LP-SS for frequency synchronization

Abstract

A method comprising: at a first apparatus, generate a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and transmit the LP-SS to a second apparatus for frequency synchronization.

Description

LP-SS FOR FREQUENCY SYNCHRONIZATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority to, and the benefit of, Finland Application No. 20245183, filed on February 16, 2024, which is incorporated herein by reference in its entirety.FIELDS

[0002] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for low power synchronization signal (LP-SS) for frequency synchronization.BACKGROUND

[0003] The study of low-power wake-up signal (LP-WUS) and low power wake-up receiver (LP-WUR, also shorted as LR) in 5G new radio (NR) may enable more power efficient operation on user equipment (UE) and more optimal resource allocation for network. The UE can be in a sleep mode or even powered off for power saving and be activated only upon the reception of the LP-WUS from the network. LP-SS can be used to enable the LP-WUR to maintain synchronization to the cell.SUMMARY

[0004] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: generate a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and transmit the LP- SS to a second apparatus for frequency synchronization.

[0005] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus iat least to: receive, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and estimate, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

[0006] In a third aspect of the present disclosure, there is provided a method. The method comprises: generating, at a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and transmitting the LP-SS to a second apparatus for frequency synchronization.

[0007] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: receiving, at a second apparatus from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and estimating, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

[0008] In a fifth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for generating a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for transmitting the LP-SS to a second apparatus for frequency synchronization.

[0009] In a sixth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for receiving, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for estimating, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

[0010] In a seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the third aspect.

[0011] In an eighth aspect of the present disclosure, there is provided a computerreadable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

[0012] It is to 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 easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0014] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0015] FIG. 2 illustrates example UE operations with an LP-WUR;

[0016] FIG. 3 illustrates a signaling chart for LP-SS transmission according to some example embodiments of the present disclosure;

[0017] FIG. 4 illustrates an example structure of an LP-SS according to some example embodiments of the present disclosure;

[0018] FIG. 5 illustrates an example frequency shifting pattern and an example on-off pattern according to some example embodiments of the present disclosure;

[0019] FIG. 6 illustrates a schematic diagram for deriving an estimated frequency offset according to some example embodiments of the present disclosure;

[0020] FIG. 7 illustrates a plot showing residual frequency offsets estimated for different signal to noise ratios (SNRs) by a wide band envelope detector with 7os according to some example embodiments of the present disclosure;

[0021] FIG. 8 illustrates a plot showing residual frequency offsets estimated for different SNRs by a wide band envelope detector with 80s according to some example embodiments of the present disclosure;

[0022] FIG. 9 illustrates a flowchart of a method implemented at a first device according to some example embodiments of the present disclosure;

[0023] FIG. 10 illustrates a flowchart of a method implemented at a second device according to some example embodiments of the present disclosure;

[0024] FIG. 11 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0025] FIG. 12 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0026] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0027] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0028] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0029] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0030] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0031] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the listof two or more elements are 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 the elements.

[0032] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0034] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0035] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example andif applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0036] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), 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- loT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0037] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0038] The term “terminal device” refers to any end device that may be capable ofwireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0039] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0040] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a first apparatus 110 and a second apparatus 120 cancommunicate with each other. In some example embodiments, the first apparatus 110 may comprise a terminal device (for example, a UE), and the second apparatus 120 may comprise a network device (for example, a gNB).

[0041] It is to be understood that the number of first apparatus 110, second apparatus 120 shown in FIG. 1 is given for the purpose of illustration without suggesting any limitations. The communication environment 100 may include any suitable number of first apparatus 110, and second apparatus 120.

[0042] In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 110 operating as a terminal device and the second apparatus 120 operating as a network device. However, in some example embodiments, operations described in connection with a terminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

[0043] In some example embodiments, if the first apparatus 110 is a terminal device or included in a terminal device and the second apparatus 120 is a network device or is included in a network device, a link from the second apparatus 120 to the first apparatus 110 is referred to as a downlink (DL), and a link from the first apparatus 110 to the second apparatus 120 is referred to as an uplink (UL). In DL, the second apparatus 120 is a transmitting (TX) device (or a transmitter) and the first apparatus 110 is a receiving (RX) device (or a receiver). In UL, the first apparatus 110 is a TX device (or a transmitter) and the second apparatus 120 is a RX device (or a receiver).

[0044] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising 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 spreadOFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0045] As briefly mentioned above, LP-WUR is being studied for NR. The study considers the usage of a separate LP-WUR at the UE, and evaluates how that can reduce the UE power consumption. FIG. 2 illustrates example UE operations with LP-WUR. The intention is that the main radio (MR) 220 of the UE 201 can be in a sleep mode or even powered off for power saving and be activated only upon the reception of the wake-up signal from the network. Basically, the network triggers the UE 201 to wake-up exactly when needed in an event-driven manner, by transmitting a special WUS to the UE 201. The special WUS is monitored by the dedicated low-power WUS receiver 210 at the UE. When the UE 201 receives the WUS, the WUS receiver 210 can trigger the wake-up of the ordinary NR transceiver and communication can start. Thus, the ultra-low power receiver 210 wakes up the main radio 220 and otherwise, the main radio 220 is OFF or kept in a deep sleep mode, as shown in FIG. 2. The assumption is that the low-power wake-up receiver can be operated in an always ‘on’ manner with very low power consumption. In fact, it is expected that it will consume significantly less power compared to the NR transceiver, by designing a simple (WUS) signal and the use of dedicated hardware for its monitoring, which is only able to receive the WUS.

[0046] LP-WUS is currently considered for both IDLE / INACTIVE mode and Connected mode. Current discussions mainly focused on DL reception where LP-WUS can be used to wake up the main radio to receive physical downlink control channel (PDCCH) / physical downlink shared channel (PDSCH) e.g., for paging or other data.

[0047] The study item in relation to possible LP-WUS content includes the objectives listed below.Table 1

[0048] To enable the LP-WUR to maintain synchronization to the cell, LP-SS is introduced. The study on LP-SS includes the objectives listed below.Table 2

[0049] Regarding LP-SS, some functionalities are listed below. Table 3

[0050] Moreover, a further related work item for LP-WUS includes the objectives listed below.Table 4

[0051] Since the LR is designed to reduce the power consumption, the design of LP- WUS predominantly converged to a waveform using on-off keying (OOK) with or without an embedded sequence. In OOK, the carrier signal is divided into ON durations and OFF durations, where the carrier signal is either turned on or off to represent binary values. This modulation technique is commonly used for low-rate applications or in situations where power efficiency is important.

[0052] To integrate the OOK signal into the Orthogonal Frequency Division Multiplexing (OFDM) framework while minimizing impact on the legacy UEs, OOK scheme follows OFDM symbol structure and generation. To address inferior performance of OOK scheme under low Signal-to-Noise Ratio (SNR) or Signal-to-Interference-plus- Noise Ratio (SINR) cell-edge cases, an additional sequence is embedded into the ON duration of the OOK signal. This ensures that OOK receivers have additional sequence detection capabilities, thereby enhancing coverage.

[0053] By employing the OOK modulation with an embedded sequence in the ON durations, two categories of receivers can be created for LP-WUS. The first category acts as an envelope detector, capable of detecting the OOK signal when the SNR is good, typically in-cell scenarios. The second category acts as a sequence detector, designed to handle worse SNR conditions, which are commonly observed at the cell edge.

[0054] To optimize power consumption and reduce the usage of power-consuming receiver blocks, it may not be efficient for the LR to continuously monitor LP-WUS all the time, since the energy consumption is directly proportional to the ON duration. Therefore, for more efficient operations, the LR is operated in a duty-cycled manner. This means that the LR turns on only at necessary instants, reducing overall power consumption.

[0055] The OOK only receiver, i.e. enveloped detector, reduces the overall power consumption of the LR as it is not required use the in-phase and quadrature (IQ) branches with higher sampling rate. Due to the removal or trim-down of major power consuming components such as Phase-Locked Loops (PLLs), Low-Noise Amplifiers (LNAs), andclock sources or synthesizers, the LR requires periodic calibration of clocks before receiving the LP-WUS signal for improved detection performance. Thus, a periodic EPSS is needed to be transmitted from a stable clock source, such as gNB.

[0056] The significance of the LP-SS lies in how effectively the LR can utilize it for detecting the LP-WUS signal, which carries payload information. The periodic LP-SS can be used by the LR for tasks such as time synchronization, frequency synchronization, Radio Resource Management (RRM) measurements. It plays a crucial role in enabling the LR to synchronize with the network and accurately detect the LP-WUS.

[0057] To achieve time synchronization, it is necessary to have smaller pulses within each symbol to ensure accurate timing. The sequence-based LR requires higher timing accuracy compared to the envelope-based LR.

[0058] For frequency synchronization, the LR may employ multiple parallel filters with reduced bandwidth (BW) compared to the LP-WUS. This allows the LR to adjust the initial frequency offset. However, the use of multiple parallel filters increases complexity. Additionally, the LR may utilize sequence receivers to synchronize with Synchronization Signal Blocks (SSBs). Multiple parallel hypotheses are used to estimate the initial frequency offset, but this approach also introduces higher complexity.

[0059] To perform RRM measurements, it is crucial for the LR to ensure coverage and reachability. Some measures need to be taken to ensure that the LR remains within the cell coverage.

[0060] At any initial boot-up of the LR after the MR obtains the request to go to sleep, the first step of the LR is to perform time synchronization, which is then followed by frequency synchronization. The time synchronization can be enabled by transmitting a known pattern in the time domain as a series of ON / OFF pulses, which can either be uniquely or partially encoded with the cell-ID. If the LP-SS is targeted for both envelope based OOK receiver and the sequence detector, the sequence embedded in the ON duration may be robust against the initial frequency offset assumption. However, if the LP-SS is aimed only for envelope detectors, the sequence of ON / OFF durations can be convolved with a pulse shaping filter, which eventually concentrates the energy of the ON duration to a narrow region.

[0061] In NR, enhanced Mobile Broadband (eMBB) UEs perform frequency synchronization through multiple parallel frequency hypothesis, which typically consumes more power and time. As the LRs are targeted for low power operation, itcannot be expected that such a complex operation can be performed at the LR without compromising on the power. For simple envelope type of LP-WUR, attaining the frequency synchronization may require use of multiple channel filters or adapt the channel filter in time to perform hypothesis testing to identify the frequency location of the transmitted signal. This can increase the complexity and / or the time required to attain and maintain the frequency synchronization.

[0062] To this end, example embodiments of the present disclosure provide a solution on LP-SS transmission. According to the example embodiments, the LP-SS is constructed to have varying pattern in frequency domain so as to facilitate a simple LR to obtain frequency synchronization. The pattern may be constructed by shifting frequency locations of the LP-SS over time, for example, over consecutive time symbols. Such a pattern is referred to as a frequency shifting pattern, or frequency hopping pattern. Upon the LP-SS is received at the LR, the frequency shifting pattern may be used by the LR to estimate a frequency offset to the network. Thus, the frequency synchronization of the LR is aided by employing the frequency shifting pattern over time. In this way, a low cost and low power consumption solution for the LP-SS can be achieved.

[0063] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0064] The reference now is made to FIG. 3, which shows a signaling chart 300 of an example process of LP-SS transmission according to some example embodiments of the present disclosure. As shown in FIG. 3, the signaling chart 300 involves a network device 310 and a terminal device 320. The network device 310 (for example, a gNB) may be an example of the first apparatus 110, or the first apparatus 110 may be included in the network device 310. The terminal device 320 (for example, a UE) may be an example of the second apparatus 120, or the second apparatus 120 may be included in the terminal device 320. The acts described with respect to the terminal device 320 may be performed by a receiver of the terminal device 320, for example, an LR of the terminal device 320.

[0065] As shown in FIG. 3, the network device 310 generates (330) an LP-SS. At least one portion of the LP-SS has a frequency shifting pattern in frequency domain, and the frequency shifting pattern defines frequency locations of the LP-SS varying over time. For example, the frequency shifting pattern may define the frequency locations of the LP- SS over consecutive time symbols.

[0066] In some embodiments, the frequency shifting pattern may be based on apredefined pattern. For example, the frequency shifting pattern may be fixed or predefined in a technical specification. Alternatively, or in addition, in some embodiments, the frequency shifting pattern may be determined based on an identification of a cell in which the LP-SS is transmitted. For example, the frequency shifting pattern may be a function of a cell-id. As such, both the terminal device 320 and the network device 310 can be aware of the pattern used. Alternatively, or in addition, in some embodiments, the frequency shifting pattern may be configured by the network device 310. For example, the network device 310 may transmit the configuration of the frequency shifting pattern to the terminal device 320 via system information, for example when the terminal device 320 is awake.

[0067] The network device 310 transmits (335) the LP-SS to the terminal device 320. Correspondingly, the terminal device 320 receives the LP-SS from the network device 310, for example via the LR of the terminal device 320. Based on the received LP-SS, the terminal device 320 estimates (340) a frequency offset for frequency synchronization with the network device 310. Herein, the frequency offset for frequency synchronization with the network device 310 may be also referred to as frequency error.

[0068] Since time synchronization with the network device 310 is required to perform proper frequency synchronization, a known pattern may be transmitted in the LP-SS to acquire time synchronization before the LR estimates the frequency offset. To this end, in some example embodiments, the LP-SS may comprise a first portion for time synchronization and a second portion for frequency synchronization. The first portion is proceeding the second portion, and the second portion has the frequency shifting pattern. FIG. 4 shows an example structure of the LP-SS. As can be seen, the LP-SS is divided into two segments or two portions. The first portion 410 may be used for time synchronization and is followed by the second portion 420 for frequency synchronization using the proposed frequency shifting pattern.

[0069] In this way, the first portion can be used for synchronizing the LR with the symbol boundary of the LP-SS, and the remaining part of the LP-SS can be dedicated for frequency synchronization. This would limit the complexity involved with the time and frequency synchronization, by allowing the LR to have fixed channel filter for LP-SS reception.

[0070] Alternatively, or in addition, in some example embodiments, before transmitting (330) the LP-SS, the network device 310 may transmit a further LP-SS for timesynchronization to the terminal device 320. Based on the received further LP-SS, the terminal device 320 may perform time synchronization with the network device 310.

[0071] For example, when the LR of the terminal device 320 is activated after the MR of the terminal device 320 goes to sleep, the LR can perform timing synchronization which can then be followed by frequency synchronization using subsequent LP-SS reception. This is mainly due to the periodic nature of LP-SS transmission. In other words, the first LP-SS, i.e., the first reception of LP-SS by the LR after the MR goes to sleep, can be used to obtain coarse timing offset, which can then be followed by the subsequent LP-SSs to acquire frequency offset estimation.

[0072] An example general procedure of LP-SS transmission is described above. Some example embodiments regarding the frequency shifting pattern are now described.

[0073] In some example embodiments, the frequency shifting pattern may define respective frequency offsets of the LP-SS within a plurality of time segments. A time segment may have any suitable time length or duration. In an example, the time segment may include one or more OFDM symbols. In another example, one time segment may be one OFDM symbol.

[0074] FIG. 5 shows an example frequency shifting pattern. As shown in FIG. 5, respective frequency offsets within a plurality of time segments 501, 502, 503, 504 and 505 are varying. In the example, the frequency offset within the time segment 501 is fo of 0, the frequency offset within the time segment 502 is - / i, the frequency offset within the time segment 503 is + / i, the frequency offset within the time segment 504 is -f, and the frequency offset within the time segment 505 is +fz. The frequency shifting pattern may be fixed (for example, defined in a specification) or configured by the network device 310 or based on the cell-id.

[0075] In the example of FIG. 5, the time segment has a size of an (NR) OFDM symbol, and M = 2 OOK waveform is used. There is an ON / OFF transition within a symbol boundary based on Manchester encoding and M denotes the number of ON durations and OFF durations within the (NR) OFDM symbol. However, it is noted that the waveform is shown as an example without any limitation.

[0076] In some example embodiments, the LP-SS may further have an on-off pattern in time domain, which is also referred to as “OOK pattern”. For each time segment of the plurality of time segments, the on-off pattern may define an on duration in presence of the LP-SS and an off duration in absence of the LP-SS. In other words, the on-off patternmay define the on duration denoted as “ON” within which the LP-SS is present, and the off duration denoted as “OFF” within which the LP-SS is not present.

[0077] In some example embodiments, the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted. The cell specific information may be the cell-id or any other cell specific information. In the example of FIG. 5, the cell-id of 5 is used as an example. In such example embodiments, the OOK pattern used to carry the cell-id or other cell specific information is known to the MR, which can then be configured or fed to the LR for detection of LP-SS.

[0078] In the example of FIG. 5, the pattern is shown in both frequency and time domains. M = 2 is used, i.e., an ON / OFF transition occurs within a (NR) OFDMA symbol. Thus, the position of the on duration can be placed in either first half of the symbol or second half of the symbol to determine 0 / 1 as information bit. For example, as shown in FIG. 5, the on duration of the time segment 501 is placed in the first half and the on duration of the time segment 503 is placed in the second half.

[0079] In some example embodiments, a waveform of the LP-SS within the on duration is pulse shaped. In this way, the on duration can be pulse shaped to ensure better detectability with the envelope detector. Pulse shaping can provide significant benefit compared to the square pulse by improving the received SNR with a filter matched to the pulse shape.

[0080] In some example embodiments, a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission, for example, the bandwidth (BW) for LP-WUS / LP-SS transmission. This means that the waveform of the LP-SS may be restricted to use a fraction of the total available physical resource blocks (PRBs) / BW for LP-WUS / LP-SS transmission. This enables placing the actual transmitted LP-SS signal in varying location in time. In other words, to assist the LR in estimating the frequency offset, the gNB transmits the LP-SS signal within a narrow section of the LP-WUS BW, which can be a factor a of the total LP-WUS BW. The value of a may take values between e.g., a E [0.5, 1] x BLP-wt7S, where BLP-WUSis the total available BW for LP-WUS / LP-SS transmission.

[0081] In an example, if it is assumed that the LP-SS occupies multiple symbols in a slot, for example, L symbols, the frequency location of the LP-SS can be altered over the L symbols, thereby aiding the LR to determine the symbol containing highest energy as the actual frequency offset. Thus, as shown in FIG. 5, the frequency hopping patternillustrates the location of energy in the spectrum over different symbols, where {A / o, +A / i, ±A2} may represent the different frequency locations (for example, center frequency locations) of the transmitted LP-SS.

[0082] It is noted that the overall performance of the frequency synchronization may depend on the frequency hopping pattern used in the LP-SS frame structure. To ensure optimal frequency synchronization performance, the gNB may use a list of frequency offsets, each of which can be applied to a symbol. The frequency offsets can either be uniformly spaced or non-uniformly spaced between the minimum, which is 0, and the maximum frequency offset, which can be 0.25 X BLP-WUS. Depending on the number of symbols used for the LP-SS, the final frequency resolution can be determined by the LR. The number of symbols used for the LP-SS may be determined at least one of the following: the number of bits used to represent cell-specific information bits, or the total number of frequency offsets required to ensure proper synchronization of frequency offset by the LR.

[0083] As described above, the terminal device 320 may estimate the frequency offset to the network device 310 so as to perform frequency synchronization with the network device 310. Some example embodiments regarding the frequency offset estimation are now described.

[0084] As mentioned above, in some example embodiments, the frequency shifting pattern may define respective frequency offsets of the LP-SS within a plurality of time segments, for example, within a plurality of consecutive OFDM symbols. In these embodiments, the terminal device 320 may determine respective energies of the LP-SS received within the plurality of time segments. Then, based on the respective energies, the terminal device 320 may select at least one time segment from the plurality of time segments. The estimated frequency offset may be derived based on a frequency offset of the LP-SS in the selected at least one time segment.

[0085] For example, the LR uses a filter with a fixed BW and location, i.e. as that of LP-WUS. The LR uses such a filter to receive the LP-SS frame, which is similar as LP- WUS filter having full bandwidth of BLP-SS. For example, the frequency offset may be deduced based on the maximum energy obtained within a symbol.

[0086] In some example embodiments, the on-off pattern in the time domain may be employed. In such example embodiments, in order to determine the energy of the LP-SS in a time segment, the terminal device 320 may obtain a first energy (also referred to asON-duration energy) received within the on duration of the time segment and a second energy (also referred to as OFF-duration energy) received within the off duration by performing filtering with a predetermined frequency range. For example, the ON-duration energy and the OFF-duration energy may be obtained using the filter with fixed BW. Then, the energy of the LP-SS received within the time segment may be derived based on the ON-duration energy and the OFF-duration energy, for example, by subtracting the OFF-duration energy from the ON-duration energy. It is noted that in some example embodiments, the estimated energy may be represented a power level.

[0087] As an example, upon receiving the LP-SS frame, the LR, which expects the ON / OFF pattern based on cell specific information (e.g., the cell-id), may use the information to determine the energy in the ON duration and OFF duration (denoted by EON,EOFF) to determine the cell-specific on-off pattern and the frequency offsets within each OFDM symbol. Since the OOK signaling suffers at lower SNR, the LR can utilize the Manchester encoded data to determine the actual ON duration energy as follows.

[0088] Since the ON duration contains both signal and noise, the energy in the ON duration can be approximated to P0N« E0N+ Enoise. In the OFF duration of the Manchester encoded signal, the energy estimated may be approximated to P0FF« Enoise. Upon receiving an information bit, which consists of both the ON and OFF durations, the LR may estimate the ON duration energy (only the signal energy) as E0N« P0N— P0FF- Since the LR uses the envelope detector, which is equivalent to the non-coherent detector, the average energy obtained in the OFF duration converges to the actual noise variance. The EONattained in a OOK symbol by the terminal device 320 / the LR may depend on the frequency shift in the transmitted signal.

[0089] Therefore, by including both the on duration and the off duration in a same symbol, the energy of the LP-SS within the same symbol can be estimated more accurately.

[0090] After deriving the energy E0Nwithin each time segment, a time segment with the highest energy may be selected from the plurality of time segments. This time segment may be also referred to as first time segment, and the frequency offset of the first time segment as defined by the frequency shifting pattern may be referred to as the first frequency offset.

[0091] In some example embodiments, the frequency offset (as defined by the frequency shifting pattern) of the LP-SS within the selected time segment may bedetermined as the estimated frequency offset for frequency synchronization. For example, the UE may compare the E0Nobtained from different symbols with different frequency shifts and determine the largest E0Nvalue(s). Then, the frequency error may be approximated as the frequency offset within the symbol with the largest E0Nvalue.

[0092] Alternatively, or in addition, using the same framework described above, the LR may perform additional signal processing to estimate the actual frequency offset. Instead of just deciding the time segment with the maximum energy as the estimated frequency offset, the LR may use an interpolation algorithm to determine the actual frequency offset.

[0093] To this end, in some example embodiments, the terminal device 320 may determine, from remaining time segments except for the first time segment, one or more second time segments based on differences between a first frequency offset within the first time segment and respective frequency offsets within the remaining time segments. For example, the one or more second time segments may be adjacent to the first time segment in terms of frequency offset as defined by the frequency shifting pattern. Then, the terminal device 320 may derive the estimated frequency offset based on the first frequency offset and respective second frequency offsets within the one or more second time segments. For example, any suitable interpolation algorithm may be applied to the first frequency offset and the respective second frequency offsets.

[0094] As an example, if the LR estimates the power versus symbol (or frequency offset) as a list {(F1;E , (-E1;E_ ), (E2, E2), (-E2, E_2), ... (Eo, Eo), ... (-EK, E_K), (EK, E )}. The list consists of K + 1 frequency offsets and the respective energy levels (such as power levels), which are symmetric and distributed either uniformly or non-uniformly. Upon populating the list with the estimated energy, the LR may then pick the entry with the highest energy and pick the adjacent two entries of the entry with the highest energy for the interpolation algorithm. For example, a simple Lagrange interpolation, which uses quadratic curve fit, may be used to determine the actual frequency offset.

[0095] Reference is now made to FIG. 6 to illustrate an example. Once the ON duration energy is determined by the LR based on the difference between the ON duration energy and the OFF duration energy, i.e., P0N— POFF ~ E0N, the LR may then determine the frequency offset 602 with the largest energy E0N. Accordingly, the adjacent frequency offsets 604 and 605 are identified. By applying the interpolation algorithm to the frequency offsets and respective energies, the actual frequency offset 601 may beidentified as shown in FIG. 6. The offset used in the simulation is around A « 200ppm. The LR performs the reception of LP-SS over each symbol and determines the signal energy, i.e., E0N. Once it estimates E0N, then the LR can stack all the energy levels (such as power levels) and the respective frequencies with which the gNB transmits, which is known prior to the LR.

[0096] Once the energy levels are sorted, the LR may then use the Lagrange interpolation to identify the actual offset to a better precision as shown in FIG. 6. This requires either side of the maximum energy level observed. The important aspect is the estimation of the LP-SS energy, which is obtained from the delta between the ON duration energy and the OFF duration energy. This ensures the robustness of LP-SS based frequency estimator down to lower SNRs as well, since the OOK only approach has limited performance up until — 3dB SNR. By using the above approach, the performance can be improved even lower to « — 6dB.

[0097] To verify the performance of the proposed approach in terms of frequency offset estimation, a simulation is performed in the link level simulator. The simulation results are shown in FIG. 7 and FIG. 8. It is observed that the OOK only receivers will experience a residual frequency offset of 60ppm.

[0098] Some example embodiments regarding the structure of the LP-SS and the implementations for frequency offset estimation have been described above. In some example embodiments, if UE does not detect the LP-SS during configured time duration by the network, the UE should initiate cell search for a new LP-SS in case cell is changed e.g., due to a position change of the UE in the network. An alternative is to use specific common LP-SS which could activate UE in a given cell. That specific LP-SS is configured by the network, and it is expected that the UE monitors it in configured time periods.

[0099] It is noted that the performance would be the same even without the proposed frequency hopping pattern based transmission from the gNB. However, LP-SS transmission without the frequency hopping pattern requires the LR to perform frequency hopping at the symbol boundary of each Manchester encoded symbol. Under the assumption that the LR is a stripped-down version of the MR with very limited number of components to reduce the power consumption, expecting such a receiver structure is too demanding. Furthermore, the settling time after each frequency jump through PLL configuration to change the center frequency will be large, thereby limiting the frequencyhopping capability. It is easier to estimate the frequency offset using the fixed LP-SS transmission in the case of the MR, but not for the LR. Thus, the present disclosure is targeting the low cost, low power device used only to detect OOK signal through envelope detector.

[0100] FIG. 9 shows a flowchart of an example method 900 implemented at a first device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the first apparatus 110 in FIG. 1.

[0101] At block 910, the first apparatus 110 generates a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain. The frequency shifting pattern defines frequency locations of the LP-SS varying over time.

[0102] At block 920, the first apparatus 110 transmits the LP-SS to a second apparatus for frequency synchronization.

[0103] In some example embodiments, the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments.

[0104] In some example embodiments, the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS.

[0105] In some example embodiments, the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

[0106] In some example embodiments, a waveform of the LP-SS within the on duration is pulse shaped.

[0107] In some example embodiments, the frequency shifting pattern is based on at least one of a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

[0108] In some example embodiments, the LP-SS comprises a first portion for time synchronization and a second portion for frequency synchronization, the first portion is proceeding the second portion, and the second portion has the frequency shifting pattern.

[0109] In some example embodiments, the method 900 further comprises: before transmitting the LP-SS, transmitting a further LP-SS for time synchronization to the second apparatus.

[0110] In some example embodiments, a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

[0111] In some example embodiments, the first apparatus 110 is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

[0112] FIG. 10 shows a flowchart of an example method 1000 implemented at a second device in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0113] At block 1010, the second apparatus 120 receives, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain. The frequency shifting pattern defines frequency locations of the LP-SS varying over time.

[0114] At block 1020, the second apparatus 120 estimates, based on the received LP- SS, a frequency offset for frequency synchronization with the first apparatus.

[0115] In some example embodiments, the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments, and the method 1000 comprises: determining respective energies of the LP-SS received within the plurality of time segments; selecting at least one time segment from the plurality of time segments based on the respective energies; and determining the estimated frequency offset based on a frequency offset of the LP-SS in the at least one time segment.

[0116] In some example embodiments, the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS. The method 1000 comprises: for each time segment of the plurality of time segment, obtaining a first energy received within the on duration and a second energy received within the off duration by performing filtering with a predetermined frequency range; and deriving an energy of the LP-SS received within the time segment based on the first energy and the second energy.

[0117] In some example embodiments, the method 1000 comprises: selecting, from the plurality of time segments, a time segment with the highest energy among the respective energies; and determining the estimated frequency offset as a frequency offset of the LP- SS within the selected time segment.

[0118] In some example embodiments, the method 1000 comprises: determining, from the plurality of time segments, a first time segment with the highest energy among the respective energies; determining, from remaining time segments except for the first time segment, one or more second time segments based on differences between a first frequency offset within the first time segment and respective frequency offsets within the remaining time segments; and deriving the estimated frequency offset based on the first frequency offset and respective second frequency offsets within the one or more second time segments.

[0119] In some example embodiments, the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

[0120] In some example embodiments, a waveform of the LP-SS within the on duration is pulse shaped.

[0121] In some example embodiments, the frequency shifting pattern is based on at least one of a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

[0122] In some example embodiments, the method 1000 further comprises: performing time synchronization with the first apparatus based on the first portion of the LP-SS.

[0123] In some example embodiments, the method 1000 further comprises: before receiving the LP-SS, receiving a further LP-SS for time synchronization from the first apparatus; and performing time synchronization with the first apparatus based on the received further LP-SS.

[0124] In some example embodiments, a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

[0125] In some example embodiments, the first apparatus is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

[0126] In some example embodiments, a first apparatus capable of performing any of the method 900 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 900. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in a network device.

[0127] In some example embodiments, the first apparatus comprises means forgenerating a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for transmitting the LP-SS to a second apparatus for frequency synchronization.

[0128] In some example embodiments, the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments.

[0129] In some example embodiments, the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS.

[0130] In some example embodiments, the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

[0131] In some example embodiments, a waveform of the LP-SS within the on duration is pulse shaped.

[0132] In some example embodiments, the frequency shifting pattern is based on at least one of a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

[0133] In some example embodiments, the LP-SS comprises a first portion for time synchronization and a second portion for frequency synchronization, the first portion is proceeding the second portion, and the second portion has the frequency shifting pattern.

[0134] In some example embodiments, the first apparatus further comprises: means for before transmitting the LP-SS, transmitting a further LP-SS for time synchronization to the second apparatus.

[0135] In some example embodiments, a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

[0136] In some example embodiments, the first apparatus is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

[0137] In some example embodiments, the first apparatus further comprises means for performing other operations in some example embodiments of the method 900 or the network device 310. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the first apparatus.

[0138] In some example embodiments, a second apparatus capable of performing any of the method 1000 (for example, the second apparatus 120 in FIG. 1 may comprise means for performing the respective operations of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in a terminal device.

[0139] In some example embodiments, the second apparatus comprises means for receiving, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for estimating, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

[0140] In some example embodiments, the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments, and the second apparatus comprises means for determining respective energies of the LP-SS received within the plurality of time segments; means for selecting at least one time segment from the plurality of time segments based on the respective energies; and means for determining the estimated frequency offset based on a frequency offset of the LP-SS in the at least one time segment.

[0141] In some example embodiments, the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS, and the second apparatus comprises for each time segment of the plurality of time segment, means for obtaining a first energy received within the on duration and a second energy received within the off duration by performing filtering with a predetermined frequency range; and means for deriving an energy of the LP-SS received within the time segment based on the first energy and the second energy.

[0142] In some example embodiments, the second apparatus comprises: means for selecting, from the plurality of time segments, a time segment with the highest energy among the respective energies; and means for determining the estimated frequency offset as a frequency offset of the LP-SS within the selected time segment.

[0143] In some example embodiments, the second apparatus comprises: means for determining, from the plurality of time segments, a first time segment with the highestenergy among the respective energies; means for determining, from remaining time segments except for the first time segment, one or more second time segments based on differences between a first frequency offset within the first time segment and respective frequency offsets within the remaining time segments; and means for deriving the estimated frequency offset based on the first frequency offset and respective second frequency offsets within the one or more second time segments.

[0144] In some example embodiments, the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

[0145] In some example embodiments, a waveform of the LP-SS within the on duration is pulse shaped.

[0146] In some example embodiments, the frequency shifting pattern is based on at least one of a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

[0147] In some example embodiments, the LP-SS comprises a first portion for time synchronization and a second portion for frequency synchronization, the first portion is proceeding the second portion, and the second portion has the frequency shifting pattern, the second apparatus further comprises: means for performing time synchronization with the first apparatus based on the first portion of the LP-SS.

[0148] In some example embodiments, the second apparatus further comprises: means for before receiving the LP-SS, receiving a further LP-SS for time synchronization from the first apparatus; and means for performing time synchronization with the first apparatus based on the received further LP-SS.

[0149] In some example embodiments, a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

[0150] In some example embodiments, the first apparatus is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

[0151] In some example embodiments, the second apparatus further comprises means for performing other operations in some example embodiments of the method 1000 or the terminal device 320. In some example embodiments, the means comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the second apparatus.

[0152] FIG. 11 is a simplified block diagram of a device 1100 that is suitable forimplementing example embodiments of the present disclosure. The device 1100 may be provided to implement a communication device, for example, the first apparatus 110 or the second apparatus 120 as shown in FIG. 1. As shown, the device 1100 includes one or more processors 1110, one or more memories 1120 coupled to the processor 1110, and one or more communication modules 1140 coupled to the processor 1110.

[0153] The communication module 1140 is for bidirectional communications. The communication module 1140 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1140 may include at least one antenna.

[0154] The processor 1110 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1100 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0155] The memory 1120 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1124, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 1122 and other volatile memories that will not last in the powerdown duration.

[0156] A computer program 1130 includes computer executable instructions that are executed by the associated processor 1110. The instructions of the program 1130 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1130 may be stored in the memory, e.g., the ROM 1124. The processor 1110 may perform any suitable actions and processing by loading the program 1130 into the RAM 1122.

[0157] The example embodiments of the present disclosure may be implemented by means of the program 1130 so that the device 1100 may perform any process of thedisclosure as discussed with reference to FIG. 2 to FIG. 10. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0158] In some example embodiments, the program 1130 may be tangibly contained in a computer readable medium which may be included in the device 1100 (such as in the memory 1120) or other storage devices that are accessible by the device 1100. The device 1100 may load the program 1130 from the computer readable medium to the RAM 1122 for execution. In some example embodiments, the computer readable medium may include any types of non -transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0159] FIG. 12 shows an example of the computer readable medium 1200 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1200 has the program 1130 stored thereon.

[0160] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0161] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the programmodules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0162] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0163] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0164] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable readonly memory (EPROM or Flash memory), an optical fiber, a portable compact disc readonly memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0165] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of thepresent disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0166] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure 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

CLAIMS1. A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: generate a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and transmit the LP-SS to a second apparatus for frequency synchronization.

2. The first apparatus of claim 1, wherein the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments.

3. The first apparatus of claim 2, wherein the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS.

4. The first apparatus of claim 3, wherein the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

5. The first apparatus of claim 3, wherein a waveform of the LP-SS within the on duration is pulse shaped.

6. The first apparatus of claim 1, wherein the frequency shifting pattern is based on at least one of: a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

7. The first apparatus of claim 1, wherein the LP-SS comprises a first portion for timesynchronization and a second portion for frequency synchronization, the first portion is proceeding the second portion, and the second portion has the frequency shifting pattern.

8. The first apparatus of claim 1, wherein the first apparatus is further caused to: before transmitting the LP-SS, transmit a further LP-SS for time synchronization to the second apparatus.

9. The first apparatus of claim 1, wherein a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

10. The first apparatus of any of claims 1 to 8, wherein the first apparatus is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

11. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: receive, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and estimate, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

12. The second apparatus of claim 11, wherein the frequency shifting pattern defines respective frequency offsets of the LP-SS within a plurality of time segments, and the second apparatus is further caused to: determine respective energies of the LP-SS received within the plurality of time segments; select at least one time segment from the plurality of time segments based on the respective energies; and determine the estimated frequency offset based on a frequency offset of the LP-SS in the at least one time segment.

13. The second apparatus of claim 12, wherein the at least one portion of the LP-SS further has an on-off pattern in time domain, and for each time segment of the plurality of time segments, the on-off pattern defines an on duration in presence of the LP-SS and an off duration in absence of the LP-SS, and the second apparatus is caused to: for each time segment of the plurality of time segment, obtain a first energy received within the on duration and a second energy received within the off duration by performing filtering with a predetermined frequency range; and derive an energy of the LP-SS received within the time segment based on the first energy and the second energy.

14. The second apparatus of claim 12, wherein the second apparatus is caused to: select, from the plurality of time segments, a time segment with the highest energy among the respective energies; and determine the estimated frequency offset as a frequency offset of the LP-SS within the selected time segment.

15. The second apparatus of claim 12, wherein the second apparatus is caused to: determine, from the plurality of time segments, a first time segment with the highest energy among the respective energies; determine, from remaining time segments except for the first time segment, one or more second time segments based on differences between a first frequency offset within the first time segment and respective frequency offsets within the remaining time segments; and derive the estimated frequency offset based on the first frequency offset and respective second frequency offsets within the one or more second time segments.

16. The second apparatus of claim 13, wherein the on-off pattern is determined based on information specific to a cell in which the LP-SS is transmitted.

17. The second apparatus of claim 13, wherein a waveform of the LP-SS within the on duration is pulse shaped.

18. The second apparatus of claim 11, wherein the frequency shifting pattern is based on at least one of: a predefined pattern, a pattern configuration determined by the first apparatus, or an identification of a cell in which the LP-SS is transmitted.

19. The second apparatus of claim 11, wherein the LP-SS comprises a first portion for time synchronization and a second portion for frequency synchronization, the first portion is proceeding the second portion, and the second portion has the frequency shifting pattern, and the second apparatus is caused to: perform time synchronization with the first apparatus based on the first portion of the LP-SS.

20. The second apparatus of claim 11, wherein the second apparatus is further caused to: before receiving the LP-SS, receive a further LP-SS for time synchronization from the first apparatus; and perform time synchronization with the first apparatus based on the received further LP- SS.

21. The second apparatus of claim 11, wherein a waveform of the at least one portion of the LP-SS occupies a fraction of a frequency range available for low power signal transmission.

22. The second apparatus of any of claims 11 to 21, wherein the first apparatus is or is comprised in a network device, and the second apparatus is or is comprised in a terminal device.

23. A method comprising: generating, at a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and transmitting the LP-SS to a second apparatus for frequency synchronization.

24. A method comprising: receiving, at a second apparatus from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and estimating, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

25. A first apparatus comprising: means for generating a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for transmitting the LP-SS to a second apparatus for frequency synchronization.

26. A second apparatus comprising: means for receiving, from a first apparatus, a low power synchronization signal, LP-SS, at least one portion of which has a frequency shifting pattern in frequency domain, wherein the frequency shifting pattern defines frequency locations of the LP-SS varying over time; and means for estimating, based on the received LP-SS, a frequency offset for frequency synchronization with the first apparatus.

27. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 25 or the method of claim 26.

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