Grayscale Image Transmission over Rayleigh Fading Channel in a MIMO System Using Different Digital Modulation Techniques with STBC

摘要

The consistent demand for higher data rates and ability to send large volumes of data without compromising the quality of communication has led the development of a new generations of wireless systems. But range and data rate limitations are there in wireless devices. In an effort to overcome these limitations, Multi Input Multi Output (MIMO) systems can be used which also increase diversity and improve the bit error rate (BER) performance of wireless systems. They also increase the channel capacity, increase the transmitted data rate through spatial multiplexing, and/or reduce interference from other users. MIMO systems thus make a promising communication systems because of their high transmission rates without additional bandwidth or transmit power and robustness against multipath fading. This paper focuses on transmission of an image file using 2x2 MIMO system that achieves a full diversity gain using Alamouti's Space Time Block Coding technique for 2 transmitting antennas and 2 receiving antennas. Different modulation techniques viz. BPSK, QPSK, 16-QAM and 64-QAM are used and performances has been evaluated in terms of BER vs. SNR to find out the best modulation technique in a given environment. Space-Time Codes have been used which in addition to the time and spectral domain, also exploit the spatial domain. Simple maximum likelihood decoding algorithm is used at the receiver side to decode the received encoded signal.