JP6646860B2 - Selection of synchronization source between devices - Google Patents

Description

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

  Third generation mobile communication systems (3G) based on WCDMA® wireless access technology are being deployed on a wide scale worldwide. As the first step in enhancing or evolving this technology, High Speed Downlink Packet Access (HSDPA) and Enhanced Uplink (also called High Speed Uplink Packet Access (HSUPA)) are introduced, Extremely competitive wireless access technologies are provided. In order to meet the increasing demands of users and to secure a competitive edge for new radio access technologies, 3GPP has introduced a new mobile communication system called Long Term Evolution (LTE). LTE is designed to provide the carriers required for high speed data and media transmission and high capacity voice support over the next decade. The ability to provide high bit rates is an important strategy in LTE. The specification of the work item (WI) related to LTE (Long Term Evolution) is 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 finally released as Release 8 (LTE Release 8). The LTE system is an efficient packet-based radio access and radio access network, providing all IP-based functions with low delay and low cost. Detailed system requirements are described in Non-Patent Document 1 (available freely on the 3GPP website).

  In LTE, to achieve flexible system deployment with 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). For the downlink, wireless access based on OFDM (Orthogonal Frequency Division Multiplexing) is employed. Because such radio access is inherently less susceptible to multipath interference (MPI) due to the lower symbol rate, uses a cyclic prefix (CP), and supports various transmission bandwidth configurations. Because it is possible. For uplink, wireless access based on SC-FDMA (Single-Carrier Frequency Division Multiple Access) is adopted. This is because, given that the transmission power of the user equipment (UE) is limited, it is prioritized to provide a wider coverage area than to improve the peak data rate. LTE Release 8 employs a number of major packet radio access technologies (eg, MIMO (Multiple Input Multiple Output) channel transmission technology) 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. 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 includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data control protocol (PDCP) layer, which provide 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 provides radio resource management, admission control, scheduling, negotiations to implement uplink QoS (quality of service), broadcast of cell information, encryption / decryption of user plane data and control plane data, downlink / uplink Performs many functions, such as user plane packet header compression / decompression. The plurality of eNBs are connected to each other by an X2 interface. In addition, a plurality of eNodeBs use an E1 (Evolved Packet Core) by an S1 interface, more specifically, a mobility management entity (MME) by an S1-MME, and a serving gateway by an S1-U. S-GW (Serving Gateway). The S1 interface supports a many-to-many relationship between the MME / serving gateway and the eNB. The SGW functions as a user plane mobility anchor during handover between eNBs while routing and forwarding user data packets, and furthermore, an anchor for mobility between LTE and another 3GPP technology (S4). Terminate the interface and relay 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 the user equipment. The SGW manages and stores user equipment contexts (eg, parameters for IP bearer services, 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 idle mode user equipment tracking and paging procedures (including retransmissions). The MME is involved in the bearer activation / deactivation process, and also selects the SGW of the user equipment at initial attach and during intra-LTE handover with relocation of core network (CN) nodes It also plays a role. The MME is responsible for authenticating the user (by interacting with the HSS). Non-Access Stratum (NAS) signaling is terminated in the MME, and the MME is also responsible for generating a temporary ID and assigning it to the user equipment. The MME checks the authentication of the user equipment to enter the service provider's Public Land Mobile Network (PLMN) and enforces the roaming restrictions of the user equipment. The MME is a terminal point in the network in NAS signal encryption / integrity protection and manages security keys. Lawful intercept of signaling is also supported by the MME. Further, the MME provides a control plane function for mobility between the LTE access network and the 2G / 3G access network, and terminates the S3 interface from the SGSN. Further, the MME terminates the S6a interface towards the home HSS for roaming user equipment.

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, where the first downlink slot occupies a control channel region (PDCCH region) in a first OFDM symbol. Prepare. Each subframe is made up 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 component carrier bandwidth. Therefore, each OFDM symbol is composed of several modulation symbols transmitted on each of N ^DL _RB × N ^RB _sc subcarriers, as also shown in FIG.

Assuming a multi-carrier communication system, eg, using OFDM, 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 (for example, seven OFDM symbols) in the time domain and N ^RB _sc consecutive subcarriers (e.g., 7 OFDM symbols) in the frequency domain as illustrated in FIG. For example, it is defined as 12 subcarriers of a component carrier). Thus, in 3GPP LTE (Release 8), the 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, 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, but instead its terminology will be changed to "cell", which indicates a combination of downlink and, optionally, uplink resources. Linking between the carrier frequency of the downlink resource and the carrier frequency of the uplink resource is indicated in system information transmitted on the downlink resource.

  The cell search procedure is the first series of tasks that a mobile device performs after the first power up in a cellular system. The mobile device can receive and initiate voice / data calls only after the search and registration procedures. In a typical cell search procedure in LTE, a carrier frequency is determined, the timing is synchronized, and a unique cell identifier is identified. Generally, these procedures are facilitated by a unique synchronization signal transmitted by the base station (BTS). However, these synchronization signals are not used continuously in the connected mode of the mobile device. Therefore, only minimal resources are allocated for the synchronization signal 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 transmit the uplink signal at the correct time. The first stage of cell search involves initial synchronization. Thus, the user equipment detects the LTE cell and decodes all information required to register with the detected cell. This procedure utilizes two physical signals broadcast on the central 62 subcarriers of each cell, a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). These signals allow for time and frequency synchronization. When the user equipment successfully detects these signals, it provides the physical cell ID, the length of the cyclic prefix, and information on whether FDD or TDD is employed. Specifically, in LTE, when the terminal is powered on, the terminal detects a primary synchronization signal. In the case of FDD, the terminal detects the primary synchronization signal at the beginning of the first subframe (subframe 0) in the radio frame. (In the case of TDD, this position is slightly different but well-defined). This allows the terminal to obtain the slot boundary independently of the cyclic prefix selected for the cell. After detecting the 5 ms timing (slot boundary), the mobile terminal searches for a secondary synchronization signal. Both the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) are transmitted on 62 subcarriers among 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), is located in the middle 72 sub-cells of the cell. Mapped to carrier only. The physical broadcast channel (PBCH) includes a master information block (MIB) containing information on 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 eight most significant bits of the system frame number (SFN).

  The terminal activates the system bandwidth after successfully detecting the Master Information Block (MIB) containing the most frequently transmitted limited number of parameters that are essential for first accessing the cell, ie 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 necessary system information in a so-called system information block (SIB). In LTE Release 10, SIB types 1 to 13 (which convey different information elements required for a specific operation) are defined. For example, in the case of FDD, SIB type 2 (SIB2) includes an uplink carrier frequency and an uplink bandwidth. The various SIBs are transmitted on the physical downlink shared channel (PDSCH), so resources for each SIB are allocated by the physical downlink control channel (PDCCH) (see the detailed description of PDSCH and PDCCH below). In order for a terminal (user equipment: UE) to correctly detect such (or another) PDCCH, it is necessary to know the downlink system bandwidth from the MIB.

The cell identifier (cell ID) mentioned above uniquely identifies a cell within a 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 transmitted in the system information and is designed for eNodeB management in the core network. Furthermore, this global cell ID is also used for the purpose of user equipment identifying a specific cell in connection with RRC / NAS layer processing. The physical cell ID is a cell identifier in the physical layer. The physical cell ID ranges from 0 to 503 and is used to scramble the data to help the mobile device 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 a 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, each group including three unique IDs. In this grouping, each physical layer cell ID belongs to only one physical layer cell ID group. Therefore, N ^cell _ID = 3N ⁽¹⁾ _ID + N ⁽²⁾ _{ID, which} is a physical layer cell ID, is a number N ⁽¹⁾ _ID in the range of 0 to 167 representing a physical layer cell ID group, and a physical layer cell ID. It is uniquely defined by the number N ⁽²⁾ _ID in the range of 0 to 2 representing the physical layer cell ID in the group.

The synchronization signal includes 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 the N ⁽²⁾ _ID . By detecting the primary synchronization signal, the N ⁽²⁾ _ID can be detected. The sequence used for the secondary synchronization signal is a concatenation of two 31-bit binary sequences in an interleaved manner. The concatenated sequence is scrambled by a scrambling sequence provided by the primary synchronization signal. The secondary synchronization 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 the 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 details regarding the primary synchronization signal and the secondary synchronization signal, see, for example, section 6.11 of Non-Patent Document 3 (available freely on the 3GPP website and incorporated herein by reference). .

  The receiving user equipment adjusts the timing after receiving the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). Specifically, the user equipment synchronizes its receiver with a downlink transmission received from a synchronization source (eNB). Then, the uplink timing is adjusted. This adjustment is performed by applying a timing advance based on the received downlink timing at the transmitter of the user equipment in order to correct a propagation delay that differs for each user equipment. The timing advance procedure is briefly described in Non-Patent Document 4, section 18.2.2.

  Proximity-based applications and services are a new trend in social technology. Current intended uses include commercial and public safety related services of interest to businesses and users. By introducing Proximity Services (ProSe) functionality into LTE, the 3GPP industry will be able to service this growing market, while simultaneously urging some public safety communities to use LTE. Can meet various needs.

  Device-to-device (D2D) communication is a technical element in LTE-A Release 12. Device-to-device (D2D) communication techniques can increase spectral efficiency in D2D as an underlay for cellular networks. For example, if the cellular network is LTE, all physical channels that carry data use SC-FDMA in D2D signaling. "D2D communication in LTE" focuses on two areas: discovery and communication. In D2D communication, user equipment transmits 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, when at least within the coverage of the eNB). Therefore, in D2D, system performance can be improved by using cellular resources. Currently, it is assumed that D2D operates in the LTE uplink spectrum of a cell providing coverage (for FDD) or in an uplink subframe (for TDD, except when out of coverage). Further, D2D transmission / reception does not use full duplex on a given carrier. From the individual user equipment's point of view, on a given carrier, full duplex by D2D signal reception and LTE uplink transmission is not used (ie, D2D signal reception and LTE uplink transmission cannot be performed simultaneously). Current further operational assumptions regarding LTE D2D wireless access are described in Non-Patent Document 5 (available freely on the 3GPP website).

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

In 3GPP RAN1, it has been agreed that, as an operational assumption, the synchronization source is any node that transmits a D2D synchronization signal (D2DSS). This node can be an eNB or regular user equipment. When the synchronization source is an eNB, the D2D synchronization signal is the same as the release 8 primary synchronization signal (PSS) and secondary synchronization signal (SSS). The D2D user equipment determines the timing of transmitting the D2D signal using the synchronization signal. As a further operational assumption, it was agreed that the D2D user equipment scans the synchronization source before starting to transmit the D2D synchronization signal. If a synchronization source is detected, the user equipment can synchronize its receiver to that synchronization source before transmitting the D2D synchronization signal. Even if no synchronization source is detected, the user equipment can transmit a D2D synchronization signal. If the user equipment detects a change in the D2D synchronization source, it can (re) select a D2D synchronization source to use as a timing reference for transmitting the D2D synchronization signal based on the following metrics.
The type of synchronization source (eNB or user equipment);
-The quality of the received D2D synchronization signal-the 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 the selection of a synchronization source.

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

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

  One main aspect of the present invention is an integrated circuit that controls operation of a synchronous reception device, wherein the operation is a synchronization source that guides its own synchronization signal from a network node, or a wireless device that generates its own synchronization signal. Receiving a predetermined wireless synchronization signal from a synchronization source; and selecting a selection metric for each of the synchronization sources; (i) the quality of the received synchronization signal; and (ii) the synchronization source transmitting the synchronization signal from a network node. (Iii) the metric obtaining process based on at least two of the number of hops to the network node, and the metric obtained by the metric obtaining process. Synchronization source selection processing for selecting a synchronization source, and the timing of data transmission or reception, the synchronization source selection processing A timing process for determining or adjusting according to the synchronization signal of the synchronization source selected in accordance with the above, a selection control process for determining the metric and for selecting a synchronization source in accordance with a reselection timer; A process in which the value of the selection timer is set by an upper layer protocol by the network node to adapt the reselection operation.

  According to an embodiment of the present invention, a synchronization receiving device includes a synchronization source for guiding its own timing from a network node and a synchronization source including a synchronization generation wireless device. The synchronization receiving unit that receives the wireless synchronization signal and the selection metric of each synchronization source, the quality of the received synchronization signal, whether the synchronization source guides its own timing from the network node, generates the timing, and hops to the network node. A metric acquisition unit that determines based on at least two of the following: a synchronization source selection unit that selects a synchronization source according to the metric determined by the metric acquisition unit; and a synchronization source selection timing for transmitting or receiving data. 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, there is provided a method for selecting a synchronization source, comprising the steps of: a synchronization source that derives its own synchronization signal from a network node; Receiving the wireless synchronization signal of the synchronization source, and selecting the selection metric of each synchronization source based on the quality of the received synchronization signal, whether the synchronization source transmits a synchronization signal originating from the network node, or a synchronization signal independent of the network node. Or a number of hops to a network node, a step of selecting a synchronization source according to the determined metric, and a timing of data transmission or reception. Determining or adjusting according to the synchronization signal of the synchronization source.

  According to another embodiment of the present invention, a computer program product comprising a computer readable medium having computer readable program code embodied, wherein the program code is adapted to perform the present invention. ,I will provide a.

  According to an embodiment of the present invention, the above-described device 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 conjunction with the accompanying drawings.

FIG. 3 is a block diagram illustrating an example of the entire architecture of LTE. FIG. 2 is a block diagram illustrating an example of an architecture of an LTE access network. FIG. 3 is a schematic diagram illustrating an example of a grid of OFDM modulation resources in a time-frequency domain. 9 is a flowchart showing a structure of a downlink protocol and multiplexing of a second layer in a state where carrier aggregation is set. 9 is a flowchart showing a structure of a second layer uplink protocol and multiplexing in a state where carrier aggregation is set. FIG. 3 is a schematic diagram illustrating a plurality of different sources of inter-device (D2D) synchronization signals. FIG. 3 is a schematic diagram illustrating an example scenario of selecting a synchronization source based on metrics based on signal quality and a table containing selection bias values. 1 is a block diagram illustrating an apparatus according to an embodiment of the present invention. 5 is a flowchart illustrating a method according to an embodiment of the present invention.

  The present invention relates to the reception of a synchronization signal and the selection of a synchronization signal source in a wireless system. The device can be a device, and the user equipment can be a mobile phone, smartphone, tablet, laptop, or other computer. Furthermore, wireless devices can derive their timing from the network or independently of the network.

  The term "network node" in this context is to 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 a macro cell, micro cell, pico cell, femto cell, or any other concept. Thus, the network node may be a base station, such as an eNodeB, or a repeater provided as part of a network.

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

  Hereinafter, embodiments will be presented based on the LTE specification. However, the invention is not limited to LTE. The concepts and examples described herein are based on one synchronization source from multiple synchronization sources including one or more network nodes and one or more wireless devices (eg, user equipment) that are not network nodes. It can be applied to any selected wireless system. The wireless device may derive its synchronization signal from the network (ie, from a network node) or generate the synchronization signal independent of network timing.

When the user equipment (UE) transmits an inter-device (D2D) signal, the rules for determining which D2D synchronization source the user equipment uses as a timing reference for transmitting the D2D signal are as follows: Can be.
1. The eNodeB D2D synchronization source has a higher priority than the user equipment D2D synchronization 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 giving priority to the D2D synchronization source that is the eNodeB, and then the D2D synchronization source that is the user equipment in the coverage, the D2D synchronization source is selected. In-coverage user equipment is user equipment that is located within the coverage of the base station and thus 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 the out-of-coverage user equipment is also out-of-coverage of another user equipment that derives its timing from the timing of the network, such out-of-coverage user equipment will generate its own timing independent of the network timing.

  In the D2D synchronization source selection procedure, this criterion is not sufficient, because other factors (eg, the quality of the received D2D synchronization signal, the 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 common scenario that occurs when communicating in a system that supports both communication between a network and a terminal and direct communication between two or more terminals. Base station eNB 610 has coverage indicated by ellipse 601. The eNB 610 sends an inter-device synchronization signal (D2D synchronization signal) 615, which has the same format as the release 8 primary synchronization signal (PSS) and secondary synchronization signal (SSS) in this scenario. Terminal 620 is a user equipment within network coverage (ie, a user equipment located within coverage 601 of base station 610). The user equipment 620 within the network coverage receives the PSS / SSS from the eNB 610 and synchronizes with the eNB 610. The eNB 610 may request some in-network coverage user equipment (such as 620) to transmit a D2D synchronization signal. Therefore, the user equipment 620 within the network coverage is set by the eNB 610 to transmit the D2D synchronization signal, as indicated by the dotted line, and thus transmits the D2D synchronization signal 625. Thus, the user equipment 620 is also a synchronization source that guides its synchronization (timing) from the network (specifically, from the network node 610).

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

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

  The problem based on the above situation is which synchronization source the D2D user equipment 660 should select to synchronize its receiver (or transmitter or both). That is, the signal is very weak but there is no hop eNB 610, or the signal is strong but the user equipment 620 in the network coverage where there are several (one in this case) hops, or the signal is strong but the hop is unknown. Out of network coverage user equipment 630 (the signal is not originating from the network).

One possible solution to this problem is that the D2D synchronization signal 615 and the D2D synchronization signal 625 derived from the eNB (and transmitted by the eNB 610 or the user equipment 620) have a D2D synchronization independent of network timing. This is to always assign a higher priority than the D2D synchronization signal received from the user equipment (eg, 630) that generated the signal 635. However, such a directly received synchronization signal, or a synchronization signal originating from a network, is generally the most accurate synchronization signal, but the following problems may occur.
The signal 615 received directly from the eNB 610 or a signal derived from such a signal (eg the signal 625) is much weaker than the signal generated by and received from the user equipment (630, etc.); And therefore may be less reliable.
-A signal derived from the eNB 610 may pass through a variable number of hops from the eNB, and the strength of the received signal may vary.

  Therefore, any extended principles that give clearer and more effective rules on how the user equipment should select the synchronization source are advantageous.

  A contribution by LGE (Non-Patent Document 6) was made in 3GPP RAN1, and the following rules have been proposed. That is, the quality of the D2D synchronization signal is used as a criterion for the preliminary selection. D2D synchronization signals that do not meet the minimum requirements for signal quality are previously excluded from further selection procedures without applying selection rules. For the D2D sync signal that has passed the preselection, either the sync source type priority or the hop count priority is used. For example, the user equipment always selects a D2D synchronization signal originating from the eNB regardless of the number of hops. On the other hand, if none of the D2D synchronization signals satisfies the signal quality requirements, the D2D synchronization signal having the highest signal quality is selected regardless of the type of synchronization source and the hop count. The problem with this method is that, for example, once the D2D synchronization signal meets the minimum signal requirements, the signal quality is not taken into account in the selection rules. Even if both signals exceed the minimum signal requirement, but one signal is much stronger than the other, the much stronger signal will not be advantageous in 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 both D2D synchronization signals meet the preliminary requirements, the user equipment is connected to the eNB. May occur. Further, when all D2D synchronization signals are below the signal requirements, only the signal quality is considered. Thus, even if the quality of the signal from the out-of-network coverage user equipment is only slightly better than the quality of the signal from the eNB, the user equipment selects the out-of-network coverage user equipment.

  In this case, the goal of the design is to consider more factors when selecting the synchronization source and to select the most reliable synchronization source (ie, improve the effectiveness of the selection of the synchronization signal). To achieve this, we provide a priority function that considers at least two of the following factors: the type of source of the synchronization source, the quality of the received signal, and the hop count counted from the eNB. Therefore, the user equipment selects the synchronization source with the highest priority value as the synchronization source with the highest reliability.

  Therefore, according to an embodiment of the present invention, a synchronization signal receiver, which transmits a predetermined synchronization signal from a plurality of different synchronization sources including at least a synchronization source transmitting a signal originating from a network node and a synchronization generation wireless device. There is provided a synchronization signal receiving unit, wherein the wireless device includes a synchronization signal receiving unit, wherein the wireless device is a user equipment instead of a network node. Further, the synchronization signal receiver further includes a metric calculation unit for determining each metric of each synchronization source from which the synchronization signal is received. The metrics include the quality of the received synchronization signal, the type of synchronization source (ie, whether the synchronization source is a synchronization source transmitting a signal originating from a network node or a wireless device generating a synchronization signal), Based on at least two of the number of hops to the network node. Further, the synchronization signal receiver includes a synchronization source selection unit for selecting a synchronization source according to the metric, and a timing for adjusting data transmission and / or reception timing according to a 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 may be particularly advantageous for mobile repeaters. It should be noted that even though the embodiments are described herein in the context of an LTE system (ie, a mobile communication system), the invention is not limited thereto. Rather, the invention can be applied to multicast / broadcast receivers, which can adapt their reception timing according to the invention. Multicast / broadcast receivers can also operate based on the LTE standard. However, the invention can be applied in other systems, such as digital video broadcasting.

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

  The selection unit selects a synchronization source based on the metric. For example, the selection unit can be configured to select the synchronization source having the highest reliability metric value. Such a selection can be performed, for example, by selecting the synchronization source having the highest metric value among the plurality of metric values when evaluating the synchronization source. However, depending on the metric design, the most reliable synchronization source may correspond to the lowest metric value instead of the highest metric value. In such a case, the synchronization source with the smallest metric value is selected. However, it should be noted that in general the selection unit can make 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. Rather, the selection can be performed periodically to check that the proper synchronization source is being used and to reselect the same or another synchronization source.

  The timing unit derives timing from a synchronization signal received from a selected synchronization source. This timing can be used to determine or adjust the data transmission or reception timing. The data transmission timing or the reception timing may be the same as the synchronization signal reception timing, or may be a timing obtained by subtracting a fixed offset or a set offset from the reception timing. Upon initial (initial) selection of the synchronization source, the user equipment determines its own timing according to the received synchronization signal. Upon reselection (a selection performed after the initial selection), instead of determining its own timing, the user equipment can simply adjust its timing according to the new synchronization source. Here, the initial selection of the synchronization source can be, for example, a 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 timing of reception can be determined as it is as the timing of the received synchronization signal, whereas in the case of transmission, the timing is advanced by applying a timing advance (ie, an offset based on the reception timing). Can be determined. Such an offset can be determined as in the case of LTE. Further, the transmission timing may be determined as it is as the timing of the received synchronization signal, or may be determined by applying a predefined offset. However, the invention is not limited to these examples, and in general, the timing unit can derive timing from the synchronization signal in any manner.

  The metric acquisition unit is advantageously configured to determine the metric as a combination of the quality of the received synchronization signal and a selection bias determined based on the number of hops and / or the type of synchronization source. In this case, the type of the synchronization source is either a synchronization source that transmits a synchronization signal originating from the network or a synchronization source independent of the network (for example, a wireless device that generates the synchronization signal without assistance from the network). It 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 (for example based on the synchronization signal). Thus, the synchronization source transmits a signal at a predetermined resource at a predetermined power. 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 a quality parameter. However, the quality parameters used in the metric can also be determined as a function of the measured power of the received signal. The quality parameter may be a ratio or difference between the transmitted signal and the received signal (indicating signal degradation). Furthermore, the measurement can be made to correspond to the measurement of CRS (cell reference signal) performed in LTE (Non-Patent Document 7).

  Next, a 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 the synchronization source type and the hop count value can be defined in the specification. One definition method is through a table. Specifically, the metric acquisition unit can be configured to determine a 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 the number of hops and the type of synchronization source with a particular value of the bias. . Alternatively, the bias can be determined based on only one of the number of hops and the type of synchronization source. In such a case, the lookup table associates only the number of hops with a particular bias value. Alternatively, the bias value can depend only on the type of synchronization source. In such an example, the table associates the type of synchronization source (a synchronization source that sends synchronization signals originating from the network, a synchronization source independent of the network) to a particular value of the selection bias.

  Note that 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 synchronization signal from the network), the offset is a positive predetermined value. If the synchronization source is user equipment independent of the network, the value of the offset is smaller than the value of the offset in the case of a network node. This value can be set to 0. Furthermore, the type of synchronization source can be distinguished between a synchronization source that is a network node and a synchronization source that is a wireless device that derives its own synchronization signal from the synchronization signal of the network (ie, from the network).

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

Similarly, penalties or bonuses 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 at the sync source)

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

  For example, counting up from the eNB means that if the eNB 610 is the source of the synchronization signal, there will be 0 hops in the direction of the synchronization user's receiving 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 from the eNB 610 to the receiving user equipment 660 (as in the case of signal 625), and this one hop is User device 620 within the coverage. There may be additional hops between the eNB 610 and the receiving user equipment 660. In each of these cases, the original source of the synchronization signal is eNB 610, and the hop, such as 620, transmits the same synchronization signal or is reconstructed based on the original synchronization signal received from eNB 610. It just sends a sync signal. When counting up hops from the original source (in this case, the network node synchronization source eNB 610), the number of hops is positive or zero.

  However, alternatively, the hops can be counted down from the synchronization signal receiver to the synchronization 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 the network node (eNB 610). Can be set to the maximum hop number NHmax. Different network nodes may have different maximum hop counts. For example, a macro eNB has a larger number of hops than a micro eNB because the macro eNB has higher timing and frequency accuracy. An advantage of the countdown is that the user equipment does not need to know the maximum hop number when the maximum hop number of the eNB is configurable. When the synchronization signal receiving apparatus 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. As in the above example, two or more devices (original) that receive a synchronization signal originating from a network node and further transmit it (or transmit a synchronization signal reconstructed from the received synchronization signal) Corresponding to the source 610 and the receiving user equipment 660), the number of hops may be even smaller (NHmax-2, NHmax-3, ..., 0, etc.). In other words, when counting down the hops, the hop count starts from the predetermined maximum hop number for the target eNB 610. In particular, the maximum number of hops for different eNBs can be set / determined as different values. The predetermined maximum number of hops of the eNB can be set by the network. The user equipment obtains information on the maximum number of hops via signaling from the eNB. This signaling can be performed via a D2D control channel or broadcast signaling or in a synchronization signal.

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

  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, a bonus may be given to a network node as a synchronization source, while no bonus is given to other synchronization sources, and a penalty may be given to a positive hop number, or vice versa.

  The relationship between bonus, synchronization source type, and hop count can be defined by a lookup table as described above. This table can be specified in a standard (ie it can be 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 penalty value 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 one example, and the function may have another form or a multiplier other than 2 that is not a simple multiplication. The choice of a particular function (and table values) will depend on the desired 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 from which the synchronization signal is generated than for the wireless device from which the synchronization signal is generated. 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 synchronization signal is not derived from the network). Such a preference is advantageous because it is generally expected that D2D communication and network-device communication will use the same bandwidth and time. Thus, adjusting the timing using the network timing helps to reduce interference and improve reception quality. Further, any coordination between network-device transmission and D2D transmission can be performed by the network.

  Alternatively or additionally, the bias may 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 hops 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 receiver increases, where again the number of hops is a positive integer. These two possible schemes are to increase the value of the metric when the synchronization signal receiving device is close to the network node synchronization source, and to 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, wherein eNB 710 has coverage indicated by ellipse 701. The D2D user equipment 770 receives the synchronization signal 715 from the eNB 710 with a received signal quality of -100 dBm. Further, the D2D user equipment 770 receives the synchronization signal 725 generated from the eNB 710 through the hop formed by the user equipment 720 in the 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 received signal quality of -78 dBm. Thus, selecting the synchronization source only according to the quality of the received signal selects the out-of-network coverage user equipment 730 because the out-of-network coverage user equipment 730 has the highest received signal quality, followed by the user equipment 720. Yes, and finally eNB 710. However, in this embodiment, the selection of the synchronization source is performed in a different manner. The lower table in FIG. 7 shows the correspondence between bonus values (third column) and combinations of synchronization source types (first column) and hop counts (second column). The original source type is either the eNB 710 or a wireless device that does not derive a synchronization signal from the network node (ie, out of network coverage user equipment 730 in this example). The number of hops distinguished in this example is zero, one, or two or more. The selection bias is in this case a bonus taking the value 10, 6, 3, or 0 depending on the type of synchronization source and the number of hops. Specifically, when the synchronization source is the wireless device 730, a bonus is not added to the quality (power) of the received signal regardless of the number of hops (a bonus of value 0 is added). Note that in these examples, the wireless device 730 generates a 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 differentiated in the type of synchronization source.

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

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

  In order to be able to derive the metric, it is advantageous for the user equipment receiving the synchronization signal to obtain 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 synchronization signal or the D2D synchronization control channel if the synchronization source is user equipment (transmitting a synchronization signal originating from the network or a synchronization signal independent of the network). it can. If the synchronization source is an eNB, this information has already been conveyed by the cell ID in the synchronization signal, that is, it is clear that the synchronization source is the eNB based on the cell ID, and thus the number of hops is 0. (Or NHmax depending on the applied hop count method). Instead of determining the selected bias value by using a table based on the type of sync source and the hop count, the bias value can be indicated directly via a D2D synchronization 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. In this way, flexibility in determining the bias value is increased, and there is no need to perform calculations or refer to tables in the receiver. For example, the user equipment 720 in FIG. 7 indicates the bonus value 6 directly through a D2D synchronization signal or a control channel such as a D2D control channel.

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

  According to another embodiment of the present invention, the metric obtaining unit comprises: a unit for determining the 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 obtain a metric as a linear combination of

Specifically, the function can be defined by the following equation.
M = a * T + b * H + c * Q
Where T is the type of source synchronization source, eg, T = 1 if the original source is an eNB, otherwise T = 0. H is the hop count (ie, the number of hops between the source of the synchronization signal and the hop transmitting the synchronization signal), which is the number of hops between the source of the synchronization signal and the synchronization signal receiver. It can also be considered as showing). Q is the signal quality, which can be represented, for example, by the power (unit: dBm) of the received signal. a, b, and c are weights for weighting the three parameters T, H, and Q, respectively. These weights a, b, c can generally be real numbers. However, the weights can be integers for the purpose of simplifying the implementation. The signal quality does not need to be measured signal power 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, a plurality of different categories (eg, “very good”, “good”, “normal”, “bad”, and “very bad”) according to the dBm value can be defined. These divisions can be represented by integers, which are easier to calculate in the above equation. For example, Equation 5 can be assigned to very good quality, Equation 4 to good quality, Equation 3 to normal quality, Equation 2 to poor quality, and Equation 1 to very poor quality.

  For example, the weighting factor a is advantageously a positive integer (a> 0) because the D2D synchronization signal derived from the eNB has a higher priority than the D2D synchronization signal derived from other synchronization sources. is there. The weighting factor b is advantageously negative (b <0) if the hop count is counted up from the eNB, and 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. . If c <0 (example: -1), -100 dBm is better than -90 dBm. If the reception quality is a negative number, metric M <0 can be satisfied. 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 synchronization source. Specific designs, 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), are implemented in any manner. be able to.

  A weighting factor, and thus a metric, can be set for each user equipment (receiving device). For out-of-network coverage user equipment, the weights a, b, and c can be preset through OAM or transmitted by the in-network coverage user equipment over a D2D control channel.

  For the user equipment in the network coverage, the weighting factors a, b, and c can be set in advance or set by the eNB. The configuration by the eNB is advantageous and can be performed, for example, by RRC signaling or other control signaling.

  The advantage of being configurable is that different metrics can be set for each user equipment. When data is transferred to the user equipment, it is advantageous that such user equipment synchronizes to its eNB. In this case, a larger weighting factor can be set for the user device than for other user devices. Also, if the receiving capability of the user equipment (the ability to detect / decode low quality signals) is low, it is advantageous for such user equipment to synchronize with the D2D synchronization signal having the highest signal quality. For such a user device, the weighting factor c can be set to a larger value than other user devices 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 source of the synchronization signal, H is the number of hops, and Q is the received The 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 invention, the synchronization source selection unit is further configured to perform a preliminary step of filtering out ineligible D2D synchronization signals. In particular, the preliminary step may exclude the ineligible synchronization source from the set of synchronization sources considered for selection. For only the D2D synchronization 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 synchronization source is selected based on the metric. That is, the synchronization sources excluded in the preliminary exclusion step are no longer considered as synchronization sources.

  According to an embodiment of the present invention relating to a synchronization signal receiving device, in the synchronization signal receiving device, the synchronization source selection unit includes a series of synchronization sources in which the number of hops to the network node exceeds a predetermined hop threshold. It is configured to perform a pre-selection of the synchronization source by excluding it from the candidates. For example, the predetermined threshold may be 3, meaning that hops with a hop count of 4 or more (when counting up hops) are excluded from further selection. However, this is merely an example, and the threshold value can take on other values (eg, 1, 2, 4, or 5 or more).

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

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

  One of the advantages of preselection is that low quality D2D synchronization signals are not selected. Therefore, selection of an unreliable synchronization source can be avoided without determining the metric of such a synchronization source. Therefore, the selection can be simplified in this way.

  The embodiments described above for how to perform metric acquisition and synchronization source selection can be further improved by controlling re-selection of synchronization sources using hysteresis. Specifically, the synchronization signal receiving device receives synchronization signals from a plurality of different synchronization sources. The synchronization signal receiving apparatus obtains the metric of the synchronization source of the reception source, and selects the synchronization source having the highest reliability in accordance with the metric, so that the synchronization source can be reselected periodically. If the quality of the received signal fluctuates significantly, such periodic reselection may change the synchronization source frequently. 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 maintains the synchronization source for a particular period of time, and thus the user equipment does not change the synchronization source frequently. This supports the stability of the synchronization source. The history decreases over time so that the best synchronization source is selected.

  Further, the synchronization signal receiving device can include a reselection timer and a selection control unit, wherein the selection control unit controls the metric acquisition unit to determine a metric according to the reselection timer, and selects a synchronization source. The synchronization source selection unit is controlled to perform 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 determine the best synchronization source (ie, the synchronization source with the highest metric value, or generally, the metric that indicates the best synchronization source). Source with a value). This allows the receiver of the synchronization signal (eg a terminal, more generally user equipment) to periodically adapt the synchronization source to the changing transmission environment. Note that the above example of 10 seconds as the reselection period is only an example, and can be set to different values (eg, 1 second, 2 seconds, 5 seconds, 15 seconds, or any other period). . 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. An 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 fluctuate more frequently, and it is therefore 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 a longer reselection period (increase the reselection period).

  Furthermore, the synchronization signal receiving device advantageously comprises a history timer which is activated when a new synchronization source is selected and which expires after a predetermined history period, in which case the reselection timer is set to a predetermined reselection time. Set the period. The reselection period may be received by the synchronization signal receiver in control signaling from the network (eg, from a network node such as a base station (eNB)). The selection control unit, if the history timer has expired, instructs the metric acquisition unit to determine a metric when the reselection timer expires, and selects a synchronization source according to the metric. To order. If the history timer has not expired, at the time the reselection timer expires, it is instructed not to select a synchronization source according to the metric. Thus, the history timer helps to avoid frequent changes in 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 the sudden disappearance of the synchronization source or the sudden deterioration of the quality of the signal from the synchronization source.

  Advantages of the present invention described in the above embodiments are distinguished not only based on reception quality but also in terms of synchronization source type and distance. Therefore, for a D2D synchronization signal having a significantly higher signal quality, the user equipment selects it. The eNB priority and hop count can be considered as an offset to the signal quality. If the signal quality of the D2D synchronization signal from the user equipment out of network coverage (such as 630) does not significantly exceed 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 present invention. The device 800 is a wireless device such as a user device. The wireless device receives various signals at different intensities from a plurality of different synchronization sources. Specifically, the apparatus may receive coverage 801 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 from the network (specifically, the eNB 810). May be received from user equipment 830 located outside of the device. The apparatus includes a synchronization signal receiving unit 840, a metric acquisition unit 850, a synchronization source selection unit 860, and a timing unit 870, which are configured as described in the above embodiment. ing. Specifically, the synchronization signal receiving unit 840 is adapted to receive synchronization signals from various D2D synchronization sources. Further, the synchronization signal receiving unit 840 can identify the synchronization source, or at least the type of the synchronization source, based on the received synchronization signal. However, this information can also be communicated later via signaling. The metric acquisition unit 850 is configured to determine or calculate a metric, and the synchronization source selection unit 860 selects a synchronization source based on the metric. After selecting the synchronization source, device 800 first determines its own timing, or adjusts its own timing (after the initial determination has already been made). Specifically, the apparatus 800 can set the received synchronization signal to timing for receiving, or add an offset to the timing. Then, a transmission timing is derived, and this step can be performed based on the derived reception timing.

  Further, apparatus 800 can include a reselection control unit 880 that controls when it performs reselection. Thus, the reselection control unit 880 controls these units so that the metric acquisition unit 850 and the selection unit 860 perform their respective functions (i.e., calculating the metric at a particular timing and selecting a synchronization source). These timings are advantageously derived from a reselection timer 885, which also forms part of the device 800. The reselection timer 885 can be configurable by signaling received from the network. Receiving signaling from the network may be performed by signaling receiving unit 890. Note that, in this block diagram, the signaling receiving unit 890 and the synchronization signal receiving unit 840 are separately illustrated. The reason for this is that these units are functional blocks. In general, apparatus 800 comprises a common reception front end formed by one or more antennas, amplifiers, demodulators, and decoders, which are also applicable for receiving signaling. ). The signaling and synchronization signals are used for different purposes as indicated by separate blocks 840 and 890 in FIG.

  Further, the signaling receiving unit can be configured to receive signaling including settings for determining a metric. For example, at least one of the weighting factors a, b, c, selection bias (offset), bonus value / penalty value can be received and passed to the metric acquisition unit 850. Further, the apparatus may include a history timer 865, wherein the synchronization source selection unit 860 may use a new synchronization source (ie, different from the currently applied synchronization source) based on the metric determined in the metric acquisition unit 850. When selecting a synchronization source), the reselection control unit 880 can use the history timer 865 to control the synchronization source selection unit 860 to change or not change the synchronization source. 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 for selecting a synchronization source in a system as described above. Specifically, such a synchronization signal receiving method includes a step (910) of receiving 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; including. Some information, such as the type of synchronization source and the number of hops, can already be conveyed by the received synchronization signal. However, this information can be conveyed in other ways. The method then determines the selection metric of each synchronization source by determining the quality of the synchronization signal received, the type of synchronization source (whether the synchronization source transmits a synchronization signal originating from the network node, or independent of the network node). Transmitting the synchronization signal) or the number of hops to the network node (930). Then, in step 940 of selecting a synchronization source according to the determined metric, a synchronization source is selected, and then in step 950, transmitting data using the synchronization source, ie, according to the synchronization signal of the selected synchronization source. Alternatively, the timing of reception is determined or adjusted.

  The metric is advantageously determined as a combination of the quality of the received synchronization signal and the selection bias determined based on the number of hops and / or the type of the synchronization source, wherein the type of the synchronization source is its own. Either a synchronization source that directs the synchronization signal from the network node, or a wireless device independent of the network. The selection bias can be obtained according to a correspondence relationship between a predetermined selection bias value and the number of hops (such as a lookup table). Specifically, the selection bias has a higher value for the network node that generates the synchronization signal than the wireless device that generates the synchronization signal, or a 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 (the number of hops) Is counted down from a predetermined maximum number of hops of the network node starting from the network node). 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 of obtaining a metric as described above, and in general, the quality of a received synchronization signal and a number indicating whether a 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 source 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 signaling information transmitted from the network node.

  Further, the method further comprises: synchronizing sources whose number of hops to the network node exceeds a predetermined hop threshold and / or synchronization sources whose signal quality does not exceed a predetermined quality threshold. Pre-selecting a synchronization source 920 by excluding it from the set of candidate synchronization sources. Then, after the preselection performed by the synchronization source selection unit, the metric is determined only for the synchronization source in the set of candidate synchronization sources.

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

  Further, the method can include maintaining a history timer that is activated when the new synchronization source is selected and expires after a predetermined history period, wherein the reselection timer is reduced to a predetermined length of time. Set. If the history timer has expired, the method determines a metric when the reselection timer expires, instructs to select a synchronization source according to the metric, and if the history timer has not expired, Commanding not to select a synchronization source according to the metric when the reselection timer expires.

  The description in the Background section is intended to provide a thorough understanding of certain example embodiments described herein, and may refer to processes and functions in a mobile communication network (such as a network compliant with the 3GPP standard). It is to be understood that this invention is not limited to the particular embodiments described. However, the improvements proposed herein can be applied immediately in the architectures / systems described in the Background section, and in some embodiments of the present invention, the standard procedures for these architectures / systems And an improved procedure can be utilized. It will be understood by those skilled in the art that various changes and / or modifications can be made to the invention shown in particular embodiments without departing from the broadly described concept or scope of the invention. Will be done.

  Another embodiment of the invention is directed to implementing the various embodiments described above using hardware and software. Various embodiments of the invention can 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 present invention may also be implemented or embodied by a combination of these devices.

  Further, various embodiments of the invention can be implemented by software modules executed by a processor or directly implemented in hardware. Also, a combination of software modules and hardware implementation is possible. The software modules can be stored on any type of computer-readable storage medium, such as, for example, RAM, EPROM, EEPROM, flash memory, registers, hard disk, CD-ROM, DVD, and the like.

  In summary, the present invention relates to selecting one synchronization source from a variety of synchronization sources, including a synchronization source that determines a synchronization signal from a network, such as a base station (network node) or a base station (network node). User equipment, possibly receiving from other stations through other hops, and synchronization sources include synchronization sources that do not determine their 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 synchronization source, adapt the timing of the device accordingly.

Claims (8)

An integrated circuit for controlling operation of a synchronous receiving device, wherein the operation includes:
A synchronization source that guides its own synchronization signal from the network node, or a synchronization source that is itself a wireless device that generates a synchronization signal, a process of receiving a predetermined wireless 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 for obtaining based on at least two of the following:
Synchronization source selection processing for selecting a synchronization source according to the metric determined by the metric acquisition processing,
Timing processing of 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,
According to a reselection timer, to determine the metric, and to control the reselection operation to select a synchronization source, selection control processing,
A process in which the value of the reselection timer is set by an upper layer protocol by the network node, whereby the reselection operation is periodically adapted to a transmission environment ;
including,
Integrated circuit. The metric acquisition process includes:
-The quality of the received synchronization signal; and
A selection bias based on the number of hops and / or the type of the synchronization source, wherein the type of the synchronization source derives its synchronization signal from a network node or a wireless device independent of the network; And configured to determine the metric as a combination of the selection bias.
The integrated circuit according to claim 1.   3. The integrated circuit according to claim 2, wherein the metric obtaining process is configured to determine the selection bias according to a correspondence between a predetermined selection bias value and a number of respective hops. The selection bias is
A higher value for the network node from which the synchronization signal is generated than for the wireless device from which the synchronization signal is generated,
-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 starting from a network node;
Increasing as the number of hops between the network node and the synchronous receiver increases when the number of hops is counted starting from a network node having a predetermined maximum number of hops; Value to
Required as one of the
An integrated circuit according to claim 2.   3. The integrated circuit according to claim 2, wherein the metric acquisition unit is configured to determine the selection bias by receiving in a 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 indicating whether the synchronization source is a network node or a wireless device, and the number of hops to a network node, The integrated circuit according to claim 1, wherein the integrated circuit is configured to determine 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 obtaining unit is configured to determine the weighting factor a, b, or c by receiving in a signaling information transmitted from the network node;
An integrated circuit according to claim 6. The synchronization source selection process,
A synchronization source whose 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 a pre-selection of sync sources by excluding from the set of candidate sync sources,
The metric acquisition process is configured to determine the metric only for the synchronization source in the series of candidate synchronization sources after the preselection performed by the synchronization source selection process.
The integrated circuit according to any one of claims 1 to 7.