CN103023850B - Variable-bandwidth OFDM (Orthogonal Frequency Division Multiplexing) transmitter and receiver - Google Patents
Variable-bandwidth OFDM (Orthogonal Frequency Division Multiplexing) transmitter and receiver Download PDFInfo
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Abstract
The invention belongs to the field of wireless communication, and relates to a variable-bandwidth OFDM (Orthogonal Frequency Division Multiplexing) transmitter and receiver which are used for transmitting and receiving the OFDM signals composed of effective information symbols and cyclic prefixes. The transmitter 100 comprises a segment manager 101, a symbol adding unit 102, a mapping unit 103, an OFDM signal generation unit 104, a frame length regulation unit 105, a carrier regulation unit 106 and a carrier amount storage unit 107; the receiver 202 comprises a cyclic prefix detection unit 201, an FFT (Fast Fourier Transform) unit 202, a data screening unit 203, a data post-processing unit 204, a carrier estimation unit 205, a channel idle bandwidth estimation unit 206, a carrier information storage unit 207 and a carrier change decision-making unit 208. The transmitter can be used for dynamically regulating the amount of carriers according to the communication bandwidth change feed-back information provided by the receiver, so as to control the communication bandwidth and dynamically change the information bit transmission rate.
Description
Technical field
The invention belongs to radio communication field, be specifically related to a kind of OFDM transmitter and receiver of bandwidth varying, for sending and receive the frame ofdm signal be made up of effective information symbol and Cyclic Prefix.
Background technology
OFDM technology is a kind of transmission plan utilizing multiple orthogonal carrier frequencies to send signal.Intrasystem high-speed data flows through serioparallel exchange, data symbol persistence length on each subcarrier is increased relatively, thus effectively reduce the intersymbol interference (ISI) that wireless channel temporal dispersion brings, and the complexity of equalizer in receiver is reduced.The equal pairwise orthogonal of all subcarriers in OFDM transmitted signal bandwidth, thus frequency spectrum can be overlapped, can maximally utilise frequency spectrum resource, and when sub-carrier number is very large, the availability of frequency spectrum can close to Nyquist maximum.From frequency domain, in channel because of multipath frequency of occurrences Selective intensity or exist arrowband interference time, only have a fraction of subcarrier to be affected, therefore, ofdm system can resist to a certain extent multipath and arrowband interference, greatly reduce the error rate.
Current OFDM transmitter and OFDM receiver are mainly divided into two large classes.
The first kind is that number of carriers is fixed, the OFDM transmitting/receiving system that namely communication bandwidth is fixing.This system Problems existing mainly contains: when the interference of relatively high power appears in side channel, and system because not changing the communication bandwidth of (reduction) this channel in real time, thus makes the edge subcarrier of this channel be subject to larger interference, the reliability of impact transmission; And when side channel is idle, because communication bandwidth is fixed, idle frequency band resource can not be effectively utilized and cause the waste of band resource.
Equations of The Second Kind is the OFDM transmitting/receiving system of adaptive-bandwidth.Although the bandwidth of this system is variable, because its bandwidth only changes with the change of source data transmission rate, therefore still effectively can not eliminates the impact of adjacent-channel interference on this channel skirt subcarrier, can not bandwidth availability ratio be improved.In addition, the change of bandwidth will through the confirmation repeatedly of transmitter and receiver, and process is very complicated, and the transmission of confirmation itself also exists disturbed risk.
Summary of the invention
For the problems referred to above, the object of the invention is the accurate estimation by taking situation to this channel width and neighbouring frequency resource thereof, control the change of this channel width in real time, dynamically, intelligently control number of subcarriers, thus farthest improve reliability and the availability of frequency spectrum of OFDM transmitter and OFDM receiver.
For achieving the above object, the present invention takes following technical scheme:
A kind of OFDM transmitter of bandwidth varying and receiver, for sending and receive the frame ofdm signal be made up of effective information symbol and Cyclic Prefix, it is characterized in that, the communication bandwidth that described transmitter can provide according to described receiver changes feedback information and dynamically adjusts variable number, thus control communication bandwidth, dynamically change transfer rate of information simultaneously.
Described transmitter 100 comprises: segment management device 101, symbol adder 102, map unit 103, ofdm signal generation unit 104, Frame Size Adjustment unit 105, carrier wave adjustment unit 106, carrier number memory cell 107.
Segment management device 101, is connected with symbol adder 102 with Frame Size Adjustment unit 105.According to the symbol internal information figure place from Frame Size Adjustment unit 105, the baseband signal transmitted by host computer is by information bit segment processing.
Symbol adder 102, input termination segment management device 101, exports termination map unit 103.Forward error correction coding and convolutional encoding are carried out to the packet sended over by segment management device 101.
Map unit 103, input termination symbol adder 102, exports termination ofdm signal generation unit 104.Adopt 16QAM, by 4 ' 0,1 ' signal is transformed to 1 a bit corresponding symbol in 16 points in IQ plane.
Ofdm signal generation unit 104, comprises pilot tone and training symbol maker 104a, data and pilot allocator 104b, IFFT unit 104c and protects interval adding device 104d.
Pilot tone and training symbol maker 104a, export and connect data and pilot allocator.Before data symbol sends, generation cycle prefix signal, and while data symbol sends, generate pilot frequency information.
Data and pilot allocator 104b, be connected with map unit 103 with training symbol maker 104a with IFFT unit, pilot tone respectively.Information data from map unit 103 is formed frequency spectrum data bag with the pilot data from pilot tone and training symbol maker 104a by certain arrangement mode, sends IFFT unit 104c to.
IFFT unit 104c, with data with pilot allocator 104b with protect interval adding device 104d to be connected.Frequency spectrum data bag from data and pilot allocator 104b is carried out Inverse Fast Fourier Transforms, after parallel data being converted to serial time domain data, exports protection interval adding device to.
Protection interval adding device 104d, is connected with IFFT unit 104c.Protection interval is added between two discontinuous information symbols of the serial time domain data sent here to IFFT unit 104c.
Frame Size Adjustment unit 105 comprises figure place computing unit 105a and frame interior transmission total information figure place computing unit 105b in symbol.
Figure place computing unit 105a in symbol, respectively with transmit total information figure place computing unit 105b in frame, carrier wave adjustment unit 106 is connected with segment management device 101.Transmissible information bit number in each symbol is gone out according to the available carrier wave number calculated signals that carrier number adjustment unit 106 provides.
In frame, transmission total information figure place computing unit 105b, is connected with figure place computing unit 105a in symbol.According to the symbol internal information figure place that figure place computing unit 105a in symbol provides, total information figure place can be transmitted in the frame calculating reaction instant messages speed, and information rate adjusts the feedback information of information bit transmission rate to host computer accordingly.
Carrier wave adjustment unit 106, carrier wave adjustment unit 106 comprises carrier number determinant 106a and pilot tone adjustment unit 106b.
Carrier number determinant 106a, is connected with carrier number memory cell 107 with the carrier wave Change Strategy unit 208 of pilot tone adjustment unit 106b, described receiver respectively.Receive the bandwidth feedback information from receiver, read the carrier information in carrier number memory cell 107, according to bandwidth feedback information, carrier information is made the appropriate adjustments and upgrades the carrier information in carrier number memory cell 107; Above-mentioned method of adjustment is: as communication bandwidth changes delta B, and corresponding number of carriers is changed to Δ C=Δ B/S
bW, wherein S
bWfor the frequency interval of subcarrier.
Pilot tone adjustment unit 106b, is connected with Frame Size Adjustment unit 106 with carrier number determinant 106a, ofdm signal generation unit 104 respectively.According to the pilot number in number of carriers adjustment transmission frame structure and the position of pilot tone in frequency band, pilot number is decided to be 1/16 of total number of subcarriers, and all pilot tones are evenly distributed in whole communication bandwidth, adjustment result sends to Frame Size Adjustment unit 106 and ofdm signal generation unit 104 respectively.Carrier number memory cell 107, is connected with carrier wave adjustment unit 106, for storing the bandwidth information of present communications.
Described receiver 200 comprises: Cyclic Prefix detecting unit 201, FFT unit 202, data screening unit 203, Data Post unit 204, carrier estimation unit 205, channel idle bandwidth estimation unit 206, carrier information memory cell 207, carrier wave Change Strategy unit 208.
Cyclic Prefix detecting unit 201, input connects antenna, exports and connects FFT unit 202.For detecting the Cyclic Prefix being positioned at each OFDM frame.
FFT unit 202, input connects Cyclic Prefix detecting unit 201, exports and connects data screening unit 203 and carrier estimation unit 205 respectively.For carrying out fast Fourier transform to received signal.
Data screening unit 203, input connects FFT unit 202, exports and connects Data Post unit 204 and channel idle bandwidth estimation unit 206 respectively.For filtering out the data being positioned at communication band, outer for band data are sent to channel idle bandwidth estimation unit 206, in order to estimate out-of-band power simultaneously.
Data Post unit 204, is connected with data screening unit 203.Map for separating 16QAM and separate forward error correction coding.
Carrier estimation unit 205 comprises small echo and is separated and reconfiguration unit 205a and frequency spectrum cross-correlation unit 205b.
Small echo is separated and reconfiguration unit 205a, is connected with described FFT unit 202 with frequency spectrum cross-correlation unit 205b.Adopt Haar small echo to carry out separating treatment to the frequency spectrum data from FFT unit 202, obtain in frequency spectrum, changing violent part and the part of relative smooth, adopt wherein level and smooth data division to be reconstructed frequency spectrum, finally obtain approximate rectangular frequency spectrum.
Frequency spectrum cross-correlation unit 205b, is separated with small echo and is connected with carrier information memory cell 207 with reconfiguration unit 205a.To the Cyclic Prefix frequency spectrum data be separated by small echo and after reconfiguration unit 205a process, carry out the cross-correlation of different starting point, finally obtain the bandwidth that namely one group of maximum bandwidth of correlation is this communication.
Channel idle bandwidth estimation unit 206 comprise edge bandwidth power density integrator 206a, noise gate comparing unit 206b and free time computing unit 206.
Edge bandwidth power density integrator 206a, is connected with data screening unit 203 with noise gate comparing unit 206b.Integration is carried out, edge calculation bandwidth power by the edge bandwidth power density beyond this communication bandwidth.
Noise gate comparing unit 206b, is connected with edge bandwidth power density integrator 206a with free time computing unit 206c.By edge bandwidth power P
inwith noise power P
noiscompare, work as P
in>1.5P
noisetime, output bandwidth Seize ACK message; Work as P
in<1.5P
noisetime, output bandwidth idle signal, if free time more than an OFDM frame length, then think that this edge bandwidth is idle.
Free time computing unit 206c, is connected with carrier wave Change Strategy unit 208 with noise gate comparing unit 206b.When receiving the bandwidth idle signal fed back by described noise gate comparing unit, record current idle bandwidth information, and start cumulative bandwidth free time, if this bandwidth remains idle condition within the whole OFDM information frame time, carrier wave Change Strategy unit 208 will send feedback information to transmitter, improves signal bandwidth.
Carrier information memory cell 207, is connected with data screening unit 203 with carrier estimation unit 205.For storing this communication bandwidth information.
Carrier wave Change Strategy unit 208, is connected with channel idle bandwidth estimation unit 206.Whether change for decision-making communication bandwidth.
In order to correctly estimated spectral information, the ofdm signal frame structure of transmission adopts Cyclic Prefix to add the compound mode of information symbol.Cyclic Prefix is made up of multiple identical training symbol, and thus, the frequency spectrum data that each training symbol is corresponding is identical in theory.A certain frequency range data in the training symbol frequency spectrum data do not obtained in the same time are carried out to cross-correlation operation and recorded correlation, when this correlation is maximum, illustrates and participate in the bandwidth that relevant frequency band is this communication.In fact, before carrying out associative operation, in order to make frequency spectrum closer to ideal situation, first carrier estimation unit carries out wavelet transformation to frequency spectrum data, extract part more level and smooth in frequency spectrum, make frequency spectrum closer to ideal rectangle, improve the reliability of carrier estimation.
Channel idle bandwidth estimation unit detects the bandwidth power outside this communication in real time.When idle during an accumulative OFDM frame length, just judge that channel exists and do not utilize frequency band, prevent from covering with side channel frequency band.
The present invention, can Real-Time Monitoring channel width utilization power owing to taking above technical scheme, and according to the estimation result of channel width, real-time dynamic conditioning subcarrier number, while reduction communication band is disturbed, also improves channel utilization outward.
Accompanying drawing explanation
Fig. 1 is the functional block diagram of bandwidth varying OFDM transmitter of the present invention;
Fig. 2 is the functional block diagram of the Frame Size Adjustment unit of bandwidth varying OFDM transmitter of the present invention;
Fig. 3 is the carrier wave adjustment unit of bandwidth varying OFDM transmitter of the present invention;
Fig. 4 is the ofdm signal generation unit of bandwidth varying OFDM transmitter of the present invention;
Fig. 5 is the functional block diagram of bandwidth varying OFDM receiver of the present invention;
Fig. 6 is the functional block diagram of the Cyclic Prefix detecting unit of bandwidth varying OFDM receiver of the present invention;
Fig. 7 is the functional block diagram of the subcarrier estimation unit of bandwidth varying OFDM receiver of the present invention;
Fig. 8 is the side channel estimation of available bandwidth Elementary Function calcspar of bandwidth varying OFDM receiver of the present invention;
The OFDM transmitter that Fig. 9 is bandwidth varying OFDM receiver of the present invention and bandwidth varying receive and the frame structure launched.
In figure, 100.OFDM transmitter, 101. segment management devices, 102. symbol adders, 103. map unit, 104.OFDM signal generation unit, 104a. data and pilot allocator, 104b.IFFT unit, 104c. protects interval adding device, 104d. pilot tone and training symbol maker, 105. Frame Size Adjustment unit, figure place computing unit in 105a. symbol, transmission total information figure place computing unit in 105b. frame, 106. carrier wave adjustment units, 106a. carrier number determinant, 106b. pilot tone adjustment unit, 107. carrier number memory cell, 200.OFDM receiver, 201. Cyclic Prefix detecting units, 201a. delay cell, 201b. complex conjugate units, 201c. multiplier, 201d. data accumulation unit, 201e. data accumulation unit, 201f. divider, 201g. buffer, 202.FFT unit, 203. data screening unit, 204. Data Post unit, 205. carrier estimation unit, 205a. small echo is separated and heavy unit, 205b. frequency spectrum cross-correlation unit, 206. channel idle bandwidth estimation unit, 206a. edge bandwidth power density integral unit, 206b. noise gate identifying unit, 206c. free time computing unit, 207. carrier information memory cell, 208. carrier wave Change Strategy unit.
Embodiment
Fig. 9 shows the OFDM frame structure relating to OFDM transmitter of the present invention and receiver launching and receiving.This OFDM frame is made up of Cyclic Prefix and data two parts.Wherein: Cyclic Prefix is made up of multiple identical training symbol; Data division is formed by protecting interval and information symbol.Protection interval is identical with the partial information data at information symbol end thereafter.In each OFDM frame, the number of information symbol and training structure is determined constant.
As shown in Figure 1, the OFDM transmitter of the bandwidth varying relevant with the first execution mode of the present invention, mainly has segment management device 101, symbol adder 102, map unit 103, ofdm signal generation unit 104, Frame Size Adjustment unit 105, carrier wave adjustment unit 106, carrier number memory cell 107.
Segment management device 101 is according to the symbol internal information figure place information from Frame Size Adjustment unit 105, and the information bit segment processing transmitted by host computer, every segment length is " symbol internal information figure place ", forms preliminary Packet Generation to symbol adder 102.
Frame Size Adjustment unit 105, upwards level one data source sends feedback information: when communication bandwidth reduction, number of carriers reduce, and transmitter sends data rate to be reduced, and now to data source feedback, the signal of the data rate of transmitter 100 is imported in reduction into; When communication bandwidth raising, number of carriers increase, transmitter sends data rate and improves, and now to data source feedback, the signal of the data rate of transmitter 100 is imported in raising into.The pass that host computer imports between data rate N with corresponding bandwidth B is:
B=KN
Wherein, K is the rate conversion factor in coding link, and as communication bandwidth changes delta B, phase code rate variable quantity is Δ B/K.
As shown in Figure 2, Frame Size Adjustment unit 105 forms by transmitting total information figure place computing unit 105b in figure place computing unit 105a in symbol and frame.When communication bandwidth changes, the information bit number entrained by symbol in each OFDM frame also will change thereupon, and namely information symbol length also will change.OFDM frame internal symbol number is fixed, and when frame internal symbol length variations, in frame, transmission total bit also can change, i.e. the rate of information throughput also respective change.
In symbol, figure place computing unit 105a goes out transmissible information bit number in each information symbol according to the available carrier wave number calculated signals that carrier number adjustment unit provides.
In frame, transmission total information figure place computing unit 105b calculates in frame according to the symbol internal information figure place that figure place computing unit 105a in symbol provides and can transmit maximum information figure place.Because maximum information figure place can be transmitted in frame reacted instant messages speed, therefore in frame transmission total information figure place computing unit 105b according to the feedback information that can transmit maximum information figure place in frame and to adjust host computer information bit transmission rate.
Symbol adder 102 carries out forward error correction coding and convolutional encoding to the packet sended over by segment management device 101, and wherein forward error correction coding comprises scrambler module and interleaving block two parts.
Symbol adder 102 carries out forward error correction coding and convolutional encoding to the packet sended over by segment management device 101.
Error correcting code comprises scrambler coding, channel code and interleaving encodes three parts.Wherein, scrambler module adopt a length be 127 frame synchronous scrambler scrambling, its generator polynomial is shown below:
S(x)=x
7+x
3+1
Wherein, it is an information bit in the shift register of 8bit that x represents length, and its upper right footmark represents the position of this information bit in whole shift register.
Its essence is feedback shift register, can effectively be confused by list entries, and correlation between output numeric code is reduced.
Convolution code adopts the convolution coder of 1/2 code check to generate: input one digit number word bit, will produce two and export data.Wherein the generator polynomial of output data A, B is respectively:
A(x)=x
6+x
5+x
3+x
2+1
B(x)=x
6+x
3+x
2+x+1
Map unit 103 adopts 16QAM, and by 4 ' 0,1 ' signal is transformed to 1 a bit corresponding symbol in 16 points in IQ plane.
Carrier wave adjustment unit 106, according to the bandwidth feedback information imported into, judges whether number of carriers increases or reduce, and adjusts pilot number and the position of pilot tone in whole communication bandwidth.As shown in Figure 3, carrier wave adjustment unit 106 is made up of available carrier wave number determinant 106a and pilot tone adjustment unit 106b.
Carrier number determinant 106a receives the bandwidth feedback information from receiver, reads the carrier information in carrier number memory cell 107, according to feedback information, is made the appropriate adjustments by carrier information afterwards and the carrier information upgraded in carrier number memory cell 107.Above-mentioned adjustment mode is: as communication bandwidth changes delta B, and corresponding number of carriers is changed to Δ C=Δ B/S
bW, wherein S
bWfor the frequency interval of subcarrier.
The result of adjustment, after completing number of carriers adjustment, also will be passed to pilot tone adjustment unit 106b by carrier number determinant 106a.Pilot tone adjustment unit 106b is according to the pilot number in the quantity adjustment transmission frame structure of carrier wave and the position of pilot tone in frequency band.In order to make to reach balance between efficiency and performance, the quantity of pilot tone is decided to be 1/16 of total number of subcarriers, and all pilot tones are evenly distributed in whole communication bandwidth.Adjustment result sends to Frame Size Adjustment unit 105 and ofdm signal generation unit 104 respectively.
The frequency spectrum data that data and pilot data from map unit 103 is formed is carried out Inverse Fast Fourier Transforms by ofdm signal generation unit 104, sends after transformation results being added protection interval as transmission signal.
Ofdm signal generation unit 104, as shown in Figure 4, by data and pilot allocator 104a, IFFT unit 104b, protects interval adding device 104c and pilot tone and training symbol maker 104d to form.Information data from map unit 103 is formed frequency spectrum data bag with the pilot data from pilot tone and training symbol maker 104d by certain arrangement mode by data and pilot allocator 104a, sends IFFT unit 104b to and carries out Inverse Fast Fourier Transforms.In addition, IFFT unit 104b also has parallel-to-serial translation function, and the parallel data exported after IFFT conversion will convert serial time domain data to and export protection interval adding device 104c to.
The function of pilot tone and training symbol maker 104d has two: the first, before data symbol sends, and generation cycle prefix signal; The second, while data symbol sends, generate pilot frequency information.
Interval adding device 104c is by the head of N number of data Replica of each Frame afterbody to this frame in protection, makes two the discontinuous frames sent by IFFT unit 104b become continuous print time domain data.In said process, suppose that the space between two frames can hold N number of data.
As shown in Figure 5, the bandwidth varying OFDM receiver 200 relevant with the first execution mode of the present invention, forms primarily of Cyclic Prefix detecting unit 201, FFT unit 202, data screening unit 203, Data Post unit 204, carrier estimation unit 205, channel idle bandwidth estimation unit 206, carrier information memory cell 207 and carrier wave Change Strategy unit 208.
Cyclic Prefix detecting unit 201 is for detecting the leading Cyclic Prefix of each Frame.Specifically, as shown in Figure 6, this unit is made up of delay cell 201a, complex conjugate units 201b, complex multiplication unit 201c, data accumulation unit 201d, data accumulation unit 201e, complex division unit 201f and buffer 201g.
Delay cell 201a length is the data length of a training symbol.
Delay cell 201a, complex conjugate units 201b, complex multiplication unit 201c, data accumulation unit 201d complete training symbol and the associative operation postponing training symbol in Cyclic Prefix in Cyclic Prefix jointly.Relevant result is called time delay correlation, and be designated as C, the expression formula of C is:
Wherein R
nfor Received signal strength,
for being delayed the conjugate of the Received signal strength of a training symbol length, D is the data length of an aforementioned training symbol.
Delay cell 201a, data accumulation unit 201e complete the energy balane operation of the training symbol in the Cyclic Prefix after delay jointly.Calculate power and be designated as P, the expression formula of P is:
Wherein R
nfor Received signal strength,
for the conjugate of Received signal strength.
Complex division unit 201f completes the calculating of judgment variables, and judgment variables is designated as J, and computational methods are: J=C/P.
When only having noise in the signal received, the time delay correlation C ideally exported is 0, because the cross-correlation coefficient of noise is 0, therefore before Frame arrives, judgment variables value is very little.When receiving second training symbol, because it is identical to participate in relevant signal, time delay correlation starts obvious increase, and occurs the associated planar of a lasting M-1 symbol lengths, imply that new ofdm signal frame arrives.Meanwhile, complex division unit 201f will feed back ofdm signal frame arrival information to data accumulation unit 201e.Notice that this feedback information comprises two states: when training symbol being detected, output state 1; When training symbol not detected, output state 2.This signal is used for controller buffer output with synchronous Received signal strength by exporting data buffer 201g to.Note, suppose in said process in Cyclic Prefix, to comprise M training symbol.
Data accumulation unit 201e completes the power calculation function of Received signal strength.When new ofdm signal frame arrives, this unit, according to the feedback information from complex division unit 201f, makes the following two kinds operation: when feedback information is state 1, record current realtime power value; When feedback information is state 2, all realtime power values of record during state 1 are got average and preserved into register by this value, and recording this mean value is P
ava.
P
avaby the threshold value whether terminated as Detection Information symbol.After Cyclic Prefix finishes receiving, data accumulation unit 201e continues to calculate realtime power P
t, and by this power and P
avacompare.Work as P
t>P
avawhen/2, then think and be currently received information symbol; Work as P
t<P
ava/ 2 and continue an information symbol cycle time, think that information symbol finishes receiving.Whether court verdict is by formation data arriving signal and export buffer 201g to, be used to indicate information symbol and arrive.
The buffer 201g course of work can be described as: when the feedback information from complex division unit 201f is state 1, exports the data in buffer memory, and exports synchronizing signal, indicate these output data to be Cyclic Prefix; When the signal instruction information symbol from data accumulation unit 201e arrives, export the data in buffer memory, and export synchronizing signal, indicate these output data to be information symbol; In addition other all state, exports synchronous all instruction and does not receive useful signal.
FFT unit 202 completes the fast Fourier transform function receiving data.When the data importing this unit into are training symbol, the frequency spectrum data after fast Fourier transform will import carrier estimation unit 205 into; When the data importing this unit into are information symbol, the frequency spectrum data after fast Fourier transform will import data screening unit 203 into.
Carrier estimation unit 205 goes out the bandwidth of this communication according to the Cyclic Prefix spectrum estimation exported from FFT unit 202.As shown in Figure 7, this unit comprises small echo separation and reconfiguration unit 205a and frequency spectrum cross-correlation unit 205b.
Under ideal case, ofdm communication bandwidth is approximately rectangle, the low-limit frequency of the starting point of rectangle and the corresponding bandwidth of terminal difference and highest frequency.But signal is after wireless channel transmission, due to interference and multipath effect, final frequency spectrum graphics and ideal rectangle difference are very large, are unfavorable for the differentiation of bandwidth.Small echo is separated and first adopts Haar small echo to carry out separating treatment to the frequency spectrum received with reconfiguration unit 205a, obtains the violent part of (details) of change in frequency spectrum and the part of relative smooth (roughly).Then adopt above-mentioned smoothed data to be reconstructed frequency spectrum, finally obtain approximate rectangular frequency spectrum.
Known Cyclic Prefix is made up of the training symbol of multiple repetition, and therefore, the spectrum information that each training symbol obtains after FFT conversion is ideally identical.Two groups of identical training symbols, after the wireless channel of complexity, carry out FFT conversion respectively to it, obtain discrete frequency spectrum { f respectively
a1, f
a2..., f
ai..., f
aj..., f
anand { f
b1, f
b2..., f
bi..., f
bj..., f
bn, wherein subscript i, j are correct communication bandwidth Origin And Destination.
Two point (f are got at random respectively in two groups of frequency spectrum datas
ae, f
af) and (f
be, f
bf), obtain the frequency spectrum data { f that two groups of bandwidth are identical
ae..., f
afand { f
be..., f
bf, cross-correlation operation is carried out to above two groups of data and obtains correlation ConvAB.Experiment proves, when starting point is respectively (f
ai, f
aj) and (f
bi, f
bj) time, the cross correlation value obtained is maximum.
Frequency spectrum cross-correlation unit 205b carries out the cross-correlation of different starting point to the Cyclic Prefix frequency spectrum data received based on above-mentioned principle, finally obtain the bandwidth that namely one group of maximum bandwidth of correlation is this communication.
Channel idle bandwidth estimation unit 206 is for estimating the wide resource of channel available.This unit monitors the edge bandwidth power beyond this communication bandwidth in real time, to judge whether edge bandwidth takies.If free time more than an OFDM frame length, then thinks that this edge bandwidth is idle.
As shown in Figure 8, channel idle bandwidth estimation unit is made up of edge bandwidth power density integrator 206a, noise gate identifying unit 206b and free time computing unit 206c.The internal register of noise gate comparator 206b, preserves noise power P when channel does not have a Signal transmissions
noise.This comparator is by the power P of input
inwith P
noisecompare, work as P
in>1.5P
noisetime, comparator output bandwidth Seize ACK message; Work as P
in<1.5P
noisetime, comparator output bandwidth idle signal.Edge bandwidth power density integrator 206a, carries out integration, edge calculation bandwidth power by the edge bandwidth power density beyond this communication bandwidth.And the performance number calculated is sent to noise gate comparing unit 206b, when receiving the bandwidth occupancy signal fed back by noise gate comparing unit 206b, edge bandwidth power density integrator 206a will reduce integration bandwidth, and continuation rated output exports noise gate comparing unit 206b to again.When receiving the bandwidth idle signal fed back by noise gate comparing unit 206b, edge bandwidth free time computing unit 206c will record current idle bandwidth information, and start cumulative bandwidth free time, if this bandwidth remains idle condition within the whole OFDM information frame time, carrier wave Change Strategy unit 208 will send feedback information to transmitter, improves signal bandwidth.
The frequency spectrum data band exported due to FFT unit 202 is wider than when time signal of communication bandwidth, and the data entrained by the bandwidth exceeded not are the data that transmitter sends.The bandwidth information that data screening unit 203 will estimate according to carrier estimation unit 205, filters out the data within this communication bandwidth, and outer for band data are sent to channel idle bandwidth estimation unit 206, for estimated edge bandwidth power.
Data Post unit 204 will complete the inverse decode procedure of transmitter stage casing manager 101, symbol adder 102, map unit 103 3 unit, namely separates 16QAM mapping, deconvolution coding, deinterleaving coding, descrambling code.
Claims (8)
1. the OFDM transmitter of bandwidth varying and receiver, for sending and receive the frame ofdm signal be made up of effective information symbol and Cyclic Prefix, it is characterized in that, the communication bandwidth that described transmitter (100) can provide according to described receiver (200) changes feedback information and dynamically adjusts variable number, thus control communication bandwidth, dynamically change transfer rate of information simultaneously;
Described transmitter (100) comprising: segment management device (101), symbol adder (102), map unit (103), ofdm signal generation unit (104), Frame Size Adjustment unit (105), carrier wave adjustment unit (106), carrier number memory cell (107); Wherein, segment management device (101), be connected with symbol adder (102) with Frame Size Adjustment unit (105), according to the symbol internal information figure place from Frame Size Adjustment unit (105), the baseband signal transmitted by host computer is by information bit segment processing; Symbol adder (102), input connects segment management device (101), exports and connects map unit (103), carry out forward error correction coding and convolutional encoding to the packet sended over by segment management device (101); Map unit (103), input connects symbol adder (102), exports and connects ofdm signal generation unit (104), adopts 16QAM, by 4 ' 0,1 ' signal is transformed to 1 a bit corresponding symbol in 16 points in IQ plane; Ofdm signal generation unit (104), being connected with carrier wave adjustment unit (106) with map unit (103), sending as transmitting after the frequency spectrum data that data and the pilot data from map unit (103) is formed is converted; Frame Size Adjustment unit (105), is connected with carrier wave adjustment unit (106) with segment management device (101), computing information symbol lengths, and to host computer feedback information bit rate adjustment signal; Carrier wave adjustment unit (106), is connected with carrier number memory cell (107) with ofdm signal generation unit (104), Frame Size Adjustment unit (105), for adjusting communication bandwidth and number of carriers; Carrier number memory cell (107), is connected with carrier wave adjustment unit (106), for storing the bandwidth information of present communications;
Described receiver (200) comprising: Cyclic Prefix detecting unit (201), FFT unit (202), data screening unit (203), Data Post unit (204), carrier estimation unit (205), channel idle bandwidth estimation unit (206), carrier information memory cell (207), carrier wave Change Strategy unit (208); Wherein, Cyclic Prefix detecting unit (201), input connects antenna, exports and connects FFT unit (202), for detecting the Cyclic Prefix being positioned at each OFDM frame; FFT unit (202), input connects Cyclic Prefix detecting unit (201), exports and connects data screening unit (203) and carrier estimation unit (205) respectively, for carrying out fast Fourier transform to received signal; Data screening unit (203), input connects FFT unit (202), export and connect Data Post unit (204) and channel idle bandwidth estimation unit (206) respectively, for filtering out the data being positioned at communication band, outer for band data are sent to channel idle bandwidth estimation unit (206), in order to estimate out-of-band power simultaneously; Data Post unit (204), is connected with data screening unit (203), maps for separating 16QAM and separates forward error correction coding; Carrier estimation unit (205), input connects FFT unit (202), exports and carries ripple information memory cell (207), for estimating this communication bandwidth and number of carriers; Channel idle bandwidth estimation unit (206), input connects data screening unit (203), exports and carries ripple Change Strategy unit (208), for the out of band spectrum resource of this communication band of Real-Time Monitoring; Carrier information memory cell (207), is connected with data screening unit (203) with carrier estimation unit (205), for storing this communication bandwidth information; Whether carrier wave Change Strategy unit (208), be connected with channel idle bandwidth estimation unit (206), change for decision-making communication bandwidth.
2. the OFDM transmitter of bandwidth varying according to claim 1 and receiver, it is characterized in that, the carrier wave adjustment unit (106) of described transmitter (100) comprises carrier number determinant (106a) and pilot tone adjustment unit (106b), wherein
Carrier number determinant (106a), be connected with carrier number memory cell (107) with the carrier wave Change Strategy unit (208) of pilot tone adjustment unit (106b), described receiver respectively, receive the bandwidth feedback information from receiver, read the carrier information in carrier number memory cell (107), according to bandwidth feedback information, carrier information is made the appropriate adjustments and upgrades the carrier information in carrier number memory cell (107); Above-mentioned method of adjustment is: as communication bandwidth changes delta B, and corresponding number of carriers is changed to Δ C=Δ B/S
bW, wherein S
bWfor the frequency interval of subcarrier;
Pilot tone adjustment unit (106b), be connected with Frame Size Adjustment unit (106) with carrier number determinant (106a), ofdm signal generation unit (104) respectively, according to the pilot number in number of carriers adjustment transmission frame structure and the position of pilot tone in frequency band, pilot number is decided to be 1/16 of total number of subcarriers, and all pilot tones are evenly distributed in whole communication bandwidth, adjustment result sends to Frame Size Adjustment unit (106) and ofdm signal generation unit (104) respectively.
3. according to OFDM transmitter and the receiver of bandwidth varying according to claim 1 or claim 2, it is characterized in that, the Frame Size Adjustment unit (105) of described transmitter (100) comprises figure place computing unit (105a) and frame interior transmission total information figure place computing unit (105b) in symbol; Wherein,
Figure place computing unit (105a) in symbol, respectively with transmit total information figure place computing unit (105b) in frame, carrier wave adjustment unit (106) is connected with segment management device (101), goes out transmissible information bit number in each symbol according to the available carrier wave number calculated signals that carrier number adjustment unit (106) provides;
Transmission total information figure place computing unit (105b) in frame, be connected with figure place computing unit (105a) in symbol, according to the symbol internal information figure place that figure place computing unit (105a) in symbol provides, can transmit total information figure place in the frame calculating reaction instant messages speed, and information rate adjusts the feedback information of information bit transmission rate to host computer accordingly.
4. according to OFDM transmitter and the receiver of bandwidth varying according to claim 1 or claim 2, it is characterized in that, the bandwidth varying ofdm signal generation unit (104) of described transmitter (100) comprises pilot tone and training symbol maker (104a), data and pilot allocator (104b), IFFT unit (104c) and protects interval adding device (104d); Wherein,
Pilot tone and training symbol maker (104a), export and connect data and pilot allocator, before data symbol sends, and generation cycle prefix signal, and while data symbol sends, generate pilot frequency information;
Data and pilot allocator (104b), be connected with map unit (103) with training symbol maker (104a) with IFFT unit, pilot tone respectively, frequency spectrum data bag will be formed from the information data of map unit (103) and the pilot data from pilot tone and training symbol maker (104a) by certain arrangement mode, send IFFT unit (104c) to;
IFFT unit (104c), with data with pilot allocator (104b) with protect interval adding device (104d) to be connected, frequency spectrum data bag from data and pilot allocator (104b) is carried out Inverse Fast Fourier Transforms, after parallel data being converted to serial time domain data, exports protection interval adding device to;
Protection interval adding device (104d), is connected with IFFT unit (104c), adds and protect interval between two discontinuous information symbols of the serial time domain data sent here to IFFT unit (104c).
5. the OFDM transmitter of bandwidth varying according to claim 1 and receiver, it is characterized in that, the carrier estimation unit (205) of described receiver (200) comprises small echo and is separated and reconfiguration unit (205a) and frequency spectrum cross-correlation unit (205b); Wherein,
Small echo is separated and reconfiguration unit 205a, be connected with described FFT unit (202) with frequency spectrum cross-correlation unit (205b), Haar small echo is adopted to carry out separating treatment to the frequency spectrum data from FFT unit (202), obtain in frequency spectrum, changing violent part and the part of relative smooth, adopt wherein level and smooth data division to be reconstructed frequency spectrum, finally obtain approximate rectangular frequency spectrum;
Frequency spectrum cross-correlation unit (205b), be separated with small echo and be connected with carrier information memory cell (207) with reconfiguration unit (205a), to be separated by small echo and reconfiguration unit (205a) process after Cyclic Prefix frequency spectrum data, carry out the cross-correlation of different starting point, finally obtain the bandwidth that namely one group of maximum bandwidth of correlation is this communication.
6. according to OFDM transmitter and the receiver of claim 1 or bandwidth varying according to claim 5, it is characterized in that, the channel idle bandwidth estimation unit (206) of described receiver (200) comprises edge bandwidth power density integrator (206a), noise gate comparing unit (206b) and free time computing unit (206c); Wherein,
Edge bandwidth power density integrator (206a), be connected with data screening unit (203) with noise gate comparing unit (206b), integration is carried out, edge calculation bandwidth power by the edge bandwidth power density beyond this communication bandwidth;
Noise gate comparing unit (206b), was connected with edge bandwidth power density integrator (206a) with free time computing unit (206c), by edge bandwidth power P
inwith noise power P
noiscompare, work as P
in>1.5P
noisetime, output bandwidth Seize ACK message; Work as P
in<1.5P
noisetime, output bandwidth idle signal, if free time more than an OFDM frame length, then think that this edge bandwidth is idle;
Free time computing unit (206c), be connected with carrier wave Change Strategy unit (208) with noise gate comparing unit (206b), when receiving the bandwidth idle signal fed back by described noise gate comparing unit, record current idle bandwidth information, and start cumulative bandwidth free time, if this bandwidth remains idle condition within the whole OFDM information frame time, carrier wave Change Strategy unit (208) will send feedback information to transmitter, improves signal bandwidth.
7., according to OFDM transmitter and the receiver of claim 1 or bandwidth varying according to claim 5, it is characterized in that:
Utilize the frequency spectrum related algorithm of cycle of training in Cyclic Prefix, identification communication bandwidth.
8., according to OFDM transmitter and the receiver of claim 1 or bandwidth varying according to claim 5, it is characterized in that:
Adopt the method for wavelet transformation to be decomposed by frequency spectrum data, utilize level and smooth part, reconstruct the frequency spectrum close to ideal case.
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