CN116827741A - FPGA implementation method for time-frequency synchronization of multipath parallel transmission millimeter wave OFDM communication system - Google Patents

Abstract

The invention discloses an FPGA implementation method for time-frequency synchronization of a multi-channel parallel transmission millimeter wave OFDM communication system. Based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission channels during FPGA implementation, a training sequence with a specific structure is generated in the time domain. ;Use the delay autocorrelation method to perform correlation operations on baseband multi-channel parallel received signals, and find the rough timing synchronization position through the streaming empirical threshold comparison method; use the angle information carried by the autocorrelation results to realize the frequency offset estimation calculation of the system; convert the local The cache sequence is correlated with the received signal sequence to obtain the precise timing synchronization position; the coarse synchronization and fine synchronization results are added to obtain the final system symbol timing synchronization result position index, and the data sequence after symbol timing synchronization is output; at the same time, the corresponding complex index is generated The signal performs frequency offset compensation operation on the sequence after timing synchronization to complete the system synchronization task. The invention can improve system synchronization accuracy and reduce hardware implementation time cost and complexity.

Description

FPGA implementation method for time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system

Technical field

The invention belongs to the field of communication technology, and specifically relates to an FPGA implementation method for time-frequency synchronization of a multi-channel parallel transmission millimeter wave OFDM communication system.

Background technique

The millimeter wave frequency band contains abundant and license-free spectrum resources, making millimeter wave communication technology gradually become a popular research direction in the field of wireless communications. But on the other hand, the inherent high-attenuation propagation characteristics of millimeter wave signals limit its main application to indoor communication scenarios, and the significant frequency offset and ultra-high symbol rate brought by high-band wide spectrum also make millimeter-wave communication systems Implementation faces daunting challenges.

Synchronization is to specify a common time reference between two devices or systems, so that in scenarios where the receiver and sender of communication cannot use the same clock source, they can ensure that they can work in unison. Especially for the receiver of the millimeter wave OFDM communication system, synchronization is the first step in baseband processing after the analog signal is converted into a digital signal, and it is also the key to correct data transmission. Its performance directly determines the quality of the communication, so Stable, reliable, and accurate synchronization in any scenario is crucial to the reliable operation of the entire communication system. Synchronization technologies in millimeter wave OFDM systems include: symbol timing synchronization and carrier frequency synchronization. Timing synchronization is mainly to find the starting position of the OFDM symbol frame and determine the starting boundary of the FFT operation for demodulation operations. Precise timing synchronization means precise symbol synchronization in the OFDM system. After obtaining the accurate starting position of the OFDM symbol data frame, and then making the corresponding delay through the known cyclic prefix time, the FFT can be calculated Provides accurate data sample location. The implementation form of timing synchronization technology is closely related to the transmission mode of the communication system in which it is located. Generally speaking, there are two transmission modes in communication systems, continuous transmission mode and burst packet transmission mode. Traditional voice mobile communication systems use a typical continuous transmission mode. In this system, pilot sequences sent periodically can be used for synchronization. Since data transmission follows a strict beat, current and past data can be used. The information continuously adjusts the synchronization results, which can improve the accuracy of the synchronization process to a certain extent. For communication systems such as Wi-Fi that use burst packet transmission mode, the starting time of the data frame is completely random, and past synchronization information cannot be used, so real-time timing synchronization is required. In this mode, the method of adding a training sequence at the frame header position is generally used for synchronization.

Carrier frequency synchronization refers to the ability to keep the RF center frequency of the system receiver consistent with the RF center frequency of the transmitter through the estimation and correction of frequency deviations. Carrier frequency offset will first destroy the orthogonality between each sub-carrier. The impact on OFDM signals is mainly reflected in the crosstalk between sub-carriers, and will cause the rotation of the constellation diagram. If the frequency offset is small, the inter-subcarrier crosstalk it generates will not be very obvious, and the direct manifestation is mainly the rotation of the constellation diagram; if the frequency offset is large, the inter-subcarrier crosstalk it generates will lead to the failure of demapping. .

Currently, common synchronization algorithms are generally divided into three categories: blind synchronization algorithms suitable for scenarios where there is no known data in the transmission frame, synchronization algorithms based on cyclic prefix and training sequence. Among them, blind synchronization refers to a synchronization process performed by transmitting signal energy or statistical information without resorting to specific sequences and frame structures. The maximum likelihood algorithm based on cyclic prefix does not require additional data overhead and has low algorithm complexity, but has poor synchronization performance under complex channel conditions. Synchronization algorithms based on training sequences also include cross-correlation algorithms and delayed autocorrelation algorithms. Although the traditional data-assisted synchronization algorithm has a large operating signal-to-noise ratio range, it cannot take into account symbol timing accuracy, algorithm complexity, frequency offset estimation accuracy and frequency offset estimation range. At the same time, its sequence correlation characteristics cannot be used in It is well reflected in multi-channel parallel transmission, so it is very meaningful to design a synchronization sequence and research on synchronization algorithm suitable for multi-channel parallel transmission in large bandwidth scenarios.

In terms of hardware implementation of OFDM systems using FPGAs, although domestic and foreign experts and scholars have also conducted relatively complete experiments and published a large number of results, research on the synchronization of OFDM synchronization technology in large bandwidth multi-channel parallel transmission in the millimeter wave band has not yet been carried out. There is little detailed analysis. OFDM millimeter wave communication system synchronization technology still has some room for improvement in terms of synchronization algorithm design, resource optimization during FPGA implementation, and modular implementation.

Contents of the invention

The technical problem to be solved by the present invention is to provide an FPGA implementation method for time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system in order to solve the problem that the large bandwidth characteristics of the signal are not considered in the existing technology. The technical problems of high computing latency and large hardware resource consumption improve system synchronization accuracy and reduce hardware implementation time cost and complexity.

The present invention adopts the following technical solutions:

The FPGA implementation method of time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system includes the following steps:

S1. Based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission paths N _path in specific FPGA implementation, a training sequence signal matrix X with a specific structure is generated in the time domain;

S2. Utilize the structural characteristics of the training sequence signal matrix Synchronization position syn_coarse;

S3. Based on the rough timing synchronization position syn_coarse obtained in step S2, use the angle information carried by the autocorrelation result. Realize the frequency offset estimation actual value cfo_est of the millimeter wave OFDM communication system;

S4. Based on the coarse timing synchronization position syn_coarse obtained in step S2, use the cross-correlation algorithm to calculate the local buffer sequence pre-stored locally in the receiver and the received signal sequence to obtain the precise timing synchronization position syn_precious;

S5. Add the coarse timing synchronization position syn_coarse obtained in step S2 and the fine timing synchronization position syn_precious obtained in step S4 to obtain the final system symbol timing synchronization result position index. According to the position index, the data sequence after symbol timing synchronization is output, and at the same time, according to the step The actual frequency offset estimate cfo_est obtained by S3 generates a corresponding complex exponential signal, and the frequency offset compensation operation is performed on the sequence after timing synchronization, and finally the system synchronization task is completed.

Specifically, in step S1, the training sequence signal matrix X is:

Among them, T is the transposition calculation, C ^M×N is a matrix with M×N dimensional elements as complex numbers, M _{T_CP} is the time domain CP part, M _{T_data} is the time domain data part, N _samp is the number of time domain sampling points of the training sequence, N _path is the number of parallel paths.

Further, the specific construction method of the training sequence is as follows:

in, Represents the Kronecker product symbol of the matrix, A=[1,1], R is a constant amplitude random sequence, S _{ZC_1} and S _{ZC_2} are N _cfft and /> respectively. ZC pseudo-random sequence of points.

Specifically, in step S2, the rough timing synchronization position syn_coarse is:

Among them, P _avg [k] is the smoothed filtered coarse synchronization sequence result, P _adv is the known empirical threshold corresponding to the training sequence, and k is the sequence number of the coarse synchronization sequence result.

Furthermore, the rough synchronization sequence result P _avg [k] after smoothing and filtering is:

Among them, L _avg is the smoothing filter window length.

Specifically, in step S3, the actual frequency offset estimate cfo_est is:

in, is the angle information carried by the autocorrelation result, N _sub is the number of subcarriers, and f _samp is the system sampling frequency.

Specifically, in step S4, the coarse synchronization timing position around The points are cross-correlated with the local N _cfft point cache sequence pattern_c. The cross-correlation result is performed by first performing an N _cfft point FFT operation on the two sequences, and then performing an N _cfft point IFFT operation on the result. The cross-correlation generates a pulse-like spike. The position corresponding to the peak is the precise timing synchronization position syn_precious.

Further, the precise timing synchronization position syn_precious is:

Among them, P _cor is the precise synchronization sequence result after the cross-correlation operation, and k is the sequence number of the precise synchronization sequence result.

Furthermore, P _cor is:

Among them, N _cfft is the number of Fourier transform sample points, fft is the fast Fourier transform operation, xn is the time domain sequence of the signal received by the receiver, syn_coarse is the coarse synchronization positioning position, and pattern_c is the N _cfft points pre-buffered by the receiver. Cache sequence.

In the second aspect, embodiments of the present invention provide an FPGA implementation system for time-frequency synchronization of a multi-channel parallel transmission millimeter wave OFDM communication system, including:

The matrix module generates a training sequence signal matrix X with a specific structure in the time domain based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission paths N _path during specific FPGA implementation;

The accumulation module uses the structural characteristics of the training sequence signal matrix Timing synchronization position syn_coarse;

The estimation module, based on the rough timing synchronization position syn_coarse obtained by the accumulation module, uses the angle information carried by the autocorrelation result Realize the frequency offset estimation actual value cfo_est of the millimeter wave OFDM communication system;

The operation module, based on the coarse timing synchronization position syn_coarse obtained by the accumulation module, uses the cross-correlation algorithm to calculate the local buffer sequence pre-stored locally in the receiver and the received signal sequence to obtain the precise timing synchronization position syn_precious;

The output module adds the coarse timing synchronization position syn_coarse obtained by the step accumulation module and the fine timing synchronization position syn_precious obtained by the operation module to obtain the final system symbol timing synchronization result position index, and outputs the data sequence after symbol timing synchronization based on the position index. At the same time According to the actual frequency offset estimate cfo_est obtained by the estimation module, the corresponding complex exponential signal is generated, and the frequency offset compensation operation is performed on the sequence after timing synchronization, and finally the system synchronization task is completed.

Compared with the prior art, the present invention at least has the following beneficial effects:

The FPGA implementation method of time-frequency synchronization of multi-channel parallel transmission millimeter-wave OFDM communication system generates a training sequence signal with a specific structure based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission channels during specific FPGA implementation, making full use of The transmission signal characteristics of specific communication scenarios improve the efficiency of the synchronization algorithm. The receiving end first uses a delay autocorrelation algorithm with low time cost and computational complexity to perform coarse timing synchronization and uses a threshold comparison method to determine the coarse synchronization position. Based on the angle information carried by the coarse synchronization sequence result, the frequency offset estimate is obtained, and then Determine whether to perform fine synchronization based on actual conditions to improve synchronization accuracy. Therefore, this method can achieve a good trade-off between higher synchronization accuracy and lower time and hardware consumption costs.

Furthermore, the training sequence signal matrix Block FPGAs work in parallel to meet large bandwidth transmission requirements.

Furthermore, the proposed training sequence for synchronization has a highly consistent structure, and will produce a slowly changing trapezoidal correlation result during the coarse synchronization autocorrelation operation, and the ZC sequence used has constant amplitude characteristics in both the time and frequency domains. It can well match the designed precise synchronization cross-correlation algorithm and produce sharp cross-correlation peaks.

Furthermore, the delayed autocorrelation method is used to perform correlation operations on the baseband multi-channel parallel received signals, and then the correlation results are accumulated. Finally, the rough timing synchronization position syn_coarse is found through the streaming experience threshold comparison method, making full use of the transmitter. The designed training sequence characteristics, and has lower hardware implementation cost and calculation time.

Furthermore, a smoothing filtering operation with a window length of L _avg is performed on the delayed autocorrelation results, which can effectively reduce the influence of uncertain factors such as received signal burrs.

Furthermore, the actual frequency offset estimate cfo_est can be directly carried by the angle information carried by the autocorrelation result. Obtained, FPGA implementation only needs to use an additional Cordic IP core for angle calculation, which greatly reduces hardware resource consumption.

Further, coarse synchronization is used to determine the timing position of the left and right The points are cross-correlated with the local N _cfft point cache sequence pattern_c. The cross-correlation result is performed by first performing an N _cfft point FFT operation on the two sequences, and then performing an N _cfft point IFFT operation on the result. The cross-correlation generates a pulse-like spike. The position corresponding to the sharp peak is the fine timing synchronization position syn_precious. Since cross-correlation will produce sharp correlation peaks, the addition of the fine synchronization step can be used as a supplement to the coarse synchronization step to improve the accuracy of timing synchronization.

Furthermore, the precise timing synchronization position syn_precious can be used as a selective supplement to the coarse timing synchronization position. When the actual environmental channel status is good (the signal-to-noise ratio is high), only coarse synchronization can be performed instead of fine synchronization to save time and hardware. consumption; when the channel environment is poor (low signal-to-noise ratio), fine synchronization can be used to improve timing synchronization accuracy.

Further, perform FFT (Fast Fourier Transform) on the received N _cfft point sequence and local point N _cfft buffer sequence respectively, and then perform N _cfft point IFFT (Inverse Fast Fourier Transform) on the result sequence after conjugate multiplication. Transform) operation is essentially equivalent to performing a cross-correlation (sliding correlation) operation on both ends of the sequence. Compared with traditional sliding correlation, it can significantly reduce the calculation time and the usage of FPGA hardware resources (especially complex multipliers).

It can be understood that the beneficial effects of the above-mentioned second aspect can be referred to the relevant descriptions in the above-mentioned first aspect, and will not be described again here.

In summary, the present invention designs a training sequence suitable for large-bandwidth multi-channel parallel transmission, and on this basis proposes a synchronization algorithm with higher synchronization accuracy than the classic algorithm under the same signal-to-noise ratio, while reducing the hardware cost. Implementation time and hardware complexity.

The technical solution of the present invention will be further described in detail below through the accompanying drawings and examples.

Description of the drawings

Figure 1 is a schematic diagram of a millimeter wave OFDM communication system applied by the method of the present invention;

Figure 2 is the flow chart of the implementation module of the proposed solution;

Figure 3 is a structural diagram of the system frame structure design in the proposed transmission scenario;

Figure 4 is a synchronization sequence design structure diagram under the proposed transmission scenario and frame structure design;

Figure 5 is a simulation diagram of the coarse synchronization and smoothing filtering results under the proposed experimental conditions;

Figure 6 shows the frequency offset estimation value and standard value mean square error of 1000 experiments under the proposed experimental conditions;

Figure 7 is a simulation diagram of the precise synchronization cross-correlation results under the proposed experimental conditions;

Figure 8 shows the probability of correct timing synchronization for 1,000 experiments under the proposed experimental conditions;

Figure 9 shows the simulation results of the proposed time-frequency synchronization algorithm on the hardware platform under the proposed experimental conditions.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

In the description of the present invention, it is to be understood that the terms "comprising" and "including" indicate the presence of described features, integers, steps, operations, elements and/or components, but do not exclude one or more other features, The existence or addition of an integer, a step, an operation, an element, a component, and/or a collection thereof.

It should also be understood that the terminology used in the description of the present invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly dictates otherwise.

It will be further understood that the term "and/or" as used in the specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items. , for example, A and/or B can mean: A alone exists, A and B exist simultaneously, and B exists alone. In addition, the character "/" in the present invention generally indicates that the related objects are in an "or" relationship.

It should be understood that although the terms first, second, third, etc. may be used to describe the preset ranges and the like in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish preset ranges from each other. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be called a second preset range, and similarly, the second preset range may also be called a first preset range.

Depending on the context, the word "if" as used herein may be interpreted as "when" or "when" or "in response to determination" or "in response to detection." Similarly, depending on the context, the phrase "if determined" or "if (stated condition or event) is detected" may be interpreted as "when determined" or "in response to determining" or "when (stated condition or event) is detected )" or "in response to detecting (a stated condition or event)".

Various structural schematic diagrams according to disclosed embodiments of the present invention are shown in the accompanying drawings. The drawings are not drawn to scale, with certain details exaggerated and may have been omitted for purposes of clarity. The shapes of the various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art will base their judgment on actual situations. Additional regions/layers with different shapes, sizes, and relative positions can be designed as needed.

The present invention provides an FPGA implementation method for time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system. First, at the transmitting end, the number of baseband parallel transmission paths N _path is based on the transmission signal physical layer frame structure (including) and the specific FPGA implementation. A training sequence The rough timing synchronization position syn_coarse is found by using the empirical threshold comparison method; and when obtaining the rough timing synchronization position, the angle information carried by the autocorrelation result is used Realize the frequency offset estimation and calculation of the system cfo_est; then, on the basis of obtaining the coarse timing synchronization position, perform a correlation operation between the local cache sequence and the received signal sequence to obtain the fine timing synchronization position syn_precious; finally, compare the coarse synchronization and fine synchronization results. The position index of the final system symbol timing synchronization result is added, and the data sequence after symbol timing synchronization is output according to the position index. At the same time, according to the frequency offset estimation result, the corresponding complex exponential signal is generated to perform frequency offset compensation operation on the sequence after timing synchronization, and finally completes the system synchronization task. The present invention can combine the characteristics of large bandwidth and high sampling rate to generate an improved synchronization sequence, and uses a coarse and fine two-level synchronization method to improve the accuracy of timing synchronization and frequency offset estimation. At the same time, it has lower resource utilization and complex algorithms in hardware implementation. degree and calculation time cost.

Please refer to Figures 1 and 2. An FPGA implementation method for time-frequency synchronization of a multi-channel parallel transmission millimeter wave OFDM communication system according to the present invention includes the following steps:

S1. The transmitter generates a training sequence X with a specific structure in the time domain based on the physical layer frame structure of the transmission signal (including) and the number of baseband parallel transmission paths N _path in specific FPGA implementation;

Due to the characteristics of large bandwidth and high transmission rate of millimeter wave systems, the system sampling rate has increased sharply. Therefore, in the baseband, it is considered to combine the advantages of FPGA parallel processing to transmit the baseband signals in multiple channels in parallel. The number of parallel paths is N _path , and the transmitter is used for synchronization. The baseband equivalent discrete time training sequence signal matrix X of the time domain structure of the training sequence is:

Among them, T represents the transposition calculation, C ^M×N represents a matrix with M×N dimensional elements as complex numbers, M _{T_CP} is the time domain CP part, M _{T_data} is the time domain data part, N _samp = N _sub +N _cp , N _samp is the number of time domain sampling points of the training sequence, N _sub is the number of subcarriers (OFDM modulation is therefore equal to the number of data symbol points), and N _cp is the number of cyclic prefix points.

The specific parallel i-th transmission data X _i is:

Please refer to Figure 3, which shows the frame structure design scheme in the experimental scenario with a signal bandwidth of 4.5GHz, 64QAM modulation method, OFDM subcarrier spacing, and reference to the 5G NR protocol for 488.28125KHz and FPGA clock frequency of 250MHz.

Each wireless frame contains 10 subframes, each subframe contains 32 time slots, each time slot contains 16 OFDM symbols, the first OFDM symbol of each time slot is a training sequence for synchronization, and the next 15 OFDM symbols are data symbols. The number of subcarriers in the frequency domain is N _sub = 4.5G÷488.28125K = 9216 subcarriers. Considering the FPGA clock frequency requirements, N _path = 36 parallel channels, each with 256 subcarriers, is used for transmission; each OFDM in the time domain The symbol contains N _samp =9792 sampling points, of which the first N _cp =576 points are the cyclic prefix CP part, and the last 9216 points are the valid data part.

The specific construction method of the training sequence at the transmitter is:

in, Represents the Kronecker product symbol of the matrix, A=[1,1],/> is a constant amplitude random sequence, in which each sampling point r _i satisfies/> S _{ZC_1} and S _{ZC_2} are N _cfft and/> respectively ZC pseudo-random sequence of points.

Please refer to Figure 4, which shows the synchronization sequence scheme designed under the frame structure as mentioned above. The structure of the training symbol part of the training sequence used for synchronization. The cyclic prefix part consists of two consistent parts. Each part includes a paragraph. A constant amplitude random sequence of points and a ZC sequence of N _cfft = 256 points. The data part Training Sequence is also composed of two consistent parts, each part includes length/> The ZC sequence Main Part of points and the sequence of 576 points are exactly the same as the CP part.

S2. At the receiving end, the delay autocorrelation method is first used to perform correlation operations on the baseband multi-channel parallel received signals, then the correlation results are accumulated, and finally the rough timing synchronization position syn_coarse is found through the streaming experience threshold comparison method;

Use the following formula to calculate the delay autocorrelation of the parallel i-th received signal:

The delay autocorrelation results of each channel are accumulated to achieve the purpose of improving the signal-to-noise ratio and reducing the timing error:

Then, in order to prevent the influence of uncertain factors such as received signal burrs, the delayed autocorrelation results are smoothed:

Among them, L _avg is the smoothing filter window length, and P _avg [k] is the rough synchronization sequence result after smoothing filtering.

The theoretical coarse synchronization timing position index syn_coarse _t should be the index position corresponding to the maximum value of the coarse synchronization sequence result after smoothing and filtering:

However, considering that the hardware carrier is FPGA that uses streams to continuously process data, the streaming threshold comparison method is used to obtain the final rough timing synchronization position syn_coarse (the threshold _Padv is generated by the empirical value of multiple prior experiments).

Please refer to Figure 5. _Lavg = 16 is used to simulate coarse synchronization and smooth filtering. From the simulation results, it can be seen that delayed autocorrelation produces trapezoid-like correlation results. The result is a slowly changing process, and the streaming threshold is applicable. Find the peak position by comparison.

S3. When obtaining the rough timing synchronization position, use the angle information carried by the autocorrelation result. Implement frequency offset estimation of the system to calculate the actual value cfo_est;

The angle information of precise timing position is used for frequency offset estimation. The theoretical value of frequency offset estimation is:

Among them, f _samp is the system sampling frequency.

The angle information of the coarse synchronization timing position is used to estimate the frequency offset, and the actual value of the frequency offset estimate cfo_est is:

Refer to Figure 6. Under design simulation conditions, Under the condition of signal-to-noise ratio ≥ 4dB, the mean square error between the frequency offset estimation value and the standard value in multiple experiments is below 10 ^-5 , which fully meets the system frequency offset estimation requirements.

S4. On the basis of obtaining the coarse timing synchronization position, use the cross-correlation algorithm to perform correlation operations on the local cache sequence and the received signal sequence to obtain the precise timing synchronization position syn_precious;

Precise timing synchronization plays a role in improving the accuracy of system timing synchronization. When the channel condition is good or the entire communication system is in the early stages of debugging, it is only necessary to ensure that the timing synchronization algorithm can be quickly implemented and to provide guaranteed functions for direct connection debugging of other system components. Use precision timing synchronization modules. At this time, the coarse timing synchronization syn_coarse result is the timing synchronization position of the synchronization module. In step S5, the timing synchronized data is output to the frequency offset compensation module according to the position.

The fine timing synchronization module uses coarse synchronization timing position left and right Points are cross-correlated with the local N _cfft point cache sequence pattern_c. In order to save hardware resources and calculation time, the cross-correlation result is obtained by first performing an N _cfft point FFT operation on the two sequences, and then performing an N _cfft point IFFT operation on the result:

Because cross-correlation will produce a pulse-like spike, the position corresponding to the spike is the precise timing position. syn_precious is:

Please refer to Figure 7. Under the above design simulation conditions, N _cfft = 256. It can be seen from the simulation results that due to the characteristics of the cross-correlation operation, the result produces a sharp correlation peak. Therefore, there is no need to preset the decision threshold, and only need to perform Peak detection can position the reference point more accurately. On the other hand, it can also eliminate the decision error introduced by the decision threshold.

S5. Add the coarse synchronization and fine synchronization results to obtain the position index of the final system symbol timing synchronization result. According to this position index, the data sequence after symbol timing synchronization is output. At the same time, according to the frequency offset estimation result in step S3, the corresponding complex exponential signal pair is generated. The sequence after timing synchronization performs frequency offset compensation operation, and finally completes the system synchronization task.

In yet another embodiment of the present invention, an FPGA implementation system for time-frequency synchronization of a multi-channel parallel transmission millimeter wave OFDM communication system is provided. This system can be used to implement the FPGA implementation of the time-frequency synchronization of the above-mentioned multi-channel parallel transmission millimeter wave OFDM communication system. Method, specifically, the FPGA implementation system for time-frequency synchronization of the multi-channel parallel transmission millimeter wave OFDM communication system includes a matrix module, an accumulation module, an estimation module, an operation module and an output module.

Among them, the matrix module generates a training sequence signal matrix X with a specific structure in the time domain based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission paths N _path in specific FPGA implementation;

The accumulation module uses the structural characteristics of the training sequence signal matrix Timing synchronization position syn_coarse;

The estimation module, based on the rough timing synchronization position syn_coarse obtained by the accumulation module, uses the angle information carried by the autocorrelation result Realize the frequency offset estimation actual value cfo_est of the millimeter wave OFDM communication system;

The operation module, based on the coarse timing synchronization position syn_coarse obtained by the accumulation module, uses the cross-correlation algorithm to calculate the local buffer sequence pre-stored locally in the receiver and the received signal sequence to obtain the precise timing synchronization position syn_precious;

The output module adds the coarse timing synchronization position syn_coarse obtained by the step accumulation module and the fine timing synchronization position syn_precious obtained by the operation module to obtain the final system symbol timing synchronization result position index, and outputs the data sequence after symbol timing synchronization based on the position index. At the same time According to the actual frequency offset estimate cfo_est obtained by the estimation module, the corresponding complex exponential signal is generated, and the frequency offset compensation operation is performed on the sequence after timing synchronization, and finally the system synchronization task is completed.

In yet another embodiment of the present invention, a terminal device is provided. The terminal device includes a processor and a memory. The memory is used to store a computer program. The computer program includes program instructions. The processor is used to execute the computer program. A storage medium stores program instructions. The processor may be a Central Processing Unit (CPU), or other general-purpose processor, Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), or off-the-shelf programmable gate Array (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, specifically Suitable for loading and executing one or more instructions to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the FPGA implementation method of time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system, include:

Based on the physical layer frame structure of the transmission signal and the number of baseband parallel transmission paths N _path during specific FPGA implementation, a training sequence signal matrix X with a specific structure is generated in the time domain; using the structural characteristics of the training sequence signal matrix X, delay autocorrelation is used The method operates on the baseband multi-channel parallel received signals, then accumulates the results, and finds the rough timing synchronization position syn_coarse through the streaming empirical threshold comparison method;

Based on the coarse timing synchronization position syn_coarse, using the angle information carried by the autocorrelation result Realize the actual frequency offset estimation value cfo_est of the millimeter wave OFDM communication system; based on the coarse timing synchronization position syn_coarse, use the cross-correlation algorithm to calculate the local buffer sequence pre-stored locally in the receiver and the received signal sequence to obtain the precise timing synchronization position syn_precious; Add the coarse timing synchronization position syn_coarse and the fine timing synchronization position syn_precious to obtain the final system symbol timing synchronization result position index. According to the position index, the data sequence after symbol timing synchronization is output, and at the same time, the corresponding complex index is generated based on the frequency offset estimation actual value cfo_est signal, perform frequency offset compensation operation on the sequence after timing synchronization, and finally complete the system synchronization task.

In yet another embodiment of the present invention, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a terminal device and is used to store programs and data. . It can be understood that the computer-readable storage medium here may include a built-in storage medium in the terminal device, and of course may also include an extended storage medium supported by the terminal device. The computer-readable storage medium provides storage space, and the storage space stores the operating system of the terminal. Furthermore, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space. These instructions may be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here may be a high-speed RAM memory or a non-volatile memory (Non-Volatile Memory), such as at least one disk memory.

One or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the FPGA implementation method for time-frequency synchronization of multi-channel parallel transmission millimeter-wave OFDM communication systems in the above embodiments; computer-readable One or more instructions in the storage medium are loaded by the processor and execute the following steps:

Based on the coarse timing synchronization position syn_coarse, using the angle information carried by the autocorrelation result Realize the actual frequency offset estimation value cfo_est of the millimeter wave OFDM communication system; based on the coarse timing synchronization position syn_coarse, use the cross-correlation algorithm to calculate the local buffer sequence pre-stored locally in the receiver and the received signal sequence to obtain the precise timing synchronization position syn_precious; Add the coarse timing synchronization position syn_coarse and the fine timing synchronization position syn_precious to obtain the final system symbol timing synchronization result position index. According to the position index, the data sequence after symbol timing synchronization is output, and at the same time, the corresponding complex index is generated based on the frequency offset estimation actual value cfo_est. signal, perform frequency offset compensation operation on the sequence after timing synchronization, and finally complete the system synchronization task.

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, rather than all embodiments. The components of the embodiments of the invention generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the appended drawings is not intended to limit the scope of the claimed invention, but rather to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

Please refer to Figure 8. Under the above design simulation conditions, the estimation of STO basically satisfies that the timing position offset does not exceed the correct position. The point is the timing accuracy standard. It can be seen that within the signal-to-noise ratio range of 4-25dB, the timing accuracy probability of the method of the present invention is higher than that of the typical SC algorithm, meeting the system timing synchronization requirements.

Please refer to Figure 9. Generate 36 parallel synchronization sequences through Matlab (there are 20 points of random noise before each sequence), and add 0.1 times normalized frequency offset. Use the Vivado2019.2 version platform to simulate the FPGA implementation of the design algorithm. In addition, the Matlab calculation hardware calculation index offset is 145; from the simulation results, it can be seen that the timing synchronization position address index (coarse_number signal) is 165=145+20, and the timing synchronization is accurate; the frequency offset estimate value (bias signal) is 4'h0333 (fix16_13) The decimal number is 0.1, the frequency offset estimation is accurate, and the entire calculation process requires 339 clock cycles, which meets the hardware conditions.

Through the software and hardware simulation verification of the method of the present invention, it can be seen that compared with the classic algorithm, the training sequence and synchronization method designed by the method of the present invention are more suitable for the transmission scenario of the large-bandwidth millimeter wave OFDM parallel transmission system. The timing synchronization and frequency offset estimation accuracy are both above industry standards, and the hardware computing time overhead and resource overhead of algorithm implementation have also been reduced.

In summary, the present invention is an FPGA implementation method for time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication systems. Compared with the cognitive millimeter wave OFDM communication system synchronization scheme, the present invention can combine the characteristics of large bandwidth and high sampling rate Generate an improved synchronization sequence and use a coarse and fine two-level synchronization method to improve the accuracy of timing synchronization and frequency offset estimation. You can choose whether to perform fine synchronization operations based on the channel conditions of the actual communication environment to consider both synchronization accuracy and computational complexity. At the same time, in terms of hardware implementation, the present invention has lower resource utilization, algorithm complexity and calculation time cost.

Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above functional units and modules is used as an example. In actual applications, the above functions can be allocated to different functional units and modules according to needs. Module completion means dividing the internal structure of the device into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be hardware-based. It can also be implemented in the form of software functional units. In addition, the specific names of each functional unit and module are only for the convenience of distinguishing each other and are not used to limit the scope of protection of the present application. For the specific working processes of the units and modules in the above system, please refer to the corresponding processes in the foregoing method embodiments, and will not be described again here.

In the above embodiments, each embodiment is described with its own emphasis. For parts that are not detailed or documented in a certain embodiment, please refer to the relevant descriptions of other embodiments.

Those of ordinary skill in the art can appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented with electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled artisans may implement the described functionality using different methods for each specific application, but such implementations should not be considered to be beyond the scope of the present invention.

In the embodiments provided by the present invention, it should be understood that the disclosed device/terminal and method can be implemented in other ways. For example, the device/terminal embodiments described above are only illustrative. For example, the division of modules or units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or units. Components may be combined or may be integrated into another system, or some features may be ignored, or not implemented. On the other hand, the coupling or direct coupling or communication connection between each other shown or discussed may be through some interfaces, indirect coupling or communication connection of devices or units, which may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or they may be distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above integrated units can be implemented in the form of hardware or software functional units.

If the integrated module/unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention can implement all or part of the processes in the methods of the above embodiments, and can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can be stored in a computer-readable storage medium. When the program is executed by the processor, the steps of each of the above method embodiments can be implemented. Wherein, the computer program includes computer program code, which may be in the form of source code, object code, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording media, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (Read-Only Memory, ROM) , random access memory (Random Access Memory, RAM), electrical carrier signals, telecommunications signals, software distribution media, etc. It should be noted that the content contained in the computer readable media can be based on the requirements of legislation and patent practice in the jurisdiction. Making appropriate additions or subtractions, for example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunications signals.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each process and/or block in the flowchart illustrations and/or block diagrams, and combinations of processes and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing device to produce a machine, such that the instructions executed by the processor of the computer or other programmable data processing device produce a use A device for realizing the functions specified in one process or multiple processes of the flowchart and/or one block or multiple blocks of the block diagram.

These computer program instructions may also be stored in a computer-readable memory that causes a computer or other programmable data processing apparatus to operate in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction means, the instructions The device implements the functions specified in a process or processes of the flowchart and/or a block or blocks of the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device, causing a series of operating steps to be performed on the computer or other programmable device to produce computer-implemented processing, thereby executing on the computer or other programmable device. Instructions provide steps for implementing the functions specified in a process or processes of a flowchart diagram and/or a block or blocks of a block diagram.

The above contents are only for illustrating the technical ideas of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made based on the technical ideas proposed by the present invention and based on the technical solutions shall fall within the scope of the claims of the present invention. within the scope of protection.

Claims (10)

1. The FPGA implementation method for time-frequency synchronization of the multipath parallel transmission millimeter wave OFDM communication system is characterized by comprising the following steps:

s1, realizing time-base band parallel transmission path number N according to a transmission signal physical layer frame structure and a specific FPGA _path Generating a training sequence signal matrix X with a specific structure in a time domain;

s2, calculating baseband multipath parallel received signals by using the structural characteristics of the training sequence signal matrix X obtained in the step S1 and adopting a delay autocorrelation method, accumulating the results, and finding a coarse timing synchronization position syn_coarse by using a stream experience threshold comparison method;

S3, based on the coarse timing synchronization position syn_coarse obtained in the step S2, utilizing angle information carried by the autocorrelation resultImplementing the actual frequency offset estimation value cfo_est of the millimeter wave OFDM communication system;

s4, based on the coarse timing synchronization position syn_coarse obtained in the step S2, calculating a local buffer sequence and a received signal sequence which are stored in the receiver in advance by using a cross-correlation algorithm to obtain a fine timing synchronization position syn_pre;

s5, adding the coarse timing synchronization position syn_coarse obtained in the step S2 and the fine timing synchronization position syn_pre obtained in the step S4 to obtain a final system symbol timing synchronization result position index, outputting a data sequence after symbol timing synchronization according to the position index, generating a corresponding complex exponential signal according to the frequency offset estimation actual value cfo_est obtained in the step S3, performing frequency offset compensation operation on the sequence after timing synchronization, and finally completing a system synchronization task.

2. The method for implementing time-frequency synchronization of a multipath parallel transmission millimeter wave OFDM communication system according to claim 1, wherein in step S1, the training sequence signal matrix X is:

wherein T is transposition calculation, C ^M×N Matrix with M multiplied by N dimension elements as complex number, M _{T_CP} For the time domain CP part, M _{T_data} For the time domain data part, N _samp For training sequence time domain sampling point number, N _path Is the number of parallel paths.

3. The method for implementing time-frequency synchronization of a multipath parallel transmission millimeter wave OFDM communication system according to claim 2, wherein the specific construction mode of the training sequence is as follows:

wherein ,cronecker product symbol representing matrix, a= [1,1]R is a constant amplitude random sequence, S _{ZC_1} 、S _{ZC_2} Respectively N _cfft And->The ZC pseudo-random sequence of points.

4. The method for implementing time-frequency synchronization of a multipath parallel transmission millimeter wave OFDM communication system according to claim 1, wherein in step S2, the coarse timing synchronization position syn_coarse is:

wherein ,P_avg [k]To smooth the post-filter coarse synchronization sequence result, P _adv K is the sequence number of the coarse synchronization sequence result, which is a known empirical threshold for the corresponding training sequence.

5. According to claimThe FPGA implementation method for time-frequency synchronization of the multipath parallel transmission millimeter wave OFDM communication system is characterized in that the method is characterized in that a coarse synchronization sequence result P after smooth filtering _avg [k]The method comprises the following steps:

wherein ,L_avg To smooth the filter window length.

6. The method for implementing time-frequency synchronization of a multipath parallel transmission millimeter wave OFDM communication system according to claim 1, wherein in step S3, an actual frequency offset estimation value cfo_est is:

wherein ,for the angle information carried by the autocorrelation result, N _sub For the number of subcarriers, f _samp Is the system sampling frequency.

7. The method for implementing time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system according to claim 1, wherein in step S4, coarse synchronization timing positions are adoptedPoint and local N _cfft The cross-correlation operation is carried out on the point buffer sequence pattern_c, and the cross-correlation result adopts N to carry out on two sections of sequences first _cfft Point FFT operation, and then N is performed on the result _cfft The IFFT operation of the points generates a peak similar to a pulse, and the position corresponding to the peak is the fine timing synchronization position syn_synchronization.

8. The method for implementing time-frequency synchronization of a multipath parallel transmission millimeter wave OFDM communication system according to claim 7, wherein the fine timing synchronization position syn_synchronization is:

wherein ,P_cor And k is the sequence number of the fine synchronization sequence result after the cross correlation operation.

9. The method for implementing time-frequency synchronization of multi-channel parallel transmission millimeter wave OFDM communication system according to claim 8, wherein P is _cor The method comprises the following steps:

wherein ,N_cfft For the number of the Fourier transform sampling points, fft is the fast Fourier transform operation, xn is the time domain sequence of the signal received by the receiver, syn_coarse is the coarse synchronization positioning position, and pattern_c is N pre-buffered by the receiver _cfft The sequence of points is cached.

10. The FPGA implementation system for time-frequency synchronization of the multipath parallel transmission millimeter wave OFDM communication system is characterized by comprising:

matrix module, according to the physical layer frame structure of the transmission signal, and specific FPGA realizes time-base band parallel transmission path number N _path Generating a training sequence signal matrix X with a specific structure in a time domain;

the accumulation module is used for calculating the baseband multipath parallel receiving signals by using the structural characteristics of the training sequence signal matrix X obtained by the matrix module and adopting a delay autocorrelation method, then accumulating the results, and finding a coarse timing synchronization position syn_coarse by using a flow empirical threshold comparison method;

an estimation module for utilizing self-timer based on the coarse timing synchronization position syn_coarse obtained by the accumulation moduleAngle information carried by correlation resultImplementing the actual frequency offset estimation value cfo_est of the millimeter wave OFDM communication system;

the operation module is used for operating a local buffer sequence which is pre-stored in the local of the receiver and a received signal sequence by using a cross-correlation algorithm based on the coarse timing synchronization position syn_coarse obtained by the accumulation module to obtain a fine timing synchronization position syn_pre;

the output module is used for adding the coarse timing synchronization position syn_coarse obtained by the step accumulation module and the fine timing synchronization position syn_pre obtained by the operation module to obtain a final system symbol timing synchronization result position index, outputting a data sequence after symbol timing synchronization according to the position index, generating a corresponding complex exponential signal according to the frequency offset estimation actual value cfo_est obtained by the estimation module, performing frequency offset compensation operation on the sequence after timing synchronization, and finally completing a system synchronization task.