Simulation Model for a Frequency-Selective Land Mobile Satellite Communication Channel

This paper investigates a three-state simulation model for a frequency-selective land mobile satellite communication (LMSC) channel. Aside from ionospheric effects, the propagation channels for LMSC systems are also characterized by wideband effects due to multipath fading which makes the channels time-variant and exhibit frequency-selective distortion. Hence, an adequate knowledge and modelling of the propagation channel is necessary for the design and performance evaluation of the LMSC systems. A three-state simulation model for a frequency-selective LMSC channel, which is a combination of Rayleigh, Rician and Loo fading processes, is developed. The propagation characteristics of the proposed LMSC channel model are presented, and comparisons are made with the Rayleigh, Rician and Loo fading channels using bit error rate (BER) as the figure of merit. The simulation results show that the degree of fading experienced by the LMSC link depends on the length of time the mobile terminal is in a particular state or location, depending on the assumed probability of occurrence of each fading process; and it is observed from the BER results that the propagation impairment of the LMSC fading channel is relatively lower than that of Rayleigh and Loo fading channels but higher than the Rician fading channel. Keywords: mobile, multipath fading, propagation channel, satellite communication, wideband.

Performance of RS and BCH Codes over Correlated Rayleigh Fading Channel using QAM Modulation Technique

The quest for a reliable reception of the replica of a transmitted signal over wireless medium has become very important in the transmission and reception of information. In order to mitigate the effect of the degradation of the transmitted signal, error correction techniques are employed to reliably recover the erroneous bits inherent especially when the channel is in deep fading. In this paper, the performance of Reed Solomon (RS) and Bose-Chaudhuri-Hochquenghem (BCH) codes over correlated Rayleigh fading is presented. This work also investigated the effect of error correction code in the variation of the modulation order of the QAM. The simulation was carried out by encoding randomly generated data using both RS and BCH codes and then modulated by varying the modulation order of the quadrature amplitude modulation before transmitted over a correlated Rayleigh distributed channel. At the receiver, the received signal was demodulated and decoded. The bits in error received were detected and corrected to retrieve back the original transmitted signal. The system was evaluated in bit error rate and the result showed that BCH code performs better for higher modulation order. Keywords: Correlated channel, Rayleigh fading, M-QAM, RS code, BCH code

Mitigation of Ionospheric Scintillation on Global Positioning System (GPS) Using Hamming and Convolutional Coding Techniques

The Global Positioning System (GPS) is a satellite-based system that can be used to locate positions anywhere on the earth surface. Any person with a GPS receiver can access the system, and it can be used for application that requires location coordinates. Currently, ionospheric scintillation is the largest error source in GPS. Scintillation causes some effects such as degradation of receiver tracking performance and in extreme cases, total loss of navigation capabilities.             Ionospheric scintillation is a problem for satellite communication because it affects the amplitude and phase of radio signals. A decrease in the amplitude of a radio signal reduces its power level which directly affects the signal to noise ratio, thus affecting a base station's ability to detect and receive the signal. Error correction codes techniques are applied in almost all digital systems as they provide better performance for dealing with the unwanted signal (noise). This research work has investigated the performance of hamming and convolutional coding techniques in mitigating error in GPS signal modeled in MATLAB/Simulink by transmitting randomly generated data through a Rayleigh fading channel. The performance metric employed in evaluating the system is Bit Error Rate (BER). The simulation results showed a comparison of the BER performance of the uncoded and coded signals (using Hamming and Convolutional coding techniques)