Power-efficient synchronization for long-distance device-to-device communication

Abstract

This disclosure relates to "Power-efficient synchronization for long-distance device-to-device communication." The invention provides a communication network that may include user equipment (UE) devices. When a first UE device goes offline and receives an emergency message, the first UE device may transmit a device-to-device signal for reception by a second UE device. This signal may include one or more preambles that precede the emergency message and are used by the second UE device to perform synchronization with the first UE device. The second UE device may periodically activate a receiver to listen for the signal during a window sequence, receive a preamble sequence during one window of the window, and synchronize the timing of the second UE device with the first UE device based on the preamble sequence to receive the emergency message. This allows the UE device to be synchronized to transmit emergency messages over long distances while consuming minimal power on the second UE device.

Description

[0001] This application claims priority to U.S. Patent Application 17 / 379,458, filed July 19, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates in its entirety to wireless communications, including wireless communications performed by user equipment. Background Technology

[0003] Communication systems typically consist of user equipment and wireless base stations. Each wireless base station has a corresponding coverage area. When the user equipment is within this coverage area, radio frequency signals are exchanged between the user equipment and the wireless base station to transmit wireless data.

[0004] In reality, there will be situations where the user equipment is no longer within the coverage area of ​​the wireless base station. In these cases, the user equipment cannot transmit wireless data with the wireless base station. However, even when the user equipment is outside the coverage area of ​​the wireless base station, there may still be situations where the user equipment needs to transmit wireless data to the receiver. Summary of the Invention

[0005] A communication network may include user equipment (UE) devices and external communication equipment (such as wireless base stations or access points). A first UE device can wirelessly communicate with the rest of the network via external communication equipment when it is connected to the network. When the first UE device goes offline, it may still occasionally need to send messages such as emergency messages to a second UE device. However, going offline may cause timing on the first UE device to drift relative to timing on the second UE device.

[0006] When the first UE device goes offline and has an emergency message or other data to transmit, the first UE device can transmit a device-to-device (D2D) signal for the second UE device to receive. The D2D signal may include one or more preambles, which are placed before the emergency message and used by the second UE device to perform time and frequency synchronization with the first UE device. The second UE device may periodically activate its receiver to listen for the D2D signal during a receiver (RX) window sequence. The second UE device may deactivate its receiver between RX windows to save power. The second UE device may receive a preamble sequence during one RX window. The second UE device may synchronize its timing with the first UE device's timing based on the preamble sequence received during the RX window for subsequent reception of the emergency message.

[0007] For example, one or more preambles may comprise an N-preamble series. Each preamble in the N-preamble series identifies a corresponding time offset between the preamble and the subsequent transmission of the emergency message. If needed, the N-preamble series may be divided into a first group of odd-numbered preambles and a second group of even-numbered preambles preceding the corresponding transmission of the emergency message. In other examples, one or more preambles may comprise an extended preamble. The second UE device may receive a portion of the extended preamble during the RX window. The second UE device may keep its receiver active after the RX window until the end of the extended preamble is received. The second UE device may then reactivate the receiver to receive the emergency message after a predetermined time offset from the end of the extended preamble. If needed, a binary overlay code may be provided for the extended preamble, which varies across the length of the extended preamble. In these examples, the second UE device may identify the time offset based on the binary overlay code and may deactivate the receiver after the RX window to save power. These technologies allow the first and second UE devices to synchronize so that emergency messages can be transmitted over long distances when one or both UE devices are offline, while consuming minimal power on the second UE device.

[0008] One aspect of this disclosure provides a user equipment device. The user equipment device may include one or more antennas. The user equipment device may include a transmitter configured to use the one or more antennas to transmit a device-to-device (D2D) signal to an auxiliary user equipment device. The user equipment device may include one or more processors. The one or more processors may be configured to transmit a message in the D2D signal. The one or more processors may be configured to transmit a preamble in the D2D signal prior to the message, the preamble being used by the auxiliary user equipment device to identify the time offset between the preamble and the message.

[0009] One aspect of this disclosure provides a user equipment device. The user equipment device may include one or more antennas. The user equipment device may include a receiver configured to receive a device-to-device (D2D) signal from an attached user equipment using the one or more antennas. The user equipment device may include one or more processors. The one or more processors may be configured to periodically activate the receiver during a receiver (RX) window series. The one or more processors may be configured to receive a preamble sequence in the D2D signal during an RX window in the RX window series. The one or more processors may be configured to deactivate the receiver after the RX window. The one or more processors may be configured to identify a time offset based on the preamble sequence received during the RX window. The one or more processors may be configured to reactivate the receiver during a message listening window that begins once the identified time offset has elapsed from the end of the preamble sequence. The one or more processors may be configured to receive a message in the D2D signal during the message listening window.

[0010] One aspect of this disclosure provides a method for operating a first user equipment (UE) device to receive a device-to-device (D2D) signal from a second UE device, comprising an emergency message preamble and an emergency message following the emergency message preamble. The method may include periodically activating a receiver on the first UE device during a receiver (RX) window sequence. The method may include receiving a portion of the emergency message preamble in the D2D signal during an RX window in the RX window sequence. The method may include keeping the receiver active until the end of the emergency message preamble is received, and then deactivating the receiver. The method may include reactivating the receiver during an emergency message listening window that begins after a predetermined time offset from the end of the emergency message preamble. The method may include receiving the emergency message in the D2D signal during the emergency message listening window. Attached Figure Description

[0011] Figure 1 This is a diagram of an exemplary communication network with user equipment and external communication equipment (such as wireless base stations or access points) according to some implementation schemes.

[0012] Figure 2 It is a block diagram of illustrative user equipment based on some implementation schemes.

[0013] Figure 3 It is a flowchart illustrating exemplary operations involved in the process of transmitting device-to-device signals from a first user equipment device to a second user equipment device while minimizing power consumption at the second user equipment device, according to some implementation schemes.

[0014] Figure 4This includes timing diagrams illustrating how an exemplary first user equipment device can transmit device-to-device signals according to some embodiments, the device-to-device signals including a series of preambles for time synchronization between an exemplary second user equipment device and the first user equipment device.

[0015] Figure 5 It is a flowchart illustrating exemplary operations involved in the process of transmitting device-to-device signals using a first user equipment device and in synchronizing the reception of messages transmitted by the first user equipment device based on the preamble sequence in the device-to-device signals using a second user equipment device, according to some implementation schemes.

[0016] Figure 6 This is a timing diagram illustrating how an exemplary first user equipment device can divide a preamble sequence among multiple transmissions of messages in a device-to-device signal, according to some implementation schemes.

[0017] Figure 7 Includes a timing diagram illustrating how an exemplary first user equipment device may transmit device-to-device signals according to some embodiments, the device-to-device signals including extended preambles for time synchronization between an exemplary second user equipment device and the first user equipment device.

[0018] Figure 8 It is a flowchart illustrating exemplary operations involved in the process of transmitting device-to-device signals using a first user equipment device and in synchronizing the reception of messages transmitted by the first user equipment device based on an extended preamble in the device-to-device signal using a second user equipment device, according to some implementation schemes.

[0019] Figure 9 It is a flowchart illustrating exemplary operations involved in the process of transmitting device-to-device signals using a first user equipment device and in synchronizing the reception of messages transmitted by the first user equipment device using a second user equipment device based on an extended preamble with an overlay code in the device-to-device signal, according to some implementation schemes. Detailed Implementation

[0020] Figure 1This is a schematic diagram of an exemplary communication system 26 (sometimes referred to herein as communication network 26) for transmitting wireless data between communication terminals. Communication system 26 may include network nodes (e.g., communication terminals). Network nodes may include user equipment (UEs), such as one or more UE devices 10. Network nodes may also include external communication equipment (e.g., communication equipment other than UE device 10), such as external communication equipment 12. For example, external communication equipment 12 may include a wireless base station or a wireless access point. UE device 10 and external communication equipment 12 may communicate with each other using a wireless communication link. If needed, UE device 10 may communicate wirelessly with external communication equipment 12 without going through any other intermediate network nodes in communication system 26 (e.g., UE device 10 may communicate directly with external communication equipment 12 over the air).

[0021] Communication system 26 may form part of a larger communication network, which includes network nodes coupled to external communication equipment 12 via wired and / or wireless links. This larger communication network may include one or more wired communication links (e.g., communication links formed using cables such as Ethernet cables, radio frequency cables such as coaxial cables or other transmission lines, optical fibers or other fiber optic cables, etc.), one or more wireless communication links (e.g., short-range wireless communication links operating within inches, feet, or tens of feet; medium-range wireless communication links operating within hundreds of feet, thousands of feet, miles, or tens of miles; and / or long-range wireless communication links operating within hundreds or thousands of miles, etc.), communication gateways, wireless access points, base stations, switches, routers, servers, modems, repeaters, telephone lines, network interface cards (NICs), line cards, ports, user equipment (e.g., computing devices, mobile devices, etc.), etc. The larger communication network may include communication (network) nodes or terminals coupled together using these components or other components (e.g., some or all of a mesh network, relay network, ring network, local area network, wireless local area network, personal area network, cloud network, star network, tree network, or a communication node network with other network topologies), the Internet, combinations thereof, etc. The UE device 10 may transmit data to other nodes or terminals in the larger communication network via external communication equipment 12 and / or receive data from other nodes or terminals (e.g., external communication equipment 12 may serve as an interface between the UE device 10 and the rest of the larger communication network). If necessary, some or all of the communication network may be operated by the corresponding network operator or service provider.

[0022] External communication equipment 12 may include one or more antennas that provide wireless coverage for UE device 10 located within a corresponding geographical area or region (such as cell 14). For example, the size of cell 14 may correspond to the maximum transmission power level of external communication equipment 12 and the air attenuation characteristics of the radio frequency signals transmitted by external communication equipment 12. When UE device 10 is located within cell 14, UE device can communicate with external communication equipment 12 via a wireless link. To support the wireless link, external communication equipment 12 may transmit radio frequency signals from external communication equipment 12 to UE device along the downlink (DL) direction, and / or UE device may transmit radio frequency signals from UE device to external communication equipment 12 along the uplink (UL) direction. Figure 1 In the example, the first UE device 10 (such as UE device 10-1) may be located within cell 14. Therefore, UE device 10-1 can communicate with external communication equipment 12 via a corresponding wireless link. Radio frequency signals 16 can be transmitted between UE device 10-1 and external communication equipment 12 to support the wireless link.

[0023] In practice, it is possible for UE device 10-1 to be outside the coverage area of ​​external communication equipment 12 and any other wireless access point or base station in communication system 26. For example, UE device 10-1 may be moved to location 18, as indicated by arrow 24. Location 18 is outside cell 14 and outside the coverage area of ​​any other wireless access point or base station in communication system 26. At location 18, UE device 10-1 may sometimes be referred to as "off-network". When external communication equipment 12 is inactive, disabled, or otherwise unavailable to UE device 10-1 (e.g., due to power outages or other obstacles to external communication equipment 12, due to disasters or other emergencies, due to network load balancing excluding UE device 10-1, due to blocked or denied access to the rest of communication network 26 by UE device 10-1, or due to obstacles, terrain, or weather preventing UE device 10-1 from transmitting radio frequency signals with external communication equipment 12), UE device 10-1 may also be off-network (e.g., outside cell 14 and outside the coverage area of ​​any other wireless access point or base station in communication system 26). Conversely, when UE device 10-1 is within a coverage area (such as coverage area 14) and is able to transmit wireless data via external communication equipment 12 and the rest of the network (e.g., communication system 26), UE device 10-1 may sometimes be referred to as "on-network."

[0024] When UE device 10-1 is in an off-network location, it may still need to provide radio data, such as message data, voice data, video data, or other data, to the communication terminals in communication system 26 or to another UE device (such as UE device 10-2). For example, a user of UE device 10-1 may encounter an emergency while off-network and may need to use UE device 10-1 to send an emergency message to authorities (e.g., emergency services) and / or another person to alert them to the user's situation and / or to call for help.

[0025] When offline, UE device 10-1 can still transmit radio frequency (RF) signals to other UE devices (such as UE device 10-2) (e.g., via a wireless device-to-device (D2D) link). UE device 10-1 may have its own coverage area 20 (e.g., extending around location 18 when UE device 10-1 is at location 18). The size of coverage area 20 is determined by the maximum transmission power level of UE device 10-1 and the air attenuation characteristics of the RF signals transmitted by UE device 10-1. When a user needs to send an emergency message while offline, UE device 10-1 may transmit an RF signal 22, which includes the emergency message or other radio data. When another UE device (such as UE device 10-2) is present in coverage area 20, UE device 10-2 may receive RF signal 22 and thus receive the emergency message transmitted by UE device 10-1. UE device 10-2 may then alert emergency services and / or provide assistance to the user of UE device 10-1. When UE device 10-2 is located within cell 14 (e.g., while UE device 10-1 is located outside cell 14), UE device 10-2 may additionally or alternatively relay emergency messages transmitted by UE device 10-1 to other network nodes (such as network nodes operated by emergency services (e.g., the US "911" service)) or to other users. Radio frequency signal 22 is a D2D signal and is therefore sometimes referred to herein as D2D signal 22. D2D signal 22 may form a corresponding wireless D2D communication link between UE device 10-1 and UE device 10-2. Specific implementations of D2D signal 22 including emergency messages transmitted by UE device 10-1 are merely illustrative and are described herein as examples. Typically, D2D signal 22 may include any desired data (e.g., message data, voice data, application data, video data, etc.) for transmission to UE device 10-2. UE device 10-2 may also transmit D2D signals to UE device 10-1 (e.g., the D2D link may be a bidirectional link).

[0026] Figure 2 This is an example of user equipment device 10 (e.g., Figure 1A block diagram of one or both of UE devices 10-1 and 10-2. UE device 10 is an electronic device and is therefore sometimes simply referred to as device 10 herein. UE device 10 may be: a computing device, such as a laptop computer, desktop computer, computer monitor containing an embedded computer, tablet computer, cellular phone, media player, or other handheld or portable electronic device; a smaller device, such as a wristwatch, a wristband device, a headset or handset device, a device embedded in glasses; or other equipment worn on a user's head; or other wearable or micro-devices, televisions, computer monitors without an embedded computer, gaming devices, navigation devices, embedded systems (such as systems in which electronic equipment with a display is installed in a kiosk or vehicle), voice-controlled speakers connected to the wireless Internet, home entertainment devices, remote control devices, game controllers, peripheral user input devices, wireless base stations or access points, equipment that implements the functions of two or more of these devices; or other electronic equipment.

[0027] like Figure 2 As shown, the UE device 10 may include components located on or within an electronic device housing (such as housing 50). Housing 50 (sometimes referred to as a shell) may be formed of plastic, glass, ceramic, fiber composite material, metal (e.g., stainless steel, aluminum, metal alloys, etc.), other suitable materials, or combinations thereof. In some cases, part or all of housing 50 may be formed of dielectric or other low-conductivity materials (e.g., glass, ceramic, plastic, sapphire, etc.). In other cases, housing 50 or at least some of the structures constituting housing 50 may be formed of metallic elements.

[0028] UE device 10 may include control circuitry 28. Control circuitry 28 may include storage devices such as storage circuitry 30. Storage circuitry 30 may include hard disk drive storage devices, non-volatile memory (e.g., flash memory configured to form a solid-state drive or other electrically programmable read-only memory), volatile memory (e.g., static random access memory or dynamic random access memory), etc. Storage circuitry 30 may include storage devices and / or removable storage media integrated within UE device 10.

[0029] Control circuitry 28 may include processing circuitry such as processing circuitry 32. Processing circuitry 32 may be used to control the operation of UE device 10. Processing circuitry 32 may include one or more processors, microprocessors, microcontrollers, digital signal processors, host processors, baseband processor integrated circuits, application-specific integrated circuits, central processing units (CPUs), graphics processing units (GPUs), etc. Control circuitry 28 may be configured to perform operations in UE device 10 using hardware (e.g., dedicated hardware or circuitry), firmware, and / or software. Software code for performing operations in UE device 10 may be stored on storage circuitry 30 (e.g., storage circuitry 30 may include a non-transitory (tangible) computer-readable storage medium storing software code). This software code may sometimes be referred to as program instructions, software, data, commands, or code. The software code stored on storage circuitry 30 may be executed by processing circuitry 32.

[0030] Control circuitry 28 can be used to run software on UE device 10, such as satellite navigation applications, internet browsing applications, Voice over Internet Protocol (VoIP) telephone calling applications, email applications, media playback applications, operating system functions, etc. To support interaction with external communication equipment, control circuitry 28 can be used to implement communication protocols. Communication protocols that can be implemented using control circuitry 28 include Internet protocols, Wireless Local Area Network (WLAN) protocols (e.g., IEEE 802.11 protocol—sometimes referred to as...). ), such as Protocols used for other short-range wireless communication links, such as protocols or other Wireless Personal Area Network (WPAN) protocols, IEEE 802.11ad protocols (e.g., Ultra Wideband protocols), cellular phone protocols (e.g., 3G protocols, 4G (LTE) protocols, 3GPP 5th Generation (5G) New Radio (NR) protocols, etc.), antenna diversity protocols, satellite navigation system protocols (e.g., Global Positioning System (GPS) protocols, Global Navigation Satellite System (GLONASS) protocols, etc.), antenna-based spatial ranging protocols, or any other desired communication protocol. Each communication protocol may be associated with a corresponding Radio Access Technology (RAT), which specifies the physical connection method used to implement the protocol.

[0031] UE device 10 may include input-output circuitry 36. Input-output circuitry 36 may include input-output devices 38. Input-output devices 38 may be used to allow data to be provided to UE device 10 and to allow data to be provided from UE device 10 to external devices. Input-output devices 38 may include user interface devices, data port devices, and other input-output components. For example, input-output devices 38 may include touch sensors, displays (e.g., touch-sensitive displays and / or force-sensitive displays), light-emitting components such as displays without touch sensor capability, buttons (mechanical, capacitive, optical, etc.), scroll wheels, touchpads, keypads, keyboards, microphones, cameras, buttons, speakers, status indicators, audio jacks and other audio port components, digital data port devices, motion sensors (accelerometers, gyroscopes, and / or compasses for detecting motion), capacitive sensors, proximity sensors, magnetic sensors, force sensors (e.g., force sensors coupled to displays to detect pressure applied to displays), temperature sensors, etc. In some configurations, keyboards, headsets, displays, pointing devices such as touchpads, mice and joysticks, and other input-output devices may be coupled to UE device 10 via wired or wireless connections (e.g., some of the input-output devices 38 may be peripheral devices coupled to the main processing unit or other parts of UE device 10 via wired or wireless links).

[0032] Input-output circuitry 36 may include wireless circuitry 34 to support wireless communication. Wireless circuitry 34 (sometimes referred to herein as wireless communication circuitry 34) may include one or more antennas 40. Wireless circuitry 34 may also include one or more radio components 44. Radio components 44 may include circuitry that operates signals at baseband frequencies (e.g., baseband circuitry) and radio frequency transceiver circuitry (such as one or more radio frequency transmitters 46 and one or more radio frequency receivers 48). Transmitters 46 may include signal generator circuitry, modulation circuitry, mixer circuitry for upconverting signals from baseband frequencies to intermediate frequencies and / or radio frequencies, amplifier circuitry (such as one or more power amplifiers), digital-to-analog converter (DAC) circuitry, control paths, power supply paths, switching circuitry, filter circuitry, and / or any other circuitry for transmitting radio frequency signals using antennas 40. Receiver 48 may include demodulation circuitry, mixer circuitry for downconverting signals from intermediate frequency and / or radio frequency to baseband frequency, amplifier circuitry (e.g., one or more low-noise amplifiers (LNAs)), analog-to-digital converter (ADC) circuitry, control paths, power supply paths, signal paths, switching circuitry, filter circuitry, and / or any other circuitry for receiving radio frequency signals using antenna 40. Components of radio component 44 may be mounted on a single substrate or integrated into a single integrated circuit, chip, package, or system-on-a-chip (SoC), or may be distributed among multiple substrates, integrated circuits, chips, packages, or SoCs.

[0033] Antenna 40 can be formed using any desired antenna structure for transmitting radio frequency signals. For example, antenna 40 may include an antenna with resonant elements, formed from a loop antenna structure, patch antenna structure, inverted F-shaped antenna structure, slot antenna structure, planar inverted F-shaped antenna structure, helical antenna structure, monopole antenna, dipole, a combination of these designs, etc. Adjustable filter circuitry, switching circuitry, impedance matching circuitry, and / or other antenna tuning components can be used to adjust the frequency response and wireless performance of antenna 40 over time. If desired, two or more antennas in antenna 40 can be integrated into a phased antenna array (sometimes referred to herein as a phased array antenna), wherein each antenna transmits a radio frequency signal with a corresponding phase and amplitude adjusted over time, such that the radio frequency signals interfere constructively and destructively to generate a signal beam along a given pointing direction.

[0034] As used herein, the term "transmitting radio frequency signals" means the transmission and / or reception of radio frequency signals (e.g., for performing one-way and / or two-way wireless communication with external wireless communication equipment). Antenna 40 can transmit radio frequency signals by radiating them into free space (or through an intermediary device structure such as a dielectric overlay). Alternatively, antenna 40 can receive radio frequency signals from free space (e.g., through an intermediary device structure such as a dielectric overlay). The transmission and reception of radio frequency signals by antenna 30 each involve the excitation or resonance of antenna currents on antenna resonant elements in the antenna by radio frequency signals within the antenna's operating frequency band.

[0035] Each radio component 44 can be coupled to one or more antennas 40 via one or more radio frequency (RF) transmission lines 42. The RF transmission lines 42 may include coaxial cables, microstrip transmission lines, stripline transmission lines, edge-coupled microstrip transmission lines, edge-coupled stripline transmission lines, transmission lines formed by combinations of these types of transmission lines, etc. If desired, the RF transmission lines 42 may be integrated into rigid and / or flexible printed circuit boards. If desired, one or more RF lines 42 may be shared among multiple radio components 44. RF front-end (RFFE) modules may be inserted onto one or more RF lines 42. The RF front-end modules may include substrates, integrated circuits, chips, or packages separate from the radio components 44, and may include filter circuitry, switching circuitry, amplifier circuitry, impedance matching circuitry, RF coupler circuitry, and / or any other desired RF circuitry for operating on RF signals transmitted via the RF transmission lines 42.

[0036] Radio component 44 can transmit and / or receive radio frequency signals within a corresponding frequency band of a radio frequency (sometimes referred to herein as a communication band or simply a "band"). The frequency band processed by radio component 44 may include a wireless local area network (WLAN) band (e.g., (IEEE 802.11) or other WLAN communication bands, such as the 2.4GHz WLAN band (e.g., 2400MHz to 2480MHz), the 5GHz WLAN band (e.g., 5180MHz to 5825MHz), 6E band (e.g., 5925MHz to 7125MHz) and / or others Bands (e.g., 1875MHz to 5160MHz); Wireless Personal Area Network (WPAN) bands such as 2.4GHz. 5G or other WPAN communication bands; cellular telephone bands (e.g., the band from about 600 MHz to about 5 GHz, the 3G band, the 4G LTE band, the 5G New Radio Frequency Range 1 (FR1) band below 10 GHz, the 5G New Radio Frequency Range 2 (FR2) band between 20 GHz and 60 GHz, etc.); other centimeter or millimeter wave bands between 10 GHz and 300 GHz; near-field communication bands (e.g., 13.56 MHz); satellite navigation bands (e.g., the GPS band from 1565 MHz to 1610 MHz, the Global Navigation Satellite System (GLONASS) band, the BeiDou Navigation Satellite System (BDS) band, etc.); ultra-wideband (UWB) bands operating under the IEEE 802.15.4 protocol and / or other ultra-wideband communication protocols; communication bands under the 3GPP wireless communication standards family; and in IEEE The following are permitted bands: communication bands under the 802.XX standard family; industrial, scientific, and medical (ISM) bands, such as ISM bands between approximately 900 MHz and 950 MHz or other ISM bands below or above 1 GHz; one or more unlicensed bands; one or more bands reserved for emergency services and / or public services; and / or any other desired bands of interest. If necessary, radio circuit 34 may also be used to perform spatial ranging operations.

[0037] When transmitter 46 is active (e.g., enabled), transmitter 46 can transmit radio frequency signals through antenna 40. When transmitter 46 is inactive (e.g., disabled or not actively transmitting symbols), transmitter 46 does not transmit radio frequency signals through antenna 40. Similarly, when receiver 48 is active (e.g., enabled), receiver 48 can receive radio frequency signals through antenna 40. When receiver 48 is inactive (e.g., disabled), receiver 48 does not receive radio frequency signals through antenna 40. Control circuit 28 can control transmitter 46 to be active or inactive at any given time. Control circuit 28 can also control receiver 48 to be active or inactive at any given time. For example, control circuit 28 can activate or deactivate transmitter 46 and / or receiver 48 at different times as specified by the communication protocol governing radio component 44 and / or based on user-provided instructions and / or instructions from other software running on control circuit 28. For example, control circuitry 28 can configure transmitter 46 to be inactive by turning off transmitter 46, by providing a control signal to a switching circuit on the power or enable line of transmitter 46, by providing a control signal to a control circuit on transmitter 46, and / or by providing a control signal to a switching circuit within transmitter 46. When transmitter 46 is inactive, some or all of transmitter 46 may be inactive (e.g., disabled or powered off), or transmitter 46 may remain powered on but not transmit radio frequency signals through antenna 40. Similarly, for example, control circuitry 28 can configure receiver 48 to be inactive by powering off receiver 48, by providing a control signal to a switching circuit on the power or enable line of receiver 48, by providing a control signal to a control circuit on receiver 48, and / or by providing a control signal to a switching circuit within receiver 48. When receiver 48 is inactive, some or all of receiver 48 may be disabled (e.g., powered off), or receiver 48 may remain powered on but not actively receive radio frequency signals incident on antenna 40. When transmitter 46 and receiver 48 are active, they consume more power on UE device 10 than when they are inactive (e.g., the battery on UE device 10 may be depleted faster when transmitter 46 and receiver 48 are active than when transmitter 46 or receiver 48 are inactive).

[0038] Figure 2 The examples are merely illustrative. Although for clarity... Figure 1In the example, control circuitry 28 is shown separately from wireless circuitry 34, but wireless circuitry 34 may include processing circuitry (e.g., one or more processors) forming part of processing circuitry 32 and / or storage circuitry (e.g., a portion of control circuitry 28 that may be implemented on wireless circuitry 34) forming part of storage circuitry 30 of control circuitry 28. As an example, control circuitry 28 may include baseband circuitry (e.g., one or more baseband processors), digital control circuitry, analog control circuitry, and / or other control circuitry forming part of radio components 44. For example, the baseband processor may access a communication protocol stack on control circuitry 28 (e.g., storage circuitry 30) to: perform user plane functions at the PHY layer, MAC layer, RLC layer, PDCP layer, SDAP layer, and / or PDU layer; and / or perform control plane functions at the PHY layer, MAC layer, RLC layer, PDCP layer, RRC layer, and / or non-access layer. If desired, PHY layer operation may be additionally or alternatively performed by radio frequency (RF) interface circuitry in wireless circuitry 34.

[0039] when Figure 1 When UE device 10-1 is offline, it should still be accessible in case its user encounters an emergency or needs to transmit wireless data to another UE device (such as UE device 10-2). To maximize the likelihood that another UE device (such as UE device 10-2) will be able to receive the D2D signal 22, UE device 10-1 should be able to transmit the D2D signal 22 over a relatively long distance (e.g., it may be desirable for UE device 10-1 to have the largest possible coverage area 20). For example, this distance (e.g., the radius of the coverage area 20) can be hundreds of meters, several kilometers, several kilometers, or tens of kilometers. UE device 10-1 can maximize the range of the D2D signal 22 by transmitting at a relatively high transmission power level (e.g., the maximum transmission power level) for a relatively long period of time.

[0040] Typically, UE device 10-1 can transmit D2D signal 22 at any desired frequency (e.g., frequencies in ISM bands, unlicensed bands, bands reserved for emergency services / public services, etc.). If needed, UE device 10-1 can transmit D2D signal 22 at relatively low frequencies (e.g., frequencies in bands below 1 GHz, below 2 GHz, below 3 GHz, below 950 MHz, etc.). This can be used to minimize air signal attenuation of D2D signal 22, thereby maximizing the size of coverage area 20. The wireless circuit 34 on UE device 10-1 may include a dedicated radio component 44 for transmitting D2D signal 22, or the radio component transmitting D2D signal 22 may also transmit other signals associated with other communication protocols or RATs (e.g., a single radio component 44 on UE device 10-1 may transmit both WLAN signals and D2D signal 22, a single radio component 44 on UE device 10-1 may transmit both cellular phone signals and D2D signal 22, etc.).

[0041] Furthermore, even when UE device 10-2 is within coverage area 20, UE device 10-2 can only correctly recover radio data (e.g., emergency messages) in D2D signal 22 when (a) receiver 48 on UE device 10-2 is active and (b) UE device 10-2 is time-synchronized with UE device 10-1. While UE device 10-2 could always keep its receiver 48 active to listen for any D2D signal 22 that happens to be transmitted, this would consume excessive power in UE device 10-2, causing UE device 10-2 to deplete its battery relatively quickly. Keeping receiver 48 always active is particularly power inefficient because off-network UE devices (such as UE device 10-1) only need to transmit emergency messages or other radio data in D2D signal 22 in very rare cases. Furthermore, while UE devices can synchronize with each other using signals from external communication equipment 12 when located within cell 14 (e.g., the base station can be configured with a sleep mode and paging cycle to allow devices to sleep when power-saving), off-network UE devices (such as UE device 10-1 and UE device 10-2) were not previously synchronized with each other or with a time reference. Even if the UE devices are time-synchronized at a point in time (e.g., when both UE devices are connected to the network), once one or both UE devices are off-network, the timing of UE device 10-1 may drift relative to the timing of UE device 10-2. Therefore, a simple paging mechanism may be insufficient to allow UE device 10-2 to correctly receive and recover radio data in D2D signal 22. Therefore, it is desirable to provide a power-efficient system and method for time-synchronized transmission of D2D signal 22 by UE device 10-1 and reception of D2D signal 22 by UE device 10-2 when at least UE device 10-1 is off-network.

[0042] Some communication protocols (such as Wi-Fi) include time synchronization methods configured for a much shorter range than those associated with coverage area 20. These short-range protocols are unsuitable for transmitting D2D signals 22 because they consume excessive power on UE devices 10-1 and / or 10-2, thus draining the battery at an excessively high rate. Furthermore, these short-range protocols operate under the control of external communication equipment (such as wireless access points (APs)) and follow the AP's timing, but no AP is available when the UE device is off-network. Other protocols (such as the Wi-Fi Neighborhood Aware Network (NAN) protocol) do not support the long distances required for D2D signals 22 and consume excessive energy to maintain synchronization, making them unsuitable for rare communication events such as emergency message transmission.

[0043] To allow UE device 10-2 to minimize power consumption while listening for potential D2D signal 22, UE device 10-2 may periodically activate its receiver 48 during a receiver (RX) window during which the receiver is able to receive D2D signal 22 (e.g., the receiver is inactive between RX windows). When the RX window is short, any transmission of D2D signal 22 is likely to arrive at UE device 10-2 while the receiver is inactive, thus preventing UE device 10-2 from properly recovering the data in D2D signal 22. When the RX window is long, transmission of D2D signal 22 is more likely to arrive at UE device 10-2. However, a long RX window causes UE device 10-2 to consume excessive power, effectively “searching” for D2D signal 22, which is rarely transmitted by another UE device. Conversely, for UE device 10-1, expending power to search for potential receiver devices (such as UE device 10-2) will be more power-efficient than the reverse. UE device 10-1 can search for potential receiver devices by transmitting one or more preambles before transmitting the expected data (e.g., an emergency message) to be received at UE device 10-2.

[0044] Figure 3 This is a flowchart illustrating the exemplary operation involved in transmitting D2D signal 22 between UE device 10-1 and UE device 10-2 in a time-synchronized and power-efficient manner. Figure 3 Operations 52-56 and 66 can be performed by UE device 10-1. Figure 3 Operations 60-66 can be performed by UE device 10-2.

[0045] At operation 52, UE device 10-1 can be connected to the network (e.g., in...). Figure 1 When the UE device 10-1 is in the cell 14, it communicates with the network (e.g., a network node or terminal of the communication system 26) via external communication equipment 12. When the UE device 10-1 becomes offline, the process can proceed to operation 54.

[0046] At operation 60, UE device 10-2 may periodically activate its receiver 48 during the RX window series. UE device 10-2 may listen for D2D signal 22 during the RX window. Receiver 48 on UE device 10-2 may be inactive between RX windows to save power.

[0047] At operation 54, when UE device 10-1 is offline, UE device 10-1 can use D2D signal 22 to identify radio data to be transmitted to another UE device (such as UE device 10-2). For example, UE device 10-1 can identify an emergency message to be transmitted in D2D signal 22. UE device 10-1 can generate an emergency message in response to user input provided to a software application running on UE device 10-1 (e.g., in response to a user pressing an emergency call, emergency message, or “SOS” button displayed on a touchscreen display, in response to a user activating an emergency response software application, etc.), in response to an application call of the software application running on UE device 10-1, in response to sensor data collected by one or more sensors on UE device 10-1 (e.g., accelerometer data or other sensor data indicating that UE device 10-1 has experienced an accident, fallen a great distance, been subjected to a strong impact, etc.), and / or in response to any other desired triggering conditions. For example, an emergency message may include information identifying the location of the UE device 10-1 (e.g., based on GPS data or other location information collected by the UE device 10-1), user information, a message drafted by the user, and / or any other expected information intended to alert another person or emergency services personnel about the user's condition or to call for help.

[0048] At operation 56, UE device 10-1 may activate its transmitter 46 and transmit a D2D signal 22, which includes one or more preambles followed by an emergency message (e.g., the D2D signal 22 may include an emergency message preceded by one or more preambles). If needed, UE device 10-1 may periodically repeat this transmission (as shown in loopback path 58) to maximize the probability that another UE device (such as UE device 10-2) will receive the D2D signal 22. The emergency message may be separated from the end of one or more preambles by a predetermined time period or offset time. If needed, UE device 10-2 may know the predetermined time period or offset time (e.g., from software or other data on UE devices 10-1 and 10-2, from the communication protocol that manages the D2D signal 22, etc.).

[0049] At operation 62, UE device 10-2 may receive at least a portion of one or more preambles transmitted by UE device 10-1 in D2D signal 22 during an X window of an RX window in which receiver 48 on UE device 10-2 is active. Control circuitry 28 on UE device 10-2 may process the received preambles to synchronize timing with UE device 10-1. For example, UE device 10-2 may identify (e.g., determine, calculate, operate, generate, produce, etc.) the timing of an emergency message listening window during which UE device 10-1 will transmit an emergency message (e.g., the emergency message listening window may begin at an initial time separated from the end of one or more preambles by a predetermined time interval or offset time). This can be used to synchronize UE device 10-2 with UE device 10-1 so that UE device 10-2 will be able to correctly recover the emergency message transmitted by UE device 10-1. If necessary, UE device 10-2 may deactivate receiver 48 after identifying the timing and / or after receiving one or more preambles to save power.

[0050] At operation 64, the control circuitry 28 on UE device 10-2 can reactivate its receiver 48 during an emergency message listening window (e.g., based on a timing identified at operation 62). Receiver 48 on UE device 10-2 can receive emergency messages transmitted during the emergency message listening window. UE device 10-2 can perform any desired follow-up processing based on the received emergency message. For example, UE device 10-2 can warn or notify its user about an emergency message and / or its content, can transmit a UL signal to external communication equipment 12 to notify the network of an emergency message (e.g., when UE device 10-2 is located within cell 14), can transmit an additional D2D signal to another UE device to notify that UE device of an emergency message (e.g., UE device 10-2 can provide an emergency message to external communication equipment 12 or other parts of the network via relays of one or more additional UE devices, the last of which is located within cell 14), etc.

[0051] If necessary, processing can proceed from operations 56 and 64 to optional operation 66. At optional operation 66, UE device 10-1 and UE device 10-2 can continue to use D2D signals for one-way or two-way communication (e.g., where communication is based on time and frequency synchronization based on an emergency preamble processed by UE device 10-2 in operation 62). Figure 3 The examples are merely illustrative. One or more iterations of operation 56 may be performed simultaneously by UE device 10-1 and by UE device 10-2 performing operations 62 and / or 64.

[0052] Figure 4Including UE device 10-1 (e.g., in Figure 3 The operation at point 56) transmits one or more preambles, including a timing diagram of an example of a series of preambles that identify the corresponding time offsets used to synchronize the timing of UE device 10-2 with the timing of UE device 10-1.

[0053] Figure 4 Timing diagram 68 shows the transmission (TX) timing of UE device 10-1 when transmitting D2D signal 22. Figure 4 Timing diagram 70 illustrates the reception (RX) timing of UE device 10-2 when receiving D2D signal 22. As shown in timing diagram 68, UE device 10-1 may begin transmitting a series of N preambles 72 at time TA, where each preamble is marked by a corresponding index n from 1 to N (e.g., first preamble 72-1, second preamble 72-2 following preamble 72-1, Nth preamble 72-N following (N-1)th preamble, etc.). Then, UE device 10-1 may begin transmitting emergency message 74 after transmitting the series of N preambles 72 (e.g., after a predetermined offset time, such as at time TC).

[0054] Each preamble 72 can be a bit sequence with a predetermined (time) preamble length T, which allows UE device 10-2 to detect the presence of a signal and allows the receiver on UE device 10-2 to synchronize the transmission timing with the transmitter in UE device 10-1. As an example, the preamble length T can be less than or equal to 1 ms. The duration of the emergency message 74 is typically much longer than the preamble length T. The preamble 72 may also be referred to herein as the preamble sequence 72 or the synchronization sequence 72. Each preamble 72 can be a known signal with relatively strong correlation characteristics (e.g., a format known to both UE device 10-1 and UE device 10-2) to allow UE device 10-2 to easily detect the preamble from background noise and distinguish the preamble from the background noise. As two examples, each preamble 72 can be a Zadoff-Chu sequence or an M sequence.

[0055] Each preamble 72 in the N preamble sequence may include or otherwise identify the corresponding offset information OFS. n Offset information OFS n The corresponding preamble and the time when the UE device 10-1 will begin transmitting the emergency message 74 can be identified. Figure 4In the example, the time offset ΔTn between time TC. For example, preamble 72-1 may include offset information OFS1, which identifies the time offset ΔT1 from the end of preamble 72-1 to the start of emergency message 74 (e.g., time offset ΔT1 may be the duration between time TA+T and time TC), preamble 72-2 may include offset information OFS2, which identifies the time offset ΔT2 from the end of preamble 72-2 to time TC, and preamble 72-N may include offset information OFS N This offset information identifies the time offset ΔTN from the end of preamble 72-N to time TC. The N preamble 72 sequence can be offset by the time offset ΔTN from emergency message 74 (in time).

[0056] As shown in timing diagrams 68 and 70, UE device 10-1 may initially be asynchronous with respect to UE device 10-2 by a priori time offset of 78. For example, the time t since one or both UE devices have left the network. -0 The time t0 maintained by UE device 10-1 may have been offset by an a priori time offset 78. UE devices 10-1 and 10-2 may maintain coarse time synchronization via internal / network standard / protocol (e.g., UTC) time (e.g., equal to T*N within the maximum supported time uncertainty 82). This internal standard time can be periodically adjusted / corrected whenever the UE device communicates with external communication equipment 12 or receives satellite navigation signals when needed (e.g., synchronizing the time t0 at each UE device with external communication equipment 12 and / or the satellite navigation system). Preamble 72 allows UE device 10-2 to fine-tune its synchronization within the maximum supported time uncertainty 82 to allow UE device 10-2 to correctly receive emergency messages 74 while consuming minimal power.

[0057] When no time reference is available, the devices will drift by D ppm, such that at some later time, the relative offset between the devices may prevent synchronization within the maximum supported time uncertainty 82. As a possible countermeasure, UE device 10-1 may occasionally transmit a global clock tick preamble when offline, which allows all nearby offline devices (such as UE device 10-2) to adjust their time t0 to match the time t0 on UE device 10-1 (e.g., if UE device 10-1 needs to transmit an urgent message later, UE device 10-2 may coarsely synchronize with UE device 10-1). As an example, such a global clock tick preamble may be transmitted once per hour with a certain random offset.

[0058] UE device 10-2 can periodically activate its receiver 48 during RX window 76, one of which is in Figure 4As shown in the figure. Each RX window 76 can be separated from the previous and next RX windows by an RX window period P (for clarity, Figure 4 (Not shown in the image). The RX window 76 may have a (time) RX window length L. The RX window length L may be greater than the preamble length T to ensure that the UE device 10-2 can fully receive at least one preamble in the N preamble 72 series. For example, the RX window length L may be equal to 2*T, 1.5*T, 3*T, 4*T, greater than 4*T, etc.

[0059] As shown in timing diagram 70, UE device 10-2 can receive preamble 72-1 during RX window 76. Control circuitry 28 on UE device 10-2 can process the received preamble 72-1 to identify time offset ΔT1 based on offset information OFS1 of preamble 72-1 (e.g., simultaneously processing...). Figure 3 (Operation 62). Then, UE device 10-2 knows that it will receive emergency message 74 after a time offset ΔT1 after the end of preamble 72-1, thereby synchronizing the timing of UE device 10-2 with the timing of UE device 10-1. UE device 10-2 can deactivate its receiver 48 to save power after the end of RX time window 76. UE device 10-2 can reactivate receiver 48 after a time offset ΔT1 from the end of preamble 72-1 (e.g., during emergency message listening window 80 starting from time TC). Then, UE device 10-2 can receive emergency message 74 during emergency message listening window 80. UE device 10-2 can correctly recover emergency message 74 from D2D signal 22 because UE device 10-2 has time-synchronized with UE device 10-1 using preamble 72. By transmitting a series of preambles 72, each preamble identifying a corresponding time offset ΔTn, UE device 10-2 will be able to synchronize its timing with UE device 10-1 (e.g., for receiving emergency message 74 at the common time TC now shared by both UE devices), regardless of where the RX window 76 happens to fall within the N series of preambles 72 transmitted by UE device 10-1. This allows UE devices 10-1 and 10-2 to be time-synchronized to receive messages (e.g., emergency message 74) in the D2D signal 22, even though one or both devices are offline and thus subject to potential clock drift between devices, while consuming minimal power on UE device 10-2.

[0060] For example, each preamble 72 can be the same type of sequence, but with different variations for each index n (e.g., where the UE device 10-2 identifies the offset information OFS based on a specific variation of the sequence received during its RX window 76). nThis allows for the identification of the time offset ΔTn. Each variant may have strong autocorrelation characteristics and low cross-correlation between different variants (e.g., variants in the N preamble 72 series or between different preambles). The Zadoffchu sequence or the M sequence are two non-limiting examples of sequences that may conform to these criteria. Depending on how many sequence variants are feasible (e.g., how large N is feasible), each variant may carry further information beyond the time offset. For example, each variant may identify a frequency or frequency hopping mode indication to be used for subsequent reception of the emergency message 74. The UE device 10-2 may process the preamble 72 received during its RX window 76 to identify the frequency or frequency hopping mode indication for receiving the emergency message 74. The UE device 10-2 may then use the frequency or frequency hopping mode corresponding to the frequency hopping mode indication upon receiving the emergency message 74 (e.g., within the emergency message listening window 80). If necessary, sequence variants may be used to transmit further information beyond the beam hopping mode. For example, sequence variations can be used to distinguish emergencies from other paging types (e.g., where UE device 10-1 searches for another UE device 10-2 in its contact list to chat), limit the number of potential responders to UE device 10-2 (e.g., by requesting a device with an internet connection), distribute clock synchronization information, etc.

[0061] Detecting specific variations of the preamble sequence received during RX window 76 (e.g., detecting a specific preamble 72 received during RX window 76) may introduce the risk of false positives / false negatives. However, if the false positive / false negative rate is relatively low, UE device 10-2 will consume only a small amount of energy during unnecessary emergency message reception attempts (e.g., activating the receiver on UE device 10-2 during emergency message listening window 80 will not excessively drain the battery on UE device 10-2). Preamble 72 may indicate to UE device 10-2 the presence of an upcoming emergency message while allowing time and frequency synchronization between UE devices 10-1 and 10-2. Emergency message 74 may include cyclic redundancy check (CRC) or other measures that make it virtually impossible for UE device 10-2 to decode false positive / false negative emergency messages. If necessary, UE device 10-2 may keep its RX window open after receiving preamble 72 so that UE device 10-2 receives all subsequent preambles 72. For example, this may help further reduce the presence of false positives / false negatives.

[0062] Figure 5 This demonstrates how UE devices 10-1 and 10-2 are based on Figure 4 The flowchart shown illustrates the N preamble 72 sequence used to time-synchronize the transmission of emergency message 74. Figure 5 Operations 90-94 can be performed by UE device 10-1 (e.g., simultaneously processing) Figure 3 Operation 56). Figure 5 Operations 96-102 can be performed by the UE device 10-2 (e.g., simultaneously processing) Figure 3 Operations 62 and 64).

[0063] exist Figure 5 At operation 90, the radio circuit 34 on the UE device 10-1 can generate an N-preamble sequence 72 for transmission. Each preamble 72 may include corresponding offset information OFS. n Each offset information identifies the corresponding time offset Δ from the end of the preamble until the transmission of the emergency message 74 at time TC.

[0064] At operation 92, UE device 10-1 can begin transmitting the N preamble sequence to its coverage area 20 ( Figure 1 Search for UE devices within the scope.

[0065] At operation 96, when receiver 48 on UE device 10-2 (e.g., a UE device in coverage area 20) is active, receiver 48 on UE device 10-2 can receive one of the N preambles 72 transmitted by UE device 10-1 during one RX window of its RX window 76. For example, UE device 10-2 can... Figure 4 The RX window 76 shown receives the preamble 72-1.

[0066] At operation 98, the control circuit 28 on the UE device 10-2 can identify (e.g., calculate, generate, determine, produce, operate, etc.) the time offset ΔTn associated with the received preamble 72 (e.g., the control circuit 28 can identify offset information OFS). n And it can be based on the identified offset information OFS n To identify the time offset ΔTn). Figure 4 In the example, UE device 10-2 may identify the time offset ΔT1 based on the offset information OFS1 in the preamble 72-1. UE device 10-2 may identify the time offset according to the communication protocol that manages the D2D signal 22 or any other standard or scheme known to both UE devices 10-1 and 10-2 (e.g., implemented using one or more software applications running on both UE devices 10-1 and 10-2).

[0067] At operation 100, UE device 10-2 may disable its receiver 48 (e.g., when the RX window has closed).

[0068] At operation 102, UE device 10-2 may reactivate its receiver 48 after an identified time offset ΔTn from the end of the preamble received during RX window 76 (e.g., during an emergency message listening window 80 that begins after ΔTn from the end of the preamble). UE device 10-2 may then receive emergency message 74 during emergency message listening window 80 (sometimes referred to herein as emergency message listening period 80). Figure 4 In the example, UE device 10-2 can reactivate its receiver 48 at time TC, which is time-shifted by a time offset ΔT1 from the end of preamble 72-1. UE device 10-2 can then perform any desired follow-up processing based on the received emergency message 74.

[0069] For example, the preamble length T can be 25 ms. A relatively long preamble length (such as 25 ms) allows for reliable detection of the preamble at the maximum distance. If the RX window length L is 2*T and the preamble is continuous, the duration of at least one complete preamble length T will fit within the RX window 76. For example, for an RX window period P = 5 seconds and an effective duty cycle of 1%, the RX window length L would be 50 ms. In the absence of preamble repetition (i.e., at N = 1), the maximum time offset needs to be + / - 12.5 ms to ensure that there is still a complete preamble within the RX window. With a relative time drift of + / - 10 ppm between UE device 10-1 and UE device 10-2, the UE devices drift too far after only about 20 minutes to synchronize. Instead of using the receiver to search for the transmitter, the receiver search is performed using UE device 10-1, supporting a longer drift time between UE device 10-1 and UE device 10-2 (e.g., using UE device 10-1 to transmit N preamble 72 series, where N is greater than one). For example, if N = 4, the maximum time offset needs to be + / - (N / 2)*L. When the RX window length L is 50ms and the drift is + / - 10ppm, the UE device can still use the transmitted preamble for time synchronization for up to 1.4 hours after disconnection. Increasing N can further increase this time. If needed, in addition to clock drift, the requirement for intra-device coexistence time alignment may be another motivation for the receiver. For example, variable-length time gaps can be associated with intra-device coexistence schemes, in which the transmitter needs to protect other ongoing TX / RX operations (with arbitrary durations or transmission modes) from the preamble transmission.

[0070] Since UE device 10-1 may be located relatively far from UE device 10-2, transmitter 46 on UE device 10-1 can transmit at a relatively high power level and for a relatively long period of time. In some scenarios, these high power levels may prevent the transmitter from transmitting multiple sequential preambles 72 consecutively (e.g., because the power amplifier in the transmitter may need time to cool down between transmissions). To mitigate these issues, UE device 10-1 may transmit a first subset of the N preamble sequence 72 before the first transmission of emergency message 74, and then transmit a second subset of the N preamble sequence 72 before the subsequent second transmission of emergency message 74.

[0071] Figure 6 This is a timing diagram illustrating an example of how UE device 10-1 can transmit different subsets of the N-preamble 72 series before different transmissions of emergency message 74 (e.g., to allow the power amplifier in transmitter 46 to have a cooling time). Figure 6 As shown, UE device 10-1 can transmit the first group of preambles from N preambles 72, such as odd-numbered preambles in a preamble series. For example, UE device 10-1 can transmit the first preamble 72-1 from the N preamble sequence at time TA. Then, UE device 10-1 can abandon the transmission of the second preamble from the N preamble series after the transmission of the first preamble 72-1 (e.g., for preamble length T). Then, UE device 10-1 can transmit the third preamble 72-3 from the N preamble series, and may abandon the transmission of the fourth preamble, etc. At time TC, UE device 10-1 can transmit an emergency message 74. Abandoning the transmission of even-numbered preambles allows the power amplifier in UE device 10-1 to cool between the transmissions of odd-numbered preambles.

[0072] After the transmission of emergency message 74 (e.g., after RX window period P from time TA), UE device 10-1 may then transmit an even-numbered preamble from the N preamble series 72 before retransmitting emergency message 74. For example, at time TA', UE device 10-1 may abandon the transmission of the first preamble from the N preamble series 72 (e.g., for preamble length T). After preamble length T has elapsed (e.g., at time TA'+T), UE device 10-1 may transmit a second preamble 72-2 from the N preamble series 72. Then, UE device 10-2 may abandon the transmission of a third preamble from the N preamble series 72 after the transmission of the second preamble 72-2 (e.g., for preamble length T). Then, UE device 10-1 may transmit a fourth preamble 72-4 from the N preamble series 72, and may abandon the transmission of a fifth preamble, etc. At time TC', UE device 10-1 may then retransmit emergency message 74. This allows UE device 10-2 to receive a preamble in preamble 72 before the transmission of emergency message 74, the emergency message being offset from the received preamble 72 by the time offset identified by the preamble 72, while allowing the power amplifier on UE device 10-1 to cool between transmissions at relatively high transmit power levels.

[0073] Figure 6 The examples are merely illustrative, and in general, the first and second preamble sets can include any desired preamble from the N-preamble series 72 (e.g., the first preamble set can include every other pair of sequential preambles 72, every three sequential preambles 72, etc.). The UE device 10-1 can divide the N-preamble series 72 into any desired number of sets (e.g., more than two sets) for transmission before any desired number of retransmissions of the emergency message 74. The UE device 10-1 transmits multiple preamble series 72. Figures 4 to 6 The example is merely illustrative. If necessary, the UE device 10-1 may alternatively transmit a single long (extended) preamble before transmitting the emergency message 74.

[0074] Figure 7 The timing diagram includes an example of UE device 10-1 transmitting a single extended preamble before transmitting emergency message 74. Figure 7 Timing diagram 104 shows the TX timing of UE device 10-1 during the transmission of D2D signal 22. Figure 7 Timing diagram 106 shows the RX timing of UE device 10-2 during the reception of D2D signal 22.

[0075] As shown in timing diagram 104, UE device 10-1 may transmit a single extended preamble 108 starting at time TA. The extended preamble 108 may also be referred to herein as an extended preamble sequence 108 or an extended synchronization sequence 108. The extended preamble 108 may have a duration extending from time TA to time TD. The extended preamble 108 may be a continuous preamble sequence (e.g., having a continuous bit sequence). As an example, the sequence may be a repetition of the same subsequence, such as a Zadoff-Chu sequence (e.g., where each symbol lasts 1 / 14 ms) repeated over hundreds of ms (e.g., the extended preamble 108 may be hundreds of ms long).

[0076] As shown in timing diagram 106, the receiver on UE device 10-2 can be active during an RX window 76 falling between times TA and TD. Therefore, UE device 10-2 can receive a portion (subset or subsequence) of the extended preamble 108 falling within the RX window 76. If needed, once UE device 10-2 has received a portion of the extended preamble 108 within the RX window 76, UE device 10-2 can keep its receiver 48 active after the end of the RX window 76 until UE device 10-2 receives the end of the extended preamble 108 (e.g., during an extended RX window 76E that extends the receiver's active time from RX window length L to time TD). Once UE device 10-2 has received the end of the extended preamble 108, UE device 10-2 can deactivate its receiver at a predetermined time offset 110 (e.g., UE device 10-2 can deactivate receiver 48 in response to receiving the end of the extended preamble 108).

[0077] After a predetermined time offset 110 (e.g., at time TC), UE device 10-1 may transmit emergency message 74, and UE device 10-2 may reactivate its receiver (e.g., during receiver listening window 80) to receive emergency message 74. The predetermined time offset 110 may be known to both UE device 10-1 and UE device 10-2, depending on the communication protocol governing D2D signal 22, any other standard or scheme known to both UE devices 10-1 and 10-2 and identified by information transmitted in the extended preamble 108 itself (e.g., implemented using one or more software applications running on both UE devices 10-1 and 10-2), etc. In this way, the end of the extended preamble 108 can be used as a time synchronization trigger to synchronize the timing of UE device 10-2 with the timing of UE device 10-1 to receive emergency message 74, even if the UE devices have previously drifted away from the prior time offset 78. For example, keeping the receiver on UE device 10-2 active during extended RX window 76E allows UE device 10-2 to reconfirm the initial detection of extended preamble 108 during RX window 76.

[0078] Figure 8 This is a flowchart illustrating the operations involved in transmitting and receiving emergency message 74, which is based on... Figure 7 The extended preamble 108 is used for time synchronization. Figure 8 Operations 120-124 can be performed by UE device 10-1 (e.g., simultaneously processing) Figure 3 Operation 56). Figure 8 Operations 126-132 can be performed by UE device 10-2 (e.g., simultaneously processing) Figure 3 Operations 62 and 64).

[0079] exist Figure 8 At operation 120, UE device 10-1 can generate extended preamble 108 for transmission.

[0080] At operation 122, UE device 10-1 may begin transmitting extended preamble 108 in its coverage area 20 ( Figure 1 Search for UE devices within the scope.

[0081] At operation 126, when the receiver on UE device 10-2 is active, receiver 48 on UE device 10-2 (e.g., UE device in coverage area 20) may receive a portion (subset or subsequence) of the extended preamble 108 transmitted by UE device 10-1 during one RX window of its RX window 76.

[0082] At operation 128, UE device 10-2 can, after passing through RX window 76 (e.g., in...), Figure 7 During the extended RX window 76E, the UE device 10-2 keeps its receiver 48 active. The UE device 10-2 may continue to receive the extended preamble 108 (during the extended RX window 76E) until the UE device 10-2 receives the end of the extended preamble 108.

[0083] At operation 130, once the UE device 10-2 has received the end of the extended preamble 108, the UE device 10-2 can disable its receiver 48 to save power.

[0084] At operation 124, after a predetermined time offset of 110 from the end of the self-transmission extended preamble 108, the UE device 10-1 can transmit the emergency message 74.

[0085] At operation 132, after a predetermined time offset 110 from the end of receiving the extended preamble 108, UE device 10-2 may reactivate its receiver 48 for the emergency message listening window 80 (e.g., from time TC). UE device 10-2 can then receive and decode the emergency message 74 during the emergency message listening window 80 (e.g., since UE device 10-2 is now time-synchronized with UE device 10-1 using the extended preamble 108). UE device 10-2 can perform any desired follow-up processing based on the emergency message 74.

[0086] Using extended preamble 108 to synchronize the time of UE device 10-2 with UE device 10-1 allows UE device 10-2 to implement RX window 76 with arbitrary RX window length L. For example, the RX window length L does not need to be the preamble length T. Figure 4 The size of the RX window should be at least twice that of the RX window to ensure complete sequence capture. For example, the RX window length L can be equal to the RX window size if needed. Figure 6 The preamble length T of each preamble in the N-preamble 72 series. This allows UE device 10-2 to further reduce power consumption compared to examples using the N-preamble 72 series for time synchronization. If needed, receiver 48 on UE device 10-2 can dynamically adapt or adjust the RX window length L over time (e.g., to make detection more or less sensitive and / or consume more or less power based on the current battery capacity or power consumption on UE device 10-2). Different types of UE device 10-2 can use different RX window lengths L to indicate different antenna / receiver performance if needed. UE device 10-2 can detect the end of extended preamble 108 by taking advantage of the fact that a sequence has been detected at UE device 10-2 at time TD (e.g., using coherent detection), by taking advantage of the fact that the end can only appear at a fixed position in the (sub)sequence, etc. Using extended preamble 108 (e.g., by selecting the Zadoff Chu sequence root, M sequence index, etc.), different sequence types can still be used (e.g., transmitting limited information, such as information for identifying one or more frequencies for receiving emergency message 74 or for identifying a predetermined time offset 110).

[0087] During the extended RX window 76E, UE device 10-2 keeps its receiver 48 active. Figure 7 and Figure 8 The examples are merely illustrative. If needed, UE device 10-2 may disable its receiver 48 after receiving a portion of the extended preamble 108 in the RX window 76. For example, as Figure 7As shown, UE device 10-2 can deactivate its receiver 48 at the end of RX window 76. In this example, time synchronization can be performed based on where RX window 76 falls within extended preamble 108. Therefore, extended preamble 108 may include a sequence that allows UE device 10-2 to detect where portions of extended preamble 108 received during RX window 76 are located as a whole within extended preamble 108.

[0088] For example, UE device 10-1 can generate extended preamble 108 as a continuous non-repeating sequence, which allows the positioning of any sub-sequence of extended preamble 108 within the continuous non-repeating sequence. The transmitter in UE device 10-1 can generate this sequence by applying a binary overlay code (or a non-binary overlay code) to the top of the underlying sequence, where the overlay code varies across the length of the extended preamble 108. For example, the continuous non-repeating sequence could be a repeating underlying Zadoff Chu sequence for which a binary overlay code has been provided, which varies across the length of the extended preamble 108.

[0089] Once UE device 10-2 receives a portion (subsequence) of extended preamble 108 during its RX window 76, UE device 10-2 can process the received portion (subsequence) to identify the time offset between the end of RX window 76 and time TC when UE device 10-1 transmits emergency message 74. Figure 7 In the example, UE device 10-2 can process subsequences of extended preamble 108 received during RX window 76 to identify a time offset 112 from the end of RX window 76 to the beginning of emergency message listening window 80 (e.g., including the duration to which extended window 76E will be occupied and a predetermined time offset 110). The non-repeating structure of extended preamble 108 (e.g., provided by an overlay code) allows UE device 10-2 to determine or identify the time position of subsequences within extended preamble 108, thereby allowing UE device 10-2 to identify time offset 112 (e.g., a predetermined time offset 110 between given times TD and TC). UE device 10-2 can then reactivate its receiver to receive emergency message 74 after the identified time offset 112 has elapsed since the end of RX window 76. In other words, UE device 10-2 can synchronize its timing for receiving emergency message 74 based on subsequences of extended preamble 108 received during RX window 76. For example, using an extended preamble 108 with an overlay code for timing synchronization in this manner allows the UE device 10-2 to minimize power consumption (e.g., since the UE device 10-2 can disable its receiver after RX window 76) without expending resources to detect the end of the extended preamble 108.

[0090] Figure 9This is a flowchart illustrating the operations involved in transmitting and receiving emergency message 74, which is based on... Figure 7 Time synchronization is performed using an extended preamble 108 with an overlay code. Figure 9 Operations 140-144 can be performed by UE device 10-1 (e.g., simultaneously processing) Figure 3 Operation 56). Figure 9 Operations 146-152 can be performed by UE device 10-2 (e.g., simultaneously processing) Figure 3 Operations 62 and 64).

[0091] exist Figure 9 At operation 140, UE device 10-1 can generate an extended preamble 108 for transmission. The extended preamble 108 may include a cover code, such as a binary cover code on an underlying repeating sequence (such as a Zadoff-Chu sequence or an M sequence). The cover code may vary across the length of the extended preamble 108.

[0092] At operation 142, UE device 10-1 may begin transmitting extended preamble 108 to its coverage area 20 ( Figure 1 Search for UE devices within the scope.

[0093] At operation 146, receiver 48 on UE device 10-2 (e.g., UE device in coverage area 20) can receive a portion (subsequence) of extended preamble 108 having an overlay code transmitted by UE device 10-1 during one RX window of its RX window 76.

[0094] At operation 148, UE device 10-2 can identify the time offset 112 between the end of RX window 76 and emergency message listening window 80 based on the overlay code of a subsequence of extended preamble 108 received during the RX window.

[0095] At operation 150, UE device 10-2 may disable its transmitter (e.g., once RX window 76 ends) to save power. Operations 148 and 150 may be performed simultaneously if needed, or operation 150 may be performed before operation 148.

[0096] At operation 144, after a predetermined time offset of 110 from the end of the self-transmitted extended preamble 108, the UE device 10-1 can transmit the emergency message 74.

[0097] At operation 152, after an identified time offset 112 from the end of RX window 76, UE device 10-2 may reactivate its receiver 48 for RX window listening window 80 (e.g., from time TC). UE device 10-2 may then receive and decode emergency message 74 during RX window listening window 80 (e.g., because UE device 10-2 has now time-synchronized with UE device 10-1 using a subsequence of extended preamble 108 received during RX window 76). UE device 10-2 may perform any desired follow-up processing based on emergency message 74.

[0098] If needed, UE device 10-2 may transmit a D2D signal to UE device 10-1, which includes an acknowledgment that UE device 10-2 has received emergency message 74. If UE device 10-1 does not receive an acknowledgment of its emergency message, one possible reason is that the timing assumption of the UE device has deviated from the maximum support time uncertainty 82 of N*T compared to all other potential receivers. In this case, during subsequent cycles (e.g., in...), Figure 3 During subsequent iterations of path 58, UE device 10-1 may increase the number N of preamble 72 or the length of extended preamble 108 transmitted before subsequent emergency message transmission. Additionally or alternatively, UE device 10-1 may shift its time t0 assumption forward in the first RX window period, backward in the next RX window period, and even further forward / backward in subsequent RX window periods to ultimately hit the RX window 76 of the receiver in UE device 10-2. If desired, UE device 10-1 may transmit a series of N preamble 72 and / or extended preamble 108 at a different frequency than the emergency message 74 (e.g., the preamble may be transmitted on a common channel while frequency hopping is used to transmit the emergency message 74).

[0099] UE device 10-1 transmits emergency message 74 at time TC. Figures 1 to 9The examples provided are merely illustrative. Typically, UE device 10-1 can transmit any desired data (e.g., message data, application data, control data, video data, voice data, image data, web data, etc.) instead of emergency message 74 (e.g., the synchronization operation described herein can be used to synchronize UE device 10-2 to UE device 10-1 to transmit any desired radio data using D2D signal 22). Therefore, emergency message 74 may sometimes be simply referred to as message 74. As an example, message 74 may contain emergency payload content (emergency message payload content). As another example, message 74 may include headers and control messages for CRC purposes (e.g., exclusion of false positive preamble detection) and to guide subsequent (e.g., bidirectional) communication. Message 74 may include additional information if desired. The examples described herein relating to binary overlay codes are merely illustrative, and other overlay codes, such as non-binary overlay codes, may generally be used.

[0100] Device 10 may collect and / or use personally identifiable information. It is well known that the use of personally identifiable information should comply with privacy policies and practices generally recognized as meeting or exceeding industry or governmental requirements for protecting user privacy. Specifically, personally identifiable information data should be managed and processed to minimize the risk of unintentional or unauthorized access or use, and the nature of authorized use should be clearly explained to the user.

[0101] The above text combined Figures 1 to 9 The methods and operations described (e.g., Figures 3 to 9 The operations can be performed by components of device 10 using software, firmware, and / or hardware (e.g., dedicated circuitry or hardware). The software code used to perform these operations may be stored on a non-transitory computer-readable storage medium (e.g., a tangible computer-readable storage medium) stored on one or more components of device 10 (e.g., ...). Figure 2 The storage circuit 30). This software code may sometimes be referred to as software, data, instructions, program instructions, or code. Non-transitory computer-readable storage media may include drives, non-volatile memory such as non-volatile random access memory (NVRAM), removable flash drives or other removable media, other types of random access memory, etc. The software stored on the non-transitory computer-readable storage medium may be processed by processing circuitry on one or more components of device 10 (e.g., Figure 1 The processing circuitry (e.g., 18) performs the execution. The processing circuitry may include a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC) with processing circuitry, or other processing circuitry.

[0102] If desired, an apparatus may be provided comprising means for performing one or more elements or any combination of elements of one or more methods or processes described herein.

[0103] If desired, one or more non-transitory computer-readable media may be provided, comprising instructions that, when executed by one or more processors of an electronic device, cause the electronic device to perform one or more elements or any combination of elements of one or more methods or processes described herein.

[0104] If desired, an apparatus may be provided comprising logic, modules, or circuitry comprising one or more elements or any combination of elements for performing one or more methods or processes described herein.

[0105] If desired, an apparatus may be provided comprising one or more processors, and one or more non-transitory computer-readable storage media comprising instructions that, when executed by the one or more processors, cause the one or more processors to perform one or more elements or any combination of elements of the one or more methods or processes described herein.

[0106] If required, a signal (e.g., a data-encoded signal), datagram, information element (IE), packet, frame, segment, PDU, or message may be provided, which includes or performs one or more elements or any combination of elements of one or more methods or processes described herein.

[0107] If desired, an electromagnetic signal may be provided carrying computer-readable instructions, wherein execution of the computer-readable instructions by one or more processors causes one or more processors to perform one or more elements or any combination of elements of one or more methods or processes described herein.

[0108] If desired, a computer program may be provided comprising instructions, wherein execution of the program by a processing element causes the processing element to perform one or more elements or any combination of elements of one or more methods or processes described herein.

[0109] According to an embodiment, a user equipment device is provided, the user equipment device comprising: one or more antennas; a transmitter configured to use the one or more antennas to transmit a device-to-device (D2D) signal to an additional user equipment device; and one or more processors configured to transmit a message in the D2D signal and, prior to the message, transmit a preamble in the D2D signal, the preamble being used by the additional user equipment device to identify a time offset between the preamble and the message.

[0110] According to another embodiment, the one or more processors are further configured to transmit a series of preambles in the D2D signal prior to the message, the series of preambles including the preamble and each preamble in the series identifying a corresponding time offset between the preamble and the message.

[0111] According to another embodiment, each of the preambles in the preamble series has a preamble length and the preambles in the preamble series are separated by gaps during which the transmitter is inactive.

[0112] According to another embodiment, the one or more processors are further configured to: retransmit the message in the D2D signal and, after transmitting the message and before retransmitting the message, transmit an additional preamble series in the D2D signal, the preambles in the additional preamble series being separated by additional gaps during which the transmitter is inactive, and the additional gaps being separated from the retransmitted message by a corresponding time offset identified by the preamble series.

[0113] According to another embodiment, the preamble is shorter than the receiver window length of the additional user equipment.

[0114] According to another embodiment, the preamble includes a repeating sequence and the one or more processors are configured to apply a covering code over the repeating sequence, the covering code varying across the length of the preamble.

[0115] According to another implementation, the preamble includes an M sequence or a Zadoff-Chu sequence.

[0116] According to another embodiment, the user equipment is configured to communicate with a wireless base station using one or more antennas in a connected state and to transmit the D2D signal in an off-grid state where the user equipment cannot connect to any wireless base station.

[0117] According to another embodiment, the transmitter is configured to transmit the preamble in the D2D signal at a first frequency and is configured to transmit the message in the D2D signal at a second frequency different from the first frequency.

[0118] According to an embodiment, a user equipment device is provided, the user equipment device comprising: one or more antennas; a receiver configured to receive a device-to-device (D2D) signal from an attached user equipment using the one or more antennas; and one or more processors configured to periodically activate the receiver during a receiver (RX) window series, receive a preamble sequence in the D2D signal during an RX window in the RX window series, deactivate the receiver after the RX window, identify a time offset based on the preamble sequence received during the RX window, reactivate the receiver during a message listening window that begins once the identified time offset has elapsed from the end of the preamble sequence, and receive a message in the D2D signal during the message listening window.

[0119] According to another embodiment, the one or more processors are further configured to identify a cover code applied to the preamble sequence and to identify the time offset based on the cover code.

[0120] According to another embodiment, the length of the RX window is at least twice the length of the preamble sequence.

[0121] According to another implementation, the one or more processors are further configured to relay the message to the emergency service provider.

[0122] According to another embodiment, the one or more processors are further configured to disable the receiver between the RX windows in the RX window series.

[0123] According to another embodiment, the receiver is configured to receive the preamble sequence at a first frequency and to receive the message at a second frequency different from the first frequency.

[0124] According to another embodiment, the one or more processors are further configured to identify a frequency hopping pattern based on the preamble sequence and to use the identified frequency hopping pattern to receive the message.

[0125] According to another embodiment, the one or more processors are configured to extend the duration of the RX window for receiving the preamble sequence until the one or more processors detect the end of receiving the preamble sequence.

[0126] According to an implementation scheme, a method is provided for operating a first user equipment device to receive a device-to-device (D2D) signal from a second user equipment device, comprising an emergency message preamble and an emergency message following the emergency message preamble. The method includes: periodically activating a receiver on the first user equipment device during a receiver (RX) window sequence; receiving a portion of the emergency message preamble in the D2D signal during an RX window in the RX window sequence; keeping the receiver active until the end of the emergency message preamble is received, and then deactivating the receiver; reactivating the receiver during an emergency message listening window that begins after a predetermined time offset from the end of the emergency message preamble; and receiving the emergency message in the D2D signal during the emergency message listening window.

[0127] According to another embodiment, the method includes using a Network Time Protocol (NTP) or cellular phone signal received at the first user equipment device to roughly synchronize the timing of the receiver to the timing of the second user equipment device.

[0128] According to another embodiment, the method includes using satellite navigation signals received at the first user equipment to roughly synchronize the timing of the receiver to the timing of the second user equipment.

[0129] The foregoing description is merely illustrative and various modifications can be made to the described implementation scheme. The described implementation scheme can be implemented independently or in any combination.

Claims

1. A user equipment device, the user equipment device comprising: One or more antennas; A transmitter configured to transmit device-to-device (D2D) signals to an additional user equipment device using the one or more antennas; and One or more processors, configured to use the transmitter to transmit messages in the D2D signal, and The transmitter transmits a series of preambles in the D2D signal prior to the message, each preamble in the series representing a corresponding time offset between the end of the corresponding preamble and the transmission of the message, as identified by the additional user equipment equipment.

2. The user equipment device according to claim 1, wherein each of the preambles in the preamble series has a preamble length and wherein the preambles in the preamble series are separated by gaps during which the transmitter is inactive.

3. The user equipment device according to claim 2, wherein the one or more processors are further configured to: The message is retransmitted in the D2D signal; and After the message is transmitted and before the message is retransmitted, an additional preamble series is transmitted in the D2D signal, wherein the preambles in the additional preamble series are separated by additional gaps during which the transmitter is inactive, and wherein the additional gaps are separated from the retransmitted message by the corresponding time offset identified by the preamble series.

4. The user equipment device of claim 1, wherein each preamble in the preamble series is shorter than the receiver window length of the additional user equipment device.

5. The user equipment device of claim 4, wherein each preamble in the preamble series comprises a repeating sequence and wherein the one or more processors are configured to apply a cover code over the repeating sequence, the cover code varying in length across the respective preamble.

6. The user equipment device according to claim 1, wherein each preamble in the preamble series comprises an M sequence or a Zadoff-Chu sequence.

7. The user equipment device of claim 1, wherein the user equipment device is configured to communicate with a wireless base station using the one or more antennas in a network-connected state and wherein the user equipment device is configured to transmit the D2D signal in an off-network state where the user equipment device cannot connect to any wireless base station.

8. The user equipment device of claim 1, wherein the transmitter is configured to transmit the preamble sequence in the D2D signal at a first frequency and is configured to transmit the message in the D2D signal at a second frequency different from the first frequency.

9. A user equipment device, comprising: One or more antennas; A receiver configured to receive device-to-device (D2D) signals from an attached user equipment using one or more antennas; and One or more processors are configured to periodically activate the receiver during a receiver RX window sequence. During the RX window period in the RX window series, a preamble sequence is received in the D2D signal. The receiver is disabled after the RX window. The time offset is identified based on the preamble sequence received during the RX window. The receiver is reactivated during the message listening window, which begins once the identified time offset has elapsed from the end of the preamble sequence. Messages are received in the D2D signal during the message listening window.

10. The user equipment device of claim 9, wherein the one or more processors are further configured to: Identify the overlay code applied to the preamble sequence, and The time offset is identified based on the overlay code.

11. The user equipment device of claim 9, wherein the length of the RX window is at least twice the length of the preamble sequence.

12. The user equipment device of claim 9, wherein the one or more processors are further configured to relay the message to an emergency service provider.

13. The user equipment device of claim 9, wherein the one or more processors are further configured to deactivate the receiver between the RX windows in the RX window series.

14. The user equipment device of claim 9, wherein the receiver is configured to receive the preamble sequence at a first frequency and is configured to receive the message at a second frequency different from the first frequency.

15. The user equipment device of claim 9, wherein the one or more processors are further configured to: Identifying frequency hopping patterns based on the preamble sequence; and The message is received using the identified frequency hopping pattern.

16. The user equipment device of claim 9, wherein the one or more processors are configured to extend the duration of the RX window for receiving the preamble sequence until the one or more processors detect the end of receiving the preamble sequence.

17. A method of operating a first user equipment equipment to receive a device-to-device (D2D) signal from a second user equipment equipment, comprising an emergency message preamble and an emergency message following the emergency message preamble, the method comprising: The receiver is periodically activated on the first user equipment device during the receiver RX window series; During the RX window in the RX window series, a portion of the emergency message preamble is received in the D2D signal; Keep the receiver active until the end of the emergency message preamble has been received, then deactivate the receiver; The receiver is reactivated during an emergency message listening window that begins after a predetermined time offset from the end of the emergency message preamble. as well as The emergency message is received in the D2D signal during the emergency message listening window.

18. The method according to claim 17, further comprising: The timing of the receiver is roughly synchronized to the timing of the second user equipment using the Network Time Protocol (NTP) or cellular phone signal received at the first user equipment.

19. The method of claim 17, further comprising: The timing of the receiver is roughly synchronized to the timing of the second user equipment using the satellite navigation signals received at the first user equipment.

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