Patent EA-002140-B1 (EA)
Title: Method and apparatus for determining characteristics of components of a communication channel under load
Inventor: BERTHSCHEIDER GERHARD
IPC: H04B17/40
Filed: 1998-12-17
Abstract: 1. Method for determining characteristics of components of a communication channel through which a payload signal is transmitted at a predetermined level, comprising: generating a first pseudo noise signal PN(t); modulating a clean carrier signal f(t) with said first pseudo noise signal PN(t) to generate a PN modulated clean carrier signal s(t); transmitting said PN modulated clean carrier signal s(t) simultaneously with said payload signal through said communication channel at a level below the level of said payload signal; receiving a receive signal s'(t) corresponding to said PN modulated clean carrier signal s(t) after having travelled through said communication channel; correlating said receive signal s'(t) with said first pseudo noise signal PN(t) to generate a recovered carrier signal f'(t) and determining the amplitude response and the group delay of the communication channel at selected discrete frequencies on the basis of a comparison of said clean carrier signal f(t) and said recovered carrier signal f'(t). 2. Method according to claim 1, wherein the PN modulated clean carrier signal s(t) has a narrow bandwidth such that the runtime of the PN modulated clean carrier signal s(t) corresponds to the group delay at its centre frequency. 3. Method according to claim 1 or 2, wherein the attenuation of the recovered carrier signal f'(t) corresponds to the amplitude response of the communication channel. 4. Method according to one of the claims 1 to 3, wherein said correlating of said receive signal s'(t) and said first pseudo noise signal PN(t) is achieved by delaying said first pseudo noise signal PN(t) and multiplying the delayed first pseudo noise signal PN(t) and said receive signal s'(t). 5. Method according to claim 4, wherein the pseudo noise signal PN(t) is delayed such that the amplitude of the recovered carrier signal f'(t) becomes maximal. 6. Method according to one of the claims 1 to 5, wherein the amplitude response and the group delay are determined over the pass band of a communication channel relative to the amplitude response and the group delay at the centre frequency of the pass band. 7. Method according to claim 6, wherein the amplitude and the delay at the centre frequency are subtracted from the amplitude and the delay at any other frequency in s, the pass band. 8. Method according to one of the claims 1 to 7, further comprising: generating a second pseudo noise signal PNRR(t); modulating a reference carrier signal fR(t) with said second pseudo noise signal PNR(t) to generate a PN modulated reference carrier signal SR(t); transmitting said PN modulated reference carrier signal SR(t) simultaneously with said payload signal through said communication channel at a level below the level of said payload signal; receiving a reference receive signal SR'(t) corresponding to said PN modulated reference carrier signal SR(t) after having travelled through said communication channel; correlating said reference receive signal SR'(t) with said second pseudo noise signal PNR(t) to generate a recovered reference carrier signal fR'(t); and determining the amplitude response and the group delay of the communication channel at selected discrete frequencies also on the basis of a comparison of said reference carrier signal fR(t) and said recovered reference carrier signal fR'(t). 9. Method according to claim 8, wherein a corrected an amplitude response and a corrected group delay of the communications channel are obtained by subtracting the values obtained by the reference carrier signal fR(t) and the recovered carrier signal fR'(t) from the values obtained by the clean carrier signal f(t) and the recovered reference carrier signal f'(t). 10. Apparatus for determining characteristics of components of a communication channel through which a payload signal is transmitted at a predetermined level, comprising: means for generating a first pseudo noise signal PN(t); means for modulating a clean carrier signal f(t) with said first pseudo noise signal PN(t) to generate a PN modulated clean carrier signal s(t); means for transmitting said PN modulated clean carrier signal s(t) simultaneously with said payload signal through said communication channel at a level below the level of said payload signal; means for receiving a receive signal s'(t) corresponding to said PN modulated clean carrier signal s(t) after having travelled through said communication channel; means for correlating said receive signal s'(t) with said first pseudo noise signal PN(t) to generate a recovered carrier signal f'(t); and means for determining the amplitude response and the group delay of the communication channel at selected discrete frequencies on the basis of a comparison of said clean carrier signal f(t) and said recovered carrier signal f'(t). 11. Apparatus according to claim 10, wherein the PN modulated clean carrier signal s(t) has a narrow bandwidth such that the runtime of the PN modulated clean carrier signal s(t) corresponds to the group delay at its centre frequency. 12. Apparatus according to claim 10 or 11, wherein the attenuation of the recovered carrier signal f'(t) corresponds to the amplitude response of the communication channel. 13. Apparatus according to one of the claims 10 to 12, wherein said correlating comprises a delaying means for delaying said first pseudo noise signal PN(t) and a multiplying means for multiplying the delayed first pseudo noise signal PN(t) and said receive signal s'(t). 14. Apparatus according to claim 13, wherein the delay time of said delaying means is such that the amplitude of the recovered carrier signal f'(t) becomes maximal. 15. Apparatus according to one of the claims 10 to 14, wherein the amplitude response and the group delay are determined over the pass band of a communication channel relative to the amplitude response and the group delay at the centre frequency of the pass band. 16. Apparatus according to claim 15, wherein the amplitude and the delay at the centre frequency are subtracted from the amplitude and the delay at any other frequency in the pass band. 17. Apparatus according to one of the claims 10 to 16, further comprising: means for generating a second pseudo noise signal PNR(t); means for modulating a reference carrier signal fR(t) with said second pseudo noise signal PNR(t) to generate a PN modulated reference carrier signal SR(t); means for transmitting said PN modulated reference carrier signal SR(t) simultaneously with said payload signal through said communication channel at a level below the level of said payload signal; means for receiving a reference receive signal SR'(t) corresponding to said PN modulated reference carrier signal SR(t) after having travelled through said communication channel; means for correlating said reference receive signal SR'(t) with said second pseudo noise signal PNR(t) to generate a recovered reference carrier signal fR'(t); and means for determining the amplitude response and the group delay of the communication channel at selected discrete frequencies also on the basis of a comparison of said reference carrier signal fR(t) and said recovered reference carrier signal fR'(t). 18. Apparatus according to claim 17, wherein a corrected amplitude response and a corrected group delay of the communications channel are obtained by subtracting the values obtained by the reference carrier signal fR(t) and the recovered carrier signal fR' (t) from the values obtained by the clean carrier signal f(t) and the recovered reference carrier signal f'(t).