CN101527702A - Coarse symbol timing estimation method and receiver - Google Patents

Abstract

The invention discloses a coarse symbol timing estimation method and a receiver for a broadcast communication system. In an STiMi system, the success rate of coarse symbol timing estimation of a receiving terminal is improved by a method of changing power weight coefficient according to the result of AGC adjustment, and the complexity is little increased.

Description

Coarse symbol timing estimation method and receiver

Technical field

The present invention relates to the field of information transmission in the broadcast communication system, particularly the method for synchronous of broadcast communication receiver.

Background technology

Thick symbol timing estimation is by the correlation computations between OFDM symbol and the Cyclic Prefix thereof is obtained.Its slip correlation function computational methods are as follows:

λ(θ)＝|γ(θ)|-ρΦ(θ)

Wherein,

$\mathrm{\γ}\left(\mathrm{\θ}\right)=\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}r\left(k\right)\·r^{*}(k-N)$

$\mathrm{\Φ}\left(\mathrm{\θ}\right)=\frac{1}{2}\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}({\left|r\left(k\right)\right|}^2+{\left|r(k-N)\right|}^2)$

Wherein, r (k) is a k sampling value of baseband receiving signals, N is the time interval number that carries out between the sample of signal of correlation computations, just in time equal the OFDM symbol and carry out counting of FFT computing, ρ is the power weightings factor (definite), L is the length of related operation window, just in time equals the length of OFDM symbol cyclic prefix CP here.

Locate the starting position of OFDM symbol by correlation function value.If correlation function value is greater than fixed gate limit value (as 0), this estimates so

It is exactly the estimated value of OFDM character position.The concrete principle of coarse symbol timing estimation method as shown in Figure 3.

In the existing coarse symbol timing estimation method, the power weightings factor is fixed, do not consider since the variation of signal to noise ratio to thick symbol timing estimation Effect on Performance, so when transmission channel signal to noise ratio excursion is bigger, it is not optimum adopting fixing power weightings factor performance, as shown in Figure 5.

What need improvement is exactly to come the adaptive selection power weightings factor in the situation that will change according to the signal to noise ratio of channel, and the specific implementation method of estimated snr can not be too complicated, make full use of various channel informations, under the very little situation of implementation complexity increase, it is optimum that performance reaches.

Summary of the invention

The purpose of this invention is to provide a kind of coarse symbol timing estimation method and receiver.

For achieving the above object, a kind of STiMi system receiver comprises:

Radio-frequency module becomes radiofrequency signal into baseband signal;

The power amplification determination module is controlled according to power amplification and to be amplified the signal that receives;

D/A converter module quantizes analog signal, becomes digital signal;

The correcting frequency deviation module is corrected the frequency shift (FS) of signal;

Frequency deviation estimating modules, the frequency shift (FS) of estimated signal;

The FFT module is carried out the FFT operation to the OFDM symbol;

The channel decoding module utilizes decoder to solve digital information;

Automatic gain is controlled the AGC module, determines the multiplication factor of power amplifier according to the amplitude of received signal;

Power weightings factor determination module is determined the power weightings factor values according to the adjusted value of AGC;

Slip correlation function computing module is to the OFDM sign computation slip correlation function value that receives;

The correlation function comparison module compares the correlation function value and the threshold value of the OFDM symbol that receives;

Symbol correlation function computing module is to the OFDM sign computation correlation function value that receives;

Average power is calculated module, to the OFDM sign computation average power content that receives;

Thick symbol is determination module regularly, determines thick symbol timing value according to the result of correlation function comparison.

Description of drawings

Fig. 1 is the improved structure chart that self adaptation is adjusted the STiMi receiver of the thick symbol timing estimation of power weight coefficient that has;

Fig. 2 is the improved schematic diagram that self adaptation is adjusted the coarse symbol timing estimation method of power weight coefficient that has;

Fig. 3 is the schematic diagram that self adaptation is adjusted definite method of power weight coefficient;

Fig. 4

The schematic diagram of present coarse symbol timing estimation method;

Fig. 5 is the performance simulation figure of present coarse symbol timing estimation method;

Fig. 6 is that the improved coarse symbol timing estimation method that has self adaptation adjustment power weight coefficient compares with the timing estimation performance of not improving one's methods.

Embodiment

We need find one can embody the parameter that signal to noise ratio changes, and adjust power weightings factor ρ value in the thick symbol timing estimation according to this parameter, thereby make the better effects if of thick symbol timing estimation.For the amplitude that remains on AD conversion front received signal keeps steady state value, just need utilize AGC to control the gain of the amplifier VGA of AD conversion front end.

The basic principle of AGC is as follows:

At first, calculate the mean value of the power of received signal

$\mathrm{\Φ}=\underset{k=1}{\overset{L}{\mathrm{\Σ}}}{\left|r\left(k\right)\right|}^2$

Wherein

r(k)＝s(k)+n(k)

Wherein s (k) is a signal, and n (k) is a noise.

Secondly, the thresholding that the amplitude and the AGC control of the received signal calculated are set compares, and the amplitude that obtains received signal and AGC control the difference of the thresholding of setting.

Then, the difference of the thresholding of setting according to the amplitude of received signal and AGC control is determined the adjusted value of the gain of amplifier VGA, and adjusts.

That is, the adjusted value μ of AGC equals

μ=threshold value-Φ (dB)

In the specific implementation of STiMi system, the threshold value of AGC is fixed.Because the STiMi system is a broadcast system, and is less from other users' interference ratio, it is slower that noise changes, and amplitude is smaller.We can suppose the changing with the adjusted value of AGC of variation approximately linear of signal to noise ratio, therefore can adjust power weightings factor ρ according to the adjusted value of AGC, promptly adjust power weightings factor ρ according to the approximation of the variation of signal to noise ratio.

Thick symbol timing estimation is to be correlated with according to the symbol of OFDM to realize, its slip correlation function can be expressed as:

λ(θ)＝|γ(θ)|-ρΦ(θ)

Wherein,

$\mathrm{\γ}\left(\mathrm{\θ}\right)=\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}r\left(k\right)\·r^{*}(k-N)$

$=\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}(s\left(k\right)+n\left(k\right)){\·(s(k-N)+n(k-N))}^{*}$

$\≅\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}s\left(k\right)\·s^{*}(k-N)$

$\mathrm{\Φ}\left(\mathrm{\θ}\right)=\frac{1}{2}\underset{k=\mathrm{\θ}}{\overset{\mathrm{\θ}+L-1}{\mathrm{\Σ}}}({\left|r\left(k\right)\right|}^2+{\left|r(k-N)\right|}^2)$

And

r(k)＝s(k)+n(k)

Wherein, r (k) is a k sampling value of baseband receiving signals, N is the time interval number that carries out between the sample of signal of correlation computations, just in time equal the OFDM symbol and carry out counting of FFT computing, ρ is the power weightings factor (definite), and L is the length of related operation window, just in time equals the length of OFDM symbol cyclic prefix CP here, s (k) is the base band sampling value that sends signal, and n (k) is the base band sampling value that receives noise.

According to top formula, the power of receiving symbol r (k) and transmission symbol are expressed by the available following formula of the relation between the power of s (k) behind the channel.

$P_s=P_r\&CenterDot;\left(\frac{\mathrm{<figure-callout\; id="1"\; label="SNR"\; filenames="A20081008210600111.png,A20081008210600132.png"\; state="\{\{state\}\}">SNR</figure-callout>}}{1+\mathrm{SNR}}\right)$

After AGC, power Φ (θ) is just basic to keep constant, but the correlation γ (θ) of received signal but can change along with the variation of signal to noise ratio, therefore, in order accurately to estimate thick symbol regularly, power weightings factor ρ will change along with the variation of signal to noise ratio.But in the specific implementation process of system, the exact value difficulty that obtains the signal to noise ratio variation still is that the method for the thick symbol timing estimation is here adjusted power weightings factor ρ with the adjusted value of AGC as the signal to noise ratio changing value greatly

Being implemented as follows of the coarse symbol timing estimation method that the present invention proposes:

At first, determine the initial value of the power weightings factor;

Then, determine the adjusted value of power weightings factor ρ (Rou) according to the adjusted value of AGC.Just the adjustment amount with AGC increases or reduces certain step value, and the power weight factor reduces or increases certain step value, as shown in Figure 2.

Fig. 1 shows the STiMi receiver that self adaptation is adjusted the thick symbol timing estimation of power weight coefficient that has of the present invention.Receiver comprises:

Radio-frequency module becomes radiofrequency signal into baseband signal;

(VGA) module is determined in power amplification, controls according to power amplification and amplifies the signal that receives;

Digital-to-analogue conversion (A/D) module quantizes analog signal, becomes digital signal;

The correcting frequency deviation module is corrected the frequency shift (FS) of signal;

Frequency deviation estimating modules, the frequency shift (FS) of estimated signal;

The FFT module is carried out the FFT operation to the OFDM symbol;

The channel decoding module utilizes decoder to solve digital information;

Automatic gain is controlled (AGC) module, determines the multiplication factor of power amplifier according to the amplitude of received signal;

Power weightings factor determination module is determined the power weightings factor values according to the adjusted value of AGC;

Slip correlation function computing module is to the OFDM sign computation slip correlation function value that receives;

The correlation function comparison module compares the correlation function value and the threshold value of the OFDM symbol that receives;

Symbol correlation function computing module is to the OFDM sign computation correlation function value that receives;

Average power is calculated module, to the OFDM sign computation average power content that receives;

Thick symbol is determination module regularly, determines thick symbol timing value according to the result of correlation function comparison.

The present invention has taken into full account the influence that signal to noise ratio is calculated thick symbol slip correlation function regularly when carrying out thick symbol timing estimation, under the very little situation of implementation complexity increase, performance improves a lot.

It is 0.5 that the present invention has adopted initial power weight factor ρ.The power weight factor is adjusted with the adjustment amount of AGC then, and the adjustment amount of AGC increases or reduce 1dB, and the power weight factor reduces or increases by 0.02.

The timing estimation performance that we see improved coarse symbol timing estimation method from Fig. 6 improves significantly than the performance of original coarse symbol timing estimation method, and abscissa is the SNR of the noise of the gross power of transmitting terminal and receiving terminal.Ordinate is the success rate (absolute value of deviation that is timing estimation is smaller or equal to 64) of timing estimation.

Claims (7)

1. STiMi system receiver comprises:

Radio-frequency module (101) becomes radiofrequency signal into baseband signal;

Power amplification determination module (102) is controlled according to power amplification and to be amplified the signal that receives;

D/A converter module (103) quantizes analog signal, becomes digital signal;

Correcting frequency deviation module (104) is corrected the frequency shift (FS) of signal;

Frequency deviation estimating modules (105), the frequency shift (FS) of estimated signal;

FFT module (106) is carried out the FFT operation to the OFDM symbol;

Channel decoding module (107) utilizes decoder to solve digital information;

Automatic gain is controlled AGC module (108), determines the multiplication factor of power amplifier according to the amplitude of received signal;

Power weightings factor determination module (109) is determined the power weightings factor values according to the adjusted value of AGC;

Slip correlation function computing module (110) is to the OFDM sign computation slip correlation function value that receives;

Correlation function comparison module (111) compares the correlation function value and the threshold value of the OFDM symbol that receives;

Symbol correlation function computing module (112) is to the OFDM sign computation correlation function value that receives;

Average power is calculated module (113), to the OFDM sign computation average power content that receives;

Thick symbol is determination module (114) regularly, determines thick symbol timing value according to the result of correlation function comparison.

2. by the described receiver of claim 1, it is characterized in that described receiver is the OFDM wireless communication system.

3. by the described receiver of claim 1, it is characterized in that described receiver is for comprising the Cyclic Prefix in OFDM System system.

4. coarse symbol timing estimation method comprises step:

Radiofrequency signal is become baseband signal;

Control according to power amplification and to amplify the signal that receives;

Analog signal is quantized, become digital signal;

The frequency shift (FS) of signal is corrected;

The frequency shift (FS) of estimated signal;

The OFDM symbol is carried out the FFT operation;

Utilize decoder to solve digital information;

Determine the multiplication factor of power amplifier according to the amplitude of received signal;

Determine the power weightings factor values according to the adjusted value of AGC;

To the OFDM sign computation slip correlation function value that receives;

Correlation function value and threshold value to the OFDM symbol that receives compare;

To the OFDM sign computation correlation function value that receives;

To the OFDM sign computation average power content that receives;

Result according to the correlation function comparison determines thick symbol timing value.

5. by the described method of claim 4, it is characterized in that described adjusted value according to AGC determines that the power weightings factor values comprises:

Determine the initial value of the power weightings factor;

Adjusted value with AGC on the basis of initial value increases or reduces certain step value.

6. by the described method of claim 4, it is characterized in that being calculated as follows the slip correlation function:

λ(θ)＝|γ(θ)|-ρΦ(θ)

Wherein,

$\mathrm{\&gamma;}\left(\mathrm{\&theta;}\right)=\underset{k=\mathrm{\&theta;}}{\overset{\mathrm{\&theta;}+L-1}{\mathrm{\&Sigma;}}}r\left(k\right)\&CenterDot;r^{*}(k-N)$

$=\underset{k=\mathrm{\&theta;}}{\overset{\mathrm{\&theta;}+L-1}{\mathrm{\&Sigma;}}}{(s\left(k\right)+n\left(k\right))\&CenterDot;(s(k-N)+n(k-N))}^{*}$

$\&cong;\underset{k=\mathrm{\&theta;}}{\overset{\mathrm{\&theta;}+L-1}{\mathrm{\&Sigma;}}}s\left(k\right)\&CenterDot;s^{\&CenterDot;}(k-N)$

$\mathrm{\&Phi;}\left(\mathrm{\&theta;}\right)=\frac{1}{2}\underset{k=\mathrm{\&theta;}}{\overset{\mathrm{\&theta;}+L-1}{\mathrm{\&Sigma;}}}({\left|r\left(k\right)\right|}^2+{\left|r(k-N)\right|}^2)$

Wherein, r (k) is a k sampling value of baseband receiving signals, N is the time interval number that carries out between the sample of signal of correlation computations, just in time equal the OFDM symbol and carry out counting of FFT computing, ρ is the power weightings factor (definite), and L is the length of related operation window, just in time equals the length of OFDM symbol cyclic prefix CP here, s (k) is the base band sampling value that sends signal, and n (k) is the base band sampling value that receives noise.

7. by the described method of claim 6, it is characterized in that described calculating slip correlation function will consider the influence of average power.

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