Variable-rate equal-power waterfilling for non-binary LDPC coded multicarrier systems

This paper presents a link adaptation strategy for non-binary LDPC code over a time-variant frequency-selective channel. The algorithm is based first on the adoption of waterfilling technique to wisely adapt the transmitted power. It is shown that as long as best subchannels are identified with the waterfilling algorithm, an equal power distribution can be applied with performance comparable to the ideal power adaptation. What it is more important is to decide which are the subchannels that should not be used in order to increase the energy efficiency of the system. The throughput is increased with the adoption of multilevel modulations that changes the rate of each subchannel depending on the channel-to-noise ratio and the quality of service required. The Galois Field GF(64) code symbols are mapped into four modulation schemes (BPSK, 4QAM, 16QAM, 64QAM) and the channel is assumed to be constant over six OFDM symbols. Simulation results are presented when a perfect channel state information is available at the transmitter and at the receiver side. In real dynamic channel environments, the performance of the system degrades due to the delay and the approximation of the feedback information. Simulation of partial channel state information scenario is also reported.