Energy efficient synchronization of user equipment in a wireless communication system

Abstract

A first wireless communication device (201) assists with synchronizing a second wireless communication device (209) by wirelessly receiving (303) a first timing information signal (203) transmitted from a target wireless communication network (205), wherein the first timing information signal (203) has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal (203) comprises radio signal timing information and system information. The first wireless communication device (201) produces (305) a second timing information signal (207) that comprises the radio signal timing information, wherein the second timing information signal has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity. The second timing information signal (207) is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity; and transmitting (307) the second timing information signal (207) for receipt by the second wireless communication device (209).

Description

[0001] ENERGY EFFICIENT SYNCHRONIZATION OF USER EQUIPMENT IN A WIRELESS COMMUNICATION SYSTEM

[0002] BACKGROUND

[0003] The present invention relates to system synchronization of user equipment in a wireless communication system, and more particularly to providing user equipment with system synchronization signaling that can be received and / or processed with reduced processing load and / or energy consumption.

[0004] Some or all of the following abbreviations are used in this specification:

[0005] Abbreviation Explanation

[0006] 3 GPP Third Generation Partnership Project eDRX Extended Discontinuous Reception

[0007] DRX Discontinuous Reception

[0008] DTX Discontinuous Transmission

[0009] FFT Fast Fourier Transform

[0010] HFN Hyper Frame Number

[0011] IF Intermediate Frequency loT Internet of Things

[0012] LTE Long Term Evolution

[0013] MCC Mobile Country Code

[0014] MIB Master Information Block

[0015] MNC Mobile Network Code

[0016] MTC Machine Type Communication

[0017] NR New Radio

[0018] OFDM Orthogonal Frequency Division Multiplexing

[0019] OOK On / Off Keying

[0020] PBCH Physical Broadcast Channel

[0021] PSM Power Saving Mode

[0022] PSS Primary Synchronization Signals

[0023] RF Radio Frequency

[0024] RSS Re-Synchronization Signal

[0025] SIB System Information Block SIM Subscriber Identity Module

[0026] SFN System Frame Number

[0027] SNR Signal-to-Noise Ratio

[0028] SSB Synchronization Signal Block

[0029] SSS Secondary Synchronization signals

[0030] TTI Transmission Time Interval

[0031] Timing synchronization among different entities in a wireless communication system is important, and for this purpose a system frame timing is often utilized. In some instances this has the network determining a timing reference that is used to define such things as transmission time scheduling and other time dependent functionalities of the communication system. In some examples the system frame timing may include definitions of time periods such as transmit symbols, slots, frames, Transmission Time Interval (TTI) or similar.

[0032] When a wireless device such as a User Equipment (UE) is utilized in a communication system, it may be in various states of activity. The device may, for example, be in an idle state or in an active state. Several different levels of required or expected activity to be performed by the device may be defined for such states. In one type of state the device may transmit or receive signals within a communication with the network. Such a state may be an active state. In some of the idle states (e.g., the 3GPP-defined “RRC Inactive” state or the so-called “connected mode DRX”) the UE may keep a connectivity context with the network such as a so-called “RRC connection”. In the case of such idle states, the UE may periodically or occasionally abstain from transmissions and / or receptions (DTX / DRX). However, since synchronization is required for the UE to engage in activities associated with a more active state, the UE remains synchronized with the system frame timing even while being idle in order to be able to quickly enter a more active state and transmit or receive information and / or data.

[0033] By contrast, the UE may be more dormant in other idle states (e.g., RRC Idle state as defined in 3GPP standards). In some examples, the device may be in an idle mode in which the UE periodically wakes up to receive one or more network signals that may be indicative of potential downlink data transmissions to the UE. Such idle cases may use an idle mode DRX or extended DRX or similar, in which the time periods in-between any signal reception may be seconds, minutes or in certain instances even hours.

[0034] In the more dormant instances of idle mode as discussed above, the UE may typically need to re-synchronize with the network frame timing before being able to receive any signals that contain control or data information. In many communication systems such as 3 GPP LTE and NR, the UE will be able to perform the re-synchronization utilizing downlink synchronization signals transmitted by network base stations (gNB / eNB). Such synchronization signals may be referred to as PSS (Primary Synchronization Signals) and SSS (Secondary Synchronization Signals) and may often be transmitted in a broadcast fashion. The PSS and SSS may be included in a so-called Synchronization Signal Block (SSB) and may be transmitted with different spatial characteristics by the network to identify special transmit beams from the network base stations.

[0035] Additionally, in 3GPP LTE Release 15 and later releases, a specific Re-Synchronization Signal (RSS) has been introduced within the work that concerns Internet of Things (loT) centric protocol optimizations. See, for example, the RSS specification in 3GPP TS26.211 and the RSS configuration information element signaling in 3GPP TS36.331. Compared to the LTE PSS / SSS, the RSS transmissions have a longer time duration, and this results in improved possibilities for a device operating within a bad radio coverage area to receive the RSS and perform resynchronization quicker than what is possible with the PSS / SSS signals. The usage of RSS in an LTE network is optional for the network base stations.

[0036] Further, technologies for sidelink synchronization are available, such as shown in Figure 1 in which a first wireless device 101 is located within a network coverage area 100 and second and third wireless devices are each outside of the network coverage area 100. In this arrangement, the first wireless device 101 receives network frame timing information 103 from a network node 105 and then forwards 107 that information to the one or more second wireless devices 109. As shown in the example of Figure 1, the second wireless device 109 is configured to provide a sidelink synchronization reference 111 to the third wireless device 113 that is configured to keep the same frame timing on sidelink communications with the third wireless device 113 as exist on the uplink / downlink communications between the second wireless device 109 and the network node 105.

[0037] Presently, the 3GPP is considering a UE-assisted topology for ambient Internet of Things (loT) devices (e.g., backscattering communication devices), in which UEs support battery constrained devices. Such devices are required to perform a re-synchronization activity at the beginning of each activity period of idle mode operation. In case the UE is an loT device transmitting and receiving a very limited amount of data, the energy consumption from the repeated re-synchronization may constitute a relatively large amount of the total energy consumed by the device. This may especially be the case if the received signal strength of the synchronization signals is low, making it necessary for the device to be active for a long time and receive multiple instances of synchronization signals before being able to acquire an accurate time synchronization with the network. Further, since the RSS transmissions are optional, a device may not be able to use such improved synch signals for the re-synch.

[0038] Conventional sidelink synchronization mechanisms are, to some extent, a functionality for additional synchronization for a wireless device. However, there are severe limitations. First, since it is a sidelink protocol feature, they require a first device to be connected to a 3GPP network in which sidelink functionality is activated by the network. Second, both the first device 101 and the second device 109 must support the sidelink protocol. Third, the synchronization signals used for sidelink synchronization utilize very similar modulation and coding as the network transmitted signals for synchronization. They target the reception with the same receiver performance and capabilities as for other communication signals from the system and are therefore not tailored to support simple, ultra-low power transceiver architectures that can allow for energy efficient synchronization such as required for long battery life in low-power loT devices.

[0039] As one example, consider a use case involving a smartwatch having 3 GPP protocol support. The smartwatch may here be considered a battery constrained device, where the size limitations and other constraints may significantly limit its battery lifetime compared to other (e.g., larger) devices such as smartphones or other wireless devices. It would be very useful to find solutions to prolong the battery life of such battery constrained devices.

[0040] Therefore, improvements in the area of supporting a wireless device acquire resynchronization with the network while using low amount of energy is required.

[0041] In view of the foregoing, there is a need for technology that addresses the abovedescribed and related problems, including but not limited to problems associated with supporting a wireless device’s need to acquire re-synchronization with a network while using a low amount of energy.

[0042] SUMMARY

[0043] It should be emphasized that the terms “comprises” and “comprising”, when used in this specification, are taken to specify the presence of stated features, integers, steps or components; but the use of these terms does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0044] Moreover, reference letters may be provided in some instances (e.g., in the claims and summary) to facilitate identification of various steps and / or elements. However, the use of reference letters is not intended to impute or suggest that the so-referenced steps and / or elements are to be performed or operated in any particular order.

[0045] In accordance with one aspect of the present invention, the foregoing and other objects are achieved in technology (e.g., methods, apparatuses, nontransitory computer readable storage media, program means) in which a first wireless communication device assists in synchronizing a second wireless communication device.

[0046] In an aspect of some but not necessarily all embodiments consistent with the invention, the first device wirelessly receives a first timing information signal transmitted from a target wireless communication network, wherein the first timing information signal has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal comprises radio signal timing information and system information. The first wireless communication device produces a second timing information signal that comprises the radio signal timing information, wherein the second timing information signal has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity. Further, the second timing information signal is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity; and transmitting the second timing information signal for receipt by the second wireless communication device.

[0047] In another aspect of some but not necessarily all embodiments consistent with the invention, the second timing information signal further comprises at least a portion of the system information.

[0048] In yet another aspect of some but not necessarily all embodiments consistent with the invention, transmitting the second timing information signal comprises wirelessly transmitting the second timing information signal using an unlicensed radiofrequency spectrum. For example and without limitation, the unlicensed radiofrequency spectrum can be an Industrial, Scientific, and Medical (ISM) radiofrequency band or a radiofrequency band at 2.4 GHz.

[0049] In still another aspect of some but not necessarily all embodiments consistent with the invention, the first timing information signal further comprises a network identifier; and the second timing information signal further comprises the network identifier. In another aspect of some but not necessarily all embodiments consistent with the invention, the target wireless communication network is one of a plurality of wireless communication networks, and the first wireless communication device’s actions include, prior to wirelessly receiving the first timing information signal transmitted from the wireless communication network, identifying the target wireless communication network as a source of the first timing information signal.

[0050] In yet another aspect of some but not necessarily all embodiments consistent with the invention, the first wireless communication device is not registered with the target wireless communication network.

[0051] In still another aspect of some but not necessarily all embodiments consistent with the invention, transmitting the second timing information signal for receipt by the second wireless communication device comprises broadcasting the second timing information signal for receipt by the second wireless communication device.

[0052] In another aspect of some but not necessarily all embodiments consistent with the invention, the second timing information signal is an on / off keying-modulated signal. In another aspect of some but not necessarily all of such embodiments, transmitting the second timing information signal comprises randomly selecting a frequency offset from a plurality of different frequency offsets that are different integer or non-integer multiples of a modulation bit rate used for the on / off keying-modulated signal; and transmitting the second timing information signal on a carrier frequency that is a nominal carrier frequency plus or minus the selected frequency offset. And in yet another aspect of some but not necessarily all of such embodiments, a first frequency offset is randomly selected for use in determining the carrier frequency when transmitting the second timing information signal at a first time; and a second frequency offset is randomly selected for use in determining the carrier frequency when transmitting the second timing information signal at a second time.

[0053] In yet another aspect of some but not necessarily all embodiments consistent with the invention, the second coding format is a block coding format.

[0054] In still another aspect of some but not necessarily all embodiments consistent with the invention, the first timing information signal is one or more of: a primary synchronization signal; a secondary synchronization signal; a master information block; and a system information block. In another aspect of some but not necessarily all embodiments consistent with the invention, a modulation timing of the second timing information signal is synchronized with respect to broadcasts received by the first wireless communication device from the target wireless communication network.

[0055] In yet another aspect of some but not necessarily all embodiments consistent with the invention, the second bandwidth is no more than 2Mhz.

[0056] In still another aspect of some but not necessarily all embodiments consistent with the invention, the second timing information signal comprises a first part and a second part, where the first part comprises information for synchronizing the second wireless communication device with the target wireless communication network and the second part comprises network information. The first part is transmitted in a first transmission; and the second part is transmitted in a second transmission.

[0057] In some but not necessarily all alternatives of such embodiments, the first transmission is repeated at a first repetition rate, and the second transmission is repeated at a second repetition rate. And in some but not necessarily all of these embodiments, the first repetition rate is different from the second repetition rate.

[0058] In another aspect of some but not necessarily all embodiments consistent with the invention, the target wireless communication network is a first target wireless communication network having a first radio signal timing, and the first wireless communications device’s actions further include wirelessly receiving a third timing information signal transmitted from a second target wireless communication network having a second radio signal timing that is different from the first radio signal timing, wherein the third timing information signal has a third bandwidth, a third order of modulation, and a third coding format associated with a third coding complexity, and wherein the third timing information signal comprises third radio signal timing information and third system information. The first wireless communications device produces a fourth timing information signal that comprises the third radio signal timing information, wherein the fourth timing information signal has a fourth bandwidth, a fourth order of modulation, and a fourth coding format associated with a fourth coding complexity. The fourth timing information signal is characterized by one or more of: the fourth bandwidth is lower than the third bandwidth; the fourth order of modulation is lower than the third order of modulation; and the fourth coding complexity is lower than the third coding complexity; and transmitting the fourth timing information signal for receipt by the second wireless communication device.

[0059] In another aspect of some but not necessarily all embodiments consistent with the invention, one or both of time multiplexing and frequency multiplexing are used when transmitting the second timing information signal and the fourth timing information signal.

[0060] In accordance with another aspect of the present invention, the foregoing and other objects are achieved in technology (e.g., methods, apparatuses, nontransitory computer readable storage media, program means) in which a second wireless communication device synchronizes itself with assistance from a first wireless communication device.

[0061] In an aspect of some but not necessarily all such embodiments consistent with the invention, the second wireless communication device responds to a decision to communicate with a target wireless communication network by using a first radio receiver to listen for a second timing information signal that is transmitted by a first wireless device, and receiving the second timing information signal when the second timing information signal is detected. When the second timing information signal is not detected, the second wireless communication device uses the first radio receiver or a second radio receiver to listen for a first timing information that is transmitted by the target wireless communication network, wherein: the first timing information signal has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal comprises radio signal timing information and system information; and the second timing information signal has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity, wherein the second timing information signal is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity.

[0062] In another aspect of some but not necessarily all embodiments involving the second receiver’s activity, the second timing information signal comprises a first wireless communication system identifier; and when the first wireless communication system identifier is not an identifier of the target wireless communication network, the second timing information signal is considered to be not detected. In yet another aspect of some but not necessarily all embodiments involving the second receiver’s activity, the decision to communicate with the target wireless communication network is in response to one or more of an instance of a regular paging occasion reception; a decision to measure signals transmitted from the target wireless communication network; and a decision to communicate data.

[0063] In still another aspect of some but not necessarily all embodiments involving the second receiver’s activity, the second radio receiver is characterized by a higher rate of power consumption than the first radio receiver.

[0064] In another aspect of some but not necessarily all embodiments, the second receiver’s actions include, when the second timing information signal is received, using the second timing information signal to synchronize the second wireless communication device with the target wireless communication system; when the first timing information signal is received, using the first timing information signal to synchronize the second wireless communication device with the target wireless communication system; and following synchronization of the second wireless communication device with the target wireless communication system, using the second radio receiver to perform a network communication task with the target wireless communication system.

[0065] In yet another aspect of some but not necessarily all embodiments involving the second receiver’s activity, the second timing information signal is an on / off keying-modulated signal.

[0066] In still another aspect of some but not necessarily all embodiments involving the second receiver’s activity, the second bandwidth is no more than 2MHz.

[0067] In another aspect of some but not necessarily all embodiments a computer program comprises instructions that, when executed by at least one processor, causes the at least one processor to carry out a method according to any of the various embodiments involving actions taken by the first wireless communication device or the second wireless communication device.

[0068] In another aspect of some but not necessarily all embodiments involving the second receiver’s activity, The computer program is embodied on a carrier, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which:

[0070] Figure 1 illustrates technologies for sidelink synchronization, in which a first wireless device is located within a network coverage area and second and third wireless devices are each outside of the network coverage area.

[0071] Figure 2 is a high level illustration of an exemplary embodiment in which a first device receives radio signal timing (e.g., frame timing) information regarding one or more wireless communication networks and in which the first device produces a second synchronization signal for synchronizing a second device to the network.

[0072] Figure 3 is, in one respect, a flowchart of actions performed by a first device and / or system for assisting synchronization of a second device in an energy-efficient way in accordance with aspects of inventive embodiments.

[0073] Figure 4 is, in one respect, a flowchart of actions performed by a second device and / or system for assisting synchronization of a second device in an energy-efficient way in accordance with aspects of inventive embodiments.

[0074] Figures 5A, 5B, 5C, and 5D illustrate different examples in which a synchronization signal produced by the first device can be constructed by combining different information parts into transmissions (e.g., with a first synchronization part and a second information part combined into one transmission).

[0075] Figures 6A and 6B illustrate synchronization signals produced by a first device that assists second devices with synchronization for different networks having different radio signals (e.g., frame) timings.

[0076] Figure 7 shows an exemplary controller that may be included in an XR device to cause any and / or all of the herein-described and illustrated actions associated with that device to be performed.

[0077] DETAILED DESCRIPTION

[0078] The various features of the invention will now be described with reference to the figures, in which like parts are identified with the same reference characters.

[0079] The various aspects of the invention will now be described in greater detail in connection with a number of exemplary embodiments. To facilitate an understanding of the invention, many aspects of the invention are described in terms of sequences of actions to be performed by elements of a computer system or other hardware capable of executing programmed instructions. It will be recognized that in each of the embodiments, the various actions could be performed by specialized circuits (e.g., analog and / or discrete logic gates interconnected to perform a specialized function), by one or more processors programmed with a suitable set of instructions, or by a combination of both. The term “circuitry configured to” perform one or more described actions is used herein to refer to any such embodiment (i.e., one or more specialized circuits alone, one or more programmed processors, or any combination of these). Moreover, the invention can additionally be considered to be embodied entirely within any form of non- transitory computer readable carrier, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein. Thus, the various aspects of the invention may be embodied in many different forms, and all such forms are contemplated to be within the scope of the invention. For each of the various aspects of the invention, any such form of embodiments as described above may be referred to herein as “logic configured to” perform a described action, or alternatively as “logic that” performs a described action.

[0080] Embodiments that include one or more aspects of the invention variously relate to, and include technology for, (re-)synchronization of devices, and especially energy efficient (re- )synchronization, which is advantageous for use with low power (e.g., loT) devices.

[0081] At least some inventive embodiments can be characterized as a device centric approach that enables a generated re-synchronization signal to be scheduled more flexibly, and / or at a more configurable power level and / or able to be received using a simple, low complexity receiver architecture compared to what is used in typical 3GPP protocols. In other words, independently of what specific features the network supports, a device-centric design makes it possible to still ensure that each device can keep network synchronization in a very energy efficient manner.

[0082] As an overview of various aspects in accordance with embodiments that are consistent with the invention, a first wireless device that has timing / synchronization information about a communications network provides an enhanced network synchronization / re-synchronization support for one or more second wireless devices that are within proximity of the first device. The first wireless device may use a receiver to detect and acquire one or more information elements from timing reference information that is broadcast from a wireless network. Further, the device may use the acquired information to generate and transmit a dedicated re-synchronization signal tailored to allow for energy efficient network synchronization by the one or more second wireless devices. This new type of signal can be referred to as an ultra-low power re-sync signal

[0083] (ULP-RSS).

[0084] In an aspect of some but not necessarily all embodiments, the signal generated by the first device may be transmitted on an unlicensed band, since that will enable the first wireless device to transmit the re-synchronization signal without network coordination of transmit resources.

[0085] In some but not necessarily all embodiments, the signal generated by the first device may be transmitted through a set of specified channel / frequency bands with a transmit modulation and coding configured to enable energy efficient reception by the other wireless devices. Examples of such modulation types include On / Off Keying (OOK), Frequency Shift Keying (FSK), Binary Phase Shift Keying (BPSK), and similar.

[0086] In some but not necessarily all embodiments, the first wireless device receives information elements from the network transmissions and incorporates one or more of these into the generated dedicated re-synchronization signal. Such information can be, for example, one or more basic information elements from system information transmitted by the wireless network. Such system information may include cell ID, network ID, cell barring information or similar network information.

[0087] In still more alternative embodiments, the first wireless device provides the correct frame time reference from multiple wireless networks using the principles outlined above. In some examples the first wireless device collects and transmits the time reference information from the multiple networks. In some other examples, the first wireless device receives information from a second wireless device indicating which synchronization source the first wireless device should utilize. In other words, the first wireless device may be configured, for example, to provide the frame time reference for a certain mobile network identity such as a mobile network code or similar.

[0088] To provide a contextualizing example, consider the smartwatch example that was mentioned earlier in the Background section. If the smartwatch supports 3 GPP technologies for communication, it may spend a significant amount of time in idle mode and perform synchronization and paging with the network, while the user’s smartphone potentially has a larger amount of energy available and also performs very similar activities. When embodiments consistent with the invention are employed, the smartphone acts as the first device and supports a short range, local signaling of synchronization information to the smartwatch. By obtaining synchronization information in this manner, the battery life of the smartwatch is improved in a simple, device centric way, not requiring any 3 GPP protocol update or any network infrastructure modifications.

[0089] In another example, a second device can be a device that lacks a battery, and that may be in a power off state for a long time. The second device cannot fetch / keep the network timing information until it harvests enough energy to power up. After powering up, it can receive / demodulate the much simplified synchronization signal broadcast by the first device. Therefore the second device can communicate to the network directly without wasting energy to acquire timing synchronization directly from the network.

[0090] To summarize above-mentioned aspects and describe further aspects, some embodiments relate to a wireless device that receives transmissions from a wireless network and determines a radio signal timing (e.g., as a non-limiting example, frame timing) for the network and at least some of the network system information transmitted by the network. The device utilizes the system frame timing and generates a (low power) re-synchronization signal and transmits the resynchronization signal to one or more second wireless devices using a smaller bandwidth and / or a lower order modulation than the network transmission, where the re-synchronization signal includes or is indicative of one or more information elements of the system information such as, without limitation:

[0091] Subframe Number o The device can estimate the Subframe number by detecting PSS / SSS which is broadcast by a network.

[0092] - The System Frame Number (SFN) o This information is available in a Master Information Block (MIB) which the network transmitted via Physical Broadcast Channel (PBCH) together with SSS / PSS in 3GPP systems (e.g., SSB in NR.) and may therefore, in some examples, also be included in the re-synchronization signal in order to support such things as, without limitation, paging time occurrence calculation by a second device.

[0093] - Hyper Frame Number (HFN) o HFN has a longer time span than the SFN so that the network can schedule the timing related parameters (e.g., eDRX, PSM configuration) for Machine Type Communication (MTC) and loT devices. In LTE, this time information is available in a first System Information Block (SIB1), which the network transmits via PDCCH. - The network identity (such as Mobile Country Code (MCC) and Mobile Network Code (MNC)) o This information is typically not available in the synchronization signals of wireless networks but, in some examples, can be included or indicated from the constructed re-synchronization signal in order for second devices to ensure that they are maintaining synchronization with the correct network

[0094] - The cell identity o Similar to the network identity, a cell identity indicator can be useful in the constructed re-synchronization signal in order for second devices to be aware of potential cell changes

[0095] The first device may continuously receive synchronization signals from the network and broadcast the generated re-synchronization signal within its proximate area in a desired use scenario.

[0096] In an alternative, the device may receive synchronization signals from the network and broadcast the generated re-synchronization signal with a configurable duty cycle.

[0097] These and further aspects are described in the following discussion.

[0098] Figure 2 is a high level illustration of aspects of inventive embodiments. As shown, a first device 201 receives radio signal timing (e.g., frame timing) information 203 regarding one or more wireless communication networks, such as but not limited to the illustrated wireless communication network 205. In some but not necessarily all embodiments, the first device 201 also receives and decodes available system information that may also be broadcasted from each of the wireless networks 205. The first device 201 utilizes the information about time and system structure to generate one or more synchronization signals that incorporate the frame timing and system information from one or more networks. The newly generated one or more synchronization signals are then transmitted 207 by the first device 205, utilizing a different, lower bandwidth, lower order modulation and / or lower coding complexity format than those that characterize the radio signal timing information signal 203 from the wireless network 205. In some but not necessarily all embodiments consistent with the invention, the transmission 207 is made on a shared, unlicensed radio spectrum. The lower bandwidth, lower order modulation, and / or lower coding complexity enable an energy efficient low-complexity demodulation of the newly generated signals. In aspects of further exemplary embodiments consistent with the invention, each of one or more second devices 209 (e.g., a smartwatch as illustrated in Figure 2) determines the identity of a network that it wants to associate with (herein referred to as a “target network”), and listens for the synchronization signals (generated by the first device 201 from the network’s synchronization signaling) that are transmitted on the shared, unlicensed spectrum. In particular, the second device 209 looks for synchronization signals that are indicated as relating to the target network 205 (e.g., by including a target network identification) and does this for the purpose of achieving synchronization or re-synchronization with the system frame timing of that target network. Once a synchronization is achieved, the second device 209 listens for downlink signals 211 from the target network 205 transmitted within the acquired system frame timing (e.g., at a paging occasion for the second device 209 within the network) and in some instances transmits signals 213 to the target network 205.

[0099] Further aspects of at least some inventive embodiments will now be described with reference to Figure 3 which, in one respect, is a flowchart of actions performed by a first device 201 for assisting synchronization of a second device 209 in an energy-efficient way. In other respects, the blocks depicted in Figure 3 can also be considered to represent means 300 (e.g., hardwired or programmable circuitry or other processing means) for carrying out the described actions.

[0100] In the exemplary embodiment of Figure 3, a first device 201 is configured to perform a synchronization signal transmission to a second device 209 based on a radio signal timing (e.g., a frame timing) for one or more target networks 205. Actions performed in this endeavor include the first device identifying a target mobile network 205 (step 301). This may be performed in a number of different ways, such as by programming the first device 201 to include the identity of the target mobile network 205 (e.g., and without limitation, via end user input). In alternatives, a target network identity can be communicated to the first device 201. Such communication can be, for example and without limitation, via a wired or wireless interface of the first device 201.

[0101] In some but not necessarily all embodiments, more than one target network 205 is identified in step 301.

[0102] Thereafter, the first device 201 acquires a first signal that comprises one or both of: the system radio signal (e.g., frame) timing and system information from the identified target network(s) (step 303). This may typically mean having the first device 201 scan one of more frequency bands to determine synchronization signals and system information broadcast from network node(s) 205. For example, in a 3 GPP-compliant system, acquiring the system radio signal timing and system information comprises receiving and demodulating, for example, a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a master information block (MIB), and one or more system information blocks (SIB) and similar type of signals transmitted by a network base station 205. Information which may be acquired can include but is not limited to the system frame timing, Orthogonal Frequency Division Multiplexing (OFDM) numerologies such as subcarrier spacing, network identity, cell identity, beam identity and cell barring status. It can be noted that the first device 201 can typically receive this information without registering with the network. Typically the first device 201 does not need to transmit any signal in order to acquire this information, since the network node 205 broadcasts this information periodically regardless. However, there may be examples where the first device 201 uses a connection with the network node 205 to receive dedicated transmissions of system information which the first device 201 may use. In one or more nonlimiting examples the first device 201 may use only broadcasted information, while in some other nonlimiting examples the first device 201 may use both broadcasted information and information received in dedicated signaling, and in some further one or more nonlimiting examples the first device 201 may use only information from the network node received in dedicated signaling.

[0103] After acquiring the system radio signal (e.g., frame) timing, the first device 201 constructs and transmits a wireless signal (second signal) for the purpose of enabling other (second) devices 209 to be able to acquire the frame timing information from the identified network (step 305). The signal may include or be indicative of one or more of the system information elements. The constructed signal is targeted to be easy to demodulate and decode with a low complexity receiver, and therefore the signal design is simplified compared to the network transmissions. This means that one or more of a lower order modulation format such as an on / off keying is used, a narrower bandwidth and more limited (lower complexity) coding such as a block coding is utilized.

[0104] The second signal produced by the first device 201 is then transmitted (step 307). The second signal can be transmitted on any frequency band, but in some but not necessarily all embodiments, transmission on a lower frequency (sub 6 GHz) would be suitable for lower path loss and less directivity of transmissions in general. Examples of frequency bands could be unlicensed sub-GHz bands such as the ISM bands, or unlicensed 2.4GHz. Other licensed bands can also be used in still other alternative embodiments, however with the practical limitation of a needed license for transmissions. Specific examples of exemplary signal structures are described below. Further aspects of some but not necessarily all embodiments consistent with the invention relate to actions carried out in a second device 209. To further describe these aspects, Figure 4 is, in one respect, a flowchart of actions performed by a second device 209 for synchronizing itself to a target network node 205 in an energy-efficient way, based on assisting signaling from a first device 201. In other respects, the blocks depicted in Figure 4 can also be considered to represent means 400 (e.g., hardwired or programmable circuitry or other processing means) for carrying out the described actions.

[0105] In the exemplary embodiment of Figure 4, a second device 209 is configured to receive a synchronization signal transmission from a first device 201, where the received synchronization signal is based on a radio signal timing (e.g., a frame timing) for one or more target networks 205. Actions performed in this endeavor include the second device identifying a target mobile network 205 (step 401), and identifying a need to communicate with the target mobile network 205 (step 403) in performance of a network activity. The type of network activity to be performed is not an essential aspect of inventive embodiments but for purposes of illustration and without limitation, it can be a regular paging occasion reception, a measurement of signals transmitted from the network, a data communication session or similar activity.

[0106] In order to perform the network activity, the second device 209 needs to be synchronized with the signal timing (e.g., frame timing) of the network. In order to minimize energy expenditure, the second device 209 is configured with a main receiver and a secondary receiver that consumes less energy than the main receiver. Accordingly, the second device 209 activates the secondary receiver (step 405) in order to detect the earlier-described signal for synchronization transmitted by the first device 201. Several examples of low complex, energy efficient receiver solutions are available in the literature, and therefore need not be described here in detail.

[0107] Further in this non-limiting exemplary embodiment, the second device 209 uses its secondary receiver to listen for the synchronization signal transmitted by the first device 201, and decides whether the signal has been detected (decision block 407). If so (“Yes” path out of decision block 407), the second device 209 receives the radio signal timing (e.g., frame timing) and system information relating to the target network node 203, all from the received synchronization signal transmitted by the first device 201. Upon receipt of this information, the second device 209 activates its other (e.g., main) receiver so that it can receive signals transmitted from the network node (e.g., base station) (step 411). However, if the synchronization signal from the first device 201 was not detected by the secondary receiver (“No” path out of decision block 407), the second device 209 responds by activating the other (e.g., main) receiver (step 413) so that it can receive signaling transmitted from the network node (e.g., base station) 205. The second device 209 then uses the other (main) receiver to receive radio signal timing (e.g., frame timing) and system information from signaling transmitted from the network node 203 (step 415).

[0108] Regardless of whether synchronization was achieved using the secondary or main receiver, having synchronized itself the second device 209 then communicates with the network according to the identified need, with those communications utilizing the acquired radio signal timing information (step 417).

[0109] As further variant in some but not necessarily all alternative embodiments, several devices are all acting as a first device as described above, each transmitting (re-)synchronization signals. In an aspect of some such alternative embodiments, the several devices are configured to cooperate rather than disturb each other (e.g., causing interference with one another). The modulation content of all transmitters can be synchronized with respect to the broadcasts they receive from the mobile network. For OOK modulation, the transmitters can be set to respective carrier frequencies with slight offsets, an integer or non-integer multiple of the modulation (bit) rate. In that case, every bit will see a number of positive beats to be detected by the envelope detector of a second device’s receiver.

[0110] To avoid the need for coordination among the several first devices, each of the first devices can randomly select its own carrier frequency offset. In another aspect of some but not necessarily all such embodiments, one or more of the first receivers makes a new random selection of frequency offset from time to time (e.g., and without limitation, with each new transmission). This has the added benefit of reducing the effects of frequency selective fading.

[0111] On the receive side in such an arrangement, the receiver need not be aware of which particular offsets are being used. In some embodiments, for example and as mentioned above, a low power receiver having a rather wide bandwidth can be used. It can, for instance, be an uncertain-IF receiver having filters with enough bandwidth to allow for the uncertainty in the IF frequency due to oscillator frequency variations.

[0112] In some alternative embodiments, a receiver can be employed that uses RF rectification for even lower power, where the bandwidth of the RF filter cannot be made very narrow due to the high center frequency. For that reason, if the transmitters have small frequency offsets as described, they will all be within the receiver bandwidth, and their signals will be added up in the receiver. By having a frequency separation between transmitters much larger than the modulation rate of the OOK, the amplitude variations of the combined signal due to carriers beating can be separated from the slower OOK modulation signal.

[0113] Having a set of offset frequencies located at certain minimum distances is can be preferable for some embodiments as it avoids low beat frequencies. If the distances are multiples of the modulation frequency, the amplitude pattern will not change from on-symbol to on- symbol. This can provide an advantage, and the multiples of the symbol frequency is the preferred set of offsets. For some implementations, this can for example be up to a selected certain max multiple, like plus minus 9 where every second multiple can be used. Other implementations may be selected, e.g., based on matching with hardware capabilities.

[0114] But other sets are still possible, for example equdistant offsets, but with a distance not an integer number of modulation frequencies. Or just a random number below say 10 times the modulation rate.

[0115] In yet some other alternative embodiments, a more advanced receiver can be used that uses an FFT to separate the signals from the different receivers, and then searches for a preamble of the signal with correlators for the different FFT taps. When the preamble is found in some taps, the signals of these taps are then combined for improved SNR of the remaining signal. But such signal processing is power consuming and may therefore not be the best choice for use cases seeking low power consumption.

[0116] Yet another alternative is to use the same center frequency in all transmitters of the first devices, but a randomized phase, changing a number of times per OOK symbol.

[0117] The (re-)synchronization signal being created by the first device 201 for the purpose of energy efficient (re-)synchronization in a second device 209 can be constructed in several ways. Here, a few non-limiting examples of implementation are provided in the following.

[0118] As described above, the signal can be constructed using a narrower bandwidth and / or with a lower order modulation and / or coding complexity compared to the signals transmitted by the network nodes 203. In this manner, the receiver utilized in a second device 209 for detection and demodulation of the signal can be built to be optimized for energy efficient operation.

[0119] Various low complexity receiver implementations (e.g., wake up receivers for reception of so-called wake up signals) are known in the literature, and they may for example be optimized for reception of signals using, for instance, on-off keying (OOK). The bandwidth of the signal may be very small, for example a few hundred kHz or similar up to, for example about 2MHz, which is the bandwidth used by Bluetooth Low Energy-compliant radio equipment. Such equipment can, for example, be adapted to receive OOK modulated signals.

[0120] In still further aspects of some but not necessarily all embodiments that are consistent with the invention, one or more information elements from the network system information are incorporated into the synchronization signal transmitted by the first device 201. This may, for example, be performed in order for the second device 209 to know the current system frame numbering (SFN) information, or for the second device 209 to be aware that the signal is coupled to the correct target network identity (e.g., MCC, MNC) and in some cases even the correct target cell (Cell ID). Other information elements could also be included, such as and without limitation, cell barring information or other relevant information.

[0121] In some examples, the signal generated by the first device 201 is divided into a synchronization signal part and a network information part. The signal may be constructed by combining such parts in different sub-transmissions, with same or different repetition patterns.

[0122] The signal may in other examples be constructed by combining such parts into the same transmissions, (e.g., with a first synchronization part and a second information part combined into one transmission). Although the exact details of a signal design are not the main focus of this description, a few examples of such signal combinations are provided in Figures 5A, 5B, 5C, and 5D. More variants and examples are also possible.

[0123] Figure 5A illustrates an example in which a synchronization signal includes network frame timing information and one or more system information elements. The synchronization signal configured in this way is broadcast at some repetition rate.

[0124] Figure 5B illustrates an example in which a first synchronization signal comprises network timing information, and this is immediately followed by a second synchronization signal that comprises system information coupled to the first synchronization signal. This pair of first and second synchronization signals is broadcast at some repetition rate.

[0125] Figure 5C illustrates an example in which three different types of synchronization signals are used: a first synchronization signal that comprises network timing information; a second synchronization signal that comprises a first system information coupled to the first synchronization signal; and a second system information, also coupled to the first synchronization signal. Transmission of these signals is performed in pairs, for example, first transmitting the first synchronization signal immediately followed by the second synchronization signal; and then after a period of time, transmitting the first synchronization signal immediately followed by the third synchronization signal. Transmission of alternating pairs in this manner is repeated at some repetition rate.

[0126] Figure 5D illustrates an example that utilizes two different types of synchronization signals: a first synchronization signal that comprises network timing information; and a second synchronization signal that comprises system information coupled to the first synchronization signal. In this embodiment, transmission comprises transmitting the pair of synchronization signals, for example, the first synchronization signal immediately followed by the second synchronization signal. After a period of time, the first synchronization signal is again transmitted, but this time not followed by the second synchronization signal. The first synchronization signal can be repeatedly transmitted alone at some periodicity. After some number of transmissions of the first synchronization signal, the pair of signals (e.g., first synchronization signal immediately followed by the second synchronization signal) are again repeated, and the transmission pattern repeated as well. In the example of Figure 5D, the pattern has a pair of first and second synchronization signals being transmitted, one immediately following the other, and this is then followed by three transmissions of the first synchronization signal alone. It can be seen that in this type of configuration, the system information repetition interval is different from that of the radio signal timing (e.g., frame timing) signal.

[0127] In still further nonlimiting exemplary alternatives, the first device 201 is configured to perform the production and transmission of a synchronization signal as described above for multiple different networks having different frame timings. In such case, the first device 201 may perform a time or frequency multiplexing of the transmissions of synchronization signals for the different network frame timings. To illustrate this aspect, examples of such combinations are shown in Figures 6A and 6B. In Figure 6A, two different synchronization signals are used: a first synchronization signal having network radio signal (e.g., frame) timing information and possibly also one or more system information elements from a first radio network; and a second synchronization signal having network radio signal (e.g., frame) timing information and possibly also one or more system information elements from a second radio network. Transmission of the first or second synchronization signals alternates at some periodicity.

[0128] Figure 6B illustrates an example in which four different synchronization signals are used: a first synchronization signal having network radio signal (e.g., frame) timing information from a first radio network; a second synchronization signal that comprises one or more system information elements from the first radio network; a third synchronization signal having network radio signal (e.g., frame) timing information from a second radio network; and a fourth synchronization signal that comprises one or more system information elements from the second radio network. Transmission of pairs of synchronization signals (one immediately following the other) is performed at some periodicity, with the first pair comprising the first synchronization signal immediately followed by the second synchronization signal, and the second pair comprising the third synchronization signal immediately followed by the fourth synchronization signal. These alternating pairs of synchronization signals are transmitted at some repetition rate.

[0129] Further aspects of embodiments consistent with the invention will now be described with reference to Figure 7, which shows an exemplary controller 701 that may be included in a first and second wireless device to cause any and / or all of the herein-described and illustrated actions associated with that first or second device or system to be performed. In particular, the controller 701 includes circuitry configured to carry out any one or any combination of the various functions described herein. Such circuitry could, for example, be entirely hard-wired circuitry (e.g., one or more Application Specific Integrated Circuits - “ASICs”). Depicted in the exemplary embodiment of Figure 7, however, is programmable circuitry, comprising a processor 703 coupled to one or more memory devices 705 (e.g., Random Access Memory, Magnetic Disc Drives, Optical Disk Drives, Read Only Memory, etc.) and to an interface 707 that enables bidirectional communication with other elements of a device as described above. A complete list of possible other elements is beyond the scope of this description.

[0130] The memory device(s) 705 store program means 709 (e.g., a set of processor instructions) configured to cause the processor 703 to control other device elements so as to carry out any of the aspects described herein. The memory device(s) 705 may also store data (not shown) representing various constant and variable parameters as may be needed by the processor 703 and / or as may be generated when carrying out its functions such as those specified by the program means 709.

[0131] Various embodiments that are consistent with the invention provide a number of benefits and advantages over conventional technology. Some of these advantages include Energy saving and thereby battery lifetime improvements in wireless devices. In particular, a second wireless device that supports the reception of the (re-)synchronization signal transmitted from the first device can receive a stronger signal tailored to achieve synchronization towards a particular network. It can be more energy efficient for the second wireless device to receive and demodulate / decode the transmitted re-synchronization signal. Hence the required energy to perform initial or re-synchronization can be reduced and the battery lifetime of the second device can be improved. Another advantage of inventive embodiments over conventional technology is its use of device centric, network independent functionality. The various inventive embodiments enable battery lifetime improvements for low-power (e.g., loT) devices within an area without any network adjustments, network features or network nodes. Since the information extracted from the network is broadcast from a network node, the device used to receive the network frame timing information does not need to have any data communication capabilities with respect to the wireless network. In other words, the device can be deployed and operated without an operator-specific SIM card, subscription, license, and the like, for wireless communication with the network. Hence, to take an example, a building owner can prolong the battery life of wireless devices deployed in the building without any interaction with network owners such as operators or infrastructure vendors.

[0132] The invention has been described with reference to particular embodiments. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the embodiment described above. Thus, the described embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is further illustrated by the appended claims, rather than only by the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.

Claims

CLAIMS:

1. A method performed by a first wireless communication device (201) for synchronizing a second wireless communication device (209), the method comprising: wirelessly receiving (303) a first timing information signal (203) transmitted from a target wireless communication network (205), wherein the first timing information signal (203) has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal (203) comprises radio signal timing information and system information; producing (305) a second timing information signal (207) that comprises the radio signal timing information, wherein the second timing information signal has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity, wherein the second timing information signal (207) is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity; and transmitting (307) the second timing information signal (207) for receipt by the second wireless communication device (209).

2. The method of claim 1, wherein the second timing information signal (207) further comprises at least a portion of the system information.

3. The method of any one of the previous claims, wherein: transmitting (307) the second timing information signal (207) comprises wirelessly transmitting the second timing information signal (207) using an unlicensed radiofrequency spectrum.

4. The method of claim 3, wherein the unlicensed radiofrequency spectrum is one of: an Industrial, Scientific, and Medical (ISM) radiofrequency band; and a radiofrequency band at 2.4 GHz.

5. The method of any one of the previous claims, wherein: the first timing information signal (203) further comprises a network identifier; andthe second timing information signal (207) further comprises the network identifier.

6. The method of any one of the previous claims, wherein the target wireless communication network (205) is one of a plurality of wireless communication networks, and wherein the method comprises: prior to wirelessly receiving (303) the first timing information signal (203) transmitted from the wireless communication network (205), identifying (301) the target wireless communication network (205) as a source of the first timing information signal (203).

7. The method of any one of the previous claims, wherein the first wireless communication device (201) is not registered with the target wireless communication network (205).

8. The method of any one of the previous claims, wherein transmitting (307) the second timing information signal (207) for receipt by the second wireless communication device (209) comprises: broadcasting the second timing information signal (207) for receipt by the second wireless communication device (209).

9. The method of any one of the previous claims, wherein the second timing information signal (207) is an on / off keying-modulated signal.

10. The method of claim 9, wherein transmitting (307) the second timing information signal (207) comprises: randomly selecting a frequency offset from a plurality of different frequency offsets that are different integer or non-integer multiples of a modulation bit rate used for the on / off keying- modulated signal; and transmitting the second timing information signal on a carrier frequency that is a nominal carrier frequency plus or minus the selected frequency offset.

11. The method of claim 10, comprising: randomly selecting a first frequency offset for use in determining the carrier frequency when transmitting the second timing information signal at a first time; andrandomly selecting a second frequency offset for use in determining the carrier frequency when transmitting the second timing information signal at a second time.

12. The method of any one of the previous claims, wherein the second coding format is a block coding format.

13. The method of any one of the previous claims, wherein the first timing information signal (203) is one or more of: a primary synchronization signal; a secondary synchronization signal; a master information block; and a system information block.

14. The method of any one of the previous claims, wherein a modulation timing of the second timing information signal (207) is synchronized with respect to broadcasts received by the first wireless communication device (201) from the target wireless communication network (205).

15. The method of any one of the previous claims, wherein the second bandwidth is no more than 2Mhz.

16. The method of any one of the previous claims, wherein: the second timing information signal (207) comprises a first part and a second part; the first part comprises information for synchronizing the second wireless communication device with the target wireless communication network (205); the second part comprises network information; the first part is transmitted in a first transmission; and the second part is transmitted in a second transmission.

17. The method of claim 16, wherein the first transmission is repeated at a first repetition rate, and the second transmission is repeated at a second repetition rate.

18. The method of claim 17, wherein the first repetition rate is different from the second repetition rate.

19. The method of any one of the previous claims, wherein the target wireless communication network (205) is a first target wireless communication network having a first radio signal timing, and wherein the method comprises: wirelessly receiving a third timing information signal transmitted from a second target wireless communication network having a second radio signal timing that is different from the first radio signal timing, wherein the third timing information signal has a third bandwidth, a third order of modulation, and a third coding format associated with a third coding complexity, and wherein the third timing information signal comprises third radio signal timing information and third system information; producing a fourth timing information signal that comprises the third radio signal timing information, wherein the fourth timing information signal has a fourth bandwidth, a fourth order of modulation, and a fourth coding format associated with a fourth coding complexity, wherein the fourth timing information signal is characterized by one or more of: the fourth bandwidth is lower than the third bandwidth; the fourth order of modulation is lower than the third order of modulation; and the fourth coding complexity is lower than the third coding complexity; and transmitting the fourth timing information signal for receipt by the second wireless communication device.

20. The method of claim 19, wherein one or both of time multiplexing and frequency multiplexing are used when transmitting the second timing information signal and the fourth timing information signal.

21. A computer program (709) comprising instructions that, when executed by at least one processor (703), causes the at least one processor (703) to carry out the method according to any one of the previous claims.

22. A carrier comprising the computer program (709) of claim 21, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium (705).

23. A method of synchronizing a second wireless communication device (209), the method being performed by the second wireless communication device (209) and comprising: in response to a decision (403) to communicate with a target wireless communication network (205), performing: using (405) a first radio receiver to listen for a second timing information signal (207) that is transmitted by a first wireless device (201), and receiving (407) the second timing information signal (207) when the second timing information signal (207) is detected; when the second timing information signal (207) is not detected, using (413) the first radio receiver or a second radio receiver to listen for a first timing information (203) that is transmitted by the target wireless communication network (205), wherein: the first timing information signal (205) has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal comprises radio signal timing information and system information; and the second timing information signal (207) has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity, wherein the second timing information signal is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity.

24. The method of claim 23, wherein: the second timing information signal (207) comprises a first wireless communication system identifier; and when the first wireless communication system identifier is not an identifier of the target wireless communication network, the second timing information signal is considered to be not detected.

25. The method of any one of claims 23 through 24, wherein the decision (403) to communicate with the target wireless communication network (205) is in response to one or more of:an instance of a regular paging occasion reception; a decision to measure signals transmitted from the target wireless communication network; and a decision to communicate data.

26. The method of any one of claims 23 through 25, wherein the second radio receiver is characterized by a higher rate of power consumption than the first radio receiver.

27. The method of any one of claims 23 through 26, comprising: when the second timing information signal (207) is received, using (409) the second timing information signal (207) to synchronize the second wireless communication device (209) with the target wireless communication system (205); when the first timing information signal (203) is received, using (415) the first timing information signal (203) to synchronize the second wireless communication device (209) with the target wireless communication system (205); and following synchronization of the second wireless communication device (209) with the target wireless communication system (205), using (417) the second radio receiver to perform a network communication task with the target wireless communication system (205).

28. The method of any one of claims 23 through 27, wherein the second timing information signal (207) is an on / off keying-modulated signal.

29. The method of any one of claims 23 through 24, wherein the second bandwidth is no more than 2MHz.

30. A computer program (709) comprising instructions that, when executed by at least one processor (703), causes the at least one processor (703) to carry out the method according to any one of claims 23 through 29.

31. A carrier comprising the computer program (709) of claim 30, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a non-transitory computer readable storage medium (705).-SO-32. An apparatus of a first wireless communication device (201) for synchronizing a second wireless communication device (209), wherein the apparatus is configured to cause the first wireless communication device (201) to perform: wirelessly receiving (303) a first timing information signal (203) transmitted from a target wireless communication network (205), wherein the first timing information signal (203) has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal (203) comprises radio signal timing information and system information; producing (305) a second timing information signal (207) that comprises the radio signal timing information, wherein the second timing information signal has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity, wherein the second timing information signal (207) is characterized by one or more of: the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity; and transmitting (307) the second timing information signal (207) for receipt by the second wireless communication device (209).

33. The apparatus of claim 32, wherein the second timing information signal (207) further comprises at least a portion of the system information.

34. The apparatus of any one of claims 32 through 33, wherein: transmitting (307) the second timing information signal (207) comprises wirelessly transmitting the second timing information signal (207) using an unlicensed radiofrequency spectrum.

35. The apparatus of claim 34, wherein the unlicensed radiofrequency spectrum is one of: an Industrial, Scientific, and Medical (ISM) radiofrequency band; and a radiofrequency band at 2.4 GHz.

36. The apparatus of any one of claims 32 through 35, wherein: the first timing information signal (203) further comprises a network identifier; andthe second timing information signal (207) further comprises the network identifier.

37. The apparatus of any one of claims 32 through 36, wherein the target wireless communication network (205) is one of a plurality of wireless communication networks, and wherein the apparatus is configured to cause the first wireless communication device (201) to perform: prior to wirelessly receiving (303) the first timing information signal (203) transmitted from the wireless communication network (205), identifying (301) the target wireless communication network (205) as a source of the first timing information signal (203).

38. The apparatus of any one of claims 32 through 37, wherein the first wireless communication device (201) is not registered with the target wireless communication network (205).

39. The apparatus of any one of claims 32 through 38, wherein transmitting (307) the second timing information signal (207) for receipt by the second wireless communication device (209) comprises: broadcasting the second timing information signal (207) for receipt by the second wireless communication device (209).

40. The apparatus of any one of claims 32 through 39, wherein the second timing information signal (207) is an on / off keying-modulated signal.

41. The apparatus of claim 40, wherein transmitting (307) the second timing information signal (207) comprises: randomly selecting a frequency offset from a plurality of different frequency offsets that are different integer or non-integer multiples of a modulation bit rate used for the on / off keying- modulated signal; and transmitting the second timing information signal on a carrier frequency that is a nominal carrier frequency plus or minus the selected frequency offset.

42. The apparatus of claim 41, wherein the apparatus is configured to cause the first wireless communication device (201) to perform:randomly selecting a first frequency offset for use in determining the carrier frequency when transmitting the second timing information signal at a first time; and randomly selecting a second frequency offset for use in determining the carrier frequency when transmitting the second timing information signal at a second time.

43. The apparatus of any one of claims 32 through 42, wherein the second coding format is a block coding format.

44. The apparatus of any one of claims 32 through 43, wherein the first timing information signal (203) is one or more of a primary synchronization signal; a secondary synchronization signal; a master information block; and a system information block.

45. The apparatus of any one of claims 32 through 44, wherein a modulation timing of the second timing information signal (207) is synchronized with respect to broadcasts received by the first wireless communication device (201) from the target wireless communication network (205).

46. The apparatus of any one claims 32 through 45, wherein the second bandwidth is no more than 2Mhz.

47. The apparatus of any one of claims 32 through 46, wherein: the second timing information signal (207) comprises a first part and a second part; the first part comprises information for synchronizing the second wireless communication device with the target wireless communication network (205); the second part comprises network information; the first part is transmitted in a first transmission; and the second part is transmitted in a second transmission.

48. The apparatus of claim 47, wherein the first transmission is repeated at a first repetition rate, and the second transmission is repeated at a second repetition rate.

49. The apparatus of claim 48, wherein the first repetition rate is different from the second repetition rate.

50. The apparatus of any one of the previous claims, wherein the target wireless communication network (205) is a first target wireless communication network having a first radio signal timing, and wherein the apparatus is configured to cause the first wireless communication device (201) to perform: wirelessly receiving a third timing information signal transmitted from a second target wireless communication network having a second radio signal timing that is different from the first radio signal timing, wherein the third timing information signal has a third bandwidth, a third order of modulation, and a third coding format associated with a third coding complexity, and wherein the third timing information signal comprises third radio signal timing information and third system information; producing a fourth timing information signal that comprises the third radio signal timing information, wherein the fourth timing information signal has a fourth bandwidth, a fourth order of modulation, and a fourth coding format associated with a fourth coding complexity, wherein the fourth timing information signal is characterized by one or more of: the fourth bandwidth is lower than the third bandwidth; the fourth order of modulation is lower than the third order of modulation; and the fourth coding complexity is lower than the third coding complexity; and transmitting the fourth timing information signal for receipt by the second wireless communication device.

51. The apparatus of claim 50, wherein one or both of time multiplexing and frequency multiplexing are used when transmitting the second timing information signal and the fourth timing information signal.

52. An apparatus of a second wireless communication device (209) for synchronizing the second wireless communication device (209), wherein the apparatus is configured to cause the second communication device (209) to perform: in response to a decision (403) to communicate with a target wireless communication network (205), performing:using (405) a first radio receiver to listen for a second timing information signal (207) that is transmitted by a first wireless device (201), and receiving (407) the second timing information signal (207) when the second timing information signal (207) is detected; when the second timing information signal (207) is not detected, using (413) the first radio receiver or a second radio receiver to listen for a first timing information (203) that is transmitted by the target wireless communication network (205), wherein: the first timing information signal (205) has a first bandwidth, a first order of modulation, and a first coding format associated with a first coding complexity, and wherein the first timing information signal comprises radio signal timing information and system information; and the second timing information signal (207) has a second bandwidth, a second order of modulation, and a second coding format associated with a second coding complexity, wherein the second timing information signal is characterized by one or more of the second bandwidth is lower than the first bandwidth; the second order of modulation is lower than the first order of modulation; and the second coding complexity is lower than the first coding complexity.

53. The apparatus of claim 52, wherein: the second timing information signal (207) comprises a first wireless communication system identifier; and when the first wireless communication system identifier is not an identifier of the target wireless communication network, the second timing information signal is considered to be not detected.

54. The apparatus of any one of claims 52 through 53, wherein the decision (403) to communicate with the target wireless communication network (205) is in response to one or more of: an instance of a regular paging occasion reception; a decision to measure signals transmitted from the target wireless communication network; and a decision to communicate data.

55. The apparatus of any one of claims 52 through 54, wherein the second radio receiver is characterized by a higher rate of power consumption than the first radio receiver.

56. The apparatus of any one of claims 52 through 55, wherein the apparatus is configured to cause the second wireless communication device (209) to perform: when the second timing information signal (207) is received, using (409) the second timing information signal (207) to synchronize the second wireless communication device (209) with the target wireless communication system (205); when the first timing information signal (203) is received, using (415) the first timing information signal (203) to synchronize the second wireless communication device (209) with the target wireless communication system (205); and following synchronization of the second wireless communication device (209) with the target wireless communication system (205), using (417) the second radio receiver to perform a network communication task with the target wireless communication system (205).

57. The apparatus of any one of claims 52 through 56, wherein the second timing information signal (207) is an on / off keying-modulated signal.

58. The apparatus of any one of claims 52 through 53, wherein the second bandwidth is no more than 2MHz.

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