CN1787509A - Method for integral multiplying frequency deviation correction of receiving terminal of WiMAX system base station - Google Patents

Abstract

This invention relates to the frequency deviation estimation of integer times to the base station receiving end of a WiMAX system and a calibration method including the following steps: determining number of a sample value based on same accessed values of the received 256 sample values of the short front pilot domain sequence after FFT and computing the middle variables of the elements corresponding to said sample number, shifting in circulation two values of the 256 domain sequence values to select the corresponding elements to compute the middle variables according to said number, repeating said step to get other variables, comparing the values to find out the subscript value j of a middle variable corresponding to the maximum value and shift (j-1)x2 values to the received frequency domain sequence.

Description

A kind of integer frequency bias correcting method that is used for WiMAX system base-station receiving terminal

Technical field

The present invention relates to communications field WiMAX (micro-wave access global inter communication) system base-station receiving terminal carrier synchronization method for optimizing.

Background technology

Recent years, just when mobile operator, equipment manufacturers, mobile-phone manufacturers, the department of national governments in the whole world is that the construction of the 3rd third generation mobile communication network (3G) and operation are when dropping into appreciable fund and energy, computer industry has been released a kind of brand-new wireless access wide band technology, and with its called after WiMAX.WiMAX is the abbreviation of Worldwide Interoperability forMicrowave Access, generally is translated into " micro-wave access global inter communication ".

The WiMAX technology is based on 802.16 series standards of IEEE.In 802.16 series standards, specified in more detail the specification requirement of the air interface between base station BS (Base Station) and the subscriber station SS (Subscriber Station), especially to the frame structure requirement of physical layer, system design parameters or the like all has detailed regulation.WiMAX system (IEEE 802.16-2004) the base station receiving terminal carrier synchronization that the present invention is primarily aimed at based on the OFDM physical layer designs.

OFDM is the abbreviation of Orthogonal Frequency Division Multiplex, and the Chinese meaning is OFDM.The basis of OFDM technology is an orthogonal multiple carrier, is a kind of multi-carrier spread spectrum technology.The great advantage of OFDM is decline of contrary frequency selectivity or narrow band interference, in single-carrier system, single decline or interference can cause whole communication link failure, but in multicarrier system, only there is very little portion of carriers to be interfered, can adopts error correcting code to carry out error correction these subchannels.In ofdm system, the carrier wave of each subchannel is mutually orthogonal, and frequency spectrum is overlapped, has so not only reduced the phase mutual interference between subcarrier, has improved the availability of frequency spectrum simultaneously again.

In the WiMAX system design based on OFDM, in order to guarantee the orthogonality between the subcarrier, it is quite high to synchronous requirement.In case step-out, the orthogonality between the subcarrier will be affected, thus the systematic function of having a strong impact on.So the superiority-inferiority of synchronized algorithm can cause the quality of whole system performance.Design a high-performance and practicable synchronized algorithm, become a key link of whole system design.

Based on the physical layer support of the 802.16-2004 agreement of OFDM pattern transmission based on frame.One frame comprises a descending sub frame and a sub-frame of uplink.Descending sub frame is made up of a down physical layer PDU, and sub-frame of uplink is made up of with one or more upstream physical layer Burst by different SS emissions the competition slot that is used for initial ranging and bandwidth request purpose.The Burst of each up SS has comprised a short lead code.

Down physical layer PDU is initial by the long preambles sign indicating number, is used for physical layer synchronization.Upstream physical layer PDU (protocol Data Unit) is initial by short lead code, is used for the synchronous of up Burst (data burst).

According to the regulation of agreement, determine by following formula in the value of frequency domain sequence based on its up short lead code of WiMAX system of OFDM:

$P_k=\left\{\begin{array}{c}\sqrt{2}{P}_{\mathrm{ALL}}\left(k\right)...........................k_{\mathrm{mod}2}=0;\\ 0.....................................k_{\mathrm{mod}2}\≠0;\end{array}\right.$

Wherein

The factor is relevant with the 3dB gain.P _ALLFrequency domain sequence has carried out same regulation by agreement, has fixing value.

According to above regulation, we obtain short leading frequency domain sequence value and are:

There is very strict requirement in WiMAX system based on OFDM for the orthogonality between the subcarrier, and whether the strictness of orthogonality directly affects the quality of systematic function.The requirement of orthogonality is finished by synchronization module.Comprise regularly synchronous and Frequency Synchronization synchronously, than higher, it is quite responsive to frequency deviation to the requirement of Frequency Synchronization in the WiMAX system, and frequency deviation not only has influence on the deflection of signal phase, and the orthogonality between the destruction subcarrier, the amplitude and the signal to noise ratio that have influence on signal change.

Frequency shift (FS) is to be caused by Doppler frequency shift of the deviation between the local carrier of transceiver, channel etc., generally frequency deviation is divided into the integral multiple skew of subcarrier spacing and the decimal of subcarrier spacing and doubly is offset, integer frequency offset and fractional part of frequency offset sum are total frequency deviation.The integral multiple skew of subcarrier spacing can not cause disturbs (ICI) between subcarrier, but dislocation has taken place the frequency domain sequence sample value that obtains later on by the FFT conversion; The decimal of subcarrier spacing doubly is offset the orthogonality of having destroyed between the subcarrier, makes the signal of receiving that amplitude and phase place deflection take place.

In the WiMAX of reality system, its synchronizing process is generally shown in figure one, the base station with the signal that receives by analog to digital conversion after, at first carry out the synchronously thick of frame, symbol, the starting point of specified data, carry out fractional part of frequency offset estimation and correction then, these two processes were carried out before the FFT conversion, generally all were based on short leading algorithm for design, after FFT changes, carry out integer frequency offset estimation and correction, carry out the synchronously thin of frame, symbol again.In existing various integer frequency deviation estimation algorithms, most of algorithm is too narrow and small to the scope of frequency offset estimating, general all within several integral multiple scopes of subcarrier spacing, the Yun Hee Kim that finds, Iickho Song, Seokho Yoon, in and So Ryoung Park " the An Efficient Frequency OffsetEstimator for OFDM Systems and Its Performance Characteristics " works, the algorithm of its design can be estimated integer frequency offset in whole bandwidth, but the complexity of this algorithm is too high, has certain degree of difficulty for the design of system; To have utilized received signal and known transmission signal to carry out relevant for this algorithm simultaneously, because the signal that receives has passed through the influence of various noises and deviation, it reduces greatly with the correlation that sends signal, and accuracy of design had certain influence.The present invention utilizes the leading frequency domain sequence of known weak point, analyze its rule, proposed frequency-region signal that a kind of utilization receives and carried out auto-correlation and carry out the algorithm that integer frequency offset is estimated, not only avoided utilizing sending signal and received signal is carried out cross-correlation, the influence that its correlation reduces greatly; And having the advantage that can in whole bandwidth, estimate and proofread and correct equally to integer frequency offset, its complexity reduces greatly simultaneously, helps the application of real system.

Summary of the invention

The object of the present invention is to provide a kind of method of finishing the estimation of micro-wave access global inter communication (WiMAX) system base-station receiving terminal integer frequency offset and proofreading and correct based on the leading frequency domain sequence value of known weak point.

A kind of method of finishing the estimation of micro-wave access global inter communication (WiMAX) system base-station receiving terminal integer frequency offset and proofreading and correct based on the leading frequency domain sequence value of known weak point provided by the invention, comprise step: according to determining the sample value numbering in the identical value that receives through in 256 sample values of the leading frequency domain sequence of weak point after fast Fourier transform (FFT) and channel estimating and the correction, select this sample value to number pairing sample value to form a set R, the element among the pair set R calculates intermediate variable $P_1={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2,$ R _i(i=1,2 ... 29) represent that sample value is numbered the sample value of i, R ^* _I+1Expression is to R _I+1Get conjugation, when the i value is 29, R ^* _I+1Get R ^* ₁Sample value; Two sample values of 256 frequency domain sequence sample value cyclic shifts with receiving obtain 256 new sample value sequences, select corresponding sample value to form a set R according to above-mentioned sample value numbering, and the element among the pair set R calculates intermediate variable $P_2={\left|\mathrm{\Σ}{R}_i{R^{*}}_{i+1}\right|}^2;$ Repeat a top step, with the sample value sequence that receives cyclic shift 4,6 successively ... 254, obtain intermediate variable value P ₃, P ₄... P ₁₂₈Compare 128 intermediate variable P _j(j=1,2 ... 128) value, the pairing intermediate variable P of maximizing _jSubscript value j, obtain integer frequency offset for (j-1) * 2, with frequency domain sequence cyclic shift (j-1) * 2 sample value that receives.

By the method for the invention, can in the entire belt wide region, finish integral multiple carrier deviation estimation, saved memory space greatly, reduced computation complexity, improved the practicality and the feasibility of this method.

Description of drawings

Fig. 1: the synchronous flow process of WiMAX system.

Embodiment

Suppose in the base station and to have carried out the estimation and the correction of the synchronously thick and fractional part of frequency offset of frame, symbol before carrying out the FFT conversion receiving signal, the leading frequency domain sequence of weak point after the FFT conversion only exists integral multiple sub-carrier frequencies deviation, that is to say that the circulation skew has taken place 256 sample values to the leading frequency domain sequence of weak point that receives.The purpose of integer frequency deviation estimation algorithm is exactly the deviant that will obtain the frequency domain sequence sample value, carries out integer frequency offset then and proofreaies and correct.

According to the regulation of IEEE 802.16-2004 agreement, by the leading frequency domain sequence value of weak point that we known SS of the analysis of front sends, by the frequency domain sequence of these 256 sample values is analyzed, we find that value is in this sequence value Frequency sequence be numbered that { 39 41 59 61 79 81 89 93 97 107 115 131 135 137 139 153 163 165,189 191 195 197 199 221 227} have 25; Value is Frequency sequence be numbered that { 29 3,337 47 49 53 57 67 69 73 77 87 91 103 105 119 121 141 147 151 155 157 159 173 183,185 201 207 229} have 29; Value is Frequency sequence be numbered that { 31 43 45 51 6,365 71 83 85 95 109 113 117 127 149 161 167 171 175 177 179 209 213 223 225} have 25; Value is

Frequency sequence be numbered that { 55 75 99 101 111 123 125 133 143 145 169,181 187 193 203 205 211 215 217 219} have 21;

Consider simultaneously and received signal before the FFT conversion, utilized the repetition sample value of short leading time domain sequences (short leading time domain sequences has 256 sample values, wherein 128 sample values of 128 sample values in front and back are identical) carried out the correction of decimal times carrier wave frequency deviation, its correcting range is (1～+ 1) subcarrier spacing, so the leading frequency domain sequence sample value of weak point after the FFT conversion only exists even-multiple subcarrier frequency deviation.The short leading frequency domain sequence sample value of known transmitting terminal only has sample value on even subcarriers, sample value on the odd subcarriers is 0, so the leading frequency domain sequence sample value of the weak point that receives also only should have the data energy on even subcarriers, have only some noise jamming energy at random on the odd subcarriers.

We get set Q={29 33 37 47 49 53 57 67 69 73 77 87 91 103 105 119 121 141,147 151 155 157 159 173 183 185 201 207 229}, this set has 29 elements, this is illustrated in the known leading frequency domain sequence sample value of 256 weak points, has 29 values and is

Sample value; Simultaneously, on behalf of unique sample value of these 29 sample value sequences, this set be spaced.So we know in 256 sample values of WiMAX base station receiving terminal to the leading frequency domain sequence of weak point of the FFT conversion that receives, exist and have 29 approximately equalised sample values, that is to say to have 29 sample values that correlation is very strong, simultaneously being spaced between these sample values has with the identical sample value of known transmission signal Q set and is spaced.

The design intermediate variable $P_1={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2,$ R _i(i=1,2 ... 29) represent the sample value that the frequency domain short leader sequence sample value that receives is stipulated according to the Q set is spaced the selected sample value sequence of order, R ^* _I+1Expression is to R _I+1Get conjugation, when the i value is 29, R ^* _I+1Can get R ^* ₁Sample value in order to finish correlation computations.By the leading frequency domain sequence sample value of the weak point that receives is calculated an intermediate variable value P ₁,, promptly establish former receiving sequence and be { R1 then with two the sample value symbols of frequency domain sequence sample value cyclic shift that receive, R2 ... R255, R256}, sequence after sample value of cyclic shift is { R3, R4 ..., R256, R1, R2} calculates intermediate variable after the sample value intervening sequences value that the sample value sequence after the displacement is continued to set according to the Q set, obtains another intermediate variable value P ₂Circulate successively and obtain 128 intermediate variable value P for 127 times later on _j(j=1,2 ... 128), 128 relatively more all P _jValue, find the wherein maximum leading frequency domain sequence value of the pairing weak point of value, be correct frequency domain sequence sample value and arrange, just obtained the estimation of integer frequency offset thus, and finished the correction of integer frequency offset.

Short leading frequency domain sequence is a pseudo random sequence, have only certain skew that fits like a glove with the frequency domain sequence that sends to receive frequency domain sequence, its 29 sample values selecting at interval according to the sample value of Q set regulation just have very strong correlation, the mould value that its complex conjugate multiplies each other after the summation square just can reach maximum, other skew receives 29 sample values of frequency domain sequence owing to do not have this strong correlation, it is output as some pseudo noise energy values, well below maximum.

For example, calculate intermediate variable P by 256 frequency domain sequence sample values that receive being offset successively the back _jValue, find when side-play amount j value is 12, we obtain maximum, we know that integer-time carrier wave frequency deviation is (12-1) * 2=22 subcarrier spacing thus, to receiving 22 sub-carrier positions of data frequency domain sequence sample value circulation deflection later on, just can finish the frequency offset correction of integral multiple subcarrier.

Than aforementioned " An Efficient Frequency Offset Estimator for OFDM Systems and ItsPerformance Characteristics " algorithm, this algorithm does not need to preserve 256 plural sample values of the short leading frequency domain sequence of known transmission, also needn't preserve the plural ratio of its 255 frequency domain sample values, only need to preserve 29 real numbers that the Q set sets, in order to definite the frequency domain sequence sample value that receives is selected, save memory space greatly, reduced computation complexity.

We know that this algorithm can finish integral multiple carrier deviation estimation in the entire belt wide region, have improved the practicality and the feasibility of this algorithm greatly by the analysis to this algorithm! Although in having the channel of frequency selective fading, some sample value may be subjected to the influence of channel fading, yet we carry out integrated treatment by 29 sample values that all had strong correlation, and these a spot of sample values of channel influence of fading that are subjected to are for intermediate variable P _jValue, just reduced the amplitude of peak value slightly, do not influence the determined frequency deviation of peak value fully because have a large amount of strong correlation sample values in 29 sample values of this sequence, and 29 sample values of other sequence do not have strong correlation.

In conjunction with top analysis, below concrete implementation step of the present invention is elaborated:

Step (one): the WiMAX base station receiver is at interval successively selected 29 sample values through 256 frequency domain sequence sample values after the FFT conversion according to the sample value sequence number and the sample value of Q set regulation to what receive, calculates intermediate variable $P_1={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2,$ R _i(i=1,2 ... 29) represent the sample value that the frequency domain short leader sequence sample value that receives is stipulated according to the Q set is spaced the selected sample value sequence of order, R ^* _I+1Expression is to R _I+1Get conjugation, when the i value is 29, R ^* _I+1Can get R ^* ₁Sample value in order to finish correlation computations.

Step (two): two sample values of 256 frequency domain sequence sample value cyclic shifts that will receive, make the sample value sequence by R1, R2 ... R255, R256} become R3, R4 ... R256, R1, R2} selects 29 sample values at interval successively according to the sample value sequence number and the sample value of Q set regulation, calculates intermediate variable $P_2={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2,$ R wherein _i(i=1,2 ... 29) expression is to 29 sample values selecting value in order.

Step (three): repeating step two, the sample value sequence that receives is shifted 4,6 successively ... 254, obtain intermediate variable P ₃, P ₄... P ₁₂₈

Step (four): compare 128 intermediate variable P _j(j=1,2 ... 128) value, the pairing intermediate variable P of maximizing _jSubscript value j, so can obtaining integer frequency offset, we are (j-1) * 2 sample value, so with frequency domain sequence cyclic shift (j-1) * 2 sample value that receives, just obtained correcting the later correct frequency domain sample value sequence of integer frequency offset, thereby finished estimation and correction integer frequency offset.In the system design process of reality, for conserve storage, the intermediate variable P that unnecessary preservation is all _jThe result.Only need be with the P that begins to obtain ₁And P ₂Compare, preserve higher value wherein, then P obtaining later ₃, P ₄... P ₁₂₈Compare with the maximum of preserving previously successively, still only preserve maximum after comparing and get final product.Simultaneously because to middle variable $P_j={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2$ Calculating, be identical process, get final product so in realization, can utilize identical module to handle.

Claims (5)

1, a kind of method of finishing the estimation of micro-wave access global inter communication (WiMAX) system base-station receiving terminal integer frequency offset and proofreading and correct based on the leading frequency domain sequence value of known weak point is characterized in that may further comprise the steps:

A) the identical value of foundation in 256 sample values of the leading frequency domain sequence of weak point of the process fast Fourier transform (FFT) that receives determined the sample value numbering, select this sample value to number pairing sample value to form a set R, the element among the pair set R calculates intermediate variable $P_1={\left|\underset{i=1}{\overset{29}{\mathrm{\Σ}}}{R}_i{R^{*}}_{i+1}\right|}^2,$ R _i(i=1,2 ... 29) represent that sample value is numbered the sample value of i, R ^* _I+1Expression is to R _I+1Get conjugation, when the i value is 29, R ^* _I+1Get R ^* ₁Sample value;

Two sample values of 256 frequency domain sequence sample value cyclic shifts that b) will receive obtain 256 new sample value sequences, select corresponding sample value to form a set R according to above-mentioned sample value numbering, and the element among the pair set R calculates intermediate variable

$P_2={\left|\mathrm{\Σ}{R}_i{R^{*}}_{i+1}\right|}^2;$

C) repeating step b, with the sample value sequence that receives cyclic shift 4,6 successively ... 254, obtain intermediate variable value P ₃, P ₄... P ₁₂₈

D) compare 128 intermediate variable P _j(j=1,2 ... 128) value, the pairing intermediate variable P of maximizing _jSubscript value j, obtain integer frequency offset for (j-1) * 2, with frequency domain sequence cyclic shift (j-1) * 2 sample value that receives.

2, method according to claim 1, it is characterized in that: described sample value numbering is formed set Q, set Q={29 3,337 47 49 53 57 67 69 73 77 87 91 103 105 119 121 141 147 151 155 157 159,173 183 185 201 207 229}.

3, according to the described method of claim 2, it is characterized in that: on behalf of unique sample value of these 29 sample value sequences, this set be spaced.

4, method according to claim 3 is characterized in that: only need to compare with the maximum of preserving previously successively in step d), only preserve maximum after comparing.

5, method according to claim 4, it is characterized in that: carried out the estimation and the correction of the synchronously thick and fractional part of frequency offset of frame, symbol in the base station before carrying out the FFT conversion to receiving signal, the leading frequency domain sequence of the weak point after the FFT conversion only exists integral multiple sub-carrier frequencies deviation.

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