RU2727060C1 - Selecting device-device synchronization source - Google Patents

Abstract

FIELD: physics.SUBSTANCE: present invention relates to selection of 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, which receives synchronization signal possibly through other transit sections from base station, and which further include 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: high efficiency of the method and apparatus for selecting a source of synchronization.7 cl, 9 dwg

Description

SELECTING A DEVICE-DEVICE SYNCHRONIZATION SOURCE

The present invention relates to devices and methods for selecting or re-selecting a timing source for wireless communications.

BACKGROUND OF THE INVENTION

Third generation (3G) mobile systems based on WCDMA radio access technology are widely deployed around the world. The first stage in the expansion or development of this technology entails the introduction of high speed downlink packet data (HSDPA) and enhanced uplink, also called high speed uplink packet data (HSUPA), giving a radio access technology that is very competitive. In order to be prepared to further increase user demands and to be competitive against new 3GPP radio access technologies, a new mobile communication system called Long Term Evolution (LTE) technology is presented. LTE is designed to meet the needs of carriers for high-speed data and media transport as well as support for high-bandwidth voice over the next ten years. The ability to deliver high bit rates is a key metric for LTE. A Work Element (WI) in a Long Term Evolution (LTE) technology called UMTS Enhanced Terrestrial Radio Access (UTRA) and UMTS Terrestrial Radio Access Network (UTRAN) is formatted as Release 8 (LTE Release 8). The LTE system is an efficient packet radio and radio access networks that provide full IP functionality with low latency and low cost. Detailed system requirements are given in 3GPP TR 25.913, "Requirements for Evolved UTRA and Evolved UTRAN", version 9.0.0, freely available at www.3gpp.org.

LTE precisely defines scalable multiple transmission bandwidths such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz to achieve flexible system deployments using a given spectrum ... Orthogonal Frequency Division Multiplexing (OFDM) radio access has been applied in the downlink due to its inherent robustness to multipath interference (MPI) due to its low symbol rate, the use of a cyclic prefix (CP), and its association with various bandwidth arrangements for transmission. Single carrier frequency division multiple access (SC-FDMA) radio access has been applied in the uplink since providing extensive coverage took priority over increasing the peak data rate given the limited transmit power of the user equipment (UE). Many key packet radio access techniques are used, including multi-channel input-multiple-output (MIMO) channel transmission techniques, and a highly efficient control signaling structure is achieved in LTE Release 8.

The general architecture is shown in Figure 1 and a more detailed view of the E-UTRAN architecture is given in Figure 2. The E-UTRAN contains the eNB, providing the UE with the E-UTRA User Plane Protocol (PDCP / RLC / MAC / PHY) and RRC Terminations. The eNB houses the physical (PHY), medium access control (MAC), radio link control (RLC), and data transmission control protocol (PDCP) layers, which include the functionality of compressing and encrypting the user plane header. It also offers radio resource control ( RRC) corresponding to the control plane.It performs many functions, including radio resource control, admission control, scheduling, implementing UL negotiated QoS, broadcasting cell information, encrypting / decrypting user plane and control plane data, and compressing / decompressing user packet headers. DL / UL planes.eNBs are interconnected to each other via X2 interface.eNBs are also connected via S1 interface to EPC (Enhanced Packet Data Core Network), more specifically to MME (Mobility Management Node) via S1-MME and to a serving gateway ( S-GW) via S1 -U. The S1 interface supports a many-to-many relationship between the MME / serving gateways and the eNB. The SGW routes and relays user data packets while also acting as a mobility anchor for the user plane during inter-eNB handoffs and as a mobility anchor between LTE and other 3GPP technologies (terminating the S4 interface and forwarding traffic between 2G / 3G and PDN GW). For a UE in the idle state, the SGW terminates the DL data path and paging when DL data for the UE arrives. It manages and stores UE contexts, for example, IP bearer service parameters, internal network routing information. It also replicates user traffic in case of lawful interception.

MME is a key control node for an LTE access network. It is responsible for monitoring the idle UE and paging procedure, including retransmissions. It is involved in the bearer activation / deactivation process and is also responsible for making the SGW selection for the UE upon initial attachment and during intra-LTE handover involving a change in the location of a core network (CN) node. It is responsible for authenticating the user (through interaction with the HSS). No Access Layer Signaling (NAS) is terminated at the MME, and it is also responsible for generating and allocating temporary identifiers for the UE. It verifies the UE's authorization to anchor in the public land mobile (PLMN) service provider, and implements the UE's roaming restrictions. The MME is the network termination point for encryption / integrity protection for NAS signaling and handles security key management. Lawful interception of signaling is also supported by the MME. The MME also provides a control plane function for mobility between LTE and 2G / 3G access networks using the S3 interface terminating at the MME from the SGSN. The MME also terminates an S6a interface to the home HSS for UE roaming.

поднесущих, как также показано на Фиг. 3.the downlink component carrier of the 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 area (PDCCH area) 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 Release 8), with each OFDM symbols spanning the entire bandwidth of the component carrier. Thus, each of the OFDM symbols consists of a certain number of modulation symbols transmitted on the corresponding

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 such as using OFDM as used in 3GPP Long Term Evolution (LTE), for example, the smallest resource unit that can be assigned by the scheduler is one "resource block". The physical resource block is defined as

consecutive OFDM symbols in the time domain and

consecutive subcarriers to the frequency domain, as exemplified in FIG. 3. In 3GPP LTE (Release 8), the physical resource block is thus composed 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 multiple 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 and optionally uplink resources. The establishment of a link between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources is indicated in the system information transmitted in the downlink resources.

Cell search routines are the first set of tasks performed by a mobile device in a cellular system after initial power up. Only after the search and registration procedures, the mobile device is able to receive and initiate voice and data calls. A typical cell search procedure in LTE may involve a combination of carrier detection, timing synchronization, and unique cell ID identification. These procedures are usually facilitated by specific timing signals transmitted by the base station (BTS). However, these sync 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 slot, are allocated for synchronization signals.

The cell search procedure enables the UE to determine the timing 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 cell search includes initial synchronization. Accordingly, the UE detects the LTE cell and decodes all information required to register the detected cell. The procedure uses two physical signals that are broadcast on the center 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 a physical cell ID, cyclic prefix length and information on whether FDD or TDD is used. Particularly 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 timeslot 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 obtain the slot boundary regardless of the selected cyclic prefix selected for the cell. After the mobile terminal detects the 5 millisecond timing (slot boundary), it searches for a secondary sync signal. Both the PSS and SSS are transmitted on 62 of the 72 reserved subcarriers around the DC carrier. In the next step, the UE has to detect the physical broadcast channel (PBCH), which, like the PSS and SSS, is mapped only to the center 72 subcarriers of the cell. The PBCH contains a Master Information Block (MIB) that includes information about system resources. In LTE up to version 10, the MIB is 24 bits long (14 bits of which are currently in use and 10 bits are spare). The MIB includes information regarding the downlink system bandwidth, the structure of the physical HARQ indicator transmission channel (PHICH), and the 8 most significant bits of the system frame number (SFN).

After successfully detecting a Master Information Block (MIB), which includes a limited number of the most commonly transmitted parameters required for initial cell access, the terminal activates the system bandwidth, meaning that it must be able to receive and detect signals across the entire system bandwidth. in the downlink. After obtaining the system bandwidth on the downlink, the UE can continue to receive additional required system information in so-called system information blocks (SIBs). In LTE Release 10, Type 1 SIBs through Type 13 SIBs are defined, carrying various information elements required for certain operations. For example, in the case of FDD, SIB type 2 (SIB2) includes a UL carrier frequency and a UL bandwidth. The various SIBs are transmitted on the Physical Downlink Shared Channel (PDSCH) and thus (see details for PDSCH and PDCCH below) respective assignments are assigned to the Physical Downlink Control Channel (PDCCH). Before a terminal (UE) can correctly detect such (or any) PDCCH, it must learn the downlink system bandwidth 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 aforementioned cell ID (cell ID) will uniquely identify a cell within the PLMN. Cell ID is a global cell ID that is used to identify a cell from an Operation and Maintenance (OAM) perspective. It is carried in system information and is designed to manage the eNodeB within the core network. The Global Cell ID is also used for the UE to identify a specific cell with regard to RRC / NAS layer processing. The physical cell ID is a cell ID at the physical layer. The physical cell ID has a range of 0-503 and is used to scramble data to help a mobile device separate 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. The 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. The grouping is such that each physical layer identifier for a cell is part of one and only one physical layer identifier group. Cell physical layer identifier

thus uniquely specified by the number

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

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

. 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 sync signal is composed of a primary sync signal (PSS) and a secondary sync signal (SSS). The sequence used for the primary synchronization signal is generated from the Zadov-Chu time-frequency sequence according to

. By detecting the sync signal, can be detected

. The sequence used for the second synchronization signal is an interleaved concatenation 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 generated by looping through each possible state of the shift register with length n. This results in a sequence with a length of 2 ^ n-1. In particular, two 31 bit long binary sequences to be combined are such M-sequences. For more information on primary and secondary timing, 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 the downlink transmission received from the sync source (eNB). The uplink timing is then adjusted. This is accomplished by applying a timing advance at the transmitter of the UE with respect to the received downlink timing in order to compensate for propagation delays that vary for different UEs. The timing advance procedure is summarized 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 socio-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 ProSe-Based Services (ProSe) capabilities in LTE will provide the 3GPP industry with the ability to serve this development market while serving the urgent needs of several public safety communities that are jointly committed to LTE.

Device-to-device (D2D) communication is a technology component for LTE-A release 12. Device-to-device (D2D) communication enables D2D as the backbone 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 communication in LTE" focuses on two areas: discovery and communication. In D2D communication, UEs transmit data signals to each other over a forward link using cellular resources instead of transmission through a base station (BS, eNodeB, eNB). D2D users communicate directly, but can remain in control of the network, i.e. at least while in the coverage area of the eNB. As a consequence, D2D can improve system performance by reusing cellular resources. Currently, it is assumed that D2D operates in the LTE uplink spectrum (in the case of FDD) or uplink subframes of the cell giving the coverage (in the case of TDD, also when out of coverage). In addition, D2D transmit / receive does not use full duplex on a given carrier. From the point of view of an individual UE, on a given carrier, D2D reception and LTE uplink transmission do not use full duplex, i. E. Simultaneous reception of D2D signal and LTE UL transmission is not possible. In addition, the current operating assumptions for 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 transmit role, UE1 sends data and UE2 receives it. UE1 and UE2 can change their transmit and receive role. The transmission from UE1 may be received by one or more UEs like UE2. Figures 4 and 5 illustrate protocol layers, overhead points and multiplexing in the downlink and uplink, respectively, for transmission on different channel types.

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

- Synchronization source type. eNB or UE

- Accepted D2DSS quality

- Number of hops from eNB.

SUMMARY OF THE INVENTION

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

This is achieved through the features of the independent claims.

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

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

in accordance with another embodiment of the present invention, there is provided a method for performing synchronization source selection, 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 metric for each of the synchronization sources based on at least two of: the quality of the received synchronization signal; whether the sync source transmits a sync signal originating from a network node or independent of the network node; and the number of hops to the network node, selecting a timing source according to the determined metric, and determining or adjusting the timing for transmitting or receiving data according to the timing signal of the selected timing source.

In accordance with another embodiment of the present invention, there is provided a computer program product comprising a computer-readable medium having a computer-readable program code embodied 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 foregoing objects and other objects and features of the present invention will become clearer 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 general LTE architecture;

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

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

Figure 4 is a flow diagram illustrating a layer 2 downlink protocol and a carrier aggregation configured multiplexing structure;

Figure 5 is a flow diagram illustrating a layer 2 uplink protocol and carrier aggregation configured multiplexing structure;

Figure 6 is a schematic diagram illustrating different sources of device-to-device timing;

Figure 7 is a schematic diagram illustrating an example scenario for performing timing source selection based on a metric based on signal quality and a table with selection offset values;

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

Figure 9 is a flow diagram 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 a synchronization signal source in a wireless system in which the synchronization signal transmitter can be a network node, such as a base station, as well as a wireless device that is not a network node, such as a user equipment (terminal ), which can be a mobile phone, smart phone, tablet, laptop, or other computer. Moreover, a 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 concept. The network node can thus be a base station such as an eNodeB or a relay provided as part of the network.

An embodiment of the present invention preferably provides an efficient approach for performing timing source selection among multiple timing sources for the purpose of device-to-device communication coexisting with network transmissions, i. E. in a system supporting wireless transmission between 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 not limited to LTE in any way. The concepts and examples described therein are applicable to a wireless system in which the clock source must be selected from among the clock 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 sync from the network, i.e. from a network node, or generate a clock signal independently of the network clock.

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

1. D2D sync sources, which is an eNodeB, have higher priority than D2D sync sources, which is a UE;

2. D2D sync sources, which is an in-coverage UE, have higher priority than D2D sync sources, which is an out-of-coverage UE;

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

In the D2D timing source selection procedure, this criterion is not sufficient because other factors such as the received D2DSS quality and the number of hops from the eNB were not considered. Soft criteria based on multiple factors are more reliable than those based on only one factor.

Figure 6 illustrates a typical scenario that occurs during communication in a system supporting both network-to-terminal communication and direct communication 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 sync signal (D2DSS) 615, which here has the same shape as the primary sync signal (PSS) and secondary sync signal (SSS) ) version 8. Terminal 620 UE in the network coverage area, i.e. UE that is located within coverage area 601 of base station 610. UE 620 in coverage area receives PSS / SSS from eNB 610 and synchronizes with eNB 610. eNB 610 may request some UE in 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 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. a terminal that is located outside the coverage area 601 of the eNB 610 does not receive any D2DSS with a reception quality exceeding some 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 device-to-device communication. The UE 630 outside the network coverage area in this example does not receive the D2DSS 615 and also does not receive the signal 625 generated by the UE 620 in the network coverage area based on the timing 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 of the network coverage area generates and transmits its own D2DSS 635.

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

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

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

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

Based on the above situation, the question is which timing source should the D2D UE 660 choose to synchronize its receiver (and / or transmitter): an eNB 610 with a very weak signal but no hops, or a UE 620 in a strong network coverage area. signal but with multiple (one in this case) hops, or UE 630 out of network coverage with a strong signal but unknown hops (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 by the eNB 610 or UE 620) always of a higher priority than the D2DSS received from the UE that generated the D2DSS 635, regardless of the network timing such as 630 However, in addition to the fact that such a synchronization signal, received directly or originated from the network, may be the most accurate signal, the following problems may arise:

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

- the signal received from the eNB 610 may pass a different number of hops from the eNB and the received signal strength may vary.

As a consequence, some extended principle is useful in order to give clearer and more efficient rules on how the UE should select the synchronization 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 in advance from the further selection procedure, even without applying the selection rules. For those D2DSSs that pass the preselection, either source type priority or hop count priority is used. For example, the UE always chooses the D2DSS originating from the eNB, no matter how many hops it has. On the other hand, if the D2DSS fails the signal quality requirement, the D2DSS with the highest signal quality is selected regardless of the source type and hop count. The problems with this approach are, for example, that the signal quality is not considered in the selection rules once it passes the minimum signal requirement. If two signals are both below the minimum signal requirement, but one signal is much stronger than the other, the much stronger signal has no advantage in the selection process. It may happen that the D2DSS originating from the eNB is much weaker than from the UE outside the network coverage area, but the UE will still select the eNB if both D2DSS pass the prerequisite. Moreover, when all D2DSS are below the signal requirement, only the signal quality is considered. This may cause the UE to still select the UE outside the network coverage even if the signal quality from the UE outside the network coverage 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 select the most reliable source, i.e. improve 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 original clock source, the quality of the received signal and the hop count counted 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 receiving unit for receiving predetermined synchronization signals from different synchronization sources, including at least a source transmitting a signal originating from a network node and a wireless synchronization generating device, the wireless device is not a network node, but rather a user equipment. The synchronization receiver further includes a metric calculator for determining a corresponding metric for each of the sync sources from which the sync signal is received. The metric is based on at least two of: the quality of the received sync 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 hops to the network node. The synchronization receiver further comprises a synchronization source selection unit for selecting a synchronization source according to the metric, and a timing unit for adjusting the timing for transmitting and / or receiving data according to the synchronization source synchronization signal selected by the synchronization source selection unit.

The sync receiver, as described above, may advantageously form part of a wireless communications device such as a terminal or any user equipment. However, the sync receiver can also be a repeater, which can be useful in the case of mobile repeaters. It should be noted that even though the 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 adapt their reception timing accordingly. The multicast / broadcast receivers can also operate based on the LTE standard. However, the present invention is also applicable in other systems such as digital video broadcasting.

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

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

Moreover, the choice is not limited to the need to perform the desired transmission at the beginning. Conversely, the selection can be performed regularly in order to check if the corresponding clock source is in use and in order to reselect the same or a different source.

The clock unit obtains clocking from the clock signal received from the selected clock source. Timing can be used to determine or adjust the timing of data transmission or reception. The data transmission or reception timing may be the same as the received timing of the sync signal, or be the received timing minus a fixed or configured offset. In the first (initial) source selection, the UE determines its timing according to the received synchronization signal. On reselection (a choice made after the initial selection), the UE may instead of determining only adjust its timing according to the new timing source. Here, the initial source selection may be, for example, a selection after switching to the UE. The clock unit may receive clocking for transmission and reception in other ways. For example, the timing for reception may be defined directly as the timing of the received sync signal, while for transmission, the timing may be determined by applying a timing advance, i. E. shift with respect to the reception clock. Such an offset can be defined in the same way as in LTE. The transmission timing can also be determined directly as the timing of the received sync signal, or determined by applying a predetermined offset. However, the present invention is not limited to these examples, in general, the clock unit can acquire clock from the clock signal in any way.

Preferably, the metric acquisition unit is configured to determine the metric as a combination of the quality of the received sync signal and the selection offset determined based on the number of hops and / or based on the type of sync source, which is either a source originating from a network or a source independent of a network. such as a wireless device that generates a synchronization signal without involving the network.

For example, the priority function (i.e., the metric) may be the sum of the received signal quality and the resulting priority offset (selection offset). The quality of the received signal is measured, for example, at the sync receiver. The signal quality measurement can be performed in any way, for example, based on the synchronization signal. Accordingly, the sync source transmits signals at a predetermined power on predetermined resources. The resources and power are known to the receiver, which measures the received signal power, which can directly be a quality parameter. However, the quality parameter used in the metric can also be defined as a function of the measured received signal power. It can be a ratio or difference between the transmitted and received signal, indicating signal degradation. The measurement may also correspond to the CRS (Cell Reference Signal) measurement 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 bias) is determined based on the number of hops and the type of source. Selection offset values corresponding to some combination of source type and hop count values may be specified in this specification. One way of doing this is with a table. In particular, the metric acquisition unit may be configured to determine a selection bias according to an association between predetermined selection bias values and a corresponding hop number. Such an association could be a table, which could be a look-up table stored in the receiver and associating a particular combination of hop count and source type with some offset value. Alternatively, the offset can only be determined based on one of the number of hops and the type of source. In this case, the lookup table will only associate the hop count with some offset value. Alternatively, the offset value may only depend on the type of source. In such an example, the table will associate the source type (network origin, network independent source) with a specific corresponding selection bias value.

It should be noted that the above shift can be a positive shift (surcharge). For example, if the source is a network node such as a base station or a UE receiving its sync 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 can also be zero. The type of source can also differ between a source that is a network node and a source that is a wireless device whose timing signal is derived from a network timing signal (ie, originating from a network).

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

Likewise, the penalty or surcharge can be based on the number of transit sections. The number of transit sections can be:

- counted backwards to the clock source (starting with a predetermined maximum hop count for that clock source), or

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

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

For example, counting downstream from the eNB means that if the eNB 610 is the sync source to the UE 660 receiving the sync, 0 hops (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 hop of the UE 660 1, one hop is represented by the UE 620 in the network coverage area (as in the case of signal 620). There may be additional hops between the eNB 610 and the receiving UE 660. In all these cases, the original sync source is the eNB 610, and hops such as 620 only transmit the same sync signal, or a sync signal reproduced based on the original sync signal received from the eNB 610. Forward hop counting from the original source (in this case the network source, eNB 610) results in a positive hop count or zero.

However, hops can alternatively be counted backwards from the sync sink to the sync source. In particular, if the timing is received directly from the eNB 610 by the UE 660 (signal 615), then the number of hops from the eNB to the receiving UE may be set to the maximum number of hops NHmax supported for that network node (eNB 660). Different network nodes can have different maximum hop counts. For example, a macro eNB has more hops than a micro eNB because 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 hop count if the maximum hop count is configurable for the eNB. If the sync receiving device 660 receives the sync signal 625 from the UE 620, then the hop count counted upstream from the eNB 610 is NHmax-1 at the receiving UE 660. As in the above example, the hop count may be even 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 a synchronization signal originating from a network node and transmitting it further (or transmitting a signal synchronization reconstructed from the received synchronization signal). In other words, when counting the hops in the reverse direction, the counting starts from the maximum hop number predetermined for a given eNB 610. In particular, the maximum hop count may be set / determined for different eNBs as a different value. A predefined maximum hop count can be set for the eNB by the network. The UE obtains information regarding the maximum number of hops through signaling from the eNB. This can be done either through a D2D control channel, broadcast signaling, or in a synchronization signal.

If the above-described increasing hop count is used, i. E. hop count starting at 0 at the network node, the priority offset function is preferably designed such that the offset value decreases as the hop count increases. If, on the other hand, a decreasing hop count is used, i.e. hop count starting with NHmax at the network node, the priority offset function is preferably designed such that the offset value increases as the hop count increases. Here, the term "priority offset function" refers to a function or rule for associating offset values with hop counts (hop count).

The above-described examples of the association between selection offset (offset) and the number of hops and / or source type are not limited by the present invention. According to another example, the penalty and the surcharge can also be combined. For example, a mark-up may be provided for a network node as a source, while for other sources, no mark-up is provided and a penalty may be granted for a positive hop count, or vice versa.

As described above, the relationship between the markup, the source type, and the hop count can be specified through a look-up table. The table can be specified in the standard, i.e. may be preset. Alternatively, the charge or surcharge can be calculated based on some function. For example, the penalty can be proportional to the number of hops (counted in the forward direction), for example, the foreclosure value can be twice the number of hops. Alternatively, the function can be inversely proportional to the number of hops counted in the opposite direction. However, this is only an example, and the function may have a different form than a 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 influence of the number of hops and / or the type of source on the indicator.

In summary, the offset is preferably defined as a value (premium or charge) that is greater for the network nodes that are the source of the sync signal than for the wireless devices that are the source of the signal. This allows network nodes to be preferred 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 can be useful since, in general, D2D communications and network device communications are expected to 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 may be performed through the network.

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

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

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

- eNB 710: The received signal power of -100 dBm is added to the overhead value 10 (0 hops, source eNB in the first row of the table) resulting in a value of -90.

- UE 720: The received signal power of -80 dBm is added to the overhead value 6 (1 hop, source eNB in the second row of the table), resulting in a metric value of -74.

- UE 730: The received signal power of -78 dBm is added to the overhead value 0 (any number of hops, source eNB in the last row of the table) resulting in a value of -78.

Accordingly, the source with the highest reception quality at -74 is the 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, forward count is used to count hops.

In order to be able to obtain the indicator, the synchronization receiving UE preferably obtains information about the source type and the number of hops from the hop transmitting the synchronization signal. This can be accomplished by decoding the D2D sync signal or the D2D sync control channel if the sync source is a UE (with a sync signal originating from the network or independent of the network). If the source is an eNB, the information is already carried to the cell ID in the sync signal - based on this, it is clear that the source is the eNB, and thus the number of hops is 0 (or NHmax, depending on the applied hop counting strategy). Instead of determining the selection offset value by using a table based on the source type and the hop count, the offset value can be indicated directly by a D2D sync signal or by a control channel such as a D2D control channel. In other words, the selection offset is determined by receiving it within the signaling information transmitted from the corresponding synchronization source. Thus, the determination of the offset value is more flexible and no computation or table lookup is necessary at the receiver. For example, the UE 720 in Figure 7 will explicitly indicate that the overhead value 6 is via a D2D sync signal or a control channel such as a D2D control channel.

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

In accordance with another embodiment of the present invention, the metric acquiring unit is configured to determine the metric as a linear combination of the received sync signal quality; a number representing whether the synchronization source is a network node or a wireless device; and the number of hops to the network node.

In particular, the function can be specified by

M = a × T + b × H + c × Q

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

For example, since the D2DSS obtained from the eNB has a higher priority than the D2DSS obtained from another source, the weighting factor a is preferably a positive integer a> 0. If the hop count is forward from the eNB, then the weighting factor b is preferably negative b <0, while if the hop count is backward, b> 0. The higher the quality of the received signal, the higher the value of the indicator should be. Thus, c> 0 if the received quality is expressed in dBm, as shown also as an example above, since the received quality is then a negative number, which means that a higher quality value is better. If c <0, for example -1, then -100dBm is better than -90dBm. The score M can be <0 if the accepted quality is negative. However, these are just examples. Those of skill in the art will understand that the metric must be designed to represent the reliability of the source. A specific design solution, such as using forward / reverse hop counting or 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 of network coverage, weights a, b, and c may be preconfigured by OAM or relayed by UEs within network coverage via a D2D control channel.

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

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

In summary, the linear combination is preferably defined as M = a × T + b × H + c × Q, where T is the timing source, H is the number of hops, and Q is the received signal quality; and a, b and c are weighting factors. Then the unit for obtaining indicators is configured to determine the weighting coefficients a, b or c by receiving them within the signaling information transmitted from the network node.

In accordance with another embodiment of the present invention, the synchronization source selection unit is further configured to perform a preliminary step for eliminating unqualified D2DSS. In particular, the preliminary stage can eliminate from the set of sources that must be considered for selection. Only for D2DSS that has been preselected, the metric will be determined based on signal quality and offset, or based on a linear metric as described above, and based on the metric, the timing source will be selected. 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 a synchronization receiving device, in a synchronization receiving device, the synchronization source selection unit is configured to preselect the synchronization sources by excluding from the set of possible synchronization sources with the number of hops to the network node exceeding a predetermined hop threshold ... For example, the predefined threshold may be 3, which means that any hop with hop count greater than 3 (in the case of forward hop counts) will be excluded from further selection. However, this is only an example, and the threshold may also take on a different value such as 1, 2, or 4, or more.

Alternatively, or in addition to preselection based on the number of hops, preselection of timing sources can be performed by excluding from the set of possible timing sources sources with signal quality not exceeding a predetermined quality threshold. For example, the predefined threshold may be -100 dBm. Thus, any hop (source), the clock signal of which is received with a power less than -100 dBm, is excluded from further selection. However, the value of -100 dBm is only an example, and the threshold may take a different 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 original source. In particular, the quality threshold may be higher for a non-networked 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 the sync signal. from the network (eNB 710 or UE 720 in the network coverage area).

In this embodiment, the metric acquiring unit is then configured to determine a metric only for those timing sources that remain in the set of possible timing sources after the preselection made by the timing source selection unit. The term "set of possible timing sources" herein refers to the sources whose timing signal is received by the timing receiver.

One of the advantages of preselection is that low quality D2DSS is not selected. Thus, it is possible to prevent the selection of unreliable synchronization sources, even without defining a metric 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 timing source are to be performed can be further improved by hysteresis source reselection control. In particular, the sync receiving device receives a sync signal from different sync sources. It can regularly re-select the timing source by determining metrics for the received sources and by selecting the most reliable source accordingly. If the signal quality reception varies significantly, this regular reselection will often change the clock 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 synchronization 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 clock source is selected.

The synchronization receiving device may further comprise a reselection timer, and a selection control unit for controlling the metric acquisition unit for determining the metric, and a synchronization source selection unit for performing selection of a synchronization source in accordance with the reselection timer. For example, the terminal can evaluate the sources from which it receives the synchronization signal every 10 seconds. Evaluation includes the above-described determination or calculation of the metric and selection of the best source, i. E. the source with the highest metric value, or more generally, the metric value indicating the best source. This allows the sync receiver (such as a terminal, or more generally a user equipment) to regularly adapt the sync source to a possibly changing transmission medium. It should be noted that the above example of 10 seconds for the reselection period is only exemplary, and may be set to a different value, such as 1, 2, 5, or 15 seconds, or any other time period. The reselection timer value can be fixed, or it can also be configurable by a higher layer protocol by a network (node) such as an eNB. The configurability of the timer provides the advantage of adapting the reselection operation to the UE's medium. If the UE is a mobile UE, the variations in channel quality may 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 changing significantly, then it may be beneficial to configure the reselection period to be longer (increase the reselection period).

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

The predetermined hysteresis period may preferably decrease with time. In particular, the hysteresis period can be decreased by increasing the number of times the reselection timer expires.

Reselection can also be triggered when the received signal quality of the current sync source falls below a certain threshold for a period of time. It is preferable to prevent the sudden disappearance of the synchronization source or significant degradation 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 sources and not only based on the reception quality. Accordingly, the UE will select a D2DSS with a higher signal quality. The eNB priority and hop count can be considered an offset for signal quality. If the D2DSS signal quality from the UE outside the network coverage area, such as 630, is not much better than the D2DSS signal quality 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 a user equipment. This wireless device receives different signals from different sources with different corresponding strengths. In particular, the device can receive signals from a network node 810, such as an eNB, or from a wireless user device 820 that is located within the coverage area 810 of the eNB 810, or from a user equipment 830 that is located outside of the network coverage area 801, and in particular eNB 810. The apparatus comprises 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 embodiments. In particular, the sync receiving unit 840 is adapted to receive a sync signal from various D2D sync sources. It can further identify the source based on the received sync signal or at least the type of source. However, this information can also be transmitted later via signaling. The metric acquisition unit 850 is configured to determine or calculate a metric based on which the sync source selector 860 selects a sync source. Upon source selection, device 800 determines (initially) or adjusts (after the initial determination has been made) its timing. In particular, it can take timing as timing for reception purposes, or it can add an offset to it. Then, a transmit timing is obtained, which can be performed based on the received receive timing.

Apparatus 800 can further include a reselection control unit 880 that controls the times at which the apparatus performs reselection. Accordingly, the reselection unit 880 controls the metric acquisition unit 850 and the selection unit 860 to perform from the functions of calculating metrics and selecting a source at specific 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. Receiving signaling from the network may be performed by the signaling receiving unit 890. It should be noted that in this block diagram, the signaling receiving unit 890 and the synchronizing signal receiving unit 840 are drawn separately. This is because they are functional blocks. In general, device 800 will have a common receive edge formed by one or more antennas, amplifiers, demodulators, and decoders (possibly used to receive signaling). Signaling and timing will then be used for different purposes as shown in Figure 8 by the separated blocks 840 and 890.

The signaling receiving unit can also be configured to receive signaling with settings for determining indicators. For example, settings for the weights a, b, c and / or for shifting the selection bias and / or the premium or penalty value may be received and provided to the metric acquisition unit 850. Moreover, the hysteresis timer 865 can be part of the device and can be used by the reselection control unit 880 to control the clock source unit 860 to change or not change the clock source if the select unit 860, based on the metrics determined in 850, selects a new clock source. those. a sync source other than the currently applied sync source. The hysteresis timer 865 may also be configured by signaling received from the network by the signaling receiving unit 890. Figure 9 illustrates a method for performing timing source selection in a system as described above. In particular, such a synchronization receiving 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 timing signals may already carry some information such as the type of source or the number of hops. However, this information can also be transmitted in other ways. The method then comprises the step of determining 930 a selection metric for each of the synchronization sources based on at least two of: the quality of the received synchronization signal; source type (whether the sync source carries a sync signal originating from a network node or independent of a network node); and the number of hops to the network node. In the next step 940 of making a selection of the synchronization source according to the determined indicator, the source is selected, which is then used for the step 950 of determining or adjusting the timing for transmitting or receiving data according to the synchronization signal of the selected synchronization source.

The metric is preferably defined as a combination of: the quality of the received sync signal and the selection offset determined based on the number of hops and / or based on the type of sync source, which is either a sync source that receives its sync signal from a network node or a wireless device independent of networks. The selection offset may be determined according to the association between the predetermined selection offset values and the corresponding number of hops, such as a lookup table. The selection bias can, in particular, be defined as one of: a value that is greater for 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 as the number of hops between the network node and the sync receiving device increases when the number of hops is counted up from the network node; or a value that increases with an increase in the number of hops between the network node and the sync receiving device when the number of hops is counted downward starting from the network node with a predetermined maximum hop. Alternatively, the selection offset may be determined by receiving it within the signaling information transmitted from the corresponding timing source. The present invention is not limited to the definition of the metric as described above, and in general, the metric can also be defined as a linear combination of the quality of the received sync signal; a number representing whether the synchronization source is a network node or a wireless device; and the number of hops to the network node. Such a linear combination is preferably defined as M = a × T + b × H + c × Q, where T is the synchronization source, H is the number of hops, and Q is the received signal quality; and a, b and c are weighting factors. At least one of the weighting factors a, b or c may be determined by receiving it within signaling information transmitted from the network node.

The method may further comprise step 920 of preselecting timing sources by excluding from the set of possible timing sources: sources with a hop number to the network node that exceeds a predetermined hop threshold and / or sources with a signal quality not exceeding a predetermined quality threshold ... Then, the metric is determined only for the timing sources in the set of possible timing sources after the preselection made by the timing source selection unit.

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

The method may also further comprise maintaining a hysteresis timer that starts after a new clock source is selected and expires after a predetermined hysteresis period, with the reselection timer set to a predetermined time period. The method then preferably includes the step of commanding to determine the metric and for performing selection of the timing source according to the metric after the reselection timer expires if the hysteresis timer has expired, and for not performing the timing source selection according to the metric after the reselection timer expires. selection if the hysteresis timer has not expired.

The explanations provided in the "Technical Environment" section above are intended to provide a better understanding of the specific exemplary embodiments described herein, and should not be understood as limiting the invention to the described specific implementations of processes and functions in a mobile communication network, such as a network compliant 3GPP standards. However, the improvements proposed herein can be readily applied to the architectures / systems described in the Technical Environment section, and may, in some embodiments, also use the standard and improved procedures of those architectures / systems. A person skilled in the art will understand that numerous variations and / or modifications can be made to the present invention as shown in specific embodiments without departing from the spirit and scope of the present invention as broadly described.

Another embodiment of the present invention relates to the implementation of the above-described various embodiments using hardware and software. It is understood that various embodiments of the present invention may be implemented or performed using computing devices (processors). The computing device or processor may be, for example, general-purpose processors, digital signal processing (DSP) processors, application-specific 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 implemented 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. Program modules can be stored on any kind of computer-readable media, for example, RAM, EPROM, EEPROM, flash memory, registers, hard disks, CD-ROMs, DVDs, 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 hops from base station, and which additionally include sources that do not determine their sync signal from the network. The selection of the synchronization source is performed by selecting the source with the most reliable synchronization signal based on the metric calculated for each of the considered sources. In particular, the metric is based on the type of source, the number of hops between the network and the source, and / or the quality of the received signal. After making a source selection, the device clocking is adapted accordingly.

Claims (15)

1. Integrated circuit, which, in action, controls the process of operation of the user equipment, the process contains the stages at which: receive a synchronization signal from a synchronization source; measure the quality of the received synchronization signal; determine the timing source as a possible timing source when the measured quality exceeds a certain threshold; a user equipment (UE) timing reference is selected from a possible timing source in accordance with the following priority order: a possible synchronization source is in the area of the highest measured quality result; the synchronization signal of the possible synchronization source is network oriented with the highest measured quality result; a possible synchronization source is outside the zone of the highest result of the measured quality and the synchronization signal, as a result, is independent in the network from the highest result of the measured quality; and adjusting the timing for transmitting or receiving data in accordance with the synchronization signal of the selected UE timing reference. 2. The integrated circuit of claim 1, wherein the process of operating the user equipment comprises transmitting a synchronization signal generated in the user equipment when the process detects a user equipment that is out of range and a possible synchronization source has not been identified. 3. The integrated circuit of claim 1, wherein the process determines whether the received timing signal is network oriented or network independent based on the received timing signal. 4. The integrated circuit of claim 1, wherein the process determines the quality of the received synchronization signal based on the received power and a determined threshold, which is hysteresis. 5. The integrated circuit of claim 1, wherein the process adjusts clocking for transmission or reception at each specified period. 6. The integrated circuit of claim 1, wherein the defined threshold is preconfigured in the user equipment. 7. The integrated circuit of claim 1, wherein the process uses a different defined threshold that is different from the defined threshold used to select a candidate timing source.

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