CORRELATOR AND DEMODULATION DEVICE INCLUDING CORRELATOR

• US 20120051472A1
• Filed: 08/17/2011
• Published: 03/01/2012
• Est. Priority Date: 08/30/2010
• Status: Active Grant

• Current Assignee: LAPIS Semiconductor Co., Ltd. (ROHM Co., Ltd.)
• Original Assignee: Oki Semiconductor Company Limited (ROHM Co., Ltd.)
• Inventors: AKAHORI, Hiroji
• Granted Patent: US 9,172,575 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2691 involving interference determination or cancellation

Abstract

The present invention provides a correlator and a demodulation device including, first and second filter sections having different non-overlapping pass-frequency characteristics, first and second delay circuits that delay the signals output from the first and second filter section by one effective OFDM symbol period, first and second complex conjugate circuits that take the complex conjugates of the delayed signals, first and second complex operation sections that compute the complex-multiplies of the signals from the first and second filter sections and the respective signals for the first and second complex conjugate circuits, first and second moving average processing sections that take moving averages of GI lengths, proportion determination circuit that compares the maximum values of the autocorrelations from each of the first and second moving average processing circuits, and selection-combination circuit that selects the autocorrelation having the largest maximum value based on the comparison result.

Claims

1. A correlator comprising:

a plurality of filter sections having different substantially non-overlapping pass-band characteristics from each other, each of the filter sections being input with an Orthogonal Frequency Division Multiplexing (OFDM) signal where one symbol period comprises an effective symbol period and a guard interval in which part of the signal of the effective symbol period has been copied; and

a plurality of autocorrelation generating sections, provided so as to correspond to each of the plurality of filter sections, that generate autocorrelation signals based on the signals passed through the corresponding filter sections.

2. The correlator of claim 1, further comprising:

an autocorrelation output section that is input with each of the autocorrelation signals and, based on each of the autocorrelation signals, either selects one of the autocorrelations or generates an autocorrelation appropriate for obtaining timing synchronization, and outputs the selected or generated autocorrelation.

3. The correlator of claim 2, wherein the autocorrelation output section selects and outputs the autocorrelation signal having the largest maximum value from the autocorrelation signals.

4. The correlator of claim 2, wherein the autocorrelation output section:

extracts the autocorrelation signal having the largest maximum value from the autocorrelation signals;

sets a threshold value by multiplying the extracted maximum value by a specific coefficient of less than 1;

extracts from the remaining autocorrelation signals any autocorrelations having a maximum value greater than the threshold value;

addition-combines the autocorrelation signal having the largest maximum value and the extracted autocorrelation signals having maximum values greater than the threshold value; and

outputs the addition-combined autocorrelation signal.

5. The correlator of claim 2, wherein the autocorrelation output section:

extracts any autocorrelation signals having a maximum value greater than a specific threshold value from the autocorrelation signals;

addition-combines the extracted autocorrelation signals; and

outputs the addition-combined autocorrelation signal.

6. The correlator of claim 1, wherein each of the plurality of autocorrelation generating sections comprises:

a delay section that delays the signal output from the corresponding filter section by the effective symbol period;

a complex conjugate section that takes the complex conjugate of the delay signal from the delay section;

a complex operation section that is input with the OFDM signal output from the filter section and the signal output from the complex conjugate section after delaying and complex conjugate processing, and that takes the complex-multiplies of the two signals; and

a moving average processing section that takes a moving average of guard interval length portions of the output from the complex operation section, and that outputs the moving average as an autocorrelation signal.

7. The correlator of claim 1, wherein each of the plurality of autocorrelation generating sections comprises:

a phase conversion section that converts the signal output from the corresponding filter section into phase information and that outputs the phase information;

a delay section that rotates the phase information by the effective symbol period;

a subtraction section that compares the phase information and the rotated phase information, derives the difference therebetween and outputs the difference as a phase rotation amount;

a vector conversion section that generates unit vectors from the phase rotation amount; and

a moving average processing section that takes a moving average of guard interval length portions of the unit vector and outputs the moving average as an autocorrelation signal.

8. The correlator of claim 2, wherein the autocorrelation output section, when selecting one of the autocorrelations or generating an autocorrelation appropriate for obtaining timing synchronization, applies a weighting to at least one of the signals employed, such that the output is similar to output from employing all the autocorrelation signals generated by the plurality of autocorrelation generating sections even for cases in which the appropriate autocorrelation is generated based on less than all of the autocorrelation signals generated by the plurality of autocorrelation generating sections.

9. The correlator of claim 1 wherein the plurality of filter section is two filter sections and the plurality of autocorrelation generating sections is two autocorrelation generating sections.

10. The correlator of claim 7, wherein the configuration from the phase conversion section to the vector conversion section is a single-row configuration, and the correlator further comprises:

a first switching section, provided after the plurality of filter sections, that switches, every specific cycle, the input to the first switching section between the output signals of the plurality of filter sections, and that outputs the input signal to the phase conversion section; and

a second switching section, provided after the vector conversion section, that switches, at the specific cycle, the output signal of the vector conversion section for input to each of the plurality of moving average processing sections.

11. The correlator of claim 10, wherein the relationship between the number of data Dd stored in the delay section, and the number of data Df flowing in each of the filter sections during each specific cycle, is given by Df=Dd/M, wherein M is an integer.

12. A demodulation device comprising:

an analog-to-digital conversion section that converts into a digital signal an analog orthogonal frequency division multiplexing (OFDM) signal where one symbol period comprises an effective symbol period and a guard interval in which part of the signal of the effective symbol period has been copied;

the correlator according of claim 1 to which the digital OFDM signal is inputted;

a timing detection section that outputs, on the basis of a correlation signal received from the correlator, a timing signal for extracting the effective symbol signal from the OFDM signal;

a fast Fourier transform section that, on the basis of the timing signal that has been outputted from the timing detection section, extracts the effective symbol signal from the OFDM signal that has been digitally converted by the analog-to-digital conversion section, and that performs Fourier transform with respect to the effective symbol signal; and

a demodulation section that performs demodulation processing on the signal after the Fourier transform process by the fast Fourier transform section to obtain a demodulated signal.