Rapid identification of transmission media channel characteristics
View Patent ↗Rapid identification and modeling of transmission media channel characteristics of a communications system using a correlation based technique. The technique provides a known training sequence used to generate a known quantity that operates on an observed or measured received signal, which is a function of the training sequence and the channel's impulse response, to give an estimate of the model of the channel. The technique decouples the training sequence from the observed or measured output, leaving the estimated impulse response. The impulse response of the transmission media channel is rapidly computed and processed to set the initial values of filter coefficients, for example, an echo canceller and an equalizer, in the communications system. Once the coefficients are initialized, if needed, a standard technique, such as least mean square (LMS) correlation, can be used to fine-tune the coefficients to converge on or model the transmission media channel's characteristics.
1. A method of rapid identification of characteristics of a transmission media channel, comprising:
generating training signal sequence of time domain signals X=[X 0 , X 1 , . . . , X T−1 ]of length T;
transmitting the training signal sequence as an input to the transmission media channel, the transmission media channel having an unknown impulse response h (n) , for n=0 to n=N−1, where N is the number of coefficients of the unknown impulse response;
obtaining an output signal sequence (Y k ) of the transmission media channel for k=0 to k=T−(N−1) approximated by
Y k =Σh n x k+n +g k;
where g k is a signal noise component;
computing a reference value from the training signal sequence; and
using the reference value to operate on the output signal sequence for decoupling the training signal sequence from the output signal sequence for computing an estimate of the impulse response h (n) of the transmission media channel.
2. The method of claim 1 , further composing using the estimate of the impulse response of the transmission media channel to remove impairments imposed by the transmission media channel on received signals.
3. The method of claim 1 , wherein the training signal sequence comprises a known training signal sequence.
4. The method of claim 1 , wherein the computing the estimate of the impulse response of the transmission media channel comprises computing an initial estimate of the impulse response.
5. The method of claim 1 , wherein the reference value is computed off-line.
6. The method of claim 1 , wherein the reference value comprises a matrix M=({overscore (X)}X) 1 {overscore (X)}, where X is a known training signal sequence in matrix form, and {overscore (X)} is the Hermitian of X, and
computation of the impulse response of the transmission media channel is expressed as H=MY, where Y is the transmission media channel output signal vector.
7. The method of claim 1 , wherein the computing the estimate of the impulse response of the transmission media channel is hardware implemented.
8. The method of claim 1 , wherein the computing the estimate of the impulse response of the transmission media channel is software implemented.
9. The method of claim 1 , further comprising using the estimate of the impulse response of the transmission media channel for removing echoes from signals received from the transmission media channel.
10. The method of claim 1 , further comprising using the estimate of the impulse response of the transmission media channel for setting the coefficients of a filter.
11. The method of claim 1 , further comprising using the estimate of the impulse response of the transmission media channel for setting the coefficients of an echo canceller.
12. The method of claim 1 , further comprising using the estimate of the impulse response of the transmission media channel for setting the coefficients of an equalizer.
13. A method of rapid identification of characteristics of a transmission media channel, comprising:
generating a known training signal sequence;
transmitting the training signal sequence over the transmission media channel to generate an observed or measured output signal;
using a minimized difference value between (a) the observed or measured output signal and (b) a signal value representation of convolution of the training signal sequence and an unknown impulse response of the transmission media channel, to derive a reference value related to the training signal sequence that can be expressed as a matrix M=({overscore (X)}X) 1 {overscore (X)}, where X is the training signal sequence in matrix form, and {overscore (X)} is the Hermitian of X; and using the reference value to operate on the observed or measured output signal for decoupling the training signal sequence from the observed or measured output signal expressed as a vector Y for computing an estimated impulse response H of the transmission media channel, expressed as H=MY.
14. The method of claim 13 , further comprising computing the matrix M off-line from communications with the transmission media channel.
15. The method of claim 13 , further comprising using the estimated impulse response of the transmission media channel to remove impairments imposed by the transmission media channel on received signals.
16. The method of claim 13 , further comprising using the estimated impulse response of the transmission media channel for setting the coefficients of a filter.
17. The method of claim 13 , further composing using the estimated impulse response of the transmission media channel for setting the coefficients of an echo canceller.
18. The method of claim 13 , further comprising using the estimated impulse response of the transmission media channel for setting the coefficients of an equalizer.
19. A system for rapid identification of characteristics of a transmission media channel, comprising:
a transmission media channel;
a processor coupled to the transmission media channel, said processor adapted to execute code to:
generate a known training signal sequence;
transmit the training signal sequence as an input to the transmission media channel;
obtain an output signal of the transmission media channel related to the transmitted training signal sequence and an unknown impulse response of the transmission media channel;
compute a reference value from the training signal sequence by executing the code to compute a matrix M=({overscore (X)}X) 1 {overscore (X)} representing the reference value, off-line from the transmission media channel, wherein X is the training signal sequence in matrix form, and {overscore (X)} is the Hermitian of X; and
decouple the training signal sequence from the output signal of the transmission media channel, expressed as a vector Y, to compute an estimated impulse response H of the transmission media channel, expressed as H=MY.
20. The system of claim 19 , wherein the processor comprises a DSP.
21. The system of claim 20 , further comprising a hybrid coupling the DSP to the transmission media channel.
22. The system of claim 19 , wherein the processor comprises a CPU of a computer.
23. The system of claim 19 , further comprising a modern coupling the processor to the transmission media channel.
24. The system of claim 19 , wherein the processor forms part of a communications system.
25. The system of claim 19 , wherein the processor forms part of a modem.
26. The system of claim 19 , further comprising a hybrid coupling the processor to the transmission media channel.
27. The system of claim 19 , wherein the processor is adapted to use the estimated impulse response of the transmission media channel to remove impairments imposed by the transmission media channel on received signals.
28. The system of claim 19 , further comprising a fitter adapted to remove transmission media channel impairments from signals received from the transmission media channel using the estimated impulse response of the transmission media channel.
29. The system of claim 28 , wherein the filter comprises an echo canceller for removing echo signals.
30. The system of claim 28 , wherein the filter comprises an equalizer whose output is equalized for gain and phase.
31. A system for rapid identification of characteristics of a transmission media channel, comprising:
a processor for executing code for generating a known training signal sequence, the known training signal sequence transmitted as an input to the transmission media channel;
a communications system coupling the processor to the transmission media channel, the processor executing the code to:
obtain an observed or measured output signal of the transmission media channel related to the transmitted training signal sequence and an unknown impulse response of the transmission media channel,
compute from the training signal sequence, a reference value matrix M=({overscore (X)}X) 1 {overscore (X)}, off-line from the transmission media channel, wherein X is the known training signal sequence, and {overscore (X)} is the Hermitian of X,
decouple the training signal sequence from the observed or measured output signal of the transmission media channel, represented as a vector Y, and
compute an estimated impulse response H of the transmission media channel expressed as H=MY; and
a disk storage medium for providing the code to the processor.
32. The system of claim 31 , wherein the processor comprises a DSP.
33. The system of claim 31 , wherein the processor comprises a CPU of a computer.
34. The system of claim 31 , further comprising a modem coupling the processor to the transmission media channel.
35. The system of claim 31 , wherein the processor forms part of the communications system.
36. The system of claim 31 , wherein the processor forms part of a modem.
37. The system of claim 31 , further comprising a hybrid coupling the processor to the transmission media channel.
38. The system of claim 31 , wherein the estimated impulse response of the transmission media channel is computed in a hardware implementation.
39. The system of claim 31 , wherein the estimated impulse response of the transmission media channel is computed in a software implementation.
40. The system of claim 31 , wherein the processor is adapted to use the estimated impulse response of the transmission media channel to remove impairments imposed by the transmission media channel on received signals.
41. The system of claim 31 , further comprising a filter adapted to remove transmission media channel impairments from signals received from the transmission media channel using the estimated impulse response of the transmission media channel.
42. The system of claim 41 , wherein the filter comprises an echo canceller for removing echo signals.
43. The system of claim 41 , wherein the filter comprises an equalizer whose output is equalized for gain and phase.