Methods and apparatuses for signaling with geometric constellations in a Rayleigh fading channel
摘要
說明書
Expressed another way, the PD capacity of a channel can be viewed in terms of the mutual information between the output bits of the encoder (such as an LDPC encoder) at the transmitter and the likelihoods computed by the demapper at the receiver. The PD capacity is influenced by both the placement of points within the constellation and by the labeling assignments.
With belief propagation iterations between the demapper and the decoder, the demapper can no longer be viewed as part of the channel, and the joint capacity of the constellation becomes the tightest known bound on the system performance. A diagram conceptually illustrating the portions of a communication system that are considered part of the channel for the purpose of determining the joint capacity of a constellation is shown in
Joint capacity is a description of the achievable capacity between the input of the mapper on the transmit side of the link and the output of the channel (including for example AWGN and Fading channels). Practical systems must often ‘ demap’ channel observations prior to decoding. In general, the step causes some loss of capacity. In fact it can be proven that CG≥CJOINT≥CPD. That is, CJOINT upper bounds the capacity achievable by CPD. The methods of the present invention are motivated by considering the fact that practical limits to a given communication system capacity are limited by CJOINT and CPD. In several embodiments of the invention, geometrically shaped constellations are selected that maximize these measures.
