In free-space optical(FSO) communications, the performance of the communication systems is severely degraded by atmospheric turbulence. Channel coding and diversity techniques are commonly used to combat channel fadin...
详细信息
In free-space optical(FSO) communications, the performance of the communication systems is severely degraded by atmospheric turbulence. Channel coding and diversity techniques are commonly used to combat channel fading induced by atmospheric turbulence. In this paper, we present the generalized block Markov superposition transmission(GBMST) of repetition codes to improve time diversity. In the GBMST scheme, information sub-blocks are transmitted in the block Markov superposition manner, with possibly different transmission memories. Based on analyzing an equivalent system, a lower bound on the bit-error-rate(BER) of the proposed scheme is presented. Simulation results demonstrate that, under a wide range of turbulence conditions, the proposed scheme improves diversity gain with only a slight reduction of transmission rate. In particular, with encoding memory sequence(0, 0, 8) and transmission rate 1/3, a diversity order of eleven is achieved under moderate turbulence conditions. Numerical results also show that, the GBMST systems with appropriate settings can approach the derived lower bound, implying that full diversity is achievable.
In this study, the authors' present a scheme, denoted as BMST-MSK, which combines the block Markov superposition transmission (BMST) with the minimum shift keying (MSK) signalling. The BMST-MSK can be implemented ...
详细信息
In this study, the authors' present a scheme, denoted as BMST-MSK, which combines the block Markov superposition transmission (BMST) with the minimum shift keying (MSK) signalling. The BMST-MSK can be implemented in two forms - the BMST with recursive MSK (BMST-RMSK) and the BMST with non-recursive MSK (BMST-NRMSK). The BMST-MSK admits a sliding-windowdecoding/demodulation algorithm, where two schedules with or without iterative processing between the BMST and MSK (referred to as outer iteration) are discussed. To analyse the asymptotic performance of BMST-MSK, the authors' first assume a genie-aided decoder and then derive the union bound for the equivalent genie-aided system. Numerical results show that the performances of the BMST-MSK match well with the derived lower bounds in the low error rate regions. From simulations, the authors' found that the outer iterations can provide performance improvement for the BMST-RMSK, but not for the BMST-NRMSK. Taking a (2,1,2) convolutional code with input length of 10 000 bits as the basic code, the BMST-NRMSK achieves a bit-error-rate of 10(-5) at E-b/N-0 = 0.45 dB over additive white Gaussian noise channels, which is away from the Shannon limit about 0.25 dB.
暂无评论