Optimal power loading for multiple-input single-output ofdm systems with bit-level interleaving

We derive a power loading procedure optimizing the bit-error rates of multiple-input single-output (MISO) bit-interleaved coded modulation (BICM) orthogonal frequency-division multiplexing (OFDM) systems performing hard-decisions at the receiver and ideal interleaving. The adaptive subcarrier power allocation is based on either perfect or outdated channel state information at the transmitter. The scheme has the same complexity as the one for the single transmit antenna case. For a standard BICM-OFDM system in Rayleigh fading, Monte Carlo simulations show that the relative signal-to-noise ratio gain by the adaptation is up to 4 dB at an average bit-error rate level of 10
^-6
6. The relative gain in MISO systems decreases to 1.05 dB for increasing the number of transmit antennas. The achievable gain decreases for decreasing cross-correlation of the outdated and the actual channel state