Improve the performance of LTE Turbo coded modulation by irregular mapping

3GPP long term evolution (LTE) Turbo coded modulation is well-known for its excellent error-control capability. However, its decoding threshold is still a few decibels away from the constellation-constrained capacity. In this paper, an irregular mapping scheme involving labeling search is proposed to improve the performance of the LTE system. The scheme first predetermines one labeling, and then searches the other one via adaptive binary switch algorithm (ABSA), which considerably increases the design freedom and can provide near-optimal match to a given channel code. By applying the scheme to the LTE specification (Release 8), a practical bit-interleaved Turbo coded modulation with iterative demapping and decoding (Turbo-BICM-ID) system is proposed. With a slight modification on the constellation mapping, the scheme can lower the signal-to-noise ratio (SNR) threshold by 0.43~0.48dB at the block error rate (BLER) of 10^-2 under different channel conditions.