Performance Analysis of Higher Order Digital Modulation Techniques for Hybrid Spread Spectrum Systems

Abstract

There are two types of digital transmission techniques that give acceptable bit rates and good performance. The first is in satellite communications, where these schemes make efficient use of the limited power available. The second is in mobile wireless, where the schemes make efficient use of the limited bandwidth available for the in-demand service. However, both systems are limited in bandwidth and vulnerable to hostile jamming and radio interference. The novelty of the spread spectrum lies primarily in its wideband, pseudorandom approach to signal transmission, which provides intrinsic benefits such as interference resistance and security. Specific implementations of spread spectrum, such as FHSS and DSSS, add their own innovative techniques to realize these benefits. Furthermore, a hybrid of the two methods can be built to improve processing gain over a single strategy. Compared to traditional narrowband methods, spread spectrum offers a fundamentally different and more robust approach to communication. Hence, the aim of this thesis is to model and simulate the three spread spectrum systems, FFHSS, DSSS, and DS/FFHSS, using Matlab /Simulink software, with Higher M-QAM (16 QAM, 32 QAM, 64 QAM and 128 QAM) modulations and Rayleigh fading channel. The DS/FFHSS system performances were then compared with FHSS, and DSSS based on Bit Error Rate (BER), signal-to-noise ratio (SNR), Q-factor, and received signal power (POWER) metrics. The results revealed that the DS/FFHSS system outperformed the DSSS and FHSS systems at fixed SNR values (0-20 dB) by 74%, 58.5%, and 32.5%, respectively, in BER, SNR, and Q- factor metrics, whereas the values in the received power signal were identical in lower SNRs and differed slightly at higher SNR levels.