Wireless communication time-frequency synchronization method based on CAZAC sequence and dual-tone signal

Abstract

The invention discloses a wireless communication time-frequency synchronization method based on a CAZAC sequence and a dual-tone signal. The method comprises the steps that a synchronization station receives a synchronization signal which is generated by a base station and comprises the CAZAC sequence and the dual-tone signal; the synchronization station performs timing estimation by using the CAZAC sequence to obtain an estimated value of timing offset; the synchronization station performs accurate frequency offset estimation by using the dual-tone signal to obtain an estimated value of frequency offset; and the synchronization station performs time-frequency synchronization adjustment according to the estimated value of the timing offset and the estimated value of the frequency offset, so that time-frequency synchronization between the synchronization station and the reference station is realized. According to the wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal, the technical problems of insufficient synchronization precision, low spectrum utilization rate and high calculation complexity in the existing wireless communication system are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of time and frequency synchronization, and particularly relates to a wireless communication time-frequency synchronization method based on CAZAC sequences and dual-tone signals. Background Art

[0002] Orthogonal frequency division multiplexing (OFDM) is a multi-carrier modulation method with advantages such as high spectrum utilization rate, resistance to frequency-selective fading, and easy modulation and demodulation. It has been widely applied in multiple wireless communication standards and wireless communication scenarios, such as 5G NR synchronization signals, radar signal processing, and underwater acoustic communication. Although OFDM technology is widely used, it is very sensitive to synchronization errors. Synchronization errors will introduce inter-carrier interference (ICI) and inter-symbol interference (ISI), reducing the demodulation performance. The synchronization errors of OFDM systems are divided into symbol timing deviation and frequency deviation. Due to the multipath delay phenomenon and various noise interferences, symbol timing deviation occurs. Symbol timing deviation causes OFDM systems to introduce ISI, affecting the transmission of effective data information. Compared with single-carrier systems, OFDM technology is very sensitive to carrier frequency deviation caused by Doppler frequency shift, the delay of different transmission paths, and the instability of local oscillators of transmitters and receivers. If there is carrier frequency deviation in the system, it will affect the orthogonality between sub-carriers of OFDM systems, introducing interference between sub-carrier channels, thus causing a sharp decline in the performance of OFDM systems. Therefore, symbol timing deviation and carrier frequency deviation will seriously affect the performance of OFDM systems, and symbol timing synchronization and carrier frequency synchronization are required. And time-frequency joint synchronization algorithms can achieve carrier frequency synchronization while performing symbol timing synchronization. Therefore, the research on time-frequency joint synchronization algorithms in OFDM systems has certain practical value.

[0003] Currently, OFDM system synchronization methods are divided into non-data-aided blind estimation algorithms and data-aided estimation algorithms. The former is applicable to continuous transmission systems and mainly uses the structural characteristics of the system itself to achieve synchronization. It has high bandwidth utilization rate but low synchronization accuracy. The latter is commonly used in burst communication systems and uses the correlation between known preamble sequence data to achieve synchronization. Its preamble sequence is mainly composed of some sequences with good auto-correlation and cross-correlation performance, such as pseudo-noise (PN) sequences or constant amplitude zero auto correlation (CAZAC) sequences.

[0004] CAZAC sequence is a constant envelope sequence with a constant amplitude for each element in the sequence. The cross-correlation value of the CAZAC sequence is zero, the autocorrelation peak curve is sharp, and the CAZAC sequence remains a CAZAC sequence after forward and inverse Fourier transforms. In a multipath fading channel, the sharp autocorrelation peak of the CAZAC sequence can still effectively detect signals, reduce inter-symbol interference (ISI), and its zero correlation also reduces the side lobes in the timing metric function, avoiding misjudgment, featuring low side lobe interference and strong anti-multipath interference ability. Common CAZAC sequences mainly include Zadoff-Chu (ZC) sequences, Chirp sequences, Frank sequences, Golomb polyphase sequences, etc. Compared with traditional PN sequences, due to its characteristics of constant amplitude and good correlation, the CAZAC sequence has been widely used in the synchronization algorithms of OFDM systems, such as the synchronization of OFDM systems, cell search and random access in LTE systems, synchronization of distributed UFMC-MIMO systems, and as a detection sequence in pulse compression systems, etc.

[0005] However, the timing synchronization of the CAZAC sequence depends on phase consistency, but carrier frequency offset will introduce a linear phase shift, destroying the characteristics of the correlation peak. Generally, additional frequency offset estimation algorithms such as joint cyclic prefix (CP) need to be introduced, which will increase the system complexity and occupy too much spectrum resources. Therefore, in practical applications, it is necessary to make up for its deficiencies by improving algorithms or combining other technologies to achieve better synchronization performance. Summary of the Invention

[0006] The present invention provides a time-frequency synchronization method for wireless communication based on CAZAC sequence and dual-tone signal to solve the above-mentioned technical problems, and specifically adopts the following technical solutions:

[0007] A time-frequency synchronization method for wireless communication based on CAZAC sequence and dual-tone signal, comprising the following steps:

[0008] The synchronization station receives a synchronization signal containing a CAZAC sequence and a dual-tone signal generated by the reference station;

[0009] The synchronization station uses the CAZAC sequence for timing estimation to obtain an estimated value of the timing offset;

[0010] The synchronization station uses the dual-tone signal for accurate frequency offset estimation to obtain an estimated value of the frequency deviation;

[0011] The synchronization station performs time-frequency synchronization adjustment according to the estimated value of the timing offset and the estimated value of the frequency deviation, so that the synchronization station and the reference station achieve time-frequency synchronization.

[0012] Further, the using the CAZAC sequence for timing estimation includes:

[0013] The synchronization station calculates the correlation function of the received signal and the locally generated CAZAC sequence;

[0014] An estimated value of the timing offset is obtained by maximizing the correlation function.

[0015] Further, after performing the timing estimation using the CAZAC sequence, the following steps are further included:

[0016] The synchronization station determines whether the peak value of the correlation function meets a set threshold;

[0017] If the peak value meets the set threshold, timing information is obtained through the position of the correlation peak, otherwise the currently received synchronization signal is discarded and waiting for the reception of the next frame of synchronization signal.

[0018] Further, the precise frequency offset estimation using the two-tone signal includes:

[0019] The synchronization station analyzes the phase difference of the two-tone signals sampled in adjacent synchronization periods;

[0020] The frequency deviation is calculated according to the phase difference.

[0021] Further, the time-frequency synchronization adjustment includes:

[0022] The synchronization station tames the local programmable crystal oscillator using the estimated value of the frequency deviation to achieve frequency synchronization;

[0023] The synchronization station adjusts the local clock according to the estimated value of the timing offset to achieve time synchronization.

[0024] Further, the CAZAC sequence has the characteristics of low sidelobe interference and anti-multipath interference, and the two-tone signal can set its operating frequency band to avoid interference.

[0025] A wireless communication time-frequency synchronization system based on CAZAC sequence and two-tone signal, comprising:

[0026] A reference station for generating a synchronization signal including a CAZAC sequence and a two-tone signal and sending it to the synchronization station;

[0027] A synchronization station for receiving the synchronization signal and performing time-frequency synchronization adjustment;

[0028] Wherein, the synchronization station includes:

[0029] A signal reception and preprocessing module for receiving wireless signals and performing preprocessing;

[0030] A synchronization module for performing timing estimation using the CAZAC sequence and performing precise frequency offset estimation using the two-tone signal;

[0031] A data demodulation and decoding module, which is used to demodulate and decode the synchronized signal.

[0032] Further, the reference station includes:

[0033] A CAZAC sequence generation module, which is used to generate a CAZAC sequence;

[0034] A dual-tone signal generation module, which is used to generate a dual-tone signal;

[0035] A communication packet data generation module, which is used to generate the required communication data.

[0036] Further, the synchronization station further includes:

[0037] The synchronization station and the reference station further include:

[0038] A digital-to-analog converter and an analog-to-digital converter, which are used to perform digital-to-analog conversion and analog-to-digital conversion of signals;

[0039] A radio frequency transceiver and a radio frequency antenna, which are used to receive and transmit radio frequency signals.

[0040] Further, the synchronization module estimates the timing deviation by calculating the correlation function between the received signal and the locally generated CAZAC sequence, and estimates the frequency deviation by analyzing the phase difference of the dual-tone signals sampled in adjacent synchronization periods.

[0041] The beneficial effect of the present invention lies in the provided time-frequency synchronization method for wireless communication based on CAZAC sequences and dual-tone signals, which effectively solves the technical problems of insufficient synchronization accuracy, low spectrum utilization rate, and high computational complexity in existing wireless communication systems. Specifically, by using a CAZAC sequence as a preamble sequence in the synchronization signal sent by the reference station for preliminary timing estimation, and then using a dual-tone signal for accurate frequency offset estimation, high-precision and high-efficiency time-frequency synchronization is achieved. The method of the present invention has a wide application prospect in actual wireless communication systems. Whether in a centralized wireless communication system or a distributed wireless communication system, it can improve the synchronization performance of the system, thereby enhancing the communication quality and efficiency of the entire system. Description of the Drawings

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0043] Figure 1Schematic diagram of the preamble sequence structure of the Jian algorithm of the present application;

[0044] Figure 2 Schematic diagram of a time-frequency synchronization method for wireless communication based on CAZAC sequences and dual-tone signals of the present application;

[0045] Figure 3 Schematic diagram of the distributed wireless synchronization system of the present application;

[0046] Figure 4 Specific schematic diagram of the distributed wireless synchronization system of the present application. Detailed implementation manners

[0047] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, in which the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application.

[0048] Classic synchronization algorithms based on CAZAC sequences include the Ren algorithm, the Fang algorithm, the Shao algorithm, and the Jian algorithm. The CAZAC sequence used in the present application is the sequence proposed in the Jian algorithm. Compared with the time-frequency synchronization algorithms based on CAZAC sequences such as Ren, Shao, and Fang, the Jian algorithm has the advantages of lower computational complexity and better performance under low signal-to-noise ratio conditions. The preamble sequence structure of the Jian algorithm is as Figure 1 shown.

[0049] Among them, the CAZAC sequence A = [a(0), a(1), …, a(n)], and the expression of a(n) is as follows:

[0050]

[0051] The sequence B = [b(0), b(1), …, b(n)] is the conjugate symmetric sequence of the sequence A, and the expression of c(n) in the sequence C = [c(0), c(1), …, c(n)] is as follows:

[0052]

[0053] The sequence D = [d(0), d(1), …, d(n)] is the conjugate sequence of the sequence C.

[0054] The timing metric function is:

[0055]

[0056] Among them,

[0057]

[0058]

[0059] In the formula, r(n) is the actually received signal, x(n) is the received signal without considering the influence of noise and multipath effects, ε is the frequency offset. It can be seen from this that the frequency offset ε is affected by n. Therefore, when there is a frequency offset, the timing synchronization performance will decline.

[0060] Energy function:

[0061]

[0062] The estimated value of the timing offset is:

[0063]

[0064] The present invention accurately estimates the frequency deviation by analyzing the phase difference of the dual-tone signals sampled in adjacent synchronization periods. Using the crystal oscillator of the reference station as the standard clock source, the measurement of the frequency offset of the crystal oscillator of the synchronization station is completed. The specific principle is as follows:

[0065] Crystal oscillator output model:

[0066] f(t) = f o + αt + f r (t)

[0067]

[0068] Where is the initial phase deviation, f o is the initial frequency deviation, α represents the frequency drift coefficient, f r (t) and represent random terms.

[0069] Suppose the counting clock of the reference station is obtained by multiplying the crystal oscillator of the master station by P o times the frequency. Taking P o = 30 and the clock frequency osc m of the crystal oscillator of the reference station being 10 MHz as an example, then the counting clock frequency f m of the reference station is:

[0070] f m = 300 MHz = P o * osc m

[0071] There is a deviation f bias between the crystal oscillator clock frequencies of the receiving station and the reference station. The counting clock frequency f s of the receiving station is:

[0072] f s = Po *osc s =f m +P o *f bias

[0073] The reference station and the receiving station rely on their own counting clocks to complete the timing. The reference station sends a two-tone signal with a frequency of f sin1 and f sin2 , and the receiving station receives and analyzes it. Due to the existence of frequency deviation, there is a counting time deviation between the two received signal analyses:

[0074]

[0075] The sampling time offset caused by the counting deviation causes the initial phase of the signal to change, that is, the initial phase of the signal in two adjacent sampling windows:

[0076] θ1=f sin1 *N bias *360°

[0077] θ2=f sin2 *N bias *360°

[0078] θ sub =θ1-θ2=(f sin1 -f sin2 )*N bias *360°

[0079] The phase of the measured signal can be obtained by multiplying the signal generated locally by the receiving station with the received signal, and because the result contains other frequency components, the phase needs to be calculated after averaging.

[0080] Combining the two equations, we can get:

[0081]

[0082] From the formula, we can know that frequency deviation and f sin1 and f sin2 When the difference is the same, the frequency deviation calculation formula is also the same, so f can be changed according to the needs. sin1 and f sin2 By setting it on different frequency bands, you can avoid interference on certain frequency bands.

[0083] Based on the above discussion, if Figure 2 As shown, the present application discloses a wireless communication time-frequency synchronization method based on a CAZAC sequence and a dual-tone signal, comprising:

[0084] Receive the synchronization signal including CAZAC sequence and dual-tone signal generated by the reference station;

[0085] The synchronization station receives the synchronization signal and uses the CAZAC sequence for timing estimation to obtain an estimated value of the timing offset;

[0086] The synchronization station uses the dual-tone signal for accurate frequency offset estimation to obtain an estimated value of the frequency deviation;

[0087] The synchronization station performs time-frequency synchronization adjustment according to the estimated value of the timing offset and the estimated value of the frequency deviation, so that the synchronization station and the reference station achieve time-frequency synchronization.

[0088] In the embodiment of the present application, using the CAZAC sequence for timing estimation includes:

[0089] The synchronization station calculates the correlation function between the received signal and the locally generated CAZAC sequence;

[0090] The estimated value of the timing offset is obtained by maximizing the correlation function.

[0091] In the embodiment of the present application, after using the CAZAC sequence for timing estimation, the following steps are further included:

[0092] The synchronization station determines whether the peak value of the correlation function meets the set threshold;

[0093] If the peak value meets the set threshold, the timing information is obtained through the position of the correlation peak, otherwise the currently received synchronization signal is discarded and the next frame of synchronization signal is awaited for reception.

[0094] In the embodiment of the present application, using the dual-tone signal for accurate frequency offset estimation includes:

[0095] The synchronization station analyzes the phase difference of the dual-tone signals sampled in adjacent synchronization periods;

[0096] The frequency deviation is calculated according to the phase difference.

[0097] In the embodiment of the present application, the time-frequency synchronization adjustment includes:

[0098] The synchronization station tames the local programmable crystal oscillator using the estimated value of the frequency deviation to achieve frequency synchronization;

[0099] The synchronization station adjusts the local clock according to the estimated value of the timing offset to achieve time synchronization.

[0100] In the embodiment of the present application, the CAZAC sequence has the characteristics of low sidelobe interference and anti-multipath interference, and the dual-tone signal is set so that the frequency band it is in avoids interference.

[0101] Such as Figures 3 - 4As shown, n synchronization stations achieve wireless synchronization by receiving the synchronization signals of the reference station, and the synchronization nodes are distinguished according to the configured node addresses. The hardware platform of the nodes includes an FPGA chip, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), a radio frequency transceiver, a local programmable crystal oscillator, and a radio frequency antenna. The radio frequency transceiver is responsible for receiving and transmitting radio frequency signals and is equipped with up and down conversion modules, enabling the signals to be mixed to a higher frequency band, improving the flexibility of the synchronization system. The transceiver control logic in the synchronization station controls the radio frequency transceiver to transmit the signals received by the antenna to the ADC. The signals after analog-to-digital conversion are sent to the FPGA for signal processing. The signal reception and preprocessing module receives the wireless signals and performs preprocessing (such as filtering), thus providing a pure received signal for the subsequent synchronization algorithm. The synchronization module calculates the received signals through a sliding window, calculates the timing result, and then measures the frequency offset using the phase information of the dual-tone signal. The obtained frequency offset information is used to tame the local programmable crystal oscillator to achieve frequency synchronization. The data demodulation and decoding module demodulates and decodes the synchronized signals to restore the original data information. The CAZAC sequence generation module and the dual-tone signal generation module of the reference station are used to generate synchronization signals, and the communication packet data generation module is used to generate the required communication data. Finally, the signals are sent out every fixed synchronization period, and the operation of the radio frequency transceiver is controlled by the signal transceiver control logic.

[0102] Based on the above description, the present application also discloses a wireless communication time-frequency synchronization system based on CAZAC sequences and dual-tone signals, including: a plurality of synchronization stations and a reference station. Among them, the reference station is used to generate synchronization signals containing CAZAC sequences and dual-tone signals and send them to the synchronization stations. The synchronization stations are used to receive the synchronization signals and perform time-frequency synchronization adjustment.

[0103] Among them, the synchronization station includes: a signal reception and preprocessing module, a synchronization module, and a data demodulation and decoding module. The signal reception and preprocessing module, the synchronization module, and the data demodulation and decoding module are arranged on the FPGA chip. The signal reception and preprocessing module is used to receive wireless signals and perform preprocessing. The synchronization module is used to perform timing estimation using CAZAC sequences and perform accurate frequency offset estimation using dual-tone signals. The data demodulation and decoding module is used to demodulate and decode the synchronized signals. The synchronization station also includes a local programmable crystal oscillator for signal synchronization.

[0104] The reference station includes: a CAZAC sequence generation module, a dual-tone signal generation module, and a communication packet data generation module. Similarly, the CAZAC sequence generation module, the dual-tone signal generation module, and the communication packet data generation module are arranged on an FPGA chip. The CAZAC sequence generation module is used to generate a CAZAC sequence. The dual-tone signal generation module is used to generate a dual-tone signal. The communication packet data generation module is used to generate the required communication data. Further, the synchronization module estimates the timing deviation by calculating the correlation function of the received signal and the locally generated CAZAC sequence, and estimates the frequency deviation by analyzing the phase difference of the dual-tone signals sampled in adjacent synchronization periods.

[0105] Further, the synchronization station and the reference station further include: a digital-to-analog converter, an analog-to-digital converter, a radio frequency transceiver, and a radio frequency antenna. The digital-to-analog converter and the analog-to-digital converter are used for digital-to-analog conversion and analog-to-digital conversion of signals. The radio frequency transceiver and the radio frequency antenna are used for receiving and transmitting radio frequency signals.

[0106] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by using equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A time-frequency synchronization method for wireless communication based on CAZAC sequences and dual-tone signals, characterized in that It includes the following steps: The synchronization station receives the synchronization signal containing the CAZAC sequence and the dual-tone signal generated by the reference station; The synchronization station uses the CAZAC sequence for timing estimation to obtain an estimated value of the timing offset; The synchronization station uses the dual-tone signal for accurate frequency offset estimation to obtain an estimated value of the frequency deviation; The synchronization station performs time-frequency synchronization adjustment according to the estimated value of the timing offset and the estimated value of the frequency deviation, so that the synchronization station and the reference station achieve time-frequency synchronization.

2. The wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal according to claim 1, characterized in that The using the CAZAC sequence for timing estimation includes: The synchronization station calculates the correlation function between the received signal and the locally generated CAZAC sequence; An estimated value of the timing offset is obtained by maximizing the correlation function.

3. The wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal according to claim 2, characterized in that After the using the CAZAC sequence for timing estimation, the following steps are further included: The synchronization station determines whether the peak value of the correlation function meets the set threshold; If the peak value meets the set threshold, timing information is obtained through the position of the correlation peak, otherwise the currently received synchronization signal is discarded and waiting for the reception of the next frame of synchronization signal.

4. The wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal according to claim 1, characterized in that The using the dual-tone signal for accurate frequency offset estimation includes: The synchronization station analyzes the phase difference of the dual-tone signals sampled in adjacent synchronization periods; The frequency deviation is calculated according to the phase difference.

5. The wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal according to claim 1, characterized in that The time-frequency synchronization adjustment includes: The synchronization station uses the estimated value of the frequency deviation to tame the local programmable crystal oscillator to achieve frequency synchronization; The synchronization station adjusts the local clock according to the estimated value of the timing offset to achieve time synchronization.

6. The wireless communication time-frequency synchronization method based on the CAZAC sequence and the dual-tone signal according to claim 1, characterized in that The CAZAC sequence has the characteristics of low sidelobe interference and anti-multipath interference, and the dual-tone signal is set so that the frequency band it is in avoids interference.

7. A time-frequency synchronization system for wireless communication based on CAZAC sequences and dual-tone signals, characterized in that, It includes: A reference station for generating a synchronization signal containing a CAZAC sequence and a dual-tone signal and sending it to the synchronization station; A synchronization station for receiving the synchronization signal and performing time-frequency synchronization adjustment; Wherein, the synchronization station includes: A signal receiving and preprocessing module for receiving wireless signals and performing preprocessing; A synchronization module for using the CAZAC sequence for timing estimation and using the dual-tone signal for accurate frequency offset estimation; A data demodulation and decoding module for demodulating and decoding the synchronized signal.

8. The wireless communication time-frequency synchronization system based on the CAZAC sequence and the dual-tone signal according to claim 7, characterized in that The reference station includes: A CAZAC sequence generation module for generating a CAZAC sequence; A dual-tone signal generation module for generating a dual-tone signal; A communication packet data generation module for generating the required communication data.

9. The wireless communication time-frequency synchronization system based on CAZAC sequences and dual-tone signals according to claim 7, wherein The synchronization station and the reference station further include: A digital-to-analog converter and an analog-to-digital converter for performing digital-to-analog conversion and analog-to-digital conversion of signals; A radio frequency transceiver and a radio frequency antenna for receiving and transmitting radio frequency signals.

10. The wireless communication time-frequency synchronization system based on CAZAC sequences and dual-tone signals according to claim 7, wherein The synchronization module estimates the timing deviation by calculating the correlation function between the received signal and the locally generated CAZAC sequence, and estimates the frequency deviation by analyzing the phase difference of the dual-tone signals sampled in adjacent synchronization periods.

Images