| 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 in 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.; The uplink-noise limited satellite channel and related channels represent a recent evolution in communications systems. As data rates have increased while power and size limitations have decreased, systems once considered downlink-noise limited are now uplink-noise limited. Applications on the horizon, such as satellite telephone systems, will also be uplink-noise limited. Until recently, there has been no need to study uplink-noise limited systems. Research in the field of relay and satellite channels has been focused on downlink-noise limited systems.; This dissertation addresses the problem of system design for an uplink-noise limited satellite channel. In particular, a new approach will be taken in the solution of the problems associated with such a channel. Modifications to key system components will be made in order to achieve near theoretical symbol-error rate performance. A unique receiver will be developed which compensates for the nonlinear channel effects in a way never considered before. A novel application of the Nyquist and matched filter criterion will be applied to the uplink channel, utilizing a transponder filter as the receive filter. System performance will be shown to be within 0.5 dB of the theoretical ideal at a symbol rate equal to the transponder's two-sided 3 dB bandwidth for various modulation formats. |
