Channel codng for 4G systems with adaptive modulation and codng

Abstract

Future 4G mobile systems, whether evolutionary (e.g., evolutions of WCDMA and cdma2000) or based on technology such as OFDM applied to a wide-area environment, can achieve very large average user throughputs by using adaptive modulation and coding (AMC) instead of fixed modulation (e.g., QPSK) and power control. This article discusses the impact of the underlying channel coding in 4G systems with AMC. It is shown that 3G-style turbo coding can provide a 0.5-4 dB link gain over 256-state convolutional codes, depending on the frame size, modulation, and channel. The link gains from channel coding (or other techniques) do not directly translate into throughput gains for AMC, but can still be expected to improve throughput significantly. A method of generating soft information for higher order modulations based on reuse of the turbo decoding circuitry is also provided.