Adjacent Channel Interference Reduction by adaptive Equalizers

by

Shahram Golestaneh

M. Eng., 1992

Abstract

One of the major limiting factors in an efficient utilization of the frequency spectrum is adjacent channel interference (ACI). This thesis investigates the performance of a finite length digitally implemented decision feedback equalizer (DFE) in an adjacent channel interference environment. Quadrature phase shift keying (QPSK) is employed as the modulation scheme. To evaluate the system performance, analytical method and direct computer simulation are used. In the analytical approach, minimum mean square error (MMSE) is used as the performance criterion. mathematical expression for MMSE is derived and the effect of different channel spacing as well as different signal to interference ratio (SIR) on MMSE is discussed. In the simulation, error rate is considered as the performance criterion. A comparison between analytical approach and simulation method is made.

It is shown that deployment of DFE leads to significant improvement of the system performance under ACI condition. it is also shown that when one interferer is dominant, the performance of the system is far better than when two interferers are present. For the investigated range of channel spacing in this thesis, which is less than the baud rate, it is shown that for the same SIR, a larger channel spacing always leads to a better system performance.

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