Joint Optimal Pilot Placement and Space Frequency (SF) Code Design for MIMO-OFDM Systems

In this paper, we propose an optimal power allocation scheme for joint pilot placement and space frequency (SF) code design for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) wireless channels. OFDM is combined with multiple antennas to increase data diversity gain on a time varying multipath fading channel, resulting in a MIMO-OFDM system. A set of fast time-varying and frequency-selective fading channels is considered. The proposed pilot assisted transmission scheme multiplexes known symbols with information bearing data to estimate the channel in the presence of inter symbol interference (ISI). The channel is assumed to be unchanged for the duration of one OFDM block and change independently from one OFDM block to the other. The number of pilot symbols for each OFDM block is held constant and the symbols are dispersed throughout the block for efficient channel estimation. However, equally distributing the total power between the data and pilots doesn´t optimize the transmission over a frequency-selective fading channel. We propose an optimal power allocation scheme for the joint pilot placement and space frequency code design scheme based on the channel response and the bit error rate (BER) values. This leads to substantial improvement in performance for a 2 times 2 MIMO-OFDM system. The results can be extended to MIMO-OFDM systems with any number of transmit and receive antennas.