Date of Award

Spring 1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Joseph Frank

Second Advisor

Alexander Haimovich

Third Advisor

Nirwan Ansari

Fourth Advisor

Zoran Siveski

Fifth Advisor

Kyoung Il Kim

Sixth Advisor

Simon Cohen

Abstract

This thesis deals with the problem of more than one subscriber transmitting data signals through a common satellite repeater using code division multiplexing to separate the signals. We are concerned with the problem of amplifying two DS spread spectrum signals, both QPSK or BPSK modulated, in a common device in which limiting occurs. One signal is considered the signal we desire to receive, and the other, having the same nominal carrier frequency with a small random offset, is considered to be a cochannel interferer. The case of a cochannel interferer on the uplink and downlink in QPSK signalling and BPSK signalling systems is analyzed in detail. This is an important practical problem in code division multiple access satellite communication systems, which usually contain limiting in the satellite amplifier, often in the form of a saturated traveling wave tube amplifier.

The satellite repeater is modeled using a bandpass hard limiter. The inverse Fourier transform method, which is applicable to the analysis of PN spread spectrum systems is applied to calculate the output of the bandpass hard limiter. The limiter output plus AWGN is taken to be the input of a correlation receiver for which we calculate the probability of error as function of the signal to noise and, signal to interference ratios.

From these results we can determine the effect on error performance due to the inclusion of a bandpass limiter in the transmission path.

The assumptions made in deriving the theoretical performance of the system have been checked by simulating the entire system using the BOSS software package. The results of the simulation show good agreement with the theoretical calculations within 1 to 2 dB in SNR. In addition by means of simulation we were able to explore some features of the system that could not be addressed analytically, such as the effect of unbalanced codes on system performance.

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