A distributed antenna system joint timing and frequency offset estimation method

Abstract

The application discloses a kind of distributed antenna system joint timing and frequency offset estimation method, it belongs to communication technical field.The application aims to solve the problem of poor real-time performance of existing DAS synchronization method for joint estimation of multiple time offsets and multiple frequency offsets in DAS.The application proposes a method for joint timing and frequency offset estimation in DAS based on the good correlation characteristics of CAZAC sequence and multiple antenna synchronization sequences, which can simultaneously estimate the time offset and frequency offset of different transceiver antenna pairs.The application uses sliding cross-correlation operation and effective peak detection to estimate the time offset and integer multiple frequency offset of different transceiver antenna pairs, and uses cyclic correlation operation to estimate the fractional multiple frequency offset of different transceiver antenna pairs.Furthermore, the application uses simultaneous detection to achieve joint estimation of the time offset and frequency offset of different transceiver antenna pairs, which has low complexity and high real-time performance, and can ensure the accuracy of the estimation result.The application can be applied to timing and frequency offset estimation of distributed antenna system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of communication, and particularly relates to a joint timing and frequency offset estimation method of a distributed antenna system. BACKGROUND

[0002] With the development and evolution of next-generation communication technology 6G, greater demand is put forward for the scale of antenna arrays. According to the different deployment of antennas in physical space, a multi-antenna system can be divided into a centralized antenna system (CAS) and a distributed antenna system (DAS). The synchronization problem is one of the key problems faced by DAS. Synchronization technology is mainly divided into symbol timing synchronization and carrier frequency synchronization. In order to realize correct demodulation and decision of signals, the receiving end needs to have a good synchronization relationship. Accurate and implementable synchronization technology is an indispensable condition for realizing reliable transmission of a communication system. In a 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 the transmitting and receiving ends are placed in a distributed manner in geographical position. 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 STO and CFO, greatly increasing the complexity of parameter estimation.

[0003] Constant Amplitude Zero Autocorrelation Code (CAZAC) as a kind of synchronization sequence with constant amplitude, good autocorrelation and cross-correlation, has been widely used in practical communication systems to solve the problem of signal synchronization. Literature 1 (Zhang Jianhua, Feng, 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.) proposes a weighted algorithm based on the cyclic shift of CAZAC sequence, which can effectively estimate the time delay between antennas, but cannot determine the timing position of each transmitting antenna through the peak point, and cannot realize frequency offset estimation. Literature 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 performs cyclic shift on CAZAC sequence and designs a synchronization sequence with good cross-correlation, but the timing and frequency offset estimation adopts the method of separate detection for each transceiver antenna pair. Literature 3 (Chen Xin. Key technology research on synchronization of distributed multi-antenna system [D]. Southeast University, 2019.) proposes a threshold decision timing synchronization algorithm based on the CAZAC sequence of cyclic shift according to the characteristics of DAS, but assumes that there is only one frequency offset in the transceiver antenna.

[0004] In summary, the existing DAS synchronization method considers only time offset or only frequency offset, usually estimates only time offset or only frequency offset, and the time offset and frequency offset estimation adopts the method of independent detection between different transceiver antenna pairs, and the real-time performance of the estimation is poor. SUMMARY

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

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

[0007] Step one, after the data of the i-th transmitting antenna is mapped by constellation, converted by serial / parallel and modulated, the modulated data is obtained, i=1, 2, 3, …, N t ;

[0008] Step two, combine the modulated data of the i-th transmitting antenna with the corresponding synchronization symbol of the i-th transmitting antenna, then add a cyclic prefix to the combined data, and perform parallel / serial conversion on the data after adding the cyclic prefix to obtain a frame of sending signal of the i-th transmitting antenna;

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

[0010] Step three, each receiving antenna receives the superimposed signal of each transmitting antenna;

[0011] For the j-th receiving antenna, the signal received by the j-th receiving antenna is converted into an analog signal through an analog-to-digital converter, and j = 1, 2, 3, …, N r ;

[0012] The time offset and the frequency offset in the converted signal received by the j-th receiving antenna are estimated.

[0013] Step four, the converted signal received by the j-th receiving antenna is compensated using the time offset and the frequency offset estimation result corresponding to the j-th receiving antenna, and a compensated signal received by the j-th receiving antenna is obtained.

[0014] Step five, the compensated signal received by the j-th receiving antenna is converted into a serial-to-parallel signal, and the converted signal is removed of a cyclic prefix, and the signal removed of the cyclic prefix is demodulated, channel equalized and demapped to obtain a demapping result of the j-th receiving antenna.

[0015] Further, the synchronization symbol of each transmitting antenna in the distributed antenna system is obtained by connecting two synchronization sequences with a length of 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] Further, the CAZAC sequence is specifically:

[0017]

[0018] wherein c1(k) is the k-th 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 natural logarithm, and j is an 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+1th, N / 2+2th, …, 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 / 2th sampling points in the second synchronization sequence are respectively the 1st, 2nd, …, N / 2th sampling points in the CAZAC sequence c1 *the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c * the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c * is a conjugate sequence of c

[0021] Further, the second, third, …, N t The calculation method of the synchronization symbol of the i-th transmitting antenna is as follows:

[0022] For the i-th transmitting antenna, i = 2, 3, …, N t , the CAZAC sequence c i is circularly shifted by s i bits to obtain the sequence c i on the i-th transmitting antenna:

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

[0024] wherein c i (k) is the k-th sample point in the sequence c i (k + s i ) mod N / 2 represents the remainder of k + s i divided by N / 2;

[0025] In the synchronization symbol of the i-th transmitting antenna, the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * is a conjugate sequence of c i .

[0026] In the synchronization symbol of the i-th transmitting antenna, the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * the first, second, …, N / 2-th sample points in the first synchronization sequence are the first, second, …, N / 2-th sample points in the sequence c i * is a conjugate sequence of c i .

[0027] Further, the CAZAC sequence c i is circularly shifted by s i bits, and the value of s

[0028]

[0029] wherein s max represents the maximum cyclic shift length, represents the floor function;

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

[0031] wherein N cp represents the length of the cyclic prefix.

[0032] Further, the superimposed signal received by the jth receiving antenna is:

[0033]

[0034] wherein 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 offset normalized by the subcarrier spacing, x i (n) represents the nth sampling point in the modulated signal of the ith transmitting antenna, n ∈ [-N cp ,N-1], δ i,j is the symbol timing offset normalized by the sampling period between the ith transmitting antenna and the jth receiving antenna, L i,j is the number of channel multipaths between the ith transmitting antenna and the jth receiving antenna, h i,j,l is the time-domain channel response of the lth path between the ith transmitting antenna and the jth receiving antenna; τ i,j,l is the time delay corresponding to the lth path between the ith transmitting antenna and the jth receiving antenna, w j (n) represents additive white Gaussian noise with mean 0 and variance .

[0035] β i,j = ε i,j + ξ i,j (6)

[0036] wherein ε i,j is the integer multiple frequency offset between the ith transmitting antenna and the jth receiving antenna; ξ i,j represents the fractional frequency offset between the ith transmitting antenna and the jth receiving antenna.

[0037] Further, the time offset and the 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, obtaining the analog-to-digital converted signal rj (n) Delay N / 2 length to get 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) 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 δ of the first synchronization sequence 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 position 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 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 signal r j (n) Sampling is performed and the sampling results are compared with the local sequence Perform cross-correlation operation and obtain the cross-correlation operation 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 operation 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 correlation peak positions 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 correlation peak positions 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 Obtain the interval difference positions of different transmitting antennas;

[0054]

[0055] Among them, jiange 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 judged separately to obtain the total number of transmitting antennas Nt new and the number of the transmitting antenna that ultimately exists;

[0058] Step 7: From position sequence Cut out the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as From the position sequence Cut out 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: According to 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 a 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 a length of N / 2, perform a 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, and 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 , Indicates position d i In the related operation results The corresponding complex value in , arg represents the calculated phase angle.

[0074] Furthermore, the basis 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 transmit antenna, denotes the peak position of the i-th transmit antenna.

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

[0078]

[0079] Further, the maximum cyclic shift length s max satisfies:

[0080]

[0081] where ΔSTO max denotes the maximum timing deviation between different transmit antennas, and ΔIFO max denotes the maximum integer multiple frequency deviation between different transmit antennas.

[0082] The present application has the following advantages:

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

[0084] Meanwhile, the timing estimation and frequency offset estimation results are simulated and analyzed under a fading channel, which proves the effectiveness of the method of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0085] Figure 1 is a simplified model diagram of a distributed antenna system;

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

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

[0088] Figure 4 is a flowchart of signal processing for time and frequency offset estimation at a receiving end;

[0089] Figure 5 is a curve diagram of a self-correlation function of a receiving signal;

[0090] Figure 6 schematic diagram for effective peak detection;

[0091] Figure 7 timing metric function curve for case 1;

[0092] Figure 8 timing metric function curve for case 2;

[0093] FIG. 9(a) is a FFO estimation mean curve;

[0094] FIG. 9(b) is a FFO estimation mean square error curve. DETAILED DESCRIPTION

[0095] DETAILED DESCRIPTION Figure 2 This embodiment is described. The distributed antenna system joint timing and frequency offset estimation method described in this embodiment, the distributed antenna system is including N t root transmitting antennas and N r root receiving antennas, the method specifically includes the following steps:

[0096] Step one, after the data of the i-th transmitting antenna is subjected to constellation mapping, serial / parallel conversion and modulation (the modulation mode can be selected as any multicarrier modulation mode), the modulated data is obtained, i = 1, 2, 3, …, N t .

[0097] Step two, the modulated data of the i-th transmitting antenna is combined with the synchronization symbol corresponding to the i-th transmitting antenna (i.e. the modulated data of the i-th transmitting antenna is directly connected after the synchronization symbol corresponding to the i-th transmitting antenna), and then a cyclic prefix (CP) is added to the combined data (as shown in the figure, a CP is added before the first synchronization sequence and the second synchronization sequence in the combined data. For the modulated data part of the i-th transmitting antenna in the combined data, a CP is added before each symbol, ensuring the consistency of the synchronization symbol and the data symbol structure), and then parallel / serial conversion is performed on the data with added CP to obtain a frame of sending signal of the i-th transmitting antenna; Figure 3

[0098] The sending signal of the i-th transmitting antenna is subjected to digital-to-analog conversion (DAC), and the data after digital-to-analog conversion is transmitted to a wireless channel;

[0099] Step three, each receiving antenna receives the superimposed signal of each transmitting antenna;

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

[0101] and the time offset and the frequency offset in the analog-to-digital converted signal received by the jth receiving antenna are estimated (the synchronization of the DAS needs to complete the joint estimation of the time offset and the frequency offset, which can be regarded as the parameter estimation problem of N r independent Multiple-Input Single-Output (MISO) systems);

[0102] Step four, using the time offset and the frequency offset estimation result corresponding to the jth receiving antenna (i.e. the estimation result of step three), compensating the analog-to-digital converted signal received by the jth receiving antenna to obtain a compensated signal received by the jth receiving antenna;

[0103] Step five, performing serial / parallel conversion on the compensated signal received by the jth receiving antenna, removing the cyclic prefix from the serial / parallel conversion result, and then demodulating, channel equalizing and demapping the signal after removing the cyclic prefix to obtain the demapping result of the jth receiving antenna.

[0104] As shown in Figure 1 , in the distributed antenna system, the transceiving antennas are placed in a distributed manner in geographical position. Different transmitting antennas can transmit the same data information to realize spatial diversity, or transmit different data information to realize spatial multiplexing. Due to the different distances between different transmitting antennas and receiving antennas, the time of arrival of the signals transmitted by different transmitting antennas at the receiving antennas is different, and the system has multiple timing offsets. The transmission paths between different transmitting antennas and receiving antennas are different, and different channel fading and multipath effects are experienced. Different transmitting antennas and receiving antennas are driven by independent local oscillators, and the system has multiple frequency offsets.

[0105] Specific implementation method two: combine Figure 3 to illustrate the embodiment. The embodiment is different from the specific implementation method one in that the synchronization symbol of each transmitting antenna in the distributed antenna system is obtained by connecting two synchronization sequences with the same length N, wherein the first synchronization sequence is obtained by connecting two identical CAZAC sequences, and the second synchronization sequence is the conjugate sequence of the first synchronization sequence.

[0106] The other steps and parameters are the same as those of the specific implementation method one.

[0107] Specific implementation method three: the CAZAC sequence in the embodiment is specifically

[0108]

[0109] wherein c1(k) is the kth sample 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 natural logarithm, and j is the imaginary unit;

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

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

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

[0113] The fourth embodiment is different from the first to third embodiments in that the calculation method of the synchronization symbol of the second, third, …, N t th transmitting antenna is as follows:

[0114] For the ith transmitting antenna, i = 2, 3, …, N t , the CAZAC sequence c1 is circularly shifted by s i , and the sequence c i on the ith transmitting antenna is obtained:

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

[0116] wherein c i (k) is the kth sample point in the sequence c i , and (k + s i ) mod N / 2 represents the remainder of k + s i divided by N / 2;

[0117] In the synchronization symbol of the ith transmitting antenna, the 1st, 2nd, …, N / 2th sample points in the first synchronization sequence are respectively the 1st, 2nd, …, N / 2th sample points in the sequence ci the first N / 2+1, N / 2+2, …, N sample points in the first synchronization sequence are c i the first N / 2+1, N / 2+2, …, N sample points in the first synchronization sequence are c

[0118] the first N / 2+1, N / 2+2, …, N sample points in the first synchronization sequence are c i * the first N / 2+1, N / 2+2, …, N sample points in the first synchronization sequence are c i * the first N / 2+1, N / 2+2, …, N sample points in the first synchronization sequence are c i * is a conjugate sequence of c i .

[0119] The other steps and parameters are the same as those in one of Embodiments One to Three.

[0120] Embodiment Five: The embodiment is different from one of Embodiments One to Four in that the CAZAC sequence c1 is cyclically shifted by s i bits, and the value of s i is specifically:

[0121]

[0122] where s max represents the maximum cyclic shift length, represents rounding down;

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

[0124] where N cp represents the length of the cyclic prefix.

[0125] The other steps and parameters are the same as those in one of Embodiments One to Four.

[0126] Embodiment Six: The embodiment is different from one of Embodiments One to Five in that the superimposed signal received by the jth receiving antenna is:

[0127]

[0128] where r j '(n) represents the nth sample point in the superimposed signal received by the jth receiving antenna, β i,j is the subcarrier spacing normalized carrier frequency offset, and 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 the first to fifth embodiments.

[0132] Specific implementation method seven: combination Figure 4 This embodiment differs from any one of 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 in the following specific estimation process:

[0133] Step 1: Convert the analog-to-digital signal r received by the jth receiving antenna j (n) Delay N / 2 length to get 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)th sample point of the (δ+n)th sample point of the signal r j (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r (n+N / 2)th sample point of the signal r

[0137] (n+N / 2)th sample point of the signal r Figure 5 (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r j,coarse,1 ;

[0138] (n+N / 2)th sample point of the signal r j,coarse,1 (n+N / 2)th sample point of the signal r cp (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r j,coarse,2 ;

[0139] (n+N / 2)th sample point of the signal r j,start,1 (n+N / 2)th sample point of the signal r j,coarse,1 (n+N / 2)th sample point of the signal r cp (n+N / 2)th sample point of the signal r j,start,2 (n+N / 2)th sample point of the signal r j,coarse,2 (n+N / 2)th sample point of the signal r cp (n+N / 2)th sample point of the signal r

[0140] (n+N / 2)th sample point of the signal r j,start,1 (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r xy,1 ;

[0141] (n+N / 2)th sample point of the signal r j,start,1 (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r xy,2 ;

[0142] (n+N / 2)th sample point of the signal r j,start,2 (n+N / 2)th sample point of the signal r j (n+N / 2)th sample point of the signal r correlation operation to obtain a cross-correlation operation result R xy,3 ;

[0143] from position δ j,start,2 start sampling the delayed signal r j (n+N / 2), and multiply the sampling result with the local sequence correlation operation to obtain a cross-correlation operation result R xy,4 ;

[0144] Step 4, multiply the cross-correlation operation result R xy,1 and R xy,2 to obtain a timing metric function Λ j,1 (δ), multiply the cross-correlation operation result R xy,3 and R xy,4 to obtain a timing metric function Λ j,2 (δ);

[0145]

[0146] The timing metric function is obtained by multiplying the cross-correlation operation of two parts, which can improve the 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), 2014 IEEE International Conference on. IEEE, 2014: 2227-2232.);

[0147] Step 5, search for the maximum N j,1 correlation peaks in the timing metric function Λ t (δ) and the positions of the N t correlation peaks, sort the recorded N t correlation peak positions from small to large to obtain a position sequence

[0148] Search for the maximum N j,2 correlation peaks in the timing metric function Λ t (δ) and the positions of the N t correlation peaks, sort the recorded N t correlation peak positions from small to large to obtain a position sequence

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

[0150]

[0151] Among them, jiange 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), 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;

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

[0154] Step 7: From position sequence Cut out the front Nt new elements, the intercepted Nt new The position sequence composed of elements is recorded as From the position sequence Cut out 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: According to 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 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 a length of N / 2, perform a 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, and 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 retrieved, and the positions corresponding to the 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 , Indicates position d i In the related operation results corresponding complex value, arg represents the calculated phase angle.

[0171] The other steps and parameters are the same as one of embodiments 1-6.

[0172] Embodiment 8: The embodiment is different from one of embodiments 1-7 in that the step of determining the maximum cyclic shift length s and The integer multiple frequency offset between the ithtransmitting antenna and the jthreceiving antenna is estimated, specifically:

[0173]

[0174] wherein, represents the peak position of the ithtransmitting antenna in the position sequence represents the peak position of the ithtransmitting antenna in the position sequence

[0175] The other steps and parameters are the same as one of embodiments 1-7.

[0176] For a system of 4 transmitting antennas, if the 1st, 3rdand 4thtransmitting antennas exist, the first 3 elements are intercepted from the position sequence , and the first 3 elements are intercepted from the position sequence , then the 1stelement in the position sequence and the 1stelement in the position sequence are the peak position of the 1sttransmitting antenna, the 2ndelement in the position sequence and the 2ndelement in the position sequence are the peak position of the 3rdtransmitting antenna, and the 3rdelement in the position sequence and the 3rdelement in the position sequence are the peak position of the 4thtransmitting antenna.

[0177] Embodiment 9: The embodiment is different from one of embodiments 1-8 in that the specific process of step 8 is:

[0178]

[0179] The other steps and parameters are the same as one of embodiments 1-8.

[0180] Embodiment 10: The embodiment is different from one of embodiments 1-9 in that the maximum cyclic shift length s max satisfies:

[0181]

[0182] wherein, ΔSTOmax denotes the maximum timing offset between different transmit antennas, ΔIFO max denotes the maximum integer multiple frequency offset between different transmit antennas, N t > 1.

[0183] The other steps and parameters are the same as one of the first nine embodiments.

[0184] The present application limits the range difference of the maximum time offset and frequency offset that can be detected by the transmit antennas, and as the number of transmit antennas N t increases, the detectable range decreases.

[0185] Simulation results

[0186] Taking a 4x1 DAS as an example, the simulation verification of the system joint timing and frequency offset estimation method based on the CAZAC sequence distributed antenna proposed by the present application is carried out, and the simulation content includes:

[0187] (1) When there are multiple time offsets and frequency offsets, the timing estimation and IFO estimation results of different pairs of transceiver antennas

[0188] (2) The FFO estimation mean and FFO estimation mean square error curve of different pairs of transceiver antennas.

[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 starting position of the pre-sequence noise N n , and in the ideal case when there is no STO and CFO between the transceiver 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) When there are time offsets and frequency offsets, the timing estimation and IFO estimation results of different pairs of transceiver antennas

[0194] When the maximum time offset and the maximum integer multiple frequency offset between different transmit antennas satisfy the relationship of formula (17) and the simulation parameter settings, the joint timing and frequency offset estimation algorithm proposed by the present application can be used for estimation. In order to facilitate the comparison and explanation of the subsequent test, the STO and CFO of different TX are set as follows:

[0195] Table 2 Case 1 STO and CFO parameter settings of different TX

[0196]

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

[0198]

[0199] Tables 2 and 3 show two different time and frequency offset scenarios that meet the specified constraints. Case 1 corresponds to an increase in the time and frequency offset of different TX signals as the number of antennas increases, while Case 2 corresponds to a decrease in the time and frequency offset of different TX signals as the number of antennas increases. Other random distribution scenarios fall between these two special cases, and the analysis process and approach are the same.

[0200] like Figure 7 As shown in the figure, the timing metric function curve in case 1 is given. The black dotted line corresponds to the interval difference position of different transmitting antennas, R1 represents the peak value of the cross-correlation between the received signal and c1, and R2 represents the peak value of the cross-correlation between the received signal and c1. * The cross-correlation peaks are determined. Because the synchronization sequences of different transmit antennas are cyclically shifted, the positions of the correlation peaks shift accordingly. Using the position of TX1 as a reference, the interval range differences for TX2 to TX4 are given in sequence. When the correlation peak position of the corresponding antenna falls within the interval, the transmit antenna is considered present. In case 1, the time and frequency offsets of all TXs fall within the interval, indicating that each transmit antenna is present, with TX4 reaching the maximum value of the critical range.

[0201] After determining the presence of a valid peak, based on the correlation peak positions, 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. Calculating the IFO for different transmit and receive antenna pairs according to Equation (15) yields results of 10, 12, 14, and 16, respectively, corresponding to the IFO settings in Case 1.

[0202] Next, based on the calculated IFO estimation results, the timing positions of different TXs are corrected. According to formula (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 from the ideal case of equation (18) are 10, 12, 14, and 16, respectively, corresponding to the STO set in case 1.

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

[0204] (2) FFO estimation mean value and FFO estimation mean square error curve of different transceiver antenna pairs

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

[0206] FIGS. 9(a) and 9(b) respectively show the FFO estimation mean value and the FFO estimation mean square error curve of different transmitting antennas, and the FFO of different transmitting antennas can be estimated simultaneously through cyclic correlation calculation. As can be seen from the FFO estimation mean value, 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. As can be seen from the FFO estimation mean square error, different TXs have basically consistent mean square error performance curves, and the FFO of different transceiver antenna pairs can be estimated simultaneously.

[0207] The above calculation examples of the present application are only used to illustrate the calculation model and calculation process of the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

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, The data from the transmitting antenna is subjected to constellation mapping, serial / parallel conversion and modulation to obtain modulated data. ; Step 2: The data modulated by the first transmitting antenna is the same as the The synchronization symbol combination corresponding to the root transmitting antenna is then added with a cyclic prefix to the combined data, and the data with the cyclic prefix is ​​converted into a parallel / serial form to obtain the first One frame of signal is sent by the transmitting antenna; The synchronization symbol is obtained according to the CAZAC sequence, which is specifically: (1) in, It is a CAZAC sequence The sampling points, , is the length of the CAZAC sequence, , is the base of natural logarithms, is an imaginary unit; In the synchronization symbol of the first transmitting antenna, the first synchronization sequence The sampling points are CAZAC sequences The sampling points, the first synchronization sequence The sampling points are CAZAC sequences The sampling points; In the synchronization symbol of the first transmitting antenna, the first The sampling points are The sampling points, the first sampling point in the second synchronization sequence The sampling points are The sampling points, yes The conjugated sequence of CAZAC sequence Cyclic Move bits, and obtain the sequence on the i-th transmitting antenna , According to the maximum cyclic shift length Sure; Maximum cyclic shift length satisfy: (17) in, Indicates the maximum timing deviation between different transmitting antennas, Indicates the maximum integer frequency deviation between different transmitting antennas; The first The signal transmitted by the transmitting antenna passes through the digital-to-analog converter, and the 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 digital signal by an analog-to-digital converter. ; The time offset and frequency offset of the analog-to-digital converted signal received by the jth receiving antenna are estimated. The specific estimation process is as follows: Step 1: Convert the analog-to-digital signal received by the jth receiving antenna Delay Length, get the delayed signal , Indicates the length of the synchronization symbol; Signal and signal Perform autocorrelation operation to obtain the timing autocorrelation function for: (7) in, For the Signal received by the receiving antenna No. sampling points, represents the sampling point location, For signal No. sampling points, Indicates signal No. The signal modulus at each sampling point is express conjugation of; Step 2: When the timing autocorrelation function 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 ; From the position of the timing autocorrelation function + To begin, retrieve the timing autocorrelation function The maximum peak value and the position of the maximum peak of the second peak platform are obtained, and the maximum peak position of the second peak platform is used as the timing capture position of the second synchronization sequence ; The starting position of the coarse timing synchronization sampling point is , ,in, Indicates the length of the cyclic prefix; Step 3. From the location Start signal Sampling is performed and the sampling results are compared with the local sequence Perform cross-correlation operation to obtain the cross-correlation operation result ; From location Start the delayed signal Sampling is performed and the sampling results are compared with the local sequence Perform cross-correlation operation to obtain the cross-correlation operation result ; From location Start signal Sampling is performed and the sampling results are compared with the local sequence Perform cross-correlation operation to obtain the cross-correlation operation result ; From location Start the delayed signal Sampling is performed and the sampling results are compared with the local sequence Perform cross-correlation operation to obtain the cross-correlation operation result ; Step 4: The cross-correlation calculation results and Multiply them together to get the timing metric function , the cross-correlation result and Multiply them together to get the timing metric function ; (8) (9) Step 5: Retrieve the timing metric function The largest correlation peaks and The position of the correlation peak is recorded The correlation peak positions are sorted from small to large to obtain the position sequence ; Retrieve timing metric function The largest correlation peaks and The position of the correlation peak is recorded The correlation peak positions are sorted from small to large to obtain the position sequence ; Step 6: According to the position sequence The first correlation peak position in , get the interval difference position of different transmitting antennas; (10) in, It is Interval difference position of the root transmitting antenna; If the position sequence The Correlation peak position In the interval Inside, then The first transmitting antenna exists, otherwise If the root transmitting antenna does not exist, reduce the total number of transmitting antennas by 1; Similarly, the existence of each transmitting antenna is judged separately to obtain the total number of transmitting antennas that exist. and the number of the transmitting antenna that ultimately exists; Step 7: From position sequence Before cutting out elements, the intercepted The position sequence composed of elements is recorded as ; From the position sequence Before cutting out elements, the intercepted 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 : (15) in, express The peak position of the i-th transmitting antenna, express The peak position of the i-th transmitting antenna in; Step 8: According to 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 : The specific process of step 8 is as follows: (16) Step 9: According to Determine the starting position of the sampling point for the cyclic correlation operation: (11) in, Indicates the starting position of the sampling point of the cyclic correlation operation; From location Start signal Sampling, comparing the sampling results with the local sequence Perform cyclic correlation operations to obtain correlation operation results; (12) in, is the length of the cyclic shift, , Indicates the result of related operations The elements; and in position The signal Delay length, and the delayed signal is combined with the local sequence Perform cyclic correlation operations to obtain correlation operation results; (13) in, Indicates the result of related operations The elements; Step 10: From the relevant operation results Search The maximum peak value, and Retrieved from The positions corresponding to the peaks are sorted from small to large, and the final sorting result is recorded as ; According to the sorting results Estimate the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna : (14) in, Indicates location In the related operation results The corresponding complex value in , Indicates location In the related operation results The corresponding complex value in , arg represents the calculated phase angle; Step 4: Using the time offset and frequency offset estimation results corresponding to the j-th receiving antenna, compensate the analog-to-digital converted signal received by the j-th receiving antenna to obtain a compensated signal received by the j-th 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 using two signals of the same length. 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. The method for joint timing and frequency offset estimation of a distributed antenna system according to claim 2, wherein: The said The calculation method of the synchronization symbol of the root transmitting antenna is: For the Root transmitting antenna, , for CAZAC sequence Cyclic Move bits, and obtain the sequence on the i-th transmitting antenna : (2) in, is a sequence The sampling points, express Divide by the remainder of In the In the synchronization symbol of the root transmitting antenna, the first synchronization sequence The sampling points are the sequence The sampling points, the first synchronization sequence The sampling points are the sequence The sampling points; In the In the synchronization symbol of the root transmitting antenna, the first The sampling points are The sampling points, the first sampling point in the second synchronization sequence The sampling points are The sampling points, yes conjugated sequence.

4. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 3, characterized in that: The CAZAC sequence Cyclic Move Bit, The specific values ​​are: (3) in, Indicates the maximum cyclic shift length, Indicates rounding down; (4) in, Indicates the length of the cyclic prefix.

5. A method for joint timing and frequency offset estimation of a distributed antenna system according to claim 4, characterized in that: The superposition signal received by the j-th receiving antenna is: (5) in, Indicates the jth superposition signal received by the jth receiving antenna sampling points, is the carrier frequency offset normalized by the subcarrier spacing, represents the modulated signal of the i-th transmitting antenna sampling points, , is the symbol timing deviation normalized by the sampling period between the i-th transmitting antenna and the j-th receiving antenna, is the number of multipath channels between the i-th transmitting antenna and the j-th receiving antenna, is the time domain channel response of the lth path between the i-th transmitting antenna and the j-th receiving antenna; is the delay corresponding to the lth path between the i-th transmitting antenna and the j-th receiving antenna, The mean is 0 and the variance is Additive Gaussian white noise; (6) in, is the integer multiple frequency offset between the i-th transmitting antenna and the j-th receiving antenna; It represents the fractional frequency offset between the i-th transmitting antenna and the j-th receiving antenna.

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