Performance Analysis of Cyclic Prefix Free STBC Encoded MIMO-OFDM System Using Oblique Projection Technique

Abstract

In today’s era demand related to multimedia services are increasing rapidly. On the other hand, bandwidth is a scarce resource. So, the technologies which possess bandwidth efficiency are adopted to overcome this problem. This necessity of achieving high data rate and bandwidth efficiency draws attention towards Orthogonal Frequency Division Multiplexing (OFDM). To provide spatial diversity, multiple antennas at both transmitter and receiver are used, which further enhances the performance of OFDM system. An arrangement of multiple antennas at both transmitter and receiver is known as Multiple Input and Multiple Output (MIMO). MIMO together with OFDM is the recently proposed technique for next generation wireless systems. Although, this combination has many merits, but it has some disadvantages too like Inter Carrier Interference (ICI) and computational complexity. According to available literature, the conventional MIMO-OFDM system uses CP (Cyclic Prefix). CP is an overhead on the transmitted signal which is used to remove Inter-Symbol Interference (ISI). It should be noted that the length of CP will be greater than the delay spread. If this condition is not followed then ISI will also remain with ICI. This thesis considers CP free MIMO-OFDM model in two steps, firstly, frequency domain (FD) using decision feedback equalizer (DFE) with oblique projection (OB) to reduce the effect of ICI and ISI. Secondly, to decreases the number of computations V-BLAST with QR-decomposition (QRD) has been proposed. From the simulation results, it has been observed that the bit error rates performance for proposed OB FD-DFE-ZF technique under AWGN and Rayleigh fading wireless channel is better as compare to other model like ZF-OFDM, MMSE-OFDM and OFDM with CP. Moreover CP free ZF technique has better achievable rate than the other techniques like CP based ZF,CP free MMSE and CP based MMSE. From the results of V-BLAST technique, it has been observed that the number of complex multiplications will be very much less in the proposed system as compared to the conventional CP based MIMO-OFDM system.