Time domain symbol timing synchronization circuit and method thereof for communication systems

1. A time domain symbol timing synchronization circuit in a receiver of a communication system, for getting symbol boundary of received communication symbols having phase reference sequences performing like pseudo-noise sequences, the time domain symbol timing synchronization circuit comprising:

an autocorrelation function calculator, for calculating cyclic prefix autocorrelation functions; and

an offset time estimator, coupled to the autocorrelation function calculator, for searching positions at peaks of the cyclic prefix autocorrelation functions to indicate symbol boundary of received communication symbols,

wherein the offset time estimator compares a position at a peak of a current cyclic prefix autocorrelation function of received communication symbols and a position at a peak of a previous cyclic prefix autocorrelation function of received communication symbols;

if a difference of the positions is larger than a threshold and the peak of the current cyclic prefix autocorrelation function is smaller than a reference average peak, the peak of the current cyclic prefix autocorrelation function is determined as false; the offset time estimator weeds out and replaces the position at the peak of the current cyclic prefix autocorrelation function by the position at the peak of the previous cyclic prefix autocorrelation function; and the current peak is not introduced in calculation of the reference average peak.

2. The time domain symbol timing synchronization circuit of claim 1 , wherein the reference average peak is a moving average of peaks of a plurality of previous cyclic prefix autocorrelation functions.

3. The time domain symbol timing synchronization circuit of claim 1 , wherein the autocorrelation function calculator comprises:

a plurality of serial-connected delay units, for delaying a digital input signal;

a multiple output selector, for selecting outputs from the delay units based on a mode information and outputting a plurality of output signals;

a plurality of multipliers, each multiplying a corresponding output signal from the multiple output selector with a corresponding coefficient;

an adder, for adding outputs from the multipliers, and

an absolute unit, for getting an absolute value of an output of the adder,

the offset time estimator indicating symbol boundary of received communication symbols based on an output of the absolute unit.

4. The time domain symbol timing synchronization circuit of claim 3 , further comprising a multiplexer, coupled to the serial-connected delay units, for selecting one of the outputs from the serial-connected delay units based on a control signal from the offset time estimator.

5. The time domain symbol timing synchronization circuit of claim 1 , wherein the communication system is an OFDM system and the receiver is a DAB receiver or a DVB receiver.

6. The time domain symbol timing synchronization circuit of claim 1 , wherein the receiver is used to receive signals under Doppler fading channel.

7. A receiver in a communication system, the receiver comprising:

an converter, for converting analog input signals into digital signals;

a receiver frontend, coupled to the converter, for performing signal processing on the digital signals from the converter;

a FFT unit, coupled to the receiver frontend, for performing FFT on output signals from the receiver frontend;

a receiver backend, coupled to the FFT unit, for performing signal processing on output signals from the FFT unit; and

a time domain symbol timing synchronization circuit, coupled to the receiver frontend and the FFT unit, for indicating symbol boundary of received communication symbols and getting symbol boundary of the received communication symbols with phase reference sequences performing like pseudo-noise sequences,

wherein:

the time domain symbol timing synchronization circuit compares a position at a peak of a current cyclic prefix autocorrelation function of the received communication symbols and a position at a peak of a previous cyclic prefix autocorrelation function of the received communication symbols;

if (a) a difference of the positions is larger than a threshold and (b) the peak of the current cyclic prefix autocorrelation function is smaller than a reference average peak, the peak of the current cyclic prefix autocorrelation function is determined as false; the time domain symbol timing synchronization circuit weeds out and replaces the position at the peak of the current cyclic prefix autocorrelation function by the position at the peak of the previous cyclic prefix autocorrelation function; and the current peak is not introduced in calculation of the reference average peak.

8. The receiver of claim 7 , wherein the reference average peak is a moving average of peaks of a plurality of previous cyclic prefix autocorrelation functions.

9. The receiver of claim 7 , wherein the time domain symbol timing synchronization circuit comprises:

an autocorrelation function calculator; and

an offset time estimator, coupled to the autocorrelation function calculator;

wherein the autocorrelation function calculator comprises:

a plurality of serial-connected delay units, for delaying a digital input signal;

a multiple output selector, for selecting outputs from the delay units based on a mode information and outputting a plurality of output signals;

a plurality of multipliers, each multiplying a corresponding output signal from the multiple output selector with a corresponding coefficient;

an adder, for adding outputs from the multipliers, and

an absolute unit, for getting an absolute value of an output of the adder,

the offset time estimator indicating start of received communication symbols based on an output of the absolute unit.

10. The receiver of claim 9 , wherein the time domain symbol timing synchronization circuit further comprises a multiplexer, coupled to the serial-connected delay units, for selecting one of the outputs from the serial-connected delay units based on a control signal from the offset time estimator.

11. The receiver of claim 7 , wherein the communication system is an OFDM system and the receiver is a DAB receiver or a DVB receiver.

12. The receiver of claim 7 , wherein the receiver is used to receive signals under Doppler fading channel.

13. A time domain symbol timing synchronization method for communication systems, the method comprising:

(a) searching a position at a peak of a previous cyclic prefix autocorrelation function of the received communication symbols;

(b) searching a position at a peak of a current cyclic prefix autocorrelation function of the received communication symbols;

(c) comparing the peak positions;

(d) if a difference between the peak positions is larger than a threshold and the peak of the current cyclic prefix autocorrelation function is smaller than a reference average peak, weeding out and replacing the position at the peak of the current cyclic prefix autocorrelation function by the position at the peak of the previous cyclic prefix autocorrelation function; and

(e) indicating symbol boundary of the received communication symbols based on the peak position which is not wed out.

14. The time domain symbol timing synchronization method of claim 13 , wherein

the step (c) comprising:

calculating a position difference between the position at the peak of the current cyclic prefix autocorrelation function and the position at the peak of the previous cyclic prefix autocorrelation function; and

taking an absolute value of the position difference.

15. The time domain symbol timing synchronization method of claim 13 , wherein the reference average peak is obtained by:

ref_peak=sum (peak_amp( i−j )/ m *ratio( i−j )) from j= 1 to j=m;

wherein “ref_peak” refers to the reference average peak, sum(·) refers to summation operation, peak_amp(i-j) is a previous j-th peak corresponding to the current peak peak_amp(i), m is a sampling number, and ratio(i-j) is the weighting factor of the previous j-th peak.