Constellation Shaping and Discrete Constellation Optimization for Near-Capacity Achieving Digital Communication

Metodi Yankov

Department of Photonics Engineering
Technical University of Denmark

Abstract:

It is well known that signaling with uniformly distributed inputs results in a gap to channel capacity. We design mapping functions for turbo-coded Bit Interleaved Coded Modulation (BICM) that achieve shaping gain over conventional uniformly distributed turbo-coded QAM. The mapping functions are based on Huffman codes with binary-reflected Gray-like properties. Decoding the binary stream into the constellation symbol according to the Huffman code results in dyadic output Probability Mass Functions (PMF), and the binary-reflected Gray code ensures near-optimal performance for BICM even when iterations are allowed between the de-mapper and decoder. We also derive interesting properties of the optimal PMF of QAM for a Multiple Input Multiple Output (MIMO) channel – namely, the PMF factorizes into the product of the marginal distributions on each dimension. This allows for simpler optimization of the input. Furthermore, approximations are derived for the discrete constellation constrained MIMO capacity in the low-to-mid SNR region by using the capacity of the equivalent orthogonal channels obtained by the SVD.

Biography:

Metodi Yankov received a B. Eng. degree from the Technical University of Sofia, Bulgaria in 2010 with a specialization in Radio communications. He received his MSc. degree from the Technical University of Denmark (DTU) in 2012, with specialization in Telecommunications, Signals and Transmission Technologies. He did his master thesis with Renesas Mobile Europe, Copenhagen, where he was also employed from June 2012 until December 2012 as a design engineer. Since then, he has been a PhD student at the Department of Photonics Engineering at DTU, under the supervision of prof. Søren Forchhammer. The title of his PhD project is “Design and Optimization of Coded Modulation Systems with Iterative and Non-iterative Processing”.