A CP-free STBC-MIMO OFDM communication system for underwater multipath channel

This paper proposes a Space Time Block Code (STBC) MIMO OFDM system without Cyclic Prefix (CP) but robust for long multipath echo channel, targeting the horizontal direction underwater communication. The system consists of two transmitting elements and more than 3 receiving elements. The configuration of STBC in this paper is 2 × 3 or 2 × 4. STBC-OFDM symbol length is 32 ms with 512 sampling points. Under multipath condition without CP, Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) happens and causes severe communication performance degradation. In the proposed system, the ISI is removed by multiplying Left Null Space Vectors based on measured Channel Impulse Responses (CIRs) and the ICI is minimized by multiplying Minimum Mean Square Error (MMSE) weight. By increasing the number of receiving element (transducer), the Left Null Space Vectors can be obtained. To verify the ISI and ICI suppression performance, Matlab computer simulation is used. For 2 × 3 STBC-MIMO cases, roughly 150 (16QAM) and 190 (QAM) sampling points delayed multipath has been compensated successfully. For 2 × 4 STBC-MIMO cases, more than 250 (16QAM and QPSK) sampling points delayed multipath also compensated.