Adaptive Procedures for OFDM Systems with Bit-Interleaved Coded Modulation

Abstract– We present adaptive power and bit loading schemes for a bit-interleaved coded OFDM system with perfect channel state information and square quadrature amplitude modulation constellations. In order to minimize the bit error rates at the output of the Viterbi decoder subject to bit rate and power constraints, an analytical expression for the bit-error rate (BER) of a harddecision device has to be minimized with respect to the number of bits and the power assigned to the subcarrier channels. The prohibitive complexity of the optimum solution can be circumvented by a simple suboptimum two-step procedure where the bit and power loading parts are decoupled. For increasing the number of transmit antennas, it is shown that the procedure has the same complexity as the one for the single transmit antenna case. Monte Carlo simulations show that for broadband systems in Rayleigh fading the loading procedures provide a relative signal-to-noise (SNR) gain of up to at a BER of . The relative gain in MISO systems is less than for increasing independently of the SNR.