CN1852281B - A Synchronization Method for Orthogonal Frequency Division Multiple Access System - Google Patents

Abstract

A method for synchronizing an OFDMA system, comprising: when the number of subcarriers available in the OFDMA system is equal to the length of the inverse discrete Fourier transform, directly adopting a Gold code as a synchronization sequence; When the number of subcarriers available in the OFDMA system is not equal to the length of the inverse discrete Fourier transform, a Gold code equal to half the length of the inverse discrete Fourier transform is inserted into the symmetrical frequency on both sides of the center frequency of the inverse discrete Fourier transform. point, and insert zero at the zero frequency point and other frequency points that have not been inserted into the Gold code, convert the sequence to the time domain and use it as a synchronization sequence; transmit the synchronization sequence from the sending end to the receiving end, so that the receiving end Establish synchronization with the sending end; send the superimposed OFDMA system data and synchronization sequence to the receiving end, or directly send the OFDMA system data to the receiving end; use the dichotomy method to search for synchronization at the receiving end The sequence correlation peak value is used to perform phase compensation on the received signal by using the estimated carrier offset, so as to obtain the transmitted OFDMA system data.

Description

A Synchronization Method for Orthogonal Frequency Division Multiple Access System

technical field

The invention relates to a synchronization method suitable for Orthogonal Frequency Division Multiple Access (OFDMA) system.

Background technique

It can be predicted that multimedia services such as audio, video, image, and Internet will become the dominant services of mobile communications in the future, and these services have significantly increased requirements for wireless link transmission capabilities (peak service rate is greater than 20Mbps), in this case, the orthogonal frequency Multiplexing (OFDM) technology is gradually emerging. OFDM technology modulates high-speed data streams into multiple parallel low-speed data streams with overlapping frequency spectrums. Since the period of the OFDM symbol is significantly increased, the ability of the OFDM symbol to resist multipath delay is improved. Further, by adding a guard interval (GI) greater than the maximum multipath delay at the front end of the OFDM symbol, the multipath delay caused by multipath can be completely eliminated. The intersymbol interference (ISI) caused by the delay simplifies the burden on the equalizer at the receiving end. At present, OFDM technology has become the modulation technology of European digital audio broadcasting and terrestrial digital video broadcasting. OFDMA has gradually become a wireless LAN standard (European broadband wireless LAN standard Hiperlan/2, IEEE wireless LAN standard IEEE802.11 and multimedia mobile access communication system MMAC), and has been basically recognized as one of the basic physical layer technologies of B3G . Different subcarriers are allocated to different users, and OFDM technology naturally distinguishes users through FDMA, that is, OFDMA system. The OFDMA system reduces the interference in the cell and improves the system capacity by flexibly allocating orthogonally adjacent subcarriers to different users; and OFDMA is easy to provide variable-rate information transmission through the change of the number of user subcarriers, so OFDMA It is one of the multiple access schemes that the B3G system is likely to adopt.

In order to obtain higher spectral efficiency than traditional frequency division multiplexing (FDM), different subcarriers of OFDM overlap each other in the frequency domain. The carrier frequency offset formed by the difference between the crystal oscillators of the transmitter and the receiver causes carrier interference, and the OFDM system is very sensitive to the carrier frequency offset, so the carrier frequency offset is estimated and compensated from the noise interfered data is a very important task.

Currently, the most commonly used method for estimating carrier frequency offset in OFDMA systems is based on the training sequence of the frame header. However, since the length of the training sequence is given, the length of the frame and the accuracy of carrier frequency offset estimation are limited, and a certain spectrum utilization rate is also sacrificed. In addition, some scholars have proposed to use methods based on cyclic prefix, virtual subcarrier or subspace to estimate multi-user carrier frequency offset, but most of these algorithms have high complexity.

Contents of the invention

Aiming at the problems existing in the above-mentioned technologies, the present invention proposes a synchronization method for an OFDMA system, which provides accurate estimation of carrier frequency offset for multiple users.

According to the present invention, a kind of synchronous method for OFDMA system is provided, comprising steps:

(1) When the number of subcarriers available in the OFDMA system is equal to the length of the inverse discrete Fourier transform, directly adopt Gold (Gold) code as the synchronization sequence; in the OFDMA system When the number of available subcarriers is not equal to the length of the inverse discrete Fourier transform, a Gold code equal to half the length of the inverse discrete Fourier transform is inserted into the symmetrical frequency points on both sides of the center frequency point of the inverse discrete Fourier transform, and at Inserting zero at the zero frequency point and other frequency points not inserted into the Gold code, converting the sequence into the time domain and using it as a synchronization sequence;

(2) transmitting the synchronization sequence from the sending end to the receiving end, so that the receiving end establishes synchronization with the sending end;

(3) When the receiving end and the sending end directly establish coarse synchronization, according to the signal-to-noise ratio of the receiver, adaptively adjust the ratio σ of the OFDMA system data and the transmission power of the synchronization sequence _D ² /σ _A ² , and sending the superimposed OFDMA system data and the synchronization sequence to the receiving end;

(4) when the receiving end directly establishes fine synchronization with the sending end, directly sending OFDMA system data to the receiving end;

(5) At the receiving end, the dichotomy method is used to search for the correlation peak value of the synchronous sequence, and the phase compensation is carried out to the received signal by using the estimated carrier offset, so as to obtain the transmitted OFDMA system data;

In step (3), the following formula is used to adjust the ratio of the OFDMA system data and the transmission power of the synchronization sequence:

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SNR</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; log</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; )</span>$

Among them, SNR is the received signal-to-noise ratio fed back by the receiving end, N is the length of the discrete Fourier transform, and C is a constant determined by the channel, with a value between 8 and 16 dB.

Preferably, the synchronization sequence needs to be repeated for multiple cycle lengths during the sending process.

Preferably, in step (5), in the case of a given search accuracy of the cost function, the number of iterations of the dichotomy is Among them, _BU and _BL are the upper and lower bounds of the search, respectively, and δ is the search precision.

Preferably, step (3) also includes the steps of:

(31) When the receiving end and the sending end directly establish coarse synchronization, sending the superimposed OFDMA system data and the synchronization sequence;

(32) If the receiving end loses fine synchronization with the sending end, only send OFDMA system data;

(33) If the receiving end loses not only fine synchronization but also coarse synchronization with the sending end, the sending end establishes synchronization with the receiving end by resending a synchronization sequence.

Preferably, in step (33),

If the synchronization established by the sending end with the receiving end by resending the synchronization sequence is coarse synchronization, then the superimposed OFDMA system data and the synchronization sequence are sent to the receiving end;

If the synchronization established by the sending end with the receiving end by resending a synchronization sequence is fine synchronization, only OFDMA system data is sent.

Preferably, step (4) also includes the steps of:

(41) When fine synchronization is established between the receiving end and the sending end, only send OFDMA system data;

(42) If the receiving end loses fine synchronization with the sending end and enters a coarse synchronization state, then send the superimposed OFDMA system data and the synchronization sequence, and use the following formula to adjust the orthogonal frequency Ratio of transmission power of DMA system data to synchronization sequence:

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SNR</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; log</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; )</span>$

Among them, SNR is the received signal-to-noise ratio fed back by the receiving end, N is the length of the discrete Fourier transform, and C is a constant determined by the channel, with a value between 8 and 16dB;

(43) If the receiving end loses not only fine synchronization but also coarse synchronization with the sending end, the sending end establishes synchronization with the receiving end by resending a synchronization sequence.

Preferably, step (43) also includes the steps of:

If the synchronization established by the sending end with the receiving end by resending the synchronization sequence is coarse synchronization, then the superimposed OFDMA system data and the synchronization sequence are sent to the receiving end;

If the synchronization established by the sending end with the receiving end by resending a synchronization sequence is fine synchronization, only OFDMA system data is sent.

Preferably, in the step (2), the synchronization sequence is sent with all transmission powers, and in the step (3), the sum of the transmission power of the OFDMA system data and the transmission power of the synchronization sequence is equal to the total transmission power power, and in step (4), the OFDMA system data is sent with the full transmit power.

Preferably, in the step (2), the synchronization sequence is sent with all transmission powers, and in the step (3), the sum of the transmission power of the OFDMA system data and the transmission power of the synchronization sequence is equal to the total transmission power power, and the transmission power of the OFDMA system data is a constant transmission power; in step (4), the OFDA system data is sent with the constant transmission power.

According to the generation method of the synchronization sequence of the present invention, the power distribution of the data and the synchronization sequence can be adjusted adaptively, and a frame structure using the synchronization sequence for synchronization is proposed. The synchronization method of the invention is suitable for services with low delay requirements, and has the characteristics of low complexity, high spectrum utilization rate, accurate carrier frequency offset estimation and the like compared with the traditional serial synchronization scheme.

Description of drawings

The present invention will be further described below with reference to the accompanying drawings and in conjunction with examples. in:

Fig. 1 shows a schematic diagram of the generation of a synchronization sequence according to the present invention. When the number of available subcarriers of the OFDMA system is equal to the length of the IDFT, K3 is closed upward, and when the number of available subcarriers of the OFDMA system is not equal to the length of the IDFT, K3 is closed downward.

Fig. 2 shows the block diagram of the baseband transmitter and receiver of the OFDMA system according to the present invention, the signals transmitted are controlled by K1 and K2 switches, and there are four states of K1 and K2 closing or opening, W1 and W2 are respectively Weights used to adjust the amplitude of OFDM data and synchronization sequences.

FIG. 3 shows a state transition diagram of the OFDMA system adopting the structure shown in FIG. 2 .

Fig. 4 shows 11 examples of frame formats.

FIG. 5 shows a system flowchart of the OFDMA system adopting the structure shown in FIG. 2 .

Fig. 6 shows a schematic diagram of the dichotomy algorithm used in the one-dimensional search of the synchronization sequence.

Fig. 7 shows a flow chart of the nth iteration of the frequency offset estimation module of the receiver, where the accuracy refers to the maximum allowable error of the cost function used for correlation detection and peak search.

Detailed ways

In a preferred embodiment of the invention, the synchronization sequence is described in the form of an Additive Time Domain Training Sequence (ATTS). Fig. 1 shows a schematic diagram of the generation of ATTS sequence according to the present invention. When the number of subcarriers available in the OFDMA system is not equal to the length of IDFT, a Gold code is inserted at a specific frequency point in the frequency domain. A suggested method is to first generate a Gold code with half the order of the IDFT modulator , and then insert these Gold codes into the symmetrical frequency points on both sides of the IDFT center frequency point in turn, where the zero frequency point and other frequency points that have not been inserted into the Gold code value are zero-inserted, and the sequence is converted into a time-domain signal by IDFT , as the ATTS sequence after weighting, and when the number of available subcarriers of the OFDM system is equal to the length of the IDFT, the ATTS sequence directly adopts the weighted Gold code. This produces a period of the synchronization sequence whose length is equal to the length of one OFDMA symbol. Moreover, in the transmission process, the ATTS sequence needs to repeat multiple cycle lengths.

In the case of multiple users, in order to facilitate the realization in the actual system, each user's Gold code adopts the same generator polynomial, but the initial state is different.

Two switches K1 and K2 are added behind the IDFT modulator to control whether the OFDM data and synchronization sequence are transmitted, as shown in Figure 2, when there is no data transmission, both K1 and K2 are turned on; when synchronous capture is required or only synchronous When the sequence is finely synchronized, K1 is turned on and K2 is closed; when OFDM data and the superimposed signal of the synchronization sequence are required for fine synchronization, both K1 and K2 are closed; when only OFDM data is transmitted, K1 is closed and K2 is turned on. W1 and W2 are weights used to adjust the amplitude of OFDM data and synchronization sequence respectively.

The state transition diagram is shown in Figure 3. There are four states: the initial state of no data transmission, the state of sending only synchronization sequences, the state of superimposing OFDM data and synchronization sequences, and the state of only sending OFDM data. Specifically, the transceiver is in a "start state" before data transmission begins. When it is necessary to establish communication with the mobile user "start", the transmitter is in the "send only synchronization sequence" to send a synchronization signal. If the receiver and the transmitter achieve rough synchronization, it indicates that the received signal and the transmitted signal are "captured", and the data signal and the synchronization signal can be sent at the same time, that is, it enters the "superimposed sending" state. If the receiver and the transmitter directly achieve fine synchronization, it means that the received signal accurately tracks the transmitted signal, "thick and fine synchronization is complete", and only data signals can be sent, that is, enter the "data-only" state.

If in the process of "overlay transmission", the receiver and the transmitter achieve fine synchronization, it means that the received signal accurately tracks the transmitted signal "fine synchronization is completed", and the data signal can be transmitted separately, entering the "data-only" state. If during the process of "superimposed sending", the receiver and the transmitter lose the coarse synchronization again, it will "need to capture" and re-enter the state of "send only the synchronization sequence". If the communication transmission is completed during the "superimposed sending", it means that the communication has been "ended", and the transceiver will enter the "start state" again.

If in the process of "only sending data", the receiver and the transmitter lose fine synchronization again, the receiving signal needs to further track the sending signal "requires fine synchronization", and re-enter the "superimposed sending" state. If the receiver loses coarse synchronization with the transmitter during the "only send data", it will "need to capture" and re-enter the state of "send only sync sequence" for synchronous capture. If the data transmission is completed during "send data only", it indicates that the communication has been "ended", and the transceiver will enter the "start state" again.

According to the state transition diagram and the power allocation scheme, an example of the frame structure suggested by the present invention is shown in FIG. 4 . In these 11 frame structures, the power allocation of ATTS sequence and OFDM data can be adaptively adjusted according to the receiver feedback.

When the total transmission power is kept constant, in Example 1, the entire transmission power at the frame header is used to transmit only the ATTS sequence, and then the superposition sequence of the ATTS sequence and OFDM data is transmitted according to the power ratio of the synchronization signal to the data signal (see formula (1), where The sum of the two powers is the total transmission power). In Example 2, all the power at the frame header is used to send only the ATTS sequence, then the superposition sequence, and finally only the OFDM data. In Example 3, all the power at the frame header is used to send only the ATTS sequence, then all the power is used to only send OFDM data, and then the superposition sequence is sent according to the power ratio of the synchronization signal to the data signal, and finally all the power is used to only send OFDM data. In Example 4, all the power at the frame header is used to send only the ATTS sequence, then all the power is used to send only the OFDM data, and finally the superposition sequence is sent according to the power ratio of the synchronization signal to the data signal. In Example 5, all the power at the frame header is used to send only the ATTS sequence, then the superposition sequence is sent, and then all the power is used to only send OFDM data, and finally the superposition sequence is sent. In Example 6, all the power at the frame header is used to send only the ATTS sequence, and then all the power is used to only send OFDM data.

When the transmit power of OFDM data remains constant (its power is always lower than the full transmit power), in example 7, the full power at the frame header is used to send only the ATTS sequence, then only OFDM data, then the superposition sequence, and finally only OFDM data. In Example 8, only the ATTS sequence is sent at the frame header, then the superposition sequence is sent, and only OFDM data is sent at the end. In Example 9, all the power at the frame header is used to send only the ATTS sequence, then send the superimposed sequence, then only transmit OFDM data, and finally send the superimposed sequence. In Example 10, all the power at the frame header is used to send only the ATTS sequence, then only the OFDM data, and finally the superposition sequence. In Example 11, all the power at the frame header is used to send only ATTS sequences, and then only OFDM data.

FIG. 5 shows a system flowchart of the OFDMA system adopting the structure shown in FIG. 2 . As shown in Figure 5, the process of data transmission is as follows: (1) only send the synchronization sequence; (2) after reaching the coarse synchronization, judge whether to continue to use the synchronization sequence for fine synchronization, if so, continue to send, otherwise send the synchronization sequence and OFDM The superimposed signal of the data is finely synchronized; (3) after reaching fine synchronization, judge whether to select the state of only sending OFDM data, if so, then send the state, otherwise continue to send the superimposed signal until the end of the data; (4) if during this period If it is judged that synchronous capture is required, go to (1) for recapture, if fine synchronization is required, go to (2) for fine synchronization, and then go to (3) until the end of the data.

When the OFDM data and the synchronization sequence are superimposed and transmitted, assuming that the transmission power of the data is σ _D ² , the power ratio σ _D ² /σ _A ² of the data and the synchronization sequence is adjusted by the signal-to-noise ratio (SNR) fed back by the receiver, By adaptively changing the weights W1 and W2, the power ratio between OFDM data and synchronization sequence satisfies

$<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; SNR</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; log</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; dB</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, N is the order number of discrete Fourier transform, and C is a constant determined by the channel, and its value is 8-16dB.

It should be pointed out that, in the present invention, no matter in the initial state of the system, when the coarse synchronization is directly established by sending the synchronization sequence, or during the synchronization process, the synchronization state of the sending end and the receiving end is converted from the fine synchronization state to the coarse synchronization state , or switch from the lost coarse synchronization state to the coarse synchronization state, as long as the superimposed OFDM data and synchronization sequence are sent, the transmission power ratio of OFDM data and synchronization sequence is adjusted according to the above formula (1).

The normalized frequency offset refers to the ratio of the absolute frequency offset to the subcarrier width. The initial upper and lower bounds of the normalized frequency offset can be set according to the stability of the crystal oscillator, the carrier frequency and the subcarrier width. For example, the carrier frequency is f _c =2GHz, the crystal frame stability is Δ=10ppm, and the subcarrier bandwidth is B _S = 10kHz, the initial lower bound and upper bound of the normalized frequency offset can be set as -f _c Δ/ _BS to f _c Δ/ _BS ie -2 to 2, respectively.

The receiver uses the dichotomy method to perform correlation detection on the superimposed signal of the data and the synchronization sequence. The principle diagram of the dichotomy search is shown in Figure 6. Given the accuracy of the search peak cost function, the number of iterations of the dichotomy obeys the logarithmic order. Assuming that the upper and lower bounds of the search are _BU = 2 and _BL = -2 respectively, and the search accuracy is δ = 10 ^-12 , the number of iterations is

和两者的平均频偏信号相乘.其各支路输出与其各支路前一时刻的值相加，形成上支路，下支路和中支路三路信号。上支路信号与下支路信号绝对值与所设精度比较，如其大于精度，表明迭代结束，此时上下频偏的平均值输出作为信号实际频偏，否则，继续进行频偏迭代计算。如果上支路输出信号与中支路输出信号绝对值与中支路信号与下支路信号绝对值的差大于零，用平均频偏值作为上频偏值输出，并进行下一循环迭代。如果上支路输出信号与中支路输出信号绝对值小于或等于中支路信号与下支路信号绝对值，用平均频偏值作为下频偏值输出，并进行下一循环迭代。FIG. 7 shows a flow chart of the nth iteration of the frequency offset estimation module of the receiver, where the accuracy refers to the maximum allowable error of the cost function used for correlation detection and peak search. It can be seen from the flow chart that at the moment l of the receiving end of the mth user, the signal rm(l) received by the receiver is different from the upper frequency offset signal of the conjugate synchronization sequence frequency deviation signal

and the average frequency offset signal of both Multiplication. The output of each branch is added to the value of each branch at the previous moment to form three signals of the upper branch, the lower branch and the middle branch. The absolute value of the upper branch signal and the lower branch signal is compared with the set precision. If it is greater than the precision, it indicates that the iteration is over. At this time, the average value of the upper and lower frequency deviations is output as the actual frequency deviation of the signal, otherwise, continue to iteratively calculate the frequency deviation. If the difference between the absolute value of the output signal of the upper branch and the output signal of the middle branch and the absolute value of the signal of the middle branch and the lower branch is greater than zero, the average frequency deviation value is used as the output of the upper frequency deviation value, and the next loop iteration is performed. If the absolute value of the output signal of the upper branch and the output signal of the middle branch is less than or equal to the absolute value of the signal of the middle branch and the signal of the lower branch, the average frequency offset value is used as the output of the lower frequency offset value, and the next loop iteration is performed.

When compared with the training sequence based on the frame header of the prior art, in the present invention, the frequency offset accuracy obtained by superimposing the data and the synchronous sequence signal of more than T symbols is higher than that of a frame header training sequence. According to the difference of the channel, The threshold value T ranges from 6 to 15.

Claims (9)

1. method for synchronous that is used for orthogonal frequency division multiple access system comprises step:

(1) when the available subcarrier number of described orthogonal frequency division multiple access system equals the length of anti-discrete Fourier transform (DFT), directly adopt the gold sign indicating number as synchronizing sequence; When the available subcarrier number of described orthogonal frequency division multiple access system is not equal to the length of anti-discrete Fourier transform (DFT), half the gold sign indicating number of length that will equal described anti-discrete Fourier transform (DFT) is inserted on the symmetrical frequency of anti-discrete Fourier transform (DFT) center frequency point both sides, and be not inserted into the frequency place zero insertion of gold sign indicating number at zero-frequency point and other, described sequence is transformed into after the time domain as synchronizing sequence;

(2) described synchronizing sequence is sent to receiving terminal from transmitting terminal, described receiving terminal and described transmitting terminal are set up synchronously;

(3) directly set up slightly synchronously the time at described receiving terminal and described transmitting terminal,, adjust the ratio σ of the transmitting power of orthogonal frequency division multiple access system data and described synchronizing sequence adaptively according to the signal to noise ratio of receiver _D ²/ σ _A ², and the orthogonal frequency division multiple access system data after will superposeing and described synchronizing sequence send to described receiving terminal;

(4) directly set up carefully synchronously the time at described receiving terminal and described transmitting terminal, directly the orthogonal frequency division multiple access system data are sent to described receiving terminal;

(5) adopt dichotomizing search synchronizing sequence correlation peak at receiving terminal, utilize the carrier shift that estimates to carry out phase compensation to received signal, thereby obtain the orthogonal frequency division multiple access system data that sent;

In step (3), utilize following formula to adjust the ratio of the transmitting power of orthogonal frequency division multiple access system data and synchronizing sequence:

$({\mathrm{\&sigma;}}_D^2/{\mathrm{\&sigma;}}_A^2)\mathrm{dB}=\mathrm{SNR}+10\log N-C\left(\mathrm{dB}\right)$

Wherein SNR is the received signal noise ratio of receiving terminal feedback, and N is the length of discrete Fourier transform (DFT), and C is that value is at 8～16dB by the constant of channel decision.

2. method according to claim 1, wherein synchronizing sequence needs to repeat a plurality of Cycle Lengths in process of transmitting.

3. method according to claim 1, wherein in step (5), under the situation of the search precision of given cost function, the iterations of dichotomy is B wherein _UAnd B _LBe respectively the bound of search, δ is a search precision.

4. method according to claim 1, wherein step (3) also comprises step:

(31) described receiving terminal and described transmitting terminal directly set up thick synchronously after, send orthogonal frequency division multiple access system data and described synchronizing sequence after the stack;

(32) if described receiving terminal and described transmitting terminal from slightly transforming to thin synchronous regime synchronously, then only send the orthogonal frequency division multiple access system data;

(33) synchronously thick if described receiving terminal and described transmitting terminal lose, then described transmitting terminal is by resending the synchronous of synchronizing sequence foundation and described receiving terminal.

5. method according to claim 4, wherein in step (33),

If what described transmitting terminal was set up with described receiving terminal by resending synchronizing sequence is synchronously thick synchronously, then orthogonal frequency division multiple access system data and the described synchronizing sequence after the stack sends to described receiving terminal;

If what described transmitting terminal was set up with described receiving terminal by resending synchronizing sequence is synchronously thin synchronously, then only send the orthogonal frequency division multiple access system data.

6. method according to claim 1, wherein step (4) also comprises step:

(41) described receiving terminal and described transmitting terminal set up thin synchronously after, only send the orthogonal frequency division multiple access system data;

(42) if described receiving terminal and described transmitting terminal lose synchronously thin and enter thick synchronous regime, then send orthogonal frequency division multiple access system data and described synchronizing sequence after superposeing;

(43) if described receiving terminal and described transmitting terminal not only lose carefully synchronous but also lose slightly synchronously, described transmitting terminal is by resending the synchronous of synchronizing sequence foundation and described receiving terminal.

7. method according to claim 6, wherein step (43) also comprises step:

If what described transmitting terminal was set up with described receiving terminal by resending synchronizing sequence is synchronously thick synchronously, then orthogonal frequency division multiple access system data and the described synchronizing sequence after the stack sends to described receiving terminal;

If what described transmitting terminal was set up with described receiving terminal by resending synchronizing sequence is synchronously thin synchronously, then only send the orthogonal frequency division multiple access system data.

8. method according to claim 1, wherein

In step (2), send synchronizing sequence with whole transmitting powers,

The transmitting power sum of the transmitting power of orthogonal frequency division multiple access system data and described synchronizing sequence equals described whole transmitting power in step (3);

In step (4), send the orthogonal frequency division multiple access system data with described whole transmitting powers.

9. method according to claim 1, wherein

In step (2), send synchronizing sequence with whole transmitting powers,

The transmitting power sum of the transmitting power of orthogonal frequency division multiple access system data and described synchronizing sequence equals described whole transmitting power in step (3), and the transmitting power of orthogonal frequency division multiple access system data is a constant transmit power;

In step (4), send the orthogonal frequency division multiple access system data with described constant transmit power.

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