Published in Wolcott, T.J., & Osborne, W.P. (1995). Uplink-noise limited satellite channels. IEEE Military Communications Conference, 1995. MILCOM '95, Conference Record, v.2, 717-721. doi: 10.1109/MILCOM.1995.483559 ©1995 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.


Many applications, current and emerging, are faced with a relatively new and interesting channel model. Systems which transmit data through a nonlinear relay, such as a satellite, must deal with a composite channel that can be separated into two distinct channels - the uplink channel between the user and the relay, and the downlink channel between the relay and the final destination. If the system has a strict power limitation and high data rate demands, such as a small satellite transmitting through NASA's TDRSS Network, the dominant noise is present on the uplink rather than the downlink channel. Such a system is deemed to be uplink-noise limited and presents the designer with a number of problems not encountered in a more typical downlink-noise limited channel.

Whereas the transmitted signal constellation can be pre-distorted to take into account the effect of the nonlinearity in the down-link limited channel, no amount of pre-distortion will solve the problems encountered when the majority of the noise is present before the nonlinearity. Instead, the receiver must be modified to reflect the non- Gaussian noise due to the operation of the nonlinearity on Gaussian noise.

Under three assumptions - there is no downlink-noise present, the downlink channel is wideband relative to the data, and the filter proceeding the nonlinearity meets both matched filter and Nyquist requirements - such modifications can be made based on the nature of the nonlinearity. By mapping the ideal decision region through the nonlinearity, performance almost identical to that of a linear-wideband AWGN channel can be achieved. This paper will develop the theoretical performance of the receiver described for a nonlinearity typical of a satellite channel. Performance curves will be presented for QPSK, SPSK, 16PSK and 16QAM modulation schemes.