SPACE TIME TRELLIS CODING FOR MIMO-OFDM SYSTEM

Abstract

Space time code (STC) is a coding technique used to improve the quality of wireless communication systems. In STC multiple copies of data are transmitted from the transmitter to the receiver to ensure the chances that atleast few of them overcome the channel disturbances and reach the receiver with good quality allowing reliable retrieval of transmitted data. Space time trellis codes are one of the most important type of STC. STTC have memory and they are based on trellis. In STTC the trellis code is distributed over multiple time slots (temporal) and multiple antennas (spatial) and thus results in diversity as well as coding gain. Number of possible different STTCs increase as the number of state of trellis, no of transmitter antenna, modulation complexity increases. So finding the best STTC among them is time consuming process. Long systematic, exhaustive search is required to obtain the best performing STTC especially for higher number of states and for more number of antennas are transmitter side. An efficient and fast method to find best STTCs should be found out to reduce the exhaustive searching. A technique named as coset qr partitioning is proposed to design efficiently and quickly optimal 2 (PSK) STTCs for different number of antennas on the transmitting side. Coset partitioning is an updated extension to method of set partitioning which Ungerboeck proposed for SISO systems. Coset partitioning extends it to MIMO systems. Main idea behind this extension is the lattice and coset Calderbank approach. Seven different STTC are designed in this report .Performance evaluation of STTCs generated by the method of coset partitioning applied to a MIMO-OFDM system is evaluated with respect to various channel conditions, effect of number of multipath, delay between each multipath.