CN103297376A - Symbol synchronization method of OFDM (orthogonal frequency division multiplexing) system - Google Patents
Symbol synchronization method of OFDM (orthogonal frequency division multiplexing) system Download PDFInfo
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Abstract
The invention discloses a symbol synchronization method of an OFDM (orthogonal frequency division multiplexing) system. The method includes accumulating a currently-received sampling value with previously-received sampling values of corresponding positions in each group of training sequences TS and quantitatively processing the accumulated sampling value; combining the quantified sampling value and previously-received quantified sampling values into a group of TSs, performing autocorrelation operation on the TSs and locally-known TSs, performing modulus operation and square operation on results of the autocorrelation operation, and determining whether the current sampling value is at an autocorrelation peak value position or not through comparison with a fixed decision threshold; executing the above steps to each sampling value until starting positions of OFDM symbols are determined according to an OFDM frame structure and autocorrelation peak value position distribution conditions to realizing symbol synchronization of the OFDM system. By the symbol synchronization method of the OFDM system, influences of channel fading and channel noise on symbol synchronization performance can be effectively overcome, so that extremely-high synchronization performance is acquired and hardware resources are saved.
Description
Technical field
The present invention relates to communication technical field, relate in particular to a kind of OFDM(Orthogonal Frequency Division Multiplexing, i.e. orthogonal frequency division multiplexi) symbol timing synchronization method of system.
Background technology
Ofdm system is a kind of multicarrier modulation system, and its technical essential is that channel is divided into several orthogonal sub-channels, then high-speed data signal is converted to parallel low speed sub data flow, is modulated at each subchannel again and transmits; This system has strong, the availability of frequency spectrum advantages of higher of ability of anti-multipath, therefore extensive use in communication engineering.
The data sync of ofdm system mainly comprises: sign synchronization (being frame synchronization), carrier frequency synchronization and sampling clock are synchronous.Sign synchronization is the key component of ofdm system, and the deviation of sign synchronization not only can cause intersymbol interference (Inter Symbol Interference is abbreviated as ISI usually), and may influence the normal transmission of subcarrier.
At present, the symbol timing synchronization method of OFDM mainly is divided three classes in the prior art: one is based on training sequence (Training Sequence, usually be abbreviated as TS) symbol timing synchronization method, two are based on the symbol timing synchronization method of Cyclic Prefix, the 3rd, do not use the symbol timing synchronization method of auxiliary data.In the symbol timing synchronization method based on training sequence, symbol timing synchronization method based on time-domain training sequence is most widely used, its technical essential is the autocorrelation according to time-domain training sequence, by detecting the position at auto-correlation peak, accurately orient the start-stop position of OFDM symbol, to realize the sign synchronization of OFDM.
Physical layer frame structure with the IEEE802.11a/g/n/p standard is example below, and the symbol timing synchronization method based on time-domain training sequence in the prior art is described in detail.As shown in Figure 1, adopt the STS(Short Training Sequence of 10 groups of cycles repetitions, i.e. short training sequence): t1～t10 is as the auxiliary sequencel of symbol timing synchronization method, and the length of every group of STS is 16 sampling periods; The STS that 10 groups of cycles that directly will receive repeat and the local known STS of 1 winding receiving end carry out auto-correlation computation, thereby obtain 10 auto-correlation peaks as shown in Figure 2; Just can determine the position that STS finishes by the position of detecting these 10 auto-correlation peaks, and then just can obtain the start-stop position of OFDM symbol according to the physical layer frame structure of IEEE802.11a/g/n/p standard fixed, thereby realize the sign synchronization of OFDM.
There is following shortcoming at least in above-mentioned OFDM symbol timing synchronization method of the prior art:
On hardware was realized, the maximum that detects serial input data not only very expended hardware resource, and needs logical circuit and the control circuit of more complicated.In order to save hardware resource, to simplify hardware designs, can adopt decision threshold to detect the auto-correlation peak-to-peak value, autocorrelation value is about to autocorrelation value (so-called autocorrelation value refers to the result of auto-correlation computation) and compares with decision threshold, if can assert then that greater than decision threshold this autocorrelation value is the auto-correlation peak-to-peak value; But because symbol timing synchronization method of the prior art is directly TS and the local known TS that receives to be carried out auto-correlation computation, therefore resulting autocorrelation value can be subjected to the influence of channel fading and interchannel noise and produce dynamic change, especially the auto-correlation peak-to-peak value is easy to be flooded by interchannel noise under fading channel or low signal-to-noise ratio situation, and this makes symbol timing synchronization method of the prior art to finish symbol synchronization process by setting a fixing decision threshold.
Summary of the invention
At existing technical problem in the above-mentioned prior art, the embodiment of the invention provides a kind of symbol timing synchronization method of ofdm system, so that effectively overcome channel fading and interchannel noise to the sign synchronization Effect on Performance, thereby not only obtained high net synchronization capability, and saved hardware resource, simplified hardware designs, be easy to production and processing.
The objective of the invention is to be achieved through the following technical solutions:
A kind of symbol timing synchronization method of ofdm system may further comprise the steps:
The first step, the current sampled value that receives and the sampled value of respectively organizing correspondence position among the training sequence TS that receives are before added up, obtain the post-sampling value that adds up of current sampled value;
Second the step, the post-sampling value that adds up of current sampled value is carried out quantification treatment, obtain the quantification post-sampling value of current sampled value;
The 3rd step, the quantification post-sampling value of the quantification post-sampling value of current sampled value and the sampled value that receives before is combined into one group of TS, and this TS and local known TS are carried out auto-correlation computation, obtain the autocorrelation value of current sampled value;
The 4th step, the autocorrelation value of current sampled value is carried out modulo operation and square operation successively, obtain the autocorrelation value of current sampled value behind the delivery square;
Whether the 5th step, the autocorrelation value of current sampled value behind the delivery square and default fixed sentence threshold values are compared, be auto-correlation peak-to-peak value position thereby determine current sampled value position;
The 6th goes on foot, each sampled value is all carried out according to five steps of the first step to the, auto-correlation peak-to-peak value position distribution situation is determined the original position of OFDM symbol in according to the frame structure of OFDM and the sampled value that received, thereby realizes the sign synchronization of ofdm system.
Preferably, accordingly the current sampled value that receives and the sampled value of correspondence position of respectively organizing among the training sequence TS that receives are before added up and comprise:
If the current sampled value that receives is k sampled value, and this sampled value belongs to l sampled value among the n group TS, then this sampled value and l the sampled value of respectively organizing among the TS that receive before added up, and its formula is as follows:
Wherein, R
kRepresent the post-sampling value that adds up of k sampled value, L represents the length of every group of TS; When j=0, r
(k-Lj)Represent k sampled value, i.e. l sampled value among the n group TS; When j=1,2 ...,
The time, r
(k-Lj)(k-Lj) individual sampled value of receiving before the expression, n-1, the n-2 that receives before namely ..., l sampled value among 1 group of TS.
Preferably, accordingly the quantification post-sampling value with the quantification post-sampling value of current sampled value and the sampled value that receives before is combined into one group of TS, and this TS and local known TS are carried out auto-correlation computation comprises:
If the current sampled value that receives is k sampled value, and the length of every group of TS is L, then with the quantification post-sampling value of k sampled value and the k-1, the k-2 that receive before ..., the individual sampled value of k-(L-1) quantification post-sampling value be combined into one group of TS, and this TS and local known TS carried out auto-correlation computation, its formula is as follows:
Wherein, C
kThe autocorrelation value of representing k sampled value, L represents the length of every group of TS, Q
K-l'The quantification post-sampling value of representing k-l' sampled value,
The complex conjugate of representing L-l' the value of local known TS; When l'=0, Q
K-l'The quantification post-sampling value of representing k sampled value,
The complex conjugate of representing L the value of local known TS; When l'=1,2 ..., during L-1, Q
K-l'Represent k-1, k-2 ..., the individual sampled value of k-(L-1) quantification post-sampling value,
Represent local known TS L-1, L-2 ..., 1 value complex conjugate.
Preferably, accordingly the post-sampling value that adds up of current sampled value being carried out quantification treatment comprises:
From the post-sampling value that adds up of current sampled value, extract real part and the imaginary part of the post-sampling value that adds up, and judge the add up real part of post-sampling value and the magnitude relationship of imaginary part and 0 respectively:
If add up real part＞0 of post-sampling value, the real part of the post-sampling value that then will add up is quantified as+and 1;
Real part＜0 of post-sampling value if add up, the real part of the post-sampling value that then will add up is quantified as-1;
If add up imaginary part＞0 of post-sampling value, the imaginary part of the post-sampling value that then will add up is quantified as+and 1;
Imaginary part＜0 of post-sampling value if add up, the imaginary part of the post-sampling value that then will add up is quantified as-1.
Whether preferably, accordingly the autocorrelation value of current sampled value behind the delivery square and default fixed sentence threshold values are compared, be that auto-correlation peak-to-peak value position comprises thereby determine current sampled value position:
If the autocorrelation value of current sampled value is greater than default fixed sentence threshold values behind the delivery square, then the autocorrelation value of current sampled value is the peak value at auto-correlation peak behind this delivery square, and namely this current sampled value position is auto-correlation peak-to-peak value position.
Preferably, the original position of accordingly determining the OFDM symbol according to auto-correlation peak-to-peak value position distribution situation in the frame structure of OFDM and the sampled value that received comprises:
If comprise the TS that the N group cycle repeats in the frame structure of OFDM, the length of every group of TS is L, and N auto-correlation peak-to-peak value position is evenly distributed in continuous (LN) individual sampled value, there is (L-1) individual sampled value between adjacent two auto-correlation peak-to-peak value positions, (L-1) individual sampled value before first auto-correlation peak-to-peak value position is the frame head original position of OFDM frame structure so, the sampled value of last auto-correlation peak-to-peak value position is the frame head final position of OFDM frame structure, and then the next sampled value that is close to last auto-correlation peak-to-peak value position is exactly the original position of OFDM symbol.
As seen from the above technical solution provided by the invention, the sampled value of correspondence position adds up the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides among the TS with respectively organizing of receiving before with the current sampled value that receives, thereby can be effectively level and smooth additivity random noise guarantees the accuracy of next step quantification treatment; The post-sampling value that adds up can effectively be removed the amplitude information that receives in the signal through quantification treatment, eliminate channel fading to the sign synchronization Effect on Performance, and the resulting autocorrelation value of next step auto-correlation computation is distributed in the fixing dynamic range, this not only is conducive to the setting of fixed sentence threshold values, and can realize saving all complex multipliers at hardware, therefore save hardware resource, simplified hardware designs; Simultaneously, in this symbol timing synchronization method, after the resulting autocorrelation value of auto-correlation computation needs to carry out modulo operation and square operation successively earlier, could compare with default fixed sentence threshold values, this feasible cross-correlation peak-to-peak value less than 1 is littler, auto-correlation peak-to-peak value greater than 1 is bigger, so this has further eliminated noise, has made things convenient for the setting of fixed sentence threshold values.This shows, the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides can effectively overcome channel fading and interchannel noise to the sign synchronization Effect on Performance, thereby not only obtained high net synchronization capability, and saved hardware resource, simplified hardware designs, be easy to production and processing.
Description of drawings
In order to be illustrated more clearly in the technical scheme of the embodiment of the invention, the accompanying drawing of required use is done to introduce simply in will describing embodiment below, apparently, accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite of not paying creative work, can also obtain other accompanying drawings according to these accompanying drawings.
Fig. 1 is the schematic diagram of IEEE802.11a/g/n/p physical layer frame structure in the prior art provided by the invention;
Fig. 2 is the schematic diagram at STS auto-correlation peak in the prior art provided by the invention;
The schematic flow sheet of the symbol timing synchronization method of the ofdm system that Fig. 3 provides for the embodiment of the invention;
The noise robustness schematic diagram one of the symbol timing synchronization method of the ofdm system that Fig. 4 provides for the embodiment of the invention;
The noise robustness schematic diagram two of the symbol timing synchronization method of the ofdm system that Fig. 5 provides for the embodiment of the invention;
Ber curve schematic diagram under the awgn channel that Fig. 6 provides for the embodiment of the invention;
Ber curve schematic diagram under single footpath rayleigh fading channel that Fig. 7 provides for the embodiment of the invention.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the invention, the technical scheme in the embodiment of the invention is clearly and completely described; Obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on embodiments of the invention, those of ordinary skills belong to protection scope of the present invention not making the every other embodiment that obtains under the creative work prerequisite.
At first need to prove, its scope of application of the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides is not limited to the IEEE802.11a/g/n/p standard, as long as the frame head targeting sequencing has adopted the N group TS that cycle with good autocorrelation repeats, so just can adopt the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides.
The symbol timing synchronization method of the ofdm system that the embodiment of the invention is provided is described in detail below.
As shown in Figure 3, a kind of symbol timing synchronization method of ofdm system specifically can may further comprise the steps:
The first step, the current sampled value that receives and the sampled value of respectively organizing correspondence position among the training sequence TS that receives are before added up, obtain the post-sampling value that adds up of current sampled value.
Particularly, comprise in the frame structure with OFDM that the N group cycle TS of repetition is example, the specific embodiments of this step can comprise:
If the current sampled value that receives is k sampled value, and this sampled value belongs to the individual sampled value of l(l among the n group TS≤L), then this sampled value and l the sampled value of respectively organizing among the TS that receive before added up, and its formula is as follows:
Wherein, R
kRepresent the post-sampling value that adds up of k sampled value, L represents the length of every group of TS; When j=0, r
(k-Lj)Represent k sampled value, i.e. l sampled value among the n group TS; When j=1,2 ...,
The time, r
(k-Lj)(k-Lj) individual sampled value of receiving before the expression, n-1, the n-2 that receives before namely ..., l sampled value among 1 group of TS.Not only can effectively level and smooth additivity random noise through the accumulation process of this step, and can guarantee the accuracy of next step quantification treatment.
Second the step, the post-sampling value that adds up of current sampled value is carried out quantification treatment, obtain the quantification post-sampling value of current sampled value.
Particularly, the specific embodiments of this step can comprise: extract real part and the imaginary part of the post-sampling value that adds up from the post-sampling value that adds up of current sampled value, and judge the add up real part of post-sampling value and the magnitude relationship of imaginary part and 0 respectively:
If add up real part＞0 of post-sampling value, the real part of the post-sampling value that then will add up is quantified as+and 1;
Real part＜0 of post-sampling value if add up, the real part of the post-sampling value that then will add up is quantified as-1;
If add up imaginary part＞0 of post-sampling value, the imaginary part of the post-sampling value that then will add up is quantified as+and 1;
Imaginary part＜0 of post-sampling value if add up, the imaginary part of the post-sampling value that then will add up is quantified as-1.
For example: the post-sampling value that adds up is 1.534-0.234i, and belonging to part in fact is 1.534, and imaginary part is-0.234; Because 1.534＞0, thus real part be quantified as+1; Because-0.234＜0, so imaginary part is quantified as-1; Through after the quantification treatment of this step, this post-sampling value corresponding quantitative post-sampling value that adds up is 1-1i.
Need to prove, not only can effectively remove the amplitude information that receives in the signal through the quantification treatment of this step, eliminate channel fading to the sign synchronization Effect on Performance, and the resulting autocorrelation value of next step auto-correlation computation is distributed in the fixing dynamic range, this not only is conducive to the setting of fixed sentence threshold values, and can realize saving all complex multipliers at hardware, and then have saved hardware resource, simplified hardware designs.
The 3rd step, the quantification post-sampling value of the quantification post-sampling value of current sampled value and the sampled value that receives before is combined into one group of TS, and this TS and local known TS are carried out auto-correlation computation, obtain the autocorrelation value of current sampled value.
Particularly, the specific embodiments of this step can comprise:
If the current sampled value that receives is k sampled value, and the length of every group of TS is L, then with the quantification post-sampling value of k sampled value and the k-1, the k-2 that receive before ..., the individual sampled value of k-(L-1) quantification post-sampling value be combined into one group of TS, and this TS and local known TS carried out auto-correlation computation, its formula is as follows:
Wherein, C
kThe autocorrelation value of representing k sampled value, L represents the length of every group of TS, Q
K-l'The quantification post-sampling value of representing k-l' sampled value,
The complex conjugate of representing L-l' the value of local known TS; When l'=0, Q
K-l'The quantification post-sampling value of representing k sampled value,
The complex conjugate of representing L the value of local known TS; When l'=1,2 ..., during L-1, Q
K-l'Represent k-1, k-2 ..., the individual sampled value of k-(L-1) quantification post-sampling value,
Represent local known TS L-1, L-2 ..., 1 value complex conjugate.
The 4th step, the autocorrelation value of current sampled value is carried out modulo operation and square operation successively, obtain the autocorrelation value of current sampled value behind the delivery square.
Particularly, symbol timing synchronization method of the prior art is directly TS and the local known TS that receives to be carried out auto-correlation computation, then the result of auto-correlation computation is asked successively and just can carry out peak value behind modular arithmetic and the square root calculation and detect, but the extraction of square root computing extremely expends hardware resource; And the symbol timing synchronization method in this step can make the cross-correlation peak-to-peak value less than 1 littler, auto-correlation peak-to-peak value greater than 1 is bigger, thereby widened the isolation strip width between auto-correlation peak-to-peak value and the cross-correlation peak-to-peak value, this not only can further eliminate interchannel noise, and can set the fixed sentence threshold values more easily.
Whether the 5th step, the autocorrelation value of current sampled value behind the delivery square and default fixed sentence threshold values are compared, be auto-correlation peak-to-peak value position thereby determine current sampled value position.
Wherein, in actual applications, default fixed sentence threshold values can adopt following method to determine:
Because ofdm system is when initial designs, just selected specific TS as the known local TS(of transmitting-receiving two-end be transmitting terminal and receiving terminal all with this TS as the known TS in this locality), therefore with this TS and self carry out auto-correlation computation and just can obtain an autocorrelation value, this autocorrelation value is exactly the auto-correlation peak-to-peak value under the ecotopia; Behind the auto-correlation peak-to-peak value of learning under the ecotopia, can be according to the interchannel noise situation of actual estimated or measurement, with 0.80～0.90 times (preferably 0.85 times) of the auto-correlation peak-to-peak value under the ecotopia fixed sentence threshold value as this ofdm system.For example, in the IEEE802.11a/p agreement, if one group of STS comprises 16 sampled values as shown in table 1 below, so this STS and self carry out auto-correlation computation after, auto-correlation peak-to-peak value under the ecotopia that obtains is 0.2032, then under white Gaussian noise channel (being awgn channel), the fixed sentence threshold value of this ofdm system can be got 0.2032*0.85=0.1727.In actual applications, after the fixed sentence threshold value of this ofdm system is initially determined, can be by carrying out the accuracy that the test of many times signal transmits to verify this fixed sentence threshold value at channel, also can carry out the fine setting of appropriateness as the case may be, to guarantee to possess reliable sign synchronization performance after ofdm system drops into normal the use.
Table 1:
| The ##(sequence number) | The Re(real part) | The Im(imaginary part) | The ##(sequence number) | The Re(real part) | The Im(imaginary part) |
| 0 | 0.046 | 0.046 | 1 | –0.132 | 0.002 |
| 2 | –0.013 | –0.079 | 3 | 0.143 | –0.013 |
| 4 | 0.092 | 0.000 | 5 | 0.143 | –0.013 |
| 6 | –0.013 | –0.079 | 7 | –0.132 | 0.002 |
| 8 | 0.046 | 0.046 | 9 | 0.002 | –0.132 |
| 10 | –0.079 | –0.013 | 11 | –0.013 | 0.143 |
| 12 | 0.000 | 0.092 | 13 | –0.013 | 0.143 |
| 14 | –0.079 | –0.013 | 15 | 0.002 | –0.132 |
| 16 | 0.046 | 0.046 | ? | ? | ? |
Particularly, last value of 1 group of TS that if the current sampled value that receives is transmitting terminal just to be sent, resulting autocorrelation value can be greater than default fixed sentence threshold values after the processing in these sampled value process four steps of the first step to the so, it is the auto-correlation peak-to-peak value that this autocorrelation value just can be regarded as, and namely Ci Shi current sampled value position is auto-correlation peak-to-peak value position.Last value of 1 group of TS that if the current sampled value that receives is not transmitting terminal to be sent, but the value of other parts of TS or the noise in the channel, resulting autocorrelation value all can be less than default fixed sentence threshold values after the processing in these sampled value process four steps of the first step to the so, in these autocorrelation value less than the fixed sentence threshold values, first is the cross-correlation peak-to-peak value for maximum.Therefore under the situation that does not have interchannel noise, when receiving terminal obtained an auto-correlation peak-to-peak value, receiving terminal just can assert that transmitting terminal begins transmission information.
The 6th goes on foot, each sampled value is all carried out according to five steps of the first step to the, auto-correlation peak-to-peak value position distribution situation is determined the original position of OFDM symbol in according to the frame structure of OFDM and the sampled value that received, thereby realizes the sign synchronization of ofdm system.
Particularly, because still there is the possibility that is subjected to the channel noise effect in an auto-correlation peak-to-peak value once in a while, and many group TS continuously that symbol timing synchronization method provided by the present invention can repeat in the employing cycle, be that receiving terminal can obtain a plurality of auto-correlation peak-to-peak values continuously in equal intervals, this has just significantly reduced the auto-correlation peak-to-peak value is the possibility that is subjected to the interchannel noise influence, thereby has greatly improved the performance of sign synchronization.Particularly, if comprise the TS that the N group cycle repeats in the frame structure of OFDM, the length of every group of TS is L, and N auto-correlation peak-to-peak value position is evenly distributed in continuous (LN) individual sampled value, there is (L-1) individual sampled value between adjacent two auto-correlation peak-to-peak value positions, (L-1) individual sampled value before first auto-correlation peak-to-peak value position is the frame head original position of OFDM frame structure so, and the sampled value of last auto-correlation peak-to-peak value position is the frame head final position of OFDM frame structure; Because the front end form of OFDM frame structure is " frame head+OFDM symbol ", the TS that the N group cycle repeats is exactly the frame head part, therefore the next sampled value that is close to frame head final position (being last auto-correlation peak-to-peak value position) is exactly that the original position of OFDM symbol (need to prove, can there be a plurality of continuous symbols in ofdm system, and what obtain is the original position of first OFDM symbol herein); Further, because the whole frame structure of OFDM all is known, therefore just can learns the start-stop position of each OFDM symbol according to the original position of first OFDM symbol, thereby realize the sign synchronization of ofdm system.
By technique scheme as can be seen, the realization of the embodiment of the invention not only can be saved hardware resource, be simplified hardware designs, and can effectively overcome channel fading and interchannel noise to the sign synchronization Effect on Performance, and then significantly promoted the net synchronization capability of this symbol timing synchronization method; Even the symbol timing synchronization method that also embodiment of the invention is provided under the situation of fading channel or low signal-to-noise ratio possesses preferable net synchronization capability.
For the content, purpose and the advantage that make technical solution of the present invention is clearer, be described in detail below by instantiation.
Embodiment one
Being example with the IEEE802.11a wireless local area network (WLAN) system in the ofdm system describes the specific implementation of the described technical scheme of the embodiment of the invention.The physical layer frame structure of IEEE802.11a comprises that the STS(of 10 groups of cycles repetitions is that t1～t10), the length of every group of STS is 16 sampling periods as shown in Figure 1, and the duration is 0.8 microsecond.
As shown in Figure 3, the symbol timing synchronization method of the ofdm system that provides of the embodiment of the invention can comprise the steps:
(1) the current sampled value that receives and the sampled value of respectively organizing correspondence position among the training sequence TS that receives are before added up, obtain the post-sampling value that adds up of current sampled value.
Particularly, if the current sampled value that receives is k sampled value, and this sampled value belongs to l(l≤16 among the n group TS) individual sampled value, then this sampled value and l the sampled value of respectively organizing among the TS that receives are before added up, its formula is as follows:
Wherein, R
kThe post-sampling value that adds up of representing k sampled value; When j=0, r
(k-16j)Represent k sampled value, i.e. l sampled value among the n group TS; When j=1,2 ...,
The time, r
(k-16j)(k-16j) individual sampled value of receiving before the expression, n-1, the n-2 that receives before namely ..., l sampled value among 1 group of TS.
(2) the post-sampling value that adds up of current sampled value is carried out quantification treatment, obtain the quantification post-sampling value of current sampled value.
(3) the quantification post-sampling value with the quantification post-sampling value of current sampled value and the sampled value that receives before is combined into one group of TS, and this TS and local known TS are carried out auto-correlation computation, obtains the autocorrelation value of current sampled value.
Particularly, if the current sampled value that receives is k sampled value, then with the quantification post-sampling value of k sampled value and the k-1, the k-2 that receive before ..., a k-15 sampled value quantification post-sampling value be combined into one group of TS, and this TS and local known TS carried out auto-correlation computation, its formula is as follows:
Wherein, C
kThe autocorrelation value of representing k sampled value, Q
K-l'The quantification post-sampling value of representing k-l' sampled value,
The complex conjugate of representing 16-l' the value of local known TS; When l'=0, Q
K-l'The quantification post-sampling value of representing k sampled value,
The complex conjugate of representing the 16th value of local known TS; When l'=1,2 ..., 15 o'clock, Q
K-l'Represent k-1, k-2 ..., a k-15 sampled value quantification post-sampling value,
Represent local known TS the 15th, 14 ..., 1 value complex conjugate.
(4) autocorrelation value of current sampled value is carried out modulo operation and square operation successively, obtain the autocorrelation value of current sampled value behind the delivery square.
Whether (5) autocorrelation value of current sampled value behind the delivery square and default fixed sentence threshold values (for example: this fixed sentence threshold values can be TH=2.4) are compared, be auto-correlation peak-to-peak value position thereby determine current sampled value position.
(6) each sampled value is all carried out according to five steps of the first step to the, auto-correlation peak-to-peak value position distribution situation is determined the original position of OFDM symbol in according to the frame structure of OFDM and the sampled value that received, thereby realizes the sign synchronization of ofdm system.
According to the technical scheme described in the present embodiment, when signal to noise ratio snr=10dB and signal to noise ratio snr=0dB, detect the noise robustness at each auto-correlation peak; The noise robustness schematic diagram at auto-correlation peak when Figure 4 shows that signal to noise ratio snr=10dB, its abscissa is represented the sampled point sequence number, ordinate represents that autocorrelation value surpasses the probability of fixed sentence threshold values; The noise robustness schematic diagram at auto-correlation peak when Figure 5 shows that signal to noise ratio snr=0dB, its abscissa is represented the sampled point sequence number, ordinate represents that autocorrelation value surpasses the probability of fixed sentence threshold values; Under the situation of default fixed sentence threshold values TH=2.4,160 sampled points of 10 groups of STS in 100000 frames to be added up, statistical content is the probability that surpasses the fixed sentence threshold values according to the resulting auto-correlation peak-to-peak value of technical scheme in the present embodiment.By Fig. 4 and Fig. 5 as can be known, when SNR dropped to 0dB by 10dB, the probability that the 10th auto-correlation peak-to-peak value (being the position of x=155) surpasses the fixed sentence threshold values remained 1, and its contiguous cross-correlation peak-to-peak value surpasses the probability of fixed sentence threshold values all less than 6e-005; Therefore the noise robustness at the 10th auto-correlation peak is best.This shows that the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides can obtain high sign synchronization performance under low signal-to-noise ratio.
Embodiment two
As shown in Figure 6, reflected that the distinct symbols method for synchronous of ofdm system is at AWGN(Additive White Gaussian Noise, i.e. additive white Gaussian noise) error rate simulation and analysis situation of channel and fading channel; Wherein, abscissa is represented signal to noise ratio snr (unit is dB), ordinate is represented the error rate, curve A represents to adopt the ber curve of symbol timing synchronization method in the prior art, curve B represents to adopt the ber curve of the symbol timing synchronization method that the embodiment of the invention provides, and curve C is represented the ber curve of ideal symbol method for synchronous; Simulation parameter arranges as follows: signal to noise ratio snr=-5～12dB, and no chnnel coding, nothing interweaves, the QPSK modulation, initial data is every frame 800bits, every curve emulation 1000 frames.As seen from Figure 6, under awgn channel, the ber curve of the ber curve of the symbol timing synchronization method that the embodiment of the invention provides and ideal symbol method for synchronous is identical substantially, and its net synchronization capability extreme difference of the symbol timing synchronization method of fixed sentence threshold values in the prior art.This shows that the sign synchronization performance of the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides under awgn channel and fading channel is far superior to symbol timing synchronization method in the prior art.
Embodiment three
As shown in Figure 7, the error rate simulation and analysis situation of distinct symbols method for synchronous under the rayleigh fading channel of single footpath that has reflected ofdm system; Wherein, abscissa is represented signal to noise ratio snr (unit is dB), ordinate is represented the error rate, curve D represents to adopt the ber curve of symbol timing synchronization method in the prior art, curve E represents to adopt the ber curve of the symbol timing synchronization method that the embodiment of the invention provides, and curve F represents the ber curve of ideal symbol method for synchronous; Simulation parameter arranges as follows: the average of path power gain is 0dB, and time delay is 0, signal to noise ratio snr=0～30dB, and no chnnel coding, nothing interweaves, the QPSK modulation, initial data is every frame 800bits, every curve emulation 1000 frames.As seen from Figure 7, under the rayleigh fading channel of single footpath, the ber curve of the ber curve of the symbol timing synchronization method that the embodiment of the invention provides and ideal symbol method for synchronous is identical substantially, and the symbol timing synchronization method of fixed sentence threshold values has lost net synchronization capability in the prior art.This shows that the sign synchronization performance of the symbol timing synchronization method of the ofdm system that the embodiment of the invention provides under the rayleigh fading channel of single footpath is far superior to symbol timing synchronization method in the prior art.
This shows that the enforcement of the embodiment of the invention can effectively overcome channel fading and interchannel noise to the sign synchronization Effect on Performance, thereby has not only obtained high net synchronization capability, and saved hardware resource, simplified hardware designs, be easy to production and processing.
The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.
Claims (6)
1. the symbol timing synchronization method of an ofdm system is characterized in that, may further comprise the steps:
The first step, the current sampled value that receives and the sampled value of respectively organizing correspondence position among the training sequence TS that receives are before added up, obtain the post-sampling value that adds up of current sampled value;
Second the step, the post-sampling value that adds up of current sampled value is carried out quantification treatment, obtain the quantification post-sampling value of current sampled value;
The 3rd step, the quantification post-sampling value of the quantification post-sampling value of current sampled value and the sampled value that receives before is combined into one group of TS, and this TS and local known TS are carried out auto-correlation computation, obtain the autocorrelation value of current sampled value;
The 4th step, the autocorrelation value of current sampled value is carried out modulo operation and square operation successively, obtain the autocorrelation value of current sampled value behind the delivery square;
Whether the 5th step, the autocorrelation value of current sampled value behind the delivery square and default fixed sentence threshold values are compared, be auto-correlation peak-to-peak value position thereby determine current sampled value position;
The 6th goes on foot, each sampled value is all carried out according to five steps of the first step to the, auto-correlation peak-to-peak value position distribution situation is determined the original position of OFDM symbol in according to the frame structure of OFDM and the sampled value that received, thereby realizes the sign synchronization of ofdm system.
2. the symbol timing synchronization method of ofdm system according to claim 1 is characterized in that, described the current sampled value that receives and the sampled value of correspondence position of respectively organizing among the training sequence TS that receives are before added up and comprise:
If the current sampled value that receives is k sampled value, and this sampled value belongs to l sampled value among the n group TS, then this sampled value and l the sampled value of respectively organizing among the TS that receive before added up, and its formula is as follows:
Wherein, R
kRepresent the post-sampling value that adds up of k sampled value, L represents the length of every group of TS; When j=0, r
(k-Lj)Represent k sampled value, i.e. l sampled value among the n group TS; When j=1,2 ...,
The time, r
(k-Lj)(k-Lj) individual sampled value of receiving before the expression, n-1, the n-2 that receives before namely ..., l sampled value among 1 group of TS.
3. the symbol timing synchronization method of ofdm system according to claim 2, it is characterized in that, described quantification post-sampling value with current sampled value is combined into one group of TS with the quantification post-sampling value of the sampled value that receives before, and this TS and local known TS are carried out auto-correlation computation comprises:
If the current sampled value that receives is k sampled value, and the length of every group of TS is L, then with the quantification post-sampling value of k sampled value and the k-1, the k-2 that receive before ..., the individual sampled value of k-(L-1) quantification post-sampling value be combined into one group of TS, and this TS and local known TS carried out auto-correlation computation, its formula is as follows:
Wherein, C
kThe autocorrelation value of representing k sampled value, L represents the length of every group of TS, Q
K-l'The quantification post-sampling value of representing k-l' sampled value,
The complex conjugate of representing L-l' the value of local known TS; When l'=0, Q
K-l'The quantification post-sampling value of representing k sampled value,
The complex conjugate of representing L the value of local known TS; When l'=1,2 ..., during L-1, Q
K-l'Represent k-1, k-2 ..., the individual sampled value of k-(L-1) quantification post-sampling value,
Represent local known TS L-1, L-2 ..., 1 value complex conjugate.
4. according to the symbol timing synchronization method of each described ofdm system in the claim 1 to 3, it is characterized in that the described post-sampling value that adds up to current sampled value is carried out quantification treatment and comprised:
From the post-sampling value that adds up of current sampled value, extract real part and the imaginary part of the post-sampling value that adds up, and judge the add up real part of post-sampling value and the magnitude relationship of imaginary part and 0 respectively:
If add up real part＞0 of post-sampling value, the real part of the post-sampling value that then will add up is quantified as+and 1;
Real part＜0 of post-sampling value if add up, the real part of the post-sampling value that then will add up is quantified as-1;
If add up imaginary part＞0 of post-sampling value, the imaginary part of the post-sampling value that then will add up is quantified as+and 1;
Imaginary part＜0 of post-sampling value if add up, the imaginary part of the post-sampling value that then will add up is quantified as-1.
5. according to the symbol timing synchronization method of each described ofdm system in the claim 1 to 3, it is characterized in that, whether described autocorrelation value with current sampled value behind the delivery square compares with default fixed sentence threshold values, be that auto-correlation peak-to-peak value position comprises thereby determine current sampled value position:
If the autocorrelation value of current sampled value is greater than default fixed sentence threshold values behind the delivery square, then the autocorrelation value of current sampled value is the peak value at auto-correlation peak behind this delivery square, and namely this current sampled value position is auto-correlation peak-to-peak value position.
6. according to the symbol timing synchronization method of each described ofdm system in the claim 1 to 3, it is characterized in that, described according to OFDM frame structure and the sampled value that received in the auto-correlation peak-to-peak value position distribution situation original position of determining the OFDM symbol comprise:
If comprise the TS that the N group cycle repeats in the frame structure of OFDM, the length of every group of TS is L, and N auto-correlation peak-to-peak value position is evenly distributed in continuous (LN) individual sampled value, there is (L-1) individual sampled value between adjacent two auto-correlation peak-to-peak value positions, (L-1) individual sampled value before first auto-correlation peak-to-peak value position is the frame head original position of OFDM frame structure so, the sampled value of last auto-correlation peak-to-peak value position is the frame head final position of OFDM frame structure, and then the next sampled value that is close to last auto-correlation peak-to-peak value position is exactly the original position of OFDM symbol.
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| CN106534016A (en) * | 2015-09-10 | 2017-03-22 | 中国科学院上海高等研究院 | Communication timing synchronization method and device |
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| CN114785653A (en) * | 2022-04-20 | 2022-07-22 | 桂林电子科技大学 | Symbol synchronization method, system, equipment and readable storage medium |
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| CN106534016A (en) * | 2015-09-10 | 2017-03-22 | 中国科学院上海高等研究院 | Communication timing synchronization method and device |
| CN110115007A (en) * | 2016-09-29 | 2019-08-09 | 夏普株式会社 | Terminal installation, base station apparatus, communication means and integrated circuit |
| CN108156108A (en) * | 2017-12-28 | 2018-06-12 | 锐捷网络股份有限公司 | A kind of start position of OFDM symbol determines method and apparatus |
| CN109088842A (en) * | 2018-09-03 | 2018-12-25 | 西安宇飞电子技术有限公司 | A kind of multiple simultaneous method and system for OFDM |
| CN109088842B (en) * | 2018-09-03 | 2021-02-02 | 西安宇飞电子技术有限公司 | Multiple synchronization method and system for OFDM |
| CN110224964A (en) * | 2019-06-12 | 2019-09-10 | 珠海市杰理科技股份有限公司 | Symbol timing synchronization method, device, receiver device and storage medium |
| CN110224964B (en) * | 2019-06-12 | 2021-10-15 | 珠海市杰理科技股份有限公司 | Symbol synchronization method, apparatus, receiver device and storage medium |
| CN114785653A (en) * | 2022-04-20 | 2022-07-22 | 桂林电子科技大学 | Symbol synchronization method, system, equipment and readable storage medium |
| CN114785653B (en) * | 2022-04-20 | 2023-08-04 | 桂林电子科技大学 | Symbol synchronization method, system, equipment and readable storage medium |
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