CN100353730C - Self adaption orthogonal frequency division multiplexing transmitting method and system variable subcarrier number - Google Patents

Abstract

The invention provides an orthogonal frequency division multiplexing transmission method capable of adaptively adjusting the number of sub-carriers according to changes in channel characteristics, and a system for realizing the method. The key is that the receiver uses the cross-correlation coefficient of the cyclic segment prefix of adjacent OFDM symbols in the preamble to measure the channel time coherence, and at the same time uses the channel gain of each adjacent subcarrier of the OFDM symbols The cross-correlation coefficient of the channel is used to measure the channel frequency coherence; and the transmitter estimates the optimal value of the number of subcarriers in the next data frame according to the obtained channel time coherence measure and frequency coherence measure, and uses this as the next The transmission parameters of the data domain OFDM symbol in the data frame are sent to perform adaptive OFDM transmission. The method and system can achieve the best transmission performance under the premise that the transmission bandwidth remains unchanged, can effectively enhance the transmission reliability and improve the interruption capacity of the system.

Description

Adaptive orthogonal frequency division multiplexing transmission method and system with variable sub carriers number

Technical field

The present invention relates to the radio digital communication technical field, be specifically related to a kind of adaptive orthogonal frequency division multiplexing (OFDM) transmission method with variable sub carriers number, and the adaptive orthogonal frequency division multiplexing transmission system of carrying out the method.

Background technology

OFDM (OFDM) transmission means be owing to its spectrum efficiency height, can more easily tackle the intersymbol interference (ISI) that multipath transmisstion causes, thereby obtained increasing application in wireless mobile communications.

All include the subcarrier of some in existing OFDM transmission system, promptly will data flow at a high speed when data transmit be divided into the data flow of N low speed, and with the transmission that walks abreast to the subcarrier of N quadrature of these data stream modulates.Under normal conditions, if subcarrier between frequency interval all less than the coherence bandwidth of channel, each subcarrier will be similar to the experience flat fading; And subcarrier spacing is more little, and perhaps equivalently, number of sub carrier wave is many more, and each sub-carrier channels just approaches falt fading channel more, thereby can more effectively tackle the multipath interference.But then, under wireless mobile environment, the sub-carrier number purpose increases, and means that the time span of OFDM symbol increases.Its symbol duration approaches channel coherence time more, and system might experience by Doppler more and expand caused time selective fading, causes disturbing between sub-carrier channels (ICI) to increase, and systematic function descends.

Therefore, for specific wireless environment and given transmission bandwidth, have the number of sub carrier wave an of the best, make the system transmissions performance reach best, this best number of sub carrier wave constantly changes along with the change of wireless channel in the process that system moves simultaneously.When designing the OFDM transmission system according to the conventional method, communicating pair all adopts the fixing number of sub carrier wave that sets in advance to set up transmission link, and keeps invariable number of sub carrier wave in communication process, finishes until data transmission procedure.Obviously, this traditional transmission system can not adapt to the time-varying characteristics of wireless mobile channel, can not keep the optimization of OFDM transmission performance.

Summary of the invention

The purpose of this invention is to provide a kind of adaptive orthogonal frequency division multiplexing (0FDM) transmission method with variable sub carriers number, and the system that carries out the method, make when the coherence bandwidth of channel reduces, suitably increase the number of sub carrier wave of OFDM transmission symbol; And when reduce the coherence time of channel, suitably reduce number of sub carrier wave, thereby be issued to best transmission performance, effective interruption capacity that strengthens the reliability of transmission and improve system in the constant prerequisite of system transmission bandwidth.

In order to achieve the above object, technical solution of the present invention is: on the basis of conventional orthogonal frequency division multiplexing transmission method, increase the temporal coherence of estimating the current wireless channel in real time and coherence of frequency, and calculate and adjust the OFDM symbol sub-carrier number purpose step of the optimum that is fit to Channel Transmission thus, thereby realize the adaptive orthogonal frequency division multiplexing transmission.The present invention is transmitted as follows:

(a) data bit flow that will be to be transmitted constitutes the Frame that comprises targeting sequencing, signaling territory and data field;

(b) adopt the OFDM of stator carrier number to modulate to targeting sequencing in the Frame and signaling territory, data field is then carried out the OFDM modulation according to the transmission number of sub carrier wave Nt that sets in the current signaling territory;

(c) OFDM symbol is carried out sending successively behind the time domain shaping filter, finish until the current data frame transmission;

(d) receiving data frames is received shaping filter;

(e) utilize the cross-correlation coefficient ρ of the circulation section prefix of adjacent orthogonal frequency division multiplexing symbol in the targeting sequencing _TMeasure the channel time coherence; Utilize the cross-correlation coefficient ρ of each adjacent sub-carrier channel gain of its OFDM symbol simultaneously _FMeasure the channel frequency coherence.

(f) measure the optimal value of estimating next transmission Frame number of sub carrier wave Nt according to channel time coherency measure that is obtained and coherence of frequency, and this number of sub carrier wave optimal value is inserted next signaling territory that sends Frame with the transmission parameter as next frame;

(g) OFDM that the stator carrier number is carried out in the signaling territory of receiving data frames is separated and is in harmonious proportion decoding, obtains the number of sub carrier wave Nr and the modulation coding information of data field OFDM symbol in the current receiving data frames;

(h) according to step (g) the number of sub carrier wave Nr that obtains the data field of receiving data frames is carried out OFDM separate and be in harmonious proportion decoding, receive until current data frame.

The system of the above-mentioned transmission method of implementation provided by the present invention is made up of transmitter and receiver.This system runs on the communication two ends, and works in TDD mode.Wherein, transmitter comprises data framing device, coding mapping and pilot plug-in unit, serial-parallel converter, number of sub carrier wave estimator, quick inverse-Fourier transform device (IFFT), parallel to serial converter, adds the circulation section prefix and send forming filter:

The data framing device is used for bit stream to be sent is constituted the Frame that comprises targeting sequencing, signaling territory and data field, its input termination external data stream, the output of control termination number of sub carrier wave estimator;

Coding mapping and pilot plug-in unit, its input links to each other with the output of data framing device, is used for the data bit of Frame is encoded and the mapping and the insertion pilot tone of modulation symbol;

Serial-parallel converter is used for the data flow of serial input is converted into parallel data, the output of its input termination coding mapping and pilot plug-in unit, the output of its control termination number of sub carrier wave estimator;

The number of sub carrier wave estimator, be used to estimate the optimum number of sub carrier wave that data field adopted of next transmit frame, the temporal coherence tolerance estimator of its input and receiver links to each other with coherence of frequency tolerance estimator, output and data framing device, serial-parallel converter, fast inverse-Fourier transform device, parallel to serial converter, add the circulation section prefix and link to each other with the control end of transmission forming filter;

Quick inverse-Fourier transform device, the input parallel data that is used for will comprising according to the current number of sub carrier wave that estimates pilot tone is carried out the OFDM modulation, the output of its input termination serial-parallel converter, the output of control termination number of sub carrier wave estimator;

Parallel to serial converter, being used for the data conversion after the OFDM modulation is serial data, and its input links to each other with the output of quick inverse-Fourier transform device, and control end links to each other with the output of number of sub carrier wave estimator;

Add the circulation section prefix and send forming filter, be used for forming filtering again according to the circulation section prefix that sub-carrier number purpose size is added respective length for the sequence of parallel to serial converter output, obtaining the digital baseband transmission signals outwards sends, its input links to each other with the output of parallel to serial converter, and control end links to each other with the output of number of sub carrier wave estimator;

Receiver comprises reception shaping filter and circulation section prefix separator, temporal coherence tolerance estimator, serial-parallel converter, fast fourier transformer, parallel to serial converter, coherence of frequency tolerance estimator, channel estimation and equalization device, adjudicates decoder:

Receive shaping filter and circulation section prefix separator, the digital baseband signal that receives is mated shaping filter, and from sample sequence, go out circulation section prefix and effective sample sequence and estimate to carry out temporal coherence tolerance according to current sign sub-carrier number purpose size separation, the input of its output termination serial-parallel converter, control end links to each other with the output of judgement decoder;

Temporal coherence tolerance estimator is used for measuring from the temporal coherence that the circulation section prefix and the effective sample sequence of reception shaping filter and the output of circulation section prefix separator obtain current channel, and its output links to each other with the number of sub carrier wave estimator of transmitter;

Serial-parallel converter is used for the effective sample sequence of serial is converted to parallel data, and its output links to each other with the input of fast fourier transformer, and control end links to each other with the output of judgement decoder;

Fast fourier transformer is used for the parallel data of serial-parallel converter output is carried out the demodulation of OFDM, and its output links to each other with the input of channel estimation and equalization device, and control end links to each other with the output of judgement decoder;

Parallel to serial converter, being used for the data conversion after the fast fourier transform is serial data, and its output links to each other with the input of channel estimation and equalization device with coherence of frequency tolerance estimator respectively, and control end links to each other with the output of judgement decoder;

Coherence of frequency tolerance estimator is used for from the fast fourier transform result of the targeting sequencing of parallel to serial converter output and the frequency domain coherency measure that pilot data estimates channel, and its output links to each other with the number of sub carrier wave estimator of transmitter;

The channel estimation and equalization device is used for estimating channel response and follow-up OFDM symbol being carried out channel equalization from targeting sequencing and pilot data through fast fourier transform, and its output links to each other with the input of judgement decoder;

The judgement decoder is used for the result of channel equalization is deciphered and adjudicates, and its output links to each other with the control end of circulation section prefix separator, serial-parallel converter, fast fourier transformer, parallel to serial converter with the reception shaping filter.

Among the present invention, the serial-parallel converter of the serial-parallel converter of transmitter, parallel to serial converter and receiver, parallel to serial converter all have variable conversion width, and its width is controlled by the sub-carrier number purpose size of number of sub carrier wave estimator output and the number of sub carrier wave field value in the Frame signaling territory that the judgement decoder is exported respectively.

The data framing device of transmitter is that input traffic is divided into the certain-length Frame and adds the logical block in targeting sequencing and signaling territory in its front, wherein targeting sequencing comprises 3 identical and continuous OFDM symbols at least, the number of sub carrier wave of this OFDM symbol is fixed, can be the sub-carrier number purpose maximum that system supports, the signaling territory then comprises the number of sub carrier wave field of data field OFDM symbol.

The temporal coherence tolerance estimator of receiver is an arithmetic element of calculating the cross-correlation coefficient of the circulation section prefix of each adjacent orthogonal frequency division multiplexing symbol in the targeting sequencing.

The coherence of frequency tolerance estimator of receiver is an arithmetic element of calculating the cross-correlation coefficient of each adjacent sub-carrier upper signal channel gain in the targeting sequencing.

The number of sub carrier wave estimator of transmitter is that the channel time coherency measure and the coherence of frequency that obtain according to receiver are measured the arithmetic element of estimating next transmission Frame sub-carrier number purpose optimal value.This arithmetic element can realize with the mode of approaching one by one, when channel time coherency measure during less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave reduces one times, and when channel frequency coherency measure during less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave increases and is twice.

Transmission method of the present invention is simple, and is easy to implement, and computational complexity is not high.Because native system can keep under the constant substantially situation of Channel Transmission bandwidth and bandwidth availability ratio, number according to the dynamic change adaptively modifying OFDM transmission symbol sub-carriers of channel, make it all the time near optimal value, thereby effective enhanced system anti-multipath declines and the ability of Doppler's expansion, significantly improves the performance of system transmissions.

Description of drawings

Fig. 1 is the data frame format figure of system of the present invention;

Fig. 2 is the concrete formation block diagram of system of the present invention.

Embodiment

Followingly the present invention is further described with reference to accompanying drawing.

OFDM transmission system transmitting-receiving two-end with variable sub carriers number of the present invention has adopted data frame format as shown in Figure 1.Each Frame is divided into three parts: targeting sequencing, form by the identical and continuous OFDM symbol more than three, and be used for frame synchronization, channel estimating and time selectivity, the estimation of frequency selectivity tolerance; The signaling territory comprises the number of sub carrier wave size that the OFDM symbol is adopted in the current frame data territory, can also comprise the field such as frame length, modulation coding mode of present frame; Data field, promptly the present frame net amount that will transmit is according to symbol.Fixing number of sub carrier wave (for example supported maximum number of sub carrier wave Nmax of system) is all adopted in targeting sequencing and signaling territory, modulation system (for example BPSK) is transmitted reliably, suitable coding (for example (2 also can be carried out in the signaling territory, 1,7) convolutional encoding) to guarantee the accuracy of its reception.

With reference to Fig. 2, the OFDM transmission system with variable sub carriers number provided by the present invention is made up of transmitter and receiver.This system runs on the communication two ends, and works in TDD mode.Wherein, transmitter comprises data framing device 1, coding mapping and pilot plug-in unit 2, serial-parallel converter 3, number of sub carrier wave estimator 4, quick inverse-Fourier transform device (IFFT) 5, parallel to serial converter 6, adds the circulation section prefix and send forming filter 7:

Data framing device 1, be used for bit stream to be sent is constituted the Frame that comprises targeting sequencing, signaling territory and data field, its input termination external data stream, the output of control termination number of sub carrier wave estimator 4 is to set the number of sub carrier wave field in signaling territory according to the number of sub carrier wave estimated value that it was obtained;

Coding mapping and pilot plug-in unit 2, its input links to each other with the output of data framing device 1, be used for the data bit of Frame is encoded and the mapping of modulation symbol and insert pilot tone, the course of work is identical with the counterpart of conventional orthogonal division multiplexed transmission system;

Serial-parallel converter 3, be used for the data flow of serial input is converted into parallel data, the output of its input termination coding mapping and pilot plug-in unit 2, the output of its control termination number of sub carrier wave estimator 4 is to set the data segment, length of serial to parallel conversion according to the number of sub carrier wave estimated value that it was obtained;

Number of sub carrier wave estimator 4, the channel time coherency measure and the coherence of frequency that are used for obtaining according to receiver are measured the optimum number of sub carrier wave that data field adopted of estimating next transmit frame, can realize with the mode of approaching one by one, when channel time coherency measure during less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave reduces one times, and when channel frequency coherency measure during less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave increases and is twice.The temporal coherence tolerance estimator of its input and receiver links to each other with coherence of frequency tolerance estimator, and output and data framing device, serial-parallel converter, quick inverse-Fourier transform device (IFFT), parallel to serial converter, the control end that adds circulation section prefix and transmission forming filter 7 etc. link to each other;

Quick inverse-Fourier transform device (IFFT) 5, the input parallel data that is used for will comprising according to the current number of sub carrier wave that estimates pilot tone is carried out the OFDM modulation, the output of its input termination serial-parallel converter 3, the output of control termination number of sub carrier wave estimator 4, setting the points N t of current frame data territory symbol IFFT conversion according to the number of sub carrier wave estimated value that it was obtained, and the IFFT conversion in targeting sequencing, signaling territory is counted and is default value Nmax;

Parallel to serial converter 6, being used for the data conversion after the OFDM modulation is serial data, its input links to each other with the output of quick inverse-Fourier transform device 5, control end links to each other with the output of number of sub carrier wave estimator 4, to set the data segment width of parallel serial conversion according to the number of sub carrier wave estimated value that it was obtained;

Add the circulation section prefix and send forming filter 7, be used for forming filtering again according to the circulation section prefix that sub-carrier number purpose size is added respective length for the sequence of parallel to serial converter 6 outputs, obtaining baseband signal outwards sends, its input links to each other with the output of parallel to serial converter 6, control end links to each other with the output of number of sub carrier wave estimator 4, to set the length of circulation section prefix according to the number of sub carrier wave estimated value that it was obtained, the circulation section prefix is fixed as 1/4,1/8 or the like of OFDM symbol lengths;

Receiver comprises reception shaping filter and circulation section prefix separator 8, temporal coherence tolerance estimator 9, serial-parallel converter 10, fast fourier transformer (FFT) 11, parallel to serial converter 12, coherence of frequency tolerance estimator 13, channel estimation and equalization device 14, adjudicates decoder 15:

Receive shaping filter and circulation section prefix separator 8, the digital baseband signal that receives is mated shaping filter, and from sample sequence, go out the circulation section prefix to carry out the estimation of temporal coherence tolerance according to current sign sub-carrier number purpose size separation, the input of its output termination serial-parallel converter 10, control end links to each other with the output of judgement decoder 15, with the length of the circulation section prefix determining according to the decision value of the signaling territory number of sub carrier wave field of present frame to be comprised in the OFDM symbol of follow-up data territory;

Temporal coherence tolerance estimator 9, be used for obtaining the temporal coherence tolerance of current channel from the circulation section prefix that receives shaping filter and 8 outputs of circulation section prefix separator, this tolerance can be the average cross correlation coefficient of the circulation section prefix of each adjacent OFDM symbol in the targeting sequencing, and its output links to each other with the number of sub carrier wave estimator 4 of transmitter;

Serial-parallel converter 10, be used for the OFDM symbol effective sample sequence of serial is converted to parallel data, its output links to each other with the input of fast fourier transformer (FFT) 11, control end links to each other with the output of judgement decoder 15, sets the data segment, length that follow-up data territory OFDM symbol carries out serial to parallel conversion with the decision value according to the signaling territory number of sub carrier wave field of present frame;

Fast fourier transformer (FFT) 11, be used for the parallel data of serial-parallel converter output is carried out the demodulation of OFDM, its output links to each other with the input of channel estimation and equalization device 14, control end links to each other with the output of judgement decoder 15, set the points N r that follow-up data territory OFDM symbol carries out the FFT conversion with the decision value according to the signaling territory number of sub carrier wave field of present frame, the FFT conversion in targeting sequencing, signaling territory is counted and is default value Nmax;

Parallel to serial converter 12, being used for the data conversion after the fast fourier transform is serial data, its output links to each other with the input of channel estimation and equalization device 14 with coherence of frequency tolerance estimator 13 respectively, control end links to each other with the output of judgement decoder 15, sets the data segment width that follow-up data territory OFDM symbol carries out parallel serial conversion with the decision value according to the signaling territory number of sub carrier wave field of present frame;

Coherence of frequency tolerance estimator 13, be used for from the fast fourier transform result of the targeting sequencing of parallel to serial converter 12 output and the frequency domain coherency measure that pilot data estimates channel, this tolerance can be the average cross correlation coefficient of each adjacent sub-carrier in the targeting sequencing, and its output links to each other with the number of sub carrier wave estimator 4 of transmitter;

Channel estimation and equalization device 14 is used for estimating channel response and follow-up OFDM symbol being carried out channel equalization from targeting sequencing and pilot data through fast fourier transform, and its output links to each other with the input of judgement decoder 15;

Judgement decoder 15 is used for the result of channel equalization is deciphered and adjudicates, and its output links to each other with the control end of circulation section prefix separator 8, serial-parallel converter 10, fast fourier transformer 11, parallel to serial converter 12 with the reception shaping filter.

If communicating pair is A, B, all hold system as shown in Figure 2 provided by the present invention.

During transmission, a data side to be sent (is example with A side) is arranged, at first by its data framing device 1 will be to be transmitted data bit flow constitute as shown in Figure 1 the Frame that comprises targeting sequencing, signaling territory and data field.Wherein targeting sequencing is mainly used in frame synchronization and estimates and measures channel coherence bandwidth tolerance and coherence time, the signaling territory is used for information such as number of sub carrier wave size that the current transmission Frame of notifying communication the opposing party (B side) adopted and frame length, modulation coding mode, and the number of sub carrier wave size that current transmission Frame is adopted is made as the output valve of number of sub carrier wave estimator 4; Data field is a data bit to be transmitted.

Secondly, bit in coding mapping and 2 pairs of Frames of pilot plug-in unit carries out the mapping of modulation symbol, wherein fixing simple modulation sign map modes such as BPSK are all adopted in targeting sequencing and signaling territory, targeting sequencing is not encoded, the strong low code check (2 of error correcting capability is adopted in the signaling territory, 1,7) convolutional encoding is to guarantee the accuracy of its reception, data field is then according to the requirement of different transmission rates, mapped constellation figure can adopt the coded system of constellations commonly used such as BPSK/QPSK/MQAM and higher rate, and informs B side by the signaling territory.Especially, targeting sequencing and signaling territory all adopt fixing number of sub carrier wave (for example maximum number of sub carrier wave Nmax) to transmit, and the number of sub carrier wave of data field OFDM symbol is determined by number of sub carrier wave estimator 4, and inform B side by the signaling territory.Insert frequency pilot sign periodically in the symbols streams after finishing above-mentioned coding mapping, frequency pilot sign adopts known and fixing simple modulation symbol sebolic addressing (for example BPSK), is beneficial to channel estimating.

Then, the data flow after encoded mapping and pilot tone are inserted is sent into serial-parallel converter 3 and is carried out serial to parallel conversion.When current sign belonged to targeting sequencing and signaling territory, the data segment width of serial to parallel conversion was Nmax; When current sign belonged to data field, the data segment width of serial to parallel conversion then was the estimated value Nt of number of sub carrier wave estimator 4.Result behind the serial to parallel conversion is delivered to inverse fast fourier transform (IFFT) device 5.When current sign belongs to targeting sequencing and signaling territory, Nmax point parallel data is carried out Nmax point IFFT conversion; And when current sign belongs to data field, Nt point parallel data is carried out Nt point IFFT conversion.Parallel transformation results is become the time domain sample value sequence of serial with parallel to serial converter 6.Equally, when current sign belonged to targeting sequencing and signaling territory, the data segment width of parallel serial conversion was Nmax; When current sign belonged to data field, the data segment width of parallel serial conversion then was the estimated value Nt of number of sub carrier wave estimator 4.At last, add the circulation section prefix and the sample value sequence is added the circulation section prefix that length is Ncp (being called for short CP) to constitute a complete OFDM symbol with transmission forming filter 7, the size of Ncp is decided by that the circulation section prefix accounts for the ratio and the current sub-carrier number purpose size (having determined the length of symbol) of whole symbol, the r that the circulation section prefix is fixed as the OFDM symbol lengths is (r=1/4,1/8 or the like) doubly.The complete symbols of having added the circulation section prefix sends successively through the time domain shaping filter again, sends until current data frame to finish;

During reception, the receiver of A side at first receives shaping filter with receiving shaping filter and 8 pairs of Frames from B side of circulation section prefix separator, if current sign is targeting sequencing and signaling territory, be one group of effective sample of isolating CP and symbol by every (Nmax+Ncp) individual adjacent sample; Otherwise, if current sign is a data field, be one group of effective sample of isolating CP and symbol then by every (Nr+Ncp) individual adjacent sample, here Nr adjudicates the value of the number of sub carrier wave field that is obtained after the decoding before this for adjudicating decoder 15 to the signaling territory, has shown the sub-carrier number purpose size of current frame data territory OFDM symbol.Isolated CP sends into temporal coherence tolerance estimator 9 and estimates.

Secondly, isolated symbol effective sample is sent into serial-parallel converter 10 and is carried out serial to parallel conversion.When current sign belonged to targeting sequencing and signaling territory, the data segment width of serial to parallel conversion was Nmax; When current sign belongs to data field, the judgement decode results Nr that the data segment width of serial to parallel conversion is then exported for judgement decoder 15 to signaling territory number of sub carrier wave field.Then, the result behind the serial to parallel conversion is sent to fast fourier transformer (FFT) 11.When current sign belongs to targeting sequencing and signaling territory, Nmax point parallel data is carried out Nmax point FFT conversion; And when current sign belongs to data field, Nr point parallel data is carried out Nr point FFT conversion.Parallel transformation results is become the time domain sample value sequence of serial with parallel to serial converter 12.Equally, when current sign belonged to targeting sequencing and signaling territory, the data segment width of parallel serial conversion was Nmax; When current sign belonged to data field, the data segment width of parallel serial conversion then was Nr.At last, the data flow of serial is delivered to coherence of frequency tolerance estimator 13 on the one hand and is carried out the coherence of frequency estimation, carry out channel estimation and equalization through well-known channel estimation and equalization device 14 in the conventional orthogonal division multiplexed transmission system on the other hand, and traditional judgement decoder 15 is delivered in output adjudicated decoding, recover the transmission data flow.

Set forth the temporal coherence tolerance estimator 9 of receiver, the course of work that coherence of frequency is measured the number of sub carrier wave estimator 4 of estimator 13 and transmitter below emphatically.

Temporal coherence tolerance estimator 9 utilizes and receives from the circulation section prefix (CP) (shown in dash area among Fig. 1) of isolated three adjacent OFDM symbol of institute the targeting sequencing latter two of shaping filters and circulation section prefix separator 8 and carry out temporal coherence and measure estimation.Why preferentially adopt latter two CP to estimate, mainly be because under all identical situation of three symbols, because the caused intersymbol interference of frequency selective fading almost is consistent to the influence of these two CP, like this, its cross-correlation coefficient just can reflect the temporal coherence of channel exactly.If latter two CP sequence is respectively r _j ⁽ⁱ⁾(i=1,2, j=1,2 ..., N _CP), N wherein _CPBe the length of circulation section prefix, represent the 2nd and the 3rd CP, then temporal coherence is measured bent following formula estimation:

${\mathrm{\ρ}}_T=\left|\frac{\underset{j=1}{\overset{N_{\mathrm{CP}}}{\mathrm{\Σ}}}{r}_j^{\left(i\right)}{r}_j^{{\left(2\right)}^{*}}}{\sqrt{\underset{j=1}{\overset{N_{\mathrm{CP}}}{\mathrm{\Σ}}}{\left|r_j^{\left(i\right)}\right|}^2}\sqrt{\underset{j=1}{\overset{N_{\mathrm{CP}}}{\mathrm{\Σ}}}{\left|r_j^{\left(2\right)}\right|}^2}}\right|---\left(1\right)$

Here, complex conjugate is got in " * " expression.Obviously, 0≤ρ _T≤ 1.When channel did not exist Doppler to expand, these two CP only were subjected to intersymbol interference and noise effect, so basically identical, ρ _TGet maximum 1; Otherwise when the channel translational speed was very high, two CP became independent irrelevant, at this moment ρ _TLevel off to 0.Then with ρ _TThe number of sub carrier wave estimator 4 of delivering to transmitter carries out number of sub carrier wave and estimates.

13 of estimators of coherence of frequency tolerance utilize targeting sequencing OFDM symbol frequency domain sample value of adjacent sub-carrier after fast fourier transform to carry out the estimation of coherence of frequency tolerance.If the known modulation information of each subcarrier of targeting sequencing OFDM symbol is p _j, j=1,2 ..., N _P, N wherein _PBe effective number of sub carrier wave of targeting sequencing OFDM symbol, the frequency domain sample value of each subcarrier is T after the conversion _j, j=1,2 ..., N _P, then the coherence of frequency of channel tolerance can be estimated as:

${\mathrm{\ρ}}_F=\left|\frac{\underset{j=1}{\overset{N_P-1}{\mathrm{\Σ}}}\left(Y_j{Y}_{j+1}^{*}\right)/\left(P_j{P}_{j+1}^{*}\right)}{\frac{N_P-1}{N_P}\underset{j=1}{\overset{N_P}{\mathrm{\Σ}}}{\left|\frac{Y_j}{P_j}\right|}^2}\right|---\left(2\right)$

Equally, 0≤ρ _F≤ 1.When there was not frequency selective fading (having only flat decline) in channel, the channel gain on the adjacent sub-carrier was all identical, at this moment ρ _FGet maximum 1; Otherwise when there was serious multipath frequency selective fading in channel, it is independent irrelevant that adjacent sub-carrier becomes, at this moment ρ _FLevel off to 0.Equally with ρ _FThe number of sub carrier wave estimator 4 of delivering to transmitter carries out number of sub carrier wave and estimates.

The number of sub carrier wave estimator 4 of transmitter is measured the channel time coherency measure ρ that estimator 9 is obtained according to the temporal coherence of receiver _FMeasure ρ with the channel frequency coherency measure coherence of frequency that coherence of frequency tolerance estimator 9 is obtained _FEstimate the optimum number of sub carrier wave that data field adopted of next transmit frame, realize with the mode of approaching one by one: as channel time coherency measure ρ _TDuring less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave reduces one times, and as channel frequency coherency measure ρ _FDuring less than the predetermined threshold in 0.5～0.9 scope, number of sub carrier wave increases and is twice.Current like this number of sub carrier wave just will approach optimum number of sub carrier wave gradually.

Show by Computer Simulation, transmission method of the present invention and system can be in complicated wireless mobile communications environment steady operation, improve the reliability and the capacity of system transmissions significantly.To typical broadband wireless access channel (2.5GHz IEEE802.20 channel model), the number of sub carrier wave scope of supposing system's support is 64～8192, when subscriber board 10m in the 3Km distance range, from low speed (0Km/h) under the mobile situation of full speed (250Km/h), adopt system of the present invention to transmit the system break capacity is enhanced about more than once with respect to system's (1024 subcarriers) of stator carrier number, demonstrate great advantage.

Claims (7)

1. have the adaptive orthogonal frequency division multiplexing transmission method of variable sub-carrier number, it is characterized in that it transmits as follows: (a) forming the data bit stream to be transmitted into a data frame comprising a preamble sequence, a signaling domain and a data domain; (b) Orthogonal frequency division multiplexing modulation with a fixed number of subcarriers is used for the preamble sequence and the signaling field in the data frame, and orthogonality is performed for the data field according to the number Nt of sending subcarriers set in the current signaling field frequency division multiplexing modulation; (c) performing time-domain shaping filtering on the OFDM symbols and sending them out sequentially until the current data frame is sent; (d) performing reception shaping filtering on the received data frame; (e) Use the cross-correlation coefficient ρ _T of the cyclic segment prefix of adjacent OFDM symbols in the preamble to measure the channel time coherence; at the same time, use the channel gain of each adjacent subcarrier of the OFDM symbols The cross-correlation coefficient ρ _F to measure the channel frequency coherence; (f) Estimate the optimal value of the number of subcarriers Nt of the next transmission data frame according to the obtained channel time coherence measure and frequency coherence measure, and put the optimal value of the number of subcarriers into the next transmission data frame The signaling field is used as the transmission parameter of the next frame; (g) Perform OFDM demodulation and decoding with a fixed number of subcarriers on the signaling field of the received data frame, and obtain the number of subcarriers Nr and modulation coding information; (h) Perform OFDM demodulation and decoding on the data field of the received data frame according to the number of subcarriers Nr obtained in step (g), until the current data frame is completely received. 2. the OFDM transmission method with variable subcarrier number according to claim 1 is characterized in that the said sending subcarrier number of step (b) is the channel time coherence obtained according to the receiver The metric and the frequency coherence metric are set by successive approximation methods: when the channel time coherence metric is less than the predetermined threshold in the range of 0.5-0.9, the number of subcarriers is reduced by one time; and when the channel frequency coherence metric is less than 0.5-0.9 When the predetermined threshold in the range of 0.9 is reached, the number of subcarriers is doubled. 3. the OFDM transmission method with variable subcarrier number according to claim 1 is characterized in that the cycle of adjacent OFDM symbols in the preamble sequence said in step (e) The cross-correlation coefficient ρ _T of the segment prefix is estimated by the following formula: ${\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; CP</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; *</span>}}}{\sqrt{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; CP</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; cp</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}$ In the formula, N _CP is the length of the cyclic segment prefix, r _j ⁽ⁱ⁾ , (i=1, 2, j=1, 2, ..., N _cp ), which means two adjacent OFDM in the preamble sequence Prefix the cyclic segment with the symbol, "*" means to take the complex conjugate. 4. the OFDM transmission method with variable subcarrier number according to claim 1 is characterized in that each adjacent subcarrier channel gain of said OFDM symbol in step (e) The cross-correlation coefficient ρ _{F of} is estimated by the following formula: ${\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; )</span>}{\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span>\frac{{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}<span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; |</span>$ In the formula, _NP is the number of effective subcarriers of OFDM symbols in the preamble sequence, and p _j (j=1, 2,..., N _P ) is the number of subcarriers of OFDM symbols in the preamble sequence Known modulation information, Y _j (j=1, 2, ..., N _P ) is the frequency domain sample value of each subcarrier after fast Fourier transform. 5. The system for the OFDM transmission method with variable subcarrier number as claimed in claim 1 is characterized in that it includes a transmitter and a receiver working in a time division duplex mode, wherein the transmission The machine includes a data framer (1), a code mapping and pilot insertion unit (2), a serial-to-parallel converter (3), a subcarrier number estimator (4), a fast inverse Fourier transform (5), and a parallel-to-serial transform Device (6), add cyclic segment prefix and send shaping filter (7): A data framer (1), configured to form a bit stream to be sent into a data frame comprising a preamble sequence, a signaling domain and a data domain, its input terminal is connected to an external data stream, and the control terminal is connected to a subcarrier number estimator (4) output terminal; Coding mapping and pilot frequency insertion unit (2), its input terminal is connected with the output terminal of data framer (1), is used for the mapping of the data bit in the data frame and modulation symbol and inserts pilot frequency; A serial-to-parallel converter (3), used to convert the serially input data stream into parallel data, its input terminal is connected to the output terminal of the code mapping and pilot insertion unit (2), and its control terminal is connected to the subcarrier number estimator ( 4) the output terminal; A subcarrier number estimator (4), used for estimating the optimal number of subcarriers used in the data field of the next transmission frame, its input terminal is connected with the receiver's time coherence measure estimator (9) and frequency coherence measure estimate device (13), the output end is connected with data framer (1), serial-parallel converter (3), fast inverse Fourier transformer (5), parallel-serial converter (6), adding cyclic segment prefix and sending shaping filter The control end of device (7) is connected; The fast inverse Fourier transformer (5) is used to perform OFDM modulation on the input parallel data containing the pilot frequency according to the estimated current subcarrier number, and its input terminal is connected to the output terminal of the serial-to-parallel converter (3) , the control terminal is connected to the output end of the subcarrier number estimator (4); Parallel-to-serial converter (6), used for converting the data modulated by OFDM into serial data, its input terminal is connected with the output terminal of fast inverse Fourier transformer (5), and the control terminal is connected with the number of subcarriers The output terminal of estimator (4) is connected; Adding a cyclic segment prefix and sending a shaping filter (7), used to add a cyclic segment prefix of a corresponding length to the sequence output by the parallel-to-serial converter according to the size of the number of subcarriers and then perform shaping filtering to obtain a digital baseband transmission signal and send it out. Its input terminal is connected with the output terminal of the parallel-to-serial converter (6), and the control terminal is connected with the output terminal of the subcarrier number estimator (4); The receiver includes a receive shaping filter and cyclic segment prefix separator (8), a time coherence measure estimator (9), a serial-to-parallel converter (10), a fast Fourier transformer (11), a parallel-to-serial converter (12), Frequency coherence measure estimator (13), channel estimation and equalizer (14), decision decoder (15): Receiving shaping filtering and cyclic segment prefix separator (8), performing matching shaping filtering on the received digital baseband signal, and separating the cyclic segment prefix and effective sample sequence from the sample sequence according to the number of subcarriers of the current symbol for time coherence The property metric is estimated, and its output terminal is connected to the input terminal of the serial-to-parallel converter (10), and the control terminal is connected to the output terminal of the decision decoder (15); A time coherence measure estimator (9), used for obtaining the time coherence measure of the current channel from the cyclic segment prefix and the effective sample sequence output by the receiving shaping filter and the cyclic segment prefix separator, and its output terminal is connected to the subcarrier of the transmitter The number estimator (4) is connected; A serial-to-parallel converter (10) is used to convert the serial effective sample sequence into parallel data, its output terminal is connected with the input terminal of the fast Fourier transformer (11), and the control terminal is connected with the input terminal of the decision decoder (15). connected to the output; The fast Fourier transformer (11) is used to carry out the demodulation of OFDM to the parallel data output by the serial-to-parallel converter (10), and its output end is connected with the input end of the channel estimation and equalizer (14), The control end is connected with the output end of the decision decoder (15); A parallel-to-serial converter (12), which is used to convert the data after the fast Fourier transform into serial data, and its output is connected to the input of the channel estimation and equalizer (14) and the frequency coherence measurement estimator (13) respectively , the control end is connected with the output end of the decision decoder (15); A frequency coherence metric estimator (13), used for estimating the frequency domain coherence metric of the channel from the fast Fourier transform result and the pilot data of the leading sequence output by the parallel-to-serial converter, and its output terminal is connected to the subcarrier of the transmitter The number estimator (4) is connected; Channel estimation and equalizer (14), used for estimating the channel response from the preamble sequence and the pilot data through fast Fourier transform and carrying out channel equalization to the follow-up OFDM symbol, its output end is connected with the decision decoder (15) input end is connected; Judgment decoder (15), used for decoding and judging the result of channel equalization, its output terminal is connected with receiving shaping filter and cyclic segment prefix separator (8), serial-to-parallel converter (10), fast Fourier transformer (11), the control terminal of the parallel-serial converter (12) is connected. 6. the OFDM transmission system with variable subcarrier number according to claim 5 is characterized in that the serial-to-parallel converter (3), the parallel-to-serial converter (6) and the receiver of the transmitter The conversion width of the serial-to-parallel converter (10) and the parallel-to-serial converter (12) is controlled by the size of the sub-carrier number output by the sub-carrier number estimator (4) and the data frame signaling output by the decision decoder (15) The number of subcarriers field value of the domain. 7. The OFDM transmission system with variable subcarrier number according to claim 5, characterized in that the preamble sequence formed by the data framer (1) of said transmitter comprises at least 3 The same and contiguous OFDM symbols.

Images