JP2020065275A - Device to device synchronization source selection - Google Patents

Abstract

To provide an efficient method and apparatus for performing selection of the synchronization source.SOLUTION: A synchronization signal receiving apparatus comprises the steps of: receiving predetermined wireless synchronization signals from synchronization sources including a synchronization source which derives its synchronization signal from a network node and a wireless synchronization signal generating device; determining a selection metric for each of the synchronization sources based on at least two of quality of the received synchronization signal, whether the synchronization source derives the synchronization signal from the network node or a network node independent synchronization signal, and the number of hops to the network node; determining or adjusting the timing according to the synchronization signal of the synchronization source selected; and controlling re-selecting according to a re-selection timer to regularly adapt the re-selecting to the transmission environment.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an apparatus and method for selecting or reselecting a synchronization source in wireless communication.

  Third generation mobile communication systems (3G) based on WCDMA® radio access technology are being deployed on a wide scale worldwide. High-speed downlink packet access (HSDPA) and enhanced uplink (also referred to as high-speed uplink packet access (HSUPA)) were introduced as the first step in enhancing or developing / developing this technology. , Extremely competitive radio access technology is provided. In order to meet the ever-increasing demand from users and to secure the competitiveness against new radio access technology, 3GPP has introduced a new mobile communication system called Long Term Evolution (LTE). LTE is designed to provide the carriers required for high speed transmission of data and media and high volume voice support for the next decade. The ability to provide high bit rates is an important strategy in LTE. The specifications of the work item (WI) for LTE (Long Term Evolution) are E-UTRA (Evolved UMTS Terrestrial Radio Access (UTRA): Evolved UMTS Terrestrial Radio Access) and E-UTRAN (Evolved UMTS Terrestrial Radio Access Network (UTRAN)). : Evolved UMTS Terrestrial Radio Access Network) and will eventually be released as Release 8 (LTE Release 8). The LTE system is an efficient packet-based radio access and radio access network that provides all IP-based features with low latency and low cost. Detailed system requirements are described in Non-Patent Document 1 (which is freely available on the 3GPP website).

  In LTE, in order to achieve flexible system deployment using a given spectrum, multiple scalable transmission bandwidths (eg, 1.4 MHz, 3.0 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz, And 20.0 MHz) are specified. Radio access based on OFDM (Orthogonal Frequency Division Multiplexing) is adopted for the downlink. Because such radio access is inherently less susceptible to multipath interference (MPI) due to the lower symbol rate and uses cyclic prefix (CP), it also accommodates different transmission bandwidth configurations. Because it is possible. Radio access based on SC-FDMA (Single-Carrier Frequency Division Multiple Access) is adopted for the uplink. This is because considering the limited transmission power of the user equipment (UE), it is prioritized to provide a wider coverage area than to improve the peak data rate. In LTE Release 8, a number of major packet radio access technologies (eg, MIMO (Multiple Input Multiple Output) channel transmission technology) are adopted to achieve a highly efficient control signaling structure.

  FIG. 1 shows the overall architecture of LTE, and FIG. 2 shows the E-UTRAN architecture in more detail. The E-UTRAN comprises an eNB, which terminates E-UTRA user plane (PDCP / RLC / MAC / PHY) and control plane (RRC) protocols for user equipment (UE). The eNB has a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data control protocol (PDCP) layer (these layers perform user plane header compression and encryption functions. Host). The eNB also provides a radio resource control (RRC) function corresponding to the control plane. The eNB may perform radio resource management, admission control, scheduling, perform uplink QoS (Quality of Service) by negotiation, broadcast cell information, encrypt / decrypt user plane data and control plane data, and perform downlink / uplink Performs many functions such as compression / decompression of user plane packet headers. The plurality of eNBs are connected to each other by the X2 interface. In addition, the plurality of eNodeBs is an EPC (Evolved Packet Core) by an S1 interface, more specifically, an MME (Mobility Management Entity) by S1-MME, and a serving gateway (by a S1-U). S-GW: Serving Gateway). The S1 interface supports a many-to-many relationship between the MME / Serving Gateway and the eNB. While the SGW routes and transfers user data packets, it functions as a mobility anchor of the user plane during a handover between eNBs, and further, an anchor (S4) for mobility between LTE and another 3GPP technology. It terminates the interface and relays traffic between the 2G / 3G system and the PDN GW). The SGW terminates the downlink data path for idle user equipment and triggers paging when downlink data arrives for that user equipment. The SGW manages and stores the user equipment context (eg parameters of the IP bearer service, network internal routing information). In addition, the SGW performs replication of user traffic in case of lawful interception.

  The MME is the main control node of the LTE access network. The MME is responsible for user equipment tracking and paging procedures (including retransmissions) in idle mode. The MME is involved in the bearer activation / deactivation process and also selects the SGW of the user equipment at the time of initial attach and during the LTE handover with core network (CN) node relocation. Also has a role to play. The MME is responsible for authenticating the user (by interacting with the HSS). Non-Access Stratum (NAS) signaling is terminated at the MME, which is also responsible for generating a temporary ID and assigning it to user equipment. The MME checks the authentication of the user equipment to enter the public land mobile network (PLMN) of the service provider and enforces the roaming constraint of the user equipment. The MME is a termination point in the network in encryption / integrity protection of NAS signaling and manages security keys. The legal interception of signaling is also supported by the MME. Furthermore, the MME provides the control plane function for mobility between the LTE access network and the 2G / 3G access network and terminates the S3 interface from the SGSN. In addition, the MME terminates the S6a interface towards the home HSS for roaming user equipment.

The downlink component carriers of the 3GPP LTE system are further divided in the time-frequency domain in so-called subframes. In 3GPP LTE, each subframe is divided into two downlink slots as shown in FIG. 3, in which the first downlink slot allocates a control channel area (PDCCH area) in a first OFDM symbol. Prepare Each subframe consists of a given number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)) and each OFDM symbol spans the entire bandwidth of the component carrier. Therefore, each OFDM symbol is composed of several modulation symbols transmitted on N ^DL _RB × N ^RB _sc respective subcarriers, as also shown in FIG.

Assuming a multi-carrier communication system, eg using OFDM, eg as used in 3GPP Long Term Evolution (LTE), the smallest unit of resources that can be allocated by the scheduler is one “resource block”. The physical resource block (PRB) includes N ^DL _symb consecutive OFDM symbols (eg, 7 OFDM symbols) in the time domain and N ^RB _sc consecutive subcarriers (in the frequency domain) as illustrated in FIG. For example, 12 subcarriers of a component carrier). Therefore, in 3GPP LTE (Release 8), a physical resource block is composed of N ^DL _symb × N ^RB _sc resource elements corresponding to one slot in the time domain and 180 kHz in the frequency domain (downlink resource grid). For more details on, see, for example, Section 6.2 of Non-Patent Document 2 (available freely on the 3GPP website and incorporated herein by reference). The term "component carrier" means a combination of several resource blocks. In a future release of LTE, the term "component carrier" will no longer be used, instead its terminology will be changed to "cell" which refers to a combination of downlink and optionally uplink resources. The linking between the carrier frequency of the downlink resource and the carrier frequency of the uplink resource is indicated in the system information transmitted on the downlink resource.

  The cell search procedure is the first series of tasks that a mobile device performs in a cellular system after initial power up. The mobile device can only receive and initiate voice / data calls after search and registration procedures. A typical cell search procedure in LTE is to find the carrier frequency, synchronize the timing, and identify the unique cell identifier. Generally, these procedures are facilitated by a unique synchronization signal transmitted by the base station (BTS). However, these sync signals are not continuously used in the connected mode of the mobile device. Therefore, only minimal resources are allocated for synchronization signals in terms of power, subcarrier allocation, and time slice.

  The cell search procedure allows the user equipment to determine the time and frequency parameters needed to demodulate the downlink and to transmit the uplink signal at the correct time. The initial stage of cell search involves initial synchronization. The user equipment thus detects the LTE cell and decodes all the information required to register in the detected cell. This procedure utilizes two physical signals broadcast in the middle 62 subcarriers of each cell: a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). These signals enable time and frequency synchronization. When the user equipment successfully detects these signals, it is provided with the physical cell ID, the length of the cyclic prefix, and information on whether FDD or TDD is adopted. Specifically, in LTE, when a terminal is powered on, the terminal detects a primary sync signal, which in the case of FDD is the first of the first subframe (subframe 0) in a radio frame. In the last OFDM symbol of a time slot of (in the case of TDD, this position is slightly different but well defined). This allows the terminal to acquire the slot boundary regardless of the cyclic prefix selected for the cell. The mobile terminal searches for the secondary synchronization signal after detecting the timing (slot boundary) of 5 milliseconds. Both the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) are transmitted on 62 subcarriers of the 72 reserved subcarriers before and after the DC carrier. In the next step, the user equipment detects the physical broadcast channel (PBCH) and the physical broadcast channel (PBCH) as well as the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) are located in the middle 72 sub-cells of the cell. Mapped to carrier only. The physical broadcast channel (PBCH) contains a master information block (MIB) that contains information about system resources. In LTE up to Release 10, the length of the master information block (MIB) was 24 bits (14 bits of which are currently used and 10 bits are reserved). The Master Information Block (MIB) contains information about the downlink system bandwidth, the structure of the Physical HARQ Indicator Channel (PHICH) and the 8 most significant bits of the System Frame Number (SFN).

  The terminal activates the system bandwidth after successfully detecting a master information block (MIB) that contains the most frequently transmitted limited number of parameters that are essential for first accessing the cell, ie , It must be able to receive and detect signals over the indicated downlink system bandwidth. After obtaining the downlink system bandwidth, the user equipment can receive further required system information in a so-called system information block (SIB). LTE Release 10 defines SIB type 1 to SIB type 13 (which convey different information elements required for a particular operation). For example, for FDD, SIB type 2 (SIB2) includes the uplink carrier frequency and the uplink bandwidth. The various SIBs are transmitted on the Physical Downlink Shared Channel (PDSCH) and thus the resources for each SIB are allocated by the Physical Downlink Control Channel (PDCCH) (see detailed description of PDSCH and PDCCH below). In order for the terminal (user equipment: UE) to correctly detect such (or other) PDCCH, the downlink system bandwidth needs to be known from the MIB.

The cell identifier (cell ID) referred to above uniquely identifies the cell within the PLMN (Public Land Mobile Network). The cell identifier is a global cell ID used to identify a cell from the viewpoint of operation and maintenance (OAM). This cell ID is sent in the system information and is designed for management of the eNodeB in the core network. Furthermore, this global cell ID is also used for the purpose of identifying a particular cell by the user equipment in connection with the processing of the RRC / NAS layer. The physical cell ID is a cell identifier in the physical layer. Physical cell IDs range from 0 to 503 and are used to scramble data to help mobile devices separate information from different transmitters. The sequence of the primary synchronization signal and the secondary synchronization signal is determined by the physical cell ID. The physical cell ID is similar to the scrambling code in UMTS. There are 504 unique cell IDs in the physical layer. The physical layer cell ID is divided into 168 unique physical layer cell ID groups, and each group includes three unique IDs. In this grouping, each physical layer cell ID belongs to only one physical layer cell ID group. Therefore, the physical layer cell ID N ^cell _ID = 3N ⁽¹⁾ _ID + N ⁽²⁾ _ID is a number N ⁽¹⁾ _ID within the range of 0 to 167 representing the physical layer cell ID group and the physical layer cell ID. It is uniquely defined by the number N ⁽²⁾ _ID within the range of 0 to 2 that represents the physical layer cell ID in the group.

The synchronization signal is composed of a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The sequence used for the primary synchronization signal is generated from the frequency domain Zadoff-Chu sequence according to N ⁽²⁾ _ID . The N ⁽²⁾ _ID can be detected by detecting the primary synchronization signal. The sequence used for the secondary synchronization signal is an interleaved concatenation of two 31-bit long binary sequences. The concatenated sequences are scrambled by the scrambling sequence provided by the primary sync signal. The secondary sync signal (SSS) sequence is based on a maximum length sequence (known as the M sequence), which can be created by cycling through each and every possible state of a shift register of length n. The result is a sequence of length ^2n-1 . Specifically, the two 31-bit long binary sequences to be concatenated are such M sequences. For more information on primary and secondary sync signals, see, for example, Section 6.11 of Non-Patent Document 3, freely available on the 3GPP website and incorporated herein by reference. .

  The receiving user equipment adapts the timing after receiving the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). Specifically, the user equipment synchronizes its receiver with the downlink transmission received from the synchronization source (eNB). The uplink timing is then adjusted. This adjustment is performed by applying a timing advance at the transmitter of the user equipment, referenced to the received downlink timing, in order to compensate for the different propagation delays of the user equipment. The timing advance procedure is briefly described in Section 18.2.2 of Non-Patent Document 4.

  Proximity-based applications and services are a new trend in social technology. Current intended applications include commercial and public safety related services of interest to operators and users. By introducing the Proximity Service (ProSe) feature into LTE, the 3GPP industry can serve this growing market at the same time as the emergencies of some public safety communities that use LTE in concert. Can meet various needs.

  Device-to-device (D2D) communication is a technical element in LTE-A Release 12. Device-to-device (D2D) communication technology can increase spectral efficiency in D2D as an underlay to the cellular network. For example, if the cellular network is LTE, all physical channels carrying data use SC-FDMA in D2D signaling. "D2D communication in LTE" focuses on two areas: discovery and communication. In D2D communication, user equipments transmit data signals to each other over a direct link using cellular resources without going through a base station (BS, eNodeB, eNB). D2D users communicate directly, but are still under the control of the base station (ie at least when they are within the coverage of the eNB). Therefore, in D2D, the system performance can be improved by utilizing the cellular resources. Currently, it is assumed that D2D operates in the LTE uplink spectrum of the cell providing coverage (for FDD) or in the uplink subframe (for TDD, but outside coverage). Furthermore, D2D transmission / reception does not use full duplex on a given carrier. From the perspective of the individual user equipment, it does not use full-duplex with D2D signal reception and LTE uplink transmission on a given carrier (ie D2D signal reception and LTE uplink transmission cannot occur simultaneously). Further current operational assumptions regarding LTE D2D radio access are described in Non-Patent Document 5 (freely available on the 3GPP website).

  In D2D communication, when the user equipment 1 is in the role of transmitting, the user equipment 1 sends data and the user equipment 2 receives it. The user equipment 1 and the user equipment 2 can exchange the transmitting role and the receiving role. Transmissions from user equipment 1 can be received by one or more user equipments (such as user equipment 2). 4 and 5 illustrate protocol layers, points of service, and multiplexing when transmitting on different types of channels on the downlink (FIG. 4) and uplink (FIG. 5).

In 3GPP RAN1, it was agreed that, as an operational assumption, the synchronization source is any node that transmits a D2D synchronization signal (D2DSS). This node may be an eNB or regular user equipment. When the synchronization source is the eNB, the D2D synchronization signal is the same as the release 8 primary synchronization signal (PSS) and the secondary synchronization signal (SSS). The D2D user equipment uses the sync signal to determine when to transmit the D2D signal. Further, as an operational assumption, it was also agreed that the D2D user equipment scans the sync source before initiating transmission of the D2D sync signal. If a sync source is detected, the user equipment can synchronize its receiver to that sync source before sending the D2D sync signal. Even if the sync source is not detected, the user equipment can send the D2D sync signal. If the user equipment detects a change in the D2D sync source, it can (re) select the D2D sync source to use as the timing reference for transmitting the D2D sync signal based on the following metrics.
– Type of synchronization source (eNB or user equipment)
-Quality of received D2D sync signal-Number of hops from the eNB

3GPP specification TR 25.913, “Requirements for Evolved UTRA and Evolved UTRAN”, ver. 9.0.0 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, version 8.9.0 or 9.0.0 3GPP TS 36.211, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 12)”, version 12.1.0 “LTE The UMTS Long Term Evolution: From theory to practice”, 2nd edition, ed. By S. Sesia, I. Toufik, M. Baker, Wiley, 2011 TS 36.843, v c.0.1, “Study on LTE Device to Device Proximity Services; Radio Aspects” "Discussion on D2D Synchronization Procedure" (R1-140330) 3GPP TS 36.331, v 12.1.0, “Radio Resource Control (RRC); Protocol specification”

  It is an object of the present invention to provide an efficient method and apparatus for performing synchronization source selection.

  This object is achieved by the features according to the independent claims.

  Further advantageous embodiments of the invention are the subject matter of the dependent claims.

  A main aspect of the present invention is a synchronous receiver that receives a predetermined wireless synchronization signal from a synchronization source that guides its own synchronization signal from a network node, or a synchronization source that is a wireless device that itself generates the synchronization signal. A receiver and a processor, wherein the processor provides selection metrics for each of the synchronization sources, (i) quality of the received synchronization signal, (ii) the synchronization source from the network node. According to at least two of the following: whether to derive or to derive independently from the network node, (iii) the number of hops to the network node, and the metric obtained by the metric obtaining process. The synchronization source selection process for selecting the synchronization source and the timing of data transmission or reception are specified by the synchronization source selection. And a timing control process for determining or adjusting according to a synchronization signal of the synchronization source selected by a logic selection process, and a selection control process for controlling a reselection operation for obtaining the metric and selecting a synchronization source according to a reselection timer. And a process in which the reselection operation is periodically adapted to the transmission environment by setting the value of the reselection timer.

  According to an embodiment of the present invention, a synchronization receiving device (synchronization receiving device), a synchronization source for guiding its own timing from a network node and a synchronization source including a synchronization generating wireless device, The synchronization receiving unit that receives the radio synchronization signal and the selection metric of each synchronization source, the quality of the synchronization signal received, whether the synchronization source derives its timing from the network node or generates the timing, or a hop to the network node. , A synchronization source selection unit for selecting a synchronization source according to the metric obtained by the metric acquisition unit, and a timing for transmitting or receiving data by the synchronization source selection unit. Synchronization of the synchronization source selected by the unit And a, a timing unit for determining or adjusted according to Patent, provide a synchronous reception device.

  According to another embodiment of the present invention, a method of selecting a synchronization source, the method comprising: a predetermined synchronization step from the following steps: a synchronization source which directs its own synchronization signal from a network node and a synchronization generation wireless device. Wireless synchronization signal, and the selection metric of each synchronization source, the quality of the received synchronization signal, whether the synchronization source originates the synchronization signal from the network node or the synchronization signal independent of the network node , Or at least two of the number of hops to the network node, selecting a synchronization source according to the determined metric, and selecting the timing of data transmission or reception. And determining or adjusting according to the synchronization signal of the synchronization source.

  According to another embodiment of the invention, a computer program product comprising a computer readable medium having computer readable program code embodied therein, the program code being adapted to carry out the invention. ,I will provide a.

  According to an embodiment of the invention, the device described above is embodied on an integrated circuit.

  The above objects, other objects, and features of the present invention will become more apparent from the following description and preferred embodiments presented in connection with the accompanying drawings.

FIG. 1 is a block diagram showing an example of an overall LTE architecture. FIG. 3 is a block diagram illustrating an example architecture of an LTE access network. FIG. 6 is a schematic diagram showing an example of a grid of OFDM modulation resources in the time-frequency domain. 6 is a flowchart showing a structure of a downlink protocol and multiplexing of Layer 2 in a state where carrier aggregation is set up. 6 is a flowchart showing a structure of a second layer uplink protocol and multiplexing in a state where carrier aggregation is set up. FIG. 6 is a schematic diagram illustrating multiple different sources of inter-device (D2D) synchronization signals. FIG. 6 is a schematic diagram showing an example scenario of selecting a synchronization source based on a metric based on signal quality and a table containing values of selection bias. FIG. 3 is a block diagram showing an apparatus according to an embodiment of the present invention. 6 is a flow chart illustrating a method according to an embodiment of the invention.

  The present invention relates to reception of a synchronization signal and selection of a synchronization signal source in a wireless system, and a transmitter of the synchronization signal is not only a network node such as a base station but also a user equipment (terminal) or other non-network node wireless node. The device may be a device and the user equipment may be a mobile phone, smartphone, tablet, laptop, or other computer. Furthermore, the wireless device can derive its timing from the network or independently of the network.

  The term "network node" in this context should be understood as any node connected to a cellular network. It should be noted that the term "cellular network" or "cell" means any form of cell, including macrocells, microcells, picocells, femtocells, or any other concept. Thus, the network node may be a base station such as an eNodeB or a relay provided as part of the network.

  Embodiments of the present invention are intended for inter-device communication coexisting with network transmission (that is, not only for wireless transmission between a base station and user equipment, but also for direct transmission between user equipment sharing the same resources as wireless transmission. In a supporting system), it provides an efficient way to select one sync source from multiple sync sources, which is advantageous.

  In the following, an embodiment will be presented based on the LTE specification. However, the present invention is not limited to LTE. The concepts and examples described herein show that one or more network nodes and one or more network nodes include one or more network devices that are not network nodes (eg, user equipment). It can be applied to any wireless system selected. The wireless device can derive its own synchronization signal from the network (ie, from the network node) or generate the synchronization signal independent of network timing.

When the user equipment (UE) sends an equipment-to-equipment (D2D) signal, the rules for determining which D2D synchronization source the user equipment uses as a timing reference for sending the D2D signal should be: You can
1. The eNodeB D2D sync source has a higher priority than the user equipment D2D sync source.
2. The in-coverage user equipment D2D synchronization source has a higher priority than the out-of-coverage user equipment D2D synchronization source.

  After prioritizing the D2D sync source that is the eNodeB and then the D2D sync source that is the in-coverage user equipment, select the D2D sync source. In-coverage user equipment is user equipment that is located within the coverage of a base station and therefore can derive its synchronization (timing) from the network. Out-of-coverage user equipment is user equipment that is outside the coverage of the network. If an out-of-coverage user equipment is also outside the coverage of another user equipment that derives its timing from the timing of the network, then such out-of-coverage user equipment generates its own timing independent of the timing of the network.

  In the D2D sync source selection procedure, this criterion is not sufficient, because other factors (eg quality of D2D sync signal received, number of hops from the eNB, etc.) are not considered. Soft criteria based on multiple factors are more reliable than based on only one factor.

  FIG. 6 illustrates a typical scenario that occurs when communicating in a system that supports both communication between a network and terminals and direct communication between two or more terminals. Base station eNB 610 has the coverage indicated by ellipse 601. The eNB 610 sends an inter-device sync signal (D2D sync signal) 615, which in this scenario has the same format as the release 8 primary sync signal (PSS) and secondary sync signal (SSS). Terminal 620 is a user equipment within network coverage (ie, user equipment located in coverage 601 of base station 610). User equipment in network coverage 620 receives the PSS / SSS from the eNB 610 and synchronizes to the eNB 610. The eNB 610 may request some user equipment in network coverage (such as 620) to send a D2D synchronization signal. Therefore, the user equipment 620 in network coverage is set by the eNB 610 to send the D2D sync signal, as indicated by the dotted line, and thus sends the D2D sync signal 625. In this way, the user equipment 620 is also a synchronization source that guides its own synchronization (timing) from the network (specifically from the network node 610).

  Also shown in FIG. 6 is user equipment 630 outside network coverage. User equipment out of network coverage (ie a terminal located outside the coverage 601 of the eNB 610) does not receive a D2D synchronization signal with a reception quality above a certain predetermined threshold or a predefined threshold. , Such user equipment generates and transmits its own D2D synchronization signal. Thus, such user equipment 630 may be capable of inter-device communication even if there is no network proximity. Out-of-coverage user equipment 630 in this example does not receive D2D sync signal 615 and also does not receive signal 625 generated based on the timing received by in-network coverage user equipment 620 from eNB 610, and thus The reception quality of the D2D synchronization signal 615 and the D2D synchronization signal 625 does not exceed a predetermined reception quality threshold value. Therefore, the non-network coverage user equipment 630 generates and transmits its own D2D synchronization signal 635.

Also shown in FIG. 6 is D2D user equipment 660 (ie, a terminal that can communicate directly with other terminals as well as with the network). The D2D user equipment 660 is located outside the coverage 601 of the base station 610. The D2D user equipment 660 receives the D2D synchronization signal 615 from the eNB 610, but the reception quality is low, ie the D2D synchronization signal 615 received is fairly weak. D2D user equipment 660 also receives D2D synchronization signal 635 from network coverage out-of-coverage user equipment 630, in addition to D2D synchronization signal 615. In addition to this, since the user equipment 620 in network coverage also transmits the D2D synchronization signal 625, the D2D user equipment 660 further receives the D2D synchronization signal 625 having higher quality than directly receiving the D2D synchronization signal 615 from the eNB 610. To receive. Accordingly, D2D user equipment 660 receives D2D sync signals 615, 625, 635 from the following three sync sources.
-ENB 610: The corresponding D2D sync signal 615 is very weak, but directly from the eNB, i.e. there is no hop between the D2D user equipment 660 and the sync source 610.
-User equipment in network coverage 620: The corresponding D2D synchronization signal 625 is strong and network-originated, but one hop from the network represented by the eNB 610 to the D2D user equipment 660 (user equipment in network coverage). 620) is present.
Out-of-network-coverage user equipment 630: The corresponding D2D sync signal 635 is also strong, but not originating from the network (ie eNB 610 in this case).

  The problem when basing on the above situation is which synchronization source the D2D user equipment 660 should choose to synchronize its receiver (or transmitter or both). That is, the eNB 610, which has a very weak signal but no hop, or the user equipment 620 in network coverage, which has a strong signal but has some (in this case, one) hop, or the signal is strong but the hop is unknown. Some user equipment 630 out of network coverage (the signal does not originate from the network).

One possible solution to this problem is for the D2D sync signal 615 and D2D sync signal 625 derived from the eNB (and transmitted by the eNB 610 or user equipment 620) to be D2D sync independent of network timing. Always assigning a higher priority than the D2D sync signal received from the user equipment (630, etc.) that generated the signal 635. However, although such a directly received sync signal or a sync signal originating from a network is generally the most accurate sync signal, the following problems may occur.
The signal 615 received directly from the eNB 610 or a signal derived from such a signal (eg signal 625) is much weaker than the signal generated by the user equipment (eg 630) and received from that user equipment. , And thus may be unreliable.
The signal derived from the eNB 610 may pass various numbers of hops from the eNB, and the strength of the received signal may vary.

  Therefore, any extended principle that gives a clearer and more effective rule as to how the user equipment should select the sync source is advantageous.

  In 3GPP RAN1, a contribution (Non-Patent Document 6) by LGE has been made, and the following rules have been proposed. That is, the quality of the D2D sync signal is used as a reference for preselection. D2D sync signals that do not meet the minimum signal quality requirements are pre-excluded from further selection procedures without applying selection rules. For D2D sync signals that pass preselection, either the sync source type priority or the hop count priority is used. For example, the user equipment always selects the eNB-generated D2D synchronization signal regardless of the number of hops. On the other hand, if none of the D2D sync signals meet the signal quality requirements, the D2D sync signal with the highest signal quality is selected regardless of the type of sync source and the hop count. The problem with this method is that, for example, once the D2D sync signal meets the minimum requirements of the signal, the quality of the signal is not considered in the selection rules. Although the two signals both exceed the minimum requirements for the signal, even if one signal is much stronger than the other signal, the much stronger signal does not benefit the selection process. If the D2D synchronization signal originating from the eNB is of much lower quality than the D2D synchronization signal from the user equipment out of network coverage, but if both D2D synchronization signals meet the preliminary requirement, the user equipment may Can happen. Moreover, when all D2D sync signals are below the requirements of the signal, only the quality of the signal is considered. Thus, the user equipment selects the non-network coverage user equipment even if the quality of the signal from the non-network coverage user equipment is only slightly better than the quality of the signal from the eNB.

  In this case, the design goal is to consider more factors when choosing the sync source and to choose the most reliable sync source (ie improve the effectiveness of the sync signal selection). To this end, a priority function is provided that takes into account at least two of the following factors: the type of synchronization source that generated it, the quality of the received signal, the hop count counted from the eNB. Therefore, the user equipment selects the synchronization source with the highest priority value as the most reliable synchronization source.

  Therefore, according to an embodiment of the present invention, a synchronization signal receiver is configured to generate a predetermined synchronization signal from a plurality of different synchronization sources including at least a synchronization source that transmits a signal originating from a network node and a synchronization generation wireless device. A synchronization signal receiver, comprising a synchronization signal receiving unit for receiving, wherein the wireless device is a user equipment rather than a network node. Further, the synchronization signal receiver further includes a metric calculation unit that obtains each metric of each of the synchronization sources from which the synchronization signal is received. The metric is the quality of the sync signal received, the type of sync source (ie whether the sync source is the sync source transmitting the signal originating from the network node or the radio device generating the sync signal), Based on at least two of the number of hops to the network node. Further, the synchronization signal receiver selects a synchronization source according to a metric and a timing for adjusting the timing of data transmission and / or reception according to the synchronization signal of the synchronization source selected by the synchronization source selection unit. And a unit.

  Advantageously, the synchronization signal receiver described above forms part of a wireless communication device such as a terminal or any user equipment. However, the synchronization signal receiver can also be a repeater, which can be particularly advantageous in the case of mobile repeaters. It should be noted that, even if embodiments herein are described in the context of LTE systems (ie mobile communication systems), the invention is not so limited. Instead, the invention can also be applied to a multicast / broadcast receiver, which can adapt its reception timing according to the invention. The multicast / broadcast receiver can also operate according to the LTE standard. However, the invention can also be applied in other systems such as digital video broadcasting.

  A synchronization signal is a predetermined signal known on both sides of such a signal, namely the receiver and the transmitter (synchronization source). Sync signals, or their expected properties and / or resources, are generally specified in standards. The synchronization signal may be fixedly predefined or a set of available synchronization signals, such as in the case of the LTE primary synchronization signal (PSS) and secondary synchronization signal (SSS) described above in connection with the background art. Can be selected from (determinable). The synchronization source is any entity that transmits a synchronization signal, such as a base station, a repeater, a user equipment and the like.

  The selection unit selects a synchronization source based on the metric. For example, the selection unit can be configured to select the synchronization source with the metric value that has the highest reliability. Such a selection can be performed, for example, by selecting the synchronization source having the highest metric value of the plurality of metric values when evaluating the synchronization source. However, depending on the metric design, the most reliable synchronization source can be associated with the lowest metric value instead of the highest metric value. In such a case, the sync source with the smallest metric value is selected. However, it should be noted that in general the selection unit can perform the selection in any way according to the metric.

  Furthermore, it is not limited to performing the selection at the start of the desired transmission. Instead, the selection can be performed on a regular basis for the purpose of checking if the proper synchronization source is being used and for reselecting the same or another synchronization source.

  The timing unit derives timing from the sync signal received from the selected sync source. This timing can be used to determine or adjust the timing of data transmission or reception. The data transmission timing or reception timing may be the same as the synchronization signal reception timing, or may be the timing obtained by subtracting a constant offset or a set offset from the reception timing. The user equipment determines its timing according to the received synchronization signal during the initial (initial) selection of the synchronization source. During reselection (selection performed after initial selection), instead of determining its timing, the user equipment can simply adjust its timing according to the new synchronization source. Here, the initial selection of the synchronization source may be, for example, selection when the user equipment is powered on. The timing unit can guide the timing of reception and the timing of transmission in different ways. For example, the reception timing can be determined as it is as the timing of the received synchronization signal, while in the case of transmission, the timing can be determined by applying the timing advance (that is, the offset with respect to the reception timing) Can be determined. Such an offset can be determined as in LTE. Furthermore, the transmission timing may be determined as it is as the timing of the received synchronization signal or by applying a predefined offset. However, the invention is not limited to these examples, and generally the timing unit can derive timing from the synchronization signal in any way.

  Advantageously, the metric acquisition unit is arranged to determine the metric as a combination of the quality of the synchronization signal received and a selection bias determined based on the number of hops and / or the type of synchronization source. , The type of sync source in this case is either a sync source which sends a sync signal originating from the network or a sync source which is independent of the network (eg a radio device which generates the sync signal without assistance from the network). Is.

  For example, the priority function (or metric) may be the sum of the quality of the received signal and the derived priority bias (selection bias). The quality of the received signal is measured, for example, at the receiver of the synchronization signal. The measurement of the signal quality can be performed in any way (eg based on the synchronization signal). Therefore, the synchronization source transmits a signal at a predetermined power on a predetermined resource. The resource and the power are recognized by the receiver that measures the power of the received signal, and the power of the received signal can be directly used as the quality parameter. However, the quality parameter used in the metric can also be determined as a function of the measured received signal power. The quality parameter can be the ratio or difference between the transmitted signal and the received signal (indicating signal degradation). Furthermore, the measurement can correspond to the CRS (cell reference signal) measurement performed in LTE (Non-Patent Document 7).

  Next, the selection bias (offset of received signal quality) is determined based on the number of hops and the type of synchronization source. A selection bias value corresponding to some combination of sync source type and hop count value can be defined in the specification. As one definition method, it is defined through a table. Specifically, the metric acquisition unit can be configured to determine the selection bias according to a correspondence between a predetermined selection bias value and the number of hops. Such a correspondence may be a table, which may be a lookup table stored at the receiver that associates a particular combination of hop number and sync source type with a particular value of bias. . Alternatively, the bias can be determined based on only one of the number of hops and the type of sync source. In such cases, the lookup table associates only the number of hops with a particular bias value. Alternatively, the bias value may be dependent only on the type of sync source. In such an example, the table associates the type of sync source (sync source that originates a sync signal originating in the network, sync source independent of the network) with a particular value of the selection bias.

  The above offset can be a positive offset (bonus). For example, if the synchronization source is a network node (eg a base station, or a user equipment that guides its own synchronization signal from the network), the offset is a predetermined positive value. If the synchronization source is a user equipment independent of the network, the offset value is smaller than the offset value for a network node. This value can be set to 0. Furthermore, as the type of the synchronization source, it is possible to distinguish between the synchronization source which is a network node and the synchronization source which is a wireless device which derives its own synchronization signal from the synchronization signal of the network (that is, the network).

  However, the present invention is not limited to the above, and instead of this, the offset can be a negative offset (penalty). Therefore, different penalty values are associated with different combinations of synchronization source type and number of hops. Alternatively, penalties (or bonuses) can be defined individually for each type of synchronization source and individually for each number of hops. Further alternatively, penalties can be defined only for the number of hops or only for the type of synchronization source.

Similarly, the penalty or bonus can be based on the number of hops. The number of hops can be as follows.
-Count down to the sync source (starting from a predetermined maximum number of hops of the sync source) -Count up from the sync source (eg starting from 0 in the sync source)

  In other words, the hop count from the eNB can be expressed as a hop count increasing or decreasing from the eNB as a starting point.

  For example, counting up from the eNB means that if the eNB 610 is the source of the sync signal, then there are 0 hops in the direction of the sync signal receiver user equipment 660 (as in the case of signal 615). Means If the user equipment 620 in network coverage is the source of the synchronization signal, there is one hop between the eNB 610 and the receiving user equipment 660 (as in the case of signal 625), and this one hop is the network. In-coverage user equipment 620. There may be additional hops between the eNB 610 and the receiving user equipment 660. In either of these cases, the original source of the sync signal is the eNB 610, and hops such as 620 send the same sync signal or are reconstructed based on the original sync signal received from the eNB 610. It only sends the sync signal. When counting up hops from the original source (in this case the network node synchronization source eNB 610), the number of hops will be positive or zero.

  Alternatively, however, the hops can be counted down from the sync signal receiver to the sync source. Specifically, if the synchronization signal is received directly from the eNB 610 by the user equipment 660 (signal 615), the number of hops from the eNB to the receiving user equipment is supported for that network node (eNB 610). Can be set to the maximum hop count NHmax. Different network nodes can have different maximum hop counts. For example, the macro eNB has a larger number of hops than the micro eNB, because the macro eNB has higher timing and frequency accuracy. As a benefit of the countdown, the user equipment does not need to know the maximum hop count if the maximum hop count of the eNB is configurable. When the synchronization signal receiving device 660 receives the synchronization signal 625 from the user equipment 620, the hop count counted down from the eNB 610 is NHmax-1 at the receiving user equipment 660. Similar to the example above, two or more devices that receive the sync signal originating from the network node and send it further (or send the sync signal reconstructed from the received sync signal) (the original The number of hops can be even smaller (NHmax-2, NHmax-3, ..., 0, etc.), corresponding to the source 610 and the receiving user equipment 660). In other words, when counting down the hops, it starts with a maximum number of hops predetermined for the target eNB 610. In particular, the maximum number of hops of different eNBs can be set / determined as different values. The predetermined maximum number of hops for the eNB can be set by the network. The user equipment obtains the information regarding the maximum number of hops via signaling from the eNB. This signaling can be performed via the D2D control channel or broadcast signaling, or in the sync signal.

  If the increasing hop count described above is used (ie the hop count starts at 0 in the network node), it is advantageous to set the priority bias function such that the bias value decreases as the hop count increases. On the other hand, if a decreasing hop count is used (ie the hop count starts with NHmax at the network node), it is advantageous to set the priority bias function such that the larger the hop count, the higher the bias value. Is. Here, the term "priority bias function" means a function or rule that associates a value of hop count (count of hops) with a value of bias.

  The above examples of correspondence between the selection offset (bias) and the number of hops and / or the type of synchronization source are not intended to limit the invention. According to another example, penalties and bonuses can be combined. For example, it is possible to give a bonus to a network node as a synchronization source while giving no bonus to other synchronization sources and give a penalty to a positive hop number, or vice versa.

  The relationship between bonus, sync source type, and hop count can be defined by a lookup table as described above. This table can be specified in the standard (ie predefined). Alternatively, the penalty or bonus can be calculated based on a particular function. For example, the penalty may be proportional to the number of hops (counted up), for example the value of the penalty may be twice the number of hops. Alternatively, the function can be inversely proportional to the number of hops counted down. However, this is only an example and the function may have another form that is not a simple multiplication or a multiplier other than two. The choice of a specific function (and table value) depends on the desired magnitude of the impact of the number of hops and / or the type of synchronization source on the metric.

  In summary, the bias is advantageously determined as a higher value (bonus or penalty) for the network node that is the source of the synchronization signal than for the wireless device that is the source of the synchronization signal. This allows the network node to be prioritized as a synchronization source over a wireless device that is independent of the network node (ie its own sync signal is not derived from the network). Such a priority is advantageous because it is generally expected that D2D communication and network-device communication will use the same bandwidth and time. Therefore, using the timing of the network to adjust the timing helps reduce interference and improve reception quality. Furthermore, some coordination between network-device transmissions and D2D transmissions can be performed by the network.

  Alternatively or additionally, the bias can be determined as a value (bonus or penalty) that decreases as the number of hops between the network node and the synchronization signal receiver increases, in which case the hop The number is a positive integer. Alternatively, the bias can be determined as a value that increases as the number of hops between the network node and the synchronization signal receiving device increases, and again the number of hops is a positive integer. These two possible schemes are to increase the metric value when the synchronization signal receiving device is close to the network node synchronization source and decrease the metric value when the synchronization signal receiving device is far from the network node synchronization source. Is intended. At this time, the proximity is represented by the number of nodes (wireless devices) between the network node that is the source of the synchronization signal and the synchronization signal receiving device.

  FIG. 7 illustrates an embodiment of the present invention, where the eNB 710 has coverage indicated by an ellipse 701. The D2D user equipment 770 receives the synchronization signal 715 from the eNB 710 with a received signal quality of -100 dBm. Furthermore, the D2D user equipment 770 receives the synchronization signal 725 originating from the eNB 710 over the hop formed by the user equipment 720 within network coverage with a received signal quality of -80 dBm. Further, the D2D user equipment 770 receives the synchronization signal 735 from the user equipment 730 outside the network coverage with a reception signal quality of −78 dBm. Therefore, selecting the synchronization source only according to the quality of the received signal selects the non-network coverage user equipment 730 because the non-network coverage user equipment 730 has the highest received signal quality, and then the user equipment 720. Yes, and finally eNB 710. However, in this embodiment, selection of the synchronization source is performed in a different method. The lower table of FIG. 7 shows the correspondence between the bonus value (third column) and the combination of sync source type (first column) and hop count (second column). The original source type is either the eNB 710 or a wireless device that does not direct synchronization signals from the network nodes (ie, user equipment 730 outside network coverage in this example). The number of hops distinguished in this example is 0, 1, or 2 or more. The selection bias is in this case a bonus that takes a value of 10, 6, 3, or 0 depending on the type of sync source and the number of hops. Specifically, when the synchronization source is the wireless device 730, no bonus is added to the quality (power) of the received signal (a bonus of value 0 is added) regardless of the number of hops. Note that in these examples, wireless device 730 generates the synchronization signal. However, in general, the synchronization signal can also be generated by some other wireless device, and thus the number of hops can be distinguished in its type of synchronization source.

For the synchronous source in FIG. 7, each metric is calculated as follows.
-ENB 710: A bonus value of 10 is added to the received signal power of -100 dBm (0 hops in the first row of the table, the synchronization source is eNB), resulting in a metric value of -90.
User equipment 720: Bonus value 6 is added to the received signal power of -80 dBm (the number of hops is 1 and the synchronization source is eNB in the second row of the table), resulting in a metric value of -74.
User equipment 730: A bonus value of 0 is added to the received signal power of -78 dBm (in the last row of the table, the number of hops is arbitrary, the synchronization source is user equipment), resulting in a metric value of -78.

  Therefore, the synchronization source having the highest reception quality -74 is the user equipment 720, followed by the user equipment 730 and then the eNB 710. Therefore, the D2D user equipment 770 selects the user equipment 720 in network coverage as the synchronization source because the user equipment 720 in network coverage has the highest metric value. In this example, the count-up method is used for the hop count.

  In order to be able to derive the metric, the receiving user equipment of the synchronization signal advantageously obtains information about the type of synchronization source and the number of hops from the hop transmitting the synchronization signal. This can be done by decoding the D2D sync signal or the D2D sync control channel if the sync source is a user equipment (transmitting a network-origin sync signal or a network-independent sync signal). it can. If the sync source is an eNB, then this information is already conveyed by the cell ID in the sync signal, i.e. based on the cell ID it is clear that the sync source is the eNB and thus the number of hops is 0. (Or NHmax depending on the hop count scheme applied). Instead of determining the selection bias value by using a table based on the type of sync source and hop count, the bias value can be indicated directly via the D2D sync signal or via a control channel such as a D2D control channel. . In other words, the selection bias is determined by receiving in the signaling information transmitted from each synchronization source. This gives more flexibility in determining the bias value and also eliminates the need for calculation or table lookup at the receiver. For example, the user equipment 720 in FIG. 7 directly indicates the bonus value 6 through a control channel such as a D2D sync signal or a D2D control channel.

  The above-mentioned allocation table can be set to the synchronization signal receiving device by control signaling. For example, the table of FIG. 7 can be transmitted to the receiving side apparatus (user equipment) via RRC signaling. Alternatively, the default table can be applied and further the modified table can be sent after the RRC connection with the network is established. Another alternative is to predefine multiple tables in the specification. The table selection can be set based on eNB type or by higher layer signaling.

  According to another embodiment of the invention, the metric acquisition unit comprises a quality of the received synchronization signal, a number indicating whether the synchronization source is a network node or a wireless device, and the number of hops to the network node. Is configured to find the metric as a linear combination of.

Specifically, the function can be defined by the following equation.
M = a * T + b * H + c * Q
In the formula, T is the type of the synchronization source of the generation source, for example, T = 1 if the original generation source is the eNB, and T = 0 otherwise. H is the hop count (ie, the number of hops between the sync signal generator and the hop sending the sync signal), which is the number of hops between the sync signal generator and the sync signal receiver. It can also be considered as showing). Q is the quality of the signal, and can be represented by the power (unit: dBm) of the received signal, for example. a, b, and c are weights for weighting the above three parameters T, H, and Q, respectively. These weights a, b and c can generally be real numbers. However, the weights can also be integers for the purpose of simplifying the implementation. The signal quality does not require the measured received power to be the signal quality as it is. Alternatively, the reception quality can be represented by a predefined number of levels determined based on the measured signal power. For example, it is possible to define a plurality of different categories (eg, “very good”, “good”, “normal”, “bad”, “very bad”) according to the dBm value. These partitions can be represented by integers, which are easier to calculate the above equation. For example, it is possible to assign number 5 to extremely good quality, number 4 to good quality, number 3 to normal quality, number 2 to bad quality, and number 1 to extremely poor quality.

  For example, the weighting factor a is advantageously a positive integer (a> 0) because the D2D sync signal derived from the eNB has a higher priority than the D2D sync signal derived from the other synchronization sources. is there. The weighting factor b is advantageously a negative number (b <0) if the hop count is counted up from the eNB and advantageously b> 0 if the hop count is counted down. . Also, the higher the quality of the received signal, the higher the metric value should be. Therefore, as illustrated above, when the reception quality is expressed in dBm, c> 0, because in such a case the reception quality is a negative number, that is, the higher the quality value, the better. . When c <0 (example: -1), -100 dBm is better than -90 dBm. When the reception quality is a negative number, the metric M <0 can be set. However, these are only examples. As will be apparent to those skilled in the art, the metric should be designed to represent the reliability of the sync source. Specific design, such as using hop count-up / count-down, or using positive / negative values as parameters T, H, Q (and thus weighting factors a, b, c), is implemented in any manner. be able to.

  The weighting factor, and thus the metric, can be set for each user equipment (receiving device). For user equipment outside network coverage, the weights a, b, c can be preset through OAM or transferred by the user equipment within network coverage through the D2D control channel.

  For user equipment within network coverage, the weighting factors a, b, c can be preset or set by the eNB. It is advantageous to configure by the eNB, which can be done for example by RRC signaling or other control signaling.

  As an advantage of having configurable metrics, different metrics can be configured for each user equipment. When data is transferred to user equipment, it is advantageous for such user equipment to synchronize to its eNB. In this case, a weighting factor larger than that of other user equipments can be set for that user equipment. Also, if the user equipment's reception capability (ability to detect / decode low quality signals) is low, it is advantageous for such user equipment to synchronize to the D2D sync signal with the highest signal quality. For such a user equipment, the weighting coefficient c can be set to a larger value than that of other user equipment whose reception capability is not low.

  In summary, the linear combination is advantageously defined as M = a * T + b * H + c * Q, where T is the originator of the synchronization signal, H is the number of hops, and Q is the receive. Signal quality, and a, b, and c are weighting factors. The metric acquisition unit is configured to determine the weighting factor a, b, or c by receiving in the signaling information transmitted from the network node.

  According to another embodiment of the present invention, the sync source selection unit is further configured to perform a preliminary step of eliminating the ineligible D2D sync signal. Specifically, a preliminary step may exclude unqualified sync sources from the set of sync sources considered for selection. Only for the D2D sync signal that passes the preselection, a metric is determined based on signal quality and bias, or based on the linear metric described above, and a sync source is selected based on that metric. That is, the sync source excluded in the preliminary exclusion step is no longer considered as a sync source.

  According to an embodiment of the present invention relating to a synchronization signal receiving device, in this synchronization signal receiving device, the synchronization source selection unit sets a series of synchronization sources whose number of hops to a network node exceeds a predetermined hop threshold. It is configured to perform preselection of synchronization sources by excluding them from candidates. For example, the predetermined threshold may be 3, which means that hops with a hop count of 4 or more (when counting up hops) are excluded from further selection. However, this is only an example, and the threshold value may take another value (for example, 1, 2, 4, or 5 or more).

  Instead of or in addition to preselection based on the number of hops, synchronization is achieved by excluding those sources whose signal quality does not exceed a predetermined quality threshold from the set of candidate synchronization sources. A source pre-selection can be performed. The predetermined threshold can be set to -100 dBm, for example. Therefore, hops (sync sources) for which the received sync signal power is less than -100 dBm are excluded from further selection. However, the value of -100 dBm is only an example, and the threshold value may take another value (e.g., -110 dBm, -105 dBm, or any other value). Furthermore, it may be advantageous to set the threshold values to different values, depending on the original source type. Specifically, for synchronization sources that do not belong to the network (such as user equipment 730 outside network coverage), the quality threshold can be higher, which means that in order to pass the preselection, This means that the signal from the user equipment needs to have higher quality than the synchronization source (eNB 710 or user equipment in network coverage 720) that determines its own signal based on the synchronization signal from the network.

  In this embodiment, the metric acquisition unit is configured to determine the metric only for the sync sources remaining in the set of candidate sync sources after the pre-selection performed by the sync source selection unit. Here, the term "series of candidate synchronization sources" means a synchronization source in which the synchronization signal is received by the synchronization signal receiving device.

  One of the advantages of pre-selection is that poor quality D2D sync signals are not selected. Therefore, the selection of untrusted sync sources can be avoided without determining the metric of such sync sources. Therefore, the selection can be simplified in this way.

  The above-described embodiments of the method of performing metric acquisition and synchronization source selection can be further improved by using hysteresis to control the synchronization source reselection. Specifically, the synchronization signal receiving device receives synchronization signals from a plurality of different synchronization sources. The synchronization signal receiving apparatus can periodically perform the reselection of the synchronization source by obtaining the metric of the synchronization source of the reception source and selecting the most reliable synchronization source accordingly. If the quality of the received signal fluctuates considerably, such periodic reselection can frequently change the synchronization source. It is advantageous to add a history for the purpose of avoiding such a ping-pong phenomenon. That is, when the user equipment selects a synchronization source, it keeps the synchronization source for a certain period of time, so the user equipment does not change the synchronization source frequently. This helps the stability of the synchronization source. The history diminishes over time so that the best synchronization source is selected.

  Further, the synchronization signal receiving device may include a reselection timer and a selection control unit, the selection control unit controlling the metric acquisition unit to obtain the metric and selecting the synchronization source according to the reselection timer. The sync source selection unit is controlled to For example, the terminal can evaluate the synchronization source from which the synchronization signal is received every 10 seconds. In this evaluation, the metric is determined or calculated as described above to obtain the best sync source (ie, the sync source with the highest metric value, or, in general, the metric indicating the best sync source. Sync source with a value). This allows the receiver of the synchronization signal (eg the terminal, more generally user equipment) to periodically adapt the synchronization source to the changing transmission environment. It should be noted that the above example of 10 seconds as the reselection cycle is only an example, and can be set to different values (eg, 1 second, 2 seconds, 5 seconds, 15 seconds, or any other cycle). . The value of the reselection timer can be fixed or can be set by an upper layer protocol by a network (node) such as an eNB. The advantage of the configurable timer is that the reselection operation can be adapted to the transmission environment of the user equipment. If the user equipment is moving, the channel quality may change more frequently, so it is advantageous to set a shorter reselection period. On the other hand, if the user equipment is not (currently) moving and the environment has not changed significantly, it may be advantageous to set the reselection period longer (increasing the reselection period).

  Furthermore, the synchronization signal receiving device is advantageously provided with a history timer which is activated at the time when a new synchronization source is selected and expires after a predetermined history period, in which case the reselection timer is changed to a predetermined reselection timer. Set to cycle. The reselection period can be received by the synchronization signal receiving apparatus in the control signaling from the network (for example, from a network node such as a base station (eNB)). When the history timer has expired, the selection control unit instructs the metric acquisition unit to obtain the metric when the reselection timer expires, and selects the synchronization source according to the metric. To order. If the history timer has not expired, at the time the reselection timer expires, it instructs not to select the sync source according to the metric. The history timer thus helps avoid frequent changes of the synchronization source.

  Advantageously, the predetermined history period decreases over time. In particular, the history period can decrease as the number of times the reselection timer expires increases.

  Reselection can also be triggered when the quality of the received signal of the current synchronization source falls below a certain threshold for a certain period of time. This is advantageous in avoiding sudden loss of the sync source or a sudden drop in the quality of the signal from the sync source.

  As an advantage of the present invention described in the above embodiment, not only is it based on the reception quality, but also the type of synchronization source and the distance are distinguished. Therefore, for a D2D sync signal with a significantly higher signal quality, the user equipment selects it. The eNB has priority and the hop count can be considered as an offset to the quality of the signal. If the signal quality of the D2D synchronization signal from the user equipment outside the network coverage (such as 630) is not significantly higher than the signal quality of the D2D synchronization signal from the eNB 610, the user equipment selects the eNB.

  FIG. 8 shows an apparatus 800 for receiving a synchronization signal according to an embodiment of the invention. Device 800 is a wireless device, such as user equipment. The wireless device receives various signals from different synchronization sources, each with different strength. Specifically, this device may be from a network node 810, such as an eNB, or another wireless user equipment 820 located within the coverage 801 of the eNB 810, or the coverage 801 of the network (specifically of the eNB 810). Signals may be received from user equipment 830 located outside of the. The device comprises a sync signal receiving unit 840, a metric acquisition unit 850, a sync source selecting unit 860, and a timing unit 870, which are configured as described in the above embodiments. ing. Specifically, the sync signal receiving unit 840 is adapted to receive sync signals from various D2D sync sources. Further, the sync signal receiving unit 840 can identify the sync source, or at least the type of sync source, based on the received sync signal. However, this information can also be conveyed later via signaling. The metric acquisition unit 850 is configured to determine or calculate a metric and the sync source selection unit 860 selects a sync source based on the metric. After selecting the synchronization source, the device 800 first determines its timing or (after the initial determination has already been made) adjusts its timing. Specifically, the device 800 can make the received synchronization signal a timing intended for reception or add an offset to the timing. The transmit timing is then derived, and this step can be performed based on the derived receive timing.

  Further, the device 800 can include a reselection control unit 880 that controls when it performs reselection. The reselection control unit 880 therefore controls the metric acquisition unit 850 and the selection unit 860 so that they perform their respective functions (ie calculation of the metric and selection of the synchronization source at specific times). These timings are advantageously derived from a reselection timer 885, which also forms part of the device 800. The reselection timer 885 may be configurable by signaling received from the network. Reception of signaling from the network may be performed by the signaling receiving unit 890. In this block diagram, the signaling reception unit 890 and the synchronization signal reception unit 840 are depicted separately. The reason for this is that these units are functional blocks. In general, apparatus 800 includes a common reception front end formed by one or more antennas, amplifiers, demodulators, and decoders, which are also applicable to receiving signaling. ) Has. The signaling and sync signals are used for different purposes, as shown by separate blocks 840 and 890 in FIG.

  Furthermore, the signaling receiving unit may be configured to receive signaling including the setting for determining the metric. For example, the setting of at least one of the weighting factors a, b, c, the selection bias (offset), and the bonus value / penalty value can be received and passed to the metric acquisition unit 850. In addition, the apparatus may include a history timer 865 so that the sync source selection unit 860 can generate a new sync source (ie, different from the currently applied sync source) based on the metric determined in the metric acquisition unit 850. When selecting the sync source, the reselection control unit 880 can control the sync source selection unit 860 to change or not change the sync source by using the history timer 865. The history timer 865 can also be set by the signaling received from the network by the signaling receiving unit 890. FIG. 9 illustrates a method of selecting a sync source in the system as described above. Specifically, such a synchronization signal receiving method receives a predetermined wireless synchronization signal from a synchronization source including a synchronization source for guiding its own synchronization signal from a network node and a synchronization signal generation wireless device (910), including. Some information such as the type of sync source and the number of hops can already be conveyed by the sync signal received. However, this information can be conveyed in other ways. The method then determines the selection metric of each synchronization source, the quality of the synchronization signal received, the type of synchronization source (whether the synchronization source sends the synchronization signal originating from the network node or independent of the network node). 930) based on at least two of whether to send a synchronization signal) and the number of hops to the network node. Then, in step (940) of selecting a synchronization source according to the determined metric, a synchronization source is selected, and then in step 950, the synchronization source is used, that is, transmission of data is performed according to the synchronization signal of the selected synchronization source. Alternatively, it determines or adjusts the reception timing.

  The metric is advantageously determined as a combination of the quality of the synchronization signal received and a selection bias determined based on the number of hops and / or the type of synchronization source, the type of synchronization source being its own. It is either a synchronization source that derives the synchronization signal from a network node, or a wireless device independent of the network. The selection bias can be obtained according to a correspondence relationship (a reference table or the like) between a predetermined selection bias value and the number of hops. The selection bias is, specifically, a higher value for the network node that is the source of the synchronization signal than for the wireless device that is the source of the synchronization signal, or for the hop between the network node and the synchronization signal receiving device. A value that decreases as the number increases (when the number of hops is counted up from the network node), or a value that increases as the number of hops between the network node and the synchronization signal receiver increases (number of hops). Is counted down from a predetermined maximum number of hops of the network node as a starting point), the value of the network node can be calculated as one of the following. Alternatively, the selection bias can be determined by receiving in the signaling information transmitted from each synchronization source. However, the present invention is not limited to the method for obtaining the metric as described above, and generally, the quality of the received synchronization signal and the number indicating whether the synchronization source is a network node or a wireless device, The metric can also be determined as a linear combination of the number of hops to the network node. Such a linear combination is advantageously defined as M = a * T + b * H + c * Q, where T is the generator of the synchronization signal, H is the number of hops and Q is the received signal. , And a, b, and c are weighting factors. At least one of the weighting factors a, b, or c can be determined by receiving in the signaling information transmitted from the network node.

  Further, the method comprises a synchronization source having a number of hops to a network node exceeding a predetermined hop threshold, or a synchronization source having a signal quality not exceeding a predetermined quality threshold, or both. Pre-selecting a sync source 920 by excluding it from the set of candidate sync sources. Then, after preselection performed by the sync source selection unit, the metric is determined only for the sync source in the set of candidate sync sources.

  Further, the synchronization method may include activating (maintaining) a reselection timer and controlling the determination of the metric and the selection of the synchronization source according to the reselection timer (960).

  The method may further include the step of maintaining a history timer that starts when a new sync source is selected and expires after a predetermined history period, in which case the reselection timer is set to a predetermined length of time. Set. The method asks for a metric when the reselection timer expires, if the history timer has expired, and orders the synchronization source to be selected according to that metric, and if the history timer has not expired, Advantageously, when the reselection timer expires, instructing not to select the synchronization source according to the metric.

  The description in the background section is intended to provide a thorough understanding of the particular exemplary embodiments described herein, of processes and functions in a mobile communication network (such as a network compliant with the 3GPP standard). It should be understood that the invention is not limited to the particular embodiments described. However, the improvements proposed herein can be readily applied in the architectures / systems described in the Background section and, in some embodiments of the invention, standard procedures for these architectures / systems. And improved procedures are available. It will be understood by those skilled in the art that various changes and / or modifications can be made to the invention illustrated in a particular embodiment without departing from the broadly described concept or scope of the invention. Will be done.

  Another embodiment of the invention relates to implementing the various embodiments described above using hardware and software. Various embodiments of the invention may be implemented or performed using a computing device (processor). The computing device or processor can be, for example, a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device. Various embodiments of the invention may also be implemented or embodied by combinations of these devices.

  Furthermore, various embodiments of the invention may be implemented by software modules executed by a processor or implemented directly in hardware. Also, a combination of software modules and hardware implementation is possible. The software modules may be stored in any kind of computer readable storage medium, for example RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc.

  In summary, the present invention relates to selecting one synchronization source from various synchronization sources, which may be a synchronization source that determines a synchronization signal from a network, such as a base station (network node) or a synchronization signal to a base station. User equipment received from the station, possibly over other hops, is included, and the synchronization source includes a synchronization source that does not determine its own synchronization signal from the network. The selection of the synchronization source is performed by selecting the synchronization source with the highest reliability of the synchronization signal based on the metric calculated for each considered synchronization source. Specifically, the metric is based on the type of synchronization source, the number of hops between the network and the synchronization source, and / or the quality of the received signal. After selecting the sync source, adapt the device timing accordingly.

Claims (9)

A synchronous receiver,
A synchronization source that guides its own synchronization signal from a network node, or a synchronization source that is a wireless device that itself generates a synchronization signal, and a receiving unit that receives a predetermined wireless synchronization signal,
A processor, the processor comprising:
The selection metric for each of the synchronization sources is
-The quality of the received synchronization signal,
Whether the synchronization source guides the synchronization signal from a network node or independently of the network node,
The number of hops to the network node,
A metric acquisition process based on at least two of
A synchronization source selection process of selecting a synchronization source according to the metric obtained by the metric acquisition process,
Timing processing for determining or adjusting the timing of data transmission or reception according to the synchronization signal of the synchronization source selected by the synchronization source selection processing,
A selection control process for controlling a reselection operation to obtain the metric and to select a synchronization source according to a reselection timer;
Setting the value of the reselection timer so that the reselection operation is regularly adapted to the transmission environment.
Synchronous receiver. The metric acquisition process is
-The quality of the received synchronization signal, and
A selection bias based on the number of hops and / or the type of synchronization source, the type of synchronization source directing its own synchronization signal from a network node, or a network independent radio device. , The selection bias is a combination of the selection bias, is configured to obtain the metric,
The synchronous receiver according to claim 1.   The synchronous receiving device according to claim 2, wherein the metric acquisition process is configured to obtain the selection bias according to a correspondence relationship between a predetermined selection bias value and the number of each hop. The selection bias is
A higher value for the network node that is the source of the synchronization signal than for the wireless device that is the source of the synchronization signal,
A value that decreases as the number of hops between the network node and the synchronous receiver increases when the number of hops is counted to increase starting from a network node,
-The number of hops increases as the number of hops between the network node and the synchronous receiver increases, when the number of hops is counted down from a network node having a predetermined maximum number of hops. The value to
As one of the
The synchronous receiving device according to claim 2.   The synchronous receiving device according to claim 2, wherein the metric acquisition process is configured to obtain the selection bias by receiving in the signaling information transmitted from each synchronization source.   The metric acquisition process, as a linear combination of the quality of the received synchronization signal, a number representing whether the synchronization source is a network node or a wireless device, and the number of hops to the network node, The synchronous receiving apparatus according to claim 1, wherein the synchronous receiving apparatus is configured to obtain the metric. The linear combination is defined as M = a * T + b * H + c * Q, where T is the source of the synchronization signal, H is the number of hops, Q is the quality of the received signal, and a , B, c are weighting factors,
The metric acquisition process is configured to determine the weighting factor a, b, or c by receiving in the signaling information transmitted from the network node.
The synchronous receiver according to claim 6. The synchronization source selection process,
A synchronization source in which the number of hops to the network node exceeds a predetermined hop threshold, and / or
A synchronization source whose signal quality does not exceed a predetermined quality threshold,
Is configured to perform preselection of sync sources by excluding S from the set of candidate sync sources,
The metric acquisition process is configured to determine the metric only for a sync source in the set of candidate sync sources after the preselection performed by the sync source selection process,
The synchronous receiver according to any one of claims 1 to 7. A method performed by a synchronous receiver, comprising:
A process of receiving a predetermined wireless synchronization signal from a synchronization source that guides its own synchronization signal from a network node, or a synchronization source that is a wireless device that itself generates a synchronization signal,
The selection metric for each of the synchronization sources is
-The quality of the received synchronization signal,
Whether the synchronization source guides the synchronization signal from a network node or independently of the network node,
The number of hops to the network node,
A metric acquisition process based on at least two of
A synchronization source selection process of selecting a synchronization source according to the metric obtained by the metric acquisition process,
Timing processing for determining or adjusting the timing of data transmission or reception according to the synchronization signal of the synchronization source selected by the synchronization source selection processing,
A selection control process for controlling a reselection operation to obtain the metric and to select a synchronization source according to a reselection timer;
Setting the value of the reselection timer so that the reselection operation is regularly adapted to the transmission environment.
Method.