Future trends in wireless communications: Exploring new structures of turbo codes

Topic description

Turbo codes have been adopted in various communication standards due to their near-capacity performance and low decoding complexity. But they suffer from a fattening around 10⁻⁵ of Frame Error Rate. Three-dimensional Turbo Codes (3D TCs) were introduced, combining both parallel and serial concatenation. They improve performance in the error floor compared to the TC, at the expense of an increase in complexity and a loss in convergence. Recently, a method to design efficient puncture-constrained interleavers for turbo codes (TCs) was introduced, which calls for a joint optimisation of puncturing patterns and interleaver function. Enhanced turbo codes were designed and submitted to the 3GPP standardization process for 5G. The aim of this thesis to explore new optimised turbo code structures that combat the floor while keeping a good convergence.

The PhD candidate will explore the following aspects:

Exploring different puncturing patterns that maximize the minimum distance of TCs under random interleaving, and looking for the most effective way to post-encode the parity bits
Improving the convergence threshold of 3D TCs
Exploring new structures for high coding rates using an 8-state time-varying post-encoder to increase the minimum distances of 3D TCs.
Association of 3D TCs with diversity techniques such as MIMO, non-uniform constellations or rotated constellations, like those used for the second generation of terrestrial digital TV. Since the rotated constellations technique is particularly effective in bad transmission conditions, the use of the specific Gray mapping may compensate the loss in the convergence threshold and could increase even more the gain in convergence threshold observed over fading channels.
Exploring double binary (and m-binary in general) 3D TCs. It is known that double binary TCs perform better than classical TCs at both high and low error rates. It is attractive to apply the time-varying technique in the case of double binary 3D TCs for instance.
Design of suitable permutations for irregular TCs. Find techniques that eliminate the interleavers producing low minimum distances early in the search process. In this way, the space of search would be reduced, and the optimised algorithm would become promising even for large blocks.

Skills required

The candidate should have earned an MSc degree, or equivalent, in one of the following fields: digital communications, information theory, signal processing, applied mathematics. He should have a strong background in digital communications and information theory as well as in signal processing for wireless communications. The candidate should be familiar with Matlab and C/C++ language or Python. The qualified candidate should also be knowledgeable in hardware architecture design for VHDL and FPGA implementation. Knowledge in cybersecurity would be an advantage. Preferably full-time students, however, part-time applicants are welcome!

Background reading

Kbaier Dhouha, Douillard Catherine, Kerouedan Sylvie, A survey of three-dimensional turbo codes and recent performance enhancements EURASIP Journal on Wireless Communications and Networking, SpringerOpen, 2013, 2013 (115), pp.1 - 13. 〈10.1186/1687-1499-2013-115〉.
Improving Turbo Codes for 5G with parity puncture-constrained interleavers, DOI: 10.1109/ISTC.2016.7593095, Conference: 2016 9th International Symposium on Turbo Codes and Iterative Information Processing (ISTC).
Li Meng, Abdel Nour Charbel, Jego Christophe, Douillard Catherine, Design of rotated QAM mapper/demapper for the DVB-T2 standard, SiPS 2009: IEEE workshop on Signal Processing Systems, Oct 2009, Tampere, Finland. pp.18 – 23.