PERFORMANCE MEASUREMENT AND ANALYSIS OF GMSK SIGNAL IN FADING CHANNEL

Abstract

In digital communications, errors in the received data will almost always occur. These errors can be due to the noisy channel, fading in the signal amplitude, destructive interference and a change in the channel characteristics. In this project a bit error counter system and a data acquisition system that relates the bit error data and the received signal strength (RSSI) are constructed. Based on the bit error data and the RSSI data the error performance of the transmission using GMSK modulation scheme can be monitored and analysed. For the bit error counter system , a programmable gate array logic is used to realise the pseudo random binary generator, a 8751 microprocessor is used to count the error pulses and an intelligent liquid crystal display for displaying the content of the error counter. As for the data acquisition system, an analogue to digital converter is used to digitize the signal strength and a programmable peripheral interface 8255 card is used to provide interface for digital input and output to an IBM compatible personal computer (PC).This is to enable the PC to communicate with external devices such as the 8751 microprocessor and the analogue to digital converter. Finally the personal computer provides the man machine inte1face on the screen and is used for storage and to display (and produce the hard copy) relationship of bit error rate versus RSSI in graphical form. The error data and the RSSI are collected via a Rayleigh fading channel (an enclosed room with many randomly placed objects between the transmitter and receiver) . Some plots of the relationship of bit error and RSSI are given in this report. The error data and the RSSI are collected via a Rayleigh fading channel (an enclosed room with many randomly placed objects between the transmitter and receiver). Some plots of the relationship of bit error and RSSI are given in this report.