Spectrum spreading signal demodulation method and apparatus

• US 20030161543A1
• Filed: 02/19/2003
• Published: 08/28/2003
• Est. Priority Date: 06/25/2001
• Status: Active Grant

• Current Assignee: Katsuyuki Tanaka
• Original Assignee: Katsuyuki Tanaka
• Inventors: Tanaka, Katsuyuki
• Granted Patent: US 7,231,095 B2
• Time in Patent Office: Days
• US Class Current: 382/250
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G06F 17/156 using a domain transform, e.g. Fourier transform, polynomial transform, number theoretic transform
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70751 using partial detection H04B1/70758 takes precedence
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

The present invention relates to a spread spectrum signal demodulating method whereby spread-code synchronous acquisition and carrier synchronous acquisition are performed using FFT at high speed with a relatively simple construction. A received signal, of which carrier wave is modulated with a signal obtained by spectrum-spreading data with a spread code, is subjected to the FFT and the result of the FFT is stored in a first memory. The FFT result of the received signal stored in the first memory and the result of FFT of the spread code, the result being stored in a second memory, are read out and the results are multiplied to detect the correlation between the received signal and the spread code. During the detection of the correlation, a readout address of either the FFT result of the received signal or the FFT result of the spread code is shifted by an amount corresponding to a carrier frequency of the received signal and the result is read from the first or second memory. The result of the multiplication is subjected to inverse FFT, thus detecting the correlation point between the received signal and the spread code.

Claims

1. A spread spectrum signal demodulating method comprising the steps of:

performing fast Fourier transform to a received signal, of which carrier wave is modulated with a signal obtained by spectrum-spreading data with a spread code, and then storing the result of the fast Fourier transform in a first memory;

reading the fast Fourier transform result of the received signal stored in the first memory and the fast Fourier transform result of a spread code, the result being stored in a second memory, and multiplying them to detect the correlation between the received signal and the spread code;

shifting a readout address of either the fast Fourier transform result of the received signal or the fast Fourier transform result of the spread code by an amount corresponding to a carrier frequency of the received signal, and then reading the fast Fourier transform result from the first memory or the second memory; and

performing inverse fast Fourier transform to the result of the multiplication to detect the correlation point between the received signal and the spread code.

2. A spread spectrum signal demodulating method according to claim 1, wherein the carrier frequency of the received signal is known in a receiver, the readout address is shifted by an amount corresponding to the known carrier frequency, and the fast Fourier transform result is then read from the first memory or the second memory.

4. A spread spectrum signal demodulating method according to claim 1 or 3, wherein the fast Fourier transform of the received signal and the fast Fourier transform of the spread code are performed every M periods (M is the power of two that is two or more) of the spread code.

5. A spread spectrum signal demodulating method according to claim 4, wherein in the fast Fourier transform of the received signal, the whole frequency components of the received signal are not simultaneously calculated, the fast Fourier transform is divided into L times (L is an integer of two or more) so that the same calculation structure components in the fast Fourier transform are set to a unit, and the fast Fourier transform of the received signal is performed every 1/L.

3. A spread spectrum signal demodulating method comprising the steps of:

performing fast Fourier transform to a received signal, of which carrier wave is modulated with a signal obtained by spectrum-spreading data with a spread code, and then storing the result of the fast Fourier transform in a first memory;

multiplying the fast Fourier transform result of the received signal read from the first memory by the fast Fourier transform result of a spread code, the result being read from a second memory;

performing inverse fast Fourier transform to the result of the multiplication to obtain a correlation detection output between the received signal and the spread code; and

determining the peak of the correlation, while shift-controlling a readout address of either the fast Fourier transform result of the received signal or the fast Fourier transform result of the spread code in the first memory or the second memory on the basis of the correlation detection output, to detect the correlation point between the received signal and the spread code.

6. A spread spectrum signal demodulating apparatus comprising:

fast Fourier transform means for performing fast Fourier transform to a received signal, of which carrier wave is modulated with a signal obtained by spectrum-spreading data with a spread code;

a first memory in which the result of the fast Fourier transform of the received signal obtained by the fast Fourier transform means is stored;

a second memory in which the result of fast Fourier transform of the spread code used in the received signal is stored;

multiplying means for multiplying the fast Fourier transform result of the received signal read from the first memory by the fast Fourier transform result of the spread code read from the second memory;

memory control means for shifting a readout address of either the fast Fourier transform result of the received signal or the fast Fourier transform result of the spread code by an amount corresponding to a carrier frequency of the received signal and then reading the fast Fourier transform result from the first memory or the second memory;

inverse fast Fourier transform means for performing inverse fast Fourier transform to the result of the multiplication obtained by the multiplying means to obtain a correlation detection output between the received signal and the spread code; and

means for searching the peak of the correlation between the received signal and the spread code on the basis of the correlation detection output obtained by the inverse fast Fourier transform means to detect the correlation point between the received signal and the spread code.

7. A spread spectrum signal demodulating apparatus according to claim 6, wherein the memory control means shifts the readout address by an amount corresponding to the carrier frequency of the received signal, the carrier frequency being supplied serving as a known value, and then reads the fast Fourier transform result from the first memory or the second memory.

9. A spread spectrum signal demodulating apparatus according to claim 6 or 8, wherein the fast Fourier transform of the received signal and the fast Fourier transform of the spread code are performed every M periods (M is the power of two that is two or more) of the spread code.

10. A spread spectrum signal demodulating apparatus according to claim 9, wherein the fast Fourier transform of the received signal is divided into L times (L is an integer of two or more) so that the same calculation structure components in the fast Fourier transform are set to a unit, and the fast Fourier transform of the received signal is performed every 1/L.

8. A spread spectrum signal demodulating apparatus comprising:

fast Fourier transform means for performing fast Fourier transform to a received signal, of which carrier wave is modulated with a signal obtained by spectrum-spreading data with a spread code;

a first memory in which the result of the fast Fourier transform of the received signal obtained by the fast Fourier transform means is stored;

a second memory in which the result of fast Fourier transform of the spread code used in the received signal is stored;

multiplying means for multiplying the fast Fourier transform result of the received signal read from the first memory by the fast Fourier transform result of the spread code read from the second memory;

inverse fast Fourier transform means for performing inverse fast Fourier transform to the result of the multiplication obtained by the multiplying means to obtain a correlation detection output between the received signal and the spread code; and

means for determining the peak of the correlation, while shift-controlling a readout address of either the fast Fourier transform result of the received signal or the fast Fourier transform result of the spread code in the first memory or the second memory on the basis of the correlation detection output obtained by the inverse fast Fourier transform means, to detect the correlation point between the received signal and the spread code.