Combined timing and frequency offset estimation method for distributed antenna system

Abstract

The invention discloses a combined timing and frequency offset estimation method for a distributed antenna system, and belongs to the technical field of communication. The objective of the invention is to solve the problem of poor real-time performance of joint estimation of multi-time offset and multi-frequency offset in the DAS by the existing DAS synchronization method. The invention provides a method for combining timing and frequency offset estimation in the DAS based on good correlation characteristics of a CAZAC sequence and a multi-antenna synchronization sequence, and time offset and frequency offset estimation of different receiving and transmitting antenna pairs can be realized at the same time. Sliding cross-correlation operation is adopted and effective peak detection is carried out, time offset and integer frequency offset estimation of different receiving and transmitting antenna pairs is realized, and cyclic correlation operation is adopted to estimate decimal frequency offset of different receiving and transmitting antenna pairs. Moreover, the method employs a simultaneous detection thought, can achieve the joint estimation of the time offset and frequency offset of different receiving and transmitting antenna pairs, is lower in complexity and higher in real-time performance, and can guarantee the accuracy of an estimation result. The method can be applied to timing and frequency offset estimation of a distributed antenna system.

Description

Technical Field

[0001] The present invention belongs to the field of communication technology, and in particular relates to a method for joint timing and frequency offset estimation of a distributed antenna system. Background Art

[0002] The development and evolution of the next generation communication technology 6G has put forward a greater demand for the scale of antenna arrays. According to the different deployment positions of antennas in physical space, multi-antenna systems can be divided into centralized antenna systems (CAS) and distributed antenna systems (DAS). The synchronization problem is one of the key issues faced in DAS. The synchronization technology is mainly divided into symbol timing synchronization and carrier frequency synchronization. In order to achieve correct demodulation and judgment of the signal, the receiving end needs to have a good synchronization relationship. Accurate and achievable synchronization technology is an indispensable condition for achieving reliable transmission of communication systems. In the single-input single-output (SISO) system, symbol timing offset (STO) and carrier frequency offset (CFO) will introduce inter-symbol interference (ISI) and phase rotation, resulting in deterioration of system performance. In DAS, the antennas at both ends of the transmission and reception are geographically distributed. The transmission delays between different transmitting antennas and receiving antennas are different, and each transmitting antenna and receiving antenna is generated by an independent local crystal oscillator. DAS has multiple STOs and CFOs, which greatly increases the complexity of parameter estimation.

[0003] Constant Amplitude Zero Autocorrelation Code (CAZAC), as a synchronization sequence with constant amplitude, good autocorrelation and cross-correlation, has been widely used in actual communication systems to solve signal synchronization problems. Reference 1 (Zhang Jianhua, Feng Chong, Liu Yi, et al. Timing synchronization algorithm for MIMO OFDM system [J]. Journal of Beijing University of Posts and Telecommunications, 2009, 32(01):118-121.) proposed a weighted algorithm based on cyclic shift of CAZAC sequence, which can effectively estimate the delay between antennas, but it is impossible to determine the timing position of each transmitting antenna through the peak point, and it is impossible to achieve frequency offset estimation. Reference 2 (Wang Dan, Yang Heng, Deng Qing, et al. Synchronization algorithm based on distributed UFMC-MIMO system [J]. Journal of Nanjing University of Posts and Telecommunications (Natural Science Edition), 2021, 41(03):9-13.) also cyclically shifts the CAZAC sequence and designs a synchronization sequence with good cross-correlation, but the timing and frequency offset estimation adopts the method of detecting each transmitting and receiving antenna pair separately. Reference 3 (Chen Xin. Research on Key Technologies for Synchronization of Distributed Multi-antenna Systems [D]. Southeast University, 2019.) proposes a threshold decision timing synchronization algorithm based on the cyclic shift CAZAC sequence according to the characteristics of DAS, but assumes that there is only one frequency offset between the transmitting and receiving antennas.

[0004] In summary, the existing DAS synchronization method considers the situation where only time offset or only frequency offset exists, usually only estimates the time offset or only estimates the frequency offset, and the time offset and frequency offset estimation adopts the method of independent detection between different transmitting and receiving antenna pairs, and the real-time performance of the estimation is poor. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the existing DAS synchronization method has poor real-time performance in jointly estimating multiple time offsets and multiple frequency offsets in DAS, and propose a distributed antenna system joint timing and frequency offset estimation method.

[0006] The technical solution adopted by the present invention to solve the above technical problems is: a method for joint timing and frequency offset estimation of a distributed antenna system, the method specifically comprising the following steps:

[0007] Step 1: After constellation mapping, serial / parallel conversion and modulation, the data of the i-th transmitting antenna is modulated to obtain modulated data, i = 1, 2, 3, ..., N t ;

[0008] Step 2: Combine the modulated data of the i-th transmitting antenna with the synchronization symbol corresponding to the i-th transmitting antenna, add a cyclic prefix to the combined data, and perform parallel / serial conversion on the data after the cyclic prefix is ​​added to obtain a frame of transmission signal of the i-th transmitting antenna;

[0009] The transmission signal of the i-th transmitting antenna is passed through a digital-to-analog converter, and the digital-to-analog converted data is transmitted to the wireless channel;

[0010] Step 3: Each receiving antenna receives the superimposed signals of each transmitting antenna;

[0011] For the jth receiving antenna, the signal received by the jth receiving antenna is converted into a signal after analog-to-digital conversion through an analog-to-digital converter, j = 1, 2, 3, ..., N r ;

[0012] And estimate the time deviation and frequency deviation of the analog-to-digital converted signal received by the jth receiving antenna;

[0013] Step 4: using the time offset and frequency offset estimation results corresponding to the jth receiving antenna, the analog-to-digital converted signal received by the jth receiving antenna is compensated to obtain a compensated signal received by the jth receiving antenna;

[0014] Step 5: Perform serial / parallel conversion on the compensated signal received by the j-th receiving antenna, remove the cyclic prefix from the serial / parallel conversion result, and then demodulate, channel equalize and demap the signal after removing the cyclic prefix to obtain the demapping result of the j-th receiving antenna.

[0015] Furthermore, the synchronization symbol of each transmitting antenna in the distributed antenna system is obtained by connecting two synchronization sequences of length N, wherein the first synchronization sequence is obtained by connecting two identical CAZAC sequences, and the second synchronization sequence is a conjugate sequence of the first synchronization sequence.

[0016] Furthermore, the CAZAC sequence is specifically:

[0017]

[0018] Where c1(k) is the kth sampling point in the CAZAC sequence c1, k∈[0,N / 2-1], N / 2 is the length of the CAZAC sequence, r=N / 2-1, e is the base of the natural logarithm, and j is the imaginary unit;

[0019] In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, …, N / 2th sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1, and the N / 2+1st, N / 2+2nd, …, Nth sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1;

[0020] In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, ..., N / 2nd sampling points in the second synchronization sequence are c1 and c2 respectively. *The 1st, 2nd, ..., N / 2th sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c1 * The 1st, 2nd, ..., N / 2th sampling points in c1 * is the conjugated sequence of c1.

[0021] Furthermore, the 2nd, 3rd, ..., Nth t The calculation method of the synchronization symbol of the root transmitting antenna is:

[0022] For the i-th transmitting antenna, i=2,3,…,N t , cyclic shift s for CAZAC sequence c1 i bits, and obtain the sequence c on the i-th transmitting antenna i :

[0023] c i (k) = c1[(k+s i )modN / 2] (2)

[0024] Among them, c i (k) is the sequence c i The kth sampling point in (k+s i )modN / 2 means k+s i The remainder after dividing by N / 2;

[0025] In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the first synchronization sequence are respectively the sequence c i The 1st, 2nd, ..., N / 2nd sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the first synchronization sequence are respectively the sequence c i The 1st, 2nd, ..., N / 2th sampling points in ;

[0026] In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2th sampling points in the synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2th sampling points in c i * It is c i conjugated sequence.

[0027] Furthermore, the CAZAC sequence c1 is cyclically shifted by s i Bit, s i The specific values ​​are:

[0028]

[0029] Among them, s max represents the maximum cyclic shift length, Indicates rounding down;

[0030] s max =2*(N cp -1) (4)

[0031] Among them, N cp Indicates the length of the cyclic prefix.

[0032] Furthermore, the superimposed signal received by the j-th receiving antenna is:

[0033]

[0034] Among them, r j ′(n) represents the nth sampling point in the superimposed signal received by the jth receiving antenna, β i,j is the carrier frequency deviation normalized by the subcarrier spacing, x i (n) represents the nth sampling point in the modulated signal of the i-th transmitting antenna, n∈[-N cp ,N-1],δ i,j is the symbol timing deviation normalized by the sampling period between the i-th transmitting antenna and the j-th receiving antenna, L i,j is the number of multipath channels between the i-th transmitting antenna and the j-th receiving antenna, h i,j,l is the time domain channel response of the lth path between the i-th transmitting antenna and the j-th receiving antenna; τ i,j,l is the delay corresponding to the lth path between the i-th transmitting antenna and the j-th receiving antenna, w j (n) means the mean is 0 and the variance is Additive Gaussian white noise;

[0035] β i,j =ε i,j +ξ i,j (6)

[0036] Among them, ε i,j is the integer multiple frequency offset between the i-th transmitting antenna and the j-th receiving antenna; ξ i,j Represents the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna.

[0037] Furthermore, the time offset and frequency offset in the analog-to-digital converted signal received by the jth receiving antenna are estimated, and the specific estimation process is:

[0038] Step 1: Convert the analog-to-digital converted signal r received by the jth receiving antennaj (n) delays by N / 2 length, and obtains the delayed signal r j (n+N / 2);

[0039] For signal r j (n) and signal r j (n+N / 2) performs autocorrelation operation to obtain the timing autocorrelation function λ j (δ) is:

[0040]

[0041] Among them, r j (δ+n) is the signal r received by the jth receiving antenna j (n) is the δ+nth sampling point, δ represents the sampling point position, r j (δ+n+N / 2) is the signal r j The δ+nth sampling point of (n+N / 2), |r j (δ+n+N / 2)| represents the signal r j The signal modulus value at the δ+nth sampling point of (δ+n+N / 2), Represents r j conjugation of (δ+n+N / 2);

[0042] Step 2: When the timing autocorrelation function λ j (δ) When the first peak platform appears, retrieve the maximum peak value and the position of the maximum peak of the first peak platform, and take the maximum peak position of the first peak platform as the timing capture position of the first synchronization sequence δ j,coarse,1 ;

[0043] From the position of the timing autocorrelation function δ j,coarse,1 +(N+N cp ) / 2, retrieve the timing autocorrelation function λ j The maximum peak value and the position of the maximum peak of the second peak platform of (δ), and the maximum peak position of the second peak platform is used as the timing capture position δ of the second synchronization sequence j,coarse,2 ;

[0044] Then the starting position of the coarse timing synchronization sampling point is δ j,start,1 =δ j,coarse,1 -N cp / 2,δ j,start,2 =δ j,coarse,2 -N cp / 2;

[0045] Step 3: From position δ j,start,1 Start to respond to signal r j(n) Sampling is performed, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,1 ;

[0046] From position δ j,start,1 Start to respond to the delayed signal r j (n+N / 2) is sampled, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,2 ;

[0047] From position δ j,start,2 Start to respond to signal r j (n) Sampling is performed and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,3 ;

[0048] From position δ j,start,2 Start to respond to the delayed signal r j (n+N / 2) is sampled and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,4 ;

[0049] Step 4: The cross-correlation result R xy,1 With R xy,2 Multiply them together to get the timing metric function Λ j,1 (δ), the cross-correlation result R xy,3 With R xy,4 Multiply them together to get the timing metric function Λ j,2 (δ);

[0050]

[0051] Step 5: Retrieve the timing metric function Λ j,1 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the relevant peaks are sorted from small to large to obtain the position sequence

[0052] Retrieval timing metric function Λ j,2 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the relevant peaks are sorted from small to large to obtain the position sequence

[0053] Step 6: According to the position sequence The first correlation peak position in Obtaining interval difference positions of different transmitting antennas;

[0054]

[0055] Among them, i is the interval difference position of the i-th transmitting antenna;

[0056] If the position sequence The i-th correlation peak position in In the interval i-1 ,jiange i ), then the i-th transmitting antenna exists, otherwise the i-th transmitting antenna does not exist, and the total number of transmitting antennas is reduced by 1;

[0057] Similarly, the existence of each transmitting antenna is determined separately to obtain the total number of transmitting antennas Nt that finally exists. new and the number of the transmitting antenna that ultimately exists;

[0058] Step 7: From position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as From the position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as

[0059] according to and Estimate the integer frequency offset between the i-th transmitting antenna and the j-th receiving antenna

[0060] Step 8: right The peak position of the i-th transmitting antenna is corrected to obtain the precise timing synchronization position of the i-th transmitting antenna

[0061] Step 9: According to Determine the starting position of the sampling point for the cyclic correlation operation:

[0062]

[0063] in, Indicates the starting position of the sampling point of the cyclic correlation operation;

[0064] From Location Start sampling the signal rj(n), perform cyclic correlation operation on the sampling result and the local sequence c1, and obtain the correlation operation result;

[0065]

[0066] Where m is the length of the cyclic shift, m∈[0,N / 2-1], Indicates the result of related operations The mth element in ;

[0067] and in position The signal r j (n) delay by N / 2 length, perform cyclic correlation operation on the delayed signal and the local sequence c1, and obtain the correlation operation result;

[0068]

[0069] in, Indicates the result of related operations The mth element in ;

[0070] Step 10: From the relevant operation results Search Nt new The maximum peak value is Nt retrieved from new The positions corresponding to the peaks are sorted from small to large, and the final sorting result is recorded as

[0071] According to the sorting results Estimate the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna

[0072]

[0073] in, Indicates position d i In the related operation results The corresponding complex value in is Indicates position d i In the related operation results The corresponding complex value in , arg represents the calculated phase angle.

[0074] Furthermore, according to and Estimate the integer frequency offset between the i-th transmitting antenna and the j-th receiving antenna, specifically:

[0075]

[0076] in, express The peak position of the i-th transmitting antenna in, express The peak position of the i-th transmitting antenna.

[0077] Furthermore, the specific process of step 8 is as follows:

[0078]

[0079] Furthermore, the maximum cyclic shift length s max satisfy:

[0080]

[0081] Among them, ΔSTO max Indicates the maximum timing deviation between different transmitting antennas, ΔIFO max Indicates the maximum integer frequency deviation between different transmitting antennas.

[0082] The beneficial effects of the present invention are:

[0083] The present invention proposes a method for joint timing and frequency offset estimation in DAS based on the good correlation characteristics of CAZAC sequence and multi-antenna synchronization sequence, which can realize the simultaneous estimation of time offset and frequency offset of different transceiver antenna pairs. Sliding cross-correlation operation and effective peak detection are used to realize the estimation of time offset and integer frequency offset of different transceiver antenna pairs, and cyclic correlation operation is used to estimate the fractional frequency offset of different transceiver antenna pairs. Moreover, the present invention adopts the idea of ​​simultaneous detection, which can realize the joint estimation of time offset and frequency offset of different transceiver antenna pairs, has low complexity and high real-time performance, and can ensure the accuracy of the estimation results.

[0084] At the same time, simulation analysis of the timing estimation and frequency offset estimation results under fading channels was carried out, which confirmed the effectiveness of the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 Simplified model diagram for distributed antenna system;

[0086] Figure 2 This is the block diagram of the distributed antenna MISO system;

[0087] Figure 3 A schematic diagram of a synchronization symbol structure for a distributed antenna system;

[0088] Figure 4 The signal processing flow chart of the receiving end time-frequency offset estimation;

[0089] Figure 5 is a graph of autocorrelation function of received signal;

[0090] Figure 6 Schematic diagram of effective peak detection;

[0091] Figure 7 It is the timing measurement function curve diagram of case 1;

[0092] Figure 8 It is the timing measurement function curve diagram of case 2;

[0093] Figure 9(a) is a graph of the FFO estimated mean value;

[0094] FIG9( b ) is a graph showing the mean square error of FFO estimation. DETAILED DESCRIPTION

[0095] Specific implementation method 1: Combination Figure 2 This embodiment describes a method for joint timing and frequency offset estimation of a distributed antenna system, wherein the distributed antenna system comprises N t Transmitting antennas and N r The method specifically comprises the following steps:

[0096] Step 1: After the data of the i-th transmitting antenna is subjected to constellation mapping, serial / parallel conversion and modulation (the modulation method can be selected as any multi-carrier modulation method), the modulated data is obtained, i = 1, 2, 3, ..., N t ;

[0097] Step 2: Combine the modulated data of the ith transmitting antenna with the synchronization symbol corresponding to the ith transmitting antenna (i.e., directly connect the modulated data of the ith transmitting antenna to the synchronization symbol corresponding to the ith transmitting antenna), and then add a cyclic prefix (CP) to the combined data (e.g., Figure 3 As shown, in the combined data, CP is added before the first synchronization sequence and the second synchronization sequence respectively. For the data part modulated by the i-th transmitting antenna in the combined data, CP is added before each symbol to ensure the consistency of the synchronization symbol and the data symbol structure), and the data after adding the cyclic prefix is ​​converted into a parallel / serial format to obtain a frame of transmission signal of the i-th transmitting antenna;

[0098] The signal transmitted by the i-th transmitting antenna is passed through a digital-to-analog converter (DAC), and the converted data is transmitted to the wireless channel;

[0099] Step 3: Each receiving antenna receives the superimposed signals of each transmitting antenna;

[0100] For the jth receiving antenna, the signal received by the jth receiving antenna is converted into a signal through an analog-to-digital converter (ADC), j = 1, 2, 3, ..., N r ;

[0101] And estimate the time offset and frequency offset in the analog-to-digital converted signal received by the jth receiving antenna (DAS synchronization requires the joint estimation of time offset and frequency offset, which can be regarded as N r The problem of parameter estimation of independent multiple-input single-output (MISO) systems);

[0102] Step 4: using the time offset and frequency offset estimation results corresponding to the jth receiving antenna (i.e., the estimation results of step 3), the analog-to-digital converted signal received by the jth receiving antenna is compensated to obtain the compensated signal received by the jth receiving antenna;

[0103] Step 5: Perform serial / parallel conversion on the compensated signal received by the j-th receiving antenna, remove the cyclic prefix from the serial / parallel conversion result, and then demodulate, channel equalize and demap the signal after removing the cyclic prefix to obtain the demapping result of the j-th receiving antenna.

[0104] like Figure 1 As shown in the figure, in a distributed antenna system, the transmitting and receiving antennas are distributed in geographical locations. Different transmitting antennas can send the same data information to achieve spatial diversity, or they can send different data information to achieve spatial multiplexing. Due to the different distances between different transmitting antennas and receiving antennas, the time for each transmitted signal to arrive at the receiving antenna is different, and the system has multiple timing deviations; the transmission paths between different transmitting antennas and receiving antennas are different, and they experience different channel fading and multipath effects; different transmitting antennas and receiving antennas are driven by independent local oscillators, and the system has multiple frequency deviations.

[0105] Specific implementation method 2: Combination Figure 3 This embodiment is different from the first embodiment in that the synchronization symbol of each transmitting antenna in the distributed antenna system is obtained by connecting two synchronization sequences of length N, wherein the first synchronization sequence is obtained by connecting two identical CAZAC sequences, and the second synchronization sequence is a conjugate sequence of the first synchronization sequence.

[0106] The other steps and parameters are the same as those in the first embodiment.

[0107] Specific implementation method three: This implementation method is different from specific implementation method one or two in that: the CAZAC sequence is specifically:

[0108]

[0109] Where c1(k) is the kth sampling point in the CAZAC sequence c1, k∈[0,N / 2-1], N / 2 is the length of the CAZAC sequence, r=N / 2-1, e is the base of the natural logarithm, and j is the imaginary unit;

[0110] In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, …, N / 2th sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1, and the N / 2+1st, N / 2+2nd, …, Nth sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1;

[0111] In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, ..., N / 2nd sampling points in the second synchronization sequence are c1 and c2 respectively. * The 1st, 2nd, ..., N / 2th sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c1 * The 1st, 2nd, ..., N / 2th sampling points in c1 * is the conjugated sequence of c1.

[0112] The other steps and parameters are the same as those in the first or second embodiment.

[0113] Specific implementation method 4: This implementation method is different from the specific implementation methods 1 to 3 in that: the second, third, ..., N t The calculation method of the synchronization symbol of the root transmitting antenna is:

[0114] For the i-th transmitting antenna, i=2,3,…,N t , cyclic shift s for CAZAC sequence c1 i bits, and obtain the sequence c on the i-th transmitting antenna i :

[0115] c i (k) = c1[(k+s i )modN / 2] (2)

[0116] Among them, c i (k) is the sequence c i The kth sampling point in (k+s i )modN / 2 means k+s i The remainder after dividing by N / 2;

[0117] In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the first synchronization sequence are respectively the sequence ci The 1st, 2nd, ..., N / 2nd sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the first synchronization sequence are respectively the sequence c i The 1st, 2nd, ..., N / 2th sampling points in ;

[0118] In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2nd sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2th sampling points in c i * It is c i conjugated sequence.

[0119] The other steps and parameters are the same as those in Specific Embodiments 1 to 3.

[0120] Specific implementation mode 5: This implementation mode is different from any one of the specific implementation modes 1 to 4 in that: the CAZAC sequence c1 is cyclically shifted by s i Bit, s i The specific values ​​are:

[0121]

[0122] Among them, s max represents the maximum cyclic shift length, Indicates rounding down;

[0123] s max =2*(N cp -1) (4)

[0124] Among them, N cp Indicates the length of the cyclic prefix.

[0125] The other steps and parameters are the same as those in Specific Embodiments 1 to 4.

[0126] Specific implementation method 6: This implementation method is different from any one of the specific implementation methods 1 to 5 in that: the superimposed signal received by the j-th receiving antenna is:

[0127]

[0128] Among them, r j ′(n) represents the nth sampling point in the superimposed signal received by the jth receiving antenna, β i,j is the carrier frequency deviation normalized by the subcarrier spacing, x i(n) represents the nth sampling point in the modulated signal of the i-th transmitting antenna, n∈[-N cp ,N-1],δ i,j is the symbol timing deviation normalized by the sampling period between the i-th transmitting antenna and the j-th receiving antenna, L i,j is the number of multipath channels between the i-th transmitting antenna and the j-th receiving antenna, h i,j,l is the time domain channel response of the lth path between the i-th transmitting antenna and the j-th receiving antenna; τ i,j,l is the delay corresponding to the lth path between the i-th transmitting antenna and the j-th receiving antenna, w j (n) means the mean is 0 and the variance is Additive Gaussian white noise;

[0129] β i,j =ε i,j +ξ i,j (6)

[0130] Among them, ε i,j is the integer frequency offset (IFO) between the i-th transmitting antenna and the j-th receiving antenna; ξ i,j Represents the fractional frequency offset (FFO) between the i-th transmitting antenna and the j-th receiving antenna.

[0131] The other steps and parameters are the same as those in Specific Implementations 1 to 5.

[0132] Specific implementation method seven: Combination Figure 4 This embodiment is different from the first to sixth embodiments in that the time offset and frequency offset of the analog-to-digital converted signal received by the jth receiving antenna are estimated, and the specific estimation process is:

[0133] Step 1: Convert the analog-to-digital converted signal r received by the jth receiving antenna j (n) delays by N / 2 length, and obtains the delayed signal r j (n+N / 2);

[0134] For signal r j (n) and signal r j (n+N / 2) performs autocorrelation operation to obtain the timing autocorrelation function λ j (δ) is:

[0135]

[0136] Among them, r j (δ+n) is the signal r received by the jth receiving antennaj (n) is the δ+nth sampling point, δ represents the sampling point position, r j (δ+n+N / 2) is the signal r j The δ+nth sampling point of (n+N / 2), |r j (δ+n+N / 2)| represents the signal r j The signal modulus value at the δ+nth sampling point of (δ+n+N / 2), Represents r j conjugation of (δ+n+N / 2);

[0137] Step 2: Figure 5 As shown, when the timing autocorrelation function λ j (δ) When the first peak platform appears, retrieve the maximum peak value and the position of the maximum peak of the first peak platform, and take the maximum peak position of the first peak platform as the timing capture position δ of the first synchronization sequence in each synchronization symbol j,coarse,1 ;

[0138] From the position of the timing autocorrelation function δ j,coarse,1 +(N+N cp ) / 2, retrieve the timing autocorrelation function λ j The maximum peak value and the position of the maximum peak of the second peak platform of (δ), and the maximum peak position of the second peak platform is used as the timing capture position δ of the second synchronization sequence in each synchronization symbol j,coarse,2 ;

[0139] Then the starting position of the coarse timing synchronization sampling point is δ j,start,1 =δ j,coarse,1 -N cp / 2,δ j,start,2 =δ j,coarse,2 -N cp / 2;

[0140] Step 3: From position δ j,start,1 Start to respond to signal r j (n) Sampling is performed, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,1 ;

[0141] From position δ j,start,1 Start to respond to the delayed signal r j (n+N / 2) is sampled, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,2 ;

[0142] From position δ j,start,2 Start to respond to signal r j (n) Sampling is performed and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,3 ;

[0143] From position δ j,start,2 Start to respond to the delayed signal r j (n+N / 2) is sampled and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,4 ;

[0144] Step 4: The cross-correlation result R xy,1 With R xy,2 Multiply them together to get the timing metric function Λ j,1 (δ), the cross-correlation result R xy,3 With R xy,4 Multiply them together to get the timing metric function Λ j,2 (δ);

[0145]

[0146] The timing metric function is obtained by multiplying the cross-correlation operation of the two parts, which can improve its sharpness and further improve the timing synchronization performance (YANG F, ZHANG X. Sharpening Timing-Metrics for Auto-Correlation Based Coarse Symbol Synchronization in OFDM Systems[C] / / Communications(ICC),2014IEEE International Conference on.IEEE,2014:2227-2232.);

[0147] Step 5: Retrieve the timing metric function Λ j,1 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the relevant peaks are sorted from small to large to obtain the position sequence

[0148] Retrieval timing metric function Λ j,2 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the relevant peaks are sorted from small to large to obtain the position sequence

[0149] Step 6: Figure 6 As shown, according to the position sequence The first correlation peak position in Obtaining interval difference positions of different transmitting antennas;

[0150]

[0151] Among them, i is the interval difference position of the i-th transmitting antenna. It should be noted that if the i-th transmitting antenna is the first transmitting antenna, s i The value of is 0;

[0152] If the position sequence The i-th correlation peak position in In the interval i-1 ,jiange i ) (jiange0=0), the i-th transmitting antenna exists, otherwise the i-th transmitting antenna does not exist, and the total number of transmitting antennas is reduced by 1;

[0153] Similarly, the existence of each transmitting antenna is determined separately to obtain the total number of transmitting antennas Nt that finally exists. new and the number of the transmitting antenna that ultimately exists;

[0154] Step 7: From position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as From the position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as

[0155] according to and Estimate the integer frequency offset between the i-th transmitting antenna (here still refers to the original number of the transmitting antenna) and the j-th receiving antenna

[0156] Step 8: right The peak position of the i-th transmitting antenna (the timing position of the i-th transmitting antenna) is corrected to obtain the precise timing synchronization position of the i-th transmitting antenna

[0157] Step 9: According to Determine the starting position of the sampling point for the cyclic correlation operation:

[0158]

[0159] in, Indicates the starting position of the sampling point of the cyclic correlation operation;

[0160] From Location Start to respond to signal r j (n) Sampling, performing a cyclic correlation operation on the sampling result and the local sequence c1 to obtain a correlation operation result;

[0161]

[0162] Where m is the length of the cyclic shift, m∈[0,N / 2-1], Indicates the result of related operations The mth element in ;

[0163] and in position The signal r j (n) delay by N / 2 length, perform cyclic correlation operation on the delayed signal and the local sequence c1, and obtain the correlation operation result;

[0164]

[0165] in, Indicates the result of related operations The mth element in ;

[0166] Step 10: From the relevant operation results Search Nt new The maximum peak value is Nt retrieved from new The positions corresponding to the peaks are sorted from small to large, and the final sorting result is recorded as

[0167] Similarly, from the results of related operations Search Nt new The maximum peak value is obtained, and the positions corresponding to the retrieved peak values ​​are sorted from small to large. The sorting result is therefore:

[0168] According to the sorting results Estimate the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna

[0169]

[0170] in, Indicates position d i In the related operation results The corresponding complex value in is Indicates position d i In the related operation results The corresponding complex value in , arg represents the calculated phase angle.

[0171] The other steps and parameters are the same as those in Specific Embodiments 1 to 6.

[0172] Specific implementation eight: This implementation differs from specific implementations one to seven in that: and Estimate the integer frequency offset between the i-th transmitting antenna and the j-th receiving antenna, specifically:

[0173]

[0174] in, express The peak position of the i-th transmitting antenna in, express The peak position of the i-th transmitting antenna.

[0175] The other steps and parameters are the same as those in Specific Embodiments 1 to 7.

[0176] For a system with four transmitting antennas, if the first, third and fourth transmitting antennas exist, then the position sequence is Extract the first 3 elements from the position sequence If we extract the first three elements from The first element and position sequence in The first element in is the peak position of the first transmitting antenna, and the position sequence The second element and position sequence in The second element in is the peak position of the third transmitting antenna, and the position sequence The third element and position sequence in The third element in is the peak position of the fourth transmitting antenna.

[0177] Specific implementation method 9: This implementation method is different from the specific implementation methods 1 to 8 in that the specific process of step 8 is:

[0178]

[0179] The other steps and parameters are the same as those in Specific Embodiments 1 to 8.

[0180] Specific implementation method 10: This implementation method is different from any one of specific implementation methods 1 to 9 in that: the maximum cyclic shift length s max satisfy:

[0181]

[0182] Among them, ΔSTOmax Indicates the maximum timing deviation between different transmitting antennas, ΔIFO max Indicates the maximum integer frequency deviation between different transmitting antennas, N t >1.

[0183] The other steps and parameters are the same as those in Specific Embodiments 1 to 9.

[0184] The present invention limits the range difference of the maximum time deviation and frequency deviation that can be detected by the transmitting antenna. t As the detection range increases, the detection range decreases.

[0185] Simulation Results

[0186] Taking a 4×1 DAS as an example, the CAZAC sequence-based distributed antenna system joint timing and frequency offset estimation method proposed in the present invention is simulated and verified. The simulation content includes:

[0187] (1) Timing estimation and IFO estimation results of different transmit and receive antenna pairs when there are multiple time offsets and frequency offsets;

[0188] (2) FFO estimation mean and FFO estimation mean square error curves for different transmit and receive antenna pairs.

[0189] Table 1 Simulation parameter settings

[0190]

[0191] According to the above parameter settings, the first sampling point position in the simulation process is selected to simulate the preamble noise N n The starting position of the timing is, ideally, when there is no STO and CFO between the transmitting and receiving antennas, the timing position is the first position after removing the CP:

[0192] N n +N cp +1=288+32+1=321 (18)

[0193] (1) Timing estimation and IFO estimation results for different transmit and receive antenna pairs when there is time offset and frequency offset

[0194] When the maximum timing offset and the maximum integer frequency offset between different transmitting antennas satisfy the relationship between equation (17) and the simulation parameter setting, the combined timing and frequency offset estimation algorithm proposed in the present invention can be used for estimation. In order to facilitate the comparison of subsequent experiments, the STO and CFO of different TXs are set as follows:

[0195] Table 2 STO and CFO parameter settings for different TXs in case 1

[0196]

[0197] Table 3 STO and CFO parameter settings for different TXs in case 2

[0198]

[0199] As shown in Tables 2 and 3, two different time offset and frequency offset situations are given under the limited constraints. Case 1 corresponds to the time offset and frequency offset of different TXs increasing with the increase of the number of antennas, and case 2 corresponds to the time offset and frequency offset of different TXs decreasing with the increase of the number of antennas. Other random distribution situations are between the two special situations, and the analysis process and ideas are the same.

[0200] like Figure 7 As shown in Figure 1, the timing metric function curve is given in case 1. The black dotted line corresponds to the interval difference position of different transmitting antennas, R1 represents the cross-correlation peak of the received signal and c1, and R2 represents the cross-correlation peak of the received signal and c1. * The cross-correlation peak value. Since the synchronization sequences of different transmitting antennas are cyclically shifted, the position of the correlation peak will shift accordingly. Taking the position of TX1 as the reference, the interval range difference of TX2 to TX4 is given in turn. When the correlation peak position of the corresponding antenna is within the interval, it is judged that the transmitting antenna exists. Under the time offset and frequency offset of situation 1, different TXs are all within the interval, so all transmitting antennas exist, and TX4 is at the maximum value of the critical range.

[0201] After determining that a valid peak exists, according to the correlation peak position, the correlation peaks corresponding to TX1 are 336 and 614, the correlation peak positions corresponding to TX2 are 359 and 635, the correlation peak positions corresponding to TX3 are 382 and 656, and the correlation peak positions corresponding to TX4 are 405 and 677. According to formula (15), the IFO of different transmit and receive antenna pairs is calculated, and the calculation results are 10, 12, 14, and 16, which correspond to the IFO set in case 1.

[0202] Next, according to the calculated IFO estimation results, the timing positions of different TXs are corrected. According to equation (16), the corrected position of TX1 is The corrected position of TX2 is The corrected position of TX3 is The corrected position of TX4 is The timing position differences with the ideal case of equation (18) are 10, 12, 14, and 16, respectively, corresponding to the STO set in case 1.

[0203] like Figure 8As shown, the timing metric function curve in case 2 is given. Also taking the position of TX1 as the reference, the black dotted line corresponds to the interval difference position of different transmitting antennas. Due to the influence of channel fading during the transmission process, the detected correlation peak position does not all fall within the interval range. In the range of 355-375, there is no correlation peak, that is, TX2 cannot be detected, and the total number of transmitting antennas is recorded as 3; in the range of 375-395, there is a correlation peak 379, that is, TX3 exists; in the range of 395-415, there is a correlation peak 396, that is, TX4 exists; in the range greater than 415, there is a correlation peak 473, but the correlation peak position at this time exceeds the maximum critical range of the effective antenna, so the peak position is invalid. After the effective transmitting antenna is detected, IFO estimation and timing position correction are performed according to the peak positions corresponding to R1 and R2. The process is the same as the processing method of case 1, and will not be explained here.

[0204] (2) FFO estimation mean and FFO estimation mean square error curves for different transmit and receive antenna pairs

[0205] In case 1, the corrected timing positions of different transmitting antennas are compared according to equation (11), and the smallest one is selected as the starting point of the synchronization sequence signal, that is,

[0206] Figure 9(a) and Figure 9(b) respectively show the FFO estimation mean and FFO estimation mean square error curves of different transmit antennas. After cyclic correlation calculation, the FFO of different transmit antennas can be estimated at the same time. It can be seen from the FFO estimation mean that the FFO estimation result of TX1 is 0.05, the FFO estimation result of TX2 is 0.15, the FFO estimation result of TX3 is 0.25, and the FFO estimation result of TX4 is 0.35, which is the same as the parameter setting in case 1. It can be seen from the FFO estimation mean square error that different TXs have basically consistent mean square error performance curves, and the FFO estimation of different transmit and receive antennas can be achieved at the same time.

[0207] The above calculation examples of the present invention are only used to explain the calculation model and calculation process of the present invention in detail, and are not intended to limit the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for joint timing and frequency offset estimation of a distributed antenna system, characterized in that: The method specifically comprises the following steps: Step 1: After constellation mapping, serial / parallel conversion and modulation, the data of the i-th transmitting antenna is modulated to obtain modulated data, i = 1, 2, 3, ..., N t ; Step 2: Combine the modulated data of the i-th transmitting antenna with the synchronization symbol corresponding to the i-th transmitting antenna, add a cyclic prefix to the combined data, and perform parallel / serial conversion on the data after the cyclic prefix is ​​added to obtain a frame of transmission signal of the i-th transmitting antenna; The transmission signal of the i-th transmitting antenna is passed through a digital-to-analog converter, and the digital-to-analog converted data is transmitted to the wireless channel; Step 3: Each receiving antenna receives the superimposed signals of each transmitting antenna; For the jth receiving antenna, the signal received by the jth receiving antenna is converted into a signal after analog-to-digital conversion through an analog-to-digital converter, j = 1, 2, 3, ..., N r ; And estimate the time offset and frequency offset of the analog-to-digital converted signal received by the jth receiving antenna; Step 4: using the time offset and frequency offset estimation results corresponding to the jth receiving antenna, the analog-to-digital converted signal received by the jth receiving antenna is compensated to obtain a compensated signal received by the jth receiving antenna; Step 5: Perform serial / parallel conversion on the compensated signal received by the j-th receiving antenna, remove the cyclic prefix from the serial / parallel conversion result, and then demodulate, channel equalize and demap the signal after removing the cyclic prefix to obtain the demapping result of the j-th receiving antenna.

2. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 1, characterized in that: The synchronization symbol of each transmitting antenna in the distributed antenna system is obtained by connecting two synchronization sequences of length N, wherein the first synchronization sequence is obtained by connecting two identical CAZAC sequences, and the second synchronization sequence is a conjugate sequence of the first synchronization sequence.

3. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 2, characterized in that: The CAZAC sequence is specifically: Where c1(k) is the kth sampling point in the CAZAC sequence c1, k∈[0,N / 2-1], N / 2 is the length of the CAZAC sequence, r=N / 2-1, e is the base of the natural logarithm, and j is the imaginary unit; In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, …, N / 2th sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1, and the N / 2+1st, N / 2+2nd, …, Nth sampling points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1; In the synchronization symbol of the first transmitting antenna, the 1st, 2nd, ..., N / 2nd sampling points in the second synchronization sequence are c1 and c2 respectively. * The 1st, 2nd, ..., N / 2th sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c1 * The 1st, 2nd, ..., N / 2th sampling points in c1 * is the conjugated sequence of c1.

4. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 3, characterized in that: The 2nd, 3rd, ..., Nth t The calculation method of the synchronization symbol of the root transmitting antenna is: For the i-th transmitting antenna, i=2,3,…,N t , cyclic shift s for CAZAC sequence c1 i bits, and obtain the sequence c on the i-th transmitting antenna i : c i (k)=c1[(k+s i )modN / 2] (2) Among them, c i (k) is the sequence c i The kth sampling point in (k+s i )modN / 2 means k+s i The remainder after dividing by N / 2; In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the first synchronization sequence are respectively the sequence c i The 1st, 2nd, ..., N / 2nd sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the first synchronization sequence are respectively the sequence c i The 1st, 2nd, ..., N / 2th sampling points in ; In the synchronization symbol of the i-th transmitting antenna, the 1st, 2nd, …, N / 2nd sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2th sampling points in the first synchronization sequence and the N / 2+1st, N / 2+2nd, ..., Nth sampling points in the second synchronization sequence are c i * The 1st, 2nd, ..., N / 2th sampling points in c i * It is c i conjugated sequence.

5. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 4, characterized in that: The CAZAC sequence c1 is cyclically shifted s i Bit, s i The specific values ​​are: Among them, s max represents the maximum cyclic shift length, Indicates rounding down; s max =2*(N cp -1) (4) Among them, N cp Indicates the length of the cyclic prefix.

6. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 5, characterized in that: The superimposed signal received by the j-th receiving antenna is: Among them, r j ′(n) represents the nth sampling point in the superimposed signal received by the jth receiving antenna, β i,j is the carrier frequency deviation normalized by the subcarrier spacing, x i (n) represents the nth sampling point in the modulated signal of the i-th transmitting antenna, n∈[-N cp ,N-1],δ i,j is the symbol timing deviation normalized by the sampling period between the i-th transmitting antenna and the j-th receiving antenna, L i,j is the number of multipath channels between the i-th transmitting antenna and the j-th receiving antenna, h i,j,l is the time domain channel response of the lth path between the i-th transmitting antenna and the j-th receiving antenna; τ i,j,l is the delay corresponding to the lth path between the i-th transmitting antenna and the j-th receiving antenna, w j (n) means the mean is 0 and the variance is Additive Gaussian white noise; b i,j =e i,j +ξ i,j (6) Among them, ε i,j is the integer multiple frequency offset between the i-th transmitting antenna and the j-th receiving antenna; ξ i,j Represents the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna.

7. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 6, characterized in that: The time offset and frequency offset of the analog-to-digital converted signal received by the jth receiving antenna are estimated, and the specific estimation process is: Step 1: Convert the analog-to-digital converted signal r received by the jth receiving antenna j (n) delays by N / 2 length to obtain the delayed signal r j (n+N / 2); For signal r j (n) and signal r j (n+N / 2) performs autocorrelation operation to obtain the timing autocorrelation function λ j (δ) is: Among them, r j (δ+n) is the signal r received by the jth receiving antenna j (n) is the δ+nth sampling point, δ represents the sampling point position, r j (δ+n+N / 2) is the signal r j The δ+nth sampling point of (n+N / 2), |r j (δ+n+N / 2)| represents the signal r j The signal modulus value at the δ+nth sampling point of (δ+n+N / 2), Represents r j conjugation of (δ+n+N / 2); Step 2: When the timing autocorrelation function λ j (δ) When the first peak platform appears, retrieve the maximum peak value and the position of the maximum peak of the first peak platform, and take the maximum peak position of the first peak platform as the timing capture position of the first synchronization sequence δ j,coarse,1 ; From the position of the timing autocorrelation function δ j,coarse,1 +(N+N cp ) / 2, retrieve the timing autocorrelation function λ j The maximum peak value and the position of the maximum peak of the second peak platform of (δ), and the maximum peak position of the second peak platform is used as the timing capture position δ of the second synchronization sequence j,coarse,2 ; Then the starting position of the coarse timing synchronization sampling point is δ j,start,1 =δ j,coarse,1 -N cp / 2,δ j,start,2 =δ j,coarse,2 -N cp / 2; Step 3: From position δ j,start,1 Start to respond to signal r j (n) Sampling is performed, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,1 ; From position δ j,start,1 Start to respond to the delayed signal r j (n+N / 2) is sampled, and the sampling result is cross-correlated with the local sequence c1 to obtain the cross-correlation result R xy,2 ; From position δ j,start,2 Start to respond to signal r j (n) Sampling is performed and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,3 ; From position δ j,start,2 Start to respond to the delayed signal r j (n+N / 2) is sampled and the sampling result is compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation result R xy,4 ; Step 4: The cross-correlation result R xy,1 With R xy,2 Multiply them together to get the timing metric function Λ j,1 (δ), the cross-correlation result R xy,3 With R xy,4 Multiply them together to get the timing metric function Λ j,2 (δ); Step 5: Retrieve the timing metric function Λ j,1 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the correlation peaks are sorted from small to large to obtain the position sequence Retrieval timing metric function Λ j,2 The largest N in (δ) t correlation peaks and N t The position of the correlation peak, for the recorded N t The positions of the correlation peaks are sorted from small to large to obtain the position sequence Step 6: According to the position sequence The first correlation peak position in Obtaining interval difference positions of different transmitting antennas; Among them, i is the interval difference position of the i-th transmitting antenna; If the position sequence The i-th correlation peak position in In the interval i-1 ,jiange i ), then the i-th transmitting antenna exists, otherwise the i-th transmitting antenna does not exist, and the total number of transmitting antennas is reduced by 1; Similarly, the existence of each transmitting antenna is determined separately to obtain the total number of transmitting antennas Nt that finally exists. new and the number of the transmitting antenna that ultimately exists; Step 7: From position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as From the position sequence Cut off the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as according to and Estimate the integer frequency offset between the i-th transmitting antenna and the j-th receiving antenna Step 8: right The peak position of the i-th transmitting antenna is corrected to obtain the precise timing synchronization position of the i-th transmitting antenna Step 9: According to Determine the starting position of the sampling point for the cyclic correlation operation: in, Indicates the starting position of the sampling point of the cyclic correlation operation; From Location Start sampling the signal rj(n), perform cyclic correlation operation on the sampling result and the local sequence c1, and obtain the correlation operation result; Where m is the length of the cyclic shift, m∈[0,N / 2-1], Indicates the result of related operations The mth element in ; and in position The signal r j (n) delay by N / 2 length, perform cyclic correlation operation on the delayed signal and the local sequence c1, and obtain the correlation operation result; in, Indicates the result of related operations The mth element in ; Step 10: From the relevant operation results Search Nt new The maximum peak value is Nt retrieved from new The positions corresponding to the peaks are sorted from small to large, and the final sorting results are recorded as d1, d2, ..., According to the sorting results d1, d2, ..., Estimate the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna in, Indicates position d i In the related operation results The corresponding complex value in is Indicates position d i In the related operation results The corresponding complex value in , arg represents the calculated phase angle.

8. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 7, characterized in that: The basis and Estimate the integer frequency offset between the i-th transmitting antenna and the j-th receiving antenna, specifically: in, express The peak position of the i-th transmitting antenna in, express The peak position of the i-th transmitting antenna.

9. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 8, characterized in that: The specific process of step 8 is as follows:

10. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 9, characterized in that: The maximum cyclic shift length s max satisfy: Among them, ΔSTO max Indicates the maximum timing deviation between different transmitting antennas, ΔIFO max Indicates the maximum integer frequency deviation between different transmitting antennas.

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