PhD Thesis Presentation: “Code Design for Interference Channels,” Mahdi Shakiba Herfeh (EE), EE-314, 11AM November 7 (EN)

Mahdi Shakiba Herfeh
Ph.D. in Electrical and Electronics Engineering

Prof. Tolga Mete Duman

The seminar will be on Thursday, November 7, 2019 at 11:00 @ EE-314

As the number of wireless devices dramatically increasing, wireless devices experience more interfering signals in their communications. Managing interference in wireless networks is an important challenge in future wireless communications, which can be tackled in different layers of communication. Designing good channel codes, which can build reliable communication close to the information theoretic limits in the presence of interference in channel, is one of the ways to increase the quality of service.

With the above motivation, in this research, we focus on code design for interference channels (ICs). We, first consider classical two-user fading IC and study implementation of different encoding/decoding schemes with low-density parity-check (LDPC) codes for both quasi-static and fast fading scenarios. We adopt Han-Kobayashi (HK) encoding, derive stability conditions on the degree distributions of LDPC code ensembles, and obtain explicit and practical code designs. In order to estimate the decoding thresholds, a modified form of the extrinsic information transfer (EXIT) chart analysis based on binary erasure channel (BEC) approximation for the incoming messages from the component LDPC decoders to state nodes is developed. The proposed code design is employed in several examples for both fast and quasi-static fading cases. Comprehensive set of examples demonstrate that the designed codes perform close to the achievable information theoretic limits. Furthermore, multiple antenna transmissions employing the Alamouti scheme for fading ICs are studied; a special receiver structure is developed, and specific codes are explored. Finally, advantages of the designed codes over point-to-point (P2P) optimal ones are demonstrated via both asymptotic and finite block length simulations.

Next, we consider cognitive interference channels (CICs), a variant of classical two-user ICs in which one of the transmitters (cognitive transmitter) has non-causal knowledge of the other’s (private user’s) message. Prompted by the information theoretical results, we design an explicit coding scheme for CIC in the primary decodes cognitive regime. We present a novel joint decoder and design low-density parity-check codes for our set-up. Simulation results demonstrate that the proposed joint decoder and the designed codes outperform the conventional maximum ratio combining type decoder and the point-to-point optimal codes, respectively. Later, we propose and evaluate the idea of flexible modulation for P2P communication with available channel side information at the transmitter. This technique does not perform as well as dirty paper coding (DPC), however the simplicity of this technique is the main advantage. Also the flexible modulation technique shows more robustness to the inaccuracies in the channel state information. Finally, we consider a multiple access channel (MAC) in which the non-causal knowledge of one of the users’ message is available at the other user. We consider both unfaded and fading scenarios and propose the idea of joint encoding and the simulation results show that this technique outperforms the classical coding scheme.