A Pragmatic Adaptive OFDM/FDD Cellular System in Frequency-Selective Fading Channels

In this paper, an adaptive transmission scheme using QAM and LDPC code is proposed for an OFDM cellular system employing FDD. By approximating the LLR distribution to a Gaussian distribution, only two parameters, the mean and the normalized standard deviation, are required to be fed back to the transmitter. Thus, only a few more bits are needed compared to the feedback information in currently used single carrier cellular systems, such as cdma2000-1x EV-DO. It is shown by computer simulation that the proposed adaptive transmission scheme can provide up to 3dB gain over the conventional system using the mean SNR only, at the expense of only 3 more bits in feedback information.