BR112016009716B1 - TRANSMITTER AND METHOD FOR GENERATING A SYNCHRONIZATION SIGNAL, APPARATUS, RECEIVER AND METHOD FOR DETECTING A SYNCHRONIZATION SIGNAL - Google Patents

Abstract

"TRANSMITTER AND METHOD FOR GENERATING A SYNCHRONIZATION SIGNAL, APPARATUS, RECEIVER AND METHOD FOR DETECTING A SYNCHRONIZATION SIGNAL". A transmitter (110) and a method thereof, configured to generate a timing signal for Device-to-Device (D2D) communication using a Single Carrier Frequency Division Multiple Access (SC-FDMA) waveform, in which a synchronization sequence is modulating a set of subcarriers. The transmitter (110) comprises: a processor (520), configured to determine a synchronization sequence du[l], where |du[l] = |du[L - 1 - l], l = 0.1, .. ., L - 1, and |du[l] | = K for a positive constant K where u is a root index, and L is the length of the synchronization sequence du [l]; and also configured to select the root index u from a set of root indexes; and, in addition, configured to generate the synchronization signal, based on the given synchronization sequence du [l] and the selected root index u. Also, a receiver (120) configured to detect a received synchronization signal for D2D communications using an SC-FDMA waveform is disclosed.

Description

TECHNICAL FIELD

[001] The implementations described here generally relate to a transmitter, a method on a transmitter, and a receiver. In particular, a mechanism is described herein for generating a timing signal for Device-to-Device (D2D) communication using a Single Carrier Frequency Division Multiple Access, (SC-FDMA) waveform.

BACKGROUND

[002] A mobile terminal, also known as a User Equipment (UE), wireless terminal, and/or mobile station, is capable of communicating wirelessly in a wireless communication network, sometimes also referred to as a cellular radiocommunication system. Communication can be done, for example, between two mobile terminals, between a mobile terminal and a wired telephone, and/or between a mobile terminal and a server, via a Radio Access Network (RAN), and possibly , one or more core networks. Wireless communication can comprise various communication services such as voice, messaging, packet data, video, broadcasting, etc.

[003] The mobile terminal may additionally be referred to as a mobile phone, cell phone, tablet computer, or laptop, with wireless capability, etc. The mobile terminal in the present context can be, for example, portable, storable in the pocket, held in the hand, understood in the computer, or mobile terminals mounted in a vehicle, able to communicate by voice and/or data, via the access network of radio, with another entity, such as another mobile terminal, a stationary entity, or a server.

[004] The wireless communication network covers a geographic area that is divided into cell areas, with each cell area being served by a radio network node or base station, for example, a Radio Base Station (RBS) or Base Transceiver Station (BTS), which in some networks may be referred to as "eNB", "eNodeB", "NodeB" or "node B", depending on the technology and/or terminology used.

[005] Sometimes the term "cell" may be used to denote the radio network node itself. However, cell can also in normal terminology be used for the graphical area where radio coverage is provided by the radio network node to a base station location. A radio network node, located at the base station location, can serve one or several cells. Radio network nodes can communicate over the air interface operating on radio frequencies with any mobile station within range of the respective radio network node.

[006] In some radio access networks, several radio network nodes can be connected, for example, by landlines or microwaves, to a Radio Network Controller (RNC), for example, in Telecommunications System Universal Furniture (UMTS). The RNC, also sometimes called the Base Station Controller (BSC), for example in GSM, can supervise and coordinate various activities of the plural radio network nodes connected to them. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).

[007] In the Long Term Evolution (LTE) of 3rd Generation Partnership Project (3GPP), radio network nodes, which may be referred to as eNodeBs or eNBs, may be connected to an input, for example, an input radio access to one or more core networks. LTE is based on GSM/EDGE and UMTS/HSPA network technologies, increasing capacity and speed by using a different radio interface along with base network enhancements.

[008] LTE-Advanced, i.e., LTE Release10 and later releases are tuned to provide higher bitrates in a cost efficient manner while fully fulfilling the requirements set by the International Telecommunication Union (ITU) for the International Mobile Telecommunications (IMT)-Advanced, sometimes also referred to as 4G (short for "fourth generation").

[009] Emergency communications cannot only occur in infrastructure of cellular systems, such as, for example, the LTE system, as it may be out of function, as in cases of earthquakes, tsunamis, snowstorms , hurricanes, etc. In some areas, there is no cellular system coverage at all. Therefore, there is currently an ongoing standardization operation to specify technical solutions that would allow LTE terminals, or mobile terminals, to communicate directly with each other, and even possibly send information from a single terminal, via another terminal, or multiple other terminals. Direct communication between terminals, also known as Device-to-Device (D2D) communication, must be possible both with and/or without the presence of LTE cellular infrastructure. In other words, such privately owned devices are supposed to form a backup, ad hoc communication network in disasters when the existing communication infrastructure is not working, or there is no cellular coverage to begin with. For public safety applications, broadcast communications can be used, ie the same information can be received by a number of D2D users.

[0010] An additional application is that a mobile terminal in the vicinity of other mobile or stationary terminals must be able to discover such terminals and then be able to establish D2D communication. The discovery mechanism may also be applicable to commercial applications where a D2D user may obtain direct communications with close friends, or be used for advertising. Thus, such discovery can occur even if the terminals are under the coverage of an LTE system, i.e. independently of the LTE system.

[0011] In order to establish initial contact, each mobile terminal must be able to transmit and receive D2D Synchronization Signals (D2DSS), which can serve in the receiver, for example, both as discovery signals, and as a tool for establish time and frequency synchronization with the transmitting mobile terminal. The basic signal property of a D2DSS is that it must provide a pulse-like aperiodic autocorrelation function in order to provide reliable detection at the receiver. It should also be possible to detect D2DSS with low complexity with a corresponding matched filter in the receiver. As there may be a number of concurrent D2F communication links in a preferably small geographic area, multiple D2DSSs with low cross-correlation must be available, which can be selected, for example, randomly, based on signal measurements, or by any pre-defined rules. defined, by mobile terminals, so that even in case of signal collisions at the receiver, there is a chance that a D2DSS can be reliably detected.

[0012] In the present context, the terms downlink, downstream link, or forward link, may be used for the transmission path from the radio network node to the mobile terminal. The expression uplink, uplink, or reverse link may be used for the transmission path in the opposite direction, i.e., from the mobile terminal to the radio network node.

[0013] In one example, D2D communications can be specified on the uplink (UL) resources, that is, on the UL bearer for Frequency Division Duplexing (FDD), or on UL substructures for Frequency Division Duplexing Time (TDD). In the latter case, a mobile terminal that is connected, or is connecting to the LTE network, may receive a D2DSS sent from another mobile terminal that is not synchronized to, or located within the coverage of the LTE network, while receiving signals from synchronization sent on the downlink (DL) from the radio network node. D2DSS must therefore be clearly distinguishable from all LTE DL sync signals.

[0014] In order to minimize the complexity of LTE terminals supporting D2D communication, it is clear that the basic D2D transmission method should be the same as, or in LTE DL, which is Orthogonal Frequency Division Multiplexing (OFDM ), or as in LTE UL, which is Single Carrier Frequency Division Multiple Access (SC-FDMA). It can be assumed that future LTE D2D and D2DSS communications can operate either in the LTE FDD UL bands or in UL substructures in TDD mode. SC-FDMA and OFDM are technically both OFDM signals; however, SC-FDMA uses a subcarrier change ^, and allows modulation of all subcarriers, in contrast to OFDM, which uses an unmodulated DC subcarrier, in which the frequency would be equal to the RF center frequency of the node. of radio network.

[0015] There are two key aspects that govern the design of the Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in Rel-8, which should also be highly prioritized for a D2DSS: detection performance and receiver complexity.

[0016] The detection performance depends on the amount of resources allocated to the synchronization signal, as well as the characteristics of the signals, for example, cross correlations.

[0017] The receiver typically performs matching filtering to detect the PSS. The complexity of the receiver depends on the ability to utilize certain signal properties, mainly to reduce the number of complex-valued multiplications in the receiver. PSS has a central time-domain symmetry, i.e. a signal value appears up to twice in an OFDM symbol which allows reducing the number of multiplications by ~50% by performing symmetric sample addition before multiplication with the replica sample. There are three different PSSs, which are obtained from three different modulation sequences (ie PSS sequences). Furthermore, two of the PSS sequences constitute a complex-conjugate sequence pair, and due to the central time-domain symmetry, they also become a complex-conjugate signal pair, which makes it possible to detect both PSSs with the same complexity of signal. multiplication as detecting the PSS. SSS is based on m-sequences, for which Fast Hadamard Transforms can be used in the detector. It has been observed that the cell scanner contributes to 10-15% of the total baseband cost of the LTE modem. It is therefore crucial that a D2DSS will support low complex receiver implementations and that, as far as possible, existing PSS/SSS detector implementations can be reused.

[0018] D2DSS transmitted in LTE TDD mode and existing PSS transmitted from a radio network node, or eNodeB, may give rise to mutual interference. For example, as illustrated in Figure 1a, an old mobile terminal may try to detect the PSS of the radio network node of the LTE system, for example, for cell selection, while not being able to succeed in accessing a cell if the D2D terminals in its vicinity transmit a D2DSS having a strong cross-correlation with the PSS, see Figure 1a. In this situation, the old terminal has no prior synchronization to the radio network node, and will search PSS also in UL subframes, on which D2DSS can be transmitted.

[0019] In another example illustrated in Figure 1b, a D2D terminal located outside the LTE network coverage will not be able to access any cell, but may occasionally still receive the LTE, PSS/SSS synchronization signals, see Figure 1b. These signals would constitute interference while trying to detect the D2DSS. In this situation, the D2D terminal has no synchronization to the radio network node, and the PSS can be detected in substructures, in which the D2DSS can be received.

[0020] Even if LTE PSS and D2DSS used different waveforms, it can be shown that the cross-correlation between LTE PSS (based on OFDM waveforms) and a D2DSS obtained from modulated SC-FDMA waveform with the same PSS sequence, exhibits two strong cross-correlation peaks, corresponding to about 50% of the signal energy. Furthermore, the peak cross-correlation is more than 50% higher than a maximum autocorrelation sidelobe of D2DSS. Table 1 gives an example of correlation values when D2DSS is using the same modulation sequence as for PSS, but is using the SC-FDMA waveform. The term radix index refers to a parameter in the modulation sequence definition, and different radix indices result in different sequences. Table 1

[0021] Such interference levels are not desirable, as the maximum cross-correlation may not be significantly higher than the maximum autocorrelation sidelobe, in order to be able to maintain the same detection limit at the measured receiver than if there was no interference, i.e. as in an Additive White Gaussian Noise (AWGN) channel. With these cross-correlation peaks, the detection limit has to be increased in order to preserve the target false alarm rate, which will cause the probability of detection to be decreased.

[0022] The LTE PSS sequence is chosen and mapped to the subcarriers in such a way that the resulting PSS is centrally symmetric in the time domain. PSS is generated as an OFDM signal, where the DC subcarrier, i.e. frequency ; = -1, it is unmodulated. A distinct form of the signal can be represented by: for In order to obtain central symmetry in the time domain, that is, , the PSS is mapped to the subcarriers, so the following relationship maintains the Fourier coefficients

[0023] The central symmetry of N-2 PSS samples can be used to reduce the number of multiplications in the corresponding matched filter. For example, if the PSS has N samples length, it can be shown that there are N-2 centrally symmetric samples in the PSS signal, i.e. there are (N-2)/2 unique sample values and additionally 2 samples, which cannot be equal to any other sample. Thus, by performing addition of the symmetrical samples before multiplication with the replica symbol, the matched filter can be implemented by (N-2)/2+2 multiplications by simple correlation, which is about a 50% reduction, compared to direct implementation which requires N multiplications, ie one multiplication per input sample. An example of an LTE receiver for PSS is illustrated in Figure 1c, where "*" denotes complex conjugation, and are the PSS values with root index u.

[0024] Figure 1c, therefore, illustrates an efficient matched filter for PSS signal detection using N samples. Furthermore, three different PSSs are defined in LTE, which are obtained from three different PSS sequences. Two of the sequences constitute a complex conjugate version of each other. That is, there are two root indices u and v that generate PSS sequences, so the resulting PSSs are related by . Therefore, since a complex conjugate only implies a sign change to the imaginary part of the received sample, it is possible to detect both these PSSs with the multiplication complexity of only one of the sequences. That is, no extra multiplications are needed to compute the conjugate signal correlation, ie a 50% complexity reduction. Central symmetry is preserved for any u-root index value, allowing to have only a single matched filter structure, with fixed connections between hardware elements, which can thus be reused for detecting signals other than D2DSS per change replica signal only.

[0025] The centrally symmetric PSS is obtained from the LTE PSS sequence generated from a frequency domain Zadoff-Chu sequence of length 63 according to: where is referred to as a set of root indexes. The sequence must be mapped to feature elements according to:

[0026] The continuous time low pass signal in the antenna hole in the OFDM symbol in a downlink crack is defined by: for where It is is the resource element content in the antenna hole . The variable N is equal to 2048 for for subcarrier spacing, and 4096 for subcarrier spacing. The entities are further defined in the LTE specifications.

[0027] The waveform of SC-FDMA is in LTE, so the continuous low-pass signal to the antenna hole on the SC-FDMA symbol in an uplink crack is defined by: for where . the variable equals 2048 for of subcarrier spacing, and is the resource element content in the antenna hole . The entities and are further defined in the LTE specifications.

[0028] In the context of this disclosure, an SC-FDMA waveform refers to a multi-carrier signal without any unmodulated DC subcarrier, and where the subcarriers are allocated half a subcarrier apart with respect to the DC frequency .

SUMMARY

[0029] It is therefore an objective to obviate at least some of the aforementioned disadvantages, and by enabling a mobile terminal to generate a synchronization signal, which enables a mobile receiving station to detect the transmitter, without causing interference with other synchronization signals, or at least reduce such interference.

[0030] These and other objectives are achieved by the characteristics of the attached independent claims. Additional implementation forms are apparent from the dependent claims, the description and the figures.

[0031] In order to avoid the above problems, it is disclosed here to design new synchronization sequences for D2DSS using the SC-FDMA waveform, while at the same time exhibiting signal symmetry that allows for efficient receiver implementation.

[0032] According to a first aspect, a transmitter is provided, configured to generate a synchronization signal for Device-to-Device (D2D) communications using a Carrier Frequency Division Multiple Access waveform Single (SC-FDMA), in which a sync sequence is modulating a set of subcarriers. The transmitter comprises a processor, configured to determine a synchronization sequence, where for a positive constant K , where u is a root index, and L is the length of the synchronization sequence. The processor is also configured to select the root index u from a set of root indices. In addition, the processor is configured to generate the synchronization signal, based on the given synchronization sequence and the selected root index u.

[0033] Thereby, timely and efficient synchronization signal detection is enabled, with interference eliminated or at least reduced with other synchronization signals, such as, for example, PSS and/or SSS.

[0034] In a first possible implementation of the transmitter, according to a first aspect, the processor can be additionally configured to determine the synchronization sequence, so that

[0035] In this way, an alternative implementation of the synchronization sequence is presented, having low interference with other signaling, while placing low requests on the receiver for its implementation.

[0036] In a second possible implementation of the transmitter according to the first aspect, or the first possible implementation of the first aspect, the processor can be further configured to obtain a centrally anti-symmetric D2D synchronization sequence of uniform length from a sequence of centrally symmetric D2D synchronization of uniform length by multiplying the elements of one half of the synchronization sequence by -1.

[0037] Thus, an alternative implementation is presented. One advantage of using a centrally antisymmetric signal is that it has a very low cross-correlation with a centrally symmetric signal. Consequently, when the signals are time-aligned, if the D2DSS is centrally antisymmetric, it may have low cross-correlation with the LTE PSS, which is centrally symmetric.

[0038] In a third possible implementation of the transmitter according to the first aspect, or any of the previous implementations of the first aspect, the processor can be configured to determine the synchronization sequence, so that: and also configured to select the root index to an integer other than 25, 29 and 34.

[0039] An advantage according to such an implementation is that interference with any PSS signal can be avoided or reduced by selecting different root index than that used in PSS signaling.

[0040] In a fourth possible implementation of the transmitter according to the first aspect, or any of the previous implementations of the first aspect, the processor can be configured to determine the synchronization sequence by selecting a Zadoff-Chu sequence of length odd, and removing an odd number of elements from the selected Zadoff-Chu sequence, to obtain a synchronization sequence of uniform length.

[0041] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0042] In a fifth possible implementation of the transmitter according to the first aspect, or any of the previous implementations, the processor can be configured to determine the synchronization sequence by selecting a Zadoff-Chu sequence of uniform length , extending the selected Zadoff-Chu sequence by one element, and removing a central element from the extended Zadoff-Chu sequence.

[0043] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0044] In a sixth possible implementation of the transmitter according to the first aspect, or any of the previous implementations, the processor can be configured to determine the synchronization sequence, so that

[0045] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0046] In a seventh possible implementation of the transmitter according to the first aspect, or any of the previous implementations, the processor can be configured to map the synchronization sequence to the resource elements of the SC-FDMA signal, so that for the Fourier coefficients where N is an integer not less than ..

[0047] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0048] In an eighth possible implementation of the transmitter according to the first aspect, or any of the previous implementations, the processor can be configured to map the synchronization sequence to the resource elements of the SC-FDMA signal, so that for the Fourier coefficients:

[0049] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0050] In a ninth possible implementation of the transmitter according to the first aspect, or any of the previous possible implementations, the processor can be configured to map the synchronization sequence to the resource elements of the SC-FDMA signal, so that for the Fourier coefficients:

[0051] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0052] In a tenth possible implementation of the transmitter according to the first aspect, or any of the previous possible implementations, the processor can be configured to select the root index from the set of root indices, either randomly, or by deriving it from one or more parameters internal to the transmitter.

[0053] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0054] In an eleventh possible implementation of the transmitter according to the first aspect, or any of the previous possible implementations, the processor may be configured to select the root index from the set of root indices based on information received from a server radio network node, or based on a received signal; and/or select the root index from a first set of root indices when receiving a sync signal from another D2D transmitter being synced to a cell, and from a second set of root indices when receiving a sync signal from another D2D transmitter not being synced to a cell; and/or by selecting the same, or a different, root index - as used in a received sync signal; and/or, when the synchronization signal is transmitted over multiple hops between network nodes that select the root index from the set of root indices based on the number of hops of the received sync signal.

[0055] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0056] According to a second aspect, a method is provided for use in a transmitter. The method aims to generate a synchronization signal for D2D communications using an SC-FDMA waveform, in which a synchronization sequence is modulating a set of subcarriers. The method comprises determining a synchronization sequence, where positive amount k, where u is a root index, and L is the length of the synchronization sequence. Also, the method comprises selecting the root index from a set of root indexes. Additionally, the method further comprises generating the synchronization signal, based on the determined synchronization sequence and the selected root index u.

[0057] Thereby, timely and efficient synchronization signal detection is enabled, with interference eliminated or at least reduced with other synchronization signals, such as, for example, PSS and/or SSS.

[0058] In a first possible implementation of the method according to the second aspect, the method may also comprise determining the synchronization sequence so that

[0059] In this way, an alternative implementation of the synchronization sequence is presented, having low interference with other signaling, while placing low requests on the receiver for its implementation.

[0060] In a second possible implementation of the method according to the second aspect, or the first possible implementation, a centrally antisymmetric D2D synchronization sequence of uniform length can be obtained from a centrally symmetric D2D synchronization sequence of uniform length by Multiplication of the elements of one of the halves of the synchronization sequence by -1.

[0061] Thus, an alternative implementation is presented. One advantage of using a centrally antisymmetric signal is that it has very low cross-correlation with a centrally symmetric signal. Consequently, when the signals are time-aligned, if D2DSS is centrally antisymmetric, it may have low cross-correlation with LTE PSS, which is centrally symmetric.

[0062] In a third possible implementation of the method according to the second aspect, or any of the previous implementations of the first aspect, the synchronization sequence can be determined, so that: and also configured to select the root index - to an integer other than 25, 29 and 34.

[0063] An advantage according to such an implementation is that interference with any PSS signal can be avoided or reduced by selecting a different root index than that used in the PSS signaling.

[0064] In a fourth possible implementation of the method according to the second aspect, or any of the previous implementations of the second aspect, the synchronization sequence can be determined by selecting a Zadoff-Chu sequence of odd length, and removing an odd number of elements from the selected Zadoff-Chu sequence to obtain a synchronization sequence of uniform length.

[0065] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0066] In a fifth possible implementation of the method according to the second aspect, or any of the previous implementations, the synchronization sequence can be determined by selecting a Zadoff-Chu sequence of uniform length, extending the selected sequence of Zadoff-Chu by an element, and removal of a core element from the extended Zadoff-Chu sequence.

[0067] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0068] In a sixth possible implementation of the method according to the second aspect, or any of the preceding implementations, the synchronization sequence can be determined such that L uniformly : and

[0069] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0070] In a seventh possible implementation of the method according to the second aspect, or any of the previous implementations, the synchronization sequence can be mapped to the resource elements of the SC-FDMA Signal, so that for the Fourier coefficients : , where is an integer, not less than L.

[0071] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0072] In an eighth possible implementation of the method according to the second aspect, or any of the previous implementations, the synchronization sequence can be mapped to the resource elements of the SC-FDMA signal, so that for the coefficients of Fourier:

[0073] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0074] In a ninth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the synchronization sequence can be mapped to the resource elements of the SC-FDMA signal, so that for the coefficients -Fourier entities:

[0075] In this way, an efficient and yet easily implemented synchronization signal is achieved.

[0076] In a tenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the root index u may be randomly selected from a set of root indices.

[0077] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0078] In an eleventh possible implementation of the method according to the second aspect, or any of the previous possible implementations, the root index u can be selected from the set of root indices by deriving it from one or more parameters internal to the transmitter.

[0079] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0080] In a twelfth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the root index u may be selected from the set of root indices, based on information received from a server radio network node.

[0081] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0082] In a thirteenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the root index may be selected from the set of root indices based on a received signal.

[0083] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0084] In a fourteenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the root index can be selected from a first set of root indices upon receipt of a synchronization signal from another cell-synchronized D2D transmitter, and from a second set of root indices upon receipt of a synchronizing signal from a cell-unsynchronized D2D transmitter.

[0085] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0086] In a fifteenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the same root index u may be selected as used in a received synchronization signal.

[0087] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0088] In a fifteenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, a different root u index may be selected as used in a received synchronization signal.

[0089] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0090] In a sixteenth possible implementation of the method according to the second aspect, or any of the previous possible implementations, the synchronization signal can be transmitted over multiple hops between network nodes, and in which the root index can be selected from the set of root indices based on the number of hops of the received sync signal.

[0091] An advantage of this implementation comprises increased flexibility in root index selection in the sync signal.

[0092] According to a further aspect, a computer program comprising program code for performing a method on a transmitter, according to the second aspect, or any implementation of the second aspect, is provided for generating a synchronization signal for D2D communications using an SC-FDMA waveform, in which a synchronization sequence is modulating a set of subcarriers, when the computer program is loaded into a processor of the transmitter, according to the first aspect, or any implementation of the first aspect.

[0093] Thereby, timely and efficient synchronization signal detection is enabled, with eliminated or at least reduced interference with other synchronization signals, such as, for example, PSS and/or SSS.

[0094] According to a still further aspect, a computer program product comprising a computer readable storage medium that stores program code therein for generating a synchronization signal for D2D communications using a waveform of SC-FDMA, in which a sync sequence is modulating a set of subcarriers. Program code comprising instructions for executing a method comprising determining a synchronization sequence, where , for a positive constant K, where u is a root index, and L is the length of the synchronization sequence; root index selection from the set of root indexes; and generating the sync signal based on the determined sync sequence and the selected u-root index.

[0095] Thereby, timely and efficient synchronization signal detection is enabled, with eliminated or at least reduced interference with other synchronization signals, such as, for example, PSS and/or SSS.

[0096] According to a further aspect, a receiver configured to detect a synchronization signal received for D2D communications using an SC-FDMA waveform, in which a synchronization sequence is modulating a set of subcarriers , is provided. The receiver comprises a processor, configured to detect the synchronization signal comprising a synchronization sequence, where for a positive constant K, where u is a root index, and L is the length of the synchronization sequence.

[0097] Thereby, timely and efficient synchronization signal detection is enabled, with eliminated or at least reduced interference with other synchronization signals, such as, for example, PSS and/or SSS.

[0098] Other objectives, advantages and new features of the aspects described will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Various embodiments are described in more detail with reference to the attached drawings, illustrating various examples of embodiments in which:

[00100] Figure 1a is a block diagram illustrating a conventional wireless communication network.

[00101] Figure 1b is a block diagram illustrating a conventional wireless communication network.

[00102] Figure 1c is a block diagram illustrating a conventional transmitter.

[00103] Figure 2a is a block diagram illustrating a wireless communication network in one embodiment.

[00104] Figure 2b is a block diagram illustrating a transmitter and a receiver in one embodiment.

[00105] Figure 2c is a block diagram illustrating a transmitter, a receiver, and a network node in one embodiment.

[00106] Figure 3 is a block diagram illustrating a transmitter according to an embodiment.

[00107] Figure 4 is a flowchart illustrating a method on a transmitter according to an embodiment.

[00108] Figure 5 is a block diagram illustrating a transmitter according to an embodiment.

[00109] Figure 6 is a block diagram illustrating a receiver according to an embodiment.

DETAILED DESCRIPTION

[00110] The embodiments of the invention described herein are defined as a transmitter, a method in a transmitter, and a receiver, which can be put into practice in the embodiments described below. These embodiments can, however, be exemplified and embodied in many different ways, and are not to be limited to the examples set forth herein; preferably, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

[00111] Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are intended for the purpose of illustration only, and not as a definition of the limits of the embodiments disclosed herein, to which reference is to be made to the appended claims. Additionally, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

[00112] Figure 2a is a schematic illustration of a wireless communication network 100 comprising a transmitter 110, a receiver 120, and a radio network node 130. The transmitter 110 and/or the receiver 120 may be mobile terminals, which can be served by the radio network node 130, thereby being connected to the wireless communication network 100.

[00113] The wireless communication network 100 may, at least partially, be based on radio access technologies, such as, for example, 3GPP LTE, LTE-Advanced, Evolved Universal Terrestrial Radio Access Network (E- UTRAN), Universal Mobile Telecommunications System (UMTS), Global System for Mobile Communications (originally: Groupe Spécial Mobile) (GSM)/ Enhanced Data rate for GSM Evolution (GSM/ EDGE), Wideband Code Division Multiple Access (WCDMA) ), Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, Worldwide Interoperability for Microwave Access (WiMax) , or Ultra Mobile Broadband (UMB), High Speed Packet Access (HSPA) Evolved Universal Terrestrial Radio Access (E-UTRA), Universal Terrestrial Radio Access (UTRA), GSM EDGE Radio Access Network (GERAN), 3GPP2 CDMA, for example, CDMA2000 1x RTT and High Rate Packet Data (HRPD), just to name a few options. The terms "wireless communication network", "wireless communication system", and/or "cellular communication system" may, within the technology context of this disclosure, sometimes be used interchangeably. interchangeably.

[00114] The wireless communication network 100 can be configured to operate according to the principle of Time Division Duplex (TDD) and/or Frequency Division Duplex (FDD), according to different embodiments.

[00115] TDD is a time division multiplexing application to separate uplink and downlink signals in time, possibly with a Protection Period (GP) located in the time domain between the uplink and downlink signaling. downlink. FDD means that the transmitter and receiver operate on different carrier frequencies.

[00116] The purpose of the illustration in Figure 2a is to provide a simplified overview of the wireless communication network 100 and the methods and nodes involved, such as the transmitter 110, the receiver 120, and the radio network node 130, here described, and the functionalities involved. The method, transmitter 110, receiver 120, and radio network node 130 will subsequently, as a non-limiting example, be described in a 3GPP LTE/LTE-Advanced environment. However, the disclosed embodiments can operate on a wireless communication network 100 based on other access technology, such as, for example, any of those already enumerated above. Thus, although embodiments of the invention are described based on, and using the jargon of, 3GPP LTE systems, they are not limited to 3GPP LTE. Additionally, the terms radio network node, network node, base station, and cell may be used interchangeably in the following.

[00117] The illustrated transmitter 110 in the wireless communication network 100 can send synchronization signals to be received by the receiver 120.

[00118] Figure 2b illustrates an example in which the transmitter 110 and the receiver 120 are located outside any wireless communication network 100, that is, LTE network. Transmitter 110 transmits a d2D synchronization signal (D2DSS) to be received by receiver 120.

[00119] Figure 2c further illustrates an embodiment in which multihop is illustrated. Transmitter 110 transmits a D2DSS to be received by receiver 120, via another intermediately located network node 140.

[00120] It is to be noted that the illustrated configurations of Figure 2a, Figure 2b and/or Figure 2c, of an example transmitter 110, an example receiver 120, and possibly a radio network node 130, or other network node 140, in Figure 2a, Figure 2b and/or Figure 2c, are to be related as non-limiting examples of embodiments only. The wireless communication network 100 may comprise any other number and/or combination of the discussed entities 110, 120, 130, 140. A plurality of transmitters 110, receivers 120, other network nodes 140, and other configuration of network nodes from radio 130, may thus be involved in some embodiments of the disclosed invention. Thus, for example, when reference is made here to multi-hop over another network node 140, the other network node 140 may comprise a set of a plurality of other network nodes 140, according to some embodiments.

[00121] Thus whenever "a" transmitter 110, receiver 120, another network node 140, and/or radio network node 130, is referred to in the present context, a plurality of transmitter 110, receiver 120, another radio node network 140, and/or radio network node 130, may be involved, according to some embodiments.

[00122] The transmitter 110, the receiver 120, and/or the other network node 140, can correspondingly be represented by, for example, a wireless communication terminal, a mobile cell phone, a Personal Digital Assistant (PDA), a wireless platform, a mobile station, a user equipment, a tablet computer, a portable communication device, a laptop, a computer, a wireless terminal that acts as a relay, a relay node, a relay mobile, a Customer Premises Equipment (CPE), a Fixed Wireless Access (FWA) node, or any other type of device configured to communicate wirelessly with each other by direct communication and possibly also with the radio network node 130 , according to different embodiments and different vocabulary.

[00123] Additionally, the radio network node 130 and/or the other network node 140, according to some embodiments, may be configured for downlink transmission and uplink reception, and may be referred to, respectively, such as a Base Station, a NodeB, an Evolved Node Bs (eNB, or eNode B), a Base Transceiver Station, an Access Point Base Station, a Base Station Router, a Base Station radio base station (RBS), a micro base station, a pico base station, the femto base station, a Home eNodeB, a sensor, a beacon device, a relay node, a repeater, or any other network node configured to communicate with mobile stations within cell coverage over a wireless interface, depending, for example, on the radio access technology and/or terminology used.

[00124] Some embodiments of the invention can define a modular implementation approach, and make it possible to reuse old systems, such as, for example, patterns, algorithms, implementations, components, and products.

[00125] The waveform of SC-FDMA without a cyclic prefix can be defined by: for . According to the LTE standard, , consequently it is possible to define: It is

[00126] The sampled version is obtained by setting which gives (comprising a normalized factor ), an equivalent low-pass signal: for where is a Fourier coefficient at the frequency A cyclic prefix can be inserted into the representation. Since and defining an alternative representation (still without cyclic prefix) is:

[00127] Then, from the definition of the SC-FDMA signal, conditions for obtaining a centrally symmetric signal for n = 1, ...,N can be deduced from:

[00128] This relationship can be used to identify requirements in the Fourier coefficients in order to obtain certain symmetries in the signal. It is therefore understood that:

[00129] If then

[00130] If then

[00131] A property can be referred to as a centrally antisymmetric signal.

[00132] A property can be referred to as a centrally symmetric signal.

[00133] An advantage of using a centrally antisymmetric signal is that it has very low cross-correlation with a centrally symmetric signal. For example, assume a centrally antisymmetric signal where and a centrally symmetric signal where So when the signals are aligned with time, the cross-correlation becomes which is typically much smaller than the signal energy . Consequently, when the signals are time-aligned, if the D2DSS is centrally antisymmetric, it may have low cross-correlation with the LTE PSS, which is centrally symmetric.

[00134] An embodiment of the invention comprises defining a D2DSS in which the Fourier coefficients are according to

[00135] A first embodiment comprises defining a D2DSS in which the Fourier coefficients are according to

[00136] A second embodiment comprises defining a D2DSS in which the Fourier coefficients are according to

[00137] Figure 3 represents an example of a receiver 120 for a centrally antisymmetric signal, using only .N/2+1 multiplications for an input signal of length N. It can additionally be understood that:

[00138] Therefore, according to the first embodiment, for two different sets of Fourier coefficients where follow that:

[00139] An advantage of this property is that It is can be detected with multiplication complexity of only one of the signals. That is, if a matched filter is assigned to due to the above relationship, no additionally complex valued multiplication can be required for computing a correlation value corresponding to , according to some embodiments.

[00140] Therefore, according to the second embodiment, for two different sets of Fourier coefficients where follow that:

[00141] An advantage of this property is that It is and can be detected with multiplication complexity of only one of the signals. That is, if a matched filter is assigned to , due to the above relationship, no additionally complex valued multiplication is required for computing a correlation value corresponding to

[00142] According to some embodiments, a D2D synchronization sequence is defined based on a sequence where , so that when it is mapped to Fourier coefficients (that is, , any property i) or ii), as defined on page 20, last paragraph, is filled in. Consequently, D2D sequences can be centrally symmetric or antisymmetric, so as to produce centrally antisymmetric or centrally symmetric SC-FDMA D2DSS, respectively.

[00143] In one embodiment, a centrally symmetric sequence exhibits a property where denotes the absolute value.

[00144] In one embodiment, a centrally symmetric sequence exhibits a property

[00145] In one embodiment, a centrally anti-symmetric sequence exhibits a property

[00146] It can be further understood that once the receiver 120 has detected and obtained synchronization from the D2DSS, the synchronization sequence is known to the receiver 120. In this way, the sequence can be used as reference symbols to estimate the channel. This would allow coherent detection of other signals or channels using channel estimates from D2DSS. For secure channel estimation, it is desirable that all reference symbols (ie sequence elements) are using the same transmit energy. It is also beneficial for the transmitter to use the same transmit power as the symbols as it makes less complex power control possible. Consequently, in one embodiment, the synchronization sequence exhibits a property where K is a positive constant.

[00147] When , the remnants Fourier coefficients in some cases (for example, when are uniform), can be set to zero, and property i) or ii) is filled. Furthermore, when at least one of the remaining Fourier coefficients is not set to zero, it may be related to a superposition of a centrally symmetric synchronization signal or centrally antisymmetric synchronization signal (obtained from L Fourier coefficients), and an arbitrary signal (obtained from the remnants Fourier coefficients). In this case, property i) or ii) applies only to the synchronization signal. However, this may not be a problem in practice, as filtering can be done to suppress the signals from the remnants. Fourier coefficients, such that receiver 120 only experiences signals obtained from L Fourier coefficients, in some embodiments.

[00148] In some embodiments, D2D sync sequences of uniform length that are centrally symmetric can be used.

[00149] In some embodiments, D2D synchronization sequences of uniform length that are centrally antisymmetric may be used.

[00150] One embodiment comprises constructing a centrally antisymmetric D2D sync sequence of uniform length from a centrally symmetric D2D sync sequence of uniform length by multiplying the first half or the second half of its elements by -1. For example, if there is a centrally symmetric D2D sync sequence: then a centrally antisymmetric sequence can be defined by: or

[00151] An advantage of this is the lower implementation complexity, as both the radio network node 130 and the transmitter 110 are already capable of generating the centrally symmetric LTE PSS sequence

[00152] One embodiment comprises constructing a uniform length centrally symmetric D2D sync sequence from a uniform length centrally asymmetric D2D sync sequence by multiplying the first half or the second half of its elements by -1.

[00153] In the following embodiments, a number of centrally symmetric sequences are disclosed to give some non-limiting examples of root index sets. The terms "root index" and "index", respectively, are used somewhat interchangeably here. Centrally antisymmetric sequences can be generated from the centrally symmetric sequences disclosed in some embodiments. Performance may depend on the chosen set of root indexes. The set of indices will be known to both transmitter 110 and receiver 120.

[00154] The root index u may be selected by transmitter 110 from a given set of root indices in some embodiments. When transmitter 110 is connected to a cell, radio network node 130 may signal information to transmitter 110, which may explicitly or implicitly indicate which root index u to use. In the latter case, the radio network node 130 can, for example, signal a physical layer identity from which the root index u can be derived. An advantage of root index signaling is that the radio network node 130 can perform coordination between time-frequency resources used for the D2DSS and the root indexes so as to minimize mutual interference in the system. The root index u may also, in some embodiments, be selected without any prior signaling information from network 100. This would be advantageous in order to minimize control signaling in the cell. In one example, transmitter 110 may derive the root index u randomly, or from parameters internal to transmitter 110. Furthermore, transmitter 110 may select the root index u based on other received signals. For example, when transmitter 110 receives a D2DSS from another D2D transmitter that is synchronized to a cell, transmitter 110 may select a root index u from a first set of root indices, whereas when transmitter 110 receives a D2DSS from another D2D transmitter that is not synchronized to a cell, transmitter 110 may select a root index u from a second set of root indices in some embodiments. This is advantageous, as a receiver 120 can then select which D2DSS to sync to, based on information in the sync source, for example, a sync source that has synced to a cell may be more secure. In another example, if transmitter 110 receives a D2DSS, it may select the same root index u as the received D2DSS. Alternatively, if transmitter 110 receives a D2DSS, it may select a different root index u as the received D2DSS. Furthermore, if D2DSS transmissions can be transmitted between network nodes 140, for example, being transmitted over multiple hops, and if transmitter 110 receives a D2DSS, and if it is able to determine how many D2DSS hops have been transmitted, it can select the root index u based on the number of hops. This is advantageous, as the receiver 120 can then select which D2DSS it should synchronise, based on information from the sync source, for example, a D2DSS with fewer hops may be more secure. Root index selection may also comprise a combination of the above examples in some embodiments.

[00155] In one embodiment, the LTE PSS sequence is used as a D2DSS sequence, but with different root indices. Table 2 illustrates the correlation properties for an example where the set of root indices is u ϵ {26,37,38}. Since the sequence is obtained from a punctured Zadoff-Chu sequence of length 63, typically u can be a relatively major (sometimes also referred to as mutually principal or coprincipal/coprincipal) to 63. It can further be understood that if two ue root indices are related by , the sequences constitute a complex conjugate pair, and the corresponding D2DSS signals will exhibit a complex conjugate pair property. Table 2

[00156] The maximum cross-correlation between the D2DSSs generated from the sets of root index u ϵ {26,37,38} is 0.29.

[00157] In one embodiment, Zadoff-Chus sequences of odd length L are used for which the R elements are removed to obtain a sequence of uniform length (eg, length 62). R can be a value no less than 3. A Zadoff-Chu sequence of odd length can be defined as follows, where u is relatively principal for L.

[00158] Since , the same complex-conjugate relationship between root indices It is will exist when the elements have been removed. Consequently, the advantage of being able to detect two D2DSSs with the multiplication complexity of just one D2DSS can be achieved.

[00159] The removal of elements í must ensure that the remaining sequence is centrally symmetric or centrally antisymmetric. In one example, this is achieved by removing the core elements -. It is further understood that such symmetries can be achieved by other removal options, for example, removal of one or several central elements and, additionally, elements at the beginning and at the end of the sequence. In order to preserve good self-correlation and Peak-to-Average-Power-Ratio (PAPR) properties of the Zadoff-Chus sequences, it is desirable that it be as small as possible. If the target length is 62 then it may be beneficial to use L=65 and R=3. Since the sequence is obtained from a punctured Zadoff-Chu sequence of length 65, typically u can be selected as a relatively principal at 65. When two root indices u and v are related by u = 65 - v, the corresponding signal from D2DSS will display a complex conjugate pair property.

[00160] Table 3 illustrates the correlation properties for an example where the set of root indices is u ϵ {22,24,43}. Table 3

[00161] The maximum cross-correlation between the D2DSSs generated from the set of root indices u and{222443} is 0.21.

[00162] In one embodiment, Zadoff-Chus sequences of uniform length L can be used, which are cyclically extended to length L+1, and where the central element is removed. A Zadoff-Chu sequence of uniform length can be defined as follows, where u can be relatively principal for L:

[00163] In addition Consequently, this relationship can be used to determine an association between the D2DSSs corresponding to the indices u and L - u

[00164] The punctured and prolonged sequence can be described as:

[00165] This sequence is centrally symmetric. Table 4 illustrates the correlation properties for an example where L = 62, and the set of root indices is u ϵ {21,29,41}. Table 4

[00166] The maximum cross-correlation between the D2DSSs generated from the set of root indexes

[00167] In one embodiment, the same sequence structure as for the odd-length Zadoff-Chus sequence can be assumed, but then it can be specified a same number of phases and same sequence length. Mathematically, these new sequences can be described as:

[00168] For example, it is possible to assume L = 62. It is noted that this sequence is not a Zadoff-Chu sequence. Table 5 contains the correlation properties for an example where, L = 62, and the set of root indices is u ϵ {25,27,29}. Table 5

[00169] The maximum cross-correlation between the D2DSSs generated from the set of root indices u ϵ {25,27,29} is 0.21.

[00170] Furthermore, some of the embodiments described here can be used in multiuser D2D communications compatible with the LTE system. The D2DSS described here can be transmitted by a D2D-enabled user equipment (UE), or any network node other than an eNodeB within the LTE system.

[00171] Figure 4 is a flowchart illustrating embodiments of a method 400 for use in a transmitter 110, for generating a synchronization signal for D2D communications using an SC-FDMA waveform, in which a synchronization sequence is modulating a set of subcarriers.

[00172] To generate the synchronization signal for D2D communications, the method 400 may comprise a number of actions 401-403. It is however to be noted that any, some or all of the actions described 401-403 may be performed in a somewhat different chronological order than the enumeration indicates, be performed simultaneously, or even be performed in a completely reversed order of time. according to different embodiments. Additionally, it is to be noted that some actions may be performed in a plurality of alternative ways according to different embodiments, and that some such alternative ways may be performed only within some, but not necessarily all, embodiments. Method 400 may comprise the following actions:

Action 401

[00173] A synchronization sequence is determined, where: It is

[00174] for a positive constant K, where u is an index, and L is the length of the synchronization sequence.

[00175] In some embodiments, the synchronization sequence can be determined, so that:

[00176] In some embodiments, a centrally antisymmetric D2D sync sequence of uniform length can be obtained from a centrally symmetric D2D sync sequence of uniform length by multiplying the elements of one half of the sync sequence by -1.

[00177] In some embodiments, the synchronization sequence can be determined, so that:

[00178] In some embodiments, the synchronization sequence can be determined by selecting a Zadoff-Chu sequence of odd length, and removing an odd number of elements from the selected Zadoff-Chu sequence, to obtain a sequence- centrally symmetrical synchronizing line of uniform length.

[00179] However, in some embodiments, the synchronization sequence can be determined by selecting a Zadoff-Chu sequence of uniform length, extending the selected Zadoff-Chu sequence by one element, and removing an element center of the extended Zadoff-Chu sequence.

[00180] The synchronization sequence can, in some additional embodiments, be determined so that:

[00181] Furthermore, according to some embodiments, the synchronization sequence can be mapped to the resource elements of the SC-FDMA signal, so that for the Fourier coefficients: , where N is an integer not less than L.

[00182] However in some such embodiments, , while in some other embodiments,

Action 402

[00183] The root index u is selected from a set of root indexes. In some embodiments, the indices comprised in the set of root indices can be relatively principal with respect to each other.

[00184] The root index u can be selected for an integer other than 25, 29 and 34.

[00185] The root index u may, according to some embodiments, be selected from the set of root indices at random.

[00186] The root index u can additionally be selected from the set of root indices by deriving it from one or more parameters internal to the transmitter 110.

[00187] Additionally, in some embodiments, the root index u can be selected from the set of root indices based on information received from a server radio network node 130.

[00188] In some embodiments, the root index u can be selected from the set of indices, based on a received signal, received, for example, from the receiver 120, from another network node 140, or from from radio network node 130.

[00189] The root index u can additionally be selected from a first set of root indices when receiving a synchronization signal from another D2D transmitter synchronized to a cell, and from a second set of root indices when receiving a a synchronization signal from a D2D transmitter, unsynchronized to a cell.

[00190] Also, according to some embodiments, the same root index u can be selected as used in a received synchronization signal.

[00191] However, according to other embodiments, a different root index u may be selected as used in a received synchronization signal.

[00192] The synchronization signal can, in some embodiments, be transmitted over multiple hops between network nodes 140, and in which the root index u can be selected from the set of root indices, based on the number of hops of the received synchronization signal.

Action 403

[00193] The synchronization signal is generated, based on the determined synchronization sequence 401 and the selected 402 root index u.

[00194] Figure 5 illustrates an embodiment of a transmitter 110, configured to generate a synchronization signal for Device-to-Device (D2D) communication using a Single Carrier Frequency Division Multiple Access (SC-FDMA) waveform ), in which a synchronization sequence is modulating a set of subcarriers. Transmitter 110 is further configured to perform method 400 in accordance with at least some of previously described actions 401-403.

[00195] For heightened clarity, any internal electronics, or other components of the transmitter 110, not completely essential for understanding the embodiments disclosed herein, have been omitted from Figure 5.

[00196] The transmitter 110 comprises a processor 520, configured to determine a synchronization sequence, where for a positive constant k where u is a root index, and L is the length of the sync sequence. Also, processor 520 is further configured to select the root index u from a set of root indices; and, in addition, configured to generate the D2D synchronization signal, based on the given synchronization sequence, and the selected root index u.

[00197] Processor 520 can be further configured to determine the synchronization sequence, so that:

[00198] In some embodiments, the processor 520 can be configured to obtain a centrally antisymmetric D2D sync sequence of uniform length from a centrally symmetric D2D sync sequence of uniform length by multiplying the elements of one of the sin sequence halves - chronization by -1.

[00199] The processor 520 can be further configured to determine the synchronization sequence, so that: and can, in addition, also be configured to select the root index ua an integer other than 25, 29 and/or 34.

[00200] The processor 520 can additionally be configured to determine the synchronization sequence by selecting a Zadoff-Chu sequence of odd length, and removing an odd number of elements from the selected Zadoff-Chu sequence, to obtain a sync sequence of uniform length in some embodiments.

[00201] Alternatively, processor 520 can be configured to determine the synchronization sequence by selecting a Zadoff-Chu sequence of uniform length, extending the selected Zadoff-Chu sequence by one element, and removing a central element from the extended Zadoff-Chu sequence.

[00202] Processor 520 can also be configured to determine the synchronization sequence, so that: , L uniformly

[00203] Additionally, the processor 520 can be configured to map the synchronization sequence to the resource elements of the SC-FDMA signal, so that for the Fourier coefficients: where N is an integer not less than L. In some such embodiments, processor 520 can be configured to map the synchronization sequence such that and/or

[00204] Such a processor 520 may comprise one or more examples of a processing circuit, i.e., a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit ( ASIC), a microprocessor, or other processing logic that can interpret and execute instructions. The term "processor" as used herein can therefore represent a processing circuit comprising a plurality of processing circuits, such as, for example, any, some or all of the processing circuits enumerated above.

[00205] The transmitter 110 may also comprise a transmission circuit 530, configured for transmitting a signal, such as, for example, a synchronization signal.

[00206] In addition, the transmitter 110 may comprise a receiving circuit 510, configured to receive signals, such as, for example, synchronization signals, from other network nodes 120, 130, 140 over a wireless interface, from according to some embodiments.

[00207] Furthermore, the transmitter 110 may additionally comprise at least one memory 525, according to some embodiments. Optional memory 525 may comprise a physical device used to store data or a program, i.e., a sequence of instructions, on a temporary or permanent basis. According to some embodiments, memory 525 may comprise integrated circuits comprising silicon-based transistors. Additionally, memory 525 can be volatile or non-volatile.

[00208] Some or all of the above-described actions 401-403 to be performed on the transmitter 110, may be implemented through the one or more processors 520 on the transmitter 110, along with a computer program product for performing at least some of the functions of actions 401-403. Thus, a computer program comprising program code can perform a method 400 in accordance with any, at least some, or all of the functions of actions 401-403 for generating a synchronization signal for D2D communications using a waveform of SC-FDMA, in which a sync sequence is modulating a set of subcarriers, when the computer program is loaded into a processor 520 of transmitter 110.

[00209] Additionally, a computer program product may comprise a computer-readable storage medium that stores program code thereon for use by the transmitter 110 for generating a synchronization signal for D2D communications that uses a waveform of SC-FDMA, in which a sync sequence is modulating a set of subcarriers. Program code comprising instructions for executing a method 400 comprising determining 401 a synchronization sequence, where It is , for a positive constant K, where u is a root index, and L is the length of the synchronization sequence; selecting 402 the root index u from the set of root indexes; and generating 403 the sync signal, based on the determined 401 sync sequence, and the selected 402 u-root index.

[00210] The aforementioned computer program product can be provided, for example, in the form of a data carrier that carries computer program code for carrying out at least some of the actions 401-403, in accordance with some provisions. embodiments when being loaded into processor 520. The data carrier may be, for example, a hard disk, a CD ROM disk, a memory card, an optical storage device, an optical storage device, or any other medium. appropriate, such as a disk or tape that can retain machine-readable data in a non-transient manner. The computer program product may furthermore be provided as computer program code on a server and downloaded to transmitter 110 remotely, for example over an internet connection or an intranet connection.

[00211] Figure 6 illustrates an embodiment of a receiver 120, configured to detect a synchronization signal received for D2D communications using an SC-FDMA waveform, in which a synchronization sequence is modulating a set of sub-carriers . The synchronization signal for D2D communications can be received from transmitter 110.

[00212] For enhanced clarity, any internal electronics, or other components of the receiver 120, not completely indispensable for understanding the embodiments described herein, have been omitted from Figure 6.

[00213] The receiver 120 comprises a processor 620, configured to detect the synchronization signal comprising a synchronization sequence, where , It is for a positive constant K, where u is a root index, and L is the length of the synchronization sequence.

[00214] Such a processor 620 may comprise one or more examples of a processing circuit, that is, a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, a Specific Integrated Circuit Application (ASIC), a microprocessor, or other processing logic that can interpret and execute instructions. The term "processor" used herein can therefore represent a processing circuit comprising a plurality of processing circuits, such as, for example, any, some or all of the processing circuits enumerated above.

[00215] Additionally, the receiver 120 comprises a receiving circuit 610, configured to receive a signal such as, for example, a synchronization signal, from, for example, the transmitter 110.

[00216] However, the receiving circuit 610 can be configured for receiving radio signals of various types over a wireless interface from a plurality of transmitting entities, such as other network nodes 140, or the network node radio 130.

[00217] Furthermore, the receiver 120 may also, in some embodiments, comprise a transmission circuit 630, configured for transmitting a wireless signal comprising, for example, a synchronization signal.

[00218] Furthermore, the receiver 120 may additionally comprise at least one memory 625, according to some embodiments. Optional memory 625 may comprise a physical device used to store data or programs, i.e., instruction sequences, on a temporary or permanent basis. According to some embodiments, memory 625 may comprise integrated circuits comprising silicon-based transistors. Additionally, memory 625 can be volatile or non-volatile.

[00219] The terminology used in describing the embodiments as illustrated in the accompanying drawings is not intended to be limiting to the described method 400; transmitter 110 and/or receiver 120. Various changes, substitutions and/or alterations can be made without departing from the invention as defined by the appended claims.

[00220] As used herein, the term "and/or" comprises any and all combinations of one or more of the associated listed items. In addition, the singular forms "a", "a" and "the" are to be interpreted as "at least one", thus also possibly comprising a plurality of entities of the same type, unless expressly cited otherwise. another way. It will be further understood that the terms "includes", "comprises", "including" and/or "comprising", specify the presence of cited features, actions, integers, steps, operations, elements, and/or components, but do not exclude the presence or addition of one or more other features, actions, integers, steps, operations, elements, components, and/or groups thereof. The term "or", as used here, is to be interpreted as a mathematical OR, that is, as an inclusive disjunction; not as an exclusive mathematical OR (XOR), unless expressly noted otherwise. A single unit, such as, for example, a processor, may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium, or a solid-state medium, supplied along with, or as part of, other hardware, but may also be distributed in other forms, such as such as via the Internet, or other wired and wireless communication systems.

Claims (22)

1. Transmitter (110) configured to generate a synchronization signal for Device-to-Device, D2D, communication using a Single Carrier Frequency Division Multiple Access, SC-FDMA, waveform in which a sequence of synchronization is modulating a set of subcarriers, the transmitter (110) characterized in that it comprises: a processor (520), configured to determine a synchronization sequence by modulating a set of subcarriers du[l], where |du[ l]| = |du[L - 1 - l]|,l = 0,1, ...,L - 1, and |du[l]| = K, for a positive constant K, where u is a root index, and L is the length of the synchronization sequence du[l]; and also configured to select the root index u from a set of root indexes; and, in addition, configured to generate o and transmit to a receiver (120) the synchronization signal, based on the determined synchronization sequence du[l] and the selected root index u, wherein the receiver (120) uses the synchronization signal synchronization to establish time and frequency synchronization with the transmitter (110) according to the selected u root index. 2. Transmitter (110), according to claim 1, characterized by the fact that the processor (520) is configured to determine the du[l] synchronization sequence, so that: du [l] = -du [L — 1 — l], l = 0,1,..., L — 1. 3. Transmitter (110), according to claim 1, characterized in that the processor (520) is configured to obtain a centrally antisymmetric synchronization sequence of uniform length from a centrally symmetric synchronization sequence of uniform length by multiplying the elements of one half of the synchronization sequence by -1. 4. Transmitter (110), according to claim 1, characterized in that the processor (520) is configured to determine the synchronization sequence du[n], so that: and also configured to select the root index ua an integer other than 25, 29 and 34. 5. Transmitter (110), according to any one of claims 1 to 3, characterized in that the processor (520) is configured to determine the synchronization sequence by selecting a Zadoff-Chu sequence of odd length , and removing an odd number of elements from the selected Zadoff-Chu sequence, to obtain a synchronization sequence of uniform length. 6. Transmitter (110), according to any one of claims 1 to 3, characterized in that the processor (520) is configured to determine the synchronization sequence, so that: , n = 0.1, ...,L — 1, uniform L and 7. Transmitter (110) according to any one of claims 1 to 6, characterized in that the processor (520) is configured to map the synchronization sequence to the SC-FDMA waveform resource elements , so that for the Fourier coefficients: |H[fc]| = |H[N — 1 — k]l,k = 0,1, ...,N — 1, where N is an integer not less than L and H[k] is a Fourier Coefficient at frequency k. 8. Transmitter (110), according to claim 7, characterized by the fact that: H[k] = H[N — 1 — k], k = 0.1, ...,N — 1. 9. Transmitter (110), according to claim 7 or 8, characterized in that: s[n]=-s[N-n], n=1, s[n] is a SC-FDMA signal, n =0,1,...,N-1. 10. Transmitter (110), according to claim 7, characterized by the fact that: H[k] = -H[N -1-k], k = 0.1, ...,N - 1 . 11. Transmitter (110), according to any one of claims 1 to 10, characterized in that the processor (520) is configured to select the root index u from the set of root indices, or randomly, or by deriving it from one or more parameters internal to the transmitter (110). 12. Transmitter (110), according to any one of claims 1 to 11, characterized in that the processor (520) is configured for at least one of: selecting the root index u from the set of indexes of root based on information received from a server radio network node (130), or based on a received signal; and selecting the root index u from a first set of root indices when receiving a synchronization signal from another D2D transmitter being synchronized to a cell, and from a second set of root indices when receiving a a sync signal from another D2D transmitter not being synced to a cell. 13. Method (400) in a transmitter (110), for generating a synchronization signal for D2D communication using an SC-FDMA waveform, characterized in that a synchronization sequence is modulating a set of subcarriers, the method (400) comprising: determining (401) a synchronization sequence du[Z], where MJlH = ldu[l - 1 - l]|,I = 0,1, ...,L — 1 and ldu[l] l=K, for a positive constant K, where u is a root index, and L is the length of the synchronization sequence du[l]; selecting (402) the root index u from a set of root indices; and generating (403) and transmitting to a receiver (120) the synchronization signal, based on the (401) determined synchronization sequence du[l] and the selected (402) root index u, wherein the receiver (120 ) uses the synchronization signal to establish time and frequency synchronization with the transmitter (110) according to the selected root index u. 14. Method (400), according to claim 13, characterized in that it comprises mapping the synchronization sequence to the resource elements of the SC-FDMA waveform, so that for the Fourier coefficients : |H[fc]| = IH[N - 1 - fc]|,fc = 0,1, ...,N - 1, where N is an integer not less than L, and H[k] is a Fourier coefficient at frequency k. 15. Method (400), according to claim 14, characterized by the fact that: H[k] = H[N - 1 - k], k = 0.1, ...,N - 1. 16. Method (400), according to claim 14 or 15, characterized in that: s[n] = -s[N - n],n = 1,.,N - 1, s[n] is an SC-FDMA signal, n = 0,1,.,N - 1. 17. Apparatus comprising a computer-readable storage medium that stores a method thereon for use by a transmitter (110) for generating a synchronization signal for D2D communication using an SC-FDMA waveform, wherein a sequence of synchronization is modulating a set of sub-carriers, characterized in that the method comprises instructions that, when executed by a processor in the transmitter (11), make the device execute a method (400) that comprises : determine (401) a synchronization sequence du[l], where K/llH = MJL - 1 - l]|, l = 0,1, ...,L - 1 and ldu[l]l=K, for a positive constant K, where u is a root index, and L is the length of the synchronization sequence du[l]; selecting (402) the root index u from the set of root indices; and generating (403) and transmitting to a receiver (120) the synchronization signal, based on the determined (401) synchronization sequence du[l] and the selected (402) root index u, wherein the receiver (120 ) uses the synchronization signal to establish time and frequency synchronization with the transmitter (110) according to the selected root index u. 18. Apparatus according to claim 17, characterized in that the computer-readable storage medium that stores a method therein for use by the transmitter (110) for mapping the synchronization sequence to the resource elements of the SC-FDMA waveform, so that for Fourier coefficients: |H[fc]| = \H[N - 1 - k]l,k = 0,1, ...,N - 1, where N is an integer not less than L, and H[k] is a Fourier coefficient at frequency k . 19. Appliance, according to claim 18, characterized by the fact that: H[k] = H[N - 1 - fc], k = 0.1, ...,N - 1. 20. Device, according to claim 18 or 19, characterized by the fact that: s[n] =-s[N - n],n = 1, ...,N - 1, s[n] is an SC-FDMA signal, n=0,1,.,N-1. 21. Receiver (120) configured to detect a received synchronization signal for D2D communication using an SC-FDMA waveform, wherein a synchronization sequence is modulating a set of subcarriers, the receiver (120) characterized by the fact that it comprises: a processor (620), configured to detect the synchronization signal comprising a synchronization sequence du[l], where |du[l]| = |du[L - 1 - l]|,l = 0,1, ...,L - 1, and |du[l]| = K, for a positive constant K, where u is a root index, and L is the length of the sync sequence du[l], and also configured to use the sync signal to establish time and frequency synchronization with a transmitter (110) according to a selected root index u. 22. Method at a receiver (120) for detecting a received synchronization signal for D2D communication using an SC-FDMA waveform, wherein a synchronization sequence is modulating a set of subcarriers, the method characterized in that comprising: detecting the synchronization signal comprising a synchronization sequence du[l], where |du[l]|= |^u[L - 1 - l]|,l = 0,1, ..., L - 1, and |du[l]| = K, for a positive constant K, where u is a root index, and L is the length of the synchronization sequence du[/]; using the synchronization signal to establish time and frequency synchronization with a transmitter (110) according to a selected root index u.