AWGN信道中一维调制与二维调制的信道容量

卫星通信和深空通信信道都可近似为加性高斯白噪声信道,所以研究这种信道中常用调制方式下的信道容量有重要意义.从香农信息论出发,推导出了一维调制和二维调制下的信道容量.在此基础上,阐明了在不同信噪比条件下应采用的调制方式,以及编码调制能够在不牺牲频谱利用率的前提下,得到编码增益的本质.讨论了无带宽约束下AM调制和PSK调制的香农限和在高信噪比条件下PSK的近似容量. 

Capacity of One-dimensional and Two-dimensional Modulation Under AWGN Channels

Satellite and deep space communication channels are regarded approximately as white Gaussian noise channels approximately, so it's significant to study on channel capacities using usual modulation schemes under this channel. Starting from Shannon's information theory, this paper develops the channel capacities of one-dimensional and two-dimensional modulation schemes. Based on above, it explains that special modulation schemes ought to be adopted according to different signal to noise ratio. For example, BPSK modulation schemes is used in deep space communication because of very low signal to noise ratio. It also explains the essential of coding gain with the same spectral efficiency applying coded modulation. For instance, a rate R=2/3 convolutional code can be combined with 8-PSK modulation which can be compared with uncoded QPSK modulation, since they both have the same spectral efficiency of η=2 bit/symbol. The Shannon's limit of AM and PSK without bandwidth constraint and the asymptotic capacity of PSK with high signal to ratio are discussed at the end of this paper.