Truncated and Optimized Pilot-to-Data Power Ratio for MIMO-OFDM Systems

This paper evaluates optimal pilot-to-data power ratio (PDPR) for capacity scaling in multi carrier systems. Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM must be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and also to reduce fading effects and to enhance the system capacity on time-variant and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO)-OFDM configuration. Pilot-symbol-aided or decision-directed channel estimation are used to track the channel variations in MIMO-OFDM systems. While pilot symbols facilitate channel estimation, they reduce the energy to be transmitted for data symbols over a fixed total transmit power constraint. We compute a lower bound on the capacity of a channel that is learned by training, and maximize the bound as a function of the received signal-to-noise ratio, and derive the optimal PDPR in MIMO-OFDM systems with three different types of pilot patterns: independent, scattered, and orthogonal. The result tells us that implementing the optimal PDPR in an actual MIMO-OFDM system surprisingly have broad range of PDPR values over which near optimal capacity is achieved. Performance of simulation results are demonstrated in terms of information theoretic capacity and signal to noise ratio (SNR).