Simulation of MIMO-OFDM Transceiver using Hierarchical Modulation in the Receiver

Multiple-input multiple-output (MIMO) system helps in transmitting independent channels simultaneously, and have applications in wireless communication networks for the upcoming generations. This paper deals with the implementation of a 2 × 2 MIMO-OFDM system using superposed 32QAM constellation design with the help of an OFDM transceiver. It helps in achieving higher order modulation formats. In this project, two independent signals 4QAM and 8QAM after being modulated are made to pass through the transmitter of OFDM and after undergoing the processes through it, these two signals are made to superpose at the receiver and a 32QAM is thus obtained. It is then made to pass through the OFDM receiver into a noisy channel namely, AWGN and are finally demodulated at the receiver to retrieve the original signals 4QAM and 8QAM. The high channel correlation gain is one of the defects observed in the MIMO systems. However, this can be overcome by a simple constellation de-mapping technique that is superposing the constellations of the signals using the hierarchical modulation concept. Here an OFDM transceiver is introduced, thus being worked on the concept of hierarchical modulation. After the addition of cyclic prefix, the 4QAM and 8QAM signals are superposed in the receiver and the detection of final symbol is done with the help of de-mapped constellation technique. Using this, we can improve the bit error rate (BER), spectral efficiency and also obtain gain in multiplexing and receiver diversity. The proposed system will be simulated using MATLAB and the corresponding BER vs SNR plot is obtained.