Lattice quantized coded modulation

A combined coding scheme that unifies the lattice based source coding and the coded modulation is discussed. To reduce the average power of modulation, we propose both the direct and degenerate mapping methods. Assuming an image data model, we have evaluated the performance of both mapping methods. For the degenerate mapping method, the image SNR can be improved by approximately 6 dB as compared to the non mapping in a certain range of CNR. We have also evaluated the proposed scheme performance based on a combination of E₈ or Λ₁₆ lattice and a 256 QAM modulator by using the standard image data. From the results, a gain of approximately 10 dB can be achieved for the direct mapping method, and 6 dB for the degenerate mapping method with a relatively small mapping table. We should note that the maximum likelihood decoding algorithm can be easily applied, since the proposed encoding scheme still preserves the lattice structure. We have derived an optimal mapping by using a simulated annealing method for the degenerate mapping method. An extra gain of ≃1 dB compared to the normal mapping method is obtained