Method and apparatus of estimating non-linear amplifier response in an overlaid communication system
An approach is provided estimating non-linear characteristics of an amplifier (such as a Travelling Wave Tube Amplifier) used to amplify a composite signal in a radio communication system. The composite signal, which includes a plurality of inbound signals overlay on an outbound signal, is sampled. The outbound signal is utilized as a training signal. Coarse estimates of the response of the amplifier is generated based on the samples of the composite signal and the training signal. Further, the interference associated with the inbound signals are removed from the estimation of the response of the amplifier by curve-fitting and estimating interference characteristics of the composite signal. An estimated response of the amplifier is thus output, and can be utilized to provide accurate non-linearity compensation and cancellation.
1 . A method of estimating non-linear characteristics of an amplifier used to amplify a composite signal in a radio communication system, the method comprising:
sampling the composite signal that includes a plurality of inbound signals overlay on an outbound signal, wherein the outbound signal is utilized as a training signal;
generating coarse estimates of response of the amplifier based on the samples of the composite signal and the training signal;
removing interference associated with the plurality of inbound signals from the estimation of the response of the amplifier by curve-fitting and estimating interference characteristics of the composite signal; and
outputting an estimated response of the amplifier.
2 . A method according to claim 1 , further comprising:
storing the outbound signal for use as the training signal.
3 . A method according to claim 1 , further comprising:
generating the outbound signal for use as the training signal by demodulating the composite signal.
4 . A method according to claim 1 , further comprising:
filtering the samples to remove noise components according to quantization of input power of the training signal.
5 . A method according to claim 1 , further comprising:
computing, based on the coarse estimates, amplifier parameters specifying non-linear distortion characteristics associated with the amplifier; and
determining the response of the amplifier based on the amplifier parameters.
6 . A method according to claim 1 , further comprising:
iteratively performing the removing step according to one of a predetermined number of iterations and satisfying a threshold for estimated noise power associated with the composite signal.
7 . A method according to claim 1 , wherein the radio communication system includes a plurality of terminals capable of communicating over a satellite housing the amplifier, and the inbound signals are transmitted from the respective terminals to the satellite.
8 . A method according to claim 7 , wherein the amplifier is a Travelling Wave Tube Amplifier (TWTA).
9 . A computer-readable medium bearing instructions for estimating non-linear characteristics of an amplifier used to amplify a composite signal in a radio communication system, the instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 1 .
10 . An apparatus for estimating non-linear characteristics of an amplifier operating in a radio communication system, the apparatus comprising:
means for sampling a composite signal that includes a plurality of inbound signals overlay on an outbound signal, wherein the outbound signal is utilized as a training signal;
means for generating coarse estimates of response of the amplifier based on the samples of the composite signal and the training signal;
means for removing interference associated with the plurality of inbound signals from the estimation of the response of the amplifier by curve-fitting and estimating characteristics of the composite signal; and
means for outputting an estimated response of the amplifier.
11 . An apparatus according to claim 10 , further comprising:
means for storing the outbound signal for use as the training signal.
12 . An apparatus according to claim 10 , further comprising:
means for demodulating the composite signal to generate the outbound signal for use as the training signal.
13 . An apparatus according to claim 10 , further comprising:
means for filtering the samples to remove noise components according to quantization of input power of the training signal.
14 . An apparatus according to claim 10 , further comprising:
means for computing, based on the coarse estimates, amplifier parameters specifying non-linear distortion characteristics associated with the amplifier; and
means for determining the response of the amplifier based on the amplifier parameters.
15 . An apparatus according to claim 10 , wherein the removing means iteratively removes the interference according to one of a predetermined number of iterations and satisfying a threshold for estimated noise power associated with the composite signal.
16 . An apparatus according to claim 10 , wherein the radio communication system includes a plurality of terminals capable of communicating over a satellite housing the amplifier, and the inbound signals are transmitted from the respective terminals to the satellite.
17 . An apparatus according to claim 16 , wherein the amplifier is a Travelling Wave Tube Amplifier (TWTA).
18 . A method of compensating for amplifier non-linearity in a radio communication system, the method comprising:
estimating distortion characteristics of an amplifier in real-time based on samples of a received composite signal and a training signal, wherein the composite signal includes a plurality of inbound signals overlay on an outbound signal that is utilized as the training signal;
iteratively curve-fitting to remove uplink interference and downlink interference from the estimates; and
modifying the received composite signal based on the estimates.
19 . A method according to claim 18 , wherein the radio communication system includes a plurality of terminals capable of communicating over a satellite housing the amplifier, and the inbound signals are transmitted from the respective terminals to the satellite, the amplifier being a Travelling Wave Tube Amplifier (TWTA).
20 . A computer-readable medium bearing instructions for compensating for amplifier non-linearity in a radio communication system, the instructions being arranged, upon execution, to cause one or more processors to perform the step of a method according to claim 18.