Spectral Efficiency Improvement in MIMO OFDM Systems with Interleave Division Multiplexed (IDM) Space Time Block Coding (STBC) Scheme

MIMO OFDM systems are very popular in 4G wireless standards because of higher spectral efficiency and reliable transmission. Long Term EvolutionAdvanced (LTE-A) standards use MIMO with a maximum of 8x8 antennas in the downlink and 4x4 antennas in uplink. In this paper a simple 2x1 MIMO system with Alamouti coding is considered. Orthogonal Space Time Block Codes (OSTBC) is mainly used to achieve space and time diversity which improves the reliability of the system. In the conventional schemes based on the average channel gains adaptive modulated symbols are Alamouti coded and transmitted. In adaptive modulated STBC, when different modulation schemes are employed in transmitting antennas decoding complexity increases. This paper proposes a new technique called Interleave Division Multiplexing (IDM) which is an alternate to the conventional adaptive modulation. The results show that proposed method improves the spectral efficiency of MIMO system and reduces the decoding complexity.