Abstract—In coded OFDM systems, the transmission power of each subchannel is the same. In this letter, a power optimization scheme is presented to minimize FER or BER of a coded OFDM system under constant transmission power constraint. The power optimization is shown to be a convex optimization problem.
INTRODUCTION
CODED OFDM systems offer robust communication links with the frequency diversity that results from channel coding and interleaving. However, the power allocated to the nulls of the frequency response is likely to be wasted. If there is a feedback link from the receiver to the transmitter, the transmitter can change the power level of each subchannel keeping the total transmission power constant. Therefore, with efficient power allocation, the performance of coded OFDM systems can be improved. Subchannel power allocation schemes have been proposed for uncoded and coded OFDM systems. However, previous papers have not fully investigated the power allocation for error rate minimization considering the interaction of channel coding, interleaving and channel response.
In this, the upper bounds on bit error rate (BER) and frame error rate (FER) are derived for a coded OFDM system with given interleaver, channel coding and modulation schemes. The bounds can be expressed as sums of exponential functions or sums of Q-functions that are convex functions. Therefore, the power allocation to minimize the target BER or FER under the total transmission power constraint is shown to be a convex optimization problem. By solving the power optimization problem, the performance of coded OFDM systems can be improved compared with the conventional constant power allocation.
VIDEO DEMO
