Design method and device for off-grid radio service system

Abstract

The present disclosure relates to off-grid radio service system designs. Techniques for supporting narrowband device-to-device wireless communications are disclosed, including possible techniques for performing discovery in an off-grid radio system. According to some embodiments, a wireless device may determine a synchronization signal repetition number for use in narrowband device-to-device transmissions. The wireless device may perform a transmission, including transmitting the determined synchronization signal repetition number. The transmission may include an indication of the synchronization signal repetition number used in the transmission.

Description

[0001] This application is a divisional application of the invention patent application with application date of August 31, 2018, application number 201811006609.4, and titled “Off-grid radio service system design”.

[0002] Priority information

[0003] This patent application claims priority to U.S. Provisional Patent Application Serial No. 62 / 559,813, entitled “OFF GRID RADIO SERVICE SYSTEM DESIGN,” filed September 18, 2017; U.S. Provisional Patent Application Serial No. 62 / 573,193, entitled “OFF GRID RADIO SERVICE SYSTEM DESIGN,” filed October 17, 2017; U.S. Provisional Patent Application Serial No. 62 / 596,548, entitled “OFF GRID RADIO SERVICE SYSTEM DESIGN,” filed December 8, 2017; and U.S. Provisional Patent Application Serial No. 62 / 617,998, entitled “OFF GRID RADIO SERVICE SYSTEM DESIGN,” filed January 16, 2018; all of which are hereby incorporated by reference in their entirety as if fully and completely set forth herein. Technical Field

[0004] The present application relates to wireless communications, including techniques for performing narrowband device-to-device wireless communications. Background Art

[0005] The use of wireless communication systems is growing rapidly.In addition, wireless communication technology has evolved from only voice communication to also include the transmission of data (such as the Internet and multimedia content).

[0006] Mobile electronic devices may take the form of smartphones or tablets that are commonly carried by users. Wearable devices (also known as accessory devices) are a newer form of mobile electronic device, an example of which is the smartwatch. Additionally, low-cost, low-complexity wireless devices intended for static or dynamic deployment are rapidly increasing as part of the development of the "Internet of Things." In other words, the complexity, capabilities, traffic patterns, and other characteristics of the devices required are becoming increasingly broad. In general, it would be desirable to recognize and provide improved support for a wide range of desired wireless communication features. Therefore, improvements in this area are desired. Summary of the Invention

[0007] Embodiments of, among other things, systems, devices, and methods for performing narrowband device-to-device wireless communications are presented herein.

[0008] As mentioned above, there are an increasing number of use cases for diverse wireless devices with widely varying capabilities and usage expectations. While many wireless communication systems primarily utilize infrastructure-mode communications, e.g., using one or more base stations and potentially supporting networks as intermediaries between endpoint devices, one possible use case for wireless communication involves direct device-to-device communication. This disclosure presents various techniques for supporting such communications, including features and techniques for performing device-to-device discovery communications using narrower bandwidth communication channels.

[0009] According to the technology described herein, a preamble-based approach can be used to perform device-to-device synchronization, e.g., in contrast to a synchronization master-based approach, among other possibilities. A communication framework with timing based around a common reference time such as Coordinated Universal Time (UTC) and periodic discovery intervals can be used, including a conventional synchronization preamble window, an anchor window, and a scheduled interval. During the synchronization preamble window, a device can perform synchronization and initiate discovery by selecting a public or dedicated preamble sequence from a set of preamble sequences associated with a synchronization ID suitable for the desired discovery type, such as presence discovery or peer discovery. The sequence selected and / or the frequency of the transmitted sequence can also depend on the time at which the transmission occurs, e.g., according to a common reference time. At least according to some embodiments, the frequency at which a discovery response to a preamble sequence is transmitted can also depend on time according to a common reference time, and / or, for example, based on a frequency hopping sequence, with the discovery response transmitted in response to the preamble sequence.

[0010] Furthermore, according to the techniques disclosed herein, device-to-device communications can be performed that include a variable number of synchronization signal repetitions, such as after performing initial synchronization. The wireless device can determine the number of repetitions to use in a given instance based on previously received communications, such as based on measurements (e.g., signal strength, signal quality) and / or device-level experience of receiving (e.g., number of repetitions for successful detection / decoding) those previous communications, and / or based on feedback included in previous communications (e.g., an indication of the transmit power used in those communications).

[0011] Once the repetition number has been determined, the wireless device may provide a repetition number indication as part of a transmission, e.g., to assist a receiving device in determining the repetition number to use. For example, in some embodiments, different root index values ​​used with the synchronization signal may be defined to indicate different synchronization signal repetition numbers, and the root index value selected for transmission may be the root index value defined to indicate the determined repetition number.

[0012] Thus, the number of synchronization signal repetitions can be varied to account for varying link conditions between different wireless devices and / or at different times. This can, at least according to some embodiments, help wireless devices adjust their communications to provide enhanced communication when conditions are poor and avoid unnecessary power consumption and use of communication medium resources when conditions are good.

[0013] The techniques described herein may be implemented in and / or used with a number of different types of devices, including, but not limited to, cellular telephones, tablet computers, accessory and / or wearable computing devices, portable media players, cellular base stations and other cellular network infrastructure equipment, servers, and any of a variety of other computing devices.

[0014] This summary is intended to provide a brief overview of some of the subject matter described in this document. It should be understood, therefore, that the foregoing features are merely examples and should not be construed as narrowing the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following detailed description, accompanying drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A better understanding of the present subject matter may be obtained when the following detailed description of the embodiments is considered in conjunction with the following drawings.

[0016] Figure 1 An exemplary wireless communication system including an accessory device according to some embodiments is shown;

[0017] Figure 2 An example wireless communication system is shown in which two wireless devices can perform direct device-to-device communication according to some embodiments;

[0018] Figure 3 is a block diagram illustrating an exemplary wireless device according to some embodiments;

[0019] Figure 4 is a block diagram illustrating an exemplary base station according to some embodiments;

[0020] Figure 5 is a communication flow diagram illustrating an exemplary method for performing narrowband device-to-device wireless communication according to some embodiments; and

[0021] Figure 6-Figure 25 Further possible aspects and features of exemplary possible narrowband device-to-device communications according to some embodiments are shown.

[0022] While the features described herein are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereof are not intended to limit the invention to the specific forms disclosed, but on the contrary, are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims. DETAILED DESCRIPTION

[0023] Acronyms

[0024] The following acronyms are used in this disclosure.

[0025] 3GPP: Third Generation Partnership Project

[0026] 3GPP2: Third Generation Partnership Project 2

[0027] GSM: Global System for Mobile Communications

[0028] UMTS: Universal Mobile Telecommunications System

[0029] LTE: Long Term Evolution

[0030] OGRS: Off Grid Radio Service

[0031] IoT: Internet of Things

[0032] NB: Narrow Band

[0033] D2D: Device to Device

[0034] OOC: Out of Coverage

[0035] the term

[0036] The following are definitions of terms used in this disclosure:

[0037] Memory medium - any of various types of non-transitory memory devices or storage devices. The term "memory medium" is intended to include installation media, such as CD-ROMs, floppy disks, or tape devices; computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; non-volatile memory such as flash memory, magnetic media, for example, hard drives or optical storage devices; registers or other similar types of memory elements, etc. The memory medium may also include other types of non-transitory memory or a combination thereof. In addition, the memory medium may be located in the first computer system that executes the program, or may be located in a second, different computer system that is connected to the first computer system via a network such as the Internet. In the latter case, the second computer system may provide program instructions to the first computer for execution. The term "memory medium" may include two or more memory media that may reside in different locations in different computer systems connected, for example, via a network. The memory medium may store program instructions (e.g., expressed as a computer program) that may be executed by one or more processors.

[0038] Carrier Medium—storage media as described above, and physical transmission media such as a bus, network, and / or other physical transmission media that convey signals such as electrical, electromagnetic, or digital signals.

[0039] Programmable hardware elements—including various hardware devices that include multiple programmable function blocks connected via programmable interconnects. Examples include FPGAs (field programmable gate arrays), PLDs (programmable logic devices), FPOAs (field programmable object arrays), and CPLDs (complex PLDs). Programmable function blocks can vary in granularity (combinatorial logic or lookup tables) to coarse granularity (arithmetic logic units or processor cores). Programmable hardware elements may also be referred to as "configurable logic."

[0040] Computer system - any of various types of computing or processing systems, including personal computer systems (PCs), mainframe computer systems, workstations, network appliances, Internet appliances, personal digital assistants (PDAs), television systems, grid computing systems, or other devices, or combinations of devices. In general, the term "computer system" can be broadly defined to encompass any device (or combination of devices) having at least one processor that executes instructions from a memory medium.

[0041] User Equipment (UE) (or "UE device") - any of various types of computer systems or devices that may be mobile or portable and that perform wireless communications. Examples of UE devices include mobile phones or smartphones (e.g., iPhones). TM , based on Android TMphones), portable gaming devices (e.g., Nintendo DS TM PlayStation Portable TM 、Gameboy Advance TM , iPhone TM ), laptops, wearable devices (e.g., smart watches, smart glasses), PDAs, portable Internet devices, music players, data storage devices or other handheld devices, etc. In general, the term "UE" or "UE device" can be broadly defined to cover any electronic device, computing device and / or telecommunication device (or combination of devices) that can be easily transported by a user and capable of wireless communication.

[0042] Wireless Device – Any of various types of computer systems or devices that perform wireless communications. A wireless device may be portable (or mobile), or may be fixed or stationary at a location. A UE is an example of a wireless device.

[0043] Communication Device – Any of various types of computer systems or devices that perform communication, either wired or wireless. A communication device may be portable (or mobile), or fixed or stationary at a location. A wireless device is an example of a communication device. A UE is another example of a communication device.

[0044] Base Station—The term “base station” (also referred to as “eNB”) has the full breadth of its ordinary meaning and includes at least a wireless communication station installed at a fixed location and used to communicate as part of a wireless cellular communication system.

[0045] Link budget limited – includes the full scope of its ordinary meaning and includes at least a characteristic of a wireless device (e.g., UE) that exhibits limited communication capabilities or limited power relative to devices that are not link budget limited or relative to devices for which a radio access technology (RAT) standard has been developed. A link budget limited wireless device may experience relatively limited receive capability and / or transmit capability, which may be due to one or more factors, such as device design, device size, battery size, antenna size or design, transmit power, receive power, current transmission medium conditions, and / or other factors. Such devices may be referred to herein as “link budget limited” (or “link budget constrained”) devices. A device may be inherently link budget limited due to the size of the device, battery power, and / or transmit / receive power. For example, a smartwatch communicating with a base station via LTE or LTE-A may be inherently link budget limited due to its reduced transmit / receive power and / or antenna reduction. Wearable devices such as smartwatches are generally link budget limited devices. Alternatively, a device may not be inherently link budget limited, e.g., may have sufficient size, battery power, and / or transmit / receive power for normal communication over LTE or LTE-A, but may be temporarily link budget limited due to current communication conditions, e.g., a smartphone located at a cell edge, etc. It is noted that the term "link budget limited" includes or encompasses power limitations, and thus a power limited device may be considered a link budget limited device.

[0046] Processing element (or processor) – refers to various elements or combinations of elements. Processing elements include, for example, circuits such as ASICs (application-specific integrated circuits), portions or circuits of individual processor cores, entire processor cores, individual processors, programmable hardware devices such as field-programmable gate arrays (FPGAs), and / or larger portions of systems including multiple processors.

[0047] Automatic – refers to an action or operation performed by a computer system (e.g., software executed by the computer system) or a device (e.g., a circuit, a programmable hardware element, an ASIC, etc.) without requiring user input to directly specify or execute the action or operation. Thus, the term "automatic" is in contrast to manual execution or specification of an action by a user, where the user provides input to directly execute the action. An automatic process may be initiated by input provided by a user, but the subsequent actions performed "automatically" are not specified by the user, that is, they are not performed "manually," where the user specifies each action to be performed. For example, a user filling out an electronic form by selecting each field and providing input specifying information (e.g., by typing in information, selecting checkboxes, selecting radios, etc.) is manually filling out the form, even though the computer system must update the form in response to the user's actions. The form can be automatically filled out by a computer system, where the computer system (e.g., software executed on the computer system) analyzes the fields of the form and fills it out without requiring any user input specifying the answers to the fields. As indicated above, a user can invoke automatic filling of a form without participating in the actual filling out of the form (e.g., the user does not manually specify the answers to the fields; they are automatically completed). This specification provides various examples of operations that are automatically performed in response to actions that a user has taken.

[0048] Configured to - Various components may be described as being "configured to" perform one or more tasks. In such contexts, "configured to" is a broad expression that generally means "having a structure" to perform one or more tasks during operation. Thus, a component can be configured to perform a task even when the component is not currently performing the task (e.g., a set of electrical conductors can be configured to electrically connect a module to another module even when the two modules are not connected). In some contexts, "configured to" can be a broad expression that generally means "having a circuit" to perform one or more tasks during operation. Thus, a component can be configured to perform a task even when the component is not currently turned on. Generally, the circuitry that forms the structure corresponding to "configured to" may include hardware circuitry.

[0049] For ease of description, various components may be described as performing one or more tasks. Such descriptions should be interpreted as including the phrase "configured to." Representing a component as being configured to perform one or more tasks expressly does not invoke the interpretation of 35 USC § 112, sixth paragraph, on that component.

[0050] Figure 1-Figure 2 -Wireless communication system

[0051] Figure 1 An example of a wireless cellular communication system is illustrated. It should be noted that Figure 1This represents one possibility among many, and the features of the present disclosure may be implemented by any of a variety of systems as desired. For example, the embodiments described herein may be implemented in any type of wireless device.

[0052] As shown, the exemplary wireless communication system includes a cellular base station 102 that communicates over a transmission medium with one or more wireless devices 106A, 106B, etc., and an accessory device 107. Wireless devices 106A, 106B, and 107 may be user equipment, which may be referred to herein as "user equipment" (UE) or UE devices.

[0053] Base station 102 may be a base transceiver station (BTS) or a cell site and may include hardware that enables wireless communications with UE devices 106A, 106B, and 107. Base station 102 may also be equipped to communicate with network 100 (e.g., a core network of a cellular service provider, a telecommunications network such as a public switched telephone network (PSTN), and / or the Internet, among other possibilities). Thus, base station 102 may facilitate communications between UE devices 106 and 107 and / or between UE devices 106 / 107 and network 100. In other implementations, base station 102 may be configured to provide communications via one or more other wireless technologies, such as an access point supporting one or more WLAN protocols, such as 802.11a, b, g, n, ac, ad, and / or ax, or LTE in the unlicensed band (LAA).

[0054] The communication area (or coverage area) of the base station 102 may be referred to as a “cell.” The base station 102 and the UEs 106 / 107 may be configured to communicate over a transmission medium using any of various radio access technologies (RATs) or wireless communication technologies, such as GSM, UMTS (WCDMA, TDS-CDMA), LTE, LTE-Advanced (LTE-A), NR, OGRS, HSPA, 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, etc.

[0055] Thus, base station 102 and other similar base stations (not shown) operating according to one or more cellular communication technologies can be provided as a cell network that can provide continuous or nearly continuous overlapping service to UE devices 106A-N and 107 and similar devices within a geographic area via one or more cellular communication technologies.

[0056] It should be noted that, at least in some cases, UE devices 106 / 107 may be capable of communicating using any of a variety of wireless communication technologies. For example, UE devices 106 / 107 may be configured to communicate using one or more of GSM, UMTS, CDMA2000, LTE, LTE-A, NR, OGRS, WLAN, Bluetooth, one or more global navigation satellite systems (GNSS, such as GPS or GLONASS), one and / or more mobile television broadcast standards (e.g., ATSC-M / H), etc. Other combinations of wireless communication technologies (including more than two wireless communication technologies) may also be used. Similarly, in some cases, UE devices 106 / 107 may be configured to communicate using only a single wireless communication technology.

[0057] UEs 106A and 106B may comprise handheld devices such as smartphones or tablets, and / or may comprise any of various types of devices with cellular communication capabilities. For example, one or more of UEs 106A and 106B may be wireless devices intended for static or dynamic deployment, such as appliances, measurement devices, control devices, and the like. UE 106B may be configured to communicate with a UE device 107, which may be referred to as an accessory device 107. Accessory device 107 may be any of various types of wireless devices, typically wearable devices with a smaller form factor and limited battery, output power, and / or communication capabilities relative to UE 106. As a common example, UE 106B may be a smartphone carried by a user, and accessory device 107 may be a smartwatch worn by the same user. UE 106B and accessory device 107 may communicate using any of various short-range communication protocols, such as Bluetooth or Wi-Fi.

[0058] UE 106B may also be configured to communicate with UE 106A. For example, UE 106A and UE 106B may be capable of performing direct device-to-device (D2D) communications. D2D communications may be supported by cellular base station 102 (e.g., BS 102 may facilitate discovery, as well as various possible forms of assistance), or may be performed in a manner not supported by BS 102. For example, according to at least some aspects of the present disclosure, UE 106A and UE 106B may be able to arrange and perform narrowband D2D communications (e.g., including narrowband D2D discovery communications) even when out of coverage of BS 102 and other cellular base stations.

[0059] Figure 2Example UE devices 106A, 106B are shown in D2D communication with each other. The UE devices 106A, 106B may be mobile phones, tablets or any other type of handheld device, smart watches or other wearable devices, media players, computers, laptops, or virtually any type of wireless device.

[0060] UE 106A, 106B may each include a device or integrated circuit called a cellular modem for facilitating cellular communications. The cellular modem may include one or more processors (processing elements) and various hardware components as described herein. UE 106A, 106B may each perform any of the method implementations described herein by executing instructions on one or more programmable processors. Alternatively or in addition, the one or more processors may be one or more programmable hardware elements, such as an FPGA (field programmable gate array) or other circuitry configured to perform any of the method implementations described herein or any part of any of the method implementations described herein. The cellular modem described herein may be used in a UE device as defined herein, a wireless device as defined herein, or a communication device as defined herein. The cellular modem described herein may also be used in a base station or other similar network-side device.

[0061] UE 106A, 106B may include one or more antennas for communicating using two or more wireless communication protocols or radio access technologies. In some embodiments, one or both of UE 106A or UE 106B may be configured to communicate using a single shared radio component. The shared radio component may be coupled to a single antenna, or may be coupled to multiple antennas (e.g., for MIMO) for performing wireless communications. Alternatively, UE 106A and / or UE 106B may include two or more radio components. Other configurations are also possible.

[0062] Figure 3 –Block diagram of UE equipment

[0063] Figure 3A possible block diagram of a UE device, such as UE device 106 or 107, is shown. As shown, UE device 106 / 107 may include a system-on-chip (SOC) 300, which may include components for various purposes. For example, as shown, SOC 300 may include display circuitry 304, which may perform graphics processing and provide display signals to a display 360, and one or more processors 302, which may execute program instructions for UE device 106 / 107. SOC 300 may also include motion sensing circuitry 370, which may detect motion of UE 106 using, for example, a gyroscope, an accelerometer, and / or any of various other motion sensing components. The one or more processors 302 may also be coupled to a memory management unit (MMU) 340, which may be configured to receive addresses from the one or more processors 302 and translate these addresses into locations in memory (e.g., memory 306 and read-only memory (ROM) 350, flash memory 310). MMU 340 may be configured to perform memory protection and page table translation or setup. In some embodiments, MMU 340 may be included as part of one or more processors 302 .

[0064] As shown, the SOC 300 may be coupled to various other circuits of the UE 106 / 107. For example, the UE 106 / 107 may include various types of memory (e.g., including NAND flash memory 310), a connector interface 320 (e.g., for coupling to a computer system, a docking station, a charging station, etc.), a display 360, and wireless communication circuitry 330 (e.g., for LTE, LTE-A, NR, OGRS, CDMA2000, Bluetooth, Wi-Fi, NFC, GPS, etc.).

[0065] The UE device 106 / 107 may include at least one antenna and, in some embodiments, may include multiple antennas 335a and 335b for performing wireless communications with a base station and / or other devices. For example, the UE device 106 / 107 may use antennas 335a and 335b to perform wireless communications. As noted above, the UE device 106 / 107 may, in some embodiments, be configured to perform wireless communications using multiple wireless communication standards or radio access technologies (RATs).

[0066] Wireless communication circuitry 330 may include Wi-Fi logic 332, a cellular modem 334, and Bluetooth logic 336. Wi-Fi logic 332 is configured to enable UE device 106 / 107 to perform Wi-Fi communications via an 802.11 network. Bluetooth logic 336 is configured to enable UE device 106 / 107 to perform Bluetooth communications. Cellular modem 334 may be a relatively low-power cellular modem capable of performing cellular communications according to one or more cellular communication technologies.

[0067] As described herein, UE 106 / 107 may include hardware components and software components for implementing embodiments of the present disclosure. For example, one or more components of the wireless communication circuitry 330 (e.g., cellular modem 334) of the UE device 106 / 107 may be configured to implement part or all of the methods described herein, for example, by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium), a processor configured as an FPGA (field programmable gate array), and / or a processor using dedicated hardware components that may include an ASIC (application-specific integrated circuit).

[0068] Figure 4 –Block diagram of a base station

[0069] Figure 4 An example block diagram of a base station 102 according to some embodiments is shown. Note that Figure 4 The base station 102 is only one example of a possible base station. As shown, the base station 102 may include one or more processors 404 that may execute program instructions for the base station 102. The one or more processors 404 may also be coupled to a memory management unit (MMU) 440, which may be configured to receive addresses from the one or more processors 404 and translate these addresses into locations in memory (e.g., memory 460 and read-only memory (ROM) 450) or other circuits or devices.

[0070] The base station 102 may include at least one network port 470. Figure 1 and Figure 2 As described in , the network port 470 can be configured to couple to a telephone network and provide multiple devices, such as the UE devices 106 / 107 , with access to the telephone network.

[0071] The network port 470 (or an additional network port) may also or alternatively be configured to couple to a cellular network, such as a core network of a cellular service provider. The core network may provide mobility-related services and / or other services to a plurality of devices, such as the UE devices 106 / 107. For example, the core network may include, for example, a mobility management entity (MME) for providing mobility management services, a serving gateway (SGW) and / or a packet data network gateway (PGW) for providing external data connections, such as to the Internet, and the like. In some cases, the network port 470 may be coupled to a telephone network via the core network, and / or the core network may provide a telephone network (e.g., between other UE devices served by the cellular service provider).

[0072] Base station 102 may include at least one antenna 434 and possibly multiple antennas. One or more antennas 434 may be configured to operate as a wireless transceiver and may be further configured to communicate with UE devices 106 / 107 via radio 430. One or more antennas 434 communicate with radio 430 via communication chain 432. Communication chain 432 may be a receive chain, a transmit chain, or both. Radio 430 may be configured to communicate via various wireless communication standards, including but not limited to LTE, LTE-A, NR, OGRS, GSM, UMTS, CDMA2000, Wi-Fi, and the like.

[0073] Base station 102 may be configured to communicate wirelessly using multiple wireless communication standards. In some cases, base station 102 may include multiple radio components that enable base station 102 to communicate according to multiple wireless communication technologies. For example, as one possibility, base station 102 may include an LTE radio component for communicating according to LTE and a Wi-Fi radio component for communicating according to Wi-Fi. In this case, base station 102 may be capable of operating as both an LTE base station and a Wi-Fi access point. As another possibility, base station 102 may include a multimode radio component capable of communicating according to any of multiple wireless communication technologies (e.g., LTE and Wi-Fi, LTE and UMTS, LTE and CDMA2000, UMTS and GSM, etc.).

[0074] As further described later herein, BS 102 may include hardware components and software components for implementing or supporting the implementation of the features described herein. For example, although many of the features described herein relate to device-to-device communication that can be performed by a UE device without relying on a base station, a cellular base station may be configured to also be able to perform device-to-device communication according to the features described herein. As another possibility, BS 102 may be used to configure UE 106 to perform narrowband device-to-device communication according to the features described herein, and / or certain features described herein may be performed or not performed by the device based at least in part on whether BS 102 is present within the device range to provide cellular service. According to some embodiments, the processor 404 of the base station 102 may be configured to implement part or all of the methods described herein, for example, by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). Alternatively, the processor 404 may be configured as a programmable hardware element such as an FPGA (field programmable gate array) or as an ASIC (application-specific integrated circuit) or a combination thereof. Alternatively (or additionally), in conjunction with one or more of the other components 430 , 432 , 434 , 440 , 450 , 460 , 470 , the processor 404 of the BS 102 may be configured to implement or support some or all of the features described herein or support implementation of some or all of the features described herein.

[0075] Figure 5 -Communication Flow Chart

[0076] Figure 5 A communication flow diagram illustrating a method for performing narrowband device-to-device wireless communication according to some embodiments is provided. In various embodiments, some of the method elements shown may be performed simultaneously in a different order than shown, may be replaced by other method elements, or may be omitted. Additional method elements may also be performed as needed.

[0077] Figure 5 Aspects of the method may be performed by a wireless device such as in Figure 1-Figure 3 Shown in and relative to Figure 1-Figure 3 The described UE 106A-B or UE 107 can be implemented, or more generally, can be implemented in other devices in combination with any of the computer systems or devices shown in the above figures as needed. It should be noted that although the communication technology and / or features associated with LTE, OGRS and / or 3GPP specification documents are described in a manner related to the use of the communication technology and / or features associated with LTE, OGRS and / or 3GPP specification documents, Figure 5 At least some elements of the method, but such description is not intended to limit the present disclosure and can be used in any suitable wireless communication system as needed Figure 5 Aspects of the Method: As shown, the method may operate as follows.

[0078] At 502, a first wireless device (e.g., UE 106A) may determine a number of synchronization signal repetitions to transmit as part of narrowband D2D / P2P communication. The communication may be performed using one or more narrowband Internet of Things (NB-IoT) carriers and / or may be performed using any of a variety of other possible (e.g., narrowband) carriers.

[0079] In some embodiments, a synchronization signal repetition number may be determined based at least in part on characteristics of a transmission previously received by the first wireless device from a second wireless device (e.g., a wireless device targeted by the narrowband P2P communication, such as UE 106B). For example, the first wireless device may estimate a number of repetitions that may be required by the second device to successfully detect and / or decode the narrowband P2P communication based on the signal strength, signal quality, and / or number of repetitions of the previously received transmission used by the first wireless device to detect and / or decode the narrowband P2P communication. As another possibility (e.g., if the first wireless device does not have any (e.g., sufficiently recent) previous communication to estimate a number of repetitions that may be required by the second device to successfully detect and / or decode the narrowband P2P communication), the first wireless device may conservatively select the synchronization signal repetition number (e.g., may select a configured maximum number of repetitions), may arbitrarily select the number of repetitions, or may select the number of repetitions in any other desired manner.

[0080] Narrowband P2P communication can be any of various types of communication. As one possibility, narrowband P2P communication can include discovery messages in addition to synchronization signals and can be discovery transmissions, e.g., for discovering other wireless devices and potentially establishing one or more P2P communication links with those wireless devices. As another possibility, narrowband P2P communication can be control and / or data communication, e.g., for transmitting control signaling and / or data between two wireless devices that have established a P2P communication link.

[0081] In 504, the first wireless device may perform narrowband P2P communication using the determined number of synchronization signal repetitions. At least in the case of discovery transmissions, the first wireless device may transmit repetitions of narrowband P2P communication on each frequency in a predetermined sequence of discovery transmission frequencies. The discovery transmission frequency sequence may be associated with a scan channel used by the first wireless device. The scan channel may be determined at least in part based on a public MAC address associated with the scan channel, such that other wireless devices that utilize the same public MAC address to select a scan channel for their discovery signaling may also select the same scan channel. As another possibility, the discovery transmission frequency sequence may be associated with a paging channel of a wireless device (e.g., a second wireless device) for which the discovery transmission is intended. In some embodiments, the paging channel associated with a wireless device may be determined based on the device's MAC address. As another possibility, the discovery transmission frequency sequence may be associated with a paging channel of a group of wireless devices (e.g., including the second wireless device) for which the discovery transmission is intended. For example, in some embodiments, a group of wireless devices may determine a group MAC address, which may be used to determine a group paging channel that may be monitored by group members.

[0082] The timing of the discovery transmissions (e.g., including when each discovery transmission repetition is to be transmitted and on which frequency in the discovery transmission frequency sequence) may be based at least in part on a local clock of the first wireless device. For example, depending on the P2P communication system in which the first wireless device operates, a set of discovery transmission repetitions may be performed once per "discovery cycle" (e.g., up to a specified number of discovery cycles), and the start and end times of each discovery cycle and / or the times of the set of discovery transmission repetitions within each discovery cycle may be based on a value of the local clock of the wireless device performing the discovery transmissions.

[0083] As previously described, in addition to the discovery message, each discovery transmission repetition may also include a selected number of synchronization signal repetitions. According to some embodiments, for example, a root index value of at least a portion of the synchronization signal may be used to indicate the number of synchronization signal repetitions to be used. For example, the synchronization signal may include a primary synchronization signal (PSS), and a root index value of a Zadoff-Chu sequence that may be used as the PSS may be used to indicate the number of synchronization signal repetitions to be used. Thus, in such cases, the root index value of the PSS may be selected by the first wireless device based on the selected number of synchronization signal repetitions.

[0084] According to some embodiments, the synchronization signal may further include a secondary synchronization signal (SSS), which may further include a Zadoff-Chu sequence. If desired, a root index value of the Zadoff-Chu sequence that may be used as the SSS may be used to provide a device identifier for the first wireless device.

[0085] According to some embodiments, the synchronization signal may also include a physical broadcast channel indicating a frame number and / or a subframe number according to a local clock of the first wireless device.

[0086] The second wireless device may receive narrowband P2P communications from the first wireless device. At 506, the second wireless device may determine a synchronization signal repetition count for the narrowband P2P communications received from the first wireless device. For example, as previously described, a root index value for a portion of the synchronization signal may indicate a synchronization signal repetition count for the narrowband P2P communications, such that the second wireless device may determine the synchronization signal repetition count based at least in part on the root index value for the particular portion of the synchronization signal. Based on the synchronization signal repetition count, the second wireless device may then determine when the portion of narrowband P2P communications following the synchronization signal begins.

[0087] As previously mentioned, in at least some instances, narrowband P2P communications may include discovery messages. Thus, in such instances, the second wireless device may attempt to decode the discovery message, for example, to determine whether the second wireless device is a discovery target of the first wireless device.

[0088] If the second wireless device is unable to successfully decode the discovery message, the wireless device may combine the discovery message with one or more additional discovery messages subsequently transmitted by the first wireless device. For example, the second wireless device may continue to monitor the same frequency on which the narrowband P2P communication from the first wireless device was received and may receive additional such narrowband P2P communications from the first wireless device in the next discovery window. As another possibility, the second wireless device may determine a discovery transmission frequency sequence used by the first wireless device (e.g., based at least in part on a synchronization signal portion of the narrowband P2P communication) and may follow the discovery transmission frequency sequence and receive one or more additional repetitions of the discovery transmission on other frequencies of the discovery transmission frequency sequence, e.g., in the same discovery window and / or subsequent discovery windows. Combining such repetitions may improve the effective SNR, thereby increasing the likelihood of successfully decoding the (combined) discovery message.

[0089] If the attempt to decode the discovery message is (e.g., ultimately) successful, and the second wireless device is a discovery target indicated in the discovery message, the second wireless device may perform a discovery response transmission in response to the discovery message. Similar to the discovery transmission, the discovery response transmission may include a number of repetitions for transmission on each frequency in the discovery response transmission frequency sequence. The discovery response frequency sequence may be determined at least in part based on the discovery transmission. For example, the synchronization signal and / or the discovery message may include information indicating the discovery response frequency sequence and / or information that can be used to determine the discovery response frequency sequence. In some instances, the discovery response frequency sequence may be the same frequency sequence as the discovery transmission frequency sequence.

[0090] The discovery response transmission may include a preamble. The second wireless device may determine a number of repetitions of the preamble to include in the discovery response transmission, for example, in a manner similar to how the first wireless device determines a number of synchronization signal repetitions to transmit. For example, the number of preamble repetitions may be selected based at least in part on an estimate of a number of repetitions that may be required by the first wireless device to detect and decode the discovery response transmission, which in turn may be based at least in part on a signal strength and / or quality of one or more narrowband P2P communications received from the first wireless device, and / or a number of narrowband P2P communication repetitions used by the second wireless device to successfully detect and decode the discovery transmission. According to at least some embodiments, the second wireless device may select a root index value for the preamble based on the determined number of repetitions, for example, to provide an indication of the number of preamble repetitions.

[0091] The discovery response transmission may be a response used to assist the first wireless device in tracking the second wireless device and / or may include a connection request message. In either case, according to at least some embodiments, the discovery response transmission may include a device identifier (e.g., a MAC address or an indication thereof) of the second wireless device and an indication of the local clock value of the second wireless device. If the discovery response transmission includes a connection request message, the second wireless device may synchronize with the local clock of the first wireless device (e.g., the first wireless device may be considered the master device with respect to the P2P connection between the first wireless device and the second wireless device), or the first wireless device may synchronize with the local clock of the second wireless device (e.g., the second wireless device may be considered the master device with respect to the P2P connection between the first wireless device and the second wireless device). In either case, the first wireless device may provide an acknowledgment to the second wireless device, but the timing of the acknowledgment and / or the frequency of providing the acknowledgment may vary depending on which wireless device is determined to be the master device.

[0092] As part of establishing a P2P connection between a first wireless device and a second wireless device, the devices may establish an initial anchor point and an anchor point periodicity that can be used to ensure that the connection remains current. For example, the anchor point periodicity can define a maximum length of time that the first wireless device and the second wireless device can operate without communicating and still be considered to have a valid P2P connection. If desired, the anchor point periodicity can be used as an efficient method to provide connected mode discontinuous reception (C-DRX) functionality, for example, allowing each device to enter a reduced power state between anchor points (e.g., unless other wireless communication operations are required) and wake up at each anchor point to transmit to and / or receive from the other wireless device.

[0093] Note that although Figure 5The method primarily relates to narrowband P2P communication between two wireless devices, but similar techniques can be used to establish and communicate based on any number of additional P2P connections between the wireless devices. For example, either or both the first wireless device and the second wireless device can utilize similar techniques to establish additional P2P connections with one or more other wireless devices, and communicate with the other wireless devices based on these additional P2P connections, the one or more other wireless devices being connected in parallel with the P2P communication links.

[0094] Figure 6-Figure 14 and additional information

[0095] Provided Figure 6-Figure 14 and the additional information below, which illustrates the Figure 5 Further considerations and possible specific implementation details of the method are not intended to limit the present disclosure as a whole. Various variations and alternatives to the details provided below are possible and should be considered to fall within the scope of the present disclosure.

[0096] At least some existing wireless communication technologies include framework elements for device-to-device communication, also known as sidelink communication. For example, the 3GPP standards organization includes D2D / sidelink protocols such as Proximity Services (ProSe), in which, in addition to synchronization signals transmitted in the central 6 RBs of the system bandwidth, discovery pool resources, sidelink control channel allocations, and sidelink shared channel allocations can be located in various other (e.g., outer) RBs of the system bandwidth over time. Such sidelink communication performed according to existing D2D protocols can cover relatively wideband operation, for example, covering at least 6 RBs (e.g., 1.4 MHz) and potentially up to 100 RBs (e.g., 20 MHz).

[0097] Figure 6 Possible synchronization subframe formats that can be used with D2D / sidelink communications according to some embodiments are shown. As shown, the synchronization subframe may include two types of synchronization signals and reference signals (e.g., demodulation reference symbols or DM-RS). The synchronization signal may include a side link synchronization signal (SLSS) (e.g., primary side link synchronization signal (PSSS), secondary side link synchronization signal (SSSS)), which can be used to acquire / maintain time and frequency synchronization. The synchronization signal may also include a master information block SL (MIB-SL) on the physical side link broadcast channel, which may provide at least frame and subframe numbers. Each given synchronization window / period (e.g., 40ms or any other desired length) may be transmitted once with a configurable offset. According to some embodiments, the SLSS may be transmitted in combination with data transmission in the SL-SCCH period, and the SLSS may also be transmitted in combination with discovery transmissions in the discovery period.

[0098] Figure 7Possible resource pool configurations that can be used with D2D / sidelink communications according to some embodiments are shown. According to at least some embodiments, a wireless device may have multiple resource pools for SL transmission and multiple resource pools for receiving SL communications. The resource pools may include a synchronization configuration period, an SL control period, and a set of subframes and resource blocks. The synchronization configuration may include a synchronization subframe that indicates the frame and subframe timing of the SL control period. The SL control period may include a set of subframes (e.g., one or more subframe bitmaps) and may be divided into two regions, namely a control region and a data region. The SC period may start at an offset of SFN=0 and may be repeated periodically with a configurable length (e.g., between 40ms and 320ms, or any other desired range). The control region may include a subframe bitmap that indicates candidate subframes that can be used for physical sidelink control channel communications. The data region may start after the control region and may include another bitmap ("T_RPT") indicating subframes that can be used for data transmission. This bitmap may repeat until the end of the SC period.

[0099] Sidelink Control Information (SCI) may be transmitted in the candidate PSCCH region as two identical transmissions, e.g., occupying a pair of resource blocks but in different frames. According to at least some embodiments, the SCI may be transmitted using QPSK modulation. As one possibility for selecting when to transmit the SCI, in a wireless device autonomous selection mode, the wireless device may select a subframe for SCI transmission in a random manner from a configured resource pool. According to some embodiments, the SCI may provide resource block allocations for the data region, a time resource pattern indicating the subframes used for the data region, a modulation and coding scheme, and a group designation ID (e.g., the 8 least significant bits of the ProSe Layer 2 group ID).

[0100] A Media Access Control (MAC) Protocol Data Unit (PDU) may be transmitted in the indicated Physical Sidelink Shared Channel (PSSCH) region. The MAC PDU may be sent as one transport block within one subframe and may be retransmitted three times, with each transmission having a different redundancy version according to a fixed pattern. When there is more data to send after this transmission, the wireless device may create another MAC PDU to be sent on the next four available subframes in the data region. The MAC PDU may have an SL-SCH subheader that may indicate the transmitting wireless device (e.g., a 24-bit source ID) and its intended group ID (e.g., the 16 least significant bits of the ProSe Layer 2 group ID).

[0101] Figure 8The figure shows a possible distribution of different resource pools between devices in different service areas that can be used with D2D / sidelink communication according to some embodiments. As shown, some TX and RX pools can be configured within a single cell (e.g., within cell 1 802). For communication between wireless devices in the same service cell, it may be the case that all TX and RX pools can use the synchronization signal of the service cell. As further shown, some associated TX and RX pools can also be configured in different service cells (e.g., some RX pools in cell 1 802 can be associated with TX pools in cell 2 804 and cell 3 806). For communication between wireless devices in different cells or outside of coverage, transmissions from the TX pool may need to include associated synchronization signals; reception on the RX pool may also require its associated synchronization signal. Providing multiple such TX and RX pools with different synchronization configurations can facilitate communication between wireless devices in different cells or outside of coverage.

[0102] Figure 9 Possible discovery cycles that may be used with D2D / sidelink communications according to some embodiments are shown. Sidelink discovery may include a wireless device repeatedly broadcasting a short, fixed-size message on a physical sidelink discovery channel (PSDCH) that may be directly detected by other nearby wireless devices. According to some embodiments, a fixed-size payload of 232 bits may be used for PSDCH communications. A receiving device may search for PSDCH communications in a discovery resource pool. The PSDCH subframe pool may be indicated by a periodic repetition of a subframe bitmap. The PSDCH resource block pool may include two sets of frequency-contiguous resource blocks. In at least some instances, a wireless device may autonomously select a set of subframes and resource blocks for discovery transmissions from a configured resource pool. A PSDCH transmission block may be transmitted over N+1 consecutive subframes within the discovery subframe pool; within each subframe, two frequency-contiguous resource blocks from the resource block pool may be used for discovery transmissions, with the resource blocks varying from subframe to subframe.

[0103] While such a potential wideband D2D framework may be useful in some instances, more narrowband deployments may be advantageous in at least some instances. For example, for the transmission power mechanisms of many devices, the propagation characteristics used for narrowband communication may result in greater range capacity than wideband communication. It is noted that, at least in some instances, the effective communication range may be further increased if a lower frequency communication band (e.g., as one possibility, 900 MHz unlicensed spectrum) is used for narrowband D2D communication. As another possibility, some (e.g., lower complexity) devices may be configured to perform only narrowband communication (e.g., may have RF front-end limitations, and / or may have battery limitations that functionally limit the ability to perform wider bandwidth communication). As another possibility, some devices, even if capable of both wideband and narrowband communication, may prefer to perform narrowband communication when possible, for example, if narrowband communication reduces device power consumption.

[0104] Thus, at least according to some embodiments, features for supporting narrowband (e.g., 180 kHz) D2D communications are also described herein. According to some embodiments, the techniques described herein can be used when one or more of the communicating wireless devices are not within the communication range of a cellular base station (e.g., the devices may be OOC).

[0105] For example, an Off-Grid Radio Service (OGRS) is a system developed to provide remote peer-to-peer (P2P) / D2D communications, e.g., in the absence of a wide area network (WAN) or WLAN radio connection, to support a variety of possible features. According to at least some embodiments, the OGRS system may support the previously described features with respect to Figure 5 Some or all of the features described.

[0106] According to some embodiments, the OGRS may operate in the unlicensed low ISM band, for example, between 700 MHz and 1 GHz, for extended range purposes, and may use one or more carriers of approximately 200 kHz. The OGRS may be designed to meet local spectrum regulatory requirements, such as channel duty cycle, operating frequency, frequency hopping pattern, LBT, maximum transmit power, and occupied bandwidth.

[0107] As one possibility for providing a physical narrowband carrier for narrowband D2D communications, an NB-IoT carrier can be used. According to some embodiments, the NB-IoT carrier can be configured for standalone deployment (e.g., in a repurposed global mobile communication standard frequency band), guard band deployment (e.g., in a guard band frequency between LTE carriers), and in-band deployment (e.g., within an LTE carrier). Alternatively, the NB-IoT carrier can be utilized in unlicensed bands, for example, in an OGRS environment. In any of these possible deployment modes, the NB-IoT carrier can include a number of key features. For example, according to some embodiments, among various possible features, the NB-IoT carrier may support flexible timelines for control and data channels; may support peak rates of approximately 20 kbps in the downlink and 60 kbps in the uplink; may use single-tone (e.g., 3.75 kHz and 15 kHz) and multi-tone (15 kHz) uplink modulation using pi / 2 binary phase shift keying or pi / 4 quadrature phase shift keying (quadrature phase shift keying may also be used in the downlink); may use a single antenna, half-duplex frequency division multiplexing; and / or may use a carrier bandwidth of 180 kHz per UE. Frequency hopping features for D2D communications may be supported. In some cases, the NB-IoT carrier may provide a coverage enhancement feature for supporting up to 20 dB of coverage.

[0108] Any of a variety of features may be included in the OGRS system, including when operating in regulated unlicensed spectrum, such as the unlicensed 900 MHz spectrum. For example, frequency hopping spectrum (FHSS) may be used. Channel carrier frequencies may be separated by frequency hopping channels of a minimum of 25 kHz or 20 dB bandwidth, whichever is greater. If the 20 dB bandwidth is less than 250 kHz (e.g., this may be the case if an NB-IoT carrier is used), the system may use at least 50 channels. In this case, the average dwell time on a particular channel may not exceed 400 ms over a 20 second period (e.g., duty cycle <= 2%), and / or the transmit power may be limited to 30 dBm. If the 20 dB bandwidth is 250 kHz or greater, the system may use at least 25 channels. In this case, the average dwell time on a particular channel may not exceed 400 ms over a 10 second period (e.g., duty cycle <= 4%), and / or the transmit power may be limited to 24 dBm. For example, the following table illustrates a possible set of specified characteristics for OGRS operation, depending on the 20dB bandwidth of the frequency hopping channel used:

[0109] bandwidth Channel TX power Opening time Dwell time <250KHz >＝50 30dBm 400 milliseconds 20 seconds >250KHz >＝25 24dBm 400 milliseconds 10 seconds

[0110] Thus, as an example possibility, if the unlicensed 900MHz spectrum band (US ISM 900, 902-918MHz) is used with an NB-IoT carrier (e.g., each with 200kHz, including guard bands), a pool of 80 frequencies may be configured. In other configurations, there may be a pool of 130 frequencies spanning 902-928MHz. Other frequency pools are also possible, e.g., with other numbers of available frequencies. If desired, various sets of these frequencies may be configured as "scan channels" and "paging channels," which may be used for discovery and / or other purposes.

[0111] For example, the scanned channels may be a sequence of a desired number of frequencies S (e.g., S=4, or any other desired number that meets the desired duty cycle requirements when combined with other system parameters), which may be randomly selected from a frequency pool based on a seed number.

[0112] Similarly, the paging channel may be a sequence of a desired number of frequencies N (eg, N=4, or any other desired number that meets the desired duty cycle requirements when combined with other system parameters) that are randomly selected from a pool of frequencies based on a seed number.

[0113] According to some embodiments, each OGRS UE may also be assigned an OGRS MAC address, such as a 24-bit hash ID. Thus, as one possibility, the individual MAC addresses of the OGRS UEs may be used as a seed to determine the paging channel used by the UE. As another possibility, a group of UEs may have a group MAC address that may serve as a group ID and may be used as a seed to determine the paging channel used by the UE. Furthermore, one or more public MAC addresses may be defined. In at least some instances, the UE may use a MAC address selected from the set of public MAC addresses as a seed number to determine the scanning channel used by the wireless device.

[0114] In addition, each OGRS UE may have its own OGRS clock counter ("K_native"), such as a 28-bit counter with a clock frequency of 1 ms per subframe. If desired, a frame may be defined as 10 subframes, and a superframe may be defined as 1024 frames. The value of K_native may be set to a random number upon initialization.

[0115] When operating in discontinuous reception (DRX) mode on a scanning channel, the UE may select a frequency ("F_scan") from a sequence of frequencies for the scanning channel based on its own local clock K_native, and may scan the frequencies F_scan for a specific portion of each DRX cycle, while typically operating in a reduced power consumption state for most or all of the remainder of the discovery period (e.g., unless other scanning channels or paging channels are also monitored, or another activity is otherwise performed between the DRX on-durations). In accordance with some embodiments, the on-duration length may be set to a length equal to or greater than the discovery period length. As an example, using the example values ​​provided previously, if the discovery message transmission time on one hop frequency is 40ms and the duty cycle is 2%, then the discovery period may be 2s; in this case, the DRX cycle period may be 60s and the on-duration portion may be 2s.

[0116] Similarly, when operating in DRX mode on a paging channel, the UE may select a frequency ("F_scan") from a frequency sequence of the paging channel based on its own local clock K_native, and may scan the frequencies F_scan for a specific portion of each DRX cycle, while typically operating in a reduced power consumption state for most or all of the remainder of the discovery cycle. According to some embodiments, the length of the on-duration for monitoring the paging channel may also be set to a length equal to or greater than the length of the discovery cycle. For example, if desired, a DRX cycle similar to that for the scanning channel may be used (e.g., a DRX cycle period of 60s and an on-duration portion of 2s). It is noted that, if desired, the UE may operate in parallel in DRX with respect to multiple scanning / paging channels. For example, according to some embodiments, the UE may simultaneously monitor a scanning channel (e.g., listening for discovery messages from UEs on an unknown UE paging channel) and a paging channel (e.g., listening for discovery messages from UEs on a known UE paging channel).

[0117] Since each UE may have its own local clock K_Native, it helps to provide a synchronization signal before each discovery (and possibly control / data) communication in the OGRS system. Figure 10-11 Such control / data and discovery communications are shown, including a synchronization signal that may be used as a preamble.

[0118] According to some embodiments, a narrowband primary synchronization signal (NPSS) and a narrowband secondary synchronization signal (NSSS) may be used for the sidelink synchronization signal. As one possibility, a variable number of repetitions of the NPSS may be used, where each repetition comprises 14 OFDM symbols in a subframe and each OFDM symbol has 11 Zadoff-Chu (ZC) sequences of the same length as the root index u, where the ZC sequence is mapped to the 12 subcarriers of the NB-IoT physical resource block (PRB). Different root index u values ​​of the NPSS may be used to indicate different numbers of repetitions of the sidelink synchronization signal. For example, the root index u may be used to indicate that no repetitions are used (e.g., only one transmission of the synchronization signal is provided), the root index u+1 may be used to indicate that 4 repetitions are used, the root index u+3 may be used to indicate that 8 repetitions are used, and so on. Other schemes for indicating the number of repetitions may also be used.

[0119] An NSSS subframe may have a ZC sequence of length 132 and a root index value of v. For example, four different phase cyclic shifts of the ZC sequence may be applied to each even frame in an 8-frame period. Different root index values ​​of v (e.g., v, v+1, ..., v+128) may be used to identify the transmitting UE and may also be used to indicate a discovery transmission frequency hopping sequence.

[0120] The synchronization signal may also include a specific repetition number of a physical broadcast channel (PBCH) subframe, which may indicate the current subframe and frame number depending on the UE providing the synchronization signal.

[0121] like Figure 10 As shown, for control / data communication, the sidelink control region can be transmitted as NB-IoT format N0 (23 bits) using a narrowband physical uplink shared channel (NPUSCH). A fixed transport block configuration can be used, such as 15kHz single-tone BPSK. The control region may indicate the data format of the sidelink data region, such as subcarrier indication (e.g., 15kHz / 3.75kHz subcarrier, 1, 3, 6, or 12 tones), resource allocation (e.g., multiple resource units), modulation and coding scheme, redundancy version, number of repetitions, and new data indicator. The sidelink data region may be transmitted as an NB-IoT NPUSCH data subframe, where the resources, MCS, and number of repetitions are indicated by the sidelink control region.

[0122] like Figure 11 As shown in FIG, for discovery communication, the discovery message portion of the sidelink discovery transport block may also be transmitted on the NB-IoTNPUSCH and may occupy a portion of each sidelink discovery cycle. Figure 12As further shown, each discovery cycle may include a discovery transmission period and a discovery response reception period. Each discovery transmission period may include a specific number of repetitions n for each discovery transmission, e.g., corresponding to the number of frequencies on the scanning or paging channel on which discovery is performed. Each transmission may be performed on a different frequency in the frequency set of the scanning / paging channel. The sequence of scanning / paging frequencies used may be based on the MAC address of the discovering UE and may be indicated by the NSSS root index value v.

[0123] A discovery transmission may include a specific number of repetitions of each of the NPSS subframe, the NSSS subframe, and the NPBCH subframe. According to various embodiments, the repetitions may be clustered or may be distributed between transmission periods. A discovery transmission may also include a discovery message portion, which, as previously described, may be transmitted using the NPUSCH. If desired, a fixed transport block configuration may be used. For example, as one possibility, a 15kHz single tone, QPSK modulation, a 256-bit size configuration may be used, with 3 resource units (RUs), each RU comprising 8ms, 16 time slots, each time slot comprising 7 OFDM symbols, such that the discovery message portion may be 24ms long. The discovery message portion may indicate a superframe number based on the local clock of the discovery UE, the advertised source MAC address, the advertised target (individual users or groups) MAC address, a bitmap indicating a frequency map for frequency hopping by the discovery UE, and / or any other required information.

[0124] The discovery response reception period may be followed by the discovery transmission period. During this period, the discovery UE may monitor a frequency sequence selected from the OGRS frequency pool based on the MAC address of the discovery device, where each frequency is monitored for a specified number of frames (e.g., one frame).

[0125] If the UE is discovered (e.g., the UE receives a discovery transmission and is the target of a discovery transmission), the UE may perform a discovery response transmission during a discovery response reception period. Based on the received discovery message, the UE may determine the hopping sequence used by the discovered UE during its discovery response reception period, e.g., based on the UE MAC address, superframe number, and frame number of the discovered UE, and may transmit its discovery response message on the determined hopping sequence.

[0126] According to some embodiments, the discovered UE may estimate a number of repetitions of the discovery response message that may be required by the discovering UE to successfully decode the discovery response message. For example, the estimation may be based on the RSRP / RSRQ of any or all of the primary synchronization signal, the secondary synchronization signal, the master information block, and the discovery message, and / or based on the number of repetitions required by the discovered UE to decode the MIB and the discovery message.

[0127] A discovered UE may utilize a narrowband physical random access channel (NPRACH) preamble as part of a discovery response transmission. The NPRACH preamble may include four PRACH symbol groups, each with one cyclic prefix and five PRACH symbols transmitted on one 3.75 kHz subcarrier within a total preamble length of 5.6 ms. The PRACH preamble and the number of PRACH repetitions used may be selected based at least in part on an estimated number of repetitions of the discovery response message required by the discovering UE to successfully decode the discovery response message. If desired, the root index value of the PRACH preamble may be used to indicate the number of repetitions used to discover the UE.

[0128] The discovery response message may be provided over the NB-IoT NPUSCH, and a number of discovery response message repetitions may be selected based at least in part on an estimated number of discovery response message repetitions required for the discovering UE to successfully decode the discovery response message. The content of the discovery response message may include the MAC address and local clock of the discovered UE, e.g., for tracking the response. Additionally or alternatively, to establish a connection with the discovering UE, the discovered UE may send a connection request message as part of the discovery response message.

[0129] If necessary, the discovering UE may respond to the discovered UE with a PRACH ACK after the discovered UE provides the PRACH preamble and before providing the discovery response message itself.

[0130] In accordance with some embodiments, multiple UEs may be paired to an OGRS group, for example, over other existing communication links (e.g., cellular / Wi-Fi / Bluetooth), if available. When such a group is formed, each UE may be assigned an OGRS MAC address and its OGRS K_native may be reinitialized to a random value. Each UE may maintain a list of other UE MAC addresses and K_native offsets relative to its own K_native. During periods when such an OGRS group is established, the UE's K_native offset may be updated (e.g., periodically) based on one or more messages received from the UE. Such updates may be provided via OGRS (e.g., during communications after a connection is established, or using discovery techniques such as those described herein) or over other existing communication links, if available. If a UE's K_native offset is not updated for a period of time, the K_native offset may be considered out of date (e.g., when clock drift may cause a previously stored K_native offset to be out of date / inaccurate).

[0131] Using this framework, if a UE wishes to send data to (or track) another UE, if the UE's local cache does not have the UE's K_native offset, or if it is outdated, the UE may initiate a discovery process on the UE's scanning channel or on a group paging channel that includes the target UE. During the discovery transmission period, the UE may transmit a discovery message on each frequency in the frequency set of the scanning / paging channel. If the UE's local cache has the UE's new K_native offset, the UE may initiate a discovery process on the UE's paging channel. In this case, the UE may align its discovery transmission period with the reception time of other UEs and may transmit discovery messages on three frequencies (F_left, F_page, F_right) surrounding the paging frequency.

[0132] Figure 13 Further explanation is given of how such a discovery process occurs. In the illustrated example scenario, UE A may be the discovering UE and UE B may be the UE being discovered. UE A may start a discovery timer having a value that is at least the length of the DRX cycle used by the UE monitoring the scan / paging channel. For example, in the illustrated example, a DRX cycle of 60s may be used and a discovery timer of 2*60s=120s may be used. In each discovery cycle (e.g., 2000ms in the illustrated example), UE A may send a discovery message transmission repetition on each discovery frequency in its discovery transmission frequency sequence; for example, if 4 frequency hopping is used and each discovery message transmission is 40ms, the discovering UE may transmit 160ms of each 2000ms discovery cycle. UE A may then switch to receiving on a discovery response frequency sequence (which may be the same as or different from the discovery transmission frequency sequence). If a preamble is detected, UE A may proceed to decode the control portion of the message and then the data portion. If the response message is a discovery response for tracking, UE A may save the MAC address of the discovered UE and the offset of its K_native to the K_native of UE A. If the response message is a connection request message, UE A and UE B may form a connection. When forming a connection, the discovering UE or the discovered UE may play the role of a master device, while the other one plays the role of a slave device and is synchronized with the timing of the master device. For example, if the discovered UE is a master device, UE A may send an ACK in response to the discovery response message to confirm the establishment of the connection, and UE B may be synchronized with the timing of UE A. If the discovered UE is a master device, UE A may synchronize with the local clock and frequency of UE B (for example, based on the MAC address of UE B), and then may send an ACK in response to the discovery response message.

[0133] During its paging / scanning DRX wake-up time, UE B may search on RX frequency F_n, which may be selected based on UE B's K_native. Based on the NPSS / NSSS detected on F_n, UE B may know the TX frequency sequence for UE A's discovery transmission period, and based on this, UE B may also tune to other TX frequencies if necessary, for example, to combine synchronization signals, NPBCH, and discovery messages from multiple transmissions. If NPSS is detected, but the signal strength and / or quality (e.g., SNR) is too low to decode the discovery message, UE B may combine one or more NPSS / NSSS / NPBCH / discovery messages from one or more next discovery periods until the signal strength and / or quality is sufficient for decoding, or possibly until the configured maximum number of combinations is reached.

[0134] If NPSS is detected and the signal strength and / or quality are good enough to decode the discovery message, and if UE B is the discovery target of UE A, then based on the signal strength and / or quality and / or number of repetitions / combinations required to decode the NPSS / NSSS / NPBCH / discovery message, UE B may determine the number of repetitions required for the discovery response message and may send a discovery response message. If the response is for tracking, the discovery process may be complete at this point. If the response is for establishing a connection, the response may include a connection request message, and UE B may wait for an ACK from UE A.

[0135] In at least some instances, other UEs may also utilize the discovery signal of UE A. For example, if a third UE (UE C) intends to discover the same UE or UEs as UE A, UE C may synchronize with the timing of UE A and listen for discovery responses to obtain the MAC addresses and K_native offset information of such devices.

[0136] Alternatively, if UE C intends to discover one or more UEs different from UE A, UE C may send its own discovery message, for example, at the same time location as UE A if UE C's discovery transmission frequency sequence is different from UE A, or at a different time location than UE A if UE C's discovery transmission frequency sequence is the same as UE A.

[0137] For example, Figure 14 Another exemplary scenario is shown where UE A 1402 discovers using the first discovery transmission frequency sequence at the same time as UE C 1406 discovers using the second discovery transmission frequency sequence. UE B 1404 may also discover using the first discovery transmission frequency sequence, but at a different time than UE A.

[0138] At the same time, UE D 1408 may scan on F1 during the wake-up portion of its DRX operation and may detect the discovery transmission of UE C. UE D may then determine the discovery transmission frequency sequence used by UE C and follow that frequency sequence to receive further repetitions of UE C's discovery transmission, e.g., in the remainder of the same discovery cycle and possibly again in the next discovery cycle.

[0139] Similarly, UE E 1410 may scan, but on F4 and with a different timing for the wake-up portion of the DRX operation relative to UE D. UE E may nonetheless determine the discovery transmission frequency sequence used by UE C and follow that frequency sequence to receive further repetitions of UE C's discovery transmissions, e.g., in the remainder of the same discovery cycle and possibly again in the next discovery cycle.

[0140] Similarly, UE F 1412 may also scan, but on F3, and the wake-up portion for the DRX operation also has different timing relative to UE D and UE E. Similarly, UE E may determine the discovery transmission frequency sequence used by UE C and follow that frequency sequence to receive further repetitions of UE C's discovery transmission, e.g., in the next discovery cycle, since the discovery transmission received by UE F on F3 may be the previous repetition transmitted by UE C during that particular discovery cycle.

[0141] Note that the UE may periodically hop to different frequencies for scanning if necessary (e.g., between frequencies of a scanned channel, or to frequencies of different scanned channels). For example, as one possibility, after scanning one frequency of a scanned channel for a certain number of DRX cycles during an awake period, the UE may switch to scanning the next frequency of the scanned channel during an awake period, and may continue to do so as needed, for example, to increase frequency diversity.

[0142] As previously described, a P2P connection can be established between a master and a slave. There are multiple options for selecting the master role. One possibility is that the discovering UE can become the master. In this case, the discovered UE can become the slave and synchronize its timing with the master. In this case, the discovered UE can respond to the discovery message with a Connection Request message and wait for an ACK from the master to confirm the connection establishment. The ACK message can serve as the first anchor point for the P2P connection and can indicate the anchor point periodicity to be used for the P2P connection.

[0143] As another possibility, the discovered UE may become the master device. In this case, the discovered UE may respond to the discovery message with a connection request message based on the discovering UE's timing. The discovering UE may then synchronize with the discovered UE's timing and frequency hopping sequence and send an ACK to the discovered UE to confirm the connection establishment. In this case, since the discovered UE becomes the master device, the connection request message provided as a discovery response may include an indication of the master device's MAC address and local clock, as well as an indication of the anchor point periodicity to be used for the P2P connection.

[0144] Note that multiple UEs may be slaves of one UE master, such that all slaves use the MAC address and clock K_native of the master for frequency hopping. In such cases, the first data PDU sent by the master to the slave may mark the first anchor point, thus defining when the master must periodically send a PDU to the slave to maintain a connection. Transmissions between the master and the slave may alternate, for example, such that the master may send one PDU to the slave, which may then send one PDU back to the master (e.g., using ACK / NACK), which may then send one PDU to the slave (e.g., using ACK / NACK), and so on. Each PDU may include a synchronization signal, a control region, and a data region, and the synchronization signal root index value may indicate the length of the synchronization signal, for example, as previously described herein.

[0145] In order to be relatively efficient in terms of power, repetition, and latency between the master and slave devices, the master and slave devices may provide feedback to each other, e.g., with respect to any or all of ACK / NACK indications, TX power control, estimated lengths of synchronization signals, control and data regions, etc. According to some embodiments, such feedback may be based on block error rate (BLER) and / or signal strength / quality (e.g., RSRP / RSRQ) measurements of received PDUs.

[0146] Note also that, at least according to some embodiments, one or both of the master or slave devices in a P2P connection can send discovery messages and / or scan on paging and / or scanning channels, and multiple P2P connections can be established between multiple UEs.

[0147] According to some embodiments, the UE may utilize carrier sensing (LBT) techniques, for example, by searching for a synchronization signal for a period of time before attempting a transmission. For example, if the UE receives a synchronization signal with a value above a configured threshold during the LBT window before transmitting, the UE may delay its transmission until a later opportunity (e.g., when non-collision communications are occurring).

[0148] Figure 15-Figure 25 and additional information

[0149] Provided Figure 15-Figure 25 and the additional information below, which illustrates further considerations and possible specific implementation details related to a possible D2D communication framework and is not intended to limit the present disclosure as a whole. Various variations and alternatives to the details provided below are possible and should be considered to fall within the scope of the present disclosure.

[0150] One possible approach to providing synchronization within the D2D communication framework may include a group of devices in a geographic area that synchronize to the symbol / subframe / frame timing and carrier frequency provided by one of the devices, which may be referred to as a synchronization master, as a "global" synchronization source, or provided in any other variety of ways. This approach is similar in at least some respects to cellular networks, where wireless devices in a given area can camp on a base station, and may also be referred to herein as a "global" synchronization approach.

[0151] Conceptually, D2D communication services can be used to communicate between any two wireless devices as long as they can communicate with each other based on the geographical distance between them. However, such global synchronization methods may result in the coverage range of a device being limited by the range of the synchronization master, such that two devices may not be able to communicate despite being within the communication range of each other (if one device is within the range of the synchronization master and the other device is outside the range of the synchronization master). Even if a synchronization relay system is used to extend the range of the D2D group, the actual synchronization hopping limit (e.g., 2 or any other synchronization hopping limit) may still result in the discovery range of a node being limited to the synchronization range, such that two devices in close proximity may still be unable to communicate, for example, near the boundary of a relay master.

[0152] Additionally, two devices may be within range of each other but synchronized with other synchronization masters that have other synchronization schemes. For example, nodes synchronized with masters that have different timing sources (e.g., GNSS vs. non-GNSS, or non-GNSS vs. non-GNSS) may not be able to communicate with each other despite being within geographic range.

[0153] Such approaches may also suffer from inconsistent and / or severe peer connection setup delays. For example, although two devices may be close to each other, if they are at the edge of the coverage provided by the synchronization master, they may experience relatively long connection setup delays, for example due to long synchronization times.

[0154] Additionally, such an approach may result in an additional power consumption burden on the device selected as the synchronization master, for example, because the synchronization reference signal may be expected to be transmitted at a high power level to provide the maximum possible range for the D2D communication group. Such a burden may be distributed among the devices, for example, by rotating the synchronization master position among the devices. However, this may result in communication interruptions, extended connection setup / discovery delays between devices, the need for a more complex synchronization system design to provide event-driven and / or periodically triggered master / relay selection / reselection / switching between different synchronization sources, and / or may cause instability due to such a complex multi-layer synchronization design. Furthermore, relying on an unrelated synchronization master to provide synchronization introduces an additional possible source for potential unexpected behavior that may affect the D2D communication between a pair of devices.

[0155] Additionally, such systems may have a potentially greater likelihood of collisions during discovery, for example, because many devices may be synchronized to the same timing and frequency scheme provided by the synchronization master.

[0156] Furthermore, in possible scenarios where GNSS-based timing is preferred by the sync master in a global synchronization approach, such GNSS sync master may be highly dependent on GNSS availability and accuracy (e.g., within 8 ms as a possibility), which is an unrealistic requirement in some possible use cases (e.g., hiking in the wilderness in some instances). This may result in more frequent handoffs of the sync master within GNSS coverage (if any), and may otherwise result in a fallback to non-GNSS-based timing, which may exacerbate situations where closely adjacent wireless devices are unable to communicate with each other.

[0157] Therefore, as a possible alternative, at least according to some embodiments described herein, a D2D communication framework that utilizes a synchronization scheme that does not rely on a synchronization master to provide a synchronization signal for the entire D2D communication group can be used. Such a possible framework can include any of a variety of framework elements and processes, including frequency hopping, an idle process, a peer and / or presence discovery process, a UTC time update process, a P2P communication process, any or all of a physical layer preamble sequence and packet structure, discovery conflict mitigation / handling, and / or any of various other framework elements and processes, as further described later herein.

[0158] Figure 15A possible framework structure that can be used with such a D2D communication framework according to some embodiments is shown. As shown, an overall D2D cycle may include a random access period and a P2P communication period. During the random access period, devices may transmit synchronization preambles msg1, msg2, and msg3, for example, to perform synchronization and discovery. During the P2P communication period, devices that have performed synchronization and discovery and have agreed to communicate during the random access period may perform P2P communication, for example, to exchange data.

[0159] According to at least some embodiments, each D2D cycle may last for 1 second and may be synchronized with Coordinated Universal Time (UTC), e.g., as may be obtained by each D2D-capable device via a Global Navigation Satellite System (GNSS) and / or in various other ways. The portion of the random access cycle in which the synchronization preamble is transmitted may be configured to always occur during a particular portion of each D2D cycle (e.g., as one possibility, up to the first 60 ms of each D2D cycle, as shown). This may allow idle D2D wireless devices to listen for the synchronization preamble during a particular portion of each D2D cycle using discontinuous reception (DRX) techniques, and to save power (e.g., by sleeping / reducing power to certain device components) for the remainder of each D2D cycle when the synchronization preamble is not present for the idle D2D wireless devices.

[0160] According to some embodiments, the frequency used for synchronization preamble transmission may be periodically hopped. Figure 16 As shown, the synchronization preamble may be transmitted on a first frequency in a specific number (N) of D2D cycles (e.g., N=4 as one possibility, as shown), and then progress through the configuration of the synchronization preamble frequencies, transmitted on different frequencies in a specific number of D2D cycles, and so on.

[0161] Furthermore, if desired, the frequencies and / or scrambling codes used for msg1, msg2, and msg3 communications can be individually selected, for example, based on the frequency, type, and sequence of the current synchronization preamble, and the frequencies can be different from the frequencies used for the synchronization preamble. If desired, the frequencies used for P2P communication during a P2P communication cycle can exclude the frequencies used by the current synchronization preambles msg1, msg2, and msg3. The P2P frequency hopping sequence for that cycle and / or the scrambling code or code for that cycle can be based on the master peer's clock and a P2P link ID derived from the UE IDs of both peers.

[0162] Such personalized frequency selection may help reduce the likelihood of collisions between devices during discovery and data communications, eg, due to the number of possible PHY Sync IDs, multiple possible preamble sequences per PHY Sync ID, multiple types of possible preamble sequences, etc.

[0163] Additionally or alternatively, Figure 17 Another possible interval structure is shown that can be used for P2P communication based on the synchronization preamble framework. According to the interval structure shown, the overall timeline structure can be based on the UE local UTC time, including regular discovery intervals. Each discovery interval can have a predefined length (e.g., 720ms or any other desired length) and can have a start time based on a known system-wide (or at least group-wide) public UE ID. The hopping interval can have the same length as the discovery interval and can have a predefined offset from the discovery interval (e.g., 360ms or any other desired offset).

[0164] As shown in the figure, the discovery interval may include three types of time resources: synchronization preamble, anchor preamble and frequency hopping unit (which may include one or more resource units).

[0165] According to some embodiments, each synchronization preamble may have a predefined length (e.g., 50 ms or any other desired length) and may be a Zadoff-Chu-based preamble used for initial synchronization and data access for new data sessions starting in a discovery interval, without prior synchronization. In other words, a synchronization preamble may be transmitted by the UE at the start of the discovery interval to initiate a new data session without prior synchronization. Some common synchronization preambles may be predefined for broadcast-type services, such as presence discovery. A UE may also have its own dedicated synchronization preamble, which may hop at each hopping interval based on the UE ID and the UE's local UTC time. For example, the synchronization preamble pool may be divided into a certain number of groups (e.g., each group is associated with a synchronization ID), where each group includes a certain number of synchronization sequences. Thus, the public synchronization ID set may have multiple synchronization IDs for public use, while the dedicated synchronization ID set may have the remaining synchronization IDs available to individual UEs. In such a case, the UE synchronization preamble that hops at each hopping interval may be from a dedicated synchronization ID set associated with the UE based on the UE ID and the UE's local UTC time. The frequency used to transmit the synchronization preamble may also be hopped at each hopping interval based on the UE ID and the UE local UTC time.

[0166] The synchronization preamble window may be used to receive synchronization preambles transmitted by other UEs. According to some embodiments, there may be multiple (e.g., 3 or other numbers) types of synchronization preamble windows. For example, a normal synchronization preamble window may be aligned with the start of the discovery interval, but with a + / - normal drift space (e.g., as one possibility, 15 ms, which may correspond to up to 60 minutes outside GNSS coverage if the UTC accuracy is 5 ppm; other values ​​are possible). As one possibility, the length of the normal synchronization preamble window may be equal to the synchronization preamble length plus twice the normal drift space. A long synchronization preamble window may be a synchronization preamble window that is similarly equal to the length of the discovery interval plus twice the normal drift space. An extended synchronization preamble window may be a synchronization preamble window that extends to multiple lengths of the discovery interval. For example, as one possibility, the length may be a multiple of the discovery interval length, which is equal to the number of days the UE is outside GNSS coverage. Other values ​​are possible.

[0167] The anchor preamble may be a Zadoff-Chu based reference signal (e.g., comprising N repetitions of a ZC sequence, as one possibility among various possibilities) used for synchronization tracking and data access. The anchor preamble may be transmitted at the start time of a scheduled interval to initiate a new data session with a UE that has already performed synchronization. According to some embodiments, the anchor preamble may be scrambled using a King sequence based on the UE ID and the link ID. The sequence used for the anchor preamble may hop between a set of such sequences at each hopping interval, e.g., based on the UE ID and the UE local UTC time. According to at least some embodiments, the ... Figure 17 In the framework of the NB-IoT, a scheduling interval can be the configured minimum packet exchange session length between peer UEs. It can include multiple hopping units, each of which can include one or more resource units. A data packet can span one or more hopping units. A hopping unit can be the time unit used for frequency hopping within a hopping interval. A resource unit can be a resource allocation unit specified according to NB-IoT.

[0168] As mentioned earlier, in Figure 17Frequency hopping may be used at certain intervals within a typical interval structure. According to some embodiments, a system deployed according to such a framework may include a certain number of frequency channels (e.g., 63 or any other desired number, as one possibility) that may be randomly reordered within each regular frequency hopping interval based on a common UE ID and local UTC time. A first set of frequencies (e.g., 13 or any other desired number) according to the order may be used for synchronization preamble and msg1 transmission. For example, the first frequency in the sequence may be used for synchronization preamble transmission, and a frequency for msg1 transmission may be selected from the remaining frequencies in the set based on the synchronization preamble sequence used. The remaining frequencies (e.g., a second set of frequencies, which may include 50 frequencies in a system with a total of 63 frequencies and 13 frequencies in the first set, or any other desired number of frequencies) may be used for frequency hopping between FH units in a discovery interval. According to some embodiments, the frequency hopping sequence used for hopping between the second set of frequencies may be determined by the UE ID and local UTC time. Note that a scheduled interval can be shared by one clock master and one clock slave, such that the FH units in the scheduled interval can follow the clock master's FH sequence, and the clock slave UE follows the clock master's timing and FH sequence for transmission and reception. According to at least some embodiments, different scheduled intervals can have the same or different clock master and slave pairs.

[0169] It should also be noted that, at least according to some embodiments, a scrambling code may be used with the msg1 transmission. The scrambling code for msg1 may be selected based on the synchronization preamble sequence in response to which msg1 is transmitted. The scrambling codes used in other discovery communications (e.g., msg2, msg3, msg4) may be based on the clock master's UE ID and link ID assigned by the clock master.

[0170] Figure 18 Also shown are some embodiments according to Figure 17 Possible idle procedure aspects of such a framework are shown. As shown, a UE in idle mode may periodically search for a relevant synchronization preamble in the normal synchronization preamble window in each discovery interval, e.g., to receive a synchronization preamble from the UE having a UTX time difference from the local UTC time that is less than or equal to two times the normal drift space (e.g., up to 60 minutes when out of GNSS coverage if the normal drift space value discussed previously herein is used, according to some embodiments).

[0171] In addition, the UE may be configured to periodically search for a detectable synchronization preamble in a long synchronization preamble window, performed once every X (where X can be any desired number) discovery intervals, e.g., to receive a synchronization preamble from the UE having a UTC time difference from the local UTC time that is greater than twice the normal drift space and less than or equal to the discovery interval length. In addition, the UE may initially and / or periodically search for a detectable synchronization preamble in an extended synchronization preamble window of X discovery intervals, performed once every Y (where Y can be any desired number, e.g., greater than X) discovery intervals, e.g., to receive a synchronization preamble from the UE having a UTC time difference from the local UTC time that is greater than the discovery interval length and less than or equal to X discovery intervals (e.g., up to 2 days when out of GNSS coverage, according to one possible configuration).

[0172] As previously described herein, according to some embodiments, wireless devices participating in such D2D communication schemes may be assigned a physical layer (PHY) synchronization identifier (Sync ID), which may be of a certain length (e.g., 7 bits or any other desired length). As one possibility, the Sync ID may be derived from a longer (e.g., 16-byte) UE ID and a (e.g., 8-bit) hash ID. The PHY Sync ID may represent a set of dedicated preamble sequences associated with the wireless device. One or more common preamble sequences may also be configured, for example, to indicate certain common discovery messages. Thus, if a 7-bit PHY Sync ID is used, there may be 125 PHY Sync IDs representing 125 preamble groups. If 4 sequences are provided for each group, and 4 common sequences are provided, a total of 504 preamble sequences may be configured.

[0173] The synchronization preamble sequence may be used for initial symbol timing correction and carrier frequency offset (CFO) correction, as well as synchronization preamble type detection (eg, if applicable) and PHY synchronization ID detection. Figure 19 shows the synchronization preamble transmission within the synchronization preamble window of the discovery interval, such as Figure 17 A wireless device that detects a preamble during this D2D cycle may determine whether the preamble is a common preamble or a preamble associated with its PHY synchronization ID (e.g., in which case the wireless device may further listen for one or more discovery messages), or a preamble associated with another PHY synchronization ID (e.g., in which case the wireless device may continue DRX for the remainder of the D2D cycle).

[0174] In some instances, there may also be multiple types of synchronization preambles, such as a long synchronization preamble (e.g., 60 ms) that can be used for long-range communications (e.g., with an MCL of up to 164 dB as one possibility), and a normal synchronization preamble (e.g., 20 ms) that can be used for normal-range communications (e.g., with an MCL less than or equal to 155 dB as one possibility). Figure 20 It is shown how multiple such synchronization preamble types can be adapted within the synchronization preamble window of the discovery interval according to some embodiments.

[0175] In some instances where multiple synchronization preamble lengths are possible, the wireless device can utilize synchronization preamble length adaptation. For example, utilizing prior knowledge (e.g., that a previous link with a particular power occurred a certain time period ago such that the power and / or recency are within configured thresholds), the UE can be configured to begin discovery using a "normal" synchronization preamble with a power level up to a certain threshold (e.g., 26 dBm or any other desired power level threshold). In the absence of prior knowledge (or knowledge of a previous link that does not meet the configured requirements for a "normal" synchronization preamble), the UE can be configured to begin discovery using a "long" synchronization preamble with a power level up to a certain (e.g., higher) threshold (e.g., 30 dBm or any other desired power level threshold). It should also be noted that other types of synchronization preambles with different associated communication ranges and / or other characteristics are also possible.

[0176] As a possibility of providing a preamble sequence, there may also be a design similar to the NB-IoT PSS / SSS subframe design. For example, as a possibility, N repetitions of the NB-PSS subframe may be provided, and then M repetitions of the NB-SSS subframe may be provided as the preamble sequence. The NB-PSS OFDM symbol has a ZC sequence of length 11, with a root u (e.g., u=1, 2, 3, 4, 5, 6, 7, 8, 9, 10) and with a short cover code, and the NB-SSS subframe carries a ZC sequence of length 131, with 126 roots and multiplied with 4 m sequences of length 128, a total of 126x4=504 preamble sequences are possible. If desired, a normal preamble can be constructed using such components as N=15, M=5, and u=5 for a 20ms preamble, and a long preamble can be constructed using such components as N=50, M=10, and u=3 for a 60ms preamble.

[0177] Figure 21-22 is a signal flow diagram illustrating a possible existence and peer discovery communication sequence according to the D2D communication framework. Note that, as an additional or alternative possibility, Figure 23-24 Also shown is a possible peer and presence discovery communication sequence according to which synchronization preamble frames may be based for D2D communication.

[0178] like Figure 21As shown, UE A may desire to perform presence discovery on peer devices within communication range of UE A, which may include UE B (and possibly one or more additional devices). In this case, UE A may select a common preamble sequence, may select a synchronized preamble frequency for the preamble sequence based on UTC time, and may select a msg1 frequency and scrambling code based on the preamble sequence. UE A may transmit the preamble sequence on the synchronized preamble frequency and msg1 on the msg1 frequency at a selected power level (e.g., a lower power level for initial presence discovery transmission, an increased power level for repeated presence discovery transmissions, etc.).

[0179] UE B can be an idle UE searching for preambles within its synchronization preamble group, or it can be an idle UE searching for a common sequence during the synchronization preamble portion of each D2D cycle on the synchronization preamble frequency configured for the D2D cycle based on UTC time. Thus, UE B can detect the common preamble sequence transmitted by UE A and decode msg1 on the msg1 frequency. UE B can determine the msg1 frequency based on the specific preamble sequence used by UE A. UE B can also select the msg2 frequency, scrambling code, and time slot based on the preamble sequence and transmit msg2 on the msg2 frequency. If other devices are also within communication range of UE A, they can similarly detect the common preamble sequence and respond on the msg2 frequency.

[0180] UE A may decode msg2 from UE B (and possibly other msg2s from other UEs) on the msg2 frequency and may therefore be able to determine the presence of UE B (and any other UEs that may be nearby).

[0181] like Figure 22 As shown, UE A may desire to perform peer discovery on a peer device (i.e., UE B) within communication range of UE A. In at least some instances, UE A and UE B may have previously performed presence discovery to determine that they are within communication range of each other. UE A may randomly select a preamble sequence from UE B's preamble group, may select a synchronization preamble frequency for the preamble sequence based on UTC time, and may select an msg1 frequency and scrambling code based on the preamble sequence. UE A may transmit the preamble sequence on the synchronization preamble frequency and transmit msg1 on the msg1 frequency at a selected power level (e.g., a lower power level for initial peer discovery transmissions, an increased power level for repeated peer discovery transmissions, etc.).

[0182] and Figure 19Similar to the scenario described above, UE B can be an idle UE searching for preambles in its synchronization preamble group, or it can be an idle UE searching for a common sequence on the synchronization preamble frequency configured for the D2D cycle based on UTC time during the synchronization preamble portion of each D2D cycle. Therefore, UE B can detect the preamble sequence in the preamble group transmitted by UE A and can decode msg1 on the msg1 frequency. UE B can determine the msg1 frequency based on the specific preamble sequence used by UE A. UE B can also select the msg2 frequency, scrambling code, and time slot based on the preamble sequence and can transmit msg2 on the msg2 frequency.

[0183] UE A can decode msg2 from UE B on the msg2 frequency and, again based on the preamble sequence, select the msg3 frequency and scrambling code. UE A can transmit msg3 on the msg3 frequency. UE B can decode msg3 on the msg3 frequency, completing the peer discovery process. UE A and UE B can then perform P2P communication, for example, during a P2P communication period within a D2D period.

[0184] Figure 23 shows a timeline representation of a possible peer discovery process, which can be used as Figure 22 In addition to or in lieu of the illustrated process, as shown, the initiator UE may send a dedicated synchronization preamble to the receiver UE. The synchronization preamble frequency may be selected based on the public UE ID and the local UTC time. The synchronization ID may be selected based on the peer (e.g., receiver) UE ID and the local UTC time. The synchronization preamble sequence may be randomly selected from the selected synchronization ID preamble sequence group. The selected synchronization preamble may be transmitted at the beginning of the discovery interval (e.g., based on the initiator UE's local UTC clock).

[0185] The receiver UE may detect the synchronization preamble and respond with an msg1 response. The receiver UE may determine the discovery interval start time offset and frequency offset of the initiator UE by detecting the relative position of the synchronization preamble within the synchronization preamble window. The receiver UE may send msg1 to the initiator UE at a time offset from a predefined synchronization preamble, or may be selected based on the detected synchronization preamble sequence. The msg1 frequency may be determined based on the detected synchronization preamble sequence. The msg1 content may include any or all of the receiver UE ID, receiver UTC accuracy, local UTC time of the discovery interval start time, anchor point, discovery time offset, and frequency offset. The msg1 may be transmitted using the timing and frequency of the initiator UE.

[0186] The initiator UE may detect msg1 and respond with msg2. The initiator UE may update its list of discovered UEs using the receiver UE's UE ID, discovery time offset, anchor point, and frequency offset. The initiator UE may determine the time offset from msg1 to msg2 and may determine the msg2 frequency based on the receiver UE ID and the receiver UE UTC time. The msg2 content may include any or all of the initiator UE ID, initiator UTC accuracy, the local UTC time of the discovery interval start time, and the anchor point. msg2 may be transmitted using the receiver UE's timing and frequency.

[0187] The receiver UE may receive msg2 and similarly may update its list of discovered UEs using the initiator UE's UE ID, discovery time offset, anchor point, and frequency offset.

[0188] Figure 24 shows a timeline representation of a possible peer discovery process, which can be used as Figure 21 In addition to or as an alternative to the process shown. As shown, the initiator UE may use "s-msg1" to send a common synchronization preamble to the receiver UE. The synchronization preamble frequency may be selected based on the common UE ID and the local UTC time. A related common synchronization ID may be selected. The synchronization preamble sequence may be randomly selected from the selected synchronization ID preamble sequence group. The initiator UE may determine the time offset from the synchronization preamble to the s-msg1, which may be predefined or may be based on the synchronization preamble sequence. The smsg1 frequency may be selected based on the synchronization preamble sequence. The s-msg1 content may include the initiator UE ID, the msg1 resource configuration index, and any other required presence-specific information. Note that there may be multiple predefined msg1 resource configurations, for example, multiple time offsets and multiple subcarrier configurations with different MCS and RSSI levels, such that different msg1 resource configurations may be associated with different msg1 resource configuration indices. The selected synchronization preamble and s-msg1 may be transmitted at the beginning of the discovery interval (e.g., based on the initiator UE's local UTC clock).

[0189] The receiver UE can detect the synchronization preamble and decode the S-MSG1, and respond with an MSG1 response. The receiver UE can determine the initiator UE's discovery interval start time offset and frequency offset by detecting the relative position of the synchronization preamble within the synchronization preamble window. The receiver UE can determine the time offset from the synchronization preamble to the S-MSG1, which can be predefined or based on the detected synchronization preamble sequence, and can determine the S-MSG1 frequency based on the detected synchronization preamble sequence, thereby detecting and decoding the S-MSG1. The receiver UE can determine the time offset from the S-MSG1 to the MSG1 based on the measured RSSI level and the MSG1 resource configuration index indicated in the S-MSG1, randomly select a subcarrier configuration from a subcarrier configuration set based on the MSG1 resource configuration index, and determine the MSG1 frequency based on the detected synchronization preamble sequence. The MSG1 content may include any or all of the receiver UE ID, receiver UTC accuracy, local UTC time of the discovery interval start time, anchor point, discovery time offset, and frequency offset. The MSG1 may be transmitted using the initiator UE's timing and frequency.

[0190] The initiator UE may detect msg1 and respond with msg2. The initiator UE may update its list of discovered UEs using the receiver UE's UE ID, discovery time offset, anchor point, and frequency offset. The initiator UE may determine the time offset from msg1 to msg2 and may determine the msg2 frequency based on the receiver UE ID and the receiver UE UTC time. The msg2 content may include any or all of the initiator UE ID, initiator UTC accuracy, the local UTC time of the discovery interval start time, and the anchor point. msg2 may be transmitted using the receiver UE's timing and frequency.

[0191] The receiver UE may receive msg2 and similarly may update its list of discovered UEs using the initiator UE's UE ID, discovery time offset, anchor point, and frequency offset.

[0192] Once the discovery process is complete between two wireless devices, both the initiator UE and the receiver UE may be in a discovered state relative to each other, and the wireless devices may perform D2D communications. A discovered UE may have a regular discovery interval, which may include a normal synchronization preamble window, which may continue to be used to search for associated synchronization preambles transmitted by other UEs with a UTC time difference from the UE's local UTC time that is less than or equal to the normal drift space. The discovery interval may also include an msg1 region, which may provide a time window in which msg1s are transmitted / received by other UEs (and potentially the discovered UE if it is performing other discovery), for example, if the msg1 transmission has a predefined time offset from the synchronization preamble transmission. In some instances, a UE may also transmit data packets over the msg1 region as long as the transmit power is below a configured threshold (e.g., 30 dBm or any other desired threshold). Similarly, a discovery interval may include a msg2 region, which may provide a time window in which msg2s are transmitted / received by other UEs (and potentially the discovered UE if it is performing other discovery), for example, if the msg2 transmission has a predefined time offset from the synchronization preamble transmission. According to at least some embodiments, the UE may also transmit data packets over the msg2 region as long as the transmission power is below a configured threshold (e.g., 30 dBm or any other desired threshold). The transmission and reception of data packets may be managed according to the scheduled interval of the discovery interval.

[0193] The discovered UE may have a list of N (e.g., number) discovered neighboring UEs, where each UE may be assigned to a scheduled interval in a period of N scheduled intervals. For each scheduled interval, if there is no data to be processed, the UE may listen for an anchor preamble in the anchor window of the scheduled interval. If the anchor preamble is detected, the receiving UE may become a clock master for the scheduled interval, may initiate a data session with the initiator UE, and the initiator UE and the receiver UE may continue to transmit and receive data packets over one or more consecutive scheduled intervals based on the timing and hopping sequence of the receiver UE until the data session is completed. If there is data to be processed, the UE may transmit the anchor preamble as an initiator. If an anchor msg1 is received, the initiator UE may become a clock slave for the scheduled interval, may initiate a data session with the receiver UE, and the initiator and the receiver UE may continue to transmit and receive data packets over one or more consecutive scheduled intervals based on the timing and hopping sequence of the receiver UE until the data session is completed.

[0194] The discovered UE may also listen for synchronization preambles over a long synchronization preamble window (e.g., having a length of one discovery interval plus twice the normal drift space, according to the example provided previously, or having any other desired length), performed once every certain number of discovery intervals. As previously described, such a long synchronization preamble window may be used to search for a synchronization preamble associated with the UE, sent from the UE, that has a UTC time difference from the UE's local UTC time that is greater than the normal drift space.

[0195] According to some embodiments, Figure 25 A packet structure that can be used as part of a synchronization preamble based on a P2P communication framework is shown. As shown, the packet structure may include a demodulation reference signal (DMRS) based on a Zadoff-Chu sequence as a preamble for symbol timing and frequency tracking, and it may also indicate the PHY header type (e.g., normal or long). According to some embodiments, a normal PHY header may have a fixed MCS of MCL<=155, while a long PHY header may have a fixed MCS of MCL<=163. Other configurations are also conceivable. The PHY header may indicate the payload format and may include subcarrier and resource indications, MCS and RV, number of repetitions, and a new data indicator.

[0196] The payload may include one or more MAC control elements, which may indicate the transmit power level, UTC time and accuracy level, symbol time offset and frequency offset, and the amount of data to be processed. Note that msg1, as a special payload, may include a MAC control element for UTC time, a transmit power level, an initiator symbol time offset and carrier frequency offset, a UE ID of a receiver UE, a link ID (e.g., similar to a cell radio network temporary identifier (CRNTI) assigned by the receiver UE), and an anchor point (e.g., indicating the location of the anchor preamble of the link and the anchor window). Similarly, msg2, as a special payload, may include a MAC control element for UTC time, a transmit power level, a UE ID of an initiator UE, and an anchor point.

[0197] It is important to note that because such D2D communication frameworks can utilize UTC clock information to determine D2D cycle timing, it is helpful for wireless devices operating within such frameworks to be aware of the potential UTC clock drift rate and current potential UTC clock drift at any given time, for example, to increase the likelihood that the wireless device can successfully detect synchronization signals from peer devices during DRX operation. For example, if a wireless device expects up to ±10 ppm drift within an hour when the wireless device's UTC clock has no available synchronization source, the UTC clock drift may be approximately ±36 ms. Therefore, a wireless device aware of its potential UTC clock drift can extend the DRX OnDuration length (e.g., before and / or after the nominal OnDuration length) to better detect synchronization preamble transmissions when the wireless device's UTC clock is actually drifting, although this may incur additional power consumption. Alternatively, or in addition, as previously described herein, multiple synchronization preamble windows can be configured and monitored according to different intervals to account for potential UTC clock drift of the UE and possible neighboring UEs.

[0198] Such wireless devices may also reset their estimates of potential UTC clock drift when synchronizing their UTC clock to a UTC clock source, such as by acquiring GNSS synchronization, receiving a common synchronization preamble or synchronization preamble for discovery sent by other wireless devices operating using the D2D communication framework and thus synchronized with UTC time, or otherwise performing P2P communication with other wireless devices synchronized with UTC time. This may allow the wireless device to resume using the nominal DRX on-duration length specified by the D2D communication framework, thereby reducing power consumption.

[0199] As another possibility, UEs participating in any discovery and P2P communication can update their local UTC time to the average UTC time among neighboring UEs within the UE's geographical reach using the most accurate UTC time. For example, if any UE in range has GNSS coverage, the common UTC time converged in the group can be the most accurate GNSS UTC time. If any UE in range does not have GNSS coverage, the common UTC time converged in the group can be the average UTC time among all neighbors.

[0200] According to at least some embodiments, a UE may update its UTC time in idle state according to such a UTC time update framework. Upon entering idle state from a discovered state, the UE may generally update its UTC time to the most accurate time among all UEs in its discovered list. If two or more UEs have the same (or approximately the same) accurate UTC time, the UE may update to the average UTC time of these UEs.

[0201] The UE may also continuously estimate its UTC time drift and may be configured to perform UTC time presence discovery as long as its estimated UTC time drift is less than a configured threshold (e.g., so that the estimated UTC time drift is close to the normal drift space considered by the D2D communication framework). In a similar situation, the UE may send presence discovery communications using its local UTC time and accuracy, receive msg1s with UTC time from all UEs with better UTC accuracy, and update its UTC time from the average of all UTC times with the highest accuracy.

[0202] For UEs whose UTC time drift is greater than a configured threshold (e.g., greater than a normal drift margin, e.g., if the UE is isolated for multiple days without GNSS coverage, as an example), the UE may perform an initial search (e.g., enter an initial search state) using a longer or extended (e.g., which may depend on the estimated UTC time drift) synchronization preamble window for a certain number of discovery intervals, e.g., to attempt to adjust the initial UTC time error. The UE may attempt to acquire an accurate UTC clock from GNSS synchronization and may attempt to detect any synchronization preamble sequence and then retrieve the UTC clock from the corresponding msg1 during such a search.

[0203] Additionally or alternatively, the UE may attempt to transmit a synchronization preamble during a discovery interval with a long synchronization preamble window. In a similar situation, the UE may transmit a common synchronization preamble in multiple discovery intervals, for example, starting before a target discovery interval and extending multiple intervals after the target discovery interval based at least in part on the estimated degree of UTC time drift. For example, the UE may transmit 2*m+1 consecutive discovery intervals starting from discovery interval nm, where m is the number of discovery intervals whose length is equal to (or approximately equal to) the UE's estimated UTC time drift, and n is the target discovery interval with a long synchronization preamble window.

[0204] In synchronization preambles based on a P2P communication framework such as that described herein, discovery collisions may arise from synchronization preamble collisions. In low UE density scenarios, the synchronization preamble collision rate between UEs may be relatively low, for example due to the low UE density, even though the synchronization preambles in a common synchronization preamble reception window may not be fully aligned due to the potential UTC drift space. In high UE density scenarios, all UEs in an area can quickly converge to a common UTC time, whether GNSS-based or non-GNSS-based, as long as they participate in communication. Therefore, in this case, since multiple ZC sequences are used as synchronization preambles, the synchronization preambles are aligned with the same discovery interval start time based on the same common UTC time and have the same transmission power, the possibility of a high discovery collision rate can be reduced. By comparing the coding rate of msg1 in a global synchronization method with the coding rate of the synchronization preamble, the discovery collision rate between a similar method and a global synchronization method (e.g., at the same SINR) can be estimated. For example, in at least some instances, msg1 in a global synchronization method may have 36 bits during a 32ms period. In at least some instances, the synchronization preamble may have 504 sequences in the preamble method, which is approximately 9 bits in a 50 ms period. Thus, in this example, the synchronization preamble may be approximately 8 dB better than msg1 in the global synchronization method. Note that this example is provided for illustrative purposes and is not intended to limit the present disclosure as a whole.

[0205] According to at least some embodiments, msg1 collisions in a synchronization preamble-based P2P communication framework, such as described herein, can be minimized by selecting an msg1 frequency based on a synchronization preamble sequence in response to which msg1 is provided. Furthermore, msg2 collisions and msg1 / msg2 collisions can be relatively minimized by selecting an msg2 frequency based on a receiver UE's FH sequence. Similarly, data / msg2 / msg1 collisions can also be relatively minimized by selecting a data frequency based on a receiver UE's FH sequence.

[0206] With respect to a synchronization preamble-based P2P communication framework such as that described herein, the near-far problem may need to be considered. For example, according to at least some embodiments, consider that a 30 dBm transmission on any channel may block the entire ISM band at close range (e.g., approximately 10 meters in some instances). To avoid problems for nearby UEs due to such transmissions, it may be possible to limit the 30 dBm (or other configured transmit power) synchronization preamble transmission to the synchronization preamble window in the discovery interval. In low UE density scenarios, even though the synchronization preamble window may have a relatively large UTC time drift space, the near-far problem may not be significant because interference from nearby UEs may be low. In high UE density scenarios, the near-far problem may be relatively significant, but the synchronization preamble may be limited to a smaller synchronization preamble window because the local UTC time of nearby UEs can converge quickly to a common UTC time with less UTC time drift. msg1 and msg2 transmissions for peer discovery and data communication are less likely to have high transmit power because they may be power controlled. When high transmission power is used for data communication, its interference with msg1 / msg2 can be mitigated by, for example, predefining one or more msg1 and msg2 time offsets as synchronization preambles, and / or by not allowing data to be transmitted using a transmission power above a certain threshold during the msg1 area and the msg2 area.

[0207] In certain scenarios, at least according to some embodiments, it is also worth comparing certain possible communication characteristics of approaches based on synchronization preambles with approaches based on global synchronization for providing a P2P communication framework. For example, consider a hiking use case scenario, which may be characterized by low UE density, relatively long distances between UEs, and / or infrequent P2P communication. In such scenarios, UEs may spend a relatively large amount of time idle on average. In the preamble approach, UEs within range may have large local UTC time drifts, but generally remain within a normal drift range, e.g., as long as the UEs can discover GNSS coverage approximately once an hour. It is likely that there may typically be relatively few P2P communicating device pairs, some of which may use relatively high transmission power due to long distances. A low discovery collision rate is expected, and the near-far issue may be less significant. In such scenarios, at least according to some embodiments, it is likely that the connection setup time for the preamble sequence may be relatively consistent and may require approximately 200ms, while the connection setup time for the global synchronization approach may be longer, e.g., approximately 3 seconds or longer, due to searching for and synchronizing to (or becoming) a sync master. For the preamble method, power consumption may be relatively minimal, but for the global synchronization method, power consumption may be higher due to less chance of sharing the synchronization master between UEs in the area. Of the two methods, discovery collisions may be minimal in such scenarios.

[0208] Consider also cruise scenarios, which can be characterized by high UE density, a mix of long and short distances, and / or more frequent P2P communication. In such scenarios, UEs may spend relatively more time communicating on average. In the pilot method, UEs within range may experience relatively little local UTC time drift, for example, due to rapid convergence to a common UTC time with or without GNSS coverage. It is possible that there may typically be many P2P communicating device pairs, some of which may be long-range and some of which may be short-range. A high discovery conflict rate can be expected, and the distance issue may be significant in some areas but not in others. In such scenarios, both methods may experience some discovery conflicts, but the use of multiple ZC sequences can reduce discovery conflicts for the pilot method. Furthermore, at least according to some embodiments, it is possible that the connection setup time for the pilot method may experience some delay due to discovery conflicts, while the connection setup time for the global synchronization method may still be longer, for example, due to a higher discovery conflict rate, even though a common synchronization master can be discovered relatively easily. In both cases, the power consumption mainly depends on the actual P2P communication performed, where the anchor preamble transmission power is power controlled and triggered by the pending data in the preamble method, but it can also be higher for the global synchronization method due to the additional power consumption of the high-power synchronization signal transmission of the synchronization master device.

[0209] Thus, at least according to some embodiments, such a D2D communication framework can improve the ability of a wireless device to communicate with other D2D wireless devices within a designed range, without being limited by the coverage range of a third device. In addition, such a D2D communication framework can provide relatively low discovery conflicts, reduced latency and / or reduced power consumption, for example, compared to a synchronization master-based framework. Such a synchronization design can also be relatively simple, for example, without the potential complex overhead that may otherwise be required to establish and maintain global synchronization of symbol timing and carrier frequency with a third device. In addition, at least in some embodiments, such an approach can allow all UEs within a geographically reachable range to obtain an aggregated common UTC time, which can allow for accommodation of relaxed GNSS requirements, with or without GNSS coverage.

[0210] In the following, additional exemplary embodiments are provided.

[0211] One set of embodiments may include a method comprising, by a first wireless device: determining a synchronization signal repetition number for transmission; and performing the transmission, including transmitting the determined synchronization signal repetition number.

[0212] According to some embodiments, the method further comprises selecting a first root index value for a first portion of the synchronization signal based at least in part on a determined number of synchronization signal repetitions, wherein the first root index value for the synchronization signal indicates the number of synchronization signal repetitions transmitted by the first wireless device.

[0213] According to some embodiments, the first root index value includes a root index value of a Zadoff-Chu sequence of a primary synchronization signal (SSS) used as a synchronization signal, wherein the synchronization signal also includes a secondary synchronization signal (SSS), wherein the SSS also includes a Zadoff-Chu sequence, wherein the method further includes: selecting a second root index value of the SSS, wherein the second root index value indicates a device identifier of the first wireless device; wherein the synchronization signal further includes a physical broadcast channel, and the physical broadcast channel indicates a frame number and a subframe number based on a local clock of the first wireless device.

[0214] According to some embodiments, the transmission further comprises a discovery signal, wherein the method further comprises performing the transmission on each frequency in a predetermined sequence of discovery transmission frequencies.

[0215] According to some embodiments, the method further includes, after performing the transmission on each frequency in the predetermined sequence of discovery transmission frequencies: monitoring each frequency in the predetermined sequence of discovery response frequencies for a discovery response.

[0216] According to some embodiments, the number of synchronization signal repetitions is determined based at least in part on characteristics of a transmission from the second wireless device previously received by the first wireless device.

[0217] In some embodiments, the characteristics of the transmission from the second wireless device previously received by the first wireless device include one or more of the following: a value of a signal strength indicator of the transmission from the second wireless device previously received by the first wireless device; a value of a signal quality indicator of the transmission from the second wireless device previously received by the first wireless device; or a number of repetitions used by the first wireless device to decode the transmission from the second wireless device previously received by the first wireless device.

[0218] According to some embodiments, the transmission to the second wireless device comprises narrowband peer to peer communication.

[0219] Another set of embodiments may include a method comprising: receiving, by a wireless device: a first transmission, wherein the first transmission comprises a synchronization signal and a discovery message; determining a first root index value for the synchronization signal for the first transmission; determining a number of repetitions of the synchronization signal for the first transmission based at least in part on the first root index value; and determining when the discovery message begins based at least in part on the determined number of repetitions of the synchronization signal for the first transmission.

[0220] According to some embodiments, the method further includes: determining that the wireless device is unable to decode the discovery message contained in the first transmission; receiving a second transmission, wherein the second transmission includes a synchronization signal and a discovery message; and combining the discovery message contained in the first transmission with the discovery message contained in the second transmission.

[0221] In some embodiments, the method further comprises determining, based at least in part on the synchronization signal, a sequence of discovery message transmission frequencies used by the wireless device performing the first transmission, wherein the second transmission is received at a frequency different from the first transmission, wherein the frequency at which the second transmission is received is determined based on the sequence of discovery message transmission frequencies used by the wireless device performing the first transmission.

[0222] According to some embodiments, the second transmission is received during a subsequent discovery period at the same frequency as the first transmission.

[0223] According to some embodiments, the method further comprises determining a sequence of discovery response transmission frequencies based at least in part on the first transmission; and performing a discovery response transmission on each frequency in the sequence of discovery response transmission frequencies.

[0224] According to some embodiments, the discovery response transmission includes a preamble, wherein the method further comprises: determining a number of preamble repetitions for the discovery response transmission; and selecting a root index value for the preamble based on the determined number of preamble repetitions.

[0225] According to some embodiments, the number of preamble repetitions of the discovery response transmission is determined at least in part based on signal strength, signal quality, and a number of repetitions used by the wireless device to decode the discovery message.

[0226] According to some embodiments, the discovery response transmission includes a device identifier of the wireless device and an indication of a local clock value of the wireless device.

[0227] Another group of embodiments may include a method comprising: by a wireless device: selecting a device-to-device (D2D) synchronization preamble sequence to be transmitted from a plurality of possible D2D synchronization preamble sequences; transmitting the D2D synchronization preamble sequence at a time and frequency selected based at least in part on a Coordinated Universal Time (UTC) clock maintained by the wireless device; and transmitting a D2D discovery message at a time and frequency selected based at least in part on the selected D2D synchronization preamble sequence.

[0228] According to some embodiments, the method further comprises, by the wireless device: selecting a public D2D synchronization preamble sequence to be transmitted from a plurality of possible public D2D synchronization preamble sequences, wherein the D2D public synchronization preamble sequence is selected for performing presence discovery for peer devices within a communication range of the wireless device.

[0229] According to some embodiments, the method also includes, by the wireless device: selecting a D2D synchronization preamble sequence to be transmitted in a preamble group associated with the second wireless device from a plurality of possible D2D synchronization preamble sequences in the preamble group associated with the second wireless device, wherein the D2D synchronization preamble sequence is selected for performing peer discovery with the second wireless device.

[0230] According to some embodiments, a scrambling code for the D2D discovery message is selected based at least in part on the selected D2D synchronization preamble sequence.

[0231] According to some embodiments, the method further comprises, by the wireless device: receiving a discovery response message from a second wireless device at a frequency selected based at least in part on the selected D2D synchronization preamble sequence.

[0232] According to some embodiments, the method further comprises, by the wireless device: selecting a D2D synchronization preamble type of the D2D synchronization preamble sequence, wherein the D2D synchronization preamble type is selected from at least a normal D2D synchronization preamble and a long D2D synchronization preamble.

[0233] Another set of embodiments may include a method comprising: by a wireless device: selectively monitoring a frequency channel for a device-to-device (D2D) synchronization preamble sequence according to a discontinuous reception (DRX) cycle, wherein the monitored frequency channel is selected at least in part based on a coordinated universal time (UTC) clock maintained by the wireless device, wherein DRX cycle timing is also selected at least in part based on the UTC clock maintained by the wireless device; receiving the D2D synchronization preamble sequence during the on-duration portion of the DRX cycle; and receiving the D2D discovery message at a time and frequency selected at least in part based on the received D2D synchronization preamble sequence.

[0234] In some embodiments, the method further includes, by the wireless device: estimating a potential UTC clock drift of a UTC clock maintained by the wireless device; and modifying a length of the on-duration portion of the DRX cycle based at least in part on the estimated potential UTC clock drift of the UTC clock maintained by the wireless device.

[0235] In some embodiments, the method also includes, by the wireless device, updating the common reference time clock and the estimated potential common reference time clock drift of the common reference time clock maintained by the wireless device based at least in part on synchronization of the common reference time clock maintained by the wireless device with a global navigation satellite system (GNSS) signal received by the wireless device.

[0236] According to some embodiments, the method further comprises, by the wireless device: updating a UTC clock and an estimated potential UTC clock drift of the UTC clock maintained by the wireless device based at least in part on receiving the D2D synchronization preamble sequence.

[0237] Another example embodiment may include a wireless device comprising: an antenna; a radio component coupled to the antenna; and a processing element operably coupled to the radio component, wherein the device is configured to implement any or all of the components of the preceding examples.

[0238] Another example embodiment may include an apparatus including a processing element configured to cause a wireless device to implement any or all of the components of the foregoing examples.

[0239] Another set of example embodiments may include a non-transitory computer-accessible storage medium including program instructions that, when executed at an apparatus, cause the apparatus to implement any or all portions of any of the foregoing examples.

[0240] A further exemplary set of embodiments may include a computer program comprising instructions for performing any or all of the components of any of the foregoing examples.

[0241] Another exemplary set of embodiments may include an apparatus comprising means for performing any or all of the elements of any of the preceding embodiments.

[0242] In addition to the exemplary embodiments described above, further embodiments of the present disclosure may be implemented in any of a variety of forms. For example, some embodiments may be implemented as computer-implemented methods, computer-readable storage media, or computer systems. Other embodiments may be implemented using one or more custom-designed hardware devices such as ASICs. Other embodiments may be implemented using one or more programmable hardware elements such as FPGAs.

[0243] In some embodiments, a non-transitory computer-readable storage medium may be configured such that it stores program instructions and / or data, wherein the program instructions, if executed by a computer system, cause the computer system to perform a method, such as any one of the method embodiments described herein, or any combination of the method embodiments described herein, or any subset of any of the method embodiments described herein or any combination of such subsets.

[0244] In some embodiments, a device (e.g., UE 106 or 107) may be configured to include a processor (or a group of processors) and a memory medium, wherein the memory medium stores program instructions, wherein the processor is configured to read and execute the program instructions from the memory medium, wherein the program instructions are executable to implement any of the various method embodiments described herein (or any combination of the method embodiments described herein, or any subset of any method embodiments described herein, or any combination of such subsets). The device may be implemented in any of a variety of forms.

[0245] Although the above embodiments have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to encompass all such variations and modifications.

Claims

1. A method for wireless communication, comprising: At the wireless device: selecting a D2D synchronization preamble sequence to be transmitted from a plurality of possible device-to-device D2D synchronization preamble sequences; transmitting the D2D synchronization preamble sequence at a time and frequency selected based at least in part on a local clock maintained by the wireless device, wherein the local clock is associated with a common reference time; as well as The D2D discovery message is transmitted at a time and frequency selected based at least in part on the selected D2D synchronization preamble sequence.

2. The method according to claim 1, wherein The public reference time includes Coordinated Universal Time UTC.

3. The method according to claim 1, wherein The D2D synchronization preamble sequence is selected based at least in part on a value of the local clock according to a sequence hopping pattern.

4. The method according to claim 1, wherein A frequency for transmitting the D2D synchronization preamble is further selected based at least in part on the selected D2D synchronization preamble.

5. The method of claim 1 , further comprising: A common D2D synchronization preamble sequence is selected to be transmitted from a plurality of possible common D2D synchronization preamble sequences, wherein the common D2D synchronization preamble sequence is selected for performing presence discovery for peer devices within a communication range of the wireless device.

6. The method of claim 1 , further comprising: A D2D synchronization preamble sequence to be transmitted in a preamble group associated with the second wireless device is selected from a plurality of possible D2D synchronization preamble sequences in the preamble group associated with the second wireless device, wherein the D2D synchronization preamble sequence is selected for performing peer discovery with the second wireless device.

7. The method of claim 1, wherein: A scrambling code for the D2D discovery message is selected based at least in part on the selected D2D synchronization preamble sequence.

8. The method of claim 1 , further comprising: A discovery response message is received from the second wireless device at a frequency selected based at least in part on the selected D2D synchronization preamble sequence.

9. The method of claim 8, wherein: A frequency at which the discovery response messages are received is selected based further at least in part on a value of the local clock.

10. The method of claim 1, further comprising: A D2D synchronization preamble type of the D2D synchronization preamble sequence is selected, wherein the D2D synchronization preamble type is selected from at least a normal D2D synchronization preamble and a long D2D synchronization preamble.

11. A method for wireless communication, comprising: At the wireless device: selectively monitoring a frequency channel of a device-to-device (D2D) synchronization preamble sequence according to a discontinuous reception (DRX) cycle, wherein the monitored frequency channel is selected based at least in part on a common reference time clock maintained by the wireless device, wherein DRX cycle timing is also selected based at least in part on the common reference time clock maintained by the wireless device; receiving a D2D synchronization preamble sequence during an on-duration portion of the DRX cycle; as well as The D2D discovery message is received at a time and frequency selected based at least in part on the received D2D synchronization preamble sequence.

12. The method of claim 11, wherein: Public reference times include Coordinated Universal Time (UTC).

13. The method of claim 11, wherein: The monitored frequency channel is selected based on a frequency hopping pattern.

14. The method of claim 11, wherein: A frequency for receiving the D2D discovery message is further selected based at least in part on a value of the common reference time clock maintained by the wireless device.

15. The method of claim 11, further comprising: estimating a potential common reference time clock drift of the common reference time clock maintained by the wireless device; as well as A length of the OnDuration portion of the DRX cycle is modified based at least in part on a potential common reference time clock drift of the common reference time clock maintained by the wireless device.

16. The method of claim 15, further comprising: A common reference time clock maintained by the wireless device and a potential common reference time clock drift of the common reference time clock maintained by the wireless device are updated based at least in part on synchronization of the common reference time clock maintained by the wireless device with Global Navigation Satellite System (GNSS) signals received by the wireless device.

17. The method of claim 16, further comprising: The common reference time clock and a potential common reference time clock drift of a common reference time clock maintained by the wireless device are updated based at least in part on receiving the D2D synchronization preamble sequence.

18. An apparatus for wireless communication, comprising a processor configured to cause a wireless device to implement the method according to any one of claims 1 to 17.

19. The apparatus of claim 18, further comprising a radio operatively coupled to the processor.

20. A non-transitory memory medium comprising program instructions stored thereon, the program instructions being configured to cause a wireless device to implement the method of any one of claims 1 to 17.

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