Digital signal detecting method and detector

• US 5,907,585 A
• Filed: 11/14/1996
• Issued: 05/25/1999
• Est. Priority Date: 11/16/1995
• Status: Expired due to Fees

• Current Assignee: Cingular Wireless II LLC (AT&T, Inc.)
• Original Assignee: NTT Mobile Communications Network Inc. (Nippon Telegraph and Telephone Corporation)
• Inventors: Kumagai, Ken, Suzuki, Yasunori, Nojima, Toshio
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Liu, Shuwang
• Application Number:
  US08/749,207
• Time in Patent Office: 922 Days
• Field of Search: 375/344, 375/324, 375/261, 375/326, 375/328, 375/329, 375/332, 375/355, 329/261, 329/304, 329/306, 329/302
• US Class Current: 375/324
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/3881 using sampling and digital processing, not including digital systems which imitate heterodyne or homodyne demodulation

Abstract

An automatically gain-controlled analog received signal is AD converted to a digital signal, which is subjected to quadrature demodulation processing through operation. The quadrature demodulation result is subjected to low-pass filter processing through operation, that is, a digital detection is performed by software processing to a variable in each software processing in accordance with changes in the modulation method of the received signal and in the symbol transmission rate.

Claims

1. A digital detection method comprising:

an AD conversion step of converting a received modulated signal from analog to digital form;

a quadrature demodulation step of performing a digital quadrature-demodulating operation on said converted digital signal using a local oscillation signal of a local oscillation frequency as a processing variable;

a filtering step of performing a digital low-pass filtering operation on said quadrature-demodulated digital signal using filter characteristics as processing variables; and

a control step of changing at least one of the processing variables in any one of said quadrature demodulation step and said filtering step in response to a variable change request, a change of a processing variable in said quadrature demodulation step being in accordance with a carrier frequency of the modulated signal, and a change of a processing variable in said filtering step being in accordance with the modulation scheme and transmission rate of the modulated signal.

2. The method of claim 1, wherein said quadrature demodulation step comprises:

an interpolation step on performing n-point interpolation processing on said digital signal to interpolate therein samples at n points, said n being an real number equal to or greater than 1;

a multiplication step of complex-multiplying the result of said n-point interpolation by said local oscillation signal; and

a decimation step of performing n-point decimation processing on the result of said complex-multiplication to decimate therefrom samples at n points.

3. The method of claim 2, wherein said filtering step comprises:

a smoothing step of performing smoothing processing on the result of said quadrature demodulation to reduce the number of samples of the time base; and

a digital filter step of performing band-limiting operation on the result of said smoothing processing using said filter characteristics.

4. The method of claim 2, wherein said interpolation step is a step of performing discrete Fourier transform processing on said digital signal and performing inverse discrete Fourier transform on the result of said Fourier transform processing after adding thereto a zero coefficient to obtain said result of said interpolation processing.

5. The method of claim 2, wherein said interpolation step is a step of performing a linear interpolation which approximates an m-th order function to said digital signal and interpolates therein samples which fit said m-th order function.

6. The method of claim 2, wherein said interpolation step is a step of interpolating samples estimated by an adaptive algorithm used for those preceding them in said digital signal every predetermined number of samples.

7. The method of claim 2, wherein said interpolation step is a step of decimating from said multiplication result said samples interpolated at said n points in said interpolation step.

8. The method of claim 2, wherein said decimation step is a step of processing a sequence of samples of said multiplication result by an evaluation function every predetermined number of samples to obtain one sample.

9. The method of claim 2, further comprising a step of synchronizing said local oscillation signal with said digital signal.

10. The method of claim 9, wherein said synchronizing step comprises the steps of:

synchronizing the frequency of said local oscillation signal with said digital signal; and

time-synchronizing said frequency-synchronized local oscillation signal with said n-point interpolated digital signal.

11. The method of claim 2, wherein said at least one processing variable in said quadrature demodulation step is the number n of interpolation points.

12. The method of claim 2, wherein said at least one processing variable in said quadrature demodulation step is the local oscillation frequency of said local oscillation signal.

13. The method of claim 3, wherein said at least one processing variable in said filter step is the number of smoothing points where to reduce said number of samples.

14. The method of claim 3, wherein said at least one processing variable in said filter step is a filter characteristic in said digital filter step.

15. The method of any one of claims 3 and 9 to 14, further comprising a gain control step of controlling the maximum amplitude of said received modulated signal to be a set value which is said at least one processing variable.

16. The method of claim 15, further comprising:

a variable change request detecting step of detecting a variable change request;

a processing variable determining step of responding to said variable change request to determine which processing variable is to be changed and its value; and

a step of changing said processing variable to said determined variable.

17. The method of claim 16, wherein each of said steps is executed by decoding and executing a program.

18. The method of claim 17, wherein said processing variable determining step is a step of reading out a prestored processing variable in response to said variable change request.

19. The method of claim 18, wherein said variable change request is input by manipulating set/input means.

20. The method of claim 18, wherein said variable change request detecting step is a step of detecting said variable change request from a received signal.

21. A digital detector comprising:

an AD converter for converting a received modulated analog signal to a digital signal;

quadrature demodulation means for performing a digital quadrature demodulating operation on said digital signal output from said AD converter using a digital local oscillation signal of a local oscillation frequency as a processing variable;

filter means for performing a digital lowpass-filter operation on the quadrature demodulated digital signal using filter characteristics as processing variables;

input means for inputting a processing variable change request for changing a processing variable; and

control means including means holding selectable data of at least one of modulation schemes, transmission rates and carrier frequencies, said control means being responsive to said processing variable change request and to said selectable data to change at least one process variable in at least one of said quadrature demodulation means and said filter means.

22. The detector of claim 21, wherein said quadrature demodulation means comprises:

interpolating means for performing n-point interpolation processing on said output digital signal from said AD converter to interpolate therein samples at n points, said n being a real number equal to or greater than 1;

local oscillation means for generating said digital local oscillation signal through digital operation;

multiplying means for complex-multiplying the result of said n-point interpolation and said digital local oscillation signal; and

decimating means for performing n-point decimation processing on a digital signal resulting from said complex-multiplication to decimate therefrom samples at said n points.

23. The detector of claim 22, wherein said filter means comprises:

smoothing means for smoothing the output from said quadrature demodulation means and for performing an operation for reducing the number of samples of said output; and

digital filter means for performing a band-limiting operation on the result of said operation by said smoothing means.

24. The detector of claim 23, further comprising an automatic gain controller provided at a stage preceding said AD converter, for controlling the gain of said received modulated signal so that its maximum amplitude becomes a set value which is one of said processing variables that can be changed by said control means.

25. The detector of claim 24, further comprising storage means having prestored therein a comparative table of variable change requests and processing variables, and wherein said control means is responsive to said input variable change request to read out said storage means and to change the processing variable corresponding to said read-out processing variable.

26. The detector of claim 25, wherein said input means is set/input means for inputting said variable change request by a manual operation.

27. The detector of claim 25, wherein said input means is means for detecting said variable change request from a received signal.

28. The detector of any one of claims 21 to 27, wherein said control means comprises a program and a microprocessor for decoding and executing said program.

29. The detector of claim 28, wherein said control means serves also as control means of a digital radio transceiver.