CN103997478A - Timing synchronization hardware implementation method of OFDM-WLAN system - Google Patents

Abstract

The invention provides a timing synchronization implementation method of an OFDM-WLAN system. According to the method, timing synchronization is implemented through combination of noise signals and an STF sequence with the length of 160 points. The method comprises the steps that the cumulative sum M (n) of L points of relevant calculation of signals received at the n moment and signals received at the moment of (160-L) before the n moment is calculated; the maximum value of the M(n) is found; an appropriate threshold value is set, a peak value is found, and the index position of the signals received at present and the number of delays from finding of the peak value to ending of peak detection are recorded through a counter; according to the obtained number of delays, delay adjustment is conducted on the received signals, and the initial position of a data symbol is determined finally; meanwhile, the received signal to noise ratio parameter having a statistical significance can be obtained through a small calculated amount and low complexity. By the adoption of the timing synchronization implementation method of the OFDM-WLAN system, adverse effects of noise amplification in the synchronization process can be restrained, the reliability of the found peak value is high, and hardware cost is reduced substantially.

Description

The Timing Synchronization Hardware Implementation of OFDM-WLAN system

Technical field

The invention belongs to wireless communication technology field, especially relate to the timing synchronization procedure of OFDM-WLAN system.

Background technology

OFDM (OFDM) is a kind of multi-carrier modulation technology, is widely used in high-speed radio local area network (LAN) (WLAN) transmission for example IEEE802.11a/n/ac agreement.Ofdm system can effectively be eliminated intersymbol interference (ISI), but multipath interference can make again the orthogonality between subcarrier be destroyed, thereby produces subcarrier interference (ICI).Introduce with the protection interval of Cyclic Prefix and can effectively resist ICI interference; but synchronously having relatively high expectations of this receiver for ofdm system, especially Timing Synchronization, if Timing Synchronization is accurate not; exceed the protection range of Cyclic Prefix, will cause the significantly decline of systematic function.

For this burst data transmission mode of OFDM-WLAN system, the general targeting sequencing that adopts is realized synchronously, targeting sequencing comprises the short training sequence (STF) of 10 repetitions and the long training sequence (LTF) of 2 repetitions, is mainly used in system synchronization, channel estimating, frequency deviation estimation, adaptive control etc.Existing lot of documents has proposed to realize based on short training sequence achieve frame Timing Synchronization and long training sequence comprehensive algorithm of timing synchronization before.

FPGA (Filed-Programmable Gate Array) is the most frequently used hardware development semi-custom circuit.Numerous associated auxiliary development products have also accelerated the step of the more new development of FPGA, and its Exploitation Scope is also more extensive.Utilize the PXI platform of National Instruments (NI) to carry out the FPGA exploitation of WLAN-OFDM system, break the tradition that hardware program language carries out FPGA exploitation, the programming idea of the LabVIEW of NI based on graphic language makes hardware development more convenient, construction cycle shortens greatly, makes hardware development personnel more energy can be placed on to algorithm and realizes.But, the resource of FPGA is limited after all, although the synchronization scenario performance based on STF sequence and LTF sequence is outstanding, but this type of algorithm amount of calculation is larger, complexity is higher, this has proposed huge hardware resource challenge to whole WLAN-OFDM the Hardware Design, is therefore necessary to seek the lower and efficient algorithm of performance of complexity.

K Wang, J Singh and M Faulkner has proposed the regular synchronization scheme of one " backward difference auto-correlation " algorithm based on STF sequence in " FPGA Implementation of an OFDM-WLAN Synchronizer " literary composition, utilizes the weak dependence between periodicity and strong correlation and STF sequence and the LTF sequence of STF sequence to form peak value.This algorithm amount of calculation is less, but because peak value is easily subject to channel circumstance shadow, skew or erroneous judgement occurs, thereby accuracy is not high.In the analogous diagram shown in Fig. 1, signal does not pass through channel, without any noise, in Fig. 1, first peak value of left side is the peak value of the excessive time generation of STF sequence and LTF sequence, but higher peak value has also appearred in data field, in hardware implementation procedure, this pseudo-peak value easily makes peak value detect and produces erroneous judgement.

Descendant has proposed the improvement algorithm of above-mentioned algorithm, i.e. " forward difference auto-correlation " algorithm.Before the STF sequence sending, introduce a small amount of noise sequence, realize timing synchronization thereby utilize low correlation between periodicity and strong correlation and STF sequence and the noise of STF sequence to form peak value.Meanwhile realize traditional frame Timing Synchronization algorithm, by suitable time delay adjustment, frame Timing Synchronization enable signal and timing synchronization enable signal are carried out to AND-operation, obtain the initial enable signal of final data symbol, realize complete Timing Synchronization.In the analogous diagram shown in Fig. 2, signal does not pass through channel, and without any noise, in Fig. 2, first peak value of left survey is the peak value that STF sequence and noise sequence produce when excessive.In this algorithm, what frame Timing Synchronization and timing synchronization produced combine enable signal has ensured the correctness of search peak, but compared to K Wang, the algorithm that J Singh and M Faulkner proposes, this algorithm has consumed more fpga logic resource, and in actual channel environment, still has certain synchronous error probability.In addition, the thought of autocorrelation relates to the subtraction operation of autocorrelation value, and this has the side effect of amplification for the noise in signal, thereby net synchronization capability can decline to some extent.

Therefore, the synchronous realization of WLAN-OFDM system not only needs to consider accuracy, also needs to consider hardware resource utilization simultaneously.

Summary of the invention

In order to overcome above-mentioned simultaneous techniques problem of running in hardware is realized, the invention provides that a kind of operand is less, complexity is low and the time synchronization method of the original position of specified data symbol rapidly and accurately; Meanwhile, the realization of the hardware of this algorithm can utilize less operand and complexity to be similar to and obtain a received signal to noise ratio parameter with statistical significance.

For achieving the above object, the invention provides a kind of Timing Synchronization Hardware Implementation of OFDM-WLAN system, the autocorrelation performance that is the STF sequence of 160 in conjunction with noise signal and length is realized Timing Synchronization, comprises the following steps:

(1.1) definition M (n) receives the L point cumulative sum of the related operation of signal and front (160-L) moment reception signal for the n moment

$M\left(n\right)=\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}r(n+m-(160-L))\×r^{*}(n+m)$

(1.2) definition η is notation index undetermined position, in the time that all cumulative information in M (n) all concentrates on STF sequence, be that L point auto-correlation computation is all within the scope of STF sequence time, now find the maximum of M (n), the L point that is STF sequence receives signal energy value; Now the index position η of signal just in time drops on the afterbody that receives signal STF sequence

$\mathrm{\η}=\arg \underset{n}{\max }\left(\right|M\left(n\right)\left|\right)$

(1.3) set one group of suitable threshold value (thre ₁, thre ₂), and at threshold value thre ₁～thre ₂scope in the searching peak value that may exist, and utilize counter to write down the index position η of current time signal and count delaynum from finding this peak value to start to finish experienced time delay to peak detection process;

(1.4) delaynum obtaining according to step (1.3) carries out time delay adjustment to received signal, final specified data symbol original position.

Preferably, the Timing Synchronization Hardware Implementation of described OFDM-WLAN system, in carrying out timing synchronization, is carried out following steps:

(2.1) taking the signal energy of the STF sequence that receives as the energy with reference to weighing whole signal, the default L point energy threshold that definition transmits is P ₀; In step (1.3), utilize auto-correlation accumulator module, the peak value of acquisition is the L point energy value of the STF sequence of reception, is defined as P _sTF;

(2.2) by P _sTFwith P ₀do business's comparison, the Coefficient Definition of acquisition is , the expectation amplification coefficient of the next frame signal using α as radiofrequency emitting module;

(2.3) establishing the expectation amplification coefficient that the measurement of the i time signal energy obtains is α _i+1if, α _i+1while exceeding the amplification range of amplifier, with the actual amplification upper limit α of amplifier _maxas the actual amplification coefficient of the i+1 time signal energy, otherwise with α _i+1as the actual amplification coefficient of the i+1 time signal energy;

(2.4) repeat said process, after limited number of time operation, expect that amplification coefficient α will be stabilized near 1, the energy that receives signal is controlled in default energy threshold P ₀near, thereby realize automatic gain control, be threshold value (thre in step (1.3) ₁, thre ₂) setting direct reference frame is provided.

Further, the Timing Synchronization Hardware Implementation of described OFDM-WLAN system can also be realized the measurement of the received signal to noise ratio parameter with statistical significance, comprises the following steps:

(3.1) according to the synchronizing information obtaining, to noise field, utilize energy computing module to obtain 1 L spot noise energy through suitable time delay localization, be designated as ω ₁;

(3.2) repeatedly repeat said process, the mean value that calculates L spot noise energy can obtain the noise power value of statistical significance, is designated as ${\mathrm{\ω}}_0=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\ω}}_i$ ；

(3.3) STF sequence energy P step (2.1) being recorded ₀with noise energy ω ₀do business, thereby obtain the received signal to noise ratio in statistical significance, be designated as ${\mathrm{SNR}}_0=10\×{\log }_{10}\frac{P_0}{{\mathrm{\ω}}_0}$ 。

Beneficial effect: Timing Synchronization implementation method provided by the invention can contain and amplify the adverse effect that noise brings in synchronizing process, with a high credibility while finding peak value, and reduced the expense of quite a few hardware resource.

Brief description of the drawings

Fig. 1 is the schematic diagram of backward difference peak value that auto-correlation algorithm forms;

Fig. 2 is the schematic diagram of forward difference peak value that auto-correlation algorithm forms;

Fig. 3 is the schematic diagram of the Timing Synchronization algorithm of preferred embodiment of the present invention while obtaining peak value;

Fig. 4 is the peak value schematic diagram that the Timing Synchronization algorithm of preferred embodiment of the present invention forms;

Fig. 5 is that the Performance Ratio of algorithm of the present invention and backward difference auto-correlation and forward difference auto-correlation algorithm is compared with schematic diagram.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

According to preferred embodiment of the present invention, the Timing Synchronization design realizing for OFDM-WLAN system hardware comprises following steps:

(1) be autocorrelation performance and the conventional synchronization algorithm of the STF sequence of 160 in conjunction with noise signal and length, now propose a kind of Novel timing synchronized algorithm, specific implementation step is as follows:

(1.1) definition M (n) receives the L point cumulative sum of the related operation of signal and front (160-L) moment reception signal for the n moment

$M\left(n\right)=\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}r(n+m-(160-L))\×r^{*}(n+m)$

Fig. 3 has shown autocorrelation calculation when Timing Synchronization hardware scheme based on IEEE802.11acWLAN o'clock searches out peak value in parameter L=48.

(1.2) definition η is notation index undetermined position, in the time that all cumulative information in M (n) all concentrates on STF sequence, be that L point auto-correlation computation is all within the scope of STF sequence time, now find the maximum of M (n), the L point that is STF sequence receives signal energy value.Now the index position η of signal just in time drops on the afterbody that receives signal STF sequence.

$\mathrm{\η}=\arg \underset{n}{\max }\left(\right|M\left(n\right)\left|\right)$

Fig. 4 is the peak value schematic diagram that this algorithm forms, and can find out that this peak value is very obvious, and this sets most important to the threshold value in step (1.3).

(1.3), when hardware is realized peak value searching, need to be one group of suitable threshold value (thre of this process setting ₁, thre ₂), at thre ₁～thre ₂scope in the searching peak value that may exist.When | M (n) | > thre ₁time, enter peak value searching state, record now | M (n) | be λ _max.Whenever new | M (n) | meet | M (n) | > λ _maxtime, upgrade λ _maxfor current | M (n) |, and utilize counter to write down the location index of current time signal.Constantly repeat said process until | M (n) | < thre ₂, now peak detection process finishes, current λ _maxbe peak value, and utilize counter to write down from finding this peak value to start to finish experienced time delay number to peak detection process, be defined as delaynum.

(1.4) delaynum obtaining according to step (1.3) carries out the time delay adjustment of delaynum clock to received signal, final specified data symbol original position.

(2) in carrying out timing synchronization, in order to utilize all the time the threshold value (thre setting in step (1.3) ₁, thre ₂) search out and receive accurately signal index position η, need to allow receive signal energy and be stabilized near a certain energy value, realize automatic gain control.Specific implementation step is as follows:

(2.1) taking the signal energy of the STF sequence that receives as the energy with reference to weighing whole signal, the default L point energy threshold that definition transmits is P ₀.In step (1.3), utilize auto-correlation accumulator module, the peak value of acquisition is the L point energy value of the STF sequence of reception, is defined as P _sTF.

(2.2) by P _sTFwith P ₀do business's comparison, the Coefficient Definition of acquisition is .The expectation amplification coefficient of the next frame signal using α as radiofrequency emitting module.

(2.3) establishing the expectation amplification coefficient that the measurement of the i time signal energy obtains is α _i+1if, α _i+1while exceeding the amplification range of amplifier, with the actual amplification upper limit α of amplifier _maxas the actual amplification coefficient of the i+1 time signal energy, otherwise with α _i+1as the actual amplification coefficient of the i+1 time signal energy.

(2.4) repeat said process, after limited number of time operation, expect that amplification coefficient α will be stabilized near 1, the energy that receives signal is controlled in default energy threshold P ₀near, thereby realize automatic gain control, be threshold value (thre in step (1.3) ₁, thre ₂) setting direct reference frame is provided.

Choose energy threshold P ₀time, should be noted that energy can not exceed the range of reception antenna AD conversion, to prevent from receiving signal generation peak clipping distortion; While energy also should not be chosen too small, otherwise can reduce because of the restriction of AD precision the performance of timing synchronization.

(3) according to acquired synchronizing information, to noise field, utilize energy computing module through suitable time delay localization, can obtain L spot noise energy 1 time, be designated as ω ₁.Repeatedly repeat said process, the mean value that calculates L spot noise energy can obtain the noise power value of statistical significance, is designated as .The STF sequence energy that step (2.1) is recorded and noise energy ω ₀do business, thereby obtain the received signal to noise ratio in statistical significance, be designated as .

Further illustrate implementation method below in conjunction with actual hardware designs.In the present embodiment, Timing Synchronization design and snr computation be on Virtex-5 type FPGA, complete, taking the LabVIEW2012 of NI as hardware development instrument, based on IEEE802.11ac agreement, system bandwidth is 20MHz.The method comprises the following steps:

(1) be autocorrelation performance and the conventional synchronization algorithm autocorrelation characteristic of the STF sequence of 160 in conjunction with noise signal and length, now propose a kind of Novel timing synchronized algorithm, specific implementation step is as follows:

(1.1) signal of reception antenna being received is demodulated to base band, by 112 delayers, is exported 48 cumulative sums making related operation with the reception signal of current time, obtains M (n).

$M\left(n\right)=\underset{m=0}{\overset{47}{\mathrm{\&Sigma;}}}r(n+m-112)\&times;r^{*}(n+m)$

Fig. 3 has shown autocorrelation calculation when Timing Synchronization hardware scheme based on IEEE802.11acWLAN o'clock searches out peak value in parameter L=48.

(1.2) definition η is notation index undetermined position, in the time that all cumulative information in M (n) all concentrates on STF sequence, when 48 auto-correlation computations are all within the scope of STF sequence, now find the maximum of M (n), 48 that are STF sequence receive signal energy value.Now the index position η of signal just in time drops on the afterbody of STF lead code.

$\mathrm{\&eta;}=\arg \underset{n}{\max }\left(\right|M\left(n\right)\left|\right)$

Fig. 4 is the peak value schematic diagram that this algorithm forms.With in Fig. 1 by K Wang, the peak value that the peak value that the backward difference auto-correlation algorithm that J Singh and M Faulkner proposes forms and the forward difference auto-correlation algorithm of Fig. 2 form is compared, this peak value is very obvious, and this sets most important to the threshold value in step (1.3).

(1.3), when hardware is realized peak value searching, need to be one group of suitable threshold value (thre of this process setting ₁, thre ₂), at thre ₁～thre ₂scope in the searching peak value that may exist.When | M (n) | > thre ₁time, enter peak value searching state, record now | M (n) | be λ _max.Whenever new | M (n) | meet | M (n) | > λ _maxtime, upgrade λ _maxfor current | M (n) |, and utilize counter to write down the location index of current time signal.Constantly repeat said process until | M (n) | < thre ₂, now peak detection process finishes, current λ _maxbe peak value, and utilize counter to write down from finding this peak value to start to finish experienced time delay number to peak detection process, be defined as delaynum.

(1.4) carry out to received signal the time delay adjustment of delaynum clock according to the delaynum obtaining in step (1.3), final specified data symbol original position.

(2) in carrying out timing synchronization, in order to utilize all the time the threshold value (thre setting in step (1.3) ₁, thre ₂) search out and receive accurately signal index position η, need to allow receive signal energy and be stabilized near a certain energy value, realize automatic gain control.Specific implementation step is as follows:

(2.1), because the channel circumstance of OFDM-WLAN system is comparatively complicated, antenna moves and can cause receiving signal energy and constantly change in addition.For an OFDM-WLAN system that robustness is stronger, only make to receive the stable threshold value (thre that could utilize setting in step (1.3) of signal energy ₁, thre ₂) carry out peak value searching and complete Timing Synchronization.The signal energy of the STF sequence of supposing to receive is with reference to the energy of weighing whole signal, i.e. default 48 energy thresholds that definition transmits are P ₀.In step (1.3), utilize auto-correlation accumulator module, the peak value of acquisition is 48 energy values of the STF sequence of reception, is defined as P _sTF.

(2.2) by P _sTFwith P ₀do business's comparison, the Coefficient Definition of acquisition is .The expectation amplification coefficient of the next frame signal using α as radiofrequency emitting module.

(2.3) establishing the expectation amplification coefficient that the measurement of the i time signal energy obtains is α _i+1if, α _i+1while exceeding the amplification range of amplifier, with the actual amplification upper limit α of amplifier _maxas the actual amplification coefficient of the i+1 time signal energy, otherwise with α _i+1as the actual amplification coefficient of the i+1 time signal energy.

(2.4) repeat said process, after limited number of time operation, expect that amplification coefficient α will be stabilized near 1, the energy that receives signal is controlled in default energy threshold P ₀near, thereby realize automatic gain control, be threshold value (thre in step (1.3) ₁, thre ₂) setting direct reference frame is provided.

Choose energy threshold P ₀time, should be noted that energy can not exceed the range of reception antenna AD conversion, to prevent from receiving signal generation peak clipping distortion; While energy also should not be chosen too small, otherwise can reduce because of the restriction of AD precision the performance of timing synchronization.In the present embodiment, P is set ₀=1.2 (taking the logarithm as 0.8dBm).

(3) according to acquired synchronizing information, to noise field, utilize energy computing module through suitable time delay localization, can obtain 16 spot noise energy 1 time, be designated as ω ₁.Repeat said process 16 times, the mean value that calculates the 16 spot noise energy that obtain for 16 times can obtain the noise power value of statistical significance, is designated as .48 STF sequence energy P in step (2.1), are obtained _sTF, and by automatic gain control, energy is limited to P ₀near.Thereby 16 energy of STF sequence are p ₀, by this value and noise energy ω ₀do business, thereby obtain the received signal to noise ratio parameter in statistical significance, be designated as ${\mathrm{SNR}}_0=10\&times;{\log }_{10}\frac{P_0}{3{\mathrm{\&omega;}}_0}$ 。

Algorithm of the present invention is compared with forward difference auto-correlation algorithm with known backward difference auto-correlation algorithm, has following advantage:

1. the characteristic that does not re-use autocorrelation is carried out timing synchronization, and this can contain and in synchronizing process, amplifies the adverse effect that noise brings.

2. the confidence level of finding M (n) peak value is higher, and in the time of SNR>2dB, peak value False Rate is lower than-40dB, and this mentions that than before algorithm has remarkable lifting in performance.

3. this Timing Synchronization algorithm can be realized preferably timing synchronization process of performance without the auxiliary of frame Timing Synchronization module, has reduced the expense of quite a few hardware resource.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (3)

1. a Timing Synchronization Hardware Implementation for OFDM-WLAN system, the autocorrelation performance that is the STF sequence of 160 in conjunction with noise signal and length is realized Timing Synchronization, it is characterized in that, comprises the following steps:

(1.1) definition M (n) receives the L point cumulative sum of the related operation of signal and front (160-L) moment reception signal for the n moment

$M\left(n\right)=\underset{m=0}{\overset{L-1}{\mathrm{\&Sigma;}}}r(n+m-(160-L))\&times;r^{*}(n+m)$

(1.2) definition η is notation index undetermined position, in the time that all cumulative information in M (n) all concentrates on STF sequence, be that L point auto-correlation computation is all within the scope of STF sequence time, now find the maximum of M (n), the L point that is STF sequence receives signal energy value; Now the index position η of signal just in time drops on the afterbody that receives signal STF sequence

$\mathrm{\&eta;}=\arg \underset{n}{\max }\left(\right|M\left(n\right)\left|\right)$

(1.3) set one group of suitable threshold value (thre ₁, thre ₂), and at threshold value thre ₁～thre ₂scope in the searching peak value that may exist, and utilize counter write down the index position η of current time signal and certainly find this peak value to start to finish experienced time delay to peak detection process and count delaynum;

(1.4) delaynum obtaining according to step (1.3) carries out time delay adjustment to received signal, final specified data symbol original position.

2. the Timing Synchronization Hardware Implementation of OFDM-WLAN system according to claim 1, wherein, in carrying out timing synchronization, carry out following steps:

(2.1) taking the signal energy of the STF sequence that receives as the energy with reference to weighing whole signal, the default L point energy threshold that definition transmits is P ₀; In step (1.3), utilize auto-correlation accumulator module, the peak value of acquisition is the L point energy value of the STF sequence of reception, is defined as P _sTF;

(2.2) by P _sTFwith P ₀do business's comparison, the Coefficient Definition of acquisition is , the expectation amplification coefficient of the next frame signal using α as radiofrequency emitting module;

(2.3) establishing the expectation amplification coefficient that the measurement of the i time signal energy obtains is α _i+1if, α _i+1while exceeding the amplification range of amplifier, with the actual amplification upper limit α of amplifier _maxas the actual amplification coefficient of the i+1 time signal energy, otherwise with α _i+1as the actual amplification coefficient of the i+1 time signal energy;

(2.4) repeat said process, after limited number of time operation, expect that amplification coefficient α will be stabilized near 1, the energy that receives signal is controlled in default energy threshold P ₀near, thereby realize automatic gain control, be threshold value (thre in step (1.3) ₁, thre ₂) setting direct reference frame is provided.

3. the Timing Synchronization Hardware Implementation of OFDM-WLAN system according to claim 1 and 2, its feature is further comprising the steps of:

(3.1) according to synchronizing information, to noise field, utilize energy computing module to obtain 1 L spot noise energy through suitable time delay localization, be designated as ω ₁;

(3.2) repeatedly repeat said process, the mean value that calculates L spot noise energy can obtain the noise power value of statistical significance, is designated as ${\mathrm{\&omega;}}_0=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{\mathrm{\&omega;}}_i$ ；

(3.3) STF sequence energy P step (2.1) being recorded ₀with noise energy ω ₀do business, thereby obtain the received signal to noise ratio in statistical significance, be designated as ${\mathrm{SNR}}_0=10\&times;{\log }_{10}\frac{P_0}{{\mathrm{\&omega;}}_0}$ 。