On Implicit and Explicit Channel Estimation for Compress and Forward Relaying OFDM Schemes Designed by Information Bottleneck Graphs

Recently, Information Bottleneck Graphs (IBGs) have been introduced for quantizer design in general receivers. These IBGs allow implicit channel estimation during quantization, i.e. , received pilot and data symbols are processed jointly in a two dimensional quantizer. Hence, the uncertainty in the received pilots is considered in the the quantizer design which uses the Information Bottleneck (IB) method for optimization. Furthermore, by applying channel estimation explicitly before quantization, occurring errors due to noise can as well be considered statistically in an IBG. For practical investigation, simulations are carried out for a Bit Interleaved Coded Modulation (BICM) scheme with a range of discrete transmission rates, different quantizer rates and joint decoders. Implicit and explicit channel estimation will be compared in terms of total achievable rate of the system. Results reveal that the degradation due to channel estimation errors is much more severe than the additional mismatch error of non adapted quantizer design.