Digitising the 2:1 Shannon mappings for transport over heterogeneous networks

Summary form only given. We have earlier presented a joint source-channel coding (JSCC) method for 2:1 bandwidth reduction, a method called Shannon mappings. We extend this scheme to include a digital transport network between the point of the received JSSC symbols and the ultimate destination. Since the JSCC symbols are amplitude-continuous, some form of digitising or transcoding is necessary before transmission on the digital network. Instead of decoding the JSCC symbols and subsequently applying a digital source coder, we propose using a uniform scalar quantization directly on the received channel symbols. The quantizer can be either be applied at the receiver side or it can be applied at the transmitter with jointly optimised JSCC and quantization. We compare the performance of these two approaches with a 2D entropy-constrained vector quantizer (2D-ECVQ) applied to the decoded JSCC symbols. We see that applying the quantizer at the transmitter side and jointly optimise mapping and quantization is always better than both the 2D-ECVQ and the receiver-side quantizer. Finally, we note that with the quantizer rate equal to the channel capacity, the proposed system is only 2.8 dB away from the theoretical optimum, this without any coding at all