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PERFORMANCE EVALUATION OF A TDMA DIGITAL MOBILE RADIO SYSTEM
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Mohamad R. CHAABAN
|
Univ. |
Liverpool |
Spec. |
Communication Engineering |
Deg. |
Year |
Pages |
|
Ph.D. |
1990 |
161 |
A software package simulator of a complete versatile TDMA mobile radio system has been developed. The simulator has been designed in such a way that any TDMA system can be designed and implemented. The software has been written in the C programming language under the UNIX operating system environment. As a step towards the evolution of the current TDMA system (GSM), the software has been ported to the "Comdisco" SPW‑DSP Framework platform.
The simulator has been used to assess the performance of a TDMA system based on the GSM‑DCS1800 specifications. This has been conducted through Bit Error Rate (BER) measurements under different channel conditions and with different types of receivers. The results obtained showed that a Maximum Likelihood Sequence Estimator with 2 samples/bit produced good BER performance promising good speech quality. On the other hand, the performance of an MSK‑type detector has proved to be unsatisfactory for most of the time. The results also showed that, at moderate vehicle speeds, the implemented Random Error Correcting Code (FERC) was able to correct most of the errors caused by the channel impairments (noise, co‑channel interference). However, unless frequency hopping is used at low vehicle speeds, the FERC proved to be ineffective.
The deployment of two‑branch antenna diversity reception was also considered. The results showed that the use of simple selection diversity based on the Received Signal Strength Indicator (RSSI) produces very promising BER performance. An additional gain was achieved by replacing the selection diversity with equal gain combining diversity. Furthermore, the transmission of a delayed signal from a second decorrelated antenna branch at the base station site proved to introduce some kind of diversity at the uni‑antenna mobile station. The results showed that the delay on the second antenna should be adapted according to the up‑link channel impulse response.
Aiming at low power hand‑held equipment, the channel equalizer was replaced by the simple selection diversity. This rudimentary test showed that, for highly dispersive channels, the Intersymbol Interference (ISI) was still persistent in the received signal. This led to worse BER performance as compared to that obtained with channel equalization.
