Research On Bit-interleaved Coded Modulation And Soft-demodulation Techniques

Bit-Interleaved Coded Modulation(BICM), as a typical coded modulation technique, has simple structure and excellent performance. To avoid the poor ?exibility and bad performance over fading channel of TCM, it can enhance the ?exibility of system by inserting the bit interleaver between coder and modulator and improve the performance over fading channel. Since its invention in late 1990 s, BICM has been adopted by kinds of practical wireless communication systems, such as 802.11, 802.16, HSPA,LTE, etc.At present, the study of BICM system focused on the design of constellation mapping and interleaver, as well as the combination with new advanced technologies, such as MIMO, OFDM, etc. Some improvement project for BICM has also been discussed.Although much of success has been achieved, there are still some open problems, for example, the effect on performance of mismatched demodulation algorithm causing by non-ideal interleaver, the complexity of demodulation for high-order modulation.Aiming at the above problems, we ?rst give further study on the improvement of BICM, bit-cooperative coded modulation(BCCM). The error exponent of BCCM system has been derived and it can give a theoretical foundation for the superiority of BCCM using high rate code. Meanwhile, based on the combination of BCCM and Turbo code, we discussed the effect of known bits on decoding progress. At last, much of the simulations prove the BCCM system has more than 0.2dB gain over BICM system when using high rate code.As simpli?ed demodulation algorithm is often applied at the receiver and channel estimation is imperfect, the problem of mismatched demodulation can not be ignored. Base on the concept of generalized mutual information(GMI), we discussed the demodulation algorithm of BICM-OFDM system suffered with narrow-band interference(NBI) and imperfect channel estimation, a two-dimension correction method of demodulation algorithm has been proposed and it can improve the performance without increasing complexity.High-order modulation has been adopted by some wireless communication systems due to its high spectrum e?ciency, but its high complexity for demodulation is always a problem which is worth detailed study. In this paper, a novel adaptive demodulation algorithm has been proposed, it simplify the Log-MAP demapper by ?nding the closet points to received symbol continually. Simulations can prove the proposed algorithm can decrease the complexity without losing performance.