Performance of star 16QAM using iterative decision-directed channel estimation for DFT-precoded OFDMA

This paper presents the average block error rate (BLER) performance of the star 16QAM scheme using iterative decision-directed channel estimation (DDCE) for discrete Fourier transform (DFT)-precoded orthogonal frequency division multiple access (OFDMA). The star 16QAM scheme achieves more efficient modulation compared to square 16QAM in that it decreases the actual required average received signal-to-noise power ratio (SNR) satisfying the target average BLER considering the peak-to-average power ratio (PAPR) of the transmitted signal for a low channel coding rate. Hence, the feature of the paper is that we apply iterative DDCE using soft-decision symbol estimation based on the log-likelihood ratio (LLR) of an extrinsic probability at the Max-Log-MAP (maximum a posteriori probability) decoder output to achieve an efficient modulation scheme with a low required average received SNR. Computer simulation results show that for the star 16QAM scheme, the average BLER using the iterative DDCE is very close to that with ideal channel estimation for a low channel coding rate such as an R = 1/3 turbo code. We also show that when iterative DDCE is employed, the (8, 8) star 16QAM scheme decreases the required average received SNR considering the cubic metric at the average BLER of 10^-2 by approximately 0.7 dB compared to the square 16QAM scheme.