity - the number of end devices connected to a cellular network device can be approximately 10 4 to 10 7 . Macro network devices tend to provide unified large-scale access for various types of IoT devices, thus providing a low-cost solution for supporting large-scale connections with high reliability and low latency. Commercially, telecom providers tend to adopt unified solutions. On the other hand, the business model is sporadic at any given time, with only a small fraction of potential end devices being active. Typically, machine-type end devices connect to network devices in an asynchronous and sporadic manner to send small data payloads. This sporadicity is due to the inherent burstiness of event-driven IoT communication in a controlled and / or sensed environment. Most machine-type end devices independently issue random requests with a relatively low periodicity that can be tracked and exploited. Therefore, it is impossible for network devices to predict in advance when and which end device will transmit data packets.

[0058] One of the main obstacles to the efficient cellular access proliferation of scalable cMTC stems from the flaws in the access reservation procedure, which is a key building block of the cellular access network. From 1G to 5G, the access reservation process was designed to establish connections for a relatively small number of access terminal devices. In addition, each terminal device has medium to high data rate requirements, making the overhead of the current access protocol with multiple phases relatively small. These two assumptions, namely a small number of terminal devices and medium to high data rates, are contradictory to the requirements of scalable cMTC. The traditional access reservation process uses random access to establish a connection state for terminal devices at the cost of an access latency of about 20 ms, such as the Physical Layer Random Access Channel (PRACH) in LTE / NR.

[0059] The traditional random access process accomplishes two necessary functions for successful communication, namely UAD and timing acquisition. On the one hand, before establishing a successful connection between the network device and the terminal device, the network device needs to identify the active subset among all terminal devices in the original (idle) state. On the other hand, the network device needs to estimate the propagation delay experienced by the identified terminal devices so that it can provide accurate Timing Advance (TA) information to all active terminal devices and enable synchronous UL transmission. Based on UAD and timing acquisition, the connection state of the terminal device can be established, and then data services based on scheduling or grant-free (GF) can be applied.

[0060] However, considering the scarcity of frequency resources, traditional random access is not scalable and is not suitable for large-scale and critical MTC. For example, due to the limited number of preambles of PRACH, the PRACH mechanism imposes a limit on the number of active terminal devices authorized to access the network device. In addition, relative to a large number of machine-type terminal devices, a certain coherent time-frequency block can only support a relatively small number of orthogonal preamble sequences. For example, LTE / NR only supports 64 orthogonal Zadoff-Chu (ZC) sequences of length 643 for PRACH. Large-scale terminal devices randomly access by independently selecting a sequence from the same group, inevitably causing serious conflicts and generating intolerable access delays. In addition, the repeated cycle of transmission conflict retransmissions leads to an endless cascade of signaling exchanges between the terminal device and the network device, which is much higher than the small packets that the machine-type terminal device intends to send. On the other hand, for a large number of terminal devices with potential service requests, maintaining the connection state continuously results in periodic signaling exchanges, thus causing unacceptable power and spectrum waste. As the connection density increases to 10 million terminal devices per square kilometer, this will become infeasible. In addition, for IoT devices themselves, maintaining a continuous connection state is energy-inefficient, and the device is usually expected to have a long battery life of more than 10 years. If the network device has the ability to quickly establish a connection state on demand, the maintenance cost can be avoided.

[0061] Considering that due to the lack of orthogonal preambles, the spectrum consumption is unsustainable and the performance is low, traditional PRACH procedures are not scalable and are not applicable to large-scale access with low traffic intensity when the number of simultaneously connected terminal devices expands, especially for large-scale delay-sensitive IoT access.

[0062] In fact, in a wireless fading channel, when the number of terminal devices is large but the coherence time and frequency dimensions are limited, it is impossible to allocate orthogonal preambles to all terminal devices. However, for example, when simple matched filtering or related processing is applied at the network device, non-orthogonal preamble sets are superimposed and cause significant multi-user interference, which makes UAD and timing acquisition very challenging. Therefore, new solutions are needed to manage uncertain and random access more effectively and efficiently.

[0063] To overcome the deficiencies in traditional methods, the present disclosure provides an overall design from waveform design and its transmission method at the terminal device side to the receiving method at the network device side. The principles and example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. However, it should be noted that these embodiments are shown by way of example and are not intended to limit the scope of the present application in any way.

[0064] First, refer to Figure 1A , which shows an example communication network 100 in which embodiments of the present disclosure can be implemented. As Figure 1A shown, network 100 may include a network device 120. The network device 120 may provide a cellular network for large-scale access. As Figure 1A shown, network 100 may also include terminal devices 110-1, 110-2, 110-3, 110-4, 110-5,..., 110-N, which may be collectively referred to as "terminal devices 110". The group of N terminal devices is denoted by S. The number N can be any suitable integer. Without loss of generality, it may be assumed that N is even and positive. The terminal devices may be respectively labeled with .

[0065] It should be understood that Figure 1A the number of network devices and terminal devices shown is only for illustrative purposes and does not imply any limitation. Network 100 may include any suitable number of network devices and terminal devices suitable for implementing the embodiments of the present disclosure.

[0066] The terminal devices 110 may independently and asynchronously access the network device 120 according to their own needs for sporadic traffic, typically requesting to establish a connection and generally referred to as random access. In an example scenario, by the active subset A small portion of the represented potential end devices can become active and perform a random access procedure by transmitting a UL preamble signal during a given transmission period. For example, as Figure 1A shown, the first end device 110-1 and the third end device 110-3 can be active, while the second end device 110-2, the fourth end device 110-4, and the fifth end device 110-5 are inactive. To perform random access, each end device 110 in the network 100 can be pre-assigned a unique preamble compared to traditional PRACH schemes with sequence conflicts. This preamble can also be used as the ID of the end device.

[0067] The network device 120 can be configured to identify an active subset A of the entire set of end devices through a UAD procedure before a successful connection is established between the end device and the network device. Once the network device 120 knows which end devices become active at the start of a transmission period, the network device 120 can immediately allocate UL channels to the identified active end devices, enabling the active end devices to also provide more detailed information to the network device 120, e.g., for establishing a connection state. In addition, the network device 120 can be configured to estimate the propagation delay experienced by the identified end devices, thus providing TA information to the identified end devices and enabling synchronous UL transmission. In this way, the network device 120 can quickly know which end devices become active at the start of a transmission period and quickly derive the corresponding TA information, and thus can prepare a prompt response for establishing a successful connection.

[0068] For illustrative purposes and without suggesting any limitations, each end device 110 can be equipped with a single transmit antenna. As Figure 1A shown, the active end device can transmit a baseband preamble signal S n (t) with a carrier signal. The baseband preamble signal S n (t) transmitted from the active end device n can be UE-exclusive or randomly selected from a preamble set.

[0069] In some embodiments, the transmission of all UL preambles can be triggered / synchronized by a common DL beacon signal transmitted from the network device 120 at the start. Figure 1B Shows a schematic diagram of the effective uplink channel impulse response (CIR) in a random access scenario according to some embodiments of the present disclosure. For example, a common DL beacon signal can be transmitted from the network device 120 at t = 0. In response to receiving the common DL beacon signal, the active end device n can be triggered to transmit the preamble signal S n (t) to the network device 120. In this way, the signal S n(t) will experience a round-trip propagation delay with respect to the start time, denoted in seconds by d n and arrive at the network device 120. The signal S n (t) may pass through a multipath extended channel from the terminal device n to the network device 120, whose CIR can be represented by . Here, it can be assumed that the network device 120 is equipped with a single receive antenna. Thus, as Figure 1B shown, the effective UL CIR from the terminal device n to the network device 120 can be represented by h n (t - d n ).

[0070] Returning to Figure 1A , the network device 120 can receive asynchronous and superimposed radio frequency (RF) signals. The received superimposed signal can be written as where * represents the convolution operation, f c represents the carrier frequency in Hz, and n(t) represents the additive interference including thermal noise and inter-cell interference.

[0071] Note that the propagation delay information is transmitted not only according to s n (t - d n ) by the baseband signal, but also according to the UL CPO by the carrier signal, where In other words, the propagation delay causes not only a time delay in the baseband signal, but also a UL CPO in the carrier signal. Signals transmitted from different terminal devices 110 may respectively suffer different UL CPOs. Therefore, the superimposed signal received by the network device 120 may contain multiple independent UL CPOs. It is difficult for the network device 120 to simultaneously track and compensate for multiple independent UL CPOs. In some embodiments, the UL CPO in the carrier signal introduced by the propagation delay from the terminal device 110 to the network device 120 can be pre-compensated at the terminal device side, which helps the network device identify the active subset and estimate the relevant propagation delay. The details of an example pre-compensation method for UL CPO will be described in detail below in conjunction with Figures 7A to 7B the details of the UL CPO example pre-compensation method.

[0072] In each transmission period, the network device 120 can identify the active subset S A only depending on the observation y(t) and obtain the relevant timing information. The former is a UAD problem regarding a discrete random variable, while the latter is a continuous estimation problem regarding the propagation delay.

[0073] Compared with traditional PRACH schemes that have orthogonality with preambles (such as ZC sequences), non-orthogonal preamble sets make joint UAD and timing acquisition very challenging because they will superimpose and cause severe multi-user interference. For example, when applying simple matched filtering or related processing at the network device. In addition, the impact of UL CPO also hinders accurate timing acquisition from phase estimation. Embodiments of the present disclosure provide a preamble set {s n (t)} n∈S and related detection and estimation in an overall manner.

[0074] Communication in communication network 100 can be implemented according to any suitable communication protocol, including but not limited to first-generation (1G), second-generation (2G), third-generation (3G), fourth-generation (4G), and fifth-generation (5G) or higher cellular communication protocols, such as wireless local network communication protocols like Institute of Electrical and Electronics Engineers (IEEE) 802.11, and / or any other protocol known currently or to be developed in the future. In addition, communication can utilize any suitable wireless communication technology, including but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplexing (FDD), Time Division Duplexing (TDD), Multiple Input Multiple Output (MIMO), Orthogonal Frequency Division Multiple Access (OFDM), Discrete Fourier Transform Spread OFDM (DFT-s-OFDM), and / or any other technology known currently or to be developed in the future.

[0075] Now refer to Figure 2 , which shows a schematic diagram of a process 200 for communication according to some embodiments of the present disclosure. For the purpose of discussion, process 200 will be described with reference to Figure 1A . For illustrative purposes, network device 120 and terminal device 110-1 may be involved in process 200.

[0076] In process 200, network device 120 transmits 202 a configuration 204 associated with a subcarrier set to the set S of terminal devices in the radio access network, and the subcarrier set is associated with the set S of terminal devices for transmitting modulated conjugate symmetric signals. The modulated conjugate symmetric signal indicates the activity information of the active terminal device set S A in the set S of terminal devices. In some embodiments, based on configuration 204, all potential terminal devices 110 in the set S of terminal devices may be assigned specific subcarriers. When any terminal device in the set S of terminal devices becomes active, the terminal device may transmit a preamble signal in the subcarrier associated with the terminal device to perform a random access procedure.

[0077] As Figure 2As shown, the terminal device 110-1 receives 206 the configuration 204 and transmits 208 the modulated conjugate symmetric signal 210 to the network device 120. The modulated conjugate symmetric signal 210 is generated by modulating subcarriers from the set of subcarriers with symbols. The modulated conjugate symmetric signal 210 includes sparse MC-FTN conjugate symmetric signaling associated with {s n (t)} n∈S , where the sparsity is caused by sporadic transmissions of the set of active terminal devices. The signal set {s n (t)} n∈S The required time-frequency cost can be evaluated according to the normalized time-bandwidth (NTB) product, i.e., where B n and T n are the bandwidth and symbol duration of the preamble S n (t), respectively. The smaller the NTB product, the lower the time-frequency resources consumed. Any orthogonal design requires sufficient time-frequency resources such that NTB ≥ 1. The MC-FTN conjugate symmetric signaling allows for a shorter symbol duration less than the reciprocal of the subcarrier spacing, resulting in a reduction of the inevitable latency penalty. At the same time, in the MC-FTN conjugate symmetric signaling design, the requirement of NTB ≤ 1 indicates that, in the set of terminal devices S, the modulated conjugate symmetric signals associated with {s n (t)} n∈S from different terminal devices are non-orthogonal. The details of an example MC-FTN conjugate symmetric signaling design will be described in detail below in conjunction with Figures 3A to 6 .

[0078] The network device 120 receives 212 the modulated conjugate symmetric signal 210 from the terminal device 110-1 and other modulated conjugate symmetric signals from other active terminal devices (if any). From the perspective of the network device 120, the network device 120 receives the superimposed signal y(t) associated with the modulated conjugate symmetric signal from the set of active terminal devices S A . The network device 120 identifies 214 the set of active terminal devices S A from the set of terminal devices S based on the received superimposed signal. The conjugate symmetry and sparsity of the modulated conjugate symmetric signal provide the possibility for the network device 120 to identify the active subset S A when multiple active terminal devices 110 transmit UAD signals asynchronously. In addition, the network device 120 may also estimate 216 the propagation delay related to the identified set of active terminal devices , where represents the identified set of active terminal devices. In this way, a solution for joint UAD and timing acquisition for large-scale access is provided, where the latency is reduced and the measurement resource cost is reduced. The details will be described below in conjunction withFigure 8 Describe in detail the set S of active terminal devices together with timing acquisition A The details of the example identification program are as follows.

[0079] In some embodiments, the NTB product of the sparse MC-FTN conjugate symmetric signaling can be greater than or equal to twice the ratio of the number of the set of active terminal devices to the number of the set of terminal devices, i.e., where |S A | represents the number of terminal devices active at a given transmission time or frame. In this way, the NTB product of the sparse MC-FTN conjugate symmetric signaling can be less than 1 and as small as twice the proportion of active terminal devices, regardless of how the total number of devices expands, thus providing a scalable solution for large-scale access with low measurement cost for joint UAD and optional timing acquisition.

[0080] In some embodiments, subcarriers can be specifically associated with terminal devices. In this way, the fixed allocation of subcarriers establishes a unique association between the preamble set and the terminal devices, which not only avoids preamble collisions due to random allocation but also saves additional procedures for reporting user IDs.

[0081] In some embodiments, to generate subcarriers, the terminal device 110-1 can generate a complex conjugate symmetric sine wave with a subcarrier frequency. The duration of the complex conjugate symmetric sine wave can be determined based on the reciprocal of the subcarrier spacing of the set of subcarriers, the number of the set of active terminal devices, and the number of the set of terminal devices. Then, the terminal device can add a cyclic prefix to the complex conjugate symmetric sine wave to generate subcarriers. In this way, the time-frequency resources required for qualified UAD and timing acquisition can depend only on the proportion of actual active terminal devices and are not scalable in the case of the total number N of terminal devices, thus resulting in a scalable solution for large-scale access.

[0082] In some embodiments, the terminal device 110-1 can determine a pre-compensation phase factor for the complex conjugate symmetric sine wave with a cyclic prefix Pre-compensation phase factor can pre-compensate the UL CPO of the carrier signal of the modulated conjugate symmetric signal caused by the propagation delay from the terminal device to the network device In this way, the UL CPO in the carrier signal introduced by the propagation delay from the terminal device 110-1 to the network device 120 can be pre-compensated at the terminal device side, such that the deviation between the pre-compensation phase factor and the UL CPO i.e., can be controlled within a certain range, and this range allows the phase of the symbol received from the network device to derive the desired information about the propagation delay.

[0083] The terminal device 110-1 can determine the pre-compensation phase factor in various ways. The terminal device 110 can track its DL CPO respectively. For a terminal device, considering the same propagation delay of the UL-DL pair, its UL CPO caused by the propagation delay from the terminal device to the network device 120 can be the same as its DL CPO caused by the propagation delay from the network device 120 to the terminal device. In an example implementation, the network device 120 can transmit a beacon signal indicating the transmission of sparse MC-FTN conjugate symmetric signaling to the set S of terminal devices. To determine the pre-compensation phase factor The terminal device 110-1 can determine the DL CPO of the carrier signal based on the received beacon signal, and determine the pre-compensation phase factor based on the determined DL CPO.

[0084] In some embodiments, the symbol can include a variable phase compensation factor and a fixed phase compensation factor for compensating the phase of the channel between the network device 120 and the terminal device 110-1 in the subcarrier. In this way, the variable phase compensation factor is adapted to the instantaneous phase of the channel between the network device 120 and the terminal device 110-1 in the subcarrier, so that the deviation between the variable phase compensation factor and the phase of the channel between the network device 120 and the terminal device 110-1 in the subcarrier can be controlled within a certain range. Combining the pre-compensation phase factor and the variable phase compensation factor of the UL CPO, the fixed phase compensation factor is used to tune the phase of the received symbol within an appropriate range. Therefore, the phase of the received symbol in the subcarriers of the frequency band can contain resolvable and distinguishable information about the propagation delay in the radio access network. Using the precoding strategy based on phase compensation and conjugate symmetry and sparse transmission in the frequency domain, the network device 120 can solve the received symbol completely based on the received superimposed signal of the MC-FTN signaling.

[0085] The terminal device 110-1 can determine the variable phase compensation factor in various ways. In an example implementation, the terminal device 110-1 can determine the variable phase compensation factor based on the received beacon signal and the channel reciprocity between UL and DL. In some embodiments, the terminal device 110-1 can be based on the frequency of the subcarrier, the frequency of the carrier signal, the deviation between the variable phase compensation factor and the phase of the channel between the network device 120 and the terminal device 110-1 in the subcarrier, and the pre-compensation phase factor and the UL CPO to determine the fixed phase compensation factor. In this way, it can help to meet the reconstruction conditions of the MC-FTN conjugate symmetric signaling on the network device side. The details of the example phase compensation design can be described in combination with Figures 4A to 4C below.

[0086] In some embodiments, the subcarriers may be in a frequency band. The bandwidth of the frequency band may be determined based on the maximum propagation delay in the radio access network, the deviation between the variable phase compensation factor and the phase of the channel between the network device 120 and the terminal device 110-1 in the subcarriers, and the pre-compensation phase factor and the deviation from the UL CPO In other words, the bandwidth of the frequency band, the maximum propagation delay in the radio access network, and the fixed phase compensation factor may be related, which enables the reconstruction condition to be satisfied. In some embodiments, the bandwidth of the frequency band of the UAD may be limited by a maximum value.

[0087] The terminal device 110-1 may generate a modulated conjugate symmetric signal in various ways. In an example implementation, the terminal device 110-1 may generate a discrete-time baseband conjugate symmetric signal based on the baseband frequency of the subcarriers, the variable phase compensation factor, and the fixed phase compensation factor. Then, the terminal device 110-1 may generate a continuous-time baseband conjugate symmetric signal based on the discrete-time baseband conjugate symmetric signal through digital-to-analog conversion. The modulated conjugate symmetric signal may be generated by performing a frequency shift on the continuous-time baseband conjugate symmetric signal. Different terminal devices may be distinguished by allocating different subcarriers without preamble conflicts. Based on the introduction of such phase compensation and conjugate symmetry, the effective sparse non-zero vectors of the received symbols in different subcarriers may retain the activity information of the corresponding active terminal devices. In the information vector based on hybrid / superposition observations, a sign constraint may be applied to the imaginary part of the received symbols. The inactive terminal devices in the network may remain silent, and the components corresponding to the inactive terminal devices are zero. In this way, the components corresponding to the active terminal devices may be solved from the hybrid / superposition observations.

[0088] In some embodiments, the terminal device 110-1 may perform a frequency shift with the pre-compensation phase factor to pre-compensate the UL CPO By pre-compensating the UL CPO at the terminal device side, the complexity of obtaining the activity information of the corresponding active terminal device from the hybrid / superposition observations may be reduced.

[0089] In some embodiments, to generate a discrete-time baseband conjugate-symmetric signal, the terminal device 110-1 may generate a first sequence modulated by a variable phase compensation factor and a fixed phase compensation factor by performing an inverse discrete Fourier transform (IDFT). The non-zero components of the input of the IDFT may include the variable phase compensation factor and the fixed phase compensation factor corresponding to subcarriers. Then, the terminal device 110-1 may insert a copy of the last part of the first sequence appended before the first sequence to obtain a second sequence. The inserted last part of the first sequence may include a cyclic prefix and a conjugate-symmetric component. The terminal device 110-1 may then discard the last part of the second sequence to obtain a discrete-time baseband conjugate-symmetric signal. The length of the discrete-time baseband conjugate-symmetric signal excluding the cyclic prefix may be determined based on the duration and the sampling rate of the modulated conjugate-symmetric signal. With such a length definition, as long as twice the proportion of the actual active terminal devices is less than the NTB product, qualified UAD and timing acquisition can be performed, and thus the minimum measurement cost required for qualified UAD and timing acquisition can be achieved. The designed signaling is a non-orthogonal complex conjugate-symmetric sine wave set. Such a well-designed waveform and carefully designed phase compensation make the active detection scheme more efficient and scalable. Therefore, an MC-FTN conjugate-symmetric signaling scheme for accurate, fast, and scalable UAD and timing acquisition is provided.

[0090] In some embodiments, to identify the set S of active terminal devices A , the network device 120 may determine a superimposed complex conjugate-symmetric sine sequence based on the superimposed signal. The superimposed complex conjugate-symmetric sine sequence may include symbols received in the subcarrier set associated with the set S of terminal devices. The network device 120 may determine a superimposed complex sine sequence based on the superimposed complex conjugate-symmetric sine sequence and its conjugate symmetry. The superimposed complex sine sequence may include the imaginary parts of the received symbols in the subcarriers associated with the set S of terminal devices and exclude the real parts of the received symbols in the subcarrier set associated with the set S of terminal devices. Then, the network device 120 may determine a first identified set of active terminal devices based on the superimposed complex sine sequence. Based on the superimposed complex conjugate-symmetric sine sequence and the first identified set of active terminal devices, the network device 120 may then determine a second identified set of active terminal devices as the identified set of active terminal devices. In this way, the network device 120 may determine the first identified set of active terminal devices as based on the imaginary parts of the received symbols and according to partial knowledge A rough estimate. The first set is identified from the set of terminal devices, which involves large-scale problems based on the dimension of the set of terminal devices. The first set can pursue a low miss detection rate and tolerate a relatively large false alarm rate, which may include almost all active terminal devices and inevitably includes a certain number of inactive terminal devices. In addition, the network device 120 can determine the second identified set of active terminal devices as A fine estimate. The second set is identified by also excluding the inactive terminal devices from the first set, which involves small-scale problems of dimensionality reduction based on the first set. Therefore, the network device 120 can overcome the problem of insufficient dimensionality through model reduction and determine the active subset And an accurate estimate of the relevant information of the propagation delay. The careful design of the transmission enables such a fast and accurate detection method to obtain the active information from the noisy, asynchronous, and superimposed observations, even for MC-FTN signaling.

[0091] In some embodiments, to determine the first identified set of active terminal devices, the network device 120 can determine a sparse real vector representing the imaginary part of the received symbols in the subcarrier set associated with the set of terminal devices based on the superimposed complex sine sequence. Then, the network device 120 can determine the effective non-zero components of the imaginary part of the received symbols in the subcarrier set associated with the set of terminal devices by comparing the absolute values of the components of the sparse real vector with a first predefined threshold. Based on the effective non-zero components of the imaginary part of the received symbols in the subcarrier set associated with the set of terminal devices, the network device 120 can then determine the first identified set of active terminal devices. In this way, the network device 120 can determine a rough estimate of the active subset by deriving the imaginary parts of all terminal devices.

[0092] In some embodiments, the network device 120 can determine the sparse real vector by solving an effective non-negative least squares (NLS) problem based on the superimposed complex sine sequence. The components of the sparse real vector corresponding to the imaginary part of the received symbols in the subcarrier set with a frequency lower than the carrier frequency can be non-negative, and the components of the sparse real vector corresponding to the imaginary part of the received symbols in the subcarrier set with a frequency higher than the carrier frequency can be non-positive. Such a sign constraint on the imaginary part of the received symbols helps to solve the sparse real vector from the transformed observations.

[0093] In some embodiments, to determine the second identified set of active terminal devices, network device 120 may determine a low-dimensional complex vector representing the received symbols in this subcarrier set associated with the first identified set of active terminal devices based on an overlaid complex conjugate symmetric sine sequence. In some embodiments, the low-dimensional complex vector may be determined under the following constraints: the components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols in this subcarrier set with frequencies lower than the carrier frequency are non-negative, and the components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols in this subcarrier set with frequencies higher than the carrier frequency are non-positive. Since the imaginary parts of the received symbols in this subcarrier set associated with this set of terminal devices have been derived and a rough estimate of the active subset has been determined, the real parts of the received symbols can be derived for the rough active subset by solving a small-scale subproblem after model reduction. Network device 120 may determine the valid non-zero components of the received symbols in this subcarrier set associated with the first identified set of active terminal devices by comparing the magnitudes of the components of the low-dimensional complex vector with a second predefined threshold. The second predefined threshold may be greater than the first predefined threshold for further excluding inactive terminal devices from the first set. Then, network device 120 may determine the second identified set of active terminal devices based on the valid non-zero components of the received symbols in this subcarrier set associated with the first identified set of active terminal devices. In this way, network device 120 may determine the active subset by comparing the magnitudes of the components of the low-dimensional complex vector with a lower threshold. for an accurate estimate.

[0094] In some embodiments, network device 120 may replace the imaginary parts of the received symbols in this subcarrier set associated with the first identified set of active terminal devices with corresponding imaginary parts derived from a sparse real vector. In this way, the estimation accuracy of the received symbols can be improved.

[0095] In some embodiments, network device 120 may transmit an indication indicating the identified set of active terminal devices to the set of terminal devices S via a common channel. Terminal device 110-1 may receive the indication from network device 120 and determine whether it is included in the set of active terminal devices identified by network device 120. If terminal device 110-1 is included in the set of active terminal devices identified by network device 120. then terminal device 110-1 may perform communication with network device 120. In some embodiments, the indication may further indicate the resources for the set of active terminal devices respectively. Resources for each active terminal device in [[]] to perform communication. Then, the terminal device 110-1 can use the corresponding resources related to the terminal device 110-1 to perform communication with the network device 120. For example, the terminal device 110-1 can further use the corresponding resources indicated for the terminal device 110 (e.g., for establishing a connection state) to provide further data to the network device 120. If the terminal device 110-1 is excluded from the set of active terminal devices identified by the network device 120 then the terminal device 110-1 can retransmit the modulated conjugate symmetric signal to the network device 120.

[0096] In some embodiments, the network device 120 can determine, based on the phase of the received symbols in the subcarrier set associated with the second identified set of active terminal devices the propagation delay from the second identified set of active terminal devices to the network device 120. In some embodiments, the network device 120 can determine the timing advance information related to the second identified set of active terminal devices based on the determined propagation delay from the second identified set of active terminal devices to the network device. Then, the network device 120 can transmit, via a common channel, an indication of the identified set of active terminal devices and the related timing advance information to the set of terminal devices respectively. If the terminal device 110-1 is included in the set of active terminal devices identified by the network device 120 then the terminal device 110-1 can perform communication with the network device 120 based on the corresponding timing advance information related to the terminal device 110-1. In this way, synchronous UL transmission can be enabled.

[0097] As a more efficient and effective method, the joint UAD and timing acquisition procedure is expected to replace the random access PRACH procedure. The network device can quickly know at the beginning of a transmission cycle which terminal devices have an actual need for data delivery and can prepare a prompt response for successful communication. In addition, the network device can estimate the propagation delay experienced by the identified terminal devices, so as to provide TA information to the identified terminal devices and achieve synchronous UL transmission.

[0098] In some embodiments, the terminal device 110-1 can transmit data symbols with variable phase compensation factors in subcarriers with a pre-compensation factor having a UL CPO. The data symbols can be mapped to service data, e.g., for small data transmission. In this way, synchronous UL transmission can be enabled using TA information based on a rough estimate of the propagation delay determined by the network device 120. The rough estimate can include errors due to unknown deviations between the pre-compensation phase factor and the UL CPO and / or unknown deviations between the variable phase compensation factor and the channel phase between the network device and the terminal device in the subcarrier.

[0099] Now referring to Figures 3A to 3B , example time-domain and frequency-domain structures of signals for traditional data transmission (i.e., data signals) and signals for UAD (i.e., UAD signals) according to some embodiments of the present disclosure are shown respectively. Figure 3A An example diagram of data signals and UAD signals in the time domain according to some embodiments of the present disclosure is shown. Figure 3B An example diagram of a multiplexing structure of data signals and UAD signals in the frequency domain according to some embodiments of the present disclosure is shown. As Figure 3A and Figure 3B shown, the system bandwidth configured for uplink transmission is B total Hz. The data signal and the UAD signal are multiplexed in the frequency domain, and an intended guard band (GB) is inserted between them to separate them. A continuous B UAD bandwidth frequency band for UAD 312 is configured and is centered at a center frequency with a carrier frequency f c (in Hz). The data signal and the UAD signal can use different subcarrier spacings Δf D Hz and Δf UAD Hz respectively in the frequency domain, and different lengths in the time domain. The data signal can include a cyclic prefix (CP) 304 and data symbols 302, with durations of T CP,D seconds and T syb,D seconds respectively. The UAD signal can include CP 310 and UAD symbols 306, with durations of T CP,UAD seconds and T syb,UAD seconds respectively.

[0100] In some embodiments, the data signal can adopt a standard multi-carrier design, for example, orthogonal frequency division multiple access (OFDMA) or single-carrier frequency division multiple access (SC-FDMA) in a traditional LTE / NR system. The data signal can adopt a wider subcarrier spacing Δf D Hz, and the duration T syb,D of the data symbol 304 can be set according to the Nyquist rule such that Δf D T syb,D = 1. According to the scheduling grant from the network device 120, data from different terminal devices can be multiplexed on different subsets of subcarriers in the frequency bands of data 314 and 316. The time-domain and frequency-domain structures of the data signal are shown for better understanding of the UAD signal. The present disclosure does not intend to impose any limitations on the design of the data signal. Different structures of the data signal can be designed.

[0101] In some embodiments, the frequency band of the UAD 312 can consist of N subcarriers of N terminal devices (i.e., N potential terminal devices) in the network 100, where the subcarrier spacing Δf UAD is narrow and equal. AMC-FTN conjugate symmetric signaling is proposed such that Δf UAD T syb,UAD <1. This MC-FTN conjugate symmetric design makes the UAD symbols shorter, less than 1 / Δf UAD , thus benefiting in terms of resource saving and latency reduction. As Figure 3A shown, compared with the length of the PRACH preamble following the Nyquist rule, the length of the UAD symbol 306 is shortened by the time reduction 308. In some embodiments, a guard time (GT) can be inserted to separate the UAD signal from other signals.

[0102] In some embodiments, a fixed association between the terminal device and the subcarrier is provided. Each terminal device is assigned a unique subcarrier such that the network device 120 can identify the active terminal device by checking which subcarrier components are present in the superimposed signal received by the network device. The association pattern is pre-assigned and is known to the network device 120 and the terminal device 110, for example, via an injective mapping between the core network / cell ID and the subcarrier index. As a typical example, the terminal device is assigned a dedicated subcarrier with a baseband frequency of NΔf UAD , where the direct current (DC) subcarrier is usually not utilized in practice because it may be subject to disproportionately high interference due to local oscillator leakage.

[0103] In sparse MC-FTN conjugate symmetric transmission, only the active terminal devices send symbols in their associated subcarriers (indicated by the subcarriers shown as solid lines in the frequency band of the UAD 312) with a frequency f c +NΔf UAD through sparse MC-FTN-conjugate symmetric signaling, where where ||·|| represents the l 2 form, the superscript symbol (·)* represents conjugation, P n represents the power factor of the terminal device n, and represents the estimated value of the channel coefficient between the network device and the terminal device n in the subcarrier f c +NΔf UAD , denoted as H n . That is, the symbol modulates the associated subcarrier associated subcarrier is generated through the following steps: generating with a frequency fc +NΔf UAD and a duration T CP,UAD of a complex conjugate symmetric sine waveform and adding a cyclic prefix having a duration T CP,UAD to the complex conjugate symmetric sine waveform. The complex conjugate symmetric sine waveform for -0.5T Syb，UAD < t < 0.5T Syb，UAD satisfies the complex conjugate symmetric sine waveform with a duration T syb,UAD can be determined based on the reciprocal of the subcarrier spacing Δf UAD the number of the active terminal device set (i.e., |S A |) and the number of the terminal device set (i.e., N), where |·| represents the cardinality of the set. By determining the pre-compensation phase factor in the carrier signal to pre-compensate the UL CPO the active terminal device can transmit a modulated conjugate symmetric signal, which is an RF UAD signal and can be written as Equation (1):

[0104]

[0105] The modulated conjugate symmetric signals transmitted by all active terminal devices include sparse MC-FTN conjugate symmetric signaling.

[0106] In some embodiments, the modulated conjugate symmetric signal transmitted by the active terminal device n can be described by a baseband signal, which is the continuous-time baseband conjugate symmetric signal of user n and is written as Equation (2):

[0107]

[0108] 0 ≤ t < T CP，UAD +T syb，UAD , (2)

[0109] T CP，UAD with an appropriate size comparable to the sum of the propagation delay and the spreading time of the multipath channel of the UAD

[0110] The symbol includes a variable phase compensation factor for compensating the phase of H n i.e., and a fixed phase compensation factor where represents the angle of the complex number, and H n is the CIR H n ​(t) at a frequency f corresponding to the active terminal device n∈S A and the Fourier transform under +NΔf c +NΔf UAD Thus, among the subcarriers of f c +NΔf UAD the deviation between the variable phase compensation factor and the phase of the channel between the network device and the terminal device n can be written as not greater than the maximum error and satisfying the condition fixed phase compensation factor is designed to cope with the phase compensation error caused by the imperfect variable phase compensation factor of the channel phase and / or the inaccurate pre-compensation factor of the UL CPO, so that the phase of the received symbol is within an appropriate range and promotes UAD and timing acquisition.

[0111] Now refer to Figures 4A to 4C to illustrate an example phase compensation design of the UAD signal after perfect pre-compensation of the UL CPO according to some embodiments of the present disclosure. Figure 4A shows an example diagram of the phase estimation error caused by partial prior knowledge on the corresponding UL channel according to some embodiments of the present disclosure. As Figure 4A shown, among the subcarriers of f c +NΔf UAD the channel between the network device 120 and the terminal device n, that is, H n is represented by the vector 404 in the complex plane. If the phase of the symbol transmitted by the terminal device n is the variable phase compensation factor then the symbol received at the network device 120 can be represented by the vector 402. The variable phase compensation factor can be determined based on the beacon signal received from the network device 120 and the channel reciprocity between UL and DL. In this way, the phase of the received symbol may be equal to the phase estimation error This error is not greater than the maximum error that is

[0112] To ensure that the phase of the received symbol in this subcarrier set contains solvable and distinguishable information about the propagation delay, a fixed phase compensation factor Figure 4B shows an example diagram of the phase compensation factor design according to some embodiments of the present disclosure. Figure 4C shows an example diagram of the reconstruction condition of the imaginary part of the received symbol in this subcarrier set according to some embodiments of the present disclosure. The fixed phase compensation factor can be designed to cope with the phase estimation error fixed phase compensation factor It can be determined based on the frequency of sub - carrier f c +NΔf UAD the frequency of carrier signal f c the deviation between the variable phase compensation factor and the channel phase in the sub - carrier and the pre - compensation phase factor and the deviation between ULCPO to determine. The fixed phase compensation factor can be configured through Equation (3) based on partial prior knowledge about the phase compensation error:

[0113]

[0114] As Figure 4B shown, for the terminal device n associated with a sub - carrier whose frequency is higher than the carrier frequency, i.e., n > 0, after further compensation with the fixed phase compensation factor the symbol of terminal device n received by network device 120 is represented by vector 416, and its phase is Considering the clockwise phase rotation caused by the round - trip propagation delay, the received symbol is vector 418, and its phase is where the integer represents the round - trip propagation delay of terminal device n in the samples, represents the corresponding sampling period. If the sub - carrier with baseband frequency nΔf UAD is within the frequency band with a feasible bandwidth B UAD such that then the phase of the received symbol for any n > 0 follows In other words, the received symbols in the sub - carriers higher than the carrier frequency always fall in the lower complex plane, that is, as Figure 4C shown, the imaginary part of those symbols is non - positive. The feasible bandwidth can be less than the maximum allowable bandwidth of UAD, which will be described in detail below.

[0115] For the terminal device n associated with a sub - carrier whose frequency is lower than the carrier frequency, i.e., n < 0, after further compensation with the fixed phase compensation factor the symbol of terminal device n received by network device 120 is represented by vector 426, and its phase is Considering the counter - clockwise phase rotation caused by the round - trip propagation delay, the received symbol is vector 428, and its phase is If the sub - carrier with baseband frequency nΔf UAD is within the frequency band of the feasible bandwidth B UAD such that then the phase of the received symbol for any n < 0 follows In other words, the received symbols in the subcarriers below the carrier frequency always fall in the upper complex plane, that is, as Figure 4C shown, the imaginary parts of those symbols are non - negative.

[0116] As Figure 4B and Figure 4C shown, the careful design of phase compensation ensures that the received symbols in the subcarriers with baseband frequency nΔf UAD fall in the lower complex plane for positive n, or in the upper complex plane for negative n. Considering the phase compensation error due to inaccurate pre - compensation factor of UL CPO can also be handled in this way. In this way, a sign constraint is constructed for the imaginary part of the received symbols, and the reconstruction condition that can be represented by Equation (4) is followed:

[0117]

[0118] In some embodiments, to ensure that the above - mentioned reconstruction condition represented by Equation (4) is satisfied, based on the maximum round - trip propagation delay (represented by d max seconds), the deviation between the variable phase compensation factor and the channel phase between the network device and the terminal device in the subcarrier (i.e., ), and the deviation between the pre - compensation phase factor and UL CPO (i.e., ), the maximum allowable bandwidth of UAD is determined. Although both deviations may be uncertain, they can be limited by the maximum error such that In some embodiments, the maximum allowable bandwidth of UAD can be determined as where d max can be determined based on the coverage of the radio access network, such as the cell radius of a cellular network. In this way, the feasible bandwidth configuration of the MC - FTN conjugate - symmetric signal can be formulated as Equation (5):

[0119]

[0120] In some embodiments, to ensure obtaining a qualified UAD and timing acquisition at the network device 120, sufficient time - frequency resources can be used such that the product of NTB is at least twice the proportion of the actual active terminal devices, that is, Generally speaking, due to sporadic traffic, user activity is sparse, which means always maintaining and allowing Δf UAD T sym,UAD<1. Meanwhile, the inactive terminal devices remain silent in their associated subcarriers, indicated by the subcarriers shown as dashed lines in the UAD 312 band. Considering that the number of inactive terminal devices far exceeds that of active terminal devices, there is sparse transmission in the frequency domain.

[0121] In some embodiments, based on the desired modulation waveform generate a UAD signal for accurate, fast, and scalable UAD and timing acquisition, and the required NTB product Δf UAD T sym,UAD can be as small as twice the average proportion of active terminal devices, regardless of how the total number N of devices is scaled, where E{·} represents the mathematical expectation. The waveform is a complex conjugate symmetric sinusoidal signal with a constant modulus. The constant modulus helps simplify the RF transmission of low-cost terminal devices.

[0122] Using an intention precoding strategy based on phase compensation and transmission sparsity, the UAD problem and the problem of estimating the propagation delay can be achieved by serially solving the reduced-scale large-scale subproblem and small-scale subproblem. The superimposed complex conjugate symmetric sinusoidal sequence retains the activity information and propagation delay information of the active terminal device set. By solving the large-scale subproblem based on the superimposed complex sinusoidal sequence derived from the superimposed complex conjugate symmetric sinusoidal sequence, the imaginary part of the received symbols of all terminal devices can be derived from the hybrid observations of the network device 110. Based on the derived imaginary part, the rough estimate of the active subset S A can be determined. Then, after model reduction, by solving the small-scale subproblem based on the superimposed complex conjugate symmetric sinusoidal sequence, the real part of the received symbols of the rough terminal device set can be derived. Finally, the full knowledge of the received symbols can be used to further refine the estimate of the active subset S A and estimate the relevant propagation delay. The details of an example process of the joint UAD and timing acquisition algorithm will be described in detail below in combination with Figure 9 the details.

[0123] For the sparse real vector solved from the large-scale subproblem, the components of the sparse real vector corresponding to the imaginary part of the received symbols in the subcarrier set with frequencies lower than the carrier frequency can be non-negative, and the components of the sparse real vector corresponding to the real part of the received symbols in the subcarrier set with frequencies higher than the carrier frequency can be non-positive, while the components corresponding to the inactive terminal devices are zero. Essentially, a variable phase compensation factor and a fixed phase compensation factor The precoding process compensates for the phase of the UL channel and pre-compensates the UL CPO in the carrier signal caused by the propagation delay at the terminal device side, so that the active information and the propagation delay can be determined by separately deriving the imaginary part and the real part of the complex vector composed of the received symbols.

[0124] The designed signaling is a set of non-orthogonal complex sinusoidal waveforms with conjugate symmetry. By allocating different subcarriers, different terminal devices can be distinguished without preamble collisions. The active terminal device can modulate the allocated subcarriers with a phase compensation factor based on partial prior knowledge about the channel phase and its estimation error. In addition, pre-compensation for the UL CPO caused by the propagation delay is introduced. The system design from fixed association, conjugate symmetry, phase compensation to bandwidth and NTB configuration enables the network device to reconstruct the received symbols in this subcarrier set. The non-zero / zero value of the received symbol indicates the active / inactive state of its associated terminal device. In addition, such a complex design ensures that the phase of the received symbol contains distinguishable information about the propagation delay.

[0125] Through such a well-designed sparse MC-FTN conjugate symmetric signaling, the joint UAD and timing acquisition scheme is more efficient and scalable. Specifically, the overall design in some embodiments of the present disclosure brings the following advantages:

[0126] 1) Minimize the measurement cost required for qualified UAD and timing acquisition: Although the NTB of the MC-FTN conjugate symmetric signaling is Δf UAD T sym,UAD <1, as long as the number of actual active terminal devices is less than qualified UAD and timing acquisition can be performed.

[0127] 2) Scalability for large-scale access: The time-frequency resources required for qualified UAD and timing acquisition only depend on the ratio of the number of actual active terminal devices and non-scalable devices to the total number of terminal devices in the network, resulting in a scalable scheme.

[0128] 3) Delay reduction: The MC-FTN conjugate symmetric signaling allows a short symbol duration less than the reciprocal of the subcarrier spacing (i.e., T sym,UAD <1 / Δf UAD ), thus reducing the inevitable delay penalty.

[0129] 4) Facilitate sparsity detection: The deliberate and systematic design of conjugate symmetry and phase compensation allows the network device to derive only the imaginary part of the received symbol by solving an effective NLS problem. In particular, the sign condition of the imaginary part introduces sparsity in a natural way, resulting in a fast detection algorithm with a finite number of steps of calculation.

[0130] 5) The fixed allocation between the preamble and the terminal device establishes a unique association, which not only avoids preamble collisions due to random allocation but also saves the additional procedure of reporting the user ID.

[0131] 6) Compatible with traditional LTE / NR: Both the transmission and reception procedures are compatible with the multi - carrier scheme of LTE / NR, which can be easily integrated with the random access procedure for massive access and used as a low - cost and high - performance solution.

[0132] Reference will be made to Figure 5 , from the perspective of waveform design and related precoding strategies, to describe an example transmitter of MC - FTN conjugate - symmetric signaling for joint UAD and timing acquisition. Figure 5 FIG. 500 shows an example diagram of the transmission procedure of a modulated conjugate - symmetric signal according to some embodiments of the present disclosure. For the purpose of discussion, reference will be made to Figure 1A and Figure 3B the frequency - domain structure shown to describe the transmission procedure of the MC - FTN conjugate - symmetric signal from the perspective of the terminal device 110.

[0133] As shown in Figure 5 , the terminal device can be assigned a dedicated sub - carrier with a frequency of f c + NΔf UAD . When the terminal device becomes active, a complex conjugate - symmetric sine sequence of length (2M + L CP,UAD - 1) can be generated according to the associated sub - carrier frequency. The complex conjugate - symmetric sine sequence can be formulated as Equation (6):

[0134]

[0135] where and The shifted version s′ n [m] = s n [m + L CP，UAD + M - 1] is conjugate - symmetric, i.e., for m = 0, 1, …, m - 1,

[0136] Based on the prior and partial knowledge on the corresponding UL channel, the complex sine sequence s and the fixed - phase compensation factor with a variable - phase compensation factor can be modulated by the symbol n [m] via the modulator 502. The discrete - time base - band conjugate - symmetric signal s UAD,n [m] can be generated as Equation (7):

[0137]

[0138] The discrete-time baseband conjugate-symmetric signal s UAD,n [m] can be converted into a continuous-time baseband conjugate-symmetric signal s UAD,n (t) via a digital-to-analog (D / A) converter 506. The D / A converter 506 can operate with a sampling period T s and ensure that s UAD,n [m] = s UAD,n (mT s ). The continuous-time baseband conjugate-symmetric signal s UAD,n (t) can be expressed as Equation (8):

[0139]

[0140] The local oscillator of the terminal device generates a carrier signal The carrier signal includes a pre-compensation phase factor for the corresponding UL CPO for pre-compensating the propagation delay -2πf c d n such that Based on the carrier signal, the RF module 508 can convert the baseband signal s (t) into an RF signal s UAD,n (t) for transmission, written as Equation (1). RF,UAD,n (t), written as Equation (1).

[0141] Alternatively, the discrete-time baseband conjugate-symmetric signal s UAD,n [m] can be generated by an equivalent IDFT structure. Figure 6 FIG. shows an example diagram of a process 600 for generating a discrete-time baseband conjugate-symmetric signal s UAD,n [m] according to some embodiments of the present disclosure. As Figure 6 shown, a single non-zero input is used to perform an L UAD -point IDFT 602. The input index can be determined according to the baseband frequency of the sub-carrier associated with the active terminal device , i.e., NΔf UAD . If n > 0, the input index is n. If n < 0, the input index is L UAD +n. The IDFT 602 can output L UAD -point samples. A parallel / serial (P / S) conversion 604 can be performed on the L UAD -point samples to obtain the IDFT output 606. The last part 612 (with a length of M - 1 points) of the IDFT output 506 is copied by circular shift as the conjugate-symmetric component 612' and appended before the IDFT output 508. The part of the IDFT output 506 before the last part 612 (with a length of L CP,UADThe penultimate part 610 of the (M points) is copied by cyclic shift and appended before the (M-1)-point conjugate symmetric component 612’ as CP 610’. The last L of the IDFT output 506 including the last three parts 610, 612, and 614 UAD - The M points can be discarded. The CP 610’, the (M-1)-point conjugate symmetric component 612’, and the first M points 608 of the IDFT output 506 can form s for transmission UAD,n [m] of the (2M + L CP,UAD - 1)-length signal. The CP 510’ can form the CP symbol 310 and the (M-1)-point conjugate symmetric component 612’, and the first M points 608 can form the UAD symbol 306 of the UAD signal shown in FIG. 3. Obviously, the procedure 600 is compatible with traditional multi-carrier systems such as LTE and NR.

[0142] In the transmission procedure, no coordination between terminal devices is required. Each terminal device operates independently according to its own scheduling request or traffic demand. An inactive terminal device will not perform any operation except to remain silent. The network device 120 has prior knowledge of the associated pattern between subcarriers and terminal devices, enabling the network device 120 to determine active terminal devices by detecting which subcarrier components are present in its superimposed observations.

[0143] In the transmission procedure 500, when converting the continuous-time baseband conjugate symmetric signal s UAD,n (t) to the RF UAD signal s RF,UAD,n (t), a pre-compensation method of introducing a pre-compensation phase factor in the carrier signal is adopted. As a practical solution, the pre-compensation phase factor can be estimated by a DL beacon signal broadcast from the network device to all potential terminal devices During the random access procedure, the DL beacon signal is typically used to synchronize the uplink transmission until the round-trip propagation delay, estimate the DL channel and utilize UL / DL reciprocity, and estimate the DL CPO.

[0144] Figure 7A FIG. shows an example diagram of the transmission of the DL beacon signal in the communication network 100 according to some embodiments of the present disclosure. Figure 7B FIG. shows an example diagram of the pre-compensation procedure 700 of the UL CPO according to some embodiments of the present disclosure. As Figure 7A shown, the network device 120 can broadcast a DL beacon signal to the set S of terminal devices. The DL beacon signal can contain a carrier signal Carrier signal The carrier signal may experience the corresponding DL propagation delay and then arrive at the terminal device asynchronously. In response to receiving the common DL beacon signal, the active terminal device n can be triggered to transmit the RF UAD signal sRF,UAD,n (t) is transmitted to network device 120. Thus, relative to the start time, the RF UAD signal s RF,UAD,n (t) will experience a round-trip propagation delay represented by d n . The DL propagation delay of the carrier signal in the DL beacon signal is half of the round-trip propagation delay. The carrier signal received by the terminal device n can be represented by , where . As

[0145] shown, each terminal device n can use a phase-locked loop (PLL) 702 to estimate the phase of the received carrier signal and obtain an estimated value of Figure 7B , represented by , such that . Based on the estimated , the local oscillator 704 can generate a carrier signal which can pre-compensate the UL CPO caused by the corresponding propagation delay d . n

[0146] Through the preamble design of the present disclosure, accurate, fast, and scalable UAD and timing acquisition can be constructed at a minimum measurement resource cost. The good signaling design of {s RF,UAD,n (t)} can facilitate the whole process and improve the detection efficiency and performance. The accurate result of UAD can eliminate the uncertainty in the observation model and reduce the problem dimension of timing acquisition after model reduction. Through some embodiments of the present disclosure, high capacity, scalability, and agility can be achieved. For example, fixed preamble allocation can be allowed, where dedicated sequences can be pre-allocated for each terminal device in advance. Instead of random preamble allocation, such fixed allocation prevents sequence conflicts. For random and distributed service requests, any prior coordination in sequence allocation is futile. In addition, the unique association between the sequence and the user avoids the additional cost of reporting the user ID. The required time-frequency cost may be comparable to the (average) number of active terminal devices and is independent of the number of a large number of terminal devices. The sparse C-FTN conjugate symmetric signaling design enables the NTB product to be comparable to twice the proportion of active terminal devices, where n∈S In addition, the complex precoding based on phase compensation conveys the active information and the propagation delay information, and allows accurate and fast user activity detection and timing acquisition at the network device.

[0147] A joint UAD and timing acquisition method based on NLS will be described with reference to Figure 8 . Figure 8 FIG. 800 shows an example diagram of a reception procedure of superimposed MC-FTN conjugate symmetric signaling according to some embodiments of the present disclosure. For the sake of discussion, reference will be made to​​Figure 1A and Figure 3B The frequency domain structure shown describes the reception procedure of the superimposed MC - FTN conjugate symmetric signal from the perspective of the network device 120.

[0148] As Figure 8 shown, the active terminal device n ∈ S A can send an exclusive RF UAD signal s RF,UAD,n (t) to the network device 120. The RF UAD signal s RF,UAD,n (t) may experience a round - trip propagation delay d n = τ n T s and the UL channel h n (t). According to - 2π fc τ n T s the UL CPO is canceled by the corresponding pre - compensation phase factor The network device 120 can receive the 802 asynchronous and superimposed signal g(t). The asynchronous and superimposed RF UAD signal received by the BS can be written as Equation (9):

[0149]

[0150] where n'(t) represents the additive interference including thermal noise and inter - cell interference. The network device 120 is configured to identify the unknown active subset S A and the relevant τ n .

[0151] In the reception procedure 800 for joint UAD and timing acquisition, in addition to the discrete Fourier transform (DFT) operation, the network device 120 can perform the standard processing as an OFDM receiver. In some embodiments, the network device 120 can convert 804 the received RF UAD signal g(t) into a continuous - time baseband signal z(t) by frequency - shifting based on the local carrier signal generated by the local oscillator 812. The continuous - time baseband signal z(t) can be written as Equation (10):

[0152]

[0153] where

[0154] Then, the network device 120 can convert 806 the continuous - time baseband signal z(t) into a discrete - time baseband signal z[m] of length (2M - 1+L s ) by an A / D converter operating at the sampling period t CP,UAD . The discrete - time baseband signal z[m] can be written as Equation (11):

[0155]

[0156] where \(n''[m]=n''(mT s )

[0157] Then, the network device 120 can remove the CP symbols consisting of the first \(L\) points of the discrete-time baseband signal \(z[m]\), thereby obtaining a \((2M - 1)\)-length superimposed complex conjugate symmetric sine sequence CP,UAD for joint UAD and timing acquisition. The \((2M - 1)\)-length sequence \(r[m]\) can be written as Equation (12):

[0158]

[0159] where \(n[m]=n''[m + M+L CP，UAD -1]\) and represents the received symbol in the subcarrier \(f_c + n\Delta f\) UAD associated with the terminal device \(n\in S\). In some embodiments where the pre-compensation of the UL CPO is inaccurate and thus may not be approximately 1, the received symbol can be written as \(\alpha\) n and \(P\) n both share the same index of non-zero entries caused by the active terminal devices.

[0160] The network device 120 can identify \(S\) and the relevant \(\tau\) A based on the \((2M - 1)\)-length sequence n by performing the joint UAD and timing acquisition algorithm 810. The index of the non-zero components in \(S\) is the same as the index of the active terminal devices. In Algorithm 810, the network device 120 is configured to detect the active terminal devices and estimate their propagation delays by recovering \(N\) unknowns from the \((2M - 1)\)-length observation . The observation model of Equation (12) involves an underdetermined linear system because the MC-FTN design follows the rule Without loss of generality, considering the case where \(B\) total \(=B\) UAD \(=N\Delta f\) UAD , the length of the observation satisfies which means an underdetermined linear system with more unknown variables than equations. Although is sparse with many zero entries, the non-zero components are usually complex, which makes it more challenging to solve the complex vector from the original received data.

[0161] Figure 9 illustrates an example implementation of a process for jointly using the UAD and timing acquisition algorithm 810 according to an embodiment of the present disclosure. As Figure 9 shown, at step 1, the network device may perform data preprocessing on the UAD by exploiting conjugate symmetry. The conjugate symmetry designed at the terminal device side enables the network device to remove from the original received data the real part of and thus generate the desired superimposed complex sinusoidal sequence depending only on the imaginary part of

[0162]

[0163] where denotes the imaginary part of α n , i.e.,

[0164]

[0165] The deliberate phase compensation strategy of the MC-FTN conjugate symmetric signaling at the terminal device side causes a sign constraint on the imaginary part of the received symbols, such that the imaginary part of the unknown vector is restricted to be non-positive for positive n or non-negative for negative n, as Figure 4C shown. Such a sign constraint on helps to solve for the sparse real vector from the superimposed complex sinusoidal sequence [m]. The observation model of equation (13) involves an effective non-negative underdetermined system. In addition, the complex sinusoidal sequences introduced by subcarrier allocation are crucial for capturing all the information about the unknown vector with minimal time-frequency resources. Such a careful and systematic design enables the network device 120 to implement a fast and accurate detection method, thereby recovering

[0166] from the noisy observation r[m] in the MC-FTN manner At step 2, the sparse real vector is estimated by solving a large-scale subproblem

[0167]

[0168] For n > 0, s.t. x n≤0, and for n < 0, x n ≥0. (14)

[0169] In step 3, the interference of the observation error is eliminated by determining the effective non-zero components in the estimated sparse real vector , and the rough estimate of the active subset is determined as the first identified set of active terminal devices. For example, the effective non-zero components can be the components greater than the threshold. In some embodiments, the rough estimate of the active subset can be determined by , where the first predefined threshold β low is assigned a small positive number to reduce the missed detection rate while tolerating a relatively high false alarm rate. In some embodiments, aiming for a lower missed detection rate, a decision threshold β low can be predefined such that includes almost all active terminal devices. The rough estimate of S A can be used to achieve model reduction of formula (12) by removing the components corresponding to the inactive terminal devices according to the rough estimate.

[0170] In step 4, by solving the reduced-scale small problem, a low-dimensional complex vector representing the received symbols in this subcarrier set associated with the first identified set of active terminal devices can be derived, that is For example, it can be based on the reduced observation model to solve for the dimensional unknowns, and through the small-scale linear minimum mean square error (L-MMSE) problem under non-negative constraints, an estimate of can be derived, as shown in equation (15)

[0171]

[0172] For n > 0, s.t. lm{z n} ≤ 0, and for n < 0, lm{z n} ≥ 0 (15)

[0173] where Im{·} represents the imaginary part of a complex number, and SNR represents the received signal-to-noise ratio (SNR).

[0174] In the optional step 5, the vector obtained in step 4 can be updated by replacing the imaginary part of the vector obtained in step 4 with the corresponding imaginary part in obtained in step 2, that is, for where Re{·} represents the real part of a complex number.

[0175] In step 6, by determining the estimated low-dimensional complex vector The valid non-zero components in are used to eliminate the interference of observation errors, and the active subset can be refined into a second identified set of active terminal devices. For example, the valid non-zero components can be components greater than a threshold. In some embodiments, the active subset can be refined by where β high >β low . The second predefined threshold β high is assigned a larger positive number to reduce the false alarm rate. In the case of pursuing a lower false alarm rate, the decision threshold β high can be increased, such that the number of non-active terminal devices in the refinement is reduced.

[0176] In step 7, based on the phase knowledge of , that is, , the propagation delays of the terminal devices in the refined active subset can be estimated. In some embodiments, can be derived as equation (16):

[0177]

[0178] In some embodiments, in the case where the non-perfect pre-compensation factor of the UL CPO results in a residual phase of , can be derived as equation (17):

[0179]

[0180] In this way, partial knowledge of the imaginary part can be used to derive a rough estimate of S A , and then the overall knowledge of can be used to refine via a strict threshold to reduce the false alarm rate and estimate the propagation delays of the updated active subset. In this way, the network device can implement a fast and accurate method to recover the unknown vector and obtain the propagation delays from the noisy observation r[m] in the MC-FTN manner.

[0181] Figure 10 shows an example implementation of a process 1000 for communication according to an embodiment of the present disclosure. The process 1000 shows a TDD large-scale random access procedure based on MC-FTN conjugate symmetric signaling, where UL / DL channel reciprocity can be utilized to simplify phase compensation. Note that the process 1000 can be regarded as a more specific example of the process 200 of Figure 2 . Figure 10An example implementation is depicted and described from the perspective of the active UE 1010-1, the inactive UE 1010-3, and the BS 1020.

[0182] At the start of the transmission cycle, the BS 1020 may broadcast a DL pilot sequence in the network. The DL pilot sequence may also be used as a beacon signal for synchronization. Based on the received DL pilot sequence, the active UE 1010-1 may estimate the corresponding DL channel state information (CSI) and DL CPO. The active UE 1010-1 may determine a phase compensation factor and a power factor by utilizing UL / DL based on the estimated DL CSI, and encode the symbols to be transmitted with the determined phase compensation factor and power factor. The active UE 1010-1 may further predict the UL CPO based on the estimated DL CPO, and generate a carrier signal with a pre-compensation phase factor having the UL CPO. Based on the carrier signal, the active UE 1010-1 may convert the symbols into MC-FTN conjugate symmetric signaling, and transmit the MC-FTN conjugate symmetric signaling to the BS 1020 in the associated subcarriers. The BS 1020 may perform joint UAD and timing acquisition, and obtain the identified set of active UEs and the corresponding TA information based on the superimposed observations. The BS 1020 may broadcast a mapping list through a low-rate DL channel accessible to all UEs in the network, and the mapping list indicates the identified active UEs. Each entry of the mapping list is dedicated to the identified UE, and contains the ID of the identified UE, information about the associated TA, and the allocated UL channel. The BS 1020 may allocate these resources only to the identified UEs. Table 1 shows an example of the information in the mapping list.

[0183] Table 1 Mapping List

[0184] Detected ID of UE 1 TA #UL CH,… Detected ID of UE 1 TA #UL CH,… Detected ID of UE 3 TA #UL CH,… … … …

[0185] Any UE may check the mapping list. By checking, the active UE may determine whether it has been successfully identified by the BS 1020. The identified active UE may know its scheduling grant in the mapping list, and may continue to send further data, such as for connection state establishment, through the allocated UL channel. Alternatively, the identified active UE n may transmit encoded data symbols in its associated subcarriers, which subcarriers have a pre-compensation factor with the UL CPO, for transmitting a message of several bits. For example, the identified active UE n may transmit a data signal, which may be written as where t is the CP length of the data signal, and b CP is nis a data symbol, e.g., derived from a Quadrature Amplitude Modulation (QAM) constellation. An undetected active UE may not find anything related to it in the mapping list and may be demoted to the next transmission period for attempting a new random access. For example, an undetected active UE can signal a new access by retransmitting the MC-FTN conjugate symmetric signaling in the next transmission period.

[0186] Figure 11A Shows an example implementation of MC-FTN conjugate symmetric signaling in the frequency domain according to some embodiments of the present disclosure. Figure 11B Displays an example diagram of a conventional PRACH signal in the frequency domain. Figure 11C Shows an example diagram of MC-FTN conjugate symmetric signaling and a conventional PRACH signal in the time domain. Consider a cell with a radius of 500 meters, serving a total of 720 random access UEs. In this case, the maximum possible round-trip propagation delay is 3.33 μs, and the maximum allowable bandwidth for random access may be 300 kHz. As Figure 11A shown, one UAD symbol based on MC-FTN conjugate symmetric signaling can support 240 UEs with a subcarrier spacing of 1.25 kHz, and each subcarrier is assigned to a unique UE. The NTB product of the MC-FTN conjugate symmetric signaling is 0.25, and thus the symbol duration is reduced to 0.2 ms. Therefore, a resource block of 0.9 ms × 300 kHz can accommodate three independent UAD symbols, as Figure 11C shown. A total of 720 UEs are divided into 3 subsets, each subset consisting of 240 UEs and served by dedicated symbols.

[0187] In contrast, the PRACH method supports all UEs through a single symbol with a length of 0.8 ms. According to the design criteria of LTE / NR, a source block of 0.9 ms × 300 kHz allows a u-th root ZC sequence of length 241, i.e., where N ZC = 241. n CS –1 = 2's minimum zero-correlation zone takes into account the multipath spread delay and the maximum propagation delay within a 500m radius cell. Therefore, for v = 0, 1,..., 80, there are at most 80 available orthogonal ZC sequences, i.e., where C v = vN CS . As Figure 11B shown, each UE spreads its selected sequence over all subcarriers. Active UEs i and j independently select sequences x u,vi (n) and x u,vj (n) from the same group of 80 orthogonal length-241 ZC sequences. If v i = v j, which results in sequence conflicts.

[0188] Figure 12A and Figure 12B shows the joint UAD and timing acquisition performance comparison between MC-FTN conjugate symmetric signaling according to some embodiments of the present disclosure and a conventional PRACH procedure via ZC sequences under the same time-frequency resources (0.9 ms × 300 kHz). Table 2 lists the detailed simulation parameters of these two procedures.

[0189] Table 2: Simulation settings

[0190]

[0191] The UAD performance is evaluated according to the probability of missed detection and false alarm, while the timing acquisition performance is evaluated according to the estimation deviation. The simulation results are obtained by averaging over more than 10,000 independent experiments. Figure 12A shows the UAD performance at different transmission probabilities. For MC-FTN signaling, the threshold of the transmission probability is 12.5%, beyond which the SNR improvement significantly decreases and the performance is limited by the degrees of freedom. In fact, in the simulation case, the threshold is consistent with the half NTB product of the MC-FTN conjugate symmetric signaling. Figure 12B shows the timing acquisition performance with a sampling period of 0.033 μs, where the estimation deviation is calculated only for the identified UEs. As Figure 12A and Figure 12B shown, at higher SNR conditions, longer tails of a larger number of the identified UEs are found. The simulation results show that compared with the existing PRACH scheme, the proposed MC-FTN conjugate symmetric signaling can increase the number of supported concurrent random access users by more than four times. Such a significant advantage benefits from the overall design from FTN and collision-free waveforms, conjugate symmetry, phase compensation to advanced algorithms for joint UAD and timing acquisition. In contrast, for PARCH, sequence conflicts from random selection are still the main reason for performance degradation.

[0192] Figure 13 shows a flowchart of method 1300 implemented at a terminal device according to some embodiments of the present disclosure. For example, method 1300 can be executed at terminal device 110 (e.g., the first terminal device 110-1), as Figure 1A shown. For ease of discussion, method 1300 will be described below with reference to Figure 1A . It should be understood that method 1300 may include additional blocks not shown and / or some of the shown blocks may be omitted, and the scope of the present disclosure is not limited in this regard. Through Figure 13 's method 1300, a new solution for reducing latency and measurement resource cost for joint UAD and timing acquisition in large-scale access is provided.

[0193] At block 1320, the terminal device 110 receives, from a network device 120 in a radio access network, a configuration associated with a subcarrier set, where the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal. The modulated conjugate symmetric signal indicates activity information of an active set of terminal devices in the set of terminal devices. At block 1340, the terminal device 110 transmits the modulated conjugate symmetric signal to the network device 120, where the modulated conjugate symmetric signal is generated by modulating subcarriers in the subcarrier set with symbols, and the modulated conjugate symmetric signal includes sparse MC-FTN conjugate symmetric signaling.

[0194] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate symmetric signaling may be greater than or equal to twice the ratio of the number of the active set of terminal devices to the number of the set of terminal devices. In some embodiments, the subcarriers may be associated only with the terminal device 110.

[0195] In some embodiments, to generate a subcarrier, the terminal device 110 may generate a complex conjugate symmetric sine waveform at the frequency of the subcarrier and add a cyclic prefix to the complex conjugate symmetric sine waveform. The duration of the complex conjugate symmetric sine waveform may be determined based on the reciprocal of the subcarrier spacing of the subcarrier set, the number of the active set of terminal devices, and the number of the set of terminal devices.

[0196] In some embodiments, the terminal device 110 may determine a pre-compensation phase factor for the complex conjugate symmetric sine waveform with a cyclic prefix. The pre-compensation phase factor pre-compensates the UL CPO of the carrier signal of the modulated conjugate symmetric signal caused by the propagation delay from the terminal device 110 to the network device 120.

[0197] In some embodiments, to determine the pre-compensation phase factor, the terminal device 110 may receive a beacon signal including a carrier signal from the network device 120; determine the DL CPO of the carrier signal caused by the propagation delay from the network device to the terminal device based on the received beacon signal; and determine the pre-compensation phase factor based on the determined DL CPO.

[0198] In some embodiments, the symbols may include a variable phase compensation factor and a fixed phase compensation factor for compensating the phase of the channel between the network device 120 and the terminal device 110 in the subcarriers.

[0199] In some embodiments, the terminal device 110 may determine the variable phase compensation factor based on the beacon signal and the channel reciprocity between UL and DL.

[0200] In some embodiments, the terminal device 110 may determine a fixed phase compensation factor based on the frequency of a subcarrier, the frequency of a carrier signal, the deviation between a variable phase compensation factor and the phase of the channel between the network device 120 and the terminal device 110 in the subcarrier, and the deviation between a pre-compensation phase factor and the UL CPO.

[0201] In some embodiments, the subcarrier may be in a frequency band. The bandwidth of the frequency band may be determined based on the maximum propagation delay in the radio access network, the deviation between a variable phase compensation factor and the phase of the channel between the network device and the terminal device in the subcarrier, and the deviation between a pre-compensation phase factor and the UL CPO.

[0202] In some embodiments, the terminal device 110 may generate a discrete-time baseband conjugate-symmetric signal based on the baseband frequency of a subcarrier, a variable phase compensation factor, and a fixed phase compensation factor; generate a continuous-time baseband conjugate-symmetric signal through digital-to-analog conversion based on the discrete-time baseband conjugate-symmetric signal; and perform a frequency shift on the continuous baseband conjugate-symmetric signal to generate a modulated conjugate-symmetric signal.

[0203] In some embodiments, to generate a discrete-time baseband conjugate-symmetric signal, the terminal device 110 may generate a first sequence modulated by a variable phase compensation factor and a fixed phase compensation factor by performing an IDFT; insert a copy of the last part of the first sequence appended before the first sequence to obtain a second sequence; and discard the last part of the second sequence to obtain the discrete-time baseband conjugate-symmetric signal. The non-zero components of the input of the IDFT may include the variable phase compensation factor and the fixed phase compensation factor corresponding to the subcarrier. The last part of the first sequence may include a cyclic prefix and a conjugate-symmetric component. The length of the discrete-time baseband conjugate-symmetric signal except for the cyclic prefix may be determined based on the duration and sampling rate of the modulated conjugate-symmetric signal.

[0204] In some embodiments, the terminal device 110 may perform a frequency shift using a pre-compensation phase factor for pre-compensating the UL CPO.

[0205] In some embodiments, the terminal device 110 may receive an indication from the network device 120 indicating a set of active terminal devices identified by the network device 120; determine whether the terminal device 110 is included in the set of active terminal devices identified by the network device 120; and perform communication with the network device 120 based on the determination that the terminal device 110 is included in the set of active terminal devices identified by the network device 120, or retransmit the modulated conjugate-symmetric signal to the network device 120 based on the determination that the terminal device is excluded from the set of active terminal devices identified by the network device 110.

[0206] In some embodiments, the terminal device 110 may transmit data symbols with variable phase compensation factors in subcarriers having a pre-compensation factor of UL CPO, and the data symbols are mapped to service data.

[0207] In some embodiments, the indication may indicate resources for performing communication by the set of active terminal devices respectively identified by the network device 120. The terminal device 110 may use corresponding resources related to the terminal device 110 to perform communication with the network device 120. In some embodiments, the indication may further indicate timing advance information related to the set of active terminal devices respectively identified by the network device 120. The terminal device 110 may perform communication with the network device 120 based on the corresponding timing advance information related to the terminal device 110.

[0208] Figure 14 A flowchart of a method 1400 implemented at a network device according to some embodiments of the present disclosure is shown. For example, the method 1400 may be executed at the network device 120, as Figure 1A shown. For ease of discussion, method 1400 will be described below with reference to Figure 1A the description of method 1400. It should be understood that method 1400 may include additional blocks not shown and / or some of the shown blocks may be omitted, and the scope of the present disclosure is not limited in this regard. By Figure 14 way of method 1400, a new solution for reducing latency and measurement resource cost of UAD for massive access is provided.

[0209] In block 1420, the network device 120 transmits a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network. The set of subcarriers is associated with the set of terminal devices for transmitting modulated conjugate symmetric signals. The modulated conjugate symmetric signals represent activity information of the set of active terminal devices in the set of terminal devices. In block 1440, the network device 120 receives a superimposed signal associated with the modulated conjugate symmetric signals from the set of active terminal devices. The modulated conjugate symmetric signals are generated by modulating the set of subcarriers associated with the set of active terminal devices with a set of symbols corresponding to the set of active terminal devices respectively, and include sparse MC-FTN conjugate symmetric signaling. In block 1440, the network device 120 identifies the set of active terminal devices from the set of terminal devices based on the received superimposed signal.

[0210] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate symmetric signaling may be greater than or equal to twice the ratio of the number of the set of active terminal devices to the number of the set of terminal devices.

[0211] In some embodiments, each symbol in the symbol set may include a variable phase compensation factor and a fixed phase compensation factor. The variable phase compensation factor is used to compensate for the phase of the channel between the network device 120 and the corresponding active terminal device in the associated subcarrier. The fixed phase compensation factor may be based on the deviation between the variable phase compensation factor and the phase of the channel between the network device 120 and the corresponding active device in the associated subcarrier.

[0212] In some embodiments, to identify the set of active terminal devices, the network device 120 may determine a superimposed complex conjugate symmetric sine sequence based on the superimposed signal, where the sequence includes symbols received in the subcarrier set associated with the set of terminal devices; determine a superimposed complex sine sequence based on the superimposed complex conjugate symmetric sine sequence and its conjugate symmetry, where the sequence includes the imaginary parts of the symbols received in the subcarriers associated with the set of terminal devices and excludes the real parts of the symbols received in the subcarrier set associated with the set of terminal devices; determine a first identified set of active terminal devices based on the superimposed complex sine sequence; and determine a second identified set of active terminal devices as the identified set of active terminal devices based on the superimposed complex conjugate symmetric sine sequence and the first identified set of active terminal devices.

[0213] In some embodiments, to determine the first identified set of active terminal devices, the network device 120 may determine a sparse real vector based on the superimposed complex sine sequence, where the sparse real vector represents the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices; determine the effective non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices by comparing the absolute values of the components of the sparse real vector with a first predefined threshold; and determine the first identified set of active terminal devices based on the effective non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices.

[0214] In some embodiments, the network device 120 may determine the sparse real vector by solving an effective non-negative least squares problem based on the superimposed complex sine sequence. The components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with a frequency lower than the carrier frequency may be non-negative, and the components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with a frequency higher than the carrier frequency may be non-positive.

[0215] In some embodiments, to determine the second identified set of active terminal devices, network device 120 may determine a low-dimensional complex vector based on an overlaid complex conjugate symmetric sine sequence, where the low-dimensional complex vector represents the received symbols in the subcarrier set associated with the first identified set of active terminal devices; determine the valid non-zero components of the received symbols in the subcarrier set associated with the first identified set of active terminal devices by comparing the magnitudes of the components of the low-dimensional complex vector with a second predefined threshold; and determine the second identified set of active terminal devices based on the valid non-zero components of the received symbols in the subcarrier set associated with the first identified set of active terminal devices.

[0216] In some embodiments, network device 120 may determine the low-dimensional complex vector under the following constraints: the components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols in the subcarrier set with frequencies lower than the carrier frequency are non-negative, and the components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols in the subcarrier set with frequencies higher than the carrier frequency are non-positive.

[0217] In some embodiments, network device 120 may replace the imaginary parts of the received symbols in the subcarrier set associated with the first identified set of active terminal devices with corresponding imaginary parts derived from a sparse real vector.

[0218] In some embodiments, network device 120 may determine the propagation delay from the second identified set of active terminal devices to network device 120 based on the phases of the received symbols in the subcarrier set associated with the second identified set of active terminal devices.

[0219] In some embodiments, network device 120 may determine timing advance information related to the second identified set of active terminal devices based on the determined propagation delay from the second identified set of active terminal devices to network device 120; and transmit, via a common channel, an indication indicating the identified set of active terminal devices and the related timing advance information to the set of terminal devices.

[0220] In some embodiments, the indication may indicate the resources for each active terminal device in the identified set of active terminal devices to perform communication, respectively.

[0221] In some embodiments, network device 120 may send a beacon signal to the set of terminal devices to indicate the transmission of sparse MC-FTN conjugate symmetric signaling.

[0222] In some embodiments, an apparatus (e.g., terminal device 110) capable of performing any of the methods in method 1300 may include components for performing the corresponding steps of method 1300. The components may be implemented in any suitable form. For example, the components may be implemented in circuitry or software modules.

[0223] In some embodiments, the apparatus includes: means for receiving, at a terminal device, configuration associated with a subcarrier set from a network device in a radio access network, where the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active set of terminal devices in the set of terminal devices; and means for transmitting the modulated conjugate symmetric signal to the network device, where the modulated conjugate symmetric signal is generated by modulating subcarriers from the subcarrier set with symbols, and the modulated conjugate symmetric signal includes sparse MC-FTN conjugate symmetric signaling.

[0224] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate symmetric signaling may be greater than or equal to twice the ratio of the number of the active set of terminal devices to the number of the set of terminal devices. In some embodiments, the subcarriers may be associated with only the terminal devices.

[0225] In some embodiments, the means for generating subcarriers may include means for generating a complex conjugate symmetric sine waveform having a subcarrier frequency and means for adding a cyclic prefix to the complex conjugate symmetric sine waveform. The duration of the complex conjugate symmetric sine waveform may be determined based on the reciprocal of the subcarrier spacing of the subcarrier set, the number of the active set of terminal devices, and the number of the set of terminal devices.

[0226] In some embodiments, the apparatus may further include means for determining a pre-compensation phase factor for the complex conjugate symmetric sine waveform with a cyclic prefix, where the pre-compensation phase factor pre-compensates the UL CPO of the carrier signal of the modulated conjugate symmetric signal caused by the propagation delay from the terminal device to the network device.

[0227] In some embodiments, the means for determining the pre-compensation phase factor may include means for receiving a beacon signal including a carrier signal from the network device; means for determining the DL CPO of the carrier signal caused by the propagation delay from the network device to the terminal device based on the received beacon signal; and means for determining the pre-compensation phase factor based on the determined DL CPO.

[0228] In some embodiments, the symbols may include a variable phase compensation factor and a fixed phase compensation factor for compensating the channel phase between the network device and the terminal device in the subcarriers.

[0229] In some embodiments, the apparatus may further include means for determining the variable phase compensation factor based on the beacon signal and the channel reciprocity between UL and DL.

[0230] In some embodiments, the apparatus may further include components for determining a fixed phase compensation factor based on the frequency of a subcarrier, the frequency of a carrier signal, the deviation between a variable phase compensation factor and the phase of a channel between a network device and a terminal device in the subcarrier, and the deviation between a pre-compensation phase factor and an UL CPO.

[0231] In some embodiments, the subcarrier may be in a frequency band. The bandwidth of the frequency band may be determined based on the maximum propagation delay in a radio access network, the deviation between a variable phase compensation factor and the channel phase between a network device and a terminal device in the subcarrier, and the deviation between a pre-compensation phase factor and an UL CPO.

[0232] In some embodiments, the apparatus may further include components for generating a discrete-time baseband conjugate symmetric signal based on the baseband frequency of a subcarrier, a variable phase compensation factor, and a fixed phase compensation factor; components for generating a continuous-time baseband conjugate symmetric signal based on the discrete-time baseband conjugate symmetric signal through digital-to-analog conversion; and components for performing a frequency shift on the continuous baseband conjugate symmetric signal to generate a modulated conjugate symmetric signal.

[0233] In some embodiments, the components for generating a discrete-time baseband conjugate symmetric signal may include components for generating a first sequence modulated by a variable phase compensation factor and a fixed phase compensation factor by performing an IDFT; components for inserting a copy of the last part of the first sequence appended before the first sequence to obtain a second sequence; and components for discarding the last part of the second sequence to obtain the discrete-time baseband conjugate symmetric signal. The non-zero components of the input of the IDFT may include the variable phase compensation factor and the fixed phase compensation factor corresponding to the subcarrier. The last part of the first sequence may include a cyclic prefix and a conjugate symmetric component. The length of the discrete-time baseband conjugate symmetric signal except for the cyclic prefix may be determined based on the duration and sampling rate of the modulated conjugate symmetric signal.

[0234] In some embodiments, the apparatus may further include components for performing a frequency shift with a pre-compensation phase factor for pre-compensating an UL CPO.

[0235] In some embodiments, the apparatus may further include components for receiving an indication from a network device indicating a set of active terminal devices identified by the network device; components for determining whether a terminal device is included in the set of active terminal devices identified by the network device; and components for performing communication with the network device based on the determination that the terminal device is included in the set of active terminal devices identified by the network device, or for retransmitting the modulated conjugate symmetric signal to the network device based on the determination that the terminal device is excluded from the set of active terminal devices identified by the network device.

[0236] In some embodiments, the apparatus may further include components for transmitting data symbols with variable phase compensation factors in subcarriers having a pre-compensation factor for UL CPO, where the data symbols are mapped to service data.

[0237] In some embodiments, the indication may indicate resources for performing communication for the set of active terminal devices separately identified by the network device. The apparatus may further include components for performing communication with the network device using corresponding resources related to the terminal device.

[0238] In some embodiments, the indication may indicate timing advance information related to the set of active terminal devices separately identified by the network device. The apparatus may further include components for performing communication with the network device based on corresponding timing advance information related to the terminal device.

[0239] In some embodiments, the apparatus further includes components for performing other steps in some embodiments of method 1300. In some embodiments, the components include at least one processor and at least one memory, the at least one memory including computer program code, and the at least one memory and the computer program code are configured to cause the apparatus to be executed by the at least one processor.

[0240] In some embodiments, an apparatus (e.g., network device 120) capable of performing any of the methods in method 1400 may include components for performing the corresponding steps of method 1400. The components may be implemented in any suitable form. For example, the components may be implemented in a circuit device or a software module.

[0241] In some embodiments, the apparatus includes: components for transmitting, at a network device, a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network, where the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, and the modulated conjugate symmetric signal indicates activity information of a set of active terminal devices in the set of terminal devices; components for receiving, from the set of active terminal devices, a superimposed signal associated with the modulated conjugate symmetric signal, where the modulated conjugate symmetric signal is generated by modulating the set of subcarriers associated with the set of active terminal devices with a corresponding set of symbols for the set of active terminal devices and includes sparse MC-FTN conjugate symmetric signaling; and components for identifying the set of active terminal devices from the set of terminal devices based on the received superimposed signal.

[0242] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate symmetric signaling may be greater than or equal to twice the ratio of the number of the set of active terminal devices to the number of the set of terminal devices.

[0243] In some embodiments, each symbol in the symbol set may include a variable phase compensation factor and a fixed phase compensation factor for compensating the phase of the channel between the network device and the corresponding active terminal device in the associated subcarrier. The fixed phase compensation factor may be based on the deviation between the variable phase compensation factor and the phase of the channel between the network device and the corresponding active device in the associated subcarrier.

[0244] In some embodiments, the component for identifying the set of active terminal devices may include a component for determining a superimposed complex conjugate symmetric sine sequence based on the superimposed signal, the sequence including symbols received in the subcarrier set associated with the set of terminal devices; a component for determining a superimposed complex sine sequence based on the superimposed complex conjugate symmetric sine sequence and its conjugate symmetry, the sequence including the imaginary parts of the symbols received in the subcarriers associated with the set of terminal devices and excluding the real parts of the symbols received in the subcarrier set associated with the set of terminal devices; a component for determining a first identified set of active terminal devices based on the superimposed complex sine sequence; and a component for determining a second identified set of active terminal devices as the identified set of active terminal devices based on the superimposed complex conjugate symmetric sine sequence and the first identified set of active terminal devices.

[0245] In some embodiments, the component for determining the first identified set of active terminal devices may include a component for determining a sparse real vector based on the superimposed complex sine sequence, the sparse real vector representing the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices; a component for determining the effective non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices by comparing the absolute values of the components of the sparse real vector with a first predefined threshold; and a component for determining the first identified set of active terminal devices based on the effective non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices.

[0246] In some embodiments, the apparatus may further include a component for determining the sparse real vector by solving an effective non-negative least squares problem based on the superimposed complex sine sequence. The components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with a frequency lower than the carrier frequency may be non-negative, and the components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with a frequency higher than the carrier frequency may be non-positive.

[0247] In some embodiments, the component for determining the second identified set of active terminal devices may include a component for determining a low-dimensional complex vector based on an overlaid complex conjugate symmetric sine sequence, the low-dimensional complex vector representing the received symbols in the subcarrier set associated with the first identified set of active terminal devices; a component for determining the valid non-zero components of the received symbols in the subcarrier set associated with the first identified set of active terminal devices by comparing the magnitudes of the components of the low-dimensional complex vector with a second predefined threshold; and a component for determining the second identified set of active terminal devices based on the valid non-zero components of the received symbols in the subcarrier set associated with the first identified set of active terminal devices.

[0248] In some embodiments, the apparatus may further include a component for determining the low-dimensional complex vector under the following constraints: the components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols in the subcarrier set with frequencies lower than the carrier frequency are non-negative, and the components of the low-complexity vector corresponding to the imaginary parts of the received symbols in the subcarrier set with frequencies higher than the carrier frequency are non-positive.

[0249] In some embodiments, the apparatus may further include a component for replacing the imaginary parts of the received symbols in the subcarrier set associated with the first identified set of active terminal devices with corresponding imaginary parts derived from a sparse real vector.

[0250] In some embodiments, the apparatus may further include a component for determining the propagation delay from the second identified set of active terminal devices to the network device based on the phases of the received symbols in the subcarrier set associated with the second identified set of active terminal devices.

[0251] In some embodiments, the apparatus may further include a component for determining timing advance information related to the second identified set of active terminal devices based on the determined propagation delay from the second identified set of active terminal devices to the network device; and a component for transmitting, via a common channel, an indication of the identified set of active terminal devices and the related timing advance information to the set of terminal devices, respectively.

[0252] In some embodiments, the indication may indicate resources for each active terminal device in the identified set of active terminal devices to perform communication, respectively.

[0253] In some embodiments, the apparatus may further include a component for transmitting a beacon signal to the set of terminal devices, the beacon signal indicating the transmission of sparse MC-FTN conjugate symmetric signaling.

[0254] In some embodiments, the apparatus further includes components for performing other steps in some embodiments of method 1400. In some embodiments, the components include at least one processor and at least one memory, the at least one memory including computer program code, the at least one memory and the computer program code being configured to cause the apparatus to be executed by the at least one processor.

[0255] Figure 15 is a simplified block diagram of a device 1500 suitable for implementing embodiments of the present disclosure. The device 1500 may be provided to implement a communication device, such as Figure 1A the terminal device 110 or the network device 120 shown. As shown, the device 1500 includes one or more processors 1510, one or more memories 1540 coupled to the processors 1510, and one or more communication modules 1540 coupled to the processors 1520.

[0256] The communication module 1540 is used for two-way communication. The communication module 1540 has at least one antenna to facilitate communication. The communication interface may represent any interface required for communicating with other network elements.

[0257] The processor 1510 may be of any type suitable for a local technical network and may include one or more of the following: a general-purpose computer, a special-purpose computer, a microprocessor, a digital signal processor (DSP), and a processor based on a multi-core processor architecture, as non-limiting examples. The device 1500 may have multiple processors, such as an application-specific integrated circuit chip that is subordinate to the clock of a synchronous main processor in time.

[0258] The memory 1520 may include one or more non-volatile memories and one or more volatile memories. Examples of non-volatile memories include, but are not limited to, read-only memory (ROM) 1524, electrically programmable read-only memory (EPROM), flash memory, hard disk, compact disc (CD), digital video disc (DVD), and other magnetic storage and / or optical storage. Examples of volatile memories include, but are not limited to, random access memory (RAM) 1522 and other volatile memories that do not persist during a power outage duration.

[0259] The computer program 1530 includes computer-executable instructions executed by the associated processor 1510. The program 1530 may be stored in the ROM 1524. The processor 1510 may perform any suitable actions and processes by loading the program 1530 into the RAM 1522.

[0260] Embodiments of the present disclosure may be implemented by the program 1530 such that the device 1500 may perform with reference to Figures 1A to 13Any process of the present disclosure discussed. Embodiments of the present disclosure may also be implemented by hardware or a combination of software and hardware.

[0261] In some embodiments, the program 1530 may be tangibly embodied in a computer-readable medium, which may be included in the device 1500 (such as the memory 1520) or other storage devices accessible to the device 1500. The device 1500 may load the program 1530 from the computer-readable medium into the RAM 1522 for execution. The computer-readable medium may include any type of tangible non-volatile storage device, such as ROM, EPROM, flash memory, hard disk, CD, DVD, etc. Figure 16 An example of a computer-readable medium 1600 in the form of a CD or DVD is shown. The program 1530 is stored on the computer-readable medium.

[0262] Generally, various embodiments of the present disclosure may be implemented in hardware or special-purpose circuits, software, logic, or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software, which may be executed by a controller, a microprocessor, or other computing devices. Although various aspects of the embodiments of the present disclosure are shown and described as block diagrams, flowcharts, or using some other graphical representation, it should be understood that, by way of non-limiting example, the blocks, devices, systems, techniques, or methods described herein may be implemented in hardware, software, firmware, special-purpose circuits or logic, general-purpose hardware or controllers, or other computing devices, or some combination thereof.

[0263] The present disclosure also provides at least one computer program product, which is tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as the instructions included in the program module, which are executed in a device on a target real or virtual processor to perform the methods 1300 or 1400 described above with reference to Figures 1A to 14 As described. Generally, the program module includes routines, programs, libraries, objects, classes, components, data structures, etc., which perform specific tasks or implement specific abstract data types. In various embodiments, the functions of the program module may be combined or divided as desired among the program modules. The machine-executable instructions of the program module may be executed within a local or distributed device. In a distributed device, the program module may be located in both local and remote storage media.

[0264] The program code for performing the methods of the present disclosure can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing devices, such that when the program codes are executed by the processor or controller, the functions / operations specified in the flowchart and / or block diagram are implemented. The program code can be executed entirely on the machine, partially on the machine, as a stand-alone software package, partially on the computer and partially on a remote machine, or entirely on a remote machine or server.

[0265] In the context of the present disclosure, the computer program code or related data can be carried by any suitable carrier to enable a device, apparatus, or processor to perform the various processes and operations as described above. Examples of the carrier include signals, computer-readable media, etc.

[0266] The computer-readable media can be a computer-readable signal medium or a computer-readable storage medium. The computer-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or apparatuses, or any suitable combination of the foregoing. More specific examples of the computer-readable storage media will include an electrical connection having one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. The term "non-transitory" as used herein is a limitation on the medium itself (i.e., tangible, rather than a signal), rather than a limitation on the persistence of data storage (e.g., RAM versus ROM).

[0267] Furthermore, although the operations are depicted in a specific order, this should not be construed as requiring that the operations be performed in the specific order or sequence shown, or that all of the illustrated operations be performed, to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these details should not be construed as limiting the scope of the present disclosure, but rather as descriptions of features that may be specific to a particular embodiment. Certain features described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment can also be implemented separately or in any suitable sub-combination in multiple embodiments.

[0268] Although this disclosure is described in language specific to structural features and / or methodological acts, it is to be understood that the disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts are disclosed as example forms of implementing the claims.

Claims

1. A terminal device in a radio access network, comprising: at least one processor; and at least one memory storing instructions which, when executed by the at least one processor, cause the terminal device to at least: receive from a network device in the radio access network a configuration associated with a sub - carrier set, wherein the sub - carrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate - symmetric signal, and the modulated conjugate - symmetric signal indicates activity information of an active set of terminal devices in the set of terminal devices; and transmit to the network device a modulated conjugate - symmetric signal, wherein the modulated conjugate - symmetric signal is generated by modulating sub - carriers from the sub - carrier set with symbols, and the modulated conjugate - symmetric signal includes: faster - than - Nyquist sparse multi - carrier (MC - FTN) conjugate - symmetric signaling.

2. The terminal device according to claim 1, wherein the normalized time - bandwidth product of the sparse MC - FTN conjugate - symmetric signaling is greater than or equal to twice the ratio of the number of the active set of terminal devices to the number of the set of terminal devices.

3. The terminal device according to claim 1 or 2, wherein the sub - carriers are only associated with the terminal device.

4. The terminal device according to any one of claims 1 to 3, wherein the terminal device is caused to generate the sub - carriers by: generating a complex conjugate - symmetric sine waveform having the frequency of the sub - carriers, wherein the duration of the complex conjugate - symmetric sine waveform is determined based on the reciprocal of the sub - carrier spacing of the sub - carrier set, the number of the active set of terminal devices, and the number of the set of terminal devices; and adding a cyclic prefix to the complex conjugate - symmetric sine waveform.

5. The terminal device according to claim 4, wherein the terminal device is further caused to determine a pre - compensation phase factor for the complex conjugate - symmetric sine waveform having the cyclic prefix, and the pre - compensation phase factor pre - compensates an uplink carrier phase offset (UL CPO) of a carrier signal of the modulated conjugate - symmetric signal caused by the propagation delay from the terminal device to the network device.

6. The terminal device according to claim 5, wherein the terminal device is further caused to determine the pre - compensation phase factor by: receiving from the network device a beacon signal including the carrier signal; determining, based on the received beacon signal, a downlink carrier phase offset (DL CPO) of the carrier signal caused by the propagation delay from the network device to the terminal device; and determining the pre - compensation phase factor based on the determined DL CPO.

7. The terminal device according to claim 6, wherein the symbol comprises: a variable phase compensation factor for compensating the phase of a channel between the network device and the terminal device in the sub - carriers, and a fixed phase compensation factor.

8. The terminal device according to claim 7, wherein the terminal device is further caused to determine the variable phase compensation factor based on the beacon signal and the channel reciprocity between UL and DL.

9. The terminal device according to claim 7, wherein the terminal device is further caused to determine the fixed phase compensation factor based on the frequency of the subcarrier, the frequency of the carrier signal, the deviation between the variable phase compensation factor and the phase of the channel between the network device and the terminal device in the subcarrier, and the deviation between the pre-compensation phase factor and the UL CPO.

10. The terminal device according to claim 7, wherein the subcarrier is in a frequency band, and the bandwidth of the frequency band is determined based on the maximum propagation delay in the radio access network, the deviation between the variable phase compensation factor and the phase of the channel between the network device and the terminal device in the subcarrier, and the deviation between the pre-compensation phase factor and the UL CPO.

11. The terminal device according to claim 7, wherein the terminal device is further caused to: generate a discrete-time baseband conjugate symmetric signal based on the baseband frequency of the subcarrier, the variable phase compensation factor, and the fixed phase compensation factor; generate a continuous-time baseband conjugate symmetric signal through digital-to-analog conversion based on the discrete-time baseband conjugate symmetric signal; and perform a frequency shift on the continuous baseband conjugate symmetric signal to generate the modulated conjugate symmetric signal.

12. The terminal device according to claim 11, wherein the terminal device is caused to generate the discrete-time baseband conjugate symmetric signal by: generating a first sequence modulated by the variable phase compensation factor and the fixed phase compensation factor by performing an inverse discrete Fourier transform (IDFT), wherein the non-zero components of the input of the IDFT include: the variable phase compensation factor and the fixed phase compensation coefficient corresponding to the subcarrier; inserting a copy of the last part of the first sequence appended before the first sequence to obtain a second sequence, wherein the last part of the first sequence includes a cyclic prefix and a conjugate symmetric component; and discarding the last part of the second sequence to obtain the discrete-time baseband conjugate symmetric signal, wherein the length of the discrete-time baseband conjugate symmetric signal except for the cyclic prefix is determined based on the duration and sampling rate of the modulated conjugate symmetric signal.

13. The terminal device according to claim 11, wherein the terminal device is further caused to perform a frequency shift with the pre-compensation phase factor for pre-compensating the UL CPO.

14. The terminal device according to any one of claims 1 to 13, wherein the terminal device is further caused to: receive an indication from the network device indicating a set of active terminal devices identified by the network device; determine whether the terminal device is included in the set of active terminal devices identified by the network device; and Based on the determination that the terminal device is included in the set of active terminal devices identified by the network device, perform communication with the network device, or based on the determination that the terminal device is excluded from the set of active terminal devices identified by the network device, retransmit the modulated conjugate symmetric signal to the network device.

15. The terminal device according to claim 14, wherein the terminal device transmits data symbols with the variable phase compensation factor in the subcarriers having the pre-compensation factor for UL CPO, and the data symbols are mapped to service data.

16. The terminal device according to claim 14, wherein the indication further indicates: resources for performing communication for the set of active terminal devices respectively identified by the network device, and the terminal device uses the corresponding resources related to the terminal device to perform the communication with the network device.

17. The terminal device according to any one of claims 14 to 16, wherein the indication further indicates: timing advance information related to the set of active terminal devices respectively identified by the network device, and the terminal device performs the communication with the network device based on the corresponding timing advance information related to the terminal device.

18. A network device in a radio access network, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device to at least: transmit a configuration associated with a set of subcarriers to a set of terminal devices in the radio access network, wherein the set of subcarriers is associated with the set of terminal devices for transmitting a modulated conjugate symmetric signal, and the modulated conjugate symmetric signal indicates activity information of a set of active terminal devices in the set of terminal devices; receive a superimposed signal associated with the modulated conjugate symmetric signal from the set of active terminal devices, wherein the modulated conjugate symmetric signal is generated by modulating the set of subcarriers associated with the set of active terminal devices with a symbol set corresponding to the set of active terminal devices respectively, and includes: faster-than-Nyquist sparse multi-carrier (MC-FTN) conjugate symmetric signaling; and identify the set of active terminal devices from the set of terminal devices based on the received superimposed signal.

19. The network device according to claim 18, wherein the normalized time-bandwidth product of the sparse MC-FTN conjugate symmetric signaling is greater than or equal to twice the ratio of the number of the set of active terminal devices to the number of the set of terminal devices.

20. The network device according to claim 18, wherein each symbol in the symbol set comprises: a variable phase compensation factor for compensating the phase of the channel between the network device and the corresponding active terminal device in the associated subcarriers, and a fixed phase compensation factor, wherein the fixed phase compensation factor is based on the deviation between the variable phase compensation factor and the phase of the channel between the network device and the corresponding active device in the associated subcarriers.

21. The network device according to claim 18, wherein the network device is caused to identify the set of active terminal devices by: determining a superimposed complex conjugate symmetric sine sequence based on the superimposed signal, the superimposed complex conjugate symmetric sine sequence comprising: symbols received in the subcarrier set associated with the set of terminal devices; determining a superimposed complex sine sequence based on the superimposed complex conjugate symmetric sine sequence and its conjugate symmetry, the superimposed complex sine sequence comprising: the imaginary parts of the symbols received in the subcarriers associated with the set of terminal devices, and excluding the real parts of the symbols received in the subcarrier set associated with the set of terminal devices; determining a first identified set of active terminal devices based on the superimposed complex sine sequence; and determining a second identified set of active terminal devices as the identified set of active terminal devices based on the superimposed complex conjugate symmetric sine sequence and the first identified set of active terminal devices.

22. The network device according to claim 21, wherein the network device is caused to determine the first identified set of active terminal devices by: determining a sparse real vector based on the superimposed complex sine sequence, the sparse real vector representing: the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices; determining valid non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices by comparing the absolute values of the components of the sparse real vector with a first predefined threshold; and determining the first identified set of active terminal devices based on the valid non-zero components of the imaginary parts of the symbols received in the subcarrier set associated with the set of terminal devices.

23. The network device according to claim 22, wherein the network device is caused to determine the sparse real vector by solving an effective non-negative least squares problem based on the superimposed complex sine sequence, wherein the components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with frequencies lower than the carrier frequency are non-negative, and the components of the sparse real vector corresponding to the imaginary parts of the symbols received in the subcarrier set with frequencies higher than the carrier frequency are non-positive.

24. The network device according to claim 21, wherein the network device is caused to determine the second identified set of active terminal devices by: determining a low-dimensional complex vector representing the symbols received in the subcarrier set associated with the first identified set of active terminal devices based on the superimposed complex conjugate symmetric sine sequence; determining valid non-zero components of the symbols received in the subcarrier set associated with the first identified set of active terminal devices by comparing the magnitudes of the components of the low-dimensional complex vector with a second predefined threshold; and Determine the second identified set of active terminal devices based on the valid non-zero components of the received symbols in the subcarrier set associated with the first identified set of active terminal devices.

25. The network device according to claim 24, wherein the network device is caused to determine the low-dimensional complex vector under the following constraints: the components of the low-dimensional complex vector corresponding to the imaginary part of the received symbols in the subcarrier set with a frequency lower than the carrier frequency are non-negative, and the components of the low-dimensional complex vector corresponding to the imaginary part of the received symbols in the subcarrier set with a frequency higher than the carrier frequency are non-positive.

26. The network device according to claim 24, wherein the network device is further caused to replace the imaginary part of the received symbols in the subcarrier set associated with the first identified set of active terminal devices with the corresponding imaginary part derived from the sparse real vector.

27. The network device according to any one of claims 24 to 26, wherein the network device is further caused to determine the propagation delay from the second identified set of active terminal devices to the network device based on the phase of the received symbols in the subcarrier set associated with the second identified set of active terminal devices.

28. The network device according to claim 27, wherein the network device is further caused to: Determine timing advance information related to the second identified set of active terminal devices based on the determined propagation delay from the second identified set of active terminal devices to the network device; and Transmit, via a common channel, an indication of the identified set of active terminal devices and the related timing advance information to the set of terminal devices, respectively.

29. The network device according to claim 28, wherein the indication specifies resources for communication to be performed by each active terminal device in the identified set of active terminal devices, respectively.

30. The network device according to any one of claims 18 to 29, wherein the network device is further caused to: Transmit a beacon signal to the set of terminal devices, the beacon signal indicating the transmission of the sparse MC-FTN conjugate symmetric signaling.

31. A method, comprising: At a terminal device, receive a configuration associated with a subcarrier set from a network device in a radio access network, wherein the subcarrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate symmetric signal, the modulated conjugate symmetric signal indicating activity information of an active terminal device set in the set of terminal devices; and Transmit a modulated conjugate symmetric signal to the network device, wherein the modulated conjugate symmetric signal is generated by modulating subcarriers from the subcarrier set with symbols, and the modulated conjugate symmetric signal includes: faster-than-Nyquist sparse multi-carrier (MC-FTN) conjugate symmetric signaling.

32. A method, comprising: At a network device, a configuration associated with a sub - carrier set is transmitted to a set of terminal devices in a radio access network, where the sub - carrier set is associated with the set of terminal devices for transmitting a modulated conjugate - symmetric signal, and the modulated conjugate - symmetric signal indicates activity information of an active set of terminal devices in the set of terminal devices; A superimposed signal associated with the modulated conjugate - symmetric signal is received from the active set of terminal devices, where the modulated conjugate - symmetric signal is generated by modulating the sub - carrier set associated with the active set of terminal devices with a symbol set corresponding to the active set of terminal devices respectively, and includes: faster - than - Nyquist sparse multi - carrier (MC - FTN) conjugate - symmetric signaling; And Based on the received superimposed signal, the active set of terminal devices is identified from the set of terminal devices.

33. An apparatus, Comprising: Components for receiving, at a terminal device, a configuration associated with a sub - carrier set from a network device in a radio access network, where the sub - carrier set is associated with a set of terminal devices in the radio access network for transmitting a modulated conjugate - symmetric signal, and the modulated conjugate - symmetric signal indicates activity information of an active set of terminal devices in the set of terminal devices; And Components for transmitting a modulated conjugate - symmetric signal to the network device, where the modulated conjugate - symmetric signal is generated by modulating sub - carriers from the sub - carrier set with symbols, and the modulated conjugate - symmetric signal includes: faster - than - Nyquist sparse multi - carrier (MC - FTN) conjugate - symmetric signaling.

34. An apparatus, Comprising: Components for transmitting, at a network device, a configuration associated with a sub - carrier set to a set of terminal devices in a radio access network, where the sub - carrier set is associated with the set of terminal devices for transmitting a modulated conjugate - symmetric signal, and the modulated conjugate - symmetric signal indicates activity information of an active set of terminal devices in the set of terminal devices; Components for receiving a superimposed signal associated with the modulated conjugate - symmetric signal from the active set of terminal devices, where the modulated conjugate - symmetric signal is generated by modulating the sub - carrier set associated with the active set of terminal devices with a symbol set corresponding to the active set of terminal devices respectively, and includes: faster - than - Nyquist sparse multi - carrier (MC - FTN) conjugate - symmetric signaling; And Components for identifying the active set of terminal devices from the set of terminal devices based on the received superimposed signal.

35. A computer - readable medium comprising program instructions that, when executed by a device, cause the device to perform at least the method according to claim 31 or 32.

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