Research On Bit-Interleaved Coded Modulation

Coded Modulation technique is a hot issue in code field in recent 20 years. It appeared in 1982 when G. Ungerboeck proposed trellis coded modulation(TCM) theory. It can encode efficiently while maintain the transfer rate over the channels with limited bandwidth and power. It can be proved the performance of TCM over additive white Gaussian noise(AWGN) channels is perfect but it is not true over fading channels. There is an effective method to solve this problem that combines interleave technique with coded modulation to get the gain of performance over fading channels. This paper is about coded modulation technology with bit interleaver called bit-interleaved coded modulation (BICM), another technique called bit-interleaved coded modulation with iterative decoding(BICM-ID), and analysis their performance over different channels.Firstly, BICM system and BICM-ID system are introduced in this paper, including their basic principles and key techniques. Secondly, the principle of 2-FSK/4-PSK digital modulation proposed accompany with coded modulation is emphasized on this paper. It can be proved this digital modulation extends the signal space to four dimensions. Thirdly, 2-FSK/4-PSK is introduced into BICM system, an improved BICM system based on 2-FSK/4-PSK modulation is put forward. Lastly, the main factors affected BICM system over both AWGN channels and the fading channels are analyzed, the advantages of the improved system are demonstrated.In order to study the performance of BICM, this paper designs the simulation scheme of BICM that combines the punctured convolutional code with 8PSK or 2-FSK/4-PSK modulation, matching random interleaver, and uses the way that combine coherent demodulation with Viterbi decoding in the receiver, adds the iterative feedback module for BICM-ID.Comparative simulation is done through computer. The simulation result shows that the improved BICM system outperforms the one based on 8PSK modulation by appropriate designing of the 2-FSK/4-PSK modulation over both AWGN channels and fading channels. And the improved one matches up to many times iteration of BICM-ID system based on 8PSK modulation.