Patent EA-002214-B1 (EA)
Title: Method and apparatus for determining an operating point of a non-linear amplifier of a communication channel
Inventor: BERTHSCHEIDER GERHARD
IPC: H04B17/00
Filed: 1998-12-17
Abstract: 1. Method for determining an operating point of a non-linear amplifier 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 traveled 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 operating point of said non-linear amplifier of the communication channel on the basis of said clean carrier signal f(t) and said recovered carrier signal f'(t). 2. Method according to claim 1, wherein the level of said PN modulated clean carrier signal s(t) is approx. 20 dB or more below the level of said payload signal. 3. Method according to claim 2, wherein the level of said PN modulated clean carrier signal s(t) is approx. 30 dB or more below the level of said payload signal. 4. Method according to any one of claims 1 to 3, wherein said first pseudo noise signal PN(t) is a binary pseudo noise sequence. 5. Method according to claim 4, wherein said binary pseudo noise sequence is generated by means of a feed back shift register or a memory device in which a sequence of values of a pseudo noise signal is stored. 6. Method according to any one of claims 1 to 5, 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). 7. Method according to any one of claims 1 to 6, wherein a gain is determined on the basis of said clean carrier signal f(t) and said recovered carrier signal f'(t) and said gain is used to determine the input power of said payload signal. 8. Method according to claim 7, wherein reference values are used to derive from said gain the input power of said payload signal. 9. Method according to claim 8, wherein said reference values have been prerecorded for said non-linear amplifier and represent a gain curve or a transfer curve of said non-linear amplifier over the input power of said payload signal. 10. Method according to any one of claims 1 to 9, wherein said communication channel is a transponder of a communication satellite. 11. Apparatus for determining an operating point of a non-linear amplifier of a communication channel through which a payload signal is transmitted at a predetermined level, comprising: - first pseudo noise signal generating means (19) for generating a pseudo noise signal PN(t); - first modulating means (20) 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); - transmitting means (21, 22, 23) 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; receiving means (23, 24) for receiving a receive signal s'(t) corresponding to said PN modulated clean carrier signal s(t) after having traveled through said communication channel; and - first correlating means (25, 26) for correlating said receive signal s'(t) with said pseudo noise signal PN(t) to generate a recovered carrier signal f'(t). 12. Apparatus according to claim 11, wherein the level of said PN modulated clean carrier signal s(t) is approx. 20 dB or more below the level of said payload signal. 13. Apparatus according to claim 12, wherein the level of said PN modulated clean carrier signal s(t) is approx. 30 dB or more below the level of said payload signal. 14. Apparatus according to any one of claims 11 to 13, wherein said first pseudo noise signal generating means (9) is a feed back shift register or a memory device in which a sequence of values of a pseudo noise signal is stored. 15. Apparatus according to any one of claims 11 to 14, further comprising first delaying means (26} for delaying said first pseudo noise signal PN(t). 16. Apparatus according to any one of claims 11 to l5, further comprising means (27) for determining a gain on the basis of said clean carrier signal f(t) and said recovered carrier signal f'(t). 17. Apparatus according to claim 16, further comprising means (28) for deriving from reference values and from said gain the input power of said payload signal. 18. Apparatus according to claim 17, comprising means (29} for storing said reference values having been prerecorded for said non-linear amplifier and representing a gain curve or transfer curve of said nonlinear amplifier over the input power of said payload signal.