Low level multiplexing in celluar radio systems

Tusubira, Francis Frederick (1988) Low level multiplexing in celluar radio systems. University of Southampton, Doctoral Thesis.

Abstract

Low level multiplexing is proposed as an alternative to high level multiplexing, especially for the smaller cells in cellular radio. The main problem to be overcome is shown to be the generation of intermodulation products in pre-combining and post-combining amplifiers. It is demonstrated that the required intermodulation product margins can be maintained at the combining stage through the use of cheap planar microstrip combiners plus a modest output backoff in the precombining amplifiers. To reduce intermodulation products to acceptable levels while keeping costs down, the post-combining amplifier must be linearized. Linearization techniques are reviewed with the aim of identifying a method which can be adapted to improve post-combining amplifier linearity at 900 MHz. An experimental investigation is used to show that feedforward, amplitude predistortion as well as combined amplitude and phase predistortion can all provide the necessary bandwidth and dynamic range. It is however argued that amplitude predistortion offers the best compromise between cost and performance. (DX84426)

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