阅读说明：本技术 一种基于stbc接收信号的残留频偏跟踪方法及系统 (Residual frequency offset tracking method and system based on STBC received signal ) 是由 蒋芜 吴建兵 吴帅 于 2020-06-18 设计创作，主要内容包括：本发明提供一种基于STBC接收信号的残留频偏跟踪方法及系统,所述残留频偏跟踪方法包括以下步骤：步骤S1,对发送的训练序列进行<I>LS</I>方法求解实现信道估计；步骤S2,通过训练期间内的接收信号进行信道估计得到的信道响应,并计算得到其均衡后发送信号；步骤S3,对均衡后发送信号进行解调,实现相位差估计,并以此对当前符号进行补偿。本发明在处理STBC接收信号时,完成第一个数据符号解调后,根据数据均衡后的信号和解调信号差异估计残留频偏和补偿当前符号相位,并在下个符号解调前补偿残留频偏,进而能够逐个符号迭代这个过程,最终达到提升接收性能的目的。(The invention provides a residual frequency offset tracking method and a system based on STBC received signals, wherein the residual frequency offset tracking method comprises the following steps: step S1, the transmitted training sequence is processed LS Solving the method to realize channel estimation; step S2, carrying out channel estimation through the received signal in the training period to obtain the channel response, and calculating to obtain the balanced transmitted signal; and step S3, demodulating the equalized transmission signal to realize phase difference estimation and compensate the current symbol. When the invention processes the STBC received signal, after the first data symbol is demodulated, the residual frequency offset is estimated and the current symbol phase is compensated according to the difference between the signal after data equalization and the demodulated signal, and the residual frequency offset is compensated before the next symbol is demodulated, so that the process can be iterated one by one, and the purpose of improving the receiving performance is finally achieved.)

1. A residual frequency offset tracking method based on STBC received signals is characterized by comprising the following steps:

step S1, LS method solving is carried out on the transmitted training sequence to realize channel estimation;

step S2, carrying out channel estimation on the received signal in the training period to obtain a channel response, and calculating to obtain a balanced transmitted signal;

and step S3, demodulating the equalized transmission signal to realize phase difference estimation and compensate the current symbol.

2. The method of claim 1, wherein in step S1, the training sequence X is transmitted within a transmission frame_refIs represented by X_ref＝[x_ref(1),x_ref(2),…,x_ref(L)]L is the total number of sub-carriers bearing transmission information, when STBC is used for transmission, a transmitting end uses double-antenna transmission, a receiving end uses single-antenna reception, and a training sequence needs two symbols in a receiving system with two transmissions and one reception; received signal Y during training_refIs represented by Y_ref＝[[y_ref1(1)y_ref2(1)],…,[y_ref1(L)y_ref2(L)]]Ref1 denotes a first received training symbol, ref2 denotes a second received training symbol, y_ref1(L) and y_ref2(L) respectively representing frequency domain representations of the first received training symbol and the second received training symbol when the carrier sequence number is L; transmission channel frequency domain response H_LSIs represented by H_LS＝h₁(i),i∈[1L]And h₂(i),i∈[1L]The channel responses of the first transmitting antenna and the second transmitting antenna at the carrier serial number i respectively,

3. The method of claim 2, wherein in step S1, the residual frequency offset is derived from the STBC received signal according to the formulaAnd carrying out LS method solution to realize channel estimation.

4. The method of claim 2 or 3, wherein in step S2, the transmitted data sequence is a complex sequence denoted by x_k,i,n，i＝1,…,N_SS,k＝1,…L,n＝1,…N_SYMIn which N is_SSFor transmission of spatial streams, N_SYMThe total number of the transmission symbols is L, the total number of the subcarriers bearing transmission information is L, and k and n are natural numbers; transmitting spatial stream d based on format of STBC transmission_1,k,nBy space-time flowAnd space-time streamTo carry, the received signal during the training period is Y_n＝[y_n(1),y_n(2),…,y_n(L)]Wherein, y_n(L) is a received signal Y_nFrequency domain representation when the carrier serial number is L; after channel response obtained by channel estimation, two paired received symbols Y are taken_2m-1And receiving a symbol Y_2mThen there isi is 1, …, L, wherein y_2m(i) And y_2m-1(i) Frequency domain representations h of received symbols 2m and 2m-1, respectively, on carrier number i₁(i) And h₂(i) The channel responses x of the first transmitting antenna and the second transmitting antenna at the carrier serial number i_i,1,2m-1And x_i,2,2mRespectively, frequency domain representations of the transmitted symbols 2m and 2m-1 at carrier index i,

5. The method of claim 4, wherein in step S2, the residual frequency offset is derived from the STBC-based received signal according to the formula

6. The method of claim 5, wherein in step S3, the equalized transmission signal X is subjected to residual frequency offset tracking_n＝[x_n(1),…,x_n(L)]The symbol stream is QAM demodulated, and the equalized transmitted signal X is obtained in the QAM demodulation process_nIdeal position Z of_n＝[z_n(1),…,z_n(L)]Wherein x is_n(L) is a frequency domain representation of the equalized symbol sequence n at the carrier number L, z_n(L) is x_n(L) ideal position after QAM demodulation.

7. The method of claim 6, wherein in step S3, the equalized transmission signal X is used as a basis for tracking residual frequency offset of the STBC-based received signal_nAnd ideal position Z_nBy the formula Phase ═ E [ angle (z) ]_n(i))-angle(x_n(i))]Estimating the Phase difference Phase to compensate the current symbol, wherein z_n(i) And x_n(i) Are each z_n(L) and x_n(L) a value when i ═ L, where i ═ 1, … L, angle (x) is the phase of the complex signal x, E [ x ═ L]To average the vector x.

8. The method of claim 7, wherein in step S3, the residual frequency offset is determined according to formula X_n＝[x_n(1),…,x_n(L)]Exp (j × pi × Phase) compensates the current symbol, and exp (j × pi × Phase) represents the complex signal Cos (pi × Phase) + j × Sin (pi × Phase).

9. The method of claim 8, wherein in step S3, the residual frequency offset is further determined by formula Y_n＝[y_n(1),y_n(2),…,y_n(L)]Exp (j pi Phase) compensates for the next set of symbols.

10. A system for tracking residual frequency offset based on STBC received signal, characterized in that it employs the method for tracking residual frequency offset based on STBC received signal according to any of claims 1 to 9, and comprises:

the channel estimation module is used for solving the transmitted training sequence by an LS method to realize channel estimation;

the data equalization module is used for carrying out channel estimation on a received signal in a training period to obtain a channel response, and calculating to obtain an equalized transmitted signal;

and the tracking compensation module is used for demodulating the equalized transmitted signal, realizing phase difference estimation and compensating the current symbol by the phase difference estimation.

Technical Field

The invention relates to a receiving technology based on an OFDM wireless system, in particular to a residual frequency offset tracking method based on STBC received signals in 802.11n/ac/ax standard, and further relates to a residual frequency offset tracking system adopting the residual frequency offset tracking method based on the STBC received signals.

Background

In the Wi-Fi standard (802.11n/ac/ax) of IEEE 802.11-based OFDM communication, the entire transmission bandwidth is divided into a plurality of independent sub-channels with the same bandwidth and orthogonal to each other to transmit data in parallel.

In which STBC transmission receives a combined signal of two space-time stream signals at a receiving end antenna, i.e. the combined signal In 802.11n/ac/ax transmission, if frequency offset calibration is not accurate, the existing residual frequency offset can cause phase rotation of a constellation diagram, and the phase rotation is more serious as the number of symbols increases. In order to resist the influence of residual frequency offset, pilot frequency values of known signals are embedded in each symbol, and the phase condition of the pilot frequencies can be utilized to pull back the rotation of a constellation diagram brought by the residual frequency offset to an ideal position, so that the receiving performance is improved.

However, in STBC transmission, after combining signals at the receiving end, since the pilot is ± 1,

the part is equal to 0, and the influence of the residual frequency offset cannot be corrected by using the pilot frequency at this time, so that the receiving performance is greatly influenced, and the problem that the method for correcting the residual frequency offset by using the pilot frequency for phase tracking during the reception of the STBC fails and the like is caused.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a residual frequency offset tracking method based on STBC reception, which can effectively improve the reception performance, and further provide a residual frequency offset tracking system using the residual frequency offset tracking method based on STBC received signals.

In view of the above, the present invention provides a residual frequency offset tracking method based on STBC received signals, comprising the following steps:

step S1, LS method solving is carried out on the transmitted training sequence to realize channel estimation;

step S2, carrying out channel estimation on the received signal in the training period to obtain a channel response, and calculating to obtain a balanced transmitted signal;

and step S3, demodulating the equalized transmission signal to realize phase difference estimation and compensate the current symbol.

In a further improvement of the present invention, in step S1, the training sequence X is transmitted in one transmission frame_refIs represented by X_ref＝[x_ref(1),x_ref(2),…,x_ref(L)]And L is the total number of subcarriers bearing transmission information, when STBC is used for transmission, a transmitting end uses double antennas for transmission, and a receiving end uses a single antenna for reception. In a two-transmit-one-receive receiving system, the training sequence requires two symbols.

Received signal Y during training_refIs represented by Y_ref＝[[y_ref1(1)y_ref2(1)],…,[y_ref1(L)y_ref2(L)]]Ref1 denotes a first received training symbol, ref2 denotes a second received training symbol, y_ref1(L) and y_ref2(L) respectively representing frequency domain representations of the first received training symbol and the second received training symbol when the carrier sequence number is L; transmission channel frequency domain response H_LSIs shown as

h₁(i),i∈[1L]And h₂(i),i∈[1L]The channel responses of the first transmitting antenna and the second transmitting antenna at the carrier serial number i respectively,for two received training sequences and two transmitted training sequences X_refChannel response matrix representation on carrier sequence number L; by the formulaTo indicate the transmitted training sequence X_refReceiving signal Y_refAnd a transmission channel frequency domain response H_LSRelation between y_ref1(i) And y_ref2(i) Are each y_ref1(L) and y_ref2(L) a value when i ═ L, i being a natural number from 1 to L.

In a further improvement of the present invention, in the step S1, the formula is used

And carrying out LS method solution to realize channel estimation.

In a further improvement of the present invention, in step S2, in a transmission frame, the transmitted data sequence is a complex sequence represented by x_k,i,n,i＝1,…,N_SS,k＝1,…L,n＝1,…N_SYMIn which N is_SSFor transmission of spatial streams, N_SYMThe total number of the transmission symbols is L, the total number of the subcarriers bearing transmission information is L, and k and n are natural numbers; transmitting spatial stream d based on format of STBC transmission_1,k,nBy space-time flowAnd space-time streamTo carry, the received signal during the training period is Y_n＝[y_n(1),y_n(2),…,y_n(L)]Wherein, y_n(L) is a received signal Y_nFrequency domain representation when the carrier serial number is L; after channel response obtained by channel estimation, two paired received symbols Y are taken_2m-1And receiving a symbol Y_2mThen there isWherein, y_2m(i) And y_2m-1(i) Frequency domain representations h of received symbols 2m and 2m-1, respectively, on carrier number i₁(i) And h₂(i) Channel responses, x, at carrier sequence number i for the first transmit antenna and the second transmit antenna, respectively_i,1,2m-1And x_i,2,2mRespectively the frequency domain representation of the transmitted symbols 2m and 2m-1 on the carrier number i,

andare respectively x_i,1,2m-1And x_i,2,2mComplex conjugation of (a).

In a further improvement of the present invention, in the step S2, the formula is usedSending signal X after equalization is obtained through calculation_nWherein x is_i,1,2m-1Is an odd number symbol, x_i,2,2mEven numbered symbols.

In a further improvement of the present invention, in step S3, the equalized transmission signal X is processed_n＝[x_n(1),…,x_n(L)]The symbol stream is QAM demodulated, and the equalized transmitted signal X is obtained in the QAM demodulation process_nIdeal position Z of_n＝[z_n(1),…,z_n(L)]Wherein, the frequency domain representation of the symbol sequence n after equalization when the carrier serial number is L, z_n(L) is x_n(L) ideal position after QAM demodulation.

In a further improvement of the present invention, in step S3, the equalized transmission signal X is used as the basis for the equalization_nAnd ideal position Z_nBy the formula Phase ═ E [ angle (z) ]_n(1))-angle(x_n(1))]Estimating the Phase difference Phase to compensate the current symbol, wherein z_n(i) And x_n(i) Are each z_n(L) and x_n(L) a value when i is equal to L, where i is 1, … L, angle (x) is the phase of the complex signal x, E [ x ═ L]To average the vector x.

In a further improvement of the present invention, in the step S3, the formula X is used_n＝[x_n(1),…,x_n(L)]Exp (j × pi × Phase) compensates the current symbol, and exp (j × pi × Phase) represents the complex signal Cos (pi × Phase) + j × Sin (pi × Phase).

The invention further improves the method in that in the step S3, the formula Y is used_n＝[y_n(1),y_n(2),…,y_n(L)]Exp (j pi Phase) to the next set of symbolsCompensation is performed.

The invention also provides a residual frequency offset tracking system based on the STBC received signal, which adopts the residual frequency offset tracking method based on the STBC received signal and comprises the following steps:

the channel estimation module is used for solving the transmitted training sequence by an LS method to realize channel estimation;

the data equalization module is used for carrying out channel estimation on a received signal in a training period to obtain a channel response, and calculating to obtain an equalized transmitted signal;

and the tracking compensation module is used for demodulating the equalized transmitted signal, realizing phase difference estimation and compensating the current symbol by the phase difference estimation.

Compared with the prior art, the invention has the beneficial effects that: when the STBC received signal is processed, after the demodulation of a first data symbol is finished, the residual frequency offset is estimated and the current symbol phase is compensated according to the difference between the signal after data equalization and the demodulated signal, and the residual frequency offset is compensated before the demodulation of the next symbol, so that the process can be iterated one by one, and the purpose of improving the receiving performance is finally achieved.

Drawings

FIG. 1 is a schematic diagram of a workflow configuration of an embodiment of the present invention;

fig. 2 is a block diagram of a system architecture of one embodiment of the present invention.

Detailed Description

Preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

As shown in fig. 1, this example provides a method for tracking residual frequency offset based on STBC received signal, which includes the following steps:

step S1, LS method solving is carried out on the transmitted training sequence to realize channel estimation;

step S2, carrying out channel estimation through the received signal in the training period to obtain the channel response, and calculating to obtain the balanced transmitted signal;

and step S3, demodulating the equalized transmission signal to realize phase difference estimation and compensate the current symbol.

In this example, in step S1, a training sequence X is transmitted in one transmission frame_refIs represented by X_ref＝[x_ref(1),x_ref(2),…,x_ref(L)]And L is the serial number of the effective carrier symbols, when STBC is used for transmission, a transmitting end uses double-antenna transmission, a receiving end uses single-antenna reception, and a training sequence needs two symbols in a receiving system with two transmissions and one reception. Received signal Y during training_refIs represented by Y_ref＝[[y_ref1(1)y_ref2(1)],…,[y_ref1(L)y_ref2(L)]]Ref1 denotes a first received training symbol, ref2 denotes a second received training symbol, y_ref1(L) and y_ref2(L) respectively representing frequency domain representations of the first received training symbol and the second received training symbol when the carrier sequence number is L; transmission channel frequency domain response H_LSIs shown as

，h₁(i),i∈[1L]And h₂(i),i∈[1L]The channel responses of the first transmitting antenna and the second transmitting antenna at the carrier serial number i respectively,

for two transmit antennas and two transmit training sequences X_refChannel response matrix representation on carrier sequence number L; by the formula

To indicate the transmitted training sequence X_refReceiving signal Y_refAnd a transmission channel frequency domain response H_LSRelation between y_ref1(i) And y_ref2(i) Are each y_ref1(L) and y_ref2(L) a value when i ═ L, i is a natural number from 1 to L; then by the formulaTo indicate the transmitted training sequence X_refReceiving signal Y_refAnd a transmission channel frequency domain response H_LSRelation between y_ref1(i) Is … …, y_ref2(i) … …, i is a natural number from 1 to L; finally by the formulaAnd carrying out LS method solution to realize channel estimation.

In step S2 in this example, within a transmission frame, the transmitted data sequence is represented as a complex sequence x_k,i,n,i＝1,…,N_SS,k＝1,…L,n＝1,…N_SYMIn which N is_SSFor transmission of spatial streams, N_SYMThe total number of the transmission symbols is L, the total number of the subcarriers bearing transmission information is L, and k and n are natural numbers; transmitting spatial stream d based on format of STBC transmission_1,k,nBy space-time flow

And space-time stream

To carry, 2m ═ n, where the carrying mode is:

the STBC transmission transmits one part of data on a plurality of antennas and a plurality of time slices, performs some conjugate processing on the signals, and can perform MRC combination at a receiving end to obtain diversity gain, thereby greatly improving the capability of the signals to resist complex channels.

The receiving end uses single antenna to receive, and the received signal in the training period is Y_n＝[y_n(1),y_n(2),…,y_n(L)]Wherein, y_2m(i) And y_2m-1(i) Frequency domain representations h of received symbols 2m and 2m-1, respectively, on carrier number i₁(i) And h₂(i) Channel responses, x, at carrier sequence number i for the first transmit antenna and the second transmit antenna, respectively_i,1,2m-1And x_i,2,2mRespectively, transmit symbols 2m and2m-1 in the frequency domain on carrier number i,

and

are respectively x_i,1,2m-1And x_i,2,2mComplex conjugation of (a).

Then, by the formulaSending signal X after equalization is obtained through calculation_nWherein x is_i,1,2m-1Is an odd number symbol, x_i,2,2mEven numbered symbols.

In step S3 of the present example, the equalization-followed transmission signal X is first transmitted_n＝[x_n(1),…,x_n(L)]The symbol stream is QAM demodulated, and the equalized transmitted signal X is obtained in the QAM demodulation process_nIdeal position Z of_n＝[z_n(1),…,z_n(L)]Wherein, z is_n(i) And x_n(i) Are each z_n(L) and x_n(L) the value when i equals L, i equals 1, … L.

Then, the signal X is transmitted after equalization_nAnd ideal position Z_nBy the formula Phase ═ E [ angle (z) ]_n(1))-angle(x_n(1))]Estimating a Phase difference Phase to compensate the current symbol, wherein angle (x) is the Phase of the complex signal x, E [ x ]]To average the vector x. Then, by the formula X_n＝[x_n(1),…,x_n(L)]Exp (j × pi × Phase) compensates the current symbol, and exp (j × pi × Phase) represents the complex signal Cos (pi × Phase) + j × Sin (pi × Phase).

Preferably, in step S3 of this embodiment, the formula Y is further used_n＝[y_n(1),y_n(2),…,y_n(L)]Exp (j pi Phase) compensates for the next set of symbols.

As shown in fig. 2, this example further provides a residual frequency offset tracking system based on STBC received signal, which adopts the above-mentioned residual frequency offset tracking method based on STBC received signal, and includes:

the channel estimation module is used for solving the transmitted training sequence by an LS method to realize channel estimation; the channel estimation module mainly estimates the channel response of the system by using the signal difference between the received signal training sequence and the local training sequence;

the data equalization module is used for carrying out channel estimation on a received signal in a training period to obtain a channel response, and calculating to obtain an equalized transmitted signal; the data equalization module recovers a transmission signal estimation value by using a channel estimation and a receiving signal to realize data equalization;

the tracking compensation module is used for demodulating the equalized transmitted signal, realizing phase difference estimation and compensating the current symbol according to the phase difference estimation; the tracking compensation module preferably obtains an ideal transmission signal of the transmission signal obtained by equalization by using a maximum likelihood estimation method, then tracks a phase difference between the ideal transmission signal and the transmission signal, compensates a phase difference of a current symbol, and estimates a residual frequency offset of a next symbol.

The embodiment also comprises a modified frequency offset module used for compensating the frequency offset calculated by the previous symbol for the equalized data.

The process continues to complete iterations until the parsing of all symbols in the data frame is complete.

In summary, in this embodiment, when the STBC received signal is processed, after the first data symbol demodulation is completed, the residual frequency offset is estimated and the current symbol phase is compensated according to the difference between the signal after data equalization and the demodulated signal, and the residual frequency offset is compensated before the next symbol demodulation, so that the process can be iterated symbol by symbol, and the purpose of improving the receiving performance is finally achieved.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.