CN101267419B - A method and device for adjusting time advance amount for OFDM symbol timing - Google Patents

Abstract

The invention provides a timing advance regulating method for OFDM symbol timing and a device, the method comprising the steps of: receiving an OFDM signal emitted by a transmitting terminal at a receiving terminal; according to channel frequency domain response message output by channel estimation, judging whether time of current OFDM symbol timing being in cycle prefix length of the OFDM symbol is more than a first preset threshold; if yes, turning down the timing advance of next OFDM symbol timing; judging whether time of current OFDM symbol timing not being in the cycle prefix length of the OFDM symbol is more than a second preset threshold; if yes, turning up the timing advance of next OFDM symbol timing; the method is capable of regulating timing advance self-adaptively.

Description

A method and device for adjusting time advance amount for OFDM symbol timing

technical field

The present invention relates to Orthogonal Frequency Division Multiplexing (OFDM) technology, in particular to the reception of OFDM symbols, in particular to a method and device for adjusting the timing advance of OFDM symbol timing.

Background technique

Orthogonal Frequency Division Multiplexing (OFDM: Orthogonal Frequency Division Multiplex) is a multi-carrier modulation method that divides the entire channel into many narrow parallel sub-channels, increases the symbol period, and reduces the ISI caused by the multipath environment. Its basic principle is to divide the signal into N sub-signals, and then use the N sub-signals to modulate N mutually orthogonal sub-carriers respectively. Since the frequency spectrums of the subcarriers overlap with each other, higher frequency spectrum efficiency can be obtained. OFDM has been widely used in the field of wireless communication in recent years.

Figure 1a is the working principle of the transmitter, and Figure 1b is the working principle of the receiver, where:

At the transmitting end, the bit stream is first modulated by QAM or QPSK, then undergoes serial-to-parallel transformation and IFFT transformation in turn, and then converts parallel data into serial data, and adds a guard interval (also known as "cyclic prefix") to form OFDM code Yuan.

When the receiver detects that the signal arrives, it first performs synchronization and channel estimation. After time synchronization, fractional multiple frequency offset estimation and correction are completed, integer multiple frequency offset estimation and correction are performed through FFT transformation, and the data obtained at this time is QAM or QPSK modulated data. Correspondingly demodulating the data, a bit stream can be obtained.

Orthogonal Frequency Division Multiplexing (OFDM) has become one of the attractive schemes for broadband wireless communication systems because it can effectively combat multipath channels. However, compared with single-carrier systems, OFDM is very sensitive to time and frequency deviations. Timing skew can cause inter-symbol interference (ISI) and inter-carrier interference (ICI), causing bit error rate (BER) degradation.

Usually, a cyclic prefix (CP) is added before an effective OFDM symbol, and the length of the cyclic prefix is generally greater than the impulse response length of the channel. Thus, as long as the window of the Fourier transform (FFT) is within the CP, the symbol timing has little impact.

In recent years, various methods of time synchronization have been discovered, using specially designed training symbols or CPs, frame and symbol synchronization can be obtained. In a multi-path channel, due to the effects of other paths, the frame/symbol timing obtained is often behind the arrival time of the first path. If the FFT window is taken at the position of the frame/symbol timing, it cannot be guaranteed that the paths arriving earlier (the arrival time is earlier than the frame/symbol timing) have no ISI. In addition, the variance of frame/symbol timing errors must be considered even in additive Gaussian noise (AWGN) channels. Therefore, the FFT window should be set at a position earlier than the frame/symbol timing, which is the timing advance. To ensure that the FFT window is still within the range of the CP even considering multipath channel and frame/symbol timing errors.

The timing advance may be very different for AWGN and time-dispersed multipath channels. For example, an advance of 5 samples is sufficient for an AWGN channel, but an advance of 25 samples is required for a Pedestrian Class B channel (PB). But since we don't know the model of the propagation channel at the receiving end, such as AWGN or PB, setting an advance of 25 samples should be the safest. But a too large time advance will cause the phase rotation of each subcarrier on each OFDM symbol, which is unfavorable for channel estimation using frequency correlation. A too large time advance will reduce the accuracy of channel estimation, resulting in a decrease in BER.

Contents of the invention

The purpose of the present invention is to provide a timing advance adjustment method and device for OFDM symbol timing, which can adaptively adjust the timing advance according to the average phase difference between adjacent subcarriers obtained through channel estimation.

The technical solution of the present invention is: a method for adjusting the timing advance of OFDM symbol timing, the method comprising: receiving the OFDM signal transmitted by the transmitting end at the receiving end; judging that the current OFDM symbol timing is within the OFDM symbol cyclic prefix length Whether the number of times within is higher than the first preset threshold, if so, then reduce the timing advance of the next OFDM symbol timing; judge whether the number of times that the current OFDM symbol timing is not within the length of the OFDM symbol cyclic prefix is higher than the second The preset threshold value, if yes, increase the timing advance of the next OFDM symbol timing.

The present invention also provides a timing advance adjustment device for OFDM symbol timing, which includes: a radio frequency front end for receiving OFDM signals, performing down-conversion, filtering, and digital-to-analog conversion to obtain OFDM in the form of digital baseband Symbol; frame/symbol synchronization, used to place the FFT window at a suitable position according to the time advance and the frame/symbol timing information obtained through time synchronization; FFT, perform serial-to-parallel conversion on the data, calculate FFT, and perform parallel-to-serial changes , to obtain the frequency domain signal; channel estimation and equalization: use the pilot subcarrier to estimate the frequency domain response of the channel, output the channel frequency domain response to the phase detection unit, and use the estimated channel frequency domain response to eliminate the channel influence on the data subcarrier ( That is, frequency domain equalization).

The statistical analysis unit is used for counting the number of times that the current OFDM symbol timing is located within the cyclic prefix and outside the cyclic prefix. And judge whether the number of times that the timing of the current OFDM symbol is within the length of the OFDM symbol cyclic prefix is higher than the first preset threshold, if so, then output an instruction to adjust the time advance of the timing of the next OFDM symbol; judge the current OFDM symbol Whether the number of times that the symbol timing is not within the OFDM symbol cyclic prefix length is higher than the second preset threshold value, if yes, then output an instruction to increase the timing advance of the next OFDM symbol timing; the timing advance adjustment unit is used for According to the instruction of reducing the timing advance of the next OFDM symbol timing, the timing advance of the next OFDM symbol timing is reduced; or according to the instruction of increasing the timing advance of the next OFDM symbol timing, increase the The timing advance of the next OFDM symbol timing.

The phase difference detection unit is used to determine the polarity of the average phase difference between adjacent subcarriers of the OFDM signal, and outputs the information whether the timing of the current OFDM symbol is within the length of the OFDM symbol cyclic prefix to the statistical analysis unit.

The present invention also provides a timing advance adjustment method for OFDM frame timing, which includes: receiving OFDM signals at the receiving end; judging whether the number of times the current OFDM frame timing is within the length of the OFDM frame cyclic prefix is higher than The first preset threshold, if yes, then turn down the timing advance of the next OFDM frame timing; judge whether the current OFDM frame timing is not within the OFDM frame cyclic prefix length and whether it is higher than the second preset threshold, if If yes, increase the timing advance of the next OFDM frame timing.

The present invention also provides a timing advance adjusting device for OFDM frame timing, the device comprising: a radio frequency front end, used for receiving OFDM signals, performing down-conversion, filtering, and digital-to-analog conversion to obtain OFDM symbols in digital baseband form; Frame/symbol synchronization is used to place the FFT window at a suitable position according to the frame/symbol timing information obtained by the time advance and time synchronization; FFT performs serial-to-parallel conversion on the data, calculates FFT, and performs parallel-to-serial changes, Obtain the frequency domain signal; channel estimation and equalization: use the pilot subcarrier to estimate the frequency domain response of the channel, output the channel frequency domain response to the phase detection unit, and use the estimated channel frequency domain response to eliminate the channel influence on the data subcarrier (ie frequency domain equalization).

The device also includes: a phase difference detection unit, configured to determine the polarity of the average phase difference between adjacent subcarriers of the OFDM preamble signal, and output whether the current OFDM frame timing is within the OFDM preamble symbol cyclic prefix length The information within is given to the statistical analysis unit.

The statistical analysis unit is used to count the number of times that the timing of the current OFDM frame is located within the cyclic prefix of the preamble symbol and outside the cyclic prefix. And be used for judging whether the number of times that the timing of the current OFDM frame is within the length of the OFDM preamble symbol cyclic prefix is higher than the first preset threshold, if yes, then output an instruction to reduce the timing advance of the next OFDM frame timing; judge the current OFDM Whether frame timing is not within the OFDM preamble symbol cyclic prefix length is higher than the second preset threshold, if yes, then output an instruction to increase the timing advance of the next OFDM frame timing; the timing advance adjustment unit is used for According to the instruction of reducing the timing advance of the next OFDM frame timing, adjust the timing advance of the next OFDM frame timing; or according to the instruction of adjusting the timing advance of the next OFDM frame timing, adjust it larger Timing advance of next OFDM frame timing.

The beneficial effect of the present invention is that by providing a time advance adjustment method and device for OFDM symbol timing, the time advance can be adaptively adjusted, and the time delay on the subcarriers caused by the excessive timing advance can be reduced as much as possible. Phase rotation improves the accuracy of channel estimation.

Description of drawings

Figure 1a is a block diagram of the working principle of an OFDM transmitter in the prior art;

Figure 1b is a block diagram of the working principle of the OFDM receiver in the prior art;

Fig. 2 is the flowchart of the inventive method;

Fig. 3 is the structural block diagram of device of the present invention;

Fig. 4 is the structural block diagram of the phase difference detection unit in the device of the present invention;

Fig. 5 is the structural block diagram of statistical analysis unit in the device of the present invention;

Fig. 6 is an adjustment table of the timing advance adjustment unit in the device of the present invention.

Detailed ways

The specific implementation manner of the present invention will be described below in conjunction with the accompanying drawings. The present invention describes a device and method for determining OFDM frame/symbol time advance. According to the average phase difference between adjacent subcarriers obtained by channel estimation, the method can adaptively adjust the timing advance. As shown in Figure 2, the specific steps of the method are: receiving OFDM signals, performing channel estimation in the frequency domain, calculating the average phase difference between adjacent subcarriers, determining whether the current frame/symbol timing is in the CP or not in the CP, and Count the occurrence probability of the above events; compare the probability that the current frame/symbol is in the CP and not in the CP with the threshold value, and if the threshold value is reached, then adjust the timing advance (decrease or increase the timing of the next OFDM frame/symbol) Timing Advance) finally makes the frame/symbol timing within the CP and minimal.

The average phase difference between adjacent subcarriers can be calculated from the channel impulse response on each subcarrier provided by channel estimation.

The channel impulse response on each subcarrier can be calculated from the inserted pilot subcarriers, but the interval of the corresponding pilot subcarriers needs to be considered.

The determination of whether the current frame/symbol timing is in the CP or not in the CP can be determined by determining the polarity of the phase difference between adjacent subcarriers.

Assuming that the FFT length is N and the time advance is τ samples, τ is positive when the FFT window is located before the end of the CP, and is negative when the FFT window is located after the end of the CP. The transmitted symbol on the rth subcarrier is a(r), the received symbol on the rth subcarrier is s(r), and the channel impulse response on the rth subcarrier is H(r). Then after FFT:

$\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; r\&tau;</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; if\&tau;</span>}<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ \mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; r\&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; ISI</span>}& \mathrm{<span\; class="notranslate">\; if\&tau;</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 0</span>}\end{array}\right.$

Obviously, the time advance τ (in a broad sense, also includes frame/symbol timing error) will cause phase rotation on each subcarrier, and is considered as a "channel response", here refers to the real channel response H(r) and phase rotation $\exp (-j\frac{2\mathrm{\&pi;}}{N}\mathrm{r\&tau;})$ product of .

If it is assumed that the symbols transmitted on each subcarrier are known (this assumption is satisfied for the pilot subcarrier), then the average phase difference on adjacent subcarriers:

$\mathrm{<span\; class="notranslate">\; the\; angle</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; angle</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; ,</span>$

Here, the ISI influence caused by τ<0 can be neglected through multiple averaging. The phase on each subcarrier can be provided by channel estimation.

The ideal timing advance should make the frame/symbol timing within the CP while the absolute value of the timing advance is the smallest. Therefore, the method of the present invention detects the polarity of the phase difference between adjacent subcarriers, and calculates the probability that the current frame/symbol timing is in the CP or not in the CP. If the probability that the frame/symbol timing is within the CP is higher than a certain threshold (threshold value 1), then the advance amount of the next frame/symbol timing should be reduced by 1 (move backward); if the frame/symbol timing is not within the CP If the probability is higher than a certain threshold (threshold 0), then the advance amount of the next frame/symbol timing should be increased by 1 (move forward).

A suggested threshold setting obtained through simulation is that threshold 0 is equal to 0.03*frame count, and threshold 1 is equal to 0.97*frame count.

As shown in Figure 3, it shows the structure of automatic timing advance adjustment, including: RF front-end, used to receive OFDM signals, do down-conversion, filtering, digital-to-analog conversion, and obtain OFDM symbols in digital baseband form; frame/symbol synchronization , which is used to place the FFT window at a suitable position according to the frame/symbol timing information obtained according to the time advance and time synchronization; FFT, perform serial-to-parallel transformation on the data, calculate FFT, and perform parallel-to-serial transformation to obtain the frequency domain signal ; Channel estimation and equalization: use the pilot subcarrier to estimate the frequency domain response of the channel, output the channel frequency domain response to the phase detection unit, and use the estimated channel frequency domain response to eliminate the channel influence on the data subcarrier (ie frequency domain equalization) .

The phase difference detection unit is used to determine the polarity of the average phase difference between the adjacent subcarriers corresponding to the frequency domain of the OFDM signal channel, and output the information whether the timing of the current OFDM symbol is within the length of the OFDM symbol cyclic prefix to the said OFDM signal channel. The statistical analysis unit described above;

The statistical analysis unit is used to judge whether the number of times that the current OFDM symbol timing is within the length of the OFDM symbol cyclic prefix is higher than the first preset threshold value, and if so, then output the timing advance amount of the timing of the next OFDM symbol. Instruction; judging whether the number of times that the current OFDM symbol timing is not within the OFDM symbol cyclic prefix length is higher than the second preset threshold, if yes, then output an instruction to increase the timing advance of the next OFDM symbol timing;

The timing advance adjustment unit is used to adjust the timing advance of the next OFDM symbol timing according to the instruction of reducing the timing advance of the next OFDM symbol timing; or increase the timing of the next OFDM symbol according to the instruction The timing advance instruction is used to increase the timing advance of the next OFDM symbol timing.

As shown in FIG. 4 , a block diagram of a phase difference detection unit is shown. Wherein the phase difference detection unit can be replaced by the real part symbol after the conjugate multiplication of the impulse responses H(K+1) and H(k) on the Kth and K+1th subcarriers.

As shown in Fig. 5, the structure of the statistical analysis unit is shown. Among them, the polarity of the phase difference between adjacent subcarriers is input to counter 1, and is input to counter 0 through an inverter. Counter 0 records the number of occurrences of symbol timing not within the CP, and counter 1 records the number of occurrences of symbol timing within the CP. The output of counter 0 is compared with a threshold 0 in the first threshold comparator, which is equal to the frame count multiplied by a probability factor α ₀ (Nc*α ₀ ); the output of counter 1 is compared in the second threshold comparator Compared with a threshold 1, the threshold 1 is equal to the frame count multiplied by a probability factor α ₁ (Nc*α ₁ ). It was mentioned earlier that α ₀ =0.03 and α ₁ =0.97. If any one of the counters reaches the threshold 0/1, or the frame count is equal to the counting upper limit Nf (for example: Nf=200), the counter 0 and the counter 1 will be set to 0.

In FIG. 5, two counters record the number of times the current frame/symbol timing occurs within the CP and not within the CP. An AND gate is used to generate a clear signal when either of the two counters reaches the threshold or the frame counter reaches the upper limit. A frame counter: records the number of frames. The frame number is used to calculate the probability of the frame/symbol timing position. A frame count comparator: compares the frame count to the frame count upper limit.

As shown in Figure 6, in the timing advance adjustment unit, if the counter 0 value in the first threshold comparator>Nc*α ₀ will add 1 to the timing advance, if the second threshold comparator Counter 1>Nc*α ₁ will decrement the timing advance by 1. The preset thresholds can be different, depending on the priority of reducing ISI and reducing phase rotation on adjacent subcarriers.

The timing advance adjustment unit in FIG. 6 moves the FFT window forward and backward by one step according to the output of the threshold comparison unit. The moving step can be changed according to the resolution requirement (for example, 1 sample point), and it may not be a sample point or a certain fixed value.

The above specific embodiments are only used to illustrate the present invention, but not to limit the present invention.

Claims (20)

1. A timing advance adjustment method for OFDM symbol timing, the method comprising: receiving the OFDM signal transmitted by the transmitting end at the receiving end; it is characterized in that: Judging whether the number of times that the current OFDM symbol timing is within the length of the OFDM symbol cyclic prefix is higher than the first preset threshold, if yes, then turn down the timing advance of the next OFDM symbol timing; Judging whether the number of times that the current OFDM symbol timing is not within the OFDM symbol cyclic prefix length is higher than the second preset threshold, if yes, then increase the timing advance of the next OFDM symbol timing; It is characterized in that by judging the polarity of the average phase difference between adjacent subcarriers of the OFDM signal, it is judged whether the timing of the current OFDM symbol is within the length of the OFDM symbol cyclic prefix. 2. The method according to claim 1, wherein the average phase difference between adjacent subcarriers is calculated from the channel impulse response on each subcarrier provided by channel estimation. 3. The method according to claim 2, wherein the channel impulse response on each subcarrier is calculated from the inserted pilot subcarrier. 4. method according to claim 1, it is characterized in that, the timing advance of described reducing next OFDM symbol timing refers to: move forward a step of FFT window; Described adjusting big next OFDM symbol The timing advance amount includes: moving the FFT window backward by one step size, and the step size is a fixed number of samples or a variable number of samples according to the resolution requirement. 5. A timing advance adjustment device for OFDM symbol timing, characterized in that the device comprises: The statistical analysis unit is used to count the number of times the current OFDM symbol timing is within the cyclic prefix and outside the cyclic prefix, and determine whether the number of times the current OFDM symbol timing is within the length of the OFDM symbol cyclic prefix is higher than the first preset threshold, If yes, then send an instruction to adjust the time advance of the next OFDM symbol timing; judge whether the current OFDM symbol timing is not within the OFDM symbol cyclic prefix length and whether the number of times is higher than the second preset threshold, if yes, then send An instruction to increase the timing advance of the next OFDM symbol timing; The timing advance adjustment unit is used to adjust the timing advance of the next OFDM symbol timing according to the instruction of reducing the timing advance of the next OFDM symbol timing; or increase the timing of the next OFDM symbol according to the instruction An instruction of the timing advance, which increases the timing advance of the timing of the next OFDM symbol, and The phase difference detection unit is used to determine the polarity of the average phase difference between adjacent subcarriers of the OFDM signal, and outputs whether the current OFDM symbol timing is within the OFDM symbol cyclic prefix length and sent to the statistical analysis unit . 6. The device according to claim 5, wherein the average phase difference between adjacent subcarriers is calculated from the channel impulse response on each subcarrier provided by channel estimation. 7. The device according to claim 6, wherein the channel impulse response on each subcarrier is calculated from the inserted pilot subcarrier. 8. The device according to claim 5, wherein said statistical analysis unit comprises: Counter: used to record the number of times the current OFDM symbol timing is within the length of the OFDM symbol cyclic prefix and not within the length of the OFDM symbol cyclic prefix; The first threshold comparator is used to judge whether the number of times that the current OFDM symbol timing is within the length of the OFDM symbol cyclic prefix is higher than the first preset threshold value, and if so, output the time to reduce the timing of the next OFDM symbol Advance instruction; The second threshold value comparator judges whether the number of times that the current OFDM symbol timing is not within the OFDM symbol cyclic prefix length is higher than the second preset threshold value, if yes, then output the timing advance of the next OFDM symbol timing. instruction. 9. The device according to claim 8, wherein the statistical analysis unit further comprises: a frame counter: recording the number of frames; the first preset threshold is equal to the frame count multiplied by the first probability factor, The second preset threshold is equal to the frame count multiplied by the second probability factor. 10. The device according to claim 5, characterized in that, the time advance of the timing of the next OFDM symbol to be turned down is characterized in that: the output has moved forward the FFT window of a step size; The timing advance of an OFDM symbol timing includes: outputting an FFT window moved backward by a step; the step is a fixed number of samples or a variable number of samples according to resolution requirements. 11. A timing advance adjustment method for OFDM frame timing, the method comprising: receiving the OFDM signal transmitted by the transmitting end at the receiving end; it is characterized in that: Judging whether the number of times that the current OFDM frame timing is within the length of the OFDM frame header cyclic prefix is higher than the first preset threshold, if so, then turn down the timing advance of the next OFDM frame timing; Judging whether the number of times that the current OFDM frame timing is not within the OFDM frame header cyclic prefix length is higher than the second preset threshold, if yes, then increase the timing advance of the next OFDM frame timing, Whether the current OFDM frame timing is within the length of the OFDM frame header cyclic prefix is determined by determining the polarity of the average phase difference between adjacent subcarriers of the OFDM signal. 12. The method according to claim 11, wherein the average phase difference between adjacent subcarriers is calculated from the channel impulse response on each subcarrier provided by channel estimation. 13. The method according to claim 12, wherein the channel impulse response on each subcarrier is calculated from the inserted pilot subcarrier. 14. The method according to claim 11, characterized in that, the time advance of the timing of the next OFDM frame being turned down is characterized in that: moving the FFT window forward by a step size; The timing advance amount includes: moving the FFT window backward by one step size, and the step size is a fixed number of samples or a variable number of samples according to the resolution requirement. 15. A timing advance adjustment device for OFDM frame timing, characterized in that the device comprises: The statistical analysis unit is used to judge whether the number of times that the current OFDM frame timing is within the length of the OFDM frame header cyclic prefix is higher than the first preset threshold value, and if so, output the timing advance amount for reducing the timing of the next OFDM frame An instruction; judge whether the number of times that the current OFDM frame timing is not within the OFDM frame header cyclic prefix length is higher than the second preset threshold value, if so, output an instruction to increase the timing advance of the next OFDM frame timing; The timing advance adjustment unit is used to adjust the timing advance of the next OFDM frame timing according to the instruction of reducing the timing advance of the next OFDM frame timing; or increase the timing of the next OFDM frame according to the described instruction The command of the timing advance, which increases the timing advance of the next OFDM frame timing, and The phase difference detection unit is used to determine the polarity of the average phase difference between the adjacent subcarriers of the OFDM signal, and whether the output current OFDM frame timing is within the length of the OFDM frame header cyclic prefix is sent to the statistical analysis unit. 16. The device according to claim 15, wherein the average phase difference between adjacent subcarriers is calculated from the channel frequency response on each subcarrier provided by channel estimation. 17. The device according to claim 16, wherein the channel frequency response on each subcarrier is calculated from the inserted pilot subcarriers. 18. The device according to claim 15, wherein said statistical analysis unit comprises: Counter: used to record the number of times the current OFDM frame timing is within the length of the OFDM frame header cyclic prefix and not within the length of the OFDM frame header cyclic prefix; The first threshold value comparator is used to judge whether the number of times that the current OFDM frame timing is within the length of the OFDM frame header cyclic prefix is higher than the first preset threshold value, and if so, the output is to reduce the timing of the next OFDM frame Timing advance instructions; The second threshold comparator judges whether the number of times that the current OFDM frame timing is not within the length of the OFDM frame header cyclic prefix is higher than the second preset threshold, and if so, outputs the time advance for increasing the timing of the next OFDM frame instructions. 19. The device according to claim 18, wherein the statistical analysis unit further comprises: a frame counter: recording the number of frames; the first preset threshold is equal to the frame count multiplied by the first probability factor, The second preset threshold is equal to the frame count multiplied by the second probability factor. 20. The device according to claim 15, characterized in that, the time advance of the timing of the next OFDM frame being turned down is characterized in that: the output moves forward by one step of the FFT window; The time advance of the frame timing includes: moving the FFT window backward by one step, and the step is a fixed number of samples or a variable number of samples according to the resolution requirement.

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