CN104052690B - Frequency synchronization method for cooperative communication system - Google Patents

Abstract

The invention discloses a frequency synchronization method for a cooperative communication system. In the cooperative communication system, frequency synchronization needs to be performed on both of a relay node and an objective node. In a direct link transmission mode, the problem of frequency synchronization between a source node and the objective node belongs to the problems of frequency synchronization of a point-to-point communication system. In a first cooperative stage in a cooperative mode, the relay node and the objective node only receive signals from the source node, and the problem of frequency synchronization of the relay node and the objective node also belongs to the problems of frequency synchronization of the point-to-point communication system. In a second cooperative stage, the objective node simultaneously receives superposed signals from two cooperative nodes. In the cooperative communication system, the two cooperative nodes adopt training sequences with identical structures, the training sequences are used for a frequency estimation part, therefore, superposition of two paths of signals can be regarded as the situation that a prefix passes by an equivalent signal of a multipath channel passes, and the problem of frequency synchronization also belongs to the problems of frequency synchronization of the point-to-point communication system.

Description

For cooperation communication system medium frequency synchronous method

Technical field

The present invention relates to the communications field, more particularly, to for cooperation communication system medium frequency synchronous method.

Background technology

In recent years, with the increase and the raising of people's living standard of wireless mobile communications number of users, to provide words Traditional GSM and CDMA technology based on sound has gradually been difficult to meet user's request.To meet people to wireless multimedia communication industry Business ever increasing need, under the background that frequency spectrum resource day is becoming tight, multiaerial system is due to being obviously improved system Transmission performance and spectrum efficiency, are widely paid close attention to.However, the volume of mobile terminal, Power Limitation constrain significantly it is many The practical application of antenna system.Cooperation communication system has become communication neck in recent years as a kind of extension of multi-antenna technology The focus of domain research, cooperates transmission data or adds special relay node cooperation to pass using wireless network interior joint It is defeated, can be while system spectrum utilization rate be improved, being effectively reduced increases the great amount of cost that base station is brought.

In Turbo Detection for Cooperative Communication, due between the different and multiple crystal oscillators for relaying location distribution mutually not Match somebody with somebody, there are multiple different carrier frequency shifts between multiple repeated links, this is that Turbo Detection for Cooperative Communication is different from conventional point The most salient of point to-point communication system.In academia, there are many numerous studies to frequency deviation problem.According to offset estimation The difference of algorithm application scenarios, can be divided into continuous mode algorithm and burst mode algorithm；According to the difference of algorithm applicable elements, Thick synchronized algorithm and thin synchronized algorithm can be divided into；It is different according to the data type that algorithm is utilized, blind estimate calculation can be divided into Method and training sequence algorithm for estimating.

In actual cooperation communication system, Frequency Synchronization is to realize the premise of reliable reception.In cooperation communication system, Information source node and via node all can be to destination node sending signals.Because the crystal oscillator characteristic of different nodes is different or communication process The reasons such as the phase noise of middle introducing, will appear from frequency asynchronous.Therefore, needed to set up before channel estimation and data demodulation Frequency Synchronization.

Application No. " 201010545376.2 ", entitled " for synchronous method and device in collaboration wireless network " Patent application, is to give one for synchronous method and device for collaboration wireless network.The invention proposes a kind of in association Method with synchronization is used in wireless network, including step：A, generation frequency domain training sequence, the non-zero in the frequency domain training sequence Training data is mapped on the first t easet ofasubcarriers, and the subcarrier in first t easet ofasubcarriers is with first predetermined value subcarrier It is that interval is uniformly corresponded on carrier wave；Wherein, the first t easet ofasubcarriers and other at least one cooperative nodes each corresponding to There is spacing bias between t easet ofasubcarriers, and each corresponding t easet ofasubcarriers of other at least one cooperative nodes are two-by-two There is spacing bias；B, according to frequency domain training sequence, generate corresponding time domain pilot；And C, transmission time domain pilot.This patent Purpose is to improve the precision of time offset estimation between cooperative nodes and receiver in synchronizing process and offset estimation.

This application proposes and a kind of is used at least one be cooperateed with other in the first cooperative nodes of collaboration wireless network Node collaboration sends the method and its device of pilot tone, and its training sequence design is complicated, and computation complexity is high, by its simulation result Figure can see that the mean square deviation of its Carrier frequency offset estimation is larger, that is to say, that the accuracy of its Frequency Synchronization is less high.

The patent application of " frequency offset estimation method of low-complexity collaborative relay system 201110072457.X " is for collaboration Relay system proposes a kind of frequency deviation estimating method of low complex degree.Its method of estimation for proposing, using each via node sequence is trained Receiving sequence vector median filters are homography by the periodicity of row, and then using the row conjugation symmetric properties difference of correlation matrix Corresponding real number matrix is constructed, and does the swift nature decomposition of real number matrix and quickly asking for real polynomial equation respectively Root, so as to realize quick many offset estimations.

Concrete grammar is：

1) enter line translation to receiving sequences y, be converted into the matrix Y of Q × P, wherein, the element of matrix Y can be represented For：[Y] q, p=[y] qP+p, 0≤q ＜ Q, 0≤p ＜ P, P and Q are positive integer, and P × Q=N, N are the length of training sequence, q The line index of matrix Y is represented, p represents the column index of matrix Y；

2) using normalization row conjugation symmetrical matrix, real number variance matrix is constructed；

3) to step 2) the real number variance matrix that obtains does feature decomposition, obtains special corresponding to the normalization of signal subspace Levy vector；

4) according to step 3) the normalization characteristic vector that obtains, the normalization row conjugate pair obtained using geometric maps relation Claim matrix, construct real polynomial；

5) to step 4) real polynomial that obtains carries out quick rooting computing, finds out imaginary part in all paired roots absolute To root, wherein K is the number of via node in collaboration relay system to the minimum K of value；

6) the equivalent frequency deviation to root corresponding to this K is calculated, and is rearranged according to order from small to large；

7) to step 6) K that obtains equivalent frequency deviation make respectively corresponding additive operation, obtains K frequency deviation to be estimated Value.

The method that the patent application is proposed need to carry out multi-degree matrix computing, feature decomposition etc., and computation complexity is high.

The content of the invention

The purpose of the present invention is to propose to a kind of be used for cooperation communication system medium frequency synchronous method, communication for coordination intermediate frequency is solved The asynchronous problem of rate, algorithm complex is low, easily realizes.

To achieve these goals, the technical scheme is that：

One kind is used for cooperation communication system medium frequency synchronous method, and the communication system belongs to multi-relay cooperation and is wirelessly transferred and is System, is made up of source node, via node and destination node；Each node configuration individual antenna, using with Cyclic Prefix just Hand over the multi-carrier modulation/demodulation mode of frequency division multiplexing CP-OFDM；Frame structure includes prefix, training sequence and data sequence three Part；

Frequency Synchronization includes via node Frequency Synchronization and destination node Frequency Synchronization；

The process of the via node Frequency Synchronization is：When there is frequency error, after sign synchronization is realized, training sequence Length remove reception signal interior after CP and be for the OFDM windows of N

Carry out Frequency Synchronization to training sequence to estimate including frequency error and offset frequency error：

Wherein the frequency error of training sequence estimates it is to utilize the repetitive structure for removing the training sequence after CP, repetitive structure Including s₁、s₂, s₁=s₂；

The observed value of OFDM windows isUsing based on auto-correlation second-order statisticses Method of estimation carries out frequency error estimation；Obtain the carrier frequency error Δ f of source node to via node link_srEstimated value table It is shown as

The offset frequency error of training sequence is to draw frequency error estimated value using training sequenceAfterwards, relay Node needs the time-domain signal to receiving to carry out frequency compensation, the time-domain signal after compensationSuch as formula Wherein T represents sampling period, and n represents sampling time, n=1 ..., N；Time-domain signal after compensation is based on training for follow-up The channel estimation of sequence and the process to data sequence；

After Alamouti codings are realized, via node arrives time-domain signal modulationFrequency is sent with source node identical carrier wave RateRetransmit away, to realize that frequency is compensated again；I.e. the time-domain signal of via node also needs to be multiplied by the estimated source node for arriving extremely The carrier frequency error Δ f of via node link_sr；

The destination node Frequency Synchronization includes that frequency error is estimated and offset frequency error.

In a kind of preferred scheme, the detailed process of the via node Frequency Synchronization is：

When there is frequency error, after sign synchronization is realized, the length of training sequence removes interior after CP for the OFDM windows of N Receiving signal is

WhereinSave to the l footpaths channel parameter of via node, l=0 ..., L in expression source_sr-1；s_nRepresent sending out for time domain The number of delivering letters, corresponding here is training sequence part, and s_-l=s_N-l；Δf_sr=f_s-f_rRepresent source node to via node link Carrier frequency error, f_sAnd f_rThe carrier frequency of source node and via node is then represented respectively, and T represents sampling period；

Carry out Frequency Synchronization to training sequence to estimate including frequency error and offset frequency error：

Wherein the frequency error of training sequence estimates it is to utilize the repetitive structure for removing the training sequence after CP, repetitive structure Including s₁、s₂, s₁=s₂；

The observed value of OFDM windows isUsing based on auto-correlation second-order statisticses Method of estimation carries out frequency error estimation；

Due to s₁=s₂, therefore can obtain

According to law of great number,White Gaussian noise is approximately, frequency error Δ f is obtained_srEstimated value table be shown as；

N_ST represents the size of OFDM windows, in the case of T is certain, N_SLonger, OFDM windows are bigger, and the precision of estimation is just high；

The offset frequency error of training sequence is to draw frequency error estimated value using training sequenceAfterwards, relay Node needs the time-domain signal to receiving to carry out frequency compensation, the time-domain signal after compensationSuch as formula Wherein T represents sampling period, and n represents sampling time, n=1 ..., N；Time-domain signal after compensation is based on training for follow-up The channel estimation of sequence and the process to data sequence；

After Alamouti codings are realized, via node arrives time-domain signal modulationFrequency is sent with source node identical carrier wave RateRetransmit away, to realize that frequency is compensated again；I.e. the time-domain signal of via node also needs to be multiplied by the estimated via node for arriving Frequency error Δ f between source node_sr, i.e.,For the symbol of n-th sampling time.

In a kind of preferred scheme, the detailed process of the destination node Frequency Synchronization is：

Under single or double relay cooperative transmission pattern, if source node and via node are to the frequency domain channel between destination node Respectively H^sdAnd H^rd, destination node receives the time-domain signal from source node and via node and is expressed as

Wherein Δ f_sd=f_s-f_dWith Δ f_rd=f_r-f_dThe load of source node and via node to destination node link is represented respectively Wave frequency error, f_dFor the carrier frequency of purpose node, due toEstimated value,It is not Zero, therefore can obtain

Further try to achieve

AlthoughBut due to,(Δf_sdIt is much larger than), thereforeIgnore, and then can obtain

For the signal of the training sequence part for Frequency Estimation, meetTherefore

Then its frequency error estimates Δ f_sdEstimated value table be shown asWhereinWithRespectively correspond to the time-domain received signal of training sequence part repetitive substructure；Δ f is estimated according to frequency error_sdEstimation Value carries out offset frequency error to the time-domain signal for receiving.

In a kind of preferred scheme, the prefix part of the communication system adopts [P1, P2]=[A, reverse (A)] Structure.The estimation of this structure than it is traditional based on auto-correlation second-order statisticses with obvious peak point and very steep Slope, its estimated accuracy will height.

In a kind of preferred scheme, the source node adopts length for N_SReally sequencing is arranged As training sequence, by 2 parts of identicalComposition；CP takes from the last L of s in part_CPLength thereofIn order to ensure that training sequence is not disturbed by prefix part under multi-path jamming channel circumstance, Length L of CP parts_CPMore than length L of multipath channel_h, that is, meet L_CP>L_h。

Beneficial effects of the present invention are：Frequency Estimation, frequency cancellation are carried out at via node, frequency is compensated again, so Can be with the Frequency Synchronization problem of simplified system.Because cooperation communication system can regard a virtual multiple input single output as System, destination node can receive the signal for coming from source node, via node, and due to have passed through wireless channel, frequency occurs Multiple frequencies will be synchronized by skew in destination node, algorithm can it is very complicated and also with increasing for via node it is more multiple It is miscellaneous.By means of the invention it is also possible to the problem of multiple Frequency Synchronizations of destination node is avoided, and when via node increases When, the Frequency Synchronization problem that will not also make system becomes more sophisticated.

In the present system, via node and destination node are required for carrying out Frequency Synchronization.Under direct link transmission mode, Source node belongs to the Frequency Synchronization problem of point-to-point digital communication system to the Frequency Synchronization problem between destination node；In cooperation Cooperation stage one under pattern, via node and destination node all receive only the signal from source node, and its Frequency Synchronization is asked Topic falls within the Frequency Synchronization problem of point-to-point digital communication system；Cooperation the stage two, destination node receive simultaneously from The superposed signal of two cooperative nodes (source node and via node, or two via nodes), due to two associations in the system Make node all using the training sequence (for frequency estimation portion) of identical structure, therefore the superposition of two paths of signals can be seen Into being signal of the prefix through an equivalent multipath channel, therefore its Frequency Synchronization problem falls within point-to-point digital communication department The Frequency Synchronization problem of system.

Description of the drawings

Fig. 1 is the schematic diagram of multi-relay cooperation communication system.

Fig. 2 is the schematic diagram of system frame structure.

Fig. 3 is the schematic diagram of prefix structure in system frame structure.

Fig. 4 is the schematic diagram of the structure of the training sequence in system frame structure for Frequency Estimation.

Fig. 5 is the Equivalent Base-Band communication system schematic diagram of point-to-point digital communication system.

Fig. 6 is the Equivalent Base-Band communication system schematic diagram of direct link transmission.

Fig. 7 is that source node transmitting terminal base-band digital processes block diagram.

Fig. 8 is that the destination node receiving terminal base-band digital under direct transmission mode processes block diagram.

Fig. 9 is direct link and single relay coordination transmission system schematic diagram.

Figure 10 is that source node transmitting terminal base-band digital processes block diagram.

Figure 11 processes block diagram for the base-band digital of AF via nodes.

Figure 12 processes block diagram for the base-band digital of DF via nodes.

Figure 13 is that the base-band digital of destination node under tie link and single relay cooperative transmission pattern processes block diagram (cooperation rank Section is one).

Figure 14 is that the base-band digital of destination node under tie link and single relay cooperative transmission pattern processes block diagram (cooperation rank Section is two).

Figure 15 is the process schematic of via node Frequency Synchronization of the present invention (estimate and offset).

Figure 16 is the schematic diagram of training sequence of the present invention.

The process schematic that Figure 17 via node frequencies of the present invention are compensated again.

Figure 18 is the process schematic of the object of the invention nodal frequency synchronous (estimate and offset).

Specific embodiment

Below in conjunction with the accompanying drawings the present invention will be further described, but embodiments of the present invention are not limited to this.

First, cooperation communication system model

As shown in figure 1, the system belongs to multi-relay cooperation wireless transmitting system, by a source node, multiple via nodes With a destination node composition.Each node configuration individual antenna, using the OFDM (CP- with Cyclic Prefix OFDM multi-carrier modulation/demodulation mode).

Within the system, source node is communicated with destination node, and its communication link is source node to destination node link, Also commonly referred to as tie link (Direct Link, be abbreviated as DL).There are multiple relaying sections around source node and destination node Point, for cooperation transmission.When the channel status of tie link is preferable, source node can pass through tie link reality with destination node Now communicate, without the need for relay node cooperation；When the channel status of tie link is poor, via node may participate in cooperation, to mesh Node forward information from source node, realize space diversity gain, improve communication quality.The system adopts amplification forwarding (Amplify and Forward, AF) and decoding forwarding (Decode and Forward, DF) two kinds of conventional relay cooperative sides Formula.

2nd, system frame structure

Frame structure includes prefix, three parts of training sequence and data sequence：Prefix part is used for frame detection and symbol is same Step；Training sequence is made up of two parts, is respectively used to Frequency Synchronization and channel estimation；Data sequence, for transmitting useful information, Centre can intert pilot signal, for track channel change.

1st, the structure of prefix

It is being used to carry out the prefix part of time synchronized, the system adopts [P1, P2]=[A, reverse (A)] structures, this The estimation of individual structure than it is traditional based on auto-correlation second-order statisticses with obvious peak point and very steep slope, Thus estimated accuracy will height.

2nd, for Frequency Estimation training sequence structure

In the training sequence part for Frequency Synchronization, the system adopts following structure：

Source node adopts length, and for NS, really sequencing is arrangedAs training sequence, by identical 2 partsComposition.CP takes from the last L of s in part_CPLength thereof In order to ensure that training sequence is not disturbed by prefix part under multi-path jamming channel circumstance, length L of CP parts_CPShould be more than Length L of multipath channel_h, that is, meet L_CP>L_h。

The communication process of (1) three kind of transmission mode

In the digital communication system of point-to-point, the communication such as between base station of cellular system and certain handheld terminal, its Communication process can be divided into digital end and analog end.Digital end completes the digital signal processing tasks of base band, including bit information Chnnel coding/decoding, symbol-modulated/demodulation and other processing procedures；Analog end then completes digital signal to analogue signal Conversion and analogue signal whole processing procedures, including transmitting procedure of the analogue signal in wireless channel.

In the point-to-point digital communication system being illustrated in fig. 5 shown below, by the digital end processing procedure of transmitting terminal and receiving terminal Digital end processing procedure is abstract respectively to process block diagram and receiving terminal base-band digital process block diagram for transmitting terminal base-band digital；To complete What digital signal to analogue signal was changed sends formed filter, realizes carrier modulation, Jing of the signal from low frequency to high frequency conversion Cross physical channel, realize carrier wave demodulation that signal changed from from high frequency to low frequency, realize that analogue signal to digital signal changes It is Equivalent Base-Band discrete multipath channel with a series of procedural abstractions such as wave filter and sampler；And then obtain point-to-point digital communication The Equivalent Base-Band communication system of system.(11) direct link transmission mode

Under direct link transmission mode, its communication process is that traditional point-to-point (Point-to-Point) communicated Journey.Therefore the Equivalent Base-Band communication system of the direct link Transmission system consistent with Fig. 5 can be drawn, is illustrated in fig. 6 shown below.

The transmitting terminal base-band digital of source node processes block diagram, as shown in fig. 7, mainly including prefix, training sequence and data The generation of sequence.Data sequence is made up of information sequence and pilot signal；The generation process of information sequence includes information bit Produce, cyclic redundancy check (CRC) encodes (Cyclic Redundancy Check, CRC), chnnel coding, symbol-modulated；Pilot signal It is interspersed in the middle of information sequence, through OFDM modulation the data sequence of time domain is become.Finally, prefix, training sequence and data sequence Row deliver to transmission formed filter in succession.Cyclic redundancy check (CRC) coding purpose is integrity and the conduct of check bit data Whether one of criterion of relay node cooperation is needed.

In destination node receiving terminal, as shown in figure 8, carrying out digital signal sequences of the self-matching filter after sampling first Elapsed time synchronization module, completes frame detection and sign synchronization；After sign synchronization is realized, training sequence and data can be calculated The initial sample position of sequence, and then training sequence is extracted to complete the place of Frequency Synchronization and channel estimation and data sequence Reason.

The process of data sequence includes the process of information sequence and pilot signal；For information sequence, solving through OFDM After tune, it is necessary first to carry out the equilibrium of frequency domain channel, wherein channel parameter is by the channel estimation module and base based on training sequence There is provided in the tracking module of pilot signal, then carry out symbol demodulation, modulation symbol is changed into into binary bit signal, finally Decoding is completed into channel decoding module, if any chnnel coding.Under static channel, channel parameter keeps constant, by based on instruction The channel estimation module offer for practicing sequence be enough to complete channel equalization；If there is Frequency Estimation remainder error, also need to carry out phase The tracking of position；And in the case where (time-varying) channel is moved, channel parameter is changed over, the tracking of channel parameter is estimated by based on pilot tone The tracking module of signal is provided.

(12) tie link and single relay cooperative transmission pattern

It is different from the point-to-point communication of direct transmission mode, under tie link and single relay cooperative transmission pattern, such as Fig. 9 Shown, in addition to tie link, the repeated link of also " source node-via node-destination node " participates in cooperation.Cooperation The process of communication can be divided into 2 two processes of cooperation stage one and cooperation stage.In the cooperation stage one, source node is to purpose section Point and via node are while sending signal, belongs to the broadcast communication of point-to-multipoint；In cooperation stage two, source node and via node Simultaneously to destination node sending signal, belong to how point-to-point communication.

In the cooperation stage one, the broadcast communication of point-to-multipoint can be divided into multiple independent point-to-point communication process.For Source node, it can separately constitute independent point-to-point digital communication system with destination node and via node, therefore, source node Transmitting terminal base-band digital process block diagram with tie link pattern transmitting terminal base-band digital process block diagram it is consistent, such as Figure 10 institutes Show：

Under tie link and single relay cooperative transmission pattern, the main purpose of single via node is to from source node Digital signal carries out Alamouti codings, is that the signal reception of purpose node brings space diversity gain to complete cooperation transmission, Improve the signal reception of destination node.Via node can adopt amplification forwarding (AF) and decoding to forward two kinds of (DF) different Trunk protocol.Under different trunk protocols, the signal processing of via node is different, therefore under two kinds of protocol modes The implementation of Alamouti codings is also different.

Under amplification forwarding (AF) agreement, the base-band digital processing procedure of via node includes receiving and sending two rings Section, as shown in figure 11, is receiving link, and via node is sequentially completed time synchronized, Frequency Synchronization and channel estimation, and channel is estimated Meter output channel parameter estimation value, the latter is used to calculate the judgement amount needed for relay selection.After selected participation cooperation, in OFDM demodulation (including CP and FFT changes are removed) is first carried out to the data sequence of time domain after node, the data sequence of frequency domain is drawn, Then complete Alamouti according to the Alamouti coded systems of ofdm system to encode (including information sequence and pilot signal), enter Row OFDM re-modulations (change and add new CP) including IFFT, and pass through together with training sequence and prefixFrequency compensates again mould BlockRealize that sending carrier frequency with source node aligns, and finally delivers to transmission formed filter.

Under decoding forwarding (DF) cooperation mode, the base-band digital processing procedure of via node also includes receiving and sending two Individual link, as shown in figure 12, is receiving link, and via node is sequentially completed time synchronized, Frequency Synchronization and channel estimation, believes Output channel parameter estimation value is estimated in road, and the latter is used to calculate the judgement amount needed for relay selection.Cooperate with amplification forwarding (AF) Mode is different, and DF via nodes also need to enter the information sequence in data sequence the channel equalization of line frequency, symbol demodulation and Channel decoding, and decode the bit sequence of output and be circulated redundancy check, with the integrity of check bit data, and will inspection Correctness informs relay selection module.For time varying channel, the pilot signal in data sequence in advance is also needed to carry out source node Tracking to via node channel parameter is estimated.After being chosen to participate in cooperating, the ratio that via node is exported to channel decoding Special sequence re-starts chnnel coding and follow-up symbol-modulated, draws the information sequence of frequency domain, and together with pilot signal Send into Alamouti coding modules；Then carry out OFDM modulation and draw the data sequence of time domain, and with training sequence and prefix one Rise and deliver to frequency compensating module again, realize that sending carrier frequency with source node aligns, and finally delivers to transmission formed filter.

In the cooperation stage one, following Figure 13, destination node receiving terminal receives only the signal from source node, its base band number Word processing process with it is consistent under tie link transmission mode, see the defeated of Fig. 8, channel estimation module and cyclic redundancy check (CRC) module Go out for carrying out relay selection.

In the destination node in cooperation stage two, destination node receives the superposition letter from source node and via node simultaneously Number, the purpose of its base-band digital processing procedure is to carry out Alamouti decodings and channel decoding, and its processing procedure is being amplified Forwarding (AF) is forwarded under (DF) agreement all with decoding.As shown in figure 14, to be sequentially completed time synchronized, frequency same for destination node Step and channel estimation, channel estimation output source node is estimated to the channel parameter of destination node and via node to destination node Evaluation, for the Alamouti decodings of information sequence in follow-up data sequence.For time varying channel, also need to extract in data sequence Pilot signal carry out Alamouti decoding desired parameters tracking estimate.

In the present system, via node and destination node are required for carrying out Frequency Synchronization.Under direct link transmission mode, Source node belongs to the Frequency Synchronization problem of point-to-point digital communication system to the Frequency Synchronization problem between destination node；In cooperation Cooperation stage one under pattern, via node and destination node all receive only the signal from source node, and its Frequency Synchronization is asked Topic falls within the Frequency Synchronization problem of point-to-point digital communication system；Cooperation the stage two, destination node receive simultaneously from The superposed signal of two cooperative nodes (source node and via node, or two via nodes), due to two associations in the system Make node all using the training sequence (for frequency estimation portion) of identical structure, therefore the superposition of two paths of signals can be seen Into being signal of the prefix through an equivalent multipath channel, therefore its Frequency Synchronization problem falls within point-to-point digital communication department The Frequency Synchronization problem of system.The via node in cooperation stage one and the signaling system of the destination node in cooperation stage two are described below Model and frequency synchronization algorithm.

The embodiment of invention described above, does not constitute limiting the scope of the present invention.It is any at this Done modification, equivalent and improvement etc. within bright spiritual principles, should be included in the claim protection of the present invention Within the scope of.

Claims (4)

1. a kind of to be used for cooperation communication system medium frequency synchronous method, the communication system belongs to multi-relay cooperation and is wirelessly transferred and is System, is made up of source node, via node and destination node；Each node configuration individual antenna, using with Cyclic Prefix just Hand over the multi-carrier modulation/demodulation mode of frequency division multiplexing CP-OFDM；Frame structure includes prefix, training sequence and data sequence three Part；

Characterized in that, Frequency Synchronization includes via node Frequency Synchronization and destination node Frequency Synchronization；

The process of the via node Frequency Synchronization is：When there is frequency error, after sign synchronization is realized, the length of training sequence Spend the OFDM windows for N and remove reception signal interior after CP and be

Carry out Frequency Synchronization to training sequence to estimate including frequency error and offset frequency error：

Wherein the frequency error of training sequence estimates it is the repetitive structure using the training sequence after CP is removed, and repetitive structure includes s₁、s₂, s₁=s₂；

The observed value of OFDM windows isUsing the estimation based on auto-correlation second-order statisticses Method carries out frequency error estimation；Obtain the carrier frequency error Δ f of source node to via node link_srEstimated value table be shown as

The offset frequency error of training sequence is to draw frequency error estimated value using training sequenceAfterwards, via node The time-domain signal to receiving is needed to carry out frequency compensation, the time-domain signal after compensationSuch as formulaWherein T represents sampling period, and n represents sampling time, n=1 ..., N；Time-domain signal after compensation is for subsequently based on training sequence Channel estimation and the process to data sequence；

After Alamouti codings are realized, via node is by time-domain signal modulation to source node identical carrier wave transmission frequency again Send, to realize that frequency is compensated again；I.e. the time-domain signal of via node also needs to be multiplied by the estimated source node for arriving to relaying The carrier frequency error Δ f of node link_sr；

The destination node Frequency Synchronization includes that frequency error is estimated and offset frequency error；

The detailed process of the via node Frequency Synchronization is：

When there is frequency error, after sign synchronization is realized, the length of training sequence removes reception interior after CP for the OFDM windows of N Signal is

$r_n^{sr}=e^{j2{\mathrm{\π\Δf}}_{sr}nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}{s}_{n-l}+z_n^{sr},n=1,\mathrm{...},N$

WhereinSave to the l footpaths channel parameter of via node, l=0 ..., L in expression source_sr-1；s_nRepresent the transmission letter of time domain Number, corresponding here is training sequence part, and s_-l=s_N-l；Δf_sr=f_s-f_rRepresent the load of source node to via node link Wave frequency error, f_sAnd f_rThe carrier frequency of source node and via node is then represented respectively, and T represents sampling period；

Carry out Frequency Synchronization to training sequence to estimate including frequency error and offset frequency error：

Wherein the frequency error of training sequence estimates it is the repetitive structure using the training sequence after CP is removed, and repetitive structure includes s₁、s₂, s₁=s₂；

The observed value of OFDM windows isUsing the estimation based on auto-correlation second-order statisticses Method carries out frequency error estimation；

$\begin{array}{c}{r}_1^{sr}\left(n\right)=r^{sr}\left(n\right)=e^{j2{\mathrm{\π\Δf}}_{sr}nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}s(n-l)+z_n^{sr}\\ =e^{j2{\mathrm{\π\Δf}}_{sr}nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}{s}_1(n-l)+z_n^{sr},n=1,\mathrm{...},\frac{N_S}{2}\end{array}$

$\begin{array}{c}{r}_2^{sr}\left(n\right)=r^{sr}(\frac{N_S}{2}+n)=e^{j2{\mathrm{\π\Δf}}_{sr}(\frac{N_S}{2}+n)T}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}s\left(\right(\frac{N_S}{2}+n)-l)+z_{(\frac{N_S}{2}+n)}^{sr}\\ =e^{j2{\mathrm{\π\Δf}}_{sr}\frac{N_S}{2}T}\left(e^{j2{\mathrm{\π\Δf}}_{sr}nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}{s}_2\right(n-l\left)\right)+z_{(\frac{N_S}{2}+n)}^{sr},n=1,\mathrm{...},\frac{N_S}{2}\end{array}$

Due to s₁=s₂, therefore can obtain

According to law of great number,White Gaussian noise is approximately, frequency error Δ f is obtained_srEstimated value table be shown as；

$\mathrm{\Δ}{\hat{f}}_{sr}=\frac{1}{{\mathrm{\πN}}_{S}T}\arg \left\{{\left(r_1^{sr}\right)}^H\left(r_2^{sr}\right)\right\}.$

N_ST represents the size of OFDM windows, in the case of T is certain, N_SLonger, OFDM windows are bigger, and the precision of estimation is just high；

The offset frequency error of training sequence is to draw frequency error estimated value using training sequenceAfterwards, via node The time-domain signal to receiving is needed to carry out frequency compensation, the time-domain signal after compensationSuch as formulaWherein T represents sampling period, and n represents sampling time, n=1 ..., N；Time-domain signal after compensation is for subsequently based on training sequence Channel estimation and the process to data sequence；

$\begin{array}{c}{y}_n^{sr}=e^{-j2\mathrm{\π}\mathrm{\Δ}{\hat{f}}_{sr}nT}{r}_n^{sr}\\ =e^{j2\mathrm{\π}({\mathrm{\Δf}}_{sr}-\mathrm{\Δ}{\hat{f}}_{sr})nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}{s}_{n-l}+e^{-j2\mathrm{\π}\mathrm{\Δ}{\hat{f}}_{sr}nT}{z}_n^{sr}\\ =e^{j2\mathrm{\π}({\mathrm{\Δf}}_{sr}-\mathrm{\Δ}{\hat{f}}_{sr})nT}\underset{l=0}{\overset{L_{sr}-1}{\mathrm{\Σ}}}{h}_l^{sr}{s}_{n-l}+{\hat{z}}_n^{sr}\end{array}$

After Alamouti codings are realized, via node is by time-domain signal modulation to source node identical carrier wave transmission frequency again Send, to realize that frequency is compensated again；I.e. the time-domain signal of via node also needs to be multiplied by the estimated via node for arriving and source Frequency error Δ f between node_sr, i.e., For the symbol of n-th sampling time.

2. it is according to claim 1 for cooperation communication system medium frequency synchronous method, it is characterised in that the purpose section The synchronous detailed process of dot frequency is：

Under single or double relay cooperative transmission pattern, if source node and via node are distinguished to the frequency domain channel between destination node For H^sdAnd H^rd, destination node receives the time-domain signal from source node and via node and is expressed as

$\begin{array}{c}{r}_n^d=e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2{\mathrm{\π\Δf}}_{rd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{\hat{s}}_{n-l}^r+z_n^d\\ =e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2{\mathrm{\π\Δf}}_{rd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}\left(e^{+j2\mathrm{\π}\mathrm{\Δ}{\hat{f}}_{sr}(n-l)T_s}{s}_{n-l}^r\right)+z_n^d\\ \≈e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2\mathrm{\π}(\mathrm{\Δ}{\hat{f}}_{sr}+{\mathrm{\Δf}}_{rd}){\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{s}_{n-l}^r+z_n^d\end{array}$

Wherein Δ f_sd=f_s-f_dWith Δ f_rd=f_r-f_dThe carrier frequency of source node and via node to destination node link is represented respectively Rate error, f_dFor the carrier frequency of purpose node, due toFor Δ f_sr=f_s-f_rEstimated value,It is not zero, because This can be obtained

$\begin{array}{c}\mathrm{\Δ}{\hat{f}}_{sr}+{\mathrm{\Δf}}_{rd}\\ =(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+{\mathrm{\Δf}}_{sr}+{\mathrm{\Δf}}_{rd}\\ =(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+(f_s-f_r)+(f_r-f_d)\\ =(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+f_s-f_d\\ =(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+{\mathrm{\Δf}}_{sd}\end{array}$

Further try to achieve

$\begin{array}{c}{r}_n^d=e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2\mathrm{\π}\[(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+{\mathrm{\Δf}}_{sd}\]{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{s}_{n-l}^r+z_n^d\\ =e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}(\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2\mathrm{\π}(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr}){\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{s}_{n-l}^r)+z_n^d\end{array}$

AlthoughBut due toThereforeIgnore, and then can obtain

$\begin{array}{c}{r}_n^d=e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+e^{j2\mathrm{\π}\[(\mathrm{\Δ}{\hat{f}}_{sr}-{\mathrm{\Δf}}_{sr})+{\mathrm{\Δf}}_{sd}\]{\mathrm{nT}}_s}\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{s}_{n-l}^r+z_n^d\\ =e^{j2{\mathrm{\π\Δf}}_{sd}{\mathrm{nT}}_s}(\underset{l=0}{\overset{L_{sd}-1}{\mathrm{\Σ}}}{h}_l^{sd}{s}_{n-l}+\underset{l=0}{\overset{L_{rd}-1}{\mathrm{\Σ}}}{h}_l^{rd}{s}_{n-l}^r)+z_n^d\end{array}$

For the signal of the training sequence part for Frequency Estimation, meetTherefore

Then its frequency error estimates Δ f_sdEstimated value table be shown asWhereinWithRespectively For the time-domain received signal of correspondence training sequence part repetitive substructure；Δ f is estimated according to frequency error_sdEstimated value to receive To time-domain signal carry out offset frequency error.

3. it is according to claim 1 for cooperation communication system medium frequency synchronous method, it is characterised in that the communication system The prefix part of system adopts [P1, P2]=[A, reverse (A)] structures.

4. it is according to claim 1 for cooperation communication system medium frequency synchronous method, it is characterised in that the source node Length is adopted for N_SReally sequencing is arrangedAs training sequence, by 2 parts of identicalComposition；CP takes from the last L of s in part_CPLength thereofIn order to protect Card training sequence under multi-path jamming channel circumstance is not disturbed by prefix part, length L of CP parts_CPMore than multipath channel Length L_h, that is, meet L_CP＞ L_h。