CN101039306A - Semi-blind intelligent synchronization method and apparatus fitted for 802.11a system - Google Patents

Abstract

An intelligent synchronization method and device with semi-blind type can reduce error probability of transmission packet, enhance effective signal-to-noise ratio and information transmission rate, and reduce waste of bandwidth, suitable for IEEE802.11a system. The device includes two parts-a sender and a receiver: the sender includes a Pilot information module, a training sequence module, a cyclic prefix module; the receiver includes a blind synchronization estimation module. The device is characterized by arranging a frequency and phrase detection module at the receiver, for estimating the offset of frequency and phrase of the transmitting data in the system; a compensating module is added to the sender, to compensate the deviation of frequency and phrase estimated at the receiver.

Description

Be applicable to the semi-blind intelligent synchronization method and the device of 802.11a system

Technical field

The present invention relates to the synchronized algorithm of ofdm system, be a kind of based on blind synchronously and the semi-blind intelligent synchronized algorithm of non-blind synchronized algorithm thought.This algorithm is applicable to the IEEE802.11a system, belongs to radio communication WLANs technical field.

Background technology

What the IEEE802.11a system adopted is the OFDM multi-carrier modulation technology, compare with traditional single-carrier system, ofdm system is very responsive to synchronous error, realize a communication system based on OFDM, must guarantee the precise synchronization of system, therefore, simultaneous techniques is a very important key technology in the 802.11a system.

Mobile radio system of future generation requires to provide the multimedia service of high-speed wideband, but in the communication system of high-speed mobile, it is ubiquitous problem that multipath transmisstion causes intersymbol interference (ISI).OFDM (OFDM) has characteristics such as the anti-multipath interference performance is strong, availability of frequency spectrum height, therefore is very suitable for high-speed radiocommunication system.In recent years, the 0FDM technology has been widely used in the standards such as general switch telephone network (GSTN), cellular radio (Cellular radio), DTB Digital Terrestrial Broadcasting TV (DVB-T), the transmission of floor synthetic service digits (ISDB-T), asymmetric digital subscriber line system (ADSL), high performance radio local area network (HYPERLAN/2), IEEE802.11a.

In recent years, there are a lot of scholars to be devoted to study the synchronized algorithm of ofdm system both at home and abroad, also have a lot of papers specifically to introduce synchronized algorithm.For OFDM synchronously, Chinese scholars has proposed a lot of algorithms from each emphasis, can be divided into two big classes haply: non-blind synchronized algorithm and blind synchronized algorithm.Non-blind synchronized algorithm is the method for synchronous of priori symbol, roughly be divided into training sequence is arranged, pilot frequency information and several forms of Cyclic Prefix.

Non-blind synchronized algorithm be based on the priori sequence carry out synchronously, transmission accuracy rate height, but shortcoming clearly, estimates that required symbol is long, estimated accuracy and frequency offset estimation range are less.If will make the sign synchronization of system accurately reliable, just must increase non-blind synchronous length or do relevant a large amount of continuous OFDM symbols.Can reduce so the side effect of this algorithm is an effective signal-to-noise ratio, simultaneity factor can not be applicable to burst, the short signal intelligence of information interval.Therefore, the method is not suitable for packet-based burst data transmission system.

Blind synchronized algorithm does not need to waste any bandwidth, but higher to the time synchronized performance requirement of system, and accuracy of estimation is limited synchronously.So blind synchronized algorithm is poorer than the performance of non-blind synchronized algorithm.

Traditional 802.11a's is to utilize the symbol of priori to carry out synchronously, but no matter be to use Cyclic Prefix, pilot frequency information or training sequence, all will certainly cause certain bandwidth waste.If the net synchronization capability of system requirements is very high, the knowledge symbol of these priori also can increase accordingly, will cause more waste situation, so this method reaches synchronous purpose to sacrifice effective signal-to-noise ratio.

Summary of the invention

At the shortcoming that exists in the said method, the needs that the present invention considers to reduce bandwidth waste simultaneously and improves net synchronization capability, blind synchronized algorithm and non-blind synchronized algorithm are combined, propose a kind of semi-blind intelligent synchronization method and device that is applicable to the 802.11a system.

The technical solution adopted for the present invention to solve the technical problems is:

Be applicable to the semi-blind intelligent synchronization method of 802.11a system, when transmitting terminal OFDM framing, add pilot frequency information and training sequence, after the zero padding through adding Cyclic Prefix after the IFFT computing, receiving terminal carries out demodulation to received signal, it is characterized in that also comprising the following steps:

(1) separates timing at receiving terminal and add the coherent detection algorithm, carry out coherent detection to the received signal, its phase place and symbol are estimated prediction synchronously, and output is used for representing the deviant of phase place and symbol;

(2) delay time and the compensation of phase place at transmitting terminal.

Receiving terminal coherent detection time estimation formulas is: $-\frac{1}{2\mathrm{\π}}\arg \left(\underset{m=0}{\overset{\mathrm{LN}-1}{\mathrm{\Σ}}}{\left|x_{m+1}\right|}^2\exp (-j2\mathrm{\πm}/N)\right),$ Wherein, L is every frame symbolic number, and N is the sampled value of each symbol; Receiving terminal coherent detection phase estimation formula is: $\frac{1}{M}\arg \left\{\underset{k=1}{\overset{L}{\mathrm{\Σ}}}{\left(x\left(k\right)\right)}^M\right\}.$

Be applicable to the device of the semi-blind intelligent synchronization method of 802.11a system, comprise transmitting terminal and receiving terminal, transmitting terminal comprises pilot frequency information module, training sequence module, cyclic prefix module; Receiving terminal comprises blind synchronous estimation module.It is characterized in that the frequency plot detection module being set, be used for prognoses system transmission data frequency and phase pushing figure at receiving terminal; Add compensating module at transmitting terminal, the frequency that receiving terminal is measured and the deviation of phase place compensate phase compensating module as shown in Figure 1.

Described pilot frequency information module is followed maximum likelihood (ML) estimation principle, adopts pilot tone and protection to unite at interval and carries out synchronously.

Described training sequence module is Given information to be added to wait the OFDM symbol sent out on time domain based on the synchronized algorithm of training sequence, places usually before the OFDM symbol or the front portion of the frame that is made of a plurality of OFDM symbols.

Described cyclic prefix module, the data in the Cyclic Prefix are duplicating of an OFDM symbol Back end data, are in order to eliminate the intersymbol interference (ISI) that multipath causes, and the signal of inserting in protection at interval is Cyclic Prefix (CP).

Effect of the present invention is: the semi-blind intelligent synchronization method that is applicable to the 802.11a system, non-blind synchronous and blind synchronous advantages is separately got up, can be under the prerequisite of not wasting too much bandwidth resources, realize better OFDM synchronously, the synchronous prediction accuracy of system improves, and bandwidth waste reduces.

The symbol lengths of IEEE802.11a system emulation is 64; Modulation system is an Adaptive Modulation, can select according to system's needs, has 1/2BPSK, 3/4BPSK, 1/2QPSK, 3/4QPSK, 1/216-QAM, 3/416-QAM, eight kinds of modulation systems of 2/364-QAM, 3/464-QAM to select; The channel circumstance of simulation is multipath and awgn channel, supposes that simultaneously maximum doppler frequency is 200Hz; Receiving terminal has adopted balancing technique to carry out equilibrium to the received signal, and demodulation mode also is corresponding with transmitting terminal, is all controlled by a mode index signal; By the signal of initial input and the signal of last output are compared, transport packet error probability, the signal to noise ratio that can draw system also have parameters such as bit rate.

The present invention has the following advantages: (1), take all factors into consideration blind synchronized algorithm and non-blind synchronized algorithm combines the two advantage.The priori symbol lengths of non-blind synchronized algorithm is reduced, promptly can reduce the waste of bandwidth; (2), the blind synchronized algorithm that adds coherent detection at receiving terminal carries out synchronously, and compensates at transmitting terminal.Improve synchronous predictive ability, and effectively remedied the loss that the minimizing of priori symbol brings, reduced signal to noise ratio.The present invention has certain advantage on bandwidth waste still is the performance of performances such as signal to noise ratio.

Description of drawings

Below in conjunction with drawings and Examples the present invention is described in further detail.

Fig. 1 is the system block diagram of semi-blind intelligent synchronized algorithm of the present invention;

Fig. 2 is an IEEE802.11a system model of the present invention;

Fig. 3 is the blind sync correlation detection algorithm of a receiving terminal of the present invention block diagram.

Embodiment

Be applicable to the semi-blind intelligent synchronization method of 802.11a system, when transmitting terminal OFDM framing, add pilot frequency information and training sequence, after the zero padding through adding Cyclic Prefix after the IFFT computing, receiving terminal carries out demodulation to received signal, it is characterized in that also comprising the following steps:

(1) separates timing at receiving terminal and add the coherent detection algorithm, carry out coherent detection to the received signal, its phase place and symbol are estimated prediction synchronously, and output is used for representing the deviant of phase place and symbol; (2) delay time and the compensation of phase place at transmitting terminal.Receiving terminal coherent detection time estimation formulas is: $-\frac{1}{2\mathrm{\π}}\arg \left(\underset{m=0}{\overset{\mathrm{LN}-1}{\mathrm{\Σ}}}{\left|x_{m+1}\right|}^2\exp (-j2\mathrm{\πm}/N)\right),$ Wherein, L is every frame symbolic number, and N is the sampled value of each symbol; Receiving terminal coherent detection phase estimation formula is:

$\frac{1}{M}\arg \left\{\underset{k=1}{\overset{L}{\mathrm{\Σ}}}{\left(x\left(k\right)\right)}^M\right\}.$

Among Fig. 1, the system block diagram of semi-blind intelligent synchronized algorithm of the present invention, at transmitting terminal, link to each other with the training sequence module with the pilot frequency information module in the ofdm signal module, after adding the ofdm signal process IFFT conciliation of pilot frequency information and training sequence, add Cyclic Prefix, send through phase compensation back.At receiving terminal, the signal that receives goes circulation prefix processing through the past cyclic prefix module, passes through the FFT demodulation then, after the demodulation respectively through removing training sequence module, equalizer, go the pilot frequency information module, separating and be in harmonious proportion to detect the synchronous interference module and handle.

Among Fig. 2, be applicable to the device of the semi-blind intelligent synchronization method of 802.11a system, comprise transmitting terminal and receiving terminal, transmitting terminal comprises pilot frequency information module, training sequence module, cyclic prefix module, at receiving terminal frequency plot detection module (referring to Fig. 3) is set, is used for prognoses system transmission data frequency and phase pushing figure; Add compensating module at transmitting terminal, the frequency that receiving terminal is measured and the deviation of phase place compensate.The pilot frequency information module is followed maximum likelihood (ML) estimation principle; adopting pilot tone and protection to unite at interval carries out synchronously; the training sequence module; based on the synchronized algorithm of training sequence is Given information to be added to wait the OFDM symbol sent out on time domain; the front portion of the frame that places usually before the OFDM symbol or constitute by a plurality of OFDM symbols; cyclic prefix module; data in the Cyclic Prefix are duplicating of an OFDM symbol Back end data; be in order to eliminate the intersymbol interference (ISI) that multipath causes, the signal of inserting in protection at interval is Cyclic Prefix (CP).

Among Fig. 3, the blind sync correlation detection algorithm of receiving terminal, the signal square wave clock recovers module through behind the separator, be input to the estimation computing of delaying time of time-delay estimation module, after square wave frequency recovers module process M-PSK phase bit recovery module, be input to the phase estimation module and carry out the phase estimation computing, operation result is sent to transmitting terminal is delayed time and phase compensation.

The present invention, can test the half-blindness formula method for synchronous that proposes simultaneously in conjunction with the IEEE802.11a system as a kind of intelligent synchronization algorithm of half-blindness formula.

At first, build the IEEE802.11a system according to agreement, the system that begins does not most add any synchronized algorithm, and the gained parameter is shown in table 1 the 1st row.

Then, we have added pilot frequency information and training sequence in input OFDM framing, and have added Cyclic Prefix, carry out emulation once more on this platform, and the parameter value that draws is referring to table 1 the 2nd row.As seen after having added the sequence of these prioris, the net synchronization capability of system has obtained certain raising.

At last, on this platform emulation is carried out in the invention that proposes, this invention combines with non-blind synchronized algorithm synchronously with blind.Those non-blind synchronizing sequences are carried out parameter modification, reduce the length of synchronizing symbol, and the length of Cyclic Prefix is shortened, so just can reduce the bandwidth waste of system.In order to compensate the non-blind loss that brings of reducing synchronously, it compensates synchronously and at transmitting terminal to add coherent detection at receiving terminal, draws parameter value by emulation and sees Table 1.These parameters have shown that all the semi-blind intelligent synchronization method that this invention proposed has certain advantage than before two kinds.

Table 1: various synchronized algorithm simulation parameters relatively

	Transport packet error probability (%)	Signal to noise ratio (dB)	Bit rate (Mb/s)
				1	7.4098	22.0878	30.5813
2	6.7814	23.1509	31.2750
				3	5.9181	24.4948	32.7263

Claims (6)

1, is applicable to the semi-blind intelligent synchronization method of 802.11a system, when transmitting terminal OFDM framing, add pilot frequency information and training sequence, after the zero padding through adding Cyclic Prefix after the IFFT computing, receiving terminal carries out demodulation to received signal, it is characterized in that also comprising the following steps:

(1) separates timing at receiving terminal and add the coherent detection algorithm, carry out coherent detection to the received signal, its phase place and symbol are estimated prediction synchronously, and output is used for representing the deviant of phase place and symbol;

(2) delay time and the compensation of phase place at transmitting terminal.

2, the semi-blind intelligent synchronization method that is applicable to the 802.11a system according to claim 1 is characterized in that receiving terminal coherent detection time estimation formulas is:

$-\frac{1}{2\mathrm{\π}}\arg \left(\underset{m=0}{\overset{\mathrm{LN}-1}{\mathrm{\Σ}}}{\left|x_{m+1}\right|}^2\exp (-j2\mathrm{\πm}/N)\right),$ Wherein, L is every frame symbolic number, and N is the sampled value of each symbol; Receiving terminal coherent detection phase estimation formula is: $\frac{1}{M}\arg \left\{\underset{k=1}{\overset{L}{\mathrm{\Σ}}}{\left(\left(k\right)\right)}^M\right\}.$

3, a kind of device that is applicable to the semi-blind intelligent synchronization method of the described 802.11a of above-mentioned each claim system, comprise transmitting terminal and receiving terminal: transmitting terminal comprises pilot frequency information module, training sequence module, cyclic prefix module; Receiving terminal comprises blind synchronous estimation module.It is characterized in that the frequency plot detection module being set, be used for estimating system transmission data frequency and phase pushing figure at receiving terminal; Add compensating module at transmitting terminal, the frequency that receiving terminal is estimated and the deviation of phase place compensate.

4, the device of the semi-blind intelligent synchronization method of 802.11a according to claim 2 system is characterized in that described pilot frequency information module follows maximum likelihood (ML) estimation principle, adopts pilot tone and protection to unite at interval and carries out synchronously.

5, according to the device of the semi-blind intelligent synchronization method of claim 2 or 3 described 802.11a systems, it is characterized in that described training sequence module, based on the synchronized algorithm of training sequence is Given information to be added to wait the OFDM symbol sent out on time domain, places usually before the OFDM symbol or the front portion of the frame that is made of a plurality of OFDM symbols.

6, the device of the semi-blind intelligent synchronization method of 802.11a according to claim 4 system; it is characterized in that described cyclic prefix module; data in the Cyclic Prefix are duplicating of an OFDM symbol Back end data; be in order to eliminate the intersymbol interference (ISI) that multipath causes, the signal of inserting in protection at interval is Cyclic Prefix (CP).

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