RU2717341C2 - Selecting device-device synchronization source - Google Patents

Abstract

FIELD: electrical communication engineering.

SUBSTANCE: invention relates to communication engineering and can be used to select a synchronization source from among different synchronization sources, which include sources which determine a synchronization signal from a network, such as base stations, network nodes or user equipment. For this purpose, user equipment receives a synchronization signal possibly through other transit sections from a base station and further includes sources which do not determine their synchronization signal from the network. Source of synchronization is selected by selecting the source with the most reliable synchronization signal based on the value calculated for each of the considered sources. In particular, the indicator is based on the type of source, the number of transit sections between the network and the source and/or quality of the received signal. After the selection of the source of clocking devices being adapted accordingly.

EFFECT: technical result consists in improved bandwidth.

14 cl, 9 dwg

Description

The present invention relates to devices and methods for selecting or reselecting a synchronization source for wireless communication.

BACKGROUND OF THE INVENTION

Third Generation (3G) Mobile Systems Based on WCDMA Radio Access Technology are widely deployed worldwide. The first step in expanding or developing this technology involves the introduction of high speed downlink packet data (HSDPA) and an extended uplink, also called high speed uplink packet data (HSUPA), giving a radio access technology that is very competitive. In order to be ready to further increase user demands and to be competitive against new 3GPP radio access technologies, a new mobile communication system called Long-Term Development Project (LTE) technology has been introduced. LTE is designed to meet the needs of carriers for high-speed transport of data and media, as well as support for high bandwidth for voice over the next ten years. The ability to provide high bit rates is a key metric for LTE. The Long Term Evolution (LTE) technology work item (WI) specification, called UMTS Enhanced Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN), is issued as version 8 (LTE version 8). The LTE system is an efficient packet radio access and radio access network that provides full IP functionality with low latency and low cost. Detailed system requirements are given in the 3GPP TR 25.913 specification, "Requirements for Evolved UTRA and Evolved UTRAN", version 9.0.0, freely available at www.3gpp.org.

LTE precisely defines scalable multiple transmission bands, such as 1.4, 3.0, 5.0, 10.0, 15.0 and 20.0 MHz, in order to achieve deployment of a flexible system using a given spectrum . In the downlink, orthogonal frequency division multiplexing (OFDM) radio access has been applied due to its inherent resistance to multipath interference (MPI) due to the low symbol rate, the use of cyclic prefix (CP), and its binding to different bandwidth arrangements for transmission. Single Carrier Frequency Division Multiple Access (SC-FDMA) radio access has been used in the uplink since providing extensive coverage has priority over increasing the peak data rate, given the limited transmission power of the user equipment (UE). Many key packet radio access methods are used, including multi-channel input to multi-channel output (MIMO) transmission methods, and a highly efficient control signaling structure is achieved in LTE version 8.

The general architecture is shown in Figure 1 and a more detailed representation of the E-UTRAN architecture is given in Figure 2. The E-UTRAN contains an eNB, providing the UEs of the user plane protocol (PDCP / RLC / MAC / PHY) and the E-UTRA control plane (RRC). eNB contains physical layers (PHY), medium access control (MAC), radio link control (RLC), and data transfer control protocol (PDCP), which include compression and encryption of the user plane header. It also offers radio resource management ( RRC), corresponding to the control plane, It performs many functions, including radio resource management, admission control, scheduling, implementation of consistent UL QoS, broadcast cell information, cipher user plane and control plane data decryption / decryption, and DL / UL user plane packet header compression / decompression. eNBs are interconnected via X2 interface. eNBs are also connected via S1 interface to EPC (Advanced Packet Core Network), more specifically with an MME (mobility management node) through S1-MME and with a serving gateway (S-GW) through S1-U. The S1 interface supports a many-to-many relationship between MME / serving gateways and eNB. SGW routes and relays user data packets, while also acting as a mobility binding for the user plane during handovers between the eNBs and as a mobility binding between LTE and other 3GPP technologies (terminating the S4 interface and redirecting traffic between 2G / 3G and PDN GW). For the UE in the idle state, the SGW terminates the DL data path and initiates a paging call when DL data arrives for the UE. It manages and stores UE contexts, for example, IP unidirectional service parameters, internal network routing information. It also replicates user traffic in the event of a legitimate interception.

MME is the key management node for the LTE access network. He is responsible for the standby UE tracking and paging procedure, including retransmissions. He is involved in the process of activating / deactivating a unidirectional channel and is also responsible for making SGW choices for the UEs during initial attachment and during handover within LTE, affecting the relocation of the core network (CN) node. He is responsible for user authentication (through interaction with HSS). Signaling without access (NAS) ends at the MME, and it is also responsible for generating and allocating temporary identifiers for the UE. It verifies the authorization of the UE to consolidate the service provider in the public land mobile PLMN (PLMN) and implements the roaming restrictions of the UE. The MME is a network termination point for encryption / integrity protection for NAS signaling and handles security key management. Legal signaling interception is also supported through the MME. The MME also provides a control plane function for mobility between LTE and 2G / 3G access networks using the S3 interface terminating on the MME from the SGSN. The MME also completes the S6a interface to the home HSS for roaming the UE.

поднесущих, как также показано на Фиг. 3.The downlink component carrier of a 3GPP LTE system is divided in the time-frequency domain into so-called subframes. In 3GPP LTE, each subframe is divided into two downlink slots, as shown in FIG. 3, wherein the first downlink slot comprises a control channel region (PDCCH region) within the first OFDM symbols. Each subframe consists of a predetermined number of OFDM symbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (version 8)), with each of the OFDM symbols passing through the entire bandwidth of the component carrier. Thus, each of the OFDM symbols consists of a number of modulation symbols transmitted on the respective

subcarriers, as also shown in FIG. 3.

последовательных OFDM-символов во временной области и

последовательных поднесущих к частотной области как приведено в качестве примера на Фиг. 3. В 3GPP LTE (Версии 8), блок физических ресурсов таким образом состоит из

ресурсных элементов, соответствующих одному слоту во временной области и 180 кГц в частотной области (для дополнительных сведений по ресурсной сетке нисходящей линии связи см., например, 3GPP TS 36.211, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)", версии 8.9.0 или 9.0.0, раздел 6.2, доступную бесплатно по адресу http://www.3gpp.org и включенную в настоящий документ посредством ссылки). Термин "компонентная несущая" относится к комбинации из нескольких ресурсных блоков. В будущих версиях LTE, термин "компонентная несущая" более не используется; вместо этого, терминология изменяется на "соту", что относится к комбинации ресурсов нисходящей линии связи и опционально восходящей линии связи. Установление связи между несущей частотой ресурсов нисходящей линии связи и несущей частотой ресурсов восходящей линии связи указывается в системной информации, передаваемой в ресурсах нисходящей линии связи.Assuming a multi-carrier communication system, for example using OFDM, which, for example, is used in a 3GPP long-term development (LTE) project, the smallest unit of resources that can be assigned by the scheduler is one “resource block”. The block of physical resources is set as

consecutive OFDM symbols in the time domain and

successive subcarriers to the frequency domain as exemplified in FIG. 3. In 3GPP LTE (Version 8), a block of physical resources thus consists of

resource elements corresponding to one slot in the time domain and 180 kHz in the frequency domain (for more information on the downlink resource grid, see, for example, 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, section 6.2, available free of charge at http://www.3gpp.org and incorporated herein by reference). The term "component carrier" refers to a combination of several resource blocks. In future versions of LTE, the term "component carrier" is no longer used; instead, the terminology changes to “cell”, which refers to a combination of downlink resources and optionally uplink resources. The connection between the carrier frequency of the downlink resources and the carrier frequency of the resources of the uplink is indicated in the system information transmitted in the resources of the downlink.

Cell search procedures are the first set of tasks performed by a mobile device in a cellular system after the initial power-up. Only after the search and registration procedures, the mobile device has the ability to receive and initialize voice calls and data calls. A typical LTE cell search procedure may include a combination of carrier frequency determination, clock timing, and identification of a unique cell identifier. Specific synchronization signals transmitted to a base station (BTS) typically contribute to these procedures. However, these synchronization signals are not used continuously in connection modes for a mobile device. Hence, only a minimum of resources, in terms of power, subcarrier allocation and time interval, are allocated for synchronization signals.

The cell search procedure provides the UE with the ability to determine the time and frequency parameters that are needed to demodulate the downlink signals and to determine the uplink signals with the correct timing. The first phase of the cell search includes initial synchronization. Accordingly, the UE detects the LTE cell and decodes all the information required to register the detected cell. The procedure uses two physical signals, the broadcast of which is carried out on the central 62 subcarriers of each cell, the primary and secondary synchronization signals (PSS and SSS, respectively). These signals provide the ability to synchronize in time and frequency. Their successful determination provides the UE with the physical cell ID, cyclic prefix length, and information about whether FDD or TDD is used. In particular, in LTE, when the terminal is turned on, it detects the primary synchronization signal, which for FDD is transmitted in the last OFDM symbol of the first time slot of the first subframe (subframe 0) in the radio frame (for TDD, the placement is slightly different, but still well defined). This allows the terminal to receive the slot boundary regardless of the selected cyclic prefix selected for the cell. After the mobile terminal has detected a 5 millisecond clock (slot boundaries), a secondary synchronization signal is searched. Both PSS and SSS are transmitted on 62 of the 72 reserved subcarriers around the DC carrier. In the next step, the UE must detect a physical broadcast channel (PBCH), which, like PSS and SSS, is mapped only to the central 72 cell subcarriers. PBCH contains the main information unit (MIB), which includes information about system resources. In LTE up to version 10, the MIB has a length of 24 bits (14 bits of which are currently in use and 10 bits are spare). The MIB includes information regarding the system bandwidth in the downlink, the structure of the physical transmission channel of the HARQ pointer (PHICH), and the 8 most significant bits of the system frame number (SFN).

After successfully detecting the main information block (MIB), which includes a limited number of the most frequently transmitted parameters necessary for initial access to the cell, the terminal activates the system bandwidth, meaning that it must be able to receive and detect signals over the entire system bandwidth in the downlink. After receiving the system bandwidth in the downlink, the UE may continue to receive additional required system information in the so-called system information blocks (SIB). In LTE version 10, SIBs of type 1 - SIB of type 13 are defined that carry different information elements required for some operations. For example, in the case of FDD, a Type 2 SIB (SIB2) includes a UL carrier frequency and UL bandwidth. Different SIBs are transmitted over the physical downlink shared channel (PDSCH), and thus (see details for PDSCH and PDCCH below), the corresponding allocations are assigned to the physical downlink control channel (PDCCH). Before a terminal (UE) can correctly detect such (or any) PDCCH, it must know the system bandwidth in the downlink from the MIB.

таким образом уникально задается числом

в диапазоне 0-167, представляющем группу идентификаторов физического уровня для соты, и числом

в диапазоне 0-2, представляющем идентификатор физического уровня в пределах группы идентификаторов физического уровня.The above cell identifier (cell ID) will uniquely identify the cell within the PLMN. A cell identifier is a global cell ID that is used to identify a cell in terms of operation and maintenance (OAM). It is transmitted in system information and is designed to control the eNodeB within the core network. A global cell identifier is also used for the UE to identify a specific cell with regard to RRC / NAS layer processing. A physical cell identifier is a cell identifier in a physical layer. The physical cell identifier has a range of 0-503 and is used to scramble the data to help the mobile device in sharing information from different transmitters. The physical cell ID will determine the sequence of the primary and secondary signals. This is similar to the scrambling codes from UMTS. There are 504 unique physical layer identifiers for a cell. Physical layer identifiers for a cell are grouped into 168 groups of unique physical layer identifiers for a cell, each group containing three unique identifiers. Grouping is such that each physical layer identifier for a cell is part of one and only one group of physical layer identifiers. Physical layer identifier for cell

thus uniquely specified by a number

in the range 0-167, representing the group of identifiers of the physical layer for the cell, and the number

in the range 0-2, representing the identifier of the physical layer within the group of identifiers of the physical layer.

. Посредством обнаружения сигнала синхронизации, может быть обнаружено

. Последовательность, используемая для второго сигнала синхронизации, является чередующимся объединением двоичной последовательности с длиной в 31 бит. Объединенная последовательность скремблируется с помощью последовательности скремблирования, заданной первичным сигналом синхронизации. Последовательности SSS основаны на последовательностях максимальной длины, известных как M-последовательности, которые могут быть созданы посредством циклического прохождения по каждому возможному состоянию регистра сдвига с длиной n. Это дает в результате последовательность с длиной 2^n-1. В частности, две двоичные последовательности с длиной 31 бит, которые должны быть объединены, являются такими M-последовательностями. Для дополнительных сведений по первичному и вторичному сигналу синхронизации, см., например, 3GPP TS 36.211, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 12)", версия 12.1.0, раздел 6.11, доступную бесплатно по адресу http://www.3gpp.org и включенную в настоящий документ посредством ссылки.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 time-frequency Zadov-Chu sequence according to

. By detecting the synchronization signal, can be detected

. The sequence used for the second synchronization signal is an alternating combination of a binary sequence with a length of 31 bits. The combined sequence is scrambled using the scrambling sequence specified by the primary synchronization signal. SSS sequences are based on maximum length sequences, known as M-sequences, which can be created by looping through each possible state of a shift register with length n. This results in a sequence with a length of 2 ^ n-1. In particular, two binary sequences with a length of 31 bits to be combined are such M-sequences. For additional information on the primary and secondary synchronization signal, see, for example, 3GPP TS 36.211, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 12)", version 12.1.0, section 6.11, available free of charge at http://www.3gpp.org and incorporated herein by reference.

After receiving the PPS and SSS, the timing is adapted by the receiving UE. In particular, the UE synchronizes its receiver for downlink transmission received from a synchronization source (eNB). Then the timing of the uplink is adjusted. This is accomplished by applying a time advance on the transmitter of the UE relative to the received downlink timing in order to compensate for propagation delays varying for different UEs. The timing advance procedure is briefly described in section 18.2.2 of the book “LTE The UMTS Long Term Evolution: From theory to practice”, 2nd edition, edited by S. Sesia, I. Toufik, M. Baker, Wiley, 2011.

Proximity-based applications and services represent an emerging social and technological trend. Current and intended uses include services related to commercial services and public safety that will be of interest to operators and users. The introduction of proximity capabilities (ProSe) in LTE will enable the 3GPP industry to serve this development market and at the same time serve the urgent needs of several public safety communities that share LTE.

Device-to-device (D2D) communications is a technology component for LTE-A, version 12. Device-to-device (D2D) communications technology enables D2D, as the foundation of a cellular network, to increase spectral efficiency. For example, if the cellular network is LTE, all data carrying physical channels use SC-FDMA for D2D signaling. D2D to LTE connectivity focuses on two areas: discovery and connectivity. In D2D communications, the UEs transmit data signals to each other on a forward link using cellular resources instead of transmitting through a base station (BS, eNodeB, eNB). D2D users communicate directly, but can remain under the control of the network, i.e. at least when in the eNB coverage area. As a result, D2D can improve system performance by reusing cellular resources. It is currently assumed that D2D operates in the uplink LTE spectrum (in the case of FDD) or the uplink subframes of the cell giving the coverage area (in the case of TDD, in addition, when outside the coverage area). In addition, D2D transmission / reception does not use full duplex on a given carrier. From the point of view of a separate UE, on a given carrier, D2D signal reception and LTE uplink transmission do not use full duplex, i.e. simultaneous reception of a D2D signal and LTE UL transmission are not possible. In addition, current operational assumptions regarding radio access for D2D LTE are described in 3GPP TS 36.843, vc.0.1, "Study on LTE Device to Device Proximity Services; Radio Aspects" (hereinafter referred to as "TS 36.843"), freely available at www.3gpp.org.

In D2D communication, when UE1 plays a transmission role, UE1 sends data, and UE2 receives it. UE1 and UE2 can change their role of transmission and reception. A transmission from UE1 may be received by one or more UEs similar to UE2. Figures 4 and 5 illustrate protocol layers, service points, and downlink and uplink multiplexing, respectively, for transmission on different types of channels.

In 3GPP RAN1, it was agreed as a working assumption that the source of synchronization is any node that transmits a D2D synchronization signal (D2DSS). It can be an eNB or a regular UE. When the synchronization source is an eNB, the D2DSS is the same as the PSS and SSS version 8. The D2D UE uses the synchronization signal (s) to determine the clock for transmitting the D2D signal. Also, as a working assumption, it was agreed that before starting the D2DSS transmission, the D2D UE scans for synchronization sources. If a synchronization source is detected, the UE can synchronize its receiver with it before it can transmit D2DSS. If no synchronization source is found, the UE may still transmit D2DSS. The UE may (re) select a D2D clock source that it uses as a clock pattern for its D2DSS transmission if the UE detects a change in the D2D clock source, based on the following metrics:

- Type of synchronization source. eNB or UE

- Accepted D2DSS Quality

- The number of transit sites from eNB.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an effective method and apparatus for performing a selection of a synchronization source.

This is achieved through the features of the independent claims.

In addition, preferred embodiments of the present invention are the subject of the invention for the dependent claims.

According to an embodiment of the present invention, there is provided a synchronization receiving device, comprising: a synchronization receiving unit for receiving predetermined wireless synchronization signals from synchronization sources including a synchronization source that receives its clock from a network node and a wireless synchronization generating device; an indicator obtaining unit for determining a selection indicator for each of the synchronization sources based on at least two of: the quality of the received synchronization signal; whether the clock source receives its clock from a network node or generates a clock; and the number of transit sections to the network node, a synchronization source selection unit for selecting a synchronization source according to an indicator determined by the indicator obtaining unit, and a timing unit for determining or adjusting the timing for transmitting or receiving data according to a synchronization source synchronization signal selected by the synchronization source selection unit.

in accordance with another embodiment of the present invention, there is provided a method for selecting a synchronization source, which comprises the steps of: receiving predetermined wireless synchronization signals from synchronization sources including a synchronization source that receives its synchronization signal from a network node and a wireless synchronization generating device ; determining a selection indicator for each of the synchronization sources based on at least two of: the quality of the received synchronization signal; whether the synchronization source transmits a synchronization signal originating from the network node, or independent of the network node; and the number of transit sections to the network node, selecting a synchronization source according to a certain indicator, and determining or adjusting the timing for transmitting or receiving data according to the synchronization signal of the selected synchronization source.

According to another embodiment of the present invention, there is provided a computer program product comprising a computer-readable medium having computer-readable program code implemented therein, the program code being adapted to implement the present invention.

According to an embodiment of the present invention, the above device is implemented on an integrated circuit.

The above objectives and other objects and features of the present invention will become more apparent from the following description and preferred embodiments given in conjunction with the accompanying drawings, in which:

Figure 1 is a block diagram illustrating an example of a common LTE architecture;

Figure 2 is a block diagram illustrating an example architecture of an LTE access network;

Figure 3 is a schematic view illustrating an example of an OFDM modulation resource grid in the time and frequency domain;

4 is a flowchart illustrating a layer 2 downlink protocol and a configured carrier aggregation multiplexing structure;

5 is a flowchart illustrating an uplink protocol of a layer 2 and a multiplexing structure with configured carrier aggregation;

6 is a schematic diagram illustrating various sources of a device-to-device synchronization signal;

7 is a schematic diagram illustrating an exemplary scenario for selecting a synchronization source based on a metric based on signal quality and a table with selection bias values;

Figure 8 is a block diagram illustrating a device in accordance with an embodiment of the present invention; and

9 is a flowchart illustrating a method in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to the reception of synchronization signals and to the selection of the source of the synchronization signal in a wireless system in which the transmitter of the synchronization signal can be a network node, such as a base station, as well as a wireless device that is not a network node, such as user equipment (terminal ), which may be a mobile phone, smart phone, tablet, laptop or other computer. Moreover, the wireless device can receive its clock 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” refers to any cell arrangement including macro cells, micro cells, pico cells, femto cells, or any other concepts. The network node may thus be a base station, such as an eNodeB or a relay, provided as part of a network.

An embodiment of the present invention preferably provides an effective approach for selecting a synchronization source among a plurality of synchronization sources, for device-device communication coexisting with network transmissions, i.e. in a system that supports wireless transmission between the base station (s) and user equipment, as well as direct communication between user equipment sharing the same resources.

In the following, an embodiment is provided based on the LTE specification. However, the present invention is in no way limited to LTE. The concepts and examples described therein are applicable to a wireless system in which a synchronization source must be selected from among synchronization sources, which include one or more network nodes and one or more wireless devices that are not network nodes, such as a user terminal . Wireless devices can receive their synchronization from the network, i.e. from a network node, or generate a synchronization signal regardless of network clock.

If a user equipment (UE) transmits a device-to-device (D2D) signal, the rules for determining which D2D clock source the UE uses as a clock pattern for its D2D signal transmissions can be:

1. The D2D clock sources, which are the eNodeBs, have a higher priority than the D2D clock sources, which are the UE;

2. The sources of D2D synchronization, which is the UE in the coverage area, have a higher priority than the sources of synchronization D2D, which is the UE outside the coverage area;

After prioritizing the D2D sync sources, which are the eNodeBs, followed by the UEs in the coverage area, the D2D sync source is selected. A UE in a coverage area is a UE that is located within the coverage of a base station, and which can thus receive its synchronization (timing) from the network. Out of coverage UE is a UE that is outside the coverage area of the network. If it is also outside the coverage area of another UE receiving its clock from the network, then such a UE outside the coverage area generates its own clock, regardless of network clock.

In the procedure for choosing the D2D synchronization source, this criterion is insufficient, since other factors, such as the accepted D2DSS quality and the number of transit sections from the eNB, were not taken into account. Soft criteria based on numerous factors are more reliable than those based on only one factor.

Figure 6 illustrates a typical scenario that occurs during communication in a system that supports both network-terminal communications and direct communications between two or more terminals. The base station, the eNB 610, has a coverage area indicated by ellipse 601. The eNB 610 transmits a device-to-device synchronization signal 615 (D2DSS), which has the same form here as the primary synchronization signal (PSS) and the secondary synchronization signal (SSS ) version 8. Terminal 620 UE in the network coverage area, i.e. A UE that is located within the coverage area 601 of the base station 610. The UE 620 in the network coverage area receives PSS / SSS from the eNB 610 and synchronizes with the eNB 610. The eNB 610 may request some UE in the network coverage area, such as 620, to transmit D2DSS. Accordingly, as shown by the dashed line, the UE 620 in the network coverage area is configured by the eNB 610 to transmit D2DSS and thus transmits the D2DSS 625. 620 is thus also a synchronization source that receives its synchronization (clocking) from the network, in particular from the network node 610

Moreover, Figure 6 shows the UE 630 outside the network coverage area. If the UE is out of network coverage, i.e. the terminal, which is located outside the coverage area 601 of the eNB 610, does not receive any D2DSS with reception quality exceeding a predetermined or predetermined threshold, such a UE will generate and transmit its own D2DSS. Accordingly, even in the absence of network proximity, such a UE 630 is capable of communicating device-to-device communications. The UE 630 outside the network coverage area in this example does not receive D2DSS 615 and also does not receive the signal 625 generated by the UE 620 in the network coverage area based on the clock received from the eNB 610, so that the reception quality of the D2DSS 615 and 625 does not exceed a predetermined threshold reception quality. Accordingly, the UE 630 outside the network coverage area generates and transmits its own D2DSS 635.

Figure 6 further shows the D2D UE 660, i.e. a terminal that is capable of communicating directly with other terminals, but also with the network. The D2D UE 660 is located outside the coverage area 601 of the base station 610. The D2D UE 660 still receives D2DSS 615 from the eNB 610, however, only with poor reception quality, i.e. adopted D2DSS 615 is rather weak. Apart from the D2DSS signal 615, the D2D UE 660 also receives the D2DSS 635 from the UE 630 outside the network coverage area. In addition, since the UE 620 also transmits D2DSS 625 in the network coverage area, the D2D UE 660 also receives D2DSS 625 with a quality higher than D2DSS 615 directly from the eNB 610. Accordingly, the D2D UE 660 receives D2DSS 615, 635 from the following three sources of synchronization:

- eNB 610: the corresponding D2DSS 615 is very weak, but it is directly from eNB, i.e. there are no transit sections between the D2D UE 660 and the source 610;

- UE 620 in the network coverage area: the corresponding D2DSS 625 is strong and comes from the network, but it provides one transit section from the network represented by the eNB 610 to the D2D UE 660, wherein the transit section is UE 620 in the network coverage area; and

- UE 630 outside the network coverage area: the corresponding D2DSS 635 is also strong, but it does not come from the network, i.e. in this case from eNB 610.

Based on the above situation, the question is which synchronization source should choose D2D UE 660 to synchronize its receiver (and / or transmitter): eNB 610 with a very weak signal, but without transit sections, or UE 620 in the network coverage area with a strong signal, but with several (one in this case) transit sections, or UE 630 outside the network coverage area with a strong signal, but unknown transit sections (signal not originating from the network).

A possible solution to this problem is to assign the D2DSS 615 and 625 received from the eNB (and transmitted via the eNB 610 or UE 620) to always have a higher priority than the D2DSS received from the UE that generated the D2DSS 635, regardless of network timing, such as 630 However, in addition to the fact that such a synchronization signal, received directly or originating from the network, may be the most accurate signal, the following problems may arise:

- a signal 615 received directly from the eNB 610, or a signal obtained from it (such as a signal 625), can be much weaker and thus also less reliable than a signal generated and received from a UE such as 630, and / or

- the signal received from the eNB 610 may go through a different number of transit sections from the eNB, and the strength of the received signal may vary.

As a consequence, some extended principle is useful in order to provide clearer and more efficient rules regarding how the UE should choose a timing source.

There was an LGE article in 3GPP RAN 1 numbered R1-140330, entitled "Discussion on D2D Synchronization Procedure", which suggested the following rules: D2DSS signal quality is used as preliminary selection criteria. Any D2DSS that does not meet the minimum signal quality requirement will be removed from the further selection procedure in advance even without applying selection rules. For those D2DSS that are preselected, either the source type priority or the transit count reference priority is used. For example, the UE always selects D2DSS originating from the eNB, no matter how many backhaul sites it has. On the other hand, if D2DSS does not pass the signal quality requirement, regardless of the type of source and the reference of the transit sections, D2DSS with the highest signal quality is selected. The problems of this approach are, for example, that the signal quality is not taken into account in the selection rules as soon as it passes the minimum signal requirement. If there are two signals, both are below the minimum signal requirement, but one signal is much stronger than the other, a much stronger signal has no advantage in the selection process. It may happen that a D2DSS originating from an eNB is much weaker than a UE outside the network coverage area, but the UE will still choose an eNB if both D2DSS pass the prerequisite. Moreover, when all D2DSS are below the signal requirements, only signal quality is taken into account. This may cause the UE to still select the UE outside the network coverage area, even if the signal quality from the UE outside the network coverage area is only slightly better than from the eNB.

The purpose of this design decision here is to take into account more factors when choosing a synchronization source and choose the most reliable source, i.e. increase the efficiency of the selection of the synchronization signal. In order to achieve this, a priority function is provided that takes into account at least two of the following factors: the type of the initial synchronization source, the quality of the received signal, and the count of transit sections, calculated from the eNB. Accordingly, the UE will then select the synchronization source with the highest priority value as the most reliable source.

Thus, according to an embodiment of the present invention, there is provided a synchronization receiver, which comprises a synchronization reception unit for receiving predetermined synchronization signals from various synchronization sources, including at least a source transmitting a signal originating from a network node and a wireless synchronization generating device, however, the wireless device is not a network node, but rather a user equipment. The synchronization receiver further includes a metric calculation unit for determining a corresponding metric for each of the synchronization sources from which the synchronization signal is received. The indicator is based on at least two of: the quality of the received synchronization signal; source type, i.e. whether the synchronization source is a source transmitting a signal originating from a network node or a wireless device generating a synchronization signal; and the number of transit sites to the network node. The synchronization receiver further comprises a synchronization source selection unit for selecting a synchronization source according to an indicator, and a timing unit for adjusting the timing for transmitting and / or receiving data according to a synchronization source synchronization signal selected by the synchronization source selection unit.

The synchronization receiver, as described above, can advantageously form part of a wireless communication device, such as a terminal or any user equipment. However, the synchronization receiver may also be a repeater, which may be useful in the case of mobile relays. It should be noted that even if embodiments are described herein in the context of an LTE system, i.e. mobile communication systems, the present invention is not limited to this. Conversely, it can also be applied to multicast / broadcast receivers, which can accordingly adapt their receive clock. Multicast / broadcast receivers can also operate based on the LTE standard. However, the present invention is also applicable to other systems, such as broadcast digital video.

Synchronization signals are predefined signals known to both parties, the receiver and transmitter (source) of such signals. Synchronization signals or their properties and / or resources by which they should be expected are usually well defined in the standard. They can be fixed, or can be selected (defined) from the set of available synchronization signals, as is the case, for example, for PSS and SSS from LTE, as described above in relation to the technical environment. A synchronization source is any entity that transmits a synchronization signal, such as a base station, a relay, a UE or the like.

The selection unit selects a synchronization source based on a metric. For example, the selection unit may be configured to select a source having an indicator value indicating the greatest reliability. This can be done by making a choice, for example, of a source whose indicator value is the largest among the indicator values, if the sources are estimated. However, depending on the design of the indicator, the most reliable source may correspond not to the largest, but to the smallest value of the indicator. In this case, the source with the minimum value of the indicator will be selected. However, it should be noted that, in general, the selection unit can perform the selection in any way according to the indicator.

Moreover, the choice is not limited to the need to complete the desired transmission at the beginning. Conversely, a selection can be made regularly in order to check whether an appropriate synchronization source is being used, and in order to re-select the same or different source.

The timing unit receives timing from a timing signal received from a selected timing source. Clocking can be used to determine or control the timing of data transmission or reception. The clocking of the transmission or reception of data may be the same as the clocking of the clock signal, or be the clocking minus a fixed or configured offset. In the first (initial) source selection, the UE determines its timing according to the received synchronization signal. When re-selecting (the selection performed after the initial selection), the UE may, instead of determining only adjust its timing according to a new source of synchronization. Here, the initial source selection may be, for example, the selection after switching to the UE. The timing unit may receive timing for receiving and transmitting in another manner. For example, the timing for reception can be defined directly as the timing of the received synchronization signal, while for transmission, the timing can be determined by applying a timing advance, i.e. shift in relation to the timing of the reception. Such a shift can be determined in the same way as in LTE. The transmission timing may also be defined directly as the timing of the received synchronization signal, or determined by applying a predetermined offset. However, the present invention is not limited to these examples, in general, a clock unit may receive clock from a synchronization signal in any way.

Preferably, the indicator acquisition unit is configured to determine an indicator as a combination of the quality of the received synchronization signal and the selection bias determined based on the number of transit sections and / or based on the type of synchronization source, which is either a source originating from the network or a source independent of the network such as a wireless device that generates a synchronization signal without the involvement of the network.

For example, the priority function (i.e., metric) may be the sum of the quality of the received signal and the resulting priority offset (selection bias). The quality of the received signal is measured, for example, in the receiver of the synchronization signal. Measurement of signal quality can be performed in any way, for example, based on a synchronization signal. Accordingly, the synchronization source transmits signals with predetermined power in predetermined resources. Resources and power are known to the receiver, which measures the power of the received signal, which can directly be a quality parameter. However, the quality parameter used in the indicator can also be defined as a function of the measured power of the received signal. This may be the ratio or difference between the transmitted and received signal, indicating the deterioration of the signal. The measurement may also correspond to the measurement of CRS (cell reference signal) as performed in LTE (3GPP TS 36.331, version 12.1.0, “Radio Resource Control (RRC); Protocol specification”).

Then, the selection bias (received signal quality shift) is determined based on the number of transit sections and the type of source. Selection bias values corresponding to some combination of source type and counting values of transit sections can be specified in this specification. One way to set is by using a table. In particular, the metric obtaining unit may be configured to determine a selection bias according to an association between predefined selection bias values and a corresponding number of transit sections. Such an association may be a table, which may be a correspondence table stored in the receiver and associating a specific combination of the number of transit sections and the type of source with a certain offset value. Alternatively, the offset can only be determined based on one of the number of transit sections and the type of source. In this case, the correspondence table will only associate the number of transit sections with some offset value. Alternatively, the offset value may depend only on the type of source. In such an example, the table will associate the type of source (source originating from the network, source independent of the network) with the specific corresponding selection bias value.

It should be noted that the above shift may be a positive shift (allowance). For example, if the source is a network node, such as a base station, or a UE receiving its synchronization signal from the network, the offset is a positive predetermined value. If the source is a network independent UE, the offset value is less than the offset value for the network node. It may also be zero. The type of source may also vary between a source that is a network node and a source that is a wireless device whose synchronization signal is obtained from the network's synchronization signal (i.e., originating from the network).

However, the present invention is not limited to this, and the shift may alternatively be a negative shift. Accordingly, different collection values are associated with corresponding different combinations of source type and the number of transit sites. Alternatively, a penalty (or surcharge) may be provided separately for the type of source and separately for the number of transit sections. Still as an alternative, foreclosure can only be granted for the number of transit sites or only for the type of source.

Similarly, a penalty or allowance may be based on the number of transit sites. The number of transit sections may be:

- counted in the opposite direction to the source of synchronization (starting from a predefined maximum number of transit sections for this source of synchronization) or

- calculated in the forward direction from the synchronization source (for example, starting at 0 at the synchronization source).

In other words, the count of transit sections from an eNB can be represented as an increasing count of transit sections or a decreasing count of transit sections relative to an eNB.

For example, counting in the forward direction from the eNB means that if the eNB 610 is the source of the synchronization signal, to the UE 660 receiving the synchronization, 0 transit sections (as in the case of signal 615). If the UE 620 in the network coverage area is the source of the synchronization signal, from the eNB 610 to the receiving UE 660 1 transit section, wherein one transit section is represented by the UE 620 in the network coverage area (as in the case of signal 620). Between the eNB 610 and the receiving UE 660, there may be additional transit sites. In all of these cases, the initial source of the synchronization signal is the eNB 610, and transit sections, such as 620, only transmit the same synchronization signal, or a synchronization signal reproduced based on the original synchronization signal received from the eNB 610. Counting the transit sections in the forward direction from the original source (in this case, the network source, eNB 610) results in a positive number of transit sections or zero.

However, transit sections may alternatively be counted in the opposite direction from the synchronization receiver to the synchronization source. In particular, if synchronization is received directly from the eNB 610 via the UE 660 (signal 615), then the number of transit sections from the eNB to the receiving UE can be set to the maximum number of NHmax transit sections supported for this network node (eNB 660). Different network nodes may have a different maximum number of transit sections. For example, a macro-eNB has a larger number of transit sites than a micro-eNB, since a macro-eNB has a higher clock accuracy and frequency. Counting backwards has the advantage that the UE does not need to know the maximum number of transit sections if the maximum number of transit sections is configurable for the eNB. If the synchronization receiving device 660 receives the synchronization signal 625 from the UE 620, then the count of the transit sections counted in the opposite direction from the eNB 610 is NHmax-1 at the receiving UE 660. As in the above example, the number of transit sections may even be lower, such as NHmax-2, NHmax-3, ..., 0, corresponding to more than one device (located between the original source 610 and the receiving UE 660), receiving the synchronization signal originating from the network node and transmitting it further (or transmitting the synchronization signal reconstruction of th e received synchronization signal). In other words, when counting transit sections in the opposite direction, the calculation starts from the maximum number of transit sections previously determined for a given eNB 610. In particular, the maximum number of transit sections can be set / defined for different eNBs as a different value. A predetermined maximum number of transit sites can be specified for the eNB network. The UE obtains information regarding the maximum number of transit sites by signaling from the eNB. This can be done either through the control channel D2D, or broadcast signaling, or in the synchronization signal.

If the aforementioned increasing count of transit sections, i.e. if the transit section starts from 0 at the network node, the priority offset function is preferably designed so that the offset value decreases when the transit section count increases. If, on the other hand, a decreasing count of transit sections is used, i.e. the backhaul count starts with NHmax at the network node, the priority offset function is preferably designed so that the offset value increases when the backhaul count is increased. Here, the term “priority bias function” refers to a function or rule for associating bias values with sample values of transit sections (reference of transit sections).

The above examples of the association between the shift (bias) of the selection and the number of transit sections and / or the type of source are not limited to the present invention. According to another example, the penalty and the premium may also be combined. For example, a markup may be provided for a network node as a source, while for other sources a markup is not provided, and a penalty may be provided for a positive number of transit sites, or vice versa.

As described above, the relationship between the markup, the type of source, and the count of the transit sections can be specified by means of a correspondence table. The table can be specified in the standard, i.e. may be predefined. Alternatively, a penalty or allowance may be calculated based on some function. For example, the recovery may be proportional to the number of transit sections (calculated in the forward direction), for example, the value of the recovery may be two times the number of transit sections. Alternatively, the function may be inversely proportional to the number of transit sections counted in the opposite direction. However, this is just an example, and the function may take a different form than simple multiplication, or a factor other than 2. The specific choice of the function (as well as the value of the table) depends on the desired effect of the number of transit sections and / or type of source on the indicator.

As a result, the offset is preferably defined as a value (premium or penalty), which is greater for the network nodes that are the source of the synchronization signal than for wireless devices that are the source of the signal. This makes it possible to prefer network nodes as a synchronization source over wireless devices that are independent of network nodes, i.e. which synchronization signal is received not from the network. This preference may be useful since it is generally expected that D2D communications and network device communications should use the same bandwidth and time. Thus, clocking coordinated with network clocking can help reduce interference and improve reception quality. Moreover, some coordination between network device transmissions and D2D transmissions can be accomplished via the network.

Alternatively or in addition, the offset can be defined as a value (surcharge or penalty) that decreases with an increase in the number of transit sections between a network node and a synchronization receiver, where the number of transit sections is a positive integer, or as a value that increases with an increase the number of transit sections between the network node and the synchronization receiving device, where the number of transit sections is also a positive integer. These two possibilities are aimed at increasing the value of the indicator if the synchronization receiving device is close to the network source, and decreasing the value of the indicator if it is far from the network source. The proximity here is expressed by the number of nodes (wireless devices) between the network node, which is the source of the synchronization signal, and the node receiving synchronization.

7 illustrates an embodiment of the present invention in which the eNB 710 has a coverage area indicated by ellipse 701. The D2D UE 770 receives a synchronization signal 715 from the eNB 710 with a received signal quality of -100 dBm. The D2D UE 770 further receives a synchronization signal 725 originating from the eNB 710 through a transit section formed by the UE 720 in the network coverage area with a received signal quality of -80 dBm. Finally, the D2D UE 770 receives the synchronization signal 735 from the UE 730 outside the network coverage area with a received signal quality of -78 dBm. Thus, if the synchronization source is selected only according to the quality of the received signal, then UE 730 will be selected outside the network coverage area since it has the highest received signal quality, followed by UE 720 and finally eNB 710. In this embodiment, however, The choice of synchronization is different. The tables at the bottom of Figure 7 show the association between the markup value (3rd column) and the combination of source type (1st column) and the count of transit sections (2nd column). The type of the original source can be either an eNB 710 or a wireless device that does not receive a synchronization signal from a network node, i.e. here the UE 730 is out of network coverage. The number of transit sections, distinguishable in this example, is 0, 1 or more than 1. In this case, the selection bias is a premium that can take the values 10, 6, 3, or 0, depending on the type of source and the number of transit sections. In particular, if the source is a wireless device 730, then regardless of the number of nodes, a markup (markup with a value of zero) is not added to the quality (power) of the received signal. It should be noted that in these examples, the wireless device 730 generates a synchronization signal. However, in general, a synchronization signal may also be generated by some other wireless device, and thus the number of transit sections may also be different for this type of source.

For the sources in Figure 7, thus, the corresponding indicators are calculated as follows:

- eNB 710: the received signal power of -100 dBm is added to the value of 10 increments (0 transit sections, eNB source in the first row of the table), which results in a value of -90.

- UE 720: the received signal power of -80 dBm is added to the value of 6 extra charges (1 transit section, eNB source in the second row of the table), which results in a value of -74.

- UE 730: the received signal power of -78 dBm is added to the value of the 0 premium (any number of transit sections, the eNB source in the last row of the table), which results in a value of -78.

Accordingly, the source with the highest reception quality at -74 is UE 720, followed by the UE 730 and the eNB 710. Thus, the D2D UE 770 selects the UE 720 in the network coverage area as the synchronization source, since it has the highest metric value. In this example, the forward count is used to count the transit sections.

In order to be able to obtain an indicator, the synchronization reception UE preferably obtains information about the type of source and the number of transit sections from the transit section 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 a UE (with a synchronization signal originating from the network or independent of the network). If the source is an eNB, the information is already carried in the cell ID in the synchronization signal - based on this, it is clear that the source is an eNB, and thus the number of transit sections is 0 (or NHmax, depending on the applied strategy for counting transit sections). Instead of determining the selection bias value by using a table based on the type of source and the counting of the transit sections, the bias value can be specified directly through a D2D clock signal or through a control channel such as a D2D control channel. In other words, the selection bias is determined by receiving it inside the signaling information transmitted from the corresponding synchronization source. Thus, the determination of the offset value is more flexible, and the calculation or search in the table is not necessary at the receiver. For example, the UE 720 in Figure 7 will explicitly indicate that a value of 6 is due to a D2D clock signal or a control channel such as a D2D control channel.

The assignment table, which is described above, can be configured for the synchronization receiving device by means of control signals. For example, the table of Figure 7 may be transmitted to a receiver (UE) by means of RRC signaling. Alternatively, a default table may be used, and, in addition, it may be possible to transmit a modified table after establishing an RRC connection to the network. Another alternative is that multiple tables are predefined in the specification. Table selection can be based on the eNB type or configured by higher layer signaling.

According to another embodiment of the present invention, the metric obtaining unit is configured to determine the metric as a linear combination of the quality of the received synchronization signal; a number representing whether the clock source is a network node or a wireless device; and the number of transit sites to the network node.

In particular, a function can be defined by

M = a × T + b × H + c × Q

Where T is the type of the original source of synchronization, for example T = 1, if the original source is eNB, and T = 0 otherwise; H is a count of transit sections, i.e. the number of transit sections between the original source of synchronization and the transit section of the transmission of synchronization, which may also be provided to indicate the number of transit sections between the original source and receiver of synchronization; Q is a signal quality that can be set, for example, by the received signal power in dBm; and a, b, c are weights for weighing the respective above three parameters T, H and Q. Weights a, b and c may be generally real numbers. However, in order to simplify the implementation, weights can also be integers. It should be noted that the signal quality is not necessarily directly measured measured power. Alternatively, the reception quality may be represented by a predetermined number of levels that are determined based on the measured signal power. For example, depending on the dBm value, different categories can be specified, for example, "excellent", "good", "satisfactory", "bad", "very bad". These categories can then be represented by an integer, which is easier to calculate the above equation. For example, excellent quality may be assigned number 5, good quality number 4, satisfactory quality number 3, poor quality number 2, and very poor quality number 1.

For example, since the D2DSS received from the eNB has a higher priority than the D2DSS received from another source, the weight coefficient a is preferably a positive integer a> 0. If the count of transit sections is calculated in the forward direction from eNB, then the weight coefficient b is preferably a negative number b <0, whereas if the count of transit sections is calculated in the opposite direction, b> 0. The higher the quality of the received signal, the greater should be the value of the indicator. Thus, c> 0 if the accepted quality is expressed in dBm, as also shown as an example above, since the accepted quality in this case is a negative number, which means that a higher quality value is better. If c <0, for example, -1, then -100 dBm is better than -90 dBm. The indicator M may be <0 if the accepted quality is a negative number. However, these are just examples. Those skilled in the art will appreciate that the metric should be designed in order to represent the reliability of the source. A specific design solution, such as the use of counting transit sections in the forward / reverse direction or the positive / negative values of the parameters T, H, Q and, accordingly, the weighting factors a, b, c, can be implemented in any way.

The weighting factors and thus the metric can be configured for each UE (receiving device). For UEs outside the network coverage area, the weights a, b, and c can be pre-configured by OAM or relayed by the UE in the network coverage area via the D2D control channel.

For UEs in the network coverage area, the weighting factors a, b, and c can be pre-configured or configured by the eNB. A configuration for each eNB is preferred, and may be performed, for example, by RRC signaling or other control signaling.

Configurable metric has the advantage that each UE can be configured differently. If the UE has data relayed from the eNB, it is preferred that such a UE synchronize with the eNB. Then the weighting factor a can be configured more for this UE than for another UE. If the UE has weak reception capability (low quality signal detection / decoding capability), it is preferable to synchronize such a UE with D2DSS of the highest signal quality. Then the weight coefficient c can be configured to a greater extent for such a UE than for another UE, not in this scenario.

As a result, the linear combination is preferably defined as M = a × T + b × H + c × Q, whereby T is a synchronization source, H is the number of transit sections, and Q is the quality of the received signal; and a, b, and c are weighting factors. Then, the indicator obtaining unit is configured to determine the weighting factors a, b or c by receiving them inside the signaling information transmitted from the network node.

According to another embodiment of the present invention, the synchronization source selection unit is further configured to perform a preliminary step to eliminate unqualified D2DSS. In particular, the preliminary step may eliminate from a set of sources that should be considered for selection. For pre-selected D2DSS only, the metric will be determined based on signal quality and bias, or based on a linear metric as described above, and a synchronization source will be selected based on the metric. This means that excluded sources are excluded at the preliminary stage of elimination from further consideration as synchronization sources.

According to an embodiment of the present invention related to the synchronization reception device in the synchronization reception device, the synchronization source selection unit is configured to preselect synchronization sources by excluding from the set of possible synchronization sources with the number of transit sections to the network node exceeding a predetermined threshold of transit sections . For example, a predefined threshold may be 3, which means that any transit section with a count of transit sections greater than 3 (in the case of counting transit sections in the forward direction) will be excluded from further selection. However, this is just an example, and the threshold may also take a different value, such as 1, 2 or 4, or more.

Alternatively, or in addition to pre-selection based on the number of transit sections, pre-selection of synchronization sources can be performed by excluding from a set of possible sources of synchronization sources with signal quality not exceeding a predetermined quality threshold. For example, a predefined threshold may be -100 dBm. Thus, any transit section (source), the synchronization signal of which is received with a power of less than -100 dBm, is excluded from further selection. However, a value of -100 dBm is just an example, and the threshold may take another value, such as -110 dBm or -105 dBm, or any other value. Moreover, it may be useful to set the threshold to different values, depending on the type of the original source. In particular, the quality threshold may be higher for a non-network source, such as a UE 730 outside the network coverage area, meaning that the signal from such a UE must be of higher quality to be preselected than sources that determine their signal based on a synchronization signal from the network (eNB 710 or UE 720 in the network coverage area).

In this embodiment, the indicator acquisition unit is then configured to determine an indicator only for those synchronization sources that remain in the set of possible synchronization sources after a preliminary selection made by the synchronization source selector. The term "set of possible synchronization sources" here refers to sources whose synchronization signal is received by the synchronization reception device.

One of the advantages of preselection is that low quality D2DSS is not selectable. Thus, it is possible to prevent the selection of unreliable sources of synchronization, even without defining an indicator for them. Thus, the selection can be simplified in this way.

The above-described embodiments regarding the manner in which the acquisition of the metric and the selection of the synchronization source are to be performed can be further improved by controlling the reselection of the source with hysteresis. In particular, the synchronization receiving device receives the synchronization signal from different synchronization sources. It can regularly re-select the source of synchronization by determining indicators for the received sources and by selecting the most reliable source, respectively. If the reception of signal quality varies significantly, such regular re-selection will lead to a frequent change in the synchronization source. In order to prevent such a “ping pong” effect, hysteresis can preferably be added. This means that when the UE selects a synchronization source, it will hold that source for a period of time, so that the UE will not frequently change the synchronization source. This helps the stability of the clock source. The hysteresis will decrease over time, so that the best source of synchronization will be selected.

The synchronization receiving device may further comprise a reselection timer, and a selection control unit for controlling a metric obtaining unit for determining an indicator, and a synchronization source selection unit for selecting a synchronization source in accordance with the reselection timer. For example, the terminal can evaluate every 10 seconds the sources from which it receives the synchronization signal. The assessment includes the above definition or calculation of the indicator and the selection of the best source, i.e. the source with the highest value of the indicator, or, in general, with the value of the indicator indicating the best source. This allows the receiver of the synchronization signal (such as a terminal, or more generally, user equipment) to regularly adapt the synchronization source to a possibly variable transmission medium. It should be noted that the above example of 10 seconds for the reselection period is only exemplary, and can be set to another value, for example, 1, 2, 5 or 15 seconds, or any other time period. The value of the reselection timer may be fixed, or it may also be configurable by a higher layer protocol through a network (node) such as an eNB. The configurability of the timer provides the advantage of adapting the reselection operation to the transmission medium of the UE. If the UE is a mobile UE, channel quality variations can be more frequent, which makes it useful to configure a shorter reselection period. On the other hand, if the UE is not moving (currently), and the environment is not substantially changing, then it may be useful to configure the re-selection period to be longer (increase the re-selection period).

The synchronization receiving device further comprises a hysteresis timer that starts after a new synchronization source has been selected and expires after a predetermined hysteresis period, wherein a reselection timer is set to a predetermined reselection period. The reselection period may be received by the synchronization receiving device within the control signaling from the network, for example, from a network node such as a base station (eNB). The selection control unit then instructs the indicator obtaining unit to determine the indicator and instructs the synchronization source selection unit to select the synchronization source according to the indicator after the expiration of the reselection timer if the hysteresis timer has expired, and not to select the synchronization source according to the indicator after the expiration reselection timer if the hysteresis timer has not expired. In this way, the hysteresis timer helps prevent frequent changes to the clock source.

The predetermined hysteresis period may preferably decrease in time. In particular, the hysteresis period can be reduced with an increasing number of times the expiration of the reselection timer.

Re-selection may also be triggered when the received signal quality of the current clock source falls below a threshold for a period of time. It is preferable to prevent the sudden disappearance of the synchronization source or a significant deterioration in the quality of the signal from the synchronization source.

The present invention, as described in the above embodiments, provides the advantage of differentiating between the type and distance of the sources and not only based on reception quality. Accordingly, the UE will select D2DSS with higher signal quality. The priority of the eNB and the counting of transit sections can be considered as a shift for signal quality. If the quality of the D2DSS signal from the UE outside the network coverage area, such as 630, is not much better than the quality of the D2DSS signal from the eNB 610, the UE will select the eNB.

Figure 8 illustrates an apparatus 800 for receiving a synchronization signal according to an embodiment of the present invention. Device 800 is a wireless device, such as user equipment. This wireless device receives various signals from different sources with different corresponding strengths. In particular, the device may receive signals from a network node 810, such as an eNB, or from a wireless user device 820 that is located within the eNB 810 coverage area, or from user equipment 830 that is located outside the network coverage area 801, and in particular eNB 810. The device comprises a synchronization signal receiving unit 840, a metric receiving unit 850, a synchronization source selection unit 860, and a clock unit 870 that are configured as described in the above embodiments. In particular, the synchronization signal reception unit 840 is adapted to receive a synchronization signal from various synchronization sources D2D. It can further identify the source based on the received synchronization signal or at least the type of source. However, this information may also be transmitted later through signaling. The indicator obtaining unit 850 is configured to determine or calculate an indicator based on which the synchronization source selection unit 860 selects a synchronization source. After selecting a source, device 800 determines (initially) or adjusts (after an initial determination has been made) its clock. In particular, he can take synchronization as a clock for reception purposes or can add a shift to it. Then, receive transmission timing, which can be performed based on the received reception timing.

The device 800 may further include a reselection control unit 880 that controls the times at which the device performs reselection. Accordingly, the re-selection unit 880 controls the indicators obtaining unit 850 and the selection unit 860 for performing from functions, namely, calculating the indicators and selecting the source at certain times. These times are preferably obtained from the reselection timer 885, also forming part of the device 800. The reselection timer 885 may be configurable by signaling received from the network. The reception of signaling from the network can be performed by block 890 receiving signaling. It should be noted that in this block diagram, the signal receiving unit 890 and the synchronization signal receiving unit 840 are drawn separately. This is because they are function blocks. In general, device 800 will have a common reception front formed by one or more antennas, amplifiers, demodulators, and decoders (possibly used to receive signaling). Then the alarm and synchronization will be used for different purposes, as shown in Figure 8 separated blocks 840 and 890.

The signaling reception unit may also be configured to receive signaling with settings for determining indicators. For example, settings for weights a, b, c, and / or for shifting the selection bias and / or premium or penalty values may be accepted and provided to the metric obtaining unit 850. Moreover, the hysteresis timer 865 can be part of the device and can be used by the re-selection control unit 880 to control the synchronization source unit 860 to change or not change the synchronization source, if the selection unit 860 selects a new synchronization source based on the parameters defined in 850, those. a synchronization source different from the currently used synchronization source. The hysteresis timer 865 may also be configured by signaling received from the network by the signal receiving unit 890. Figure 9 illustrates a method for selecting a synchronization source in a system as described above. In particular, such a synchronization reception method comprises the steps of: receiving predetermined wireless synchronization signals from synchronization sources, including a synchronization source that receives its synchronization signal from a network node and a wireless synchronization generating device. The received synchronization signals may already carry some information, such as the type of source or the number of transit sections. However, this information may also be transmitted in another way. Then the method comprises the step of determining 930 a selection indicator for each of the synchronization sources based on at least two of: the quality of the received synchronization signal; type of source (whether the synchronization source transmits a synchronization signal originating from a network node or independent of a network node); and the number of transit sites to the network node. In the next step 940, the selection of the synchronization source according to a certain indicator selects the source, which is then used for step 950 to determine or control the clock for transmitting or receiving data according to the synchronization signal of the selected synchronization source.

The indicator is preferably defined as a combination: the quality of the received synchronization signal and the selection bias, determined on the basis of the number of transit sections and / or based on the type of synchronization source, which is either a synchronization source that receives its synchronization signal from a network node or a wireless device independent of network. The selection bias may be determined according to the association between the predefined selection bias values and the corresponding number of transit sections, such as a correspondence table. The selection bias can, in particular, be defined as one of: a value that is greater for the network nodes that are the source of the synchronization signal than for wireless devices that are the source of the signal; a value that decreases with an increase in the number of transit sections between the network node and the synchronization receiving device, when the number of transit sections is counted with increasing starting from the network node; or a value that increases with the number of transit sections between the network node and the synchronization receiving device, when the number of transit sections is calculated in decreasing order starting from the network node with a predetermined maximum of transit sections. Alternatively, the selection bias may be determined by receiving it inside the signaling information transmitted from the corresponding synchronization source. The present invention is not limited to defining an indicator as described above, and in general, an indicator can also be defined as a linear combination of the quality of the received synchronization signal; a number representing whether the clock source is a network node or a wireless device; and the number of transit sites to the network node. Such a linear combination is preferably defined as M = a × T + b × H + c × Q, wherein T is a clock source, H is the number of transit sections, and Q is the quality of 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 it inside the signaling information transmitted from the network node.

The method may further comprise a step 920 of preliminary selection of synchronization sources by excluding from the set of possible synchronization sources: sources with the number of transit sections to a network node exceeding a predetermined threshold of transit sections and / or sources with a signal quality not exceeding a predetermined quality threshold . Then, the indicator is determined only for the synchronization sources in the set of possible synchronization sources after the preliminary selection made by the synchronization source selection unit.

The synchronization method may further comprise the step of starting (maintaining) a reselection timer, and controlling 960 to determine a metric and selecting a synchronization source in accordance with the reselection timer.

The method may also further comprise maintaining a hysteresis timer, which starts after selecting a new synchronization source and expires after a predetermined hysteresis period, wherein the reselection timer is set to a predetermined time period. The method then preferably includes the step of issuing a command to determine the metric and to select a synchronization source according to the metric after the expiration of the reselection timer if the hysteresis timer has expired, and to not select the synchronization source according to the metric after the expiration of the second timer selection if the hysteresis timer has not expired.

The explanations given in the “Technical Environment” section above are intended to better understand the specific exemplary embodiments described herein and should not be construed as limiting the invention to the described specific implementations of processes and functions in a mobile communication network, such as a network consistent with 3GPP standards. However, the improvements proposed herein can easily be applied to the architectures / systems described in the Technical Environment section, and may also use standard and improved procedures for these architectures / systems in some embodiments of the present invention. One skilled in the art will understand that numerous variations and / or modifications may be made to the present invention, as shown in specific embodiments, without departing from the spirit and scope of the present invention, as is widely described.

Another embodiment of the present invention relates to the implementation of the various embodiments described above using hardware and software. It is understood that various embodiments of the present invention can be implemented or performed using computing devices (processors). A computing device or processor may be, for example, general-purpose processors, digital signal processing processors (DSPs), specialized integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable logic devices, etc. Various embodiments of the present invention may also be made or practiced by a combination of these devices.

In addition, various embodiments of the present invention may also be implemented by software modules that are executed by a processor or directly in hardware. A combination of software modules and hardware implementation may also be possible. Software modules can be stored on any type of computer-readable storage media, for example, RAM, EPROM, EEPROM, flash-memory, registers, hard drives, CD-ROM, DVD, etc.

To summarize, the present invention relates to the selection of a synchronization source from among various synchronization sources, which include sources that determine the synchronization signal from the network, such as base stations (network nodes) or user equipment that receives the synchronization signal, possibly through other transit sections from base station, and which additionally include sources that do not determine their synchronization signal from the network. The selection of the synchronization source is carried out by selecting the source with the most reliable synchronization signal based on the indicator calculated for each of the considered sources. In particular, the indicator is based on the type of source, the number of transit sections between the network and the source, and / or the quality of the received signal. After making a source selection, the timing of the device is adapted accordingly.

Claims (31)

1. User equipment (UE), containing: a receiver that, in operating mode, receives a synchronization signal from a synchronization source; and a circuit that is in operating mode, measures the quality of the received synchronization signal; defines a synchronization source as a possible source of synchronization when the measured quality exceeds a certain threshold; selects a reference synchronization signal UE from a possible source of synchronization in accordance with the following order of priorities: a possible source of synchronization is in the area of the highest result of the measured quality; the synchronization signal of a possible synchronization source is an oriented network with the highest result of the measured quality; a possible source of synchronization is outside the zone of the highest result of the measured quality and the synchronization signal, therefore, is independent in the network from the highest result of the measured quality; and adjusts the timing for transmitting or receiving data in accordance with the synchronization signal of the selected synchronization reference signal UE. 2. The user equipment according to claim 1, which comprises a transmitter that transmits a synchronization signal generated in the UE when the circuit determines a user equipment that is out of range and a possible source of synchronization is not determined. 3. The user equipment according to claim 1, wherein the circuit, in operation mode, determines whether the received synchronization signal is an oriented network or independent in the network based on the received synchronization signal. 4. The user equipment according to claim 1, in which the circuit, in the operating mode, determines the quality of the received synchronization signal based on the received power and a certain threshold, which is a hysteresis. 5. The user equipment according to claim 1, in which the circuit, in the operating mode, adjusts the timing for reception or transmission in each specific period. 6. The user equipment according to claim 1, wherein the specific threshold is pre-configured in the user equipment. 7. The user equipment according to claim 1, wherein the circuit, in operating mode, uses a different specific threshold that is different from the specific threshold used to select a possible synchronization source. 8. A method performed by user equipment, comprising the steps of: receive a synchronization signal from a synchronization source; measuring the quality of the received synchronization signal; determining a synchronization source as a possible synchronization source when the measured quality exceeds a certain threshold; select the reference synchronization signal UE from a possible source of synchronization in accordance with the following order of priorities: a possible source of synchronization is in the area of the highest result of the measured quality; the synchronization signal of a possible synchronization source is an oriented network with the highest result of the measured quality; a possible source of synchronization is outside the zone of the highest result of the measured quality and the synchronization signal, therefore, is independent in the network from the highest result of the measured quality; and adjusts the timing for transmitting or receiving data in accordance with the synchronization signal of the selected synchronization reference signal UE. 9. The method of claim 8, comprising transmitting a synchronization signal generated by the UE when the user equipment is out of range and a possible synchronization source is not determined. 10. The method according to claim 8, in which it is determined whether the received synchronization signal is oriented network or independent in the network, based on the received synchronization signal. 11. The method of claim 8, wherein determining the quality of the received synchronization signal based on the received power and the determined threshold, which is a hysteresis. 12. The method according to p. 8, in which regulate the timing for reception or transmission in each specific period. 13. The method of claim 8, wherein the specific threshold is pre-configured in user equipment. 14. The method of claim 8, wherein another specific threshold is used that is different from the specific threshold used to select a possible synchronization source.

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