IMPACT OF IMPULSIVE NOISE ON OFDM OSTBC MIMO WIRELESS COMMUNICATION SYSTEM WITH HYBRID DIVERSITY

Abstract

Multipath-induced fading is the major performance limiting factor in broadband wireless communication systems. Link performance is severely degraded by fading and to maintain an acceptable performance, powerful countermeasures such as diversity techniques should be employed. In literature, different diversity combining schemes have been proposed which are Selection Combining (SC), Equal Gain Combining (EGC) and Maximal Ratio Combining (MRC). In this research work, Hybrid Diversity Combining techniques are well discussed with utmost importance. SC-MRC, MRC-SC and SC-EGC hybrid diversity techniques are studied, and comparative analysis is made, and it has been observed that considering implementation complexity and performance gain, SC-EGC hybrid diversity scheme shows better result. Impulsive, non-Gaussian noise is present in many wireless communication systems due to man-made electro-magnetic interference, atmospheric noise, or ignition noise etc. As above mentioned, hybrid diversity combining schemes are designed for Gaussian noise, but when impulsive noise is present, its performance may degrade. As such, the necessity of designing hybrid diversity techniques considering impulsive noise is felt. Middleton Class-A and Symmetric Alpha Stable (SαS) are the two most common widely accepted models for analysing wireless communication system under impulsive noise. In this research, an analytical approach utilizing hybrid diversity reception has been carried out to evaluate the performance improvement of a broadband wireless communication channel in Rayleigh fading and impulsive noise environment. This impulsive noise is considered time variant which has random occurrences with high power spectral density and short duration. The effect of impulsive noise and fading in terms of BER can be improved greatly by using Orthogonal Frequency Division viii Multiplexing (OFDM). The system BER is compared numerically for Binary Phase Shift Keying (BPSK) and OFDM system. It has been observed that there is a significant improvement in performance in terms of BER. Moreover, performance is tremendously amplified using hybrid diversity and BER performance is calculated analytically and also investigated using multiple antennas. Considering OFDM with BPSK modulation and using Orthogonal Space-Time Block Codes (OSTBC) expressing SNR and BER is found out through analytical process. Middleton Class-A and Symmetric Alpha Stable (SαS) model is considered to evaluate the effect of impulsive noise under Rayleigh Fading environment. The results are assessed analytically considering the multipath transfer function model. The numerical results exhibit that the system suffers significant power penalty due to impulsive noise which is higher for higher channel bandwidth and can be minimized by increasing number of OFDM subcarriers. This work investigates the effect of impulsive noise-modeled via the Middleton Class-A distribution on FDM-based MIMO systems that employ OSTBC with hybrid diversity schemes. OFDM provides resilience against frequency-selective fading, and OSTBC ensures spatial diversity; however, impulsive noise presents non-Gaussian, burst-like disturbances that degrade system performance significantly. Under such conditions, impulsive noise spreads energy across OFDM subcarriers, lowering BER performance more than conventional Gaussian noise. Mitigation strategies- such as blanking/ clipping, analog nonlinear limiting, and Maximum Likelihood (ML) detection assuming impulsive noise show significant BER improvement. In particular, ML detectors designed with Middleton based likelihood metrices provide up to 7 dB SNR gain over conventional Gaussian based ML detectors. Thus, by integrating robust detection techniques and adaptive hybrid diversity mechanisms, OFDM-OSTBC MIMO systems can tolerate impulsive impairments in harsh wireless environments such as power substations, in-vehicle networks, or PLL systems. The trade-off between complexity (e.g. ML-IN detectors, Parameter estimation) ix and performance gains (reduced BER, regained diversity order) thoroughly discussed, offering insights for designing resilient next-generation wireless links.