Abstract
In a wireless communication system, the transmitted signal is exposed to various surfaces where it bounces and results in several delayed versions of the same signal at the receiver end. The delayed signals are in the form of electromagnetic waves that are diffracted and reflected from the various object surfaces. These result in co-channel interferences for wireless systems. MIMO has proven to be a striking solution for the new generation of wireless systems. MIMO-OFDM system with QPSK modulation is considered as the wireless system for studying the performance of interference cancellation techniques. The BER performance is studied in channels such as Rayleigh and Rician Fading Channels. The effects of interference are reduced to a certain extent by the inclusion of CDMA (spread spectrum technique) as Technique 1. The effects of interference on this system have been further reduced using the LMS filter as Technique 2. Hence, to show better performance in MIMO-OFDM systems, it is recommended to employ both CDMA and LMS filters to decrease the effects of co-channel interference. It is observed that the parameter BER reduces as the SNR increases for both these channels. Doi: 10.28991/esj-2021-01313 Full Text: PDF
Highlights
Broadband technologies like WiMax and Wireless LAN employ multi-carrier modulation techniques like OFDM
The introduction of Code Division Multiple Access (CDMA) led to a reduction in co-channel interference, and employing LMS filter in CDMA-MIMO-OFDM systems is the innovation implemented in this project
8-1- Simulation Results – Technique 1 (CDMA-MIMO-OFDM) Bit Error Rate (BER) Performance of CDMA-MIMO-OFDM systems in Rayleigh channel is plotted as shown in Figure and for Rician channel in Figure correspondingly [26,27,28,29,30]
Summary
Broadband technologies like WiMax and Wireless LAN employ multi-carrier modulation techniques like OFDM. OFDM is a multiplexing technique that uses the concept of orthogonality that transmits signals digitally on multiple carrier frequencies. It multiplexes or divides a high-speed stream of data and places them on low-speed narrow-spaced subcarriers. Going along with a common notation, sij can be understood as a modulated symbol in time slot ‘i’ from antenna ‘j’ This matrix helps in combining copies and encoding as per the STBC technique. Interference can be due to external noise addition or maybe due to adjacent and co-channel frequencies interfering with the message signal It can be a major issue since it reduces the strength of a signal at the receiver. These delay blocks interfere with the transmitted signal in the same channel and it is being termed as co-channel interference
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