User Activity Detection

Abstract

[0003] Embodiments of the present disclosure relate to a method and apparatus for user activity detection (UAD), in which a terminal device receives, from a network device in a radio access network, a configuration associated with a set of subcarriers, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices, and transmits the modulated conjugate symmetric signals, the modulated conjugate symmetric signals being generated by modulating subcarriers from the set of subcarriers with symbols, the modulated conjugate symmetric signals including sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling, thereby reducing delay and measurement resource costs.

Description

[Technical Field]

[0001] Various example embodiments relate to the field of telecommunications, and in particular to methods, devices, apparatus, and computer-readable storage media for User Activity Detection (UAD). [Background technology]

[0002] With the development of communication technology, future society will become digitalized and data-driven, for example through connected industry, intelligent transportation systems, smart cities, etc., thus bringing greater convenience to daily life and industrial development. Machine Type Communication (MTC) can support large-scale connectivity and therefore offers a possible approach to realizing such a digitalized, data-driven society. At the same time, the further development of society will bring about new and more stringent requirements for wireless connectivity. Improvements to MTC's UAD are still needed. Summary of the Invention [Problem to be solved by the invention]

[0003] Generally, example embodiments of the present disclosure provide a solution for implementing UAD. [Means for solving the problem]

[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 that, when executed by the at least one processor, cause the terminal device to at least perform the following: receive, from a network device in the radio access network, a configuration associated with a set of subcarriers, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugated symmetric signals, the modulated conjugated symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; and transmit, to the network device, the modulated conjugated symmetric signals, the modulated conjugated symmetric signals being generated by modulating subcarriers from the set of subcarriers with symbols, the modulated conjugated symmetric signals comprising sparse Multicarrier Faster Than Nyquist (MC-FTN) conjugated 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 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, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; receive superimposed signals associated with the modulated conjugate symmetric signals from the set of active terminal devices, the modulated conjugate symmetric signals being generated by modulating a set of subcarriers associated with the set of active terminal devices using a set of symbols respectively corresponding to the set of active terminal devices and including sparse MC-FTN conjugate symmetric signaling; and identify an active set of terminal devices among the set of terminal devices based on the received superimposed signals.

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

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

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

[0009] In a sixth aspect, an apparatus is provided that may comprise: means, at a network device, for transmitting a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; means for receiving superimposed signals associated with the modulated conjugate symmetric signals from the set of active terminal devices, the modulated conjugate symmetric signals being generated by modulating a set of subcarriers associated with the set of active terminal devices with a set of symbols respectively corresponding to the set of active terminal devices and comprising sparse MC-FTN conjugate symmetric signaling; and means for identifying an active set of terminal devices among the set of terminal devices based on the received superimposed signals.

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

[0011] In an eighth aspect, there is provided a computer program comprising instructions that, when executed by an apparatus, cause the apparatus to at least: receive, from a network device in a wireless access network, a configuration associated with a set of subcarriers, the set of subcarriers being associated with a set of terminal devices in the wireless access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; and transmit, to the network device, the modulated conjugate symmetric signals, the modulated conjugate symmetric signals being generated by modulating subcarriers from the set of subcarriers using symbols, the modulated conjugate symmetric signals including sparse MC-FTN conjugate symmetric signaling.

[0012] In a ninth aspect, a computer program is provided that includes instructions that, when executed by an apparatus, cause the apparatus to at least: transmit a configuration associated with a set of subcarriers to a set of terminal devices in a wireless access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; receive superimposed signals associated with the modulated conjugate symmetric signals from the set of active terminal devices, the modulated conjugate symmetric signals being generated by modulating a set of subcarriers associated with the set of active terminal devices using a set of symbols respectively corresponding to the set of active terminal devices, the modulated conjugate symmetric signals including sparse MC-FTN conjugate symmetric signaling; and identify a set of active terminal devices among the set of terminal devices based on the received superimposed signals.

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

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

[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 be used to limit the scope of the present disclosure. Other features of the present disclosure will become readily apparent from the following description.

[0016] Some example embodiments will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1 illustrates an exemplary communication network in which embodiments of the present disclosure may be implemented. [Figure 1B] 1 is a schematic diagram illustrating an effective uplink (UL) channel impulse response (CIR) in a random access situation, according to some embodiments of the present disclosure. [Figure 2]FIG. 1 is a schematic diagram illustrating a process for communication according to some embodiments of the present disclosure. [Figure 3A] 1 is an exemplary diagram of a data signal and a UAD signal in the time domain, according to some embodiments of the present disclosure. [Figure 3B] FIG. 1 is an exemplary diagram of a multiplexing structure of a data signal and a UAD signal in the frequency domain, according to some embodiments of the present disclosure. [Figure 4A] 10 is an example diagram of a phase estimation error based on partial a priori knowledge on a corresponding UL channel in accordance with some embodiments of the present disclosure. [Figure 4B] FIG. 10 is an exemplary diagram of a phase compensation coefficient design, according to some embodiments of the present disclosure. [Figure 4C] FIG. 10 is an example diagram of a reconstruction condition for the sign of the imaginary part of a symbol received on a subcarrier, according to some embodiments of the present disclosure. [Figure 5] 1 is an exemplary diagram of a transmission procedure for modulated conjugate symmetric signals according to some embodiments of the present disclosure. [Figure 6] FIG. 1 is an exemplary diagram of a procedure for generating a discrete-time baseband conjugate symmetric signal, according to some embodiments of the present disclosure. [Figure 7A] 1 is an example diagram of a downlink (DL) beacon signal transmission in a communication network according to some embodiments of the present disclosure. [Figure 7B] 1 is an example diagram of a UL Carrier Phase Offset (CPO) pre-compensation procedure according to some embodiments of the present disclosure. [Figure 8] FIG. 10 is an example diagram of a receiving procedure for superimposed MC-FTN conjugate symmetric signaling, according to some embodiments of the present disclosure. [Figure 9] FIG. 1 illustrates an exemplary implementation of a joint UAD and timing acquisition algorithm process, according to an embodiment of the present disclosure. [Figure 10] FIG. 1 illustrates an exemplary implementation of a process for communication according to an embodiment of the present disclosure. [Figure 11A]FIG. 1 illustrates an example implementation of MC-FTN conjugate-symmetric signaling in the frequency domain, in accordance with some embodiments of the present disclosure. [Figure 11B] 1 is an exemplary diagram of a conventional Physical Layer Random Access Channel (PRACH) signal in the frequency domain. [Figure 11C] FIG. 1 is an example diagram of an MC-FTN conjugate symmetric signal and a conventional PRACH signal in the time domain, in accordance with some embodiments of the present disclosure. [Figures 12A-12B] FIG. 10 illustrates a performance comparison of joint UAD and timing acquisition between MC-FTN conjugate symmetric signaling according to some embodiments of the present disclosure and a conventional PRACH procedure via Zadoff-Chu (ZC) sequences under the same time-frequency resource. [Figure 13] FIG. 1 illustrates a flowchart of a method implemented in a terminal device according to some embodiments of the present disclosure. [Figure 14] FIG. 1 illustrates a flowchart of a method implemented in a network device according to some embodiments of the present disclosure. [Figure 15] FIG. 1 is a simplified block diagram of an apparatus suitable for practicing embodiments of the present disclosure. [Figure 16] 1 is a block diagram of an exemplary computer-readable medium according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] Throughout the drawings, the same or similar reference numbers refer to the same or similar elements.

[0019] The principles of the present disclosure will be described below with reference to some example embodiments. It should be understood that these embodiments are described merely for illustrative purposes, without implying any limitation on the scope of the present disclosure, and are intended to help those skilled in the art understand and practice the present disclosure. The disclosure described herein can be implemented in various ways other than those described below.

[0020] 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 belongs.

[0021] References in this disclosure to "one embodiment," "embodiment," "example embodiment," etc., indicate that the described embodiment may include a particular feature, structure, or characteristic, but that all embodiments do not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is believed to be within the knowledge of one of ordinary skill in the art to affect such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

[0022] In this specification, terms such as "first" and "second" may be used to describe various elements, but it should be understood that these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a first element could be referred to as a second element, and similarly, a second element could be referred to as a first element, without departing from the scope of the example embodiments. As used in this specification, the term "and / or" includes any and all combinations of one or more of the listed terms.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the example embodiments. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It will be further understood that the terms "comprise," "comprising," "have," "having," "include," and / or "including," when used in this patent specification, indicate the presence of stated features, elements, and / or components, etc., but do not exclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. As used herein, "at least one of: " and "at least one of " and similar phrases, when a list of two or more elements is joined by "and" or "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.

[0024] As used in this application, the term "circuit" means (a) a hardware-only circuit implementation (e.g., an implementation in analog and / or digital circuitry only); (b) (where applicable) (i) combinations of analog and / or digital hardware circuitry with software / firmware; and (ii) a combination of hardware circuitry and software, such as any portion of a hardware processor (including a digital signal processor), software, and memory, that together cause a device, such as a mobile phone or server, to perform various functions; (c) may refer to one or more or all of a hardware circuit and / or processor, such as a microprocessor or part of a microprocessor, that requires software (e.g., firmware) to operate, but the software may not be present when not required for operation.

[0025] This definition of circuit applies to all uses of the term in this application, including in any claims. As a further example, when used in this application, the term circuit also covers simply a hardware circuit or processor (or processors), or a portion of a hardware circuit or processor, as well as its (or their) accompanying software and / or firmware implementation. The term circuit also covers, for example, a baseband or processor integrated circuit for a mobile device, or a similar integrated circuit in a server, cellular network device, or other computing or network device, if applicable to certain claim elements.

[0026] As used herein, the term "communications network" refers to a network conforming to any suitable communications standard, such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed ​​Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT), etc. Furthermore, communications between terminal devices and network devices within a communications network may be performed according to any suitable generation of communications protocol, including, but not limited to, third generation (3G), fourth generation (4G), 4.5G, fifth generation (5G), or further sixth generation (6G) communications protocols, and / or any other protocols now known or developed in the future. Embodiments of the present disclosure may be applied to various communications systems. Given the rapid development in communications, there will of course be future communications technologies and systems that the present disclosure may be embodied in. This should not be considered as limiting the scope of the present disclosure to only the aforementioned systems.

[0027] As used herein, the term "network device" refers to a node in a communication network through which a terminal device accesses and receives services from the network. A network device may refer to a base station (BS) or an access point (AP), such as a Node B (Node B or NB), an evolved Node B (eNodeB or eNB), an NR NB (also called a gNB), a Remote Radio Unit (RRU), a Radio Header (RH), a Remote Radio Head (RRH), a repeater, or a low-power node such as a femto or pico, depending on the terminology and technology used.

[0028] The term "terminal device" refers to any end device that may have wireless communication capabilities. By way of example and not limitation, a terminal device may also be called a communication device, user equipment (UE), subscriber station (SS), mobile subscriber station, mobile station (MS), or access terminal (AT). The terminal devices may be mobile phones, cellular phones, smartphones, voice over IP (VoIP) phones, wireless local loop phones, tablets, wearable terminal devices, personal digital assistants (PDAs), portable computers, desktop computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback devices, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), Internet of Things (IoT) devices, watches or other wearables, head-mounted displays (HMDs), etc. The wireless communication devices may include, but are not limited to, wireless displays, vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated processing chain contexts), consumer electronics 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.

[0029] MTC in 5G is divided into ultra-reliable and low-latency communications (URLLC) or critical MTC (cMTC), which operates in controlled environments with small payloads and low data rates, and massive MTC (mMTC), which is intended for large-scale, high-density deployments with sporadic traffic patterns. Over the next decade, these two areas will evolve into multiple specialized subclasses due to emerging industrial use cases and service delivery verticalization, thus requiring multidimensional optimization and scalable design. As communications technologies evolve, evolved technologies are needed to serve a wide variety of applications, from data-rate-intensive holographic imaging and connected 360 XR (augmented, virtual, and mixed reality) to large-scale access for various types of IoT devices. One of the 6G MTC service classes is proposed to be classified as scalable critical MTC (cMTC), which refers to large-scale connectivity with high reliability and low latency, such as supporting mission-critical medical monitoring and factory automation. Scale and flexibility will continue to be key measures of 6G performance. 6G communications will be 2 It is expected to support a high connection density of 10 million devices per

[0030] In contrast to human-centric communication, machine-centric communication (e.g., scalable cMTC) generally has two distinctive features. On the one hand, the whole system needs to support large-scale connections, and the number of terminal devices connected to the cellular network device is expected to exceed 10 4 ~10 7The network traffic can be on the order of 100 Mbps. Macro network devices prefer to provide uniform, large-scale access to various types of IoT devices, offering a low-cost solution for supporting large-scale connections with high reliability and low latency. Commercially, communication vendors favor a unified solution. On the other hand, traffic patterns are sporadic, with only a small fraction of potential end devices being active at any given time. Typically, machine-type end devices connect to network devices asynchronously and sporadically to transmit small data payloads. This sporadic nature is due to the inherent burstiness of event-driven IoT communications in controlled and / or sensing environments. The majority of machine-type end devices make random requests independently, with little periodicity that can be tracked and exploited. As a result, it is impossible for network devices to predict in advance when and which end device will deliver a data packet.

[0031] One of the major obstacles to the proliferation of efficient cellular access for scalable cMTC stems from the deficiencies of the access reservation procedure, a key component of cellular access networks. From 1G to 5G, the access reservation procedure is designed to enable connection establishment when there are relatively few accessing terminal devices. Furthermore, each terminal device has moderate to high data rate requirements, so that the overhead of current access protocols, which involve multiple stages, is relatively small. Both the assumptions of a small number of terminal devices and moderate to high data rates contradict the need for scalable cMTC. Conventional access reservation procedures employ random access, such as the physical layer random access channel (PRACH) in LTE / NR, to establish a connection state for terminal devices at the expense of an access latency of approximately 20 ms.

[0032] A conventional random access procedure performs two necessary functions to prepare for successful communication: UAD and timing acquisition. On the one hand, a network device needs to identify an active subset of all terminal devices in a primitive (idle) state before establishing a successful connection between the terminal device and the network device. On the other hand, the network device needs to estimate the propagation delays 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 devices can be established, after which either scheduled or grant-free data services can be applied.

[0033] However, given the scarcity of frequency resources, conventional random access is not scalable and cannot be applied to large-scale critical MTC. For example, due to the limited number of PRACH preambles, the PRACH mechanism imposes restrictions on the number of active terminal devices allowed to access the network device. In addition, a particular coherence time-frequency block can support only a smaller number of orthogonal preamble sequences compared to a large number of machine-type terminal devices. For example, LTE / NR supports only 64 643-length orthogonal Zadoff-Chu (ZC) sequences for the PRACH. A large number of terminal devices initiate random access by independently selecting one sequence from the same small set, inevitably causing significant collisions and resulting in unacceptable access delays. Furthermore, the repeated cycle of transmission-collision-retransmission leads to an endless series of signaling exchanges between terminal devices and network devices, which are much larger than the small packets that machine-type terminal devices attempt to transmit. On the other hand, simultaneously maintaining the connection states of a large number of terminal devices with potential service requests sustains constant periodic signaling exchanges, resulting in unacceptable waste of power and spectrum. This is a connection density of 10 million terminal devices / km. 2 This becomes infeasible as the network connection costs increase exponentially. Furthermore, maintaining a continuous connection is energy inefficient for the IoT devices themselves, which are typically expected to have battery lives longer than 10 years. This maintenance cost could be avoided if network devices were capable of fast connection establishment on demand.

[0034] Considering the unsustainable spectrum consumption and poor performance caused by the lack of orthogonal preambles, the conventional PRACH procedure is not scalable and cannot be applied to large-scale access with low traffic intensity, especially for large-scale delay-sensitive IoT access as the number of simultaneously accessing terminal devices increases.

[0035] In fact, in a situation where there are a large number of potential terminal devices but the coherence time and frequency dimensions in a wireless fading channel are limited, it is impossible to assign orthogonal preambles to all terminal devices. However, for example, when simple matched filtering or correlation-based processing is applied to network devices, non-orthogonal preamble sets are superimposed, causing significant multi-user interference and making UAD and timing acquisition very difficult. Therefore, a new solution is needed to address uncertain and random access in a more efficient and effective manner.

[0036] In order to overcome the drawbacks of the conventional methods, the present disclosure provides an overall design from a waveform design and its transmission method at the terminal device side to a receiving method at the network device side. Hereinafter, the principles and embodiment examples of the present disclosure will be described in detail with reference to the accompanying drawings. However, it should be noted that these embodiments are shown as examples and are not intended to limit the scope of the present application in any way.

[0037] Reference is first made to FIG. 1A, which illustrates an exemplary communication network 100 in which embodiments of the present disclosure may be implemented. As shown in FIG. 1A, the network 100 may include a network device 120. The network device 120 may provide a cellular network for large-scale access. As shown in FIG. 1A, the network 100 may further 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 set of N terminal devices is denoted by S. The number N can be any suitable integer. Without loss of generality, N may be assumed to be an even positive number. The terminal devices may be

[0038]

number

[0039] 1A is for illustrative purposes only, without implying any limitation. Network 100 may include any suitable number of network devices and terminal devices adapted to implement embodiments of the present disclosure.

[0040] Terminal devices 110 may access network devices 120 independently and asynchronously according to their own requirements of sporadic traffic, typically requiring the establishment of a connection commonly referred to as random access. In an exemplary situation, the active subset S A A small portion of potential terminal devices, denoted by ⊆S, may become active and begin the random access procedure by transmitting an UL preamble signal in a particular transmission cycle. For example, as shown in FIG. 1A, the first terminal device 110-1 and the third terminal device 110-3 may be active, while the second, fourth, and fifth terminal devices 110-2, 110-4, and 110-5 are inactive. To perform random access, in contrast to the conventional PRACH scheme involving sequence collision, each terminal device 110 in the network 100 may be pre-assigned a unique preamble. This preamble may also serve as the ID of this terminal device.

[0041] Before establishing a successful connection between the end device and the network device, the network device 120 identifies an active subset S of the entire set S of end devices through the UAD procedure. AWhen network device 120 knows which terminal devices will be active at the start of one transmission cycle, network device 120 may immediately assign an UL channel to the identified active terminal device so that the active terminal device can further provide more detailed information to network device 120, for example, for establishing a connection state. In addition, network device 120 may be configured to estimate a propagation delay experienced by the identified terminal device, and thus provide TA information to the identified terminal device to enable synchronous UL transmission. In this way, network device 120 can quickly know which terminal devices will be active at the start of one transmission cycle and quickly derive their respective TA information, and thus a quick response to establish a successful connection can be prepared.

[0042] For purposes of illustration, and without implying any limitation, each terminal device 110 may be equipped with a single transmit antenna. As shown in FIG. 1A, the active terminal devices n∈S A ⊆S is the baseband preamble signal s together with the carrier signal n (t) may be transmitted from an active terminal device n. n (t) may be dedicated to the UE or may be randomly selected from a preamble set.

[0043] In some embodiments, the transmission of all UL preambles may be triggered / synchronized by a common DL beacon signal transmitted from network device 120 at the beginning. FIG. 1B shows a schematic diagram illustrating an effective uplink channel impulse response (CIR) in a random access situation, according to some embodiments of the present disclosure. For example, a common DL beacon signal may be transmitted from network device 120 at t=0. In response to receiving the common DL beacon signal, active terminal device n transmits a preamble signal s n(t) to the network device 120. In this way, the signal s n (t) is the starting time in seconds. n The signal s n (t) may pass through a multipath spreading channel from terminal device n to network device 120, and its CIR is

[0044]

number

[0045] 1A, the network device 120 may receive an asynchronous superimposed radio frequency (RF) signal. The received superimposed signal may be:

number

[0046] The propagation delay information is n (td n ) as well as the baseband signal for UL CPO

number

number

[0047] At each transmission cycle, the network device 120 selects an active subset S A Identify the knowledge of, and simply depending on the observation y(t),

number

[0048] In contrast to conventional PRACH schemes with orthogonality between preambles (such as ZC sequences), non-orthogonal preamble sets make joint UAD and timing acquisition very challenging, for example, when simple matched filtering or correlation-based processing is applied in network devices, as they overlap and cause severe multi-user interference. Furthermore, the impact of UL CPO hinders accurate timing acquisition from phase estimation. Embodiments of the present disclosure provide a global method for synchronizing preamble sets {s n (t)} n∈S and related detection and estimation.

[0049] Communications in communication network 100 may be conducted according to any suitable communications protocol, including, but not limited to, first generation (1G), second generation (2G), third generation (3G), fourth generation (4G), and fifth generation (5G) or later cellular communications protocols, wireless local network communications protocols such as the Institute for Electrical and Electronics Engineers (IEEE) 802.11, and / or any other protocol now known or developed in the future. Further, the communications may utilize any suitable wireless communications technology, including, but not limited to, Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM), and / or any other technology now known or developed in the future.

[0050] Reference is now made to Figure 2, which shows a schematic diagram illustrating a process 200 for communication according to some embodiments of the present disclosure. For purposes of explanation, process 200 is described with reference to Figure 1A. Network device 120 and terminal device 110-1 may be involved in process 200 for illustrative purposes.

[0051] In process 200, the network device 120 transmits 202 a configuration 204 associated with a set of subcarriers to a set S of terminal devices in the wireless access network. The set of subcarriers is associated with the set S of terminal devices for transmission of modulated conjugate-symmetric signals. These modulated conjugate-symmetric signals are transmitted to a set S of active terminal devices among the set S of terminal devices. A In some embodiments, all potential terminal devices 110 in the set S of terminal devices may be assigned specific subcarriers based on the configuration 204. When any terminal device in the set S of terminal devices becomes active, the terminal device may transmit a preamble signal on the subcarrier associated with the terminal device to perform a random access procedure.

[0052] 2, terminal device 110-1 receives (206) configuration 204 and transmits (208) modulated conjugate symmetric signal 210 to network device 120. Modulated conjugate symmetric signal 210 is generated by modulating a subcarrier from a set of subcarriers using a symbol. Modulated conjugate symmetric signal 210 is generated by modulating a subcarrier from a set of subcarriers using a symbol. n (t)} n∈S The MC-FTN involves sparse conjugate-symmetric signaling associated with the signal set {s n (t)} n∈S The time-frequency cost required for is the normalized time-bandwidth (NTB) product, i.e.

[0053]

number

[0054] Network device 120 receives 212 the modulated conjugate symmetric signal 210 from terminal device 110-1 and other modulated conjugate symmetric signals, if any, from other active terminal devices. From the perspective of network device 120, network device 120 has a set S of active terminal devices. A , a superimposed signal y(t) associated with the modulated conjugate symmetric signal. Based on the received superimposed signal, the network device 120 selects a set S of active terminal devices from the set S of terminal devices. A The conjugate symmetry and sparsity of the modulated conjugate symmetric signal allows the network device 120 to identify the active subset S when multiple active terminal devices 110 asynchronously transmit UAD signals. A In addition, the network device 120 may identify a propagation delay associated with the identified set of active end devices.

[0055]

number

number

[0056] In some embodiments, the NTB product of sparse MC-FTN conjugate symmetric signaling is greater than or equal to twice the ratio of the number of sets of active terminal devices to the number of sets of terminal devices, i.e.,

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[0057] In some embodiments, a subcarrier may be exclusively associated with a terminal device. In this way, a fixed allocation of subcarriers not only establishes a unique association between a preamble set and a terminal device, avoiding preamble collisions that would result from random allocation, but also eliminating the additional step of reporting a user ID.

[0058] In some embodiments, to generate the subcarriers, the terminal device 110-1 may generate a complex conjugated symmetric sinusoid waveform having the frequency of the subcarriers. The duration of the complex conjugated symmetric sinusoid waveform may be determined based on the inverse of the subcarrier spacing of the set of subcarriers, the number of sets of active terminal devices, and the number of sets of terminal devices. The terminal device may then add a cyclic prefix to the complex conjugated symmetric sinusoid waveform to generate the subcarriers. In this way, the time-frequency resources required for qualified UAD and timing acquisition depend solely on the ratio of actual active terminal devices and may not be scalable with the total number N of terminal devices, resulting in a scalable scheme for large-scale access.

[0059] In some embodiments, terminal device 110-1 may generate a pre-compensation phase factor (PFC) for a complex conjugate symmetric sinusoidal waveform including a cyclic prefix.

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[0060] The terminal device 110-1 may calculate the pre-compensation phase coefficients in various ways.

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[0061]

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[0062] In some embodiments, a symbol may include a variable phase-compensation factor for compensating for the phase of the channel between the network device 120 and the terminal device 110-1 at a subcarrier and a fixed phase-compensation factor. 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 at a subcarrier such that the bias between the variable phase-compensation factor at a subcarrier and the phase of the channel between the network device 120 and the terminal device 110-1 can be controlled within a range. The fixed phase-compensation factor is used together with the pre-compensation phase factor and variable phase-compensation factor of the UL CPO to adjust the phase of the received symbol within an appropriate range. Therefore, the phase of the received symbol at a subcarrier within a frequency band may contain resolvable and distinguishable information of the propagation delay within the radio access network. By utilizing a precoding strategy based on phase compensation and conjugate symmetry, as well as sparse transmission in the frequency domain, the network device 120 can fully resolve the received symbols based on the received superimposed signals of the MC-FTN signaling.

[0063] The terminal device 110-1 may determine the variable phase compensation coefficient in various ways. In an exemplary implementation, the terminal device 110-1 may determine the variable phase compensation coefficient based on the received beacon signal and the reciprocity of the channel between the UL and DL. In some embodiments, the terminal device 110-1 may determine the variable phase compensation coefficient based on the frequency of the subcarrier, the frequency of the carrier signal, the bias between the variable phase compensation coefficient at the subcarrier and the phase of the channel between the network device 120 and the terminal device 110-1, and the pre-compensation phase coefficient.

[0064]

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[0065] In some embodiments, the subcarriers may be within a frequency band whose bandwidth is determined by the maximum propagation delay in the radio access network, the bias between the variable phase compensation factor in the subcarrier and the phase of the channel between the network device 120 and the terminal device 110-1, and the pre-compensation phase factor

[0066]

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[0067] The terminal device 110-1 may generate a modulated conjugate symmetric signal in various ways. In an exemplary implementation, the terminal device 110-1 may generate a discrete-time baseband conjugate symmetric signal based on the baseband frequency of the subcarrier, a variable phase compensation coefficient, and a fixed phase compensation coefficient. 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 of the continuous-time baseband conjugate symmetric signal. Different terminal devices may be distinguished by assigning different subcarriers without preamble collisions. Based on such phase compensation and the introduction of conjugate symmetry, an effective sparse non-zero vector of symbols received on different subcarriers may maintain activity information of corresponding active terminal devices. In an information vector based on mixed / superimposed observations, a sign constraint may be applied to the imaginary part of the received symbol. 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 can be resolved from the mixed / superimposed observations.

[0068] In some embodiments, terminal device 110-1 is a UL CPO

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[0069] In some embodiments, to generate a discrete-time baseband conjugate symmetric signal, the terminal device 110-1 may generate a first sequence modulated using a variable phase compensation coefficient and a fixed phase compensation coefficient by performing an inverse discrete Fourier transform (IDFT). The non-zero components of the input of the IDFT may include the variable phase compensation coefficient and the fixed phase compensation coefficient corresponding to the subcarrier. The terminal device 110-1 may then insert a copy of the last portion of the first sequence prepended to the first sequence to obtain a second sequence. The inserted last portion of the first sequence may be included as a cyclic prefix and a conjugate symmetric component. The terminal device 110-1 may then discard the last portion 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 sampling rate of the modulated conjugate symmetric signal. Using such a length definition, qualified UAD and timing acquisition can be performed as long as twice the ratio of actual active terminal devices is less than the NTB product. In this way, the minimum measurement cost required for qualified UAD and timing acquisition can be achieved. The designed signaling is a set of non-orthogonal complex conjugate symmetric sinusoidal waveforms. Such properly designed waveforms and intentional phase compensation make the activity detection method more efficient and scalable. An MC-FTN conjugate symmetric signaling method for accurate, high-speed, and scalable UAD and timing acquisition is thus provided.

[0070] In some embodiments, a set of active terminal devices S ATo identify S, network device 120 may determine a superimposed complex conjugated symmetric sinusoid sequence based on the superimposed signal. The superimposed complex conjugated symmetric sinusoid sequence may include symbols received on a set of subcarriers associated with the set S of terminal devices. Network device 120 may determine the superimposed complex conjugated symmetric sinusoid sequence based on the superimposed complex conjugated symmetric sinusoid sequence and its conjugate symmetry. The superimposed complex sinusoid sequence may include imaginary parts of symbols received on a set of subcarriers associated with the set S of terminal devices and exclude real parts of symbols received on a set of subcarriers associated with the set S of terminal devices. Next, network device 120 may determine a first set of identified active terminal devices based on the superimposed complex sinusoid sequence. Based on the superimposed complex conjugate symmetric sinusoidal sequence and the first set of identified active terminal devices, the network device 120 may then determine the second set of identified active terminal devices as the set of identified active terminal devices. In this way, the network device 120 may determine the first set of identified active terminal devices as the S from partial knowledge based on the imaginary parts of the received symbols. A The first set may be determined as a rough estimate of S from a set of terminal devices, where the identification involves a large-scale problem based on the dimensionality of the set of terminal devices. The first set may tolerate a large false alarm rate to pursue a low false detection rate, may include nearly all active terminal devices, and may necessarily include some number of inactive terminal devices. Furthermore, the network device 120 may determine the second set of identified active terminal devices as a rough estimate of S from complete knowledge of the received symbols. AThe second set may be identified by further filtering out inactive terminal devices from the first set and may comprise a smaller set of problems based on the reduced dimensionality of the first set. Thus, the network device 120 overcomes the dimensionality deficiency problem through model reduction and provides an accurate estimate of the active subset.

[0071]

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[0072] In some embodiments, to determine the first set of identified active terminal devices, network device 120 may determine a sparse real vector representing the imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices based on the superimposed complex sinusoidal sequence. Network device 120 may then determine significant non-zero components of the imaginary parts of symbols received on a set of subcarriers 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 significant non-zero components of the imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices, network device 120 may then determine the first set of identified active terminal devices. In this manner, network device 120 may determine a coarse estimate of the active subset by deriving the imaginary parts for all terminal devices.

[0073] In some embodiments, the network device 120 may determine the sparse real vector by solving an efficient nonnegative least squares (NLS) problem based on the superimposed complex sinusoidal sequence. Components of the sparse real vector corresponding to the imaginary parts of symbols received on a set of subcarriers having frequencies lower than the carrier frequency may be nonnegative, and components of the sparse real vector corresponding to the imaginary parts of symbols received on a set of subcarriers having frequencies higher than the carrier frequency may be nonpositive. Such a sign constraint on the imaginary parts of the received symbols facilitates solving the sparse real vector from the transformed observations.

[0074] In some embodiments, to determine the second set of identified active terminal devices, network device 120 may determine a low-dimensional complex vector representing symbols received on a set of subcarriers associated with the first set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence. In some embodiments, the low-dimensional complex vector may be determined according to the constraint that components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having a frequency lower than the carrier frequency are non-negative and components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having a frequency higher than the carrier frequency are non-positive. Having derived the imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices and determined a coarse estimate of the active subset, the real parts of the received symbols may thus be derived for the coarse active subset by solving a smaller sub-problem after model reduction. The network device 120 may determine the significant non-zero components of symbols received on a set of subcarriers associated with the first set of identified active terminal devices by comparing the amplitudes 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 to further exclude inactive terminal devices from the first set. The network device 120 may then determine a second set of identified active terminal devices based on the significant non-zero components of symbols received on a set of subcarriers associated with the first set of identified active terminal devices. In this way, the network device 120 may accurately estimate the active subset by comparing the amplitudes of the components of the low-dimensional complex vector with a lower threshold.

[0075]

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[0076] In some embodiments, the network device 120 may replace the imaginary parts of the symbols received on the set of subcarriers associated with the first set of identified active terminal devices with corresponding imaginary parts derived from the sparse real vector. In this manner, the accuracy of the estimation of the received symbols may be improved.

[0077] In some embodiments, the network device 120 communicates with the set of identified active end devices over a common channel.

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[0078]

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[0079] In some embodiments, the network device 120 may select a second set of identified active end devices.

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[0081] As a more efficient and effective method, the joint UAD and timing acquisition procedure is expected to replace the PRACH procedure for random access. At the beginning of a transmission cycle, the network device can quickly know which terminal device has an actual request for data delivery, and a quick response can be prepared for successful communication. In addition, the network device can estimate the propagation delay occurring to the identified terminal device, thus providing TA information to the identified terminal device and enabling synchronous UL transmission.

[0082] In some embodiments, the terminal device 110-1 may transmit data symbols including variable phase compensation coefficients on subcarriers with pre-compensation coefficients of the UL CPO. The data symbols may be mapped to traffic data, for example, for small data transmissions. In this manner, synchronous UL transmissions may be enabled using TA information based on a coarse estimate of propagation delay determined by the network device 120. The coarse estimate may include errors due to unknown biases between the pre-compensation phase coefficients and the UL CPO and / or between the variable phase compensation coefficients on the subcarriers and the phase of the channel between the network device and the terminal device.

[0083] Reference is now made to Figures 3A-3B to respectively illustrate exemplary time-domain and frequency-domain structures of a signal for conventional data transmission (i.e., a data signal) and a signal for UAD transmission (i.e., a UAD signal) according to some embodiments of the present disclosure. Figure 3A illustrates an exemplary diagram of a data signal and a UAD signal in the time domain according to some embodiments of the present disclosure. Figure 3B illustrates an exemplary diagram of a multiplexing structure of a data signal and a UAD signal in the frequency domain according to some embodiments of the present disclosure. As shown in Figures 3A and 3B, the system bandwidth configured for uplink transmission is B total Hz. The data signal and the UAD signal are multiplexed in the frequency domain, with a designated guard band (GB) inserted between them to separate them. The UAD312 continuous B UAD The bandwidth is the carrier frequency f in Hz. c The data signal and the UAD signal are arranged at different subcarrier spacings Δf in the frequency domain. D Hz and Δf UAD Hz, and may use different lengths in the time domain. CP,D Seconds and T syb,D The UAD signal may include a Cyclic Prefix (CP) 304 and data symbols 302, each having a duration of T seconds. CP,UAD Seconds and T syb,UAD It may include a CP 310 and a UAD symbol 306 each having a duration of seconds.

[0084] In some embodiments, the data signal may employ a standard multi-carrier design, e.g., Orthogonal Frequency-Division Multiple Access (OFDMA) or Single-Carrier Frequency-Division Multiple Access (SC-FDMA), as in conventional LTE / NR systems. The data signal may employ a wider subcarrier spacing Δf D Hz may be employed, and the duration of the data symbol 304 T Syb,D is calculated as Δf according to the Nyquist law. D T Syb,D =1. Data from different terminal devices may be multiplexed among different subsets of subcarriers in the data 314 and 316 bands according to a scheduling grant from the network device 120. The time-domain and frequency-domain structures of the data signal are examples for better understanding of the UAD signal. This disclosure is not intended to provide any limitations on the design of the data signal. Various structures of the data signal may be designed.

[0085] In some embodiments, the bandwidth of the UAD 312 is narrow and equal subcarrier spacing Δf UAD Hz may be used to configure N subcarriers for N terminal devices (i.e., N potential terminal devices) in network 100. UAD T syb,UAD < 1. Such an MC-FTN conjugate-symmetric design converts UAD symbols into 1 / Δf UAD 3A, compared to the length of the Nyquist-based PRACH preamble, the length of the UAD symbol 306 is reduced by a time reduction 308. In some embodiments, a guard time (GT) may be inserted to separate the UAD signal from other signals.

[0086] In some embodiments, a fixed association between terminal devices and subcarriers is provided. Each terminal device is assigned a unique subcarrier so that the network device 120 can identify active terminal devices by checking which subcarrier components are present in the superimposed signal received by the network device. This association pattern is pre-assigned and known to the network device 120 and the terminal device 110, for example, via an injective mapping between core network / cell IDs and subcarrier indices. Representative examples include:

[0087]

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[0088] In sparse MC-FTN conjugated symmetric transmission, active end devices

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[0089] In some embodiments, the modulated conjugate symmetric signal transmitted by an active terminal device n may be described by a baseband signal, which is the continuous-time baseband conjugate symmetric signal of user n, written as equation (2):

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[0090]

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[0091]

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[0092] To ensure that the phase of the received symbols on a set of subcarriers contains resolvable and distinguishable information of the propagation delay, a fixed phase compensation factor

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[0093]

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[0094] As shown in FIG. 4B, for a terminal device n associated with a subcarrier having a frequency higher than the carrier frequency, i.e., n>0, a fixed phase compensation coefficient

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[0095] For a terminal device n associated with a subcarrier having a frequency lower than the carrier frequency, i.e., n<0, a fixed phase compensation factor

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[0096] As shown in Figures 4B and 4C, the intentional design of the phase compensation is to UAD lies in the lower complex plane for positive n or in the upper complex plane for negative n.

[0097]

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[0098] In some embodiments, to ensure that the above reconstruction condition expressed by equation (4) is met, the maximum allowable bandwidth of the UAD is d max The maximum round trip propagation delay in seconds, the bias between the variable phase compensation coefficient in the subcarrier and the phase of the channel between the network device and the terminal device, i.e.

[0099]

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[0100]

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[0101] In some embodiments, to ensure qualified UAD and timing acquisition at network device 120, the NTB product should be at least twice the ratio of actual active end devices, i.e.,

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[0102] In some embodiments, the UAD signal maintains the required NTB product Δf regardless of how the total number of devices N increases. UAD Tsym,UAD is twice the average percentage of active terminal devices (

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[0103] By utilizing a precoding strategy based on phase compensation and sparsity in transmission, the UAD problem and the estimation problem regarding the propagation delay can be realized by sequentially solving large-scale sub-problems and small-scale sub-problems for model reduction. The superimposed complex conjugate symmetric sinusoidal sequence maintains activity information and propagation delay information of a set of active terminal devices. The imaginary parts of the received symbols can be derived for all terminal devices from the mixed observations by the network device 110 by solving large-scale sub-problems based on the superimposed complex sinusoidal sequence derived from the superimposed complex conjugate symmetric sinusoidal sequence. Based on the derived imaginary parts, the active subset S A A coarse estimate of σ can be determined. Then, after model reduction, the real part of the received symbols can be derived for a coarse set of terminal devices by solving a small sub-problem based on superimposed complex conjugate symmetric sinusoidal sequences. Finally, the active subset S AThe entire acquired knowledge of the received symbols may be utilized to further refine the estimation of and estimate the associated propagation delay. Details of an exemplary process for the joint UAD and timing acquisition algorithm are described in detail below in conjunction with FIG.

[0104] For the sparse real vector solved from the large sub-problem, the components of the sparse real vector corresponding to the imaginary parts of the symbols received on the set of subcarriers having frequencies 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 on the set of subcarriers having frequencies higher than the carrier frequency may be non-positive, while the components corresponding to the inactive terminal devices are zero. Essentially, a variable phase compensation factor (VDC) is used to compensate for the phase of the UL channel and to pre-compensate for the UL CPO in the carrier signal caused by the propagation delay at the terminal device side, so that the activity information and propagation delay can be determined by separately deriving the imaginary and real parts of the complex vector consisting of the received symbols.

[0105]

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[0106] The designed signaling is a set of nonorthogonal complex sinusoid waveforms with conjugate symmetry, which can be used to distinguish different terminal devices by allocating different subcarriers without preamble collisions. Active terminal devices may modulate their assigned subcarriers using phase compensation coefficients based on partial a priori knowledge of the channel phase and its estimation error. Furthermore, pre-compensation of UL CPOs caused by propagation delays is introduced. A systematic design, from fixed association, conjugate symmetry, and phase compensation to bandwidth and NTB configuration, allows network devices to reconstruct received symbols on a set of subcarriers. A non-zero / zero value of a received symbol indicates the active / inactive state of the associated terminal device. Furthermore, such a sophisticated design ensures that the phase of a received symbol contains distinguishable information of the propagation delay.

[0107] Using such a well-designed sparse MC-FTN conjugate-symmetric signaling, the joint UAD and timing acquisition scheme becomes more efficient and scalable. In particular, the overall design in some embodiments of the present disclosure provides the following advantages:

[0108] (1) Minimize the measurement costs required for qualified UAD and timing acquisition: NTB for MC-FTN conjugate symmetric signaling is Δf UAD T sym,UAD <1, but the actual number of active terminal devices is

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[0109] (2) Scalability for large-scale access: The time-frequency resources required for qualified UAD and timing acquisition depend solely on the ratio of actual active terminal devices, resulting in a scalable scheme that is not scalable with the total number of terminal devices in the network.

[0110] (3) Delay Reduction: MC-FTN conjugate symmetric signaling reduces the delay time by a symbol duration shorter than the reciprocal of the subcarrier spacing (i.e., T sym,UAD <1 / Δf UAD ), resulting in a reduction in the inevitable delay penalty.

[0111] (4) Facilitates sparsity detection: The deliberate and systematic design of conjugate symmetry and phase compensation allows network devices to derive the imaginary part of a received symbol simply by solving an effective NLS problem. In particular, the sign condition on the imaginary part naturally introduces sparsity, leading to a fast detection algorithm with finite-step computation.

[0112] (5) The fixed assignment between the preamble and the terminal device not only establishes a unique association and avoids preamble collisions that would result from random assignment, but also eliminates the additional step of reporting the user ID.

[0113] (6) Compatibility with conventional LTE / NR: Both transmission and reception procedures are compatible with the LTE / NR multi-carrier scheme and can be easily integrated with random access procedures for large-scale access, serving as a low-cost, high-performance solution.

[0114] An example transmitter of MC-FTN conjugate-symmetric signaling for joint UAD and timing acquisition is described with respect to waveform design and associated precoding strategies with reference to FIG. 5, which shows an example diagram of a transmission procedure 500 for modulated conjugate-symmetric signals according to some embodiments of the present disclosure. For purposes of explanation, the transmission procedure for MC-FTN conjugate-symmetric signals is described from the perspective of terminal device 110 with reference to the frequency-domain structures shown in FIGS. 1A and 3B.

[0115] As shown in Figure 5, the terminal device

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[0117] Based on partial prior knowledge of the corresponding UL channel, a complex sinusoidal sequence s n[m] is a variable phase compensation coefficient via the modulator 502

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[0118] Discrete-time baseband conjugate symmetric signal s UAD,n [m] is a continuous-time baseband conjugate symmetric signal s UAD,n The D / A converter 506 may be converted into a sampling period T s It works well with s UAD,n [m]=s UAD,n (mT s ) is guaranteed. Continuous-time baseband conjugate symmetric signal s UAD,n (t) may be shown as equation (8) as follows:

[0119]

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[0120] The local oscillator of the terminal device generates the carrier signal

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[0121] Alternatively, a discrete-time baseband conjugate symmetric signal s UAD,n [m] may be generated by an equivalent IDFT structure. UAD,n 6 shows an exemplary diagram of a procedure 600 for generating [m]. As shown in FIG. UAD The IDFT602 of point 602 is a single non-zero input

[0122]

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[0123] The transmission procedure does not require coordination between the terminal devices. Each terminal device operates independently according to its own scheduling or traffic requirements, and inactive terminal devices refrain from any action except remaining silent. Network device 120 has a priori knowledge of the association patterns between subcarriers and terminal devices, allowing network device 120 to determine active terminal devices by detecting subcarrier components present in the superimposed observations.

[0124] In the transmission procedure 500, a continuous-time baseband conjugate symmetric signal s UAD,n (t) is the RF UAD signal s RF,UAD,nA pre-compensation method is employed by introducing a pre-compensation phase factor into the carrier signal when transforming it into (t). As a practical solution, the pre-compensation phase factor is transmitted via a DL beacon signal broadcast from the network device to all potential terminal devices.

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[0126] 7A illustrates an example diagram of DL beacon signal transmission within communication network 100, according to some embodiments of the present disclosure. FIG. 7B illustrates an example diagram of a UL CPO pre-compensation procedure 700, according to some embodiments of the present disclosure. As shown in FIG. 7A, network device 120 may broadcast a DL beacon signal to a set S of terminal devices. The DL beacon signal includes a carrier signal

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[0128]

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[0129] As shown in FIG. 7B, each terminal device n uses a phase-locked loop (PLL) 702 to estimate the phase of the received carrier signal,

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[0130] Using the preamble designs of this disclosure, accurate, fast, and scalable UAD and timing acquisition can be built with minimal cost in measurement resources. RF,UAD,n (t)} n∈SA good signaling design can facilitate the entire process and promote detection efficiency and performance. Accurate UAD results remove uncertainty in the observation model and, after model reduction, reduce the dimension of the timing acquisition problem. Some embodiments of the present disclosure can achieve large capacity, scalability, and agility. For example, fixed preamble assignment may be permitted, where each terminal device may be pre-assigned a dedicated sequence. Instead of random preamble assignment, such fixed preamble assignment prevents sequence collisions. Any pre-adjustment in sequence assignment is wasteful for random, distributed service requests. Furthermore, the unique association between sequences and users avoids the costs associated with reporting user IDs. The required time-frequency cost corresponds to the (average) number of active terminal devices and can be independent of the large number of terminal devices. A sparse MC-FTN conjugate-symmetric signaling design allows the NTB product to be:

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[0132] An exemplary joint UAD and timing acquisition method based on NLS will be described with reference to FIG. 8, which shows an exemplary diagram of a reception procedure 800 for superimposed MC-FTN conjugate symmetric signaling according to some embodiments of the present disclosure. For purposes of explanation, the reception procedure for superimposed MC-FTN conjugate symmetric signals will be described from the perspective of network device 120 with reference to the frequency domain structures shown in FIGS. 1A and 3B.

[0133] As shown in Figure 8, if an active terminal device n∈S A is a dedicated RF UAD signalRF,UAD,n (t) may be transmitted to the network device 120. The RF UAD signal s RF,UAD,n (t) includes the round trip propagation delay d n =τ n T s and UL channel h n (t) may occur. -2πf c τ n T s The UL CPO for each pre-compensation phase factor

[0134]

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[0135] In the receiving procedure 800 for joint UAD and timing acquisition, the network device 120 may perform standard processing as an OFDM receiver, except for a Discrete Fourier transform (DFT) operation. In some embodiments, the network device 120 receives a local carrier signal generated by a local oscillator 812.

[0136]

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[0137] The network device 120 then calculates the sampling period T s The continuous-time baseband signal z(t) is converted to a digital signal z(t) via an A / D converter operating at (2M-1+L CP,UAD ) into a discrete-time baseband signal z[m] of length 806. The discrete-time baseband signal z[m] may be written as equation (11) as follows:

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[0139] Next, the network device 120 extracts the first L CP,UAD CP symbols consisting of points may be removed (808), thus obtaining a (2M-1) length superimposed complex conjugate symmetric sinusoidal sequence for joint UAD and timing acquisition.

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[0141] The network device 120 executes the joint UAD and timing acquisition algorithm 810 to generate a sequence of length (2M-1).

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[0142] 9 illustrates an exemplary implementation of the process of the joint UAD and timing acquisition algorithm 810 according to an embodiment of the present disclosure. As shown in FIG. 9, in step 1, the network device may perform data pre-processing of the UAD by utilizing conjugate symmetry. The conjugate symmetry designed on the terminal device side allows the network device to

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[0144] The intentional phase compensation strategy for MC-FTN conjugate symmetric signal transmission at the terminal device side is to compensate for the unknown vector

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[0145]

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[0146] In step 2, a sparse real vector representing the imaginary parts of the symbols received on the set of subcarriers associated with the set of terminal devices in the network

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[0147] In step 3, to remove the disturbance of the observation error, the estimated sparse real vector

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[0148]

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[0149] In step 4, a low-dimensional complex vector representing symbols received on the set of subcarriers associated with the first set of identified active terminal devices, i.e.

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[0150] In optional step 5, the imaginary part is converted into the

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[0151] In step 6, to remove the disturbance of the observation error, the estimated low-dimensional complex vector

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[0152] Step 7: Improved active subset

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[0153] In this way, the imaginary part

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[0154] 10 illustrates an example implementation of a process 1000 for communication according to an embodiment of the present disclosure. Process 1000 illustrates a TDD massive random access procedure based on MC-FTN conjugate symmetric signaling, in which UL / DL channel reciprocity may be exploited to facilitate phase compensation. Note that process 1000 may be considered a more specific example of process 200 of FIG. 2. The example implementation of FIG. 10 is depicted and described from the perspectives of an active UE 1010-1, an inactive UE 1010-3, and a BS 1020.

[0155] At the start of a transmission cycle, the BS 1020 may broadcast a DL pilot sequence within the network. The DL pilot sequence may also serve as a beacon signal for synchronization. Based on the received DL pilot sequence, the active UE 1010-1 may estimate its respective DL Channel State Information (CSI) and DL CPO. The active UE 1010-1 may determine a phase compensation coefficient and a power factor based on the estimated DL CSI by utilizing the UL / DL, and encode symbols to be transmitted with the determined phase compensation coefficient and power factor. The active UE 1010-1 may further predict a UL CPO based on the estimated DL CPO and generate a carrier signal using a pre-compensation phase coefficient of the UL CPO. Based on the carrier signal, the active UE 1010-1 may convert symbols to MC-FTN conjugate-symmetric signaling and transmit the MC-FTN conjugate-symmetric signaling to the BS 1020 on associated subcarriers. The BS 1020 may perform joint UAD and timing acquisition and obtain the set of identified active UEs and their respective TA information based on the superimposed observations. The BS 1020 may broadcast a mapping list indicating the set of identified active UEs over a low-rate DL channel that can be accessed by all UEs in the network. Each row in the mapping list that is dedicated to an identified UE includes the ID of the identified UE, associated TA information, and assigned UL channel. The BS 1020 may allocate these resources only to the identified UE. Table 1 shows an example of the information in the mapping list.

[0156] [Table 1]

[0157] Any UE can check the mapping list. By checking, an active UE can determine whether it has been successfully identified by the BS 1020. The identified active UE may recognize the scheduling grant in the mapping list and proceed to transmit further data over the assigned UL channel, e.g., for connection state establishment. Alternatively, the identified active UE n may transmit a scheduling grant in the associated subcarrier with a pre-compensation factor of the UL CPO to convey a few bits of message.

[0158]

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[0159] Figure 11A illustrates an exemplary implementation of MC-FTN conjugate symmetric signaling in the frequency domain, according to some embodiments of the present disclosure. Figure 11B illustrates an exemplary diagram of a conventional PRACH signal in the frequency domain. Figure 11C illustrates an exemplary diagram of an MC-FTN conjugate symmetric signal and a conventional PRACH signal in the time domain, according to some embodiments of the present disclosure. Consider a 500-m radius cell serving a total of 720 random access UEs. In this case, the maximum possible round-trip propagation delay would be 3.33 μs, and the maximum allowed bandwidth for random access would be 300 kHz. As shown in Figure 11A, one UAD symbol based on MC-FTN conjugate symmetric signaling can support 240 UEs with a subcarrier spacing of 1.25 kHz, with each subcarrier assigned to a unique UE. The NTB product of MC-FTN conjugate symmetric signaling is 0.25, and therefore, the symbol duration is reduced to 0.2 ms. Therefore, as shown in Figure 11C, a 0.9 ms x 300 kHz resource block can accommodate three independent UAD symbols. The total of 720 UEs are divided into three subsets, each consisting of 240 UEs and served by a dedicated symbol.

[0160] In contrast, the PRACH method supports all UEs with a single symbol of length 0.8 ms. According to the LTE / NR design criteria, a 0.9 ms × 300 kHz resource block is allocated to the u-th root ZC sequence of length 241, i.e.,

[0161]

number

[0162]

number

[0163] 12A and 12B show a performance comparison of joint UAD and timing acquisition 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 resource (0.9 ms × 300 kHz). Table 2 shows detailed simulation parameters of the two procedures.

[0164] [Table 2]

[0165] UAD performance is evaluated in terms of the probability of false detection and false alarm, while timing acquisition performance is evaluated in terms of the estimation bias. Simulation results are derived by averaging over 10,000 independent experiments. Figure 12A shows UAD performance under various transmission probabilities. For MC-FTN signaling, the transmission probability threshold is 12.5%, above which the SNR improvement drops significantly and performance is limited by the degrees of freedom. In fact, this threshold coincides with half the NTB product of MC-FTN conjugate-symmetric signaling for this simulation. Figure 12B shows timing acquisition performance with a sampling period of 0.033 μs, where the estimation bias is calculated only for identified UEs. As shown in Figures 12A and 12B, the more identified UEs are, the longer the tail is found in the higher SNR region. The simulation results demonstrate that the proposed MC-FTN conjugate-symmetric signaling can support more than four times the number of simultaneous random access users compared to existing PRACH schemes. Such significant advantages benefit from the overall design, from FTN and collision-free waveforms, conjugate symmetry, and phase compensation, to advanced algorithms for joint UAD and timing acquisition. In contrast, for PARCH, sequence collisions from random selection remain a significant source of performance degradation.

[0166] FIG. 13 illustrates a flowchart of a method 1300 implemented in a terminal device according to some embodiments of the present disclosure. For example, method 1300 may be performed in a terminal device 110 (e.g., a first terminal device 110-1) as shown in FIG. 1A. Below, for illustrative purposes, method 1300 is described with reference to FIG. 1A. It should be understood that method 1300 may include additional blocks not shown and / or omit some blocks as shown, and the scope of the present disclosure is not limited in this respect. Using method 1300 of FIG. 13, a new solution for large-access collaborative UAD and timing acquisition is provided with reduced delay and reduced measurement resource costs.

[0167] At block 1320, the terminal device 110 receives a configuration associated with a set of subcarriers from a network device 120 in a wireless access network, the set of subcarriers being associated with a set of terminal devices in the wireless access network for transmission of modulated conjugate symmetric signals. These modulated conjugate symmetric signals indicate activity information of a set of active terminal devices among the set of terminal devices. At block 1340, the terminal device 110 transmits a modulated conjugate symmetric signal to the network device 120, the modulated conjugate symmetric signal being generated by modulating subcarriers from the set of subcarriers with symbols, the modulated conjugate symmetric signal comprising sparse MC-FTN conjugate symmetric signaling.

[0168] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate-symmetric signaling may be greater than or equal to two times the ratio of the number of sets of active terminal devices to the number of sets of terminal devices. In some embodiments, a subcarrier may be exclusively associated with a terminal device 110.

[0169] In some embodiments, to generate the subcarriers, the terminal device 110 may generate a complex conjugate symmetric sinusoidal waveform having the frequency of the subcarriers and add a cyclic prefix to the complex conjugate symmetric sinusoidal waveform. The duration of the complex conjugate symmetric sinusoidal waveform may be determined based on the inverse of the subcarrier spacing of the set of subcarriers, the number of sets of active terminal devices, and the number of sets of terminal devices.

[0170] In some embodiments, the terminal device 110 may determine a pre-compensation phase factor for the complex conjugate symmetric sinusoidal waveform including the cyclic prefix, which pre-compensates for the UL CPO of the carrier signal of the modulated conjugate symmetric signal caused by a propagation delay from the terminal device 110 to the network device 120.

[0171] 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 a DL CPO of the carrier signal caused by a 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.

[0172] In some embodiments, the symbols may include a variable phase compensation factor to compensate for the phase of the channel between the network device 120 and the terminal device 110 in the subcarrier, and a fixed phase compensation factor.

[0173] In some embodiments, the terminal device 110 may determine the variable phase compensation coefficient based on the beacon signal and the reciprocity of the channel between the UL and DL.

[0174] In some embodiments, the terminal device 110 may determine the fixed phase compensation coefficient based on the frequency of the subcarrier, the frequency of the carrier signal, the bias between the variable phase compensation coefficient at the subcarrier and the phase of the channel between the network device 120 and the terminal device 110, and the bias between the pre-compensation phase coefficient and the UL CPO.

[0175] In some embodiments, the subcarriers may be within a frequency band, the bandwidth of which may be determined based on a maximum propagation delay in the radio access network, a bias between a variable phase compensation factor at the subcarrier and the phase of the channel between the network device and the terminal device, and a bias between the pre-compensation phase factor and the UL CPO.

[0176] In some embodiments, the terminal device 110 may generate a discrete-time baseband conjugate symmetric signal based on the baseband frequency of the subcarrier, a variable phase compensation coefficient, and a fixed phase compensation coefficient, generate a continuous-time baseband conjugate symmetric signal based on the discrete-time baseband conjugate symmetric signal through digital-to-analog conversion, and perform frequency shift of the continuous-time baseband conjugate symmetric signal to generate a modulated conjugate symmetric signal.

[0177] In some embodiments, to generate a discrete-time baseband conjugate symmetric signal, the terminal device 110 may perform an IDFT to generate a first sequence modulated using a variable phase compensation coefficient and a fixed phase compensation coefficient, insert a copy of the last portion of the first sequence prepended to the first sequence to obtain a second sequence, and discard the last portion 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 coefficient and the fixed phase compensation coefficient corresponding to the subcarrier. The last portion of the first sequence may include a cyclic prefix and a conjugate symmetric component. The length of the discrete-time baseband conjugate symmetric signal, excluding the cyclic prefix, may be determined based on the duration and sampling rate of the modulated conjugate symmetric signal.

[0178] In some embodiments, the terminal device 110 may perform frequency shifting using a pre-compensation phase factor to pre-compensate for the UL CPO.

[0179] In some embodiments, terminal device 110 may receive an indication from network device 120 indicating a set of active terminal devices identified by network device 120, determine whether terminal device 110 is included in the set of active terminal devices identified by network device 120, and perform communication with network device 120 based on a determination that terminal device 110 is included in the set of active terminal devices identified by network device 120, or retransmit the modulated conjugate symmetric signal to network device 120 based on a determination that terminal device 110 is excluded from the set of active terminal devices identified by network device 120.

[0180] In some embodiments, the terminal device 110 may transmit data symbols with variable phase compensation coefficients in subcarriers with UL CPO pre-compensation coefficients, which data symbols are mapped to traffic data.

[0181] In some embodiments, the indication may indicate resources for each of the set of active terminal devices identified by network device 120 to perform communication. Terminal device 110 may perform communication with network device 120 using the respective resources associated with terminal device 110. In some embodiments, the indication may further indicate timing advance information associated with each of the set of active terminal devices identified by network device 120. Terminal device 110 may perform communication with network device 120 based on the respective timing advance information associated with terminal device 110.

[0182] FIG. 14 illustrates a flowchart of a method 1400 implemented in a network device according to some embodiments of the present disclosure. For example, method 1400 may be performed in network device 120 as shown in FIG. 1A. Below, for purposes of explanation, method 1400 is described with reference to FIG. 1A. It should be understood that method 1400 may include additional blocks not shown and / or omit some blocks as shown, and the scope of the present disclosure is not limited in this respect. Using method 1400 of FIG. 14, a new solution for large-access UADs is provided with reduced latency and reduced measurement resource costs.

[0183] At block 1420, network device 120 transmits a configuration associated with a set of subcarriers to a set of terminal devices in the radio access network. The set of subcarriers is associated with the set of terminal devices for transmission of modulated conjugate symmetric signals. These modulated conjugate symmetric signals indicate activity information of an active set of terminal devices among the set of terminal devices. At block 1440, network device 120 receives superimposed signals associated with the modulated conjugate symmetric signals from the set of active terminal devices. These modulated conjugate symmetric signals are generated by modulating a set of subcarriers associated with the set of active terminal devices using a set of symbols respectively corresponding to the set of active terminal devices and include sparse MC-FTN conjugate symmetric signaling. At block 1440, network device 120 identifies an active set of terminal devices among the set of terminal devices based on the received superimposed signals.

[0184] 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 sets of active terminal devices to the number of sets of terminal devices.

[0185] In some embodiments, each of the sets of symbols may include a variable phase compensation factor for compensating for the phase of the channel between the network device 120 and the corresponding active terminal device at the associated subcarrier, and a fixed phase compensation factor, which may be based on a bias between the variable phase compensation factor at the associated subcarrier and the phase of the channel between the network device 120 and the corresponding active device.

[0186] In some embodiments, to identify a set of active terminal devices, network device 120 may determine, based on the superimposed signal, a superimposed complex conjugate symmetric sinusoidal sequence including symbols received on a set of subcarriers associated with the set of terminal devices, determine, based on this superimposed complex conjugate symmetric sinusoidal sequence and its conjugate symmetry, a superimposed complex sinusoidal sequence that includes the imaginary parts of the symbols received on the subcarriers associated with the set of terminal devices and excludes the real parts of the symbols received on the set of subcarriers associated with the set of terminal devices, determine a first set of identified active terminal devices based on this superimposed complex conjugate symmetric sinusoidal sequence, and determine a second set of identified active terminal devices as the set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence and the first set of identified active terminal devices.

[0187] In some embodiments, to determine the first set of identified active terminal devices, network device 120 may determine a sparse real vector representing the imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices based on the superimposed complex sinusoidal sequence, determine significant non-zero components of the imaginary parts of symbols received on a set of subcarriers 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 set of identified active terminal devices based on the significant non-zero components of the imaginary parts of symbols received on the set of subcarriers associated with the set of terminal devices.

[0188] In some embodiments, the network device 120 may determine the sparse real vector by solving an efficient non-negative least-squares problem based on the superimposed complex sinusoidal sequences. Components of the sparse real vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies lower than the carrier frequency may be non-negative, and components of the sparse real vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies higher than the carrier frequency may be non-positive.

[0189] In some embodiments, to determine the second set of identified active terminal devices, network device 120 may determine a low-dimensional complex vector representing symbols received on a set of subcarriers associated with the first set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence, determine significant non-zero components of the symbols received on the set of subcarriers associated with the first set of identified active terminal devices by comparing the amplitudes of the components of the low-dimensional complex vector with a second predefined threshold, and determine the second set of identified active terminal devices based on the significant non-zero components of the symbols received on the set of subcarriers associated with the first set of identified active terminal devices.

[0190] In some embodiments, the network device 120 may determine the low-dimensional complex vector according to the constraint that components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies lower than the carrier frequency are non-negative and components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies higher than the carrier frequency are non-positive.

[0191] In some embodiments, the network device 120 may replace the imaginary parts of symbols received on a set of subcarriers associated with the first set of identified active terminal devices with corresponding imaginary parts derived from the sparse real vector.

[0192] In some embodiments, network device 120 may determine a propagation delay from the second set of identified active terminal devices to network device 120 based on the phase of symbols received on a set of subcarriers associated with the second set of identified active terminal devices.

[0193] In some embodiments, network device 120 may determine timing advance information associated with the second set of identified active terminal devices based on the determined propagation delay from the second set of identified active terminal devices to network device 120 and transmit an indication indicating the set of identified active terminal devices and the associated timing advance information to each set of terminal devices via a common channel.

[0194] In some embodiments, the indication may indicate resources for carrying out respective communications by each of the set of identified active terminal devices.

[0195] In some embodiments, network device 120 may transmit a beacon signal to a set of terminal devices indicating the transmission of sparse MC-FTN conjugate-symmetric signaling.

[0196] In some embodiments, an apparatus capable of performing any of the methods 1300 (e.g., terminal device 110) may comprise means for performing each step of the method 1300. These means may be implemented in any suitable form. For example, these means may be implemented in a circuit or a software module.

[0197] In some embodiments, the apparatus comprises means for receiving, at a terminal device, a configuration associated with a set of subcarriers from a network device in a radio access network, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; and means for transmitting the modulated conjugate symmetric signals to the network device, the modulated conjugate symmetric signals being generated by modulating subcarriers from the set of subcarriers using symbols, the modulated conjugate symmetric signals comprising sparse MC-FTN conjugate symmetric signaling.

[0198] In some embodiments, the normalized time-bandwidth product of the sparse MC-FTN conjugate-symmetric signaling may be greater than or equal to two times the ratio of the number of sets of active terminal devices to the number of sets of terminal devices. In some embodiments, a subcarrier may be exclusively associated with a terminal device.

[0199] In some embodiments, the means for generating the subcarriers may comprise means for generating a complex conjugate symmetric sinusoidal waveform having a frequency of the subcarriers and means for adding a cyclic prefix to the complex conjugate symmetric sinusoidal waveform. A duration of the complex conjugate symmetric sinusoidal waveform may be determined based on the inverse of a subcarrier spacing of the set of subcarriers, the number of sets of active terminal devices, and the number of sets of terminal devices.

[0200] In some embodiments, the apparatus may further comprise means for determining a pre-compensation phase coefficient for a complex conjugate symmetric sinusoidal waveform including a cyclic prefix, the pre-compensation phase coefficient pre-compensating for a UL CPO of a carrier signal of the modulated conjugate symmetric signal caused by a propagation delay from the terminal device to the network device.

[0201] In some embodiments, the means for determining a pre-compensation phase factor may include means for receiving a beacon signal including a carrier signal from the network device; means for determining a DL CPO of the carrier signal caused by a propagation delay from the network device to the terminal device based on the received beacon signal; and means for determining a pre-compensation phase factor based on the determined DL CPO.

[0202] In some embodiments, the symbols may include a variable phase compensation factor and a fixed phase compensation factor for compensating for the phase of the channel between the network device and the terminal device at the subcarrier.

[0203] In some embodiments, the apparatus may further comprise means for determining a variable phase compensation coefficient based on the beacon signal and the reciprocity of the channel between the UL and DL.

[0204] In some embodiments, the apparatus may further comprise means for determining a fixed phase compensation coefficient based on a frequency of the subcarrier, a frequency of the carrier signal, a bias between the variable phase compensation coefficient at the subcarrier and the phase of the channel between the network device and the terminal device, and a bias between the pre-compensation phase coefficient and the UL CPO.

[0205] In some embodiments, the subcarriers may be within a frequency band, the bandwidth of which may be determined based on a maximum propagation delay in the radio access network, a bias between a variable phase compensation factor at the subcarrier and the phase of the channel between the network device and the terminal device, and a bias between the pre-compensation phase factor and the UL CPO.

[0206] In some embodiments, the apparatus may further include means for generating a discrete-time baseband conjugate symmetric signal based on a baseband frequency of the subcarrier, a variable phase compensation coefficient, and a fixed phase compensation coefficient; means for generating a continuous-time baseband conjugate symmetric signal based on the discrete-time baseband conjugate symmetric signal by digital-to-analog conversion; and means for performing frequency shift of the continuous-time baseband conjugate symmetric signal to generate a modulated conjugate symmetric signal.

[0207] In some embodiments, the means for generating a discrete-time baseband conjugate symmetric signal may include means for generating a first sequence modulated using a variable phase compensation coefficient and a fixed phase compensation coefficient by performing an IDFT; means for inserting a copy of a final portion of the first sequence prepended to the first sequence to obtain a second sequence; and means for discarding the final portion 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 coefficient and the fixed phase compensation coefficient corresponding to the subcarrier. The final portion of the first sequence may include a cyclic prefix and a conjugate symmetric component. The length of the discrete-time baseband conjugate symmetric signal, excluding the cyclic prefix, may be determined based on the duration and sampling rate of the modulated conjugate symmetric signal.

[0208] In some embodiments, the apparatus may further comprise means for performing a frequency shift using a pre-compensation phase factor to pre-compensate for the UL CPO.

[0209] In some embodiments, the apparatus may further comprise means for receiving an indication from the network device indicating a set of active terminal devices identified by the network device; means for determining whether the terminal device is included in the set of active terminal devices identified by the network device; and means for performing communication with the network device based on a determination that the terminal device is included in the set of active terminal devices identified by the network device, or means for retransmitting the modulated conjugate symmetric signal to the network device based on a determination that the terminal device is excluded from the set of active terminal devices identified by the network device.

[0210] In some embodiments, the apparatus may further comprise means for transmitting data symbols including variable phase compensation coefficients on subcarriers having pre-compensation coefficients of the UL CPO, the data symbols being mapped to traffic data.

[0211] In some embodiments, the indication may indicate resources for performing communications with each of the set of active terminal devices identified by the network device. The apparatus may further comprise means for performing communications with the network device using the respective resources associated with the terminal devices.

[0212] In some embodiments, the indication may indicate timing advance information associated with each of a set of active terminal devices identified by the network device. The apparatus may further comprise means for performing communication with the network device based on the respective timing advance information associated with the terminal devices.

[0213] In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of method 1300. In some embodiments, these means comprise at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code configured, together with the at least one processor, to cause execution of the apparatus.

[0214] In some embodiments, an apparatus capable of performing any of the methods 1400 (e.g., network device 120) may comprise means for performing each step of the method 1400. These means may be implemented in any suitable form. For example, these means may be implemented in a circuit or a software module.

[0215] In some embodiments, the apparatus comprises: means, at a network device, for transmitting a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; means for receiving superimposed signals associated with the modulated conjugate symmetric signals from the set of active terminal devices, the modulated conjugate symmetric signals being generated by modulating a set of subcarriers associated with the set of active terminal devices using a set of symbols respectively corresponding to the set of active terminal devices and including sparse MC-FTN conjugate symmetric signaling; and means for identifying an active set of terminal devices among the set of terminal devices based on the received superimposed signals.

[0216] 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 sets of active terminal devices to the number of sets of terminal devices.

[0217] In some embodiments, each of the sets of symbols may include a variable phase compensation factor for compensating for the phase of a channel between the network device and a corresponding active terminal device at an associated subcarrier, and a fixed phase compensation factor, which may be based on a bias between the variable phase compensation factor at the associated subcarrier and the phase of the channel between the network device and the corresponding active device.

[0218] In some embodiments, the means for identifying a set of active terminal devices may include: means for determining, based on the superimposed signal, a superimposed complex conjugate symmetric sinusoidal sequence including symbols received on a set of subcarriers associated with the set of terminal devices; means for determining, based on the superimposed complex conjugate symmetric sinusoidal sequence and its conjugate symmetry, a superimposed complex sinusoidal sequence including imaginary parts of symbols received on the subcarriers associated with the set of terminal devices and excluding real parts of symbols received on the set of subcarriers associated with the set of terminal devices; means for determining, based on the superimposed complex sinusoidal sequence, a first set of identified active terminal devices; and means for determining, as the set of identified active terminal devices, a second set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence and the first set of identified active terminal devices.

[0219] In some embodiments, the means for determining a first set of identified active terminal devices may comprise: means for determining a sparse real vector representing imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices based on the superimposed complex sinusoidal sequence; means for determining significant non-zero components of the imaginary parts of symbols received on a set of subcarriers associated with the set of terminal devices by comparing absolute values ​​of the components of the sparse real vector with a first predefined threshold; and means for determining the first set of identified active terminal devices based on the significant non-zero components of the imaginary parts of symbols received on the set of subcarriers associated with the set of terminal devices.

[0220] In some embodiments, the apparatus may further comprise means for determining a sparse real vector by solving an efficient non-negative least-squares problem based on the superimposed complex sinusoidal sequence, where components of the sparse real vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies lower than the carrier frequency may be non-negative, and components of the sparse real vector corresponding to imaginary parts of symbols received on a set of subcarriers having frequencies higher than the carrier frequency may be non-positive.

[0221] In some embodiments, the means for determining the second set of identified active terminal devices may comprise: means for determining a low-dimensional complex vector representing symbols received on a set of subcarriers associated with the first set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence; means for determining significant non-zero components of the symbols received on the set of subcarriers associated with the first set of identified active terminal devices by comparing the amplitudes of the components of the low-dimensional complex vector with a second predefined threshold; and means for determining the second set of identified active terminal devices based on the significant non-zero components of the symbols received on the set of subcarriers associated with the first set of identified active terminal devices.

[0222] In some embodiments, the apparatus may further comprise means for determining a low-dimensional complex vector subject to the constraint that components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having a frequency lower than the carrier frequency are non-negative and components of the low-dimensional complex vector corresponding to imaginary parts of symbols received on a set of subcarriers having a frequency higher than the carrier frequency are non-positive.

[0223] In some embodiments, the apparatus may further comprise means for replacing imaginary parts of symbols received on a set of subcarriers associated with the first set of identified active terminal devices with corresponding imaginary parts derived from the sparse real vector.

[0224] In some embodiments, the apparatus may further comprise means for determining a propagation delay from the second set of identified active terminal devices to the network device based on a phase of symbols received on a set of subcarriers associated with the second set of identified active terminal devices.

[0225] In some embodiments, the apparatus may further comprise means for determining timing advance information associated with the second set of identified active terminal devices based on the determined propagation delay from the second set of identified active terminal devices to the network device, and means for transmitting an indication indicating the set of identified active terminal devices and the associated timing advance information to each of the set of terminal devices via a common channel.

[0226] In some embodiments, the indication may indicate resources for carrying out respective communications by each of the set of identified active terminal devices.

[0227] In some embodiments, the apparatus may further comprise means for transmitting a beacon signal to a set of terminal devices indicating transmission of the sparse MC-FTN conjugate-symmetric signaling.

[0228] In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of method 1400. In some embodiments, these means comprise at least one processor and at least one memory containing computer program code, the at least one memory and the computer program code configured, together with the at least one processor, to cause execution of the apparatus.

[0229] 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 the terminal device 110 or the network device 120, as shown in FIG. 1A. 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 1510.

[0230] The communication module 1540 is for two-way communication. The communication module 1540 includes at least one antenna to facilitate communication. The communication interface may represent any interface necessary for communication with other network elements.

[0231] The processor 1510 may be of any type suitable for a local technology network and may include, by way of non-limiting example, one or more of 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. The device 1500 may include multiple processors, such as application-specific integrated circuit chips time-slaved to a clock that synchronizes the main processor.

[0232] The memory 1520 may include one or more nonvolatile memories and one or more volatile memories. Examples of nonvolatile memory include, but are not limited to, read only memory (ROM) 1524, electrically programmable read only memory (EPROM), flash memory, hard disks, compact discs (CDs), digital video discs (DVDs), and other magnetic and / or optical storage. Examples of volatile memory include, but are not limited to, random access memory (RAM) 1522 and other volatile memory that does not persist while power is off.

[0233] The computer program 1530 includes computer-executable instructions that are executed by the associated processor 1510. The program 1530 may be stored in the ROM 1524. The processor 1510 may load the program 1530 into the RAM 1522 to perform any suitable operations and processes.

[0234] The embodiments of the present disclosure may be implemented using a program 1530 such that the device 1500 may execute any of the processes of the present disclosure described with reference to Figures 1A to 13. The embodiments of the present disclosure may also be implemented by hardware or a combination of software and hardware.

[0235] In some embodiments, the program 1530 may be tangibly contained on a computer-readable medium, which may be included in the device 1500 (such as the memory 1520) or other storage device accessible by the device 1500. The device 1500 may load the program 1530 from the computer-readable medium into RAM 1522 for execution. The computer-readable medium may include any type of tangible non-volatile storage, such as a ROM, an EPROM, a flash memory, a hard disk, a CD, a DVD, etc. Figure 16 shows an example of a computer-readable medium 1600 in the form of a CD or DVD. The computer-readable medium has the program 1530 stored on it.

[0236] In general, 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 that may be executed by a controller, microprocessor, or other computing device. While various aspects of the embodiments of the present disclosure have been illustrated and described as block diagrams, flowcharts, or using some other graphical representations, it should be understood that the blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing device, or some combination thereof.

[0237] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, that execute on a real or virtual target processor in a device to perform the method 1300 or 1400 described above with reference to FIGS. 1A-14. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or divided among program modules as desired in various embodiments. The machine-executable instructions of the program modules may be executed in a local device or a distributed device. In a distributed device, the program modules may be located in both local and remote storage media.

[0238] Program code for carrying out the methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus such that, when executed by the processor or controller, the program code causes the functions / acts specified in the flowcharts and / or block diagrams to be performed. The program code may be executed entirely on the machine, partially on the machine as a stand-alone software package, partially on both the machine and a remote machine, or entirely on a remote machine or server.

[0239] In the context of the present disclosure, computer program code or associated data may 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 which include a signal, a computer-readable medium, etc.

[0240] The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. More specific examples of computer-readable storage media include an electrical connection including one or more wires, a portable floppy 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 thereof. The term "non-transitory" as used herein refers to a limitation of the medium itself (i.e., tangible rather than signal) as opposed to a limitation on the persistence of data storage (e.g., RAM vs. ROM).

[0241] Furthermore, while acts are shown in a particular order, it should not be understood that such acts need to be performed in the particular order shown, or in any sequential order, or that all of the shown acts need to be performed, to achieve desirable results. In certain environments, multitasking and parallel processing may be advantageous. Similarly, while the above description includes details of specific implementations, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, individual features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.

[0242] Although the present disclosure has been described in language specific to structural features and / or method acts, it is to be understood that the present disclosure, as defined in the appended claims, is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. 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: receiving, from a network device in the radio access network, a configuration associated with a set of subcarriers, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; and transmitting a modulated conjugate symmetric signal to the network device, the modulated conjugate symmetric signal being generated by modulating subcarriers from the set of subcarriers with symbols, the modulated conjugate symmetric signal comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling.

2. The terminal device of claim 1 , wherein a 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 sets of the active terminal devices to the number of sets of the terminal devices.

3. 3. The terminal device according to claim 1, wherein the subcarriers are exclusively associated with the terminal device.

4. The terminal device, generating a complex conjugate symmetric sinusoidal waveform having a frequency of the subcarriers, wherein a duration of the complex conjugate symmetric sinusoidal waveform is determined based on an inverse of a subcarrier spacing of the set of subcarriers, the number of the sets of active terminal devices, and the number of the sets of terminal devices; A terminal device according to any one of claims 1 to 3, which is caused to generate said subcarriers by adding a cyclic prefix to said complex conjugate symmetric sinusoidal waveform.

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

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

7. The terminal device of claim 6 , wherein the symbols include a variable phase compensation factor and a fixed phase compensation factor for compensating for the phase of a channel between the network device and the terminal device at the subcarrier.

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

9. 8. The terminal device of claim 7, wherein the terminal device is further caused to determine the fixed phase compensation coefficient based on the frequency of the subcarrier, the frequency of the carrier signal, a bias between the variable phase compensation coefficient at the subcarrier and the phase of the channel between the network device and the terminal device, and a bias between the pre-compensation phase coefficient and the UL CPO.

10. 8. The terminal device of claim 7, wherein the subcarriers are within a frequency band, and a bandwidth of the frequency band is determined based on a maximum propagation delay in the radio access network, the bias between the variable phase compensation coefficient in the subcarrier and the phase of the channel between the network device and the terminal device, and the bias between the pre-compensation phase coefficient and the UL CPO.

11. The terminal device, generating a discrete-time baseband conjugate-symmetric signal based on the baseband frequencies of the subcarriers, the variable phase compensation coefficient, and the fixed phase compensation coefficient; generating a continuous-time baseband conjugate symmetric signal based on the discrete-time baseband conjugate symmetric signal by digital-to-analog conversion; 8. The terminal device of claim 7, further caused to perform a frequency shift of the continuous-time baseband conjugate symmetric signal to generate the modulated conjugate symmetric signal.

12. The terminal device, generating a first sequence modulated using the variable phase compensation coefficients and the fixed phase compensation coefficients by performing an inverse discrete Fourier transform (IDFT), wherein non-zero components of an input of the IDFT include the variable phase compensation coefficients and the fixed phase compensation coefficients corresponding to the subcarriers; inserting a copy of a last portion of the first sequence prepended to the first sequence to obtain a second sequence, wherein the last portion of the first sequence includes a cyclic prefix and a conjugate symmetric component; 12. The terminal device of claim 11, wherein generating the discrete-time baseband conjugate symmetric signal is caused by discarding a last portion of the second sequence to obtain the discrete-time baseband conjugate symmetric signal, wherein a length of the discrete-time baseband conjugate symmetric signal excluding the cyclic prefix is ​​determined based on a duration and a sampling rate of the modulated conjugate symmetric signal.

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

14. The terminal device, receiving an indication from the network device indicating a set of active end devices identified by the network device; determining whether the terminal device is included in the set of active terminal devices identified by the network device; The terminal device according to any one of claims 1 to 13, further caused to perform 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 to retransmit a 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.

15. 15. The terminal device of claim 14, wherein the terminal device transmits data symbols including the variable phase compensation coefficients in the subcarriers having the pre-compensation coefficients of a UL CPO, and the data symbols are mapped to traffic data.

16. The terminal device of claim 14 , wherein the instructions further indicate resources for performing communications by each of the set of active terminal devices identified by the network device, and the terminal devices perform the communications with the network devices using the respective resources associated with the terminal devices.

17. A terminal device according to any one of claims 14 to 16, wherein the instruction further indicates timing advance information respectively associated with the set of active terminal devices identified by the network device, and the terminal device performs the communication with the network device based on the respective timing advance information associated with the terminal devices.

18. at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network device to: transmitting a configuration associated with a set of subcarriers to a set of terminal devices in the radio access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; receiving, from the set of active terminal devices, superimposed signals associated with the modulated conjugate symmetric signals, the modulated conjugate symmetric signals being generated by modulating the set of subcarriers associated with the set of active terminal devices using sets of symbols respectively corresponding to the set of active terminal devices, and comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling; and identifying the set of active terminal devices from the set of terminal devices based on the received superimposed signal.

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

20. 20. The network device of claim 18, wherein each of the sets of symbols includes a variable phase compensation coefficient for compensating for the phase of a channel between the network device and a corresponding active terminal device at the associated subcarrier, and a fixed phase compensation coefficient, the fixed phase compensation coefficient being based on a bias between the variable phase compensation coefficient at the associated subcarrier and the phase of the channel between the network device and the corresponding active device.

21. The network device: determining a superposed complex conjugate symmetric sinusoidal sequence comprising symbols received on the set of subcarriers associated with the set of terminal devices based on the superposed signal; determining a superposed complex sinusoidal sequence based on the superposed complex conjugate-symmetric sinusoidal sequence and its conjugate symmetry, the superposed complex sinusoidal sequence including imaginary parts of the received symbols on the subcarriers associated with the set of terminal devices and excluding real parts of the received symbols on the set of subcarriers associated with the set of terminal devices; determining a first set of identified active terminal devices based on the superimposed complex sine wave sequence; 20. The network device of claim 18, wherein the network device is caused to identify the set of active terminal devices by determining a second set of identified active terminal devices as the set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence and the first set of identified active terminal devices.

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

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

24. The network device: determining a low-dimensional complex vector representing the received symbols on the set of subcarriers associated with the first set of identified active terminal devices based on the superimposed complex conjugate symmetric sinusoidal sequence; determining effective non-zero components of the received symbols on the set of subcarriers associated with the identified first set of active terminal devices by comparing amplitudes of components of the low-dimensional complex vector with a second predefined threshold; 22. The network device of claim 21, wherein the network device is caused to determine the second set of identified active terminal devices by determining the second set of identified active terminal devices based on the significant non-zero components of the received symbols on the set of subcarriers associated with the first set of identified active terminal devices.

25. 25. The network device of claim 24, wherein the network device is caused to determine the low-dimensional complex vector according to constraints that components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols on the set of subcarriers having frequencies lower than the carrier frequency are non-negative and components of the low-dimensional complex vector corresponding to the imaginary parts of the received symbols on the set of subcarriers having frequencies higher than the carrier frequency are non-positive.

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

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

28. The network device: determining timing advance information associated with the second set of identified active terminal devices based on the determined propagation delay from the second set of identified active terminal devices to the network device; and 28. The network device of claim 27, further caused to transmit, via a common channel, an indication to the set of identified active terminal devices and the associated timing advance information, respectively, to the set of terminal devices.

29. 30. The network device of claim 28, wherein the indication indicates resources for carrying out respective communications by each of the set of identified active terminal devices.

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

31. receiving, at a terminal device, from a network device in a radio access network, a configuration associated with a set of subcarriers, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of a set of active terminal devices among the set of terminal devices; transmitting a modulated conjugate symmetric signal to the network device, the modulated conjugate symmetric signal being generated by modulating subcarriers from the set of subcarriers using symbols, the modulated conjugate symmetric signal comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling.

32. transmitting, at a network device, a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; receiving, from the set of active terminal devices, superimposed signals associated with the modulated conjugate symmetric signals, the modulated conjugate symmetric signals being generated by modulating the set of subcarriers associated with the set of active terminal devices using sets of symbols respectively corresponding to the set of active terminal devices, and comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling; and identifying the set of active terminal devices from the set of terminal devices based on the received superimposed signals.

33. means for receiving, at a terminal device, a configuration associated with a set of subcarriers from a network device in a radio access network, the set of subcarriers being associated with a set of terminal devices in the radio access network for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of a set of active terminal devices among the set of terminal devices; means for transmitting a modulated conjugate symmetric signal to the network device, the modulated conjugate symmetric signal being generated by modulating a subcarrier from the set of subcarriers with a symbol, the modulated conjugate symmetric signal comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling.

34. means, at a network device, for transmitting a configuration associated with a set of subcarriers to a set of terminal devices in a radio access network, the set of subcarriers being associated with the set of terminal devices for transmission of modulated conjugate symmetric signals, the modulated conjugate symmetric signals indicating activity information of an active set of terminal devices among the set of terminal devices; means for receiving from the set of active terminal devices superimposed signals associated with the modulated conjugate symmetric signals, the modulated conjugate symmetric signals being generated by modulating the set of subcarriers associated with the set of active terminal devices using sets of symbols respectively corresponding to the set of active terminal devices, the means comprising sparse faster-than-Nyquist multicarrier (MC-FTN) conjugate symmetric signaling; means for identifying the set of active terminal devices from the set of terminal devices based on the received superimposed signal.

35. 33. A computer readable medium containing program instructions which, when executed by an apparatus, cause the apparatus to perform at least the method of claim 31 or 32.

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