Simple Bit Allocation Algorithms with BER-Constraint for OFDM-Based Systems

Orthogonal frequency division multiplexing (OFDM) has been thoroughly investigated as an enabling technology for future broadband multimedia communication. In this paper, we suggest adaptive bit allocation algorithms that operate in a frequency selective fading channel environment by exploiting channel state information obtained through a feedback channel. The proposed algorithms try to maximize the overall throughput of the system with significantly reduced complexity while guaranteeing that mean bit error rate (BER) of all sub-channels remains below the pre-defined BER threshold. To do that, the first proposed algorithm divides all sub-channels into several groups according to their signal-to-noise ratio (SNR). The grouping criteria are adaptive to the current channel state and BER constraint. The second algorithm tries to find the appropriate constellation size for each sub-channel. The proposed algorithms were compared with existing algorithms through simulation. The simulation results show that the proposed algorithms are close to optimum solution with significantly lower complexity.