Browsing by Subject "Code design"

Now showing 1 - 7 of 7

Open Access
Code design for interference channels
(2019-11) Herfeh, Mahdi Shakiba
As the number of wireless devices dramatically increases, they experience more interference in their communications. As a result, managing interference in wireless networks is an important challenge in future wireless communication systems, which can be tackled in di erent layers of communications. Designing good channel codes, which can enable reliable communication close to the information theoretic limits in the presence of interference, 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, rst consider classical two-user fading IC and study implementation of di erent encoding/decoding schemes with low-density paritycheck (LDPC) codes for both quasi-static and fast fading scenarios. We adopt the Han-Kobayashi (HK) type 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 modi ed 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. A comprehensive set of examples demonstrates 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 speci c codes are explored. Finally, advantages of the designed codes over point-to-point (P2P) optimal ones are demonstrated via both asymptotic and nite 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 LDPC 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 exible 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, its simplicity is a major advantage. Also the exible modulation technique shows more robustness to inaccuracy 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 Gaussian channel and fading scenarios. We propose the idea of joint encoding, and study its performance via simulations demonstrating that the proposed approach outperforms the classical coding scheme.
Open Access
Implementing the Han-Kobayashi scheme using low density parity check codes over Gaussian interference channels
(Institute of Electrical and Electronics Engineers Inc., 2015) Sharifi S.; Tanc, A. K.; Duman, T. M.
We focus on Gaussian interference channels (GICs) and study the Han-Kobayashi coding strategy for the two-user case with the objective of designing implementable (explicit) channel codes. Specifically, low-density parity-check codes are adopted for use over the channel, their benefits are studied, and suitable codes are designed. Iterative joint decoding is used at the receivers, where independent and identically distributed channel adapters are used to prove that log-likelihood-ratios exchanged among the nodes of the Tanner graph enjoy symmetry when BPSK or QPSK with Gray coding is employed. This property is exploited in the proposed code optimization algorithm adopting a random perturbation technique. Code optimization and convergence threshold computations are carried out for different GICs employing finite constellations by tracking the average mutual information. Furthermore, stability conditions for the admissible degree distributions under strong and weak interference levels are determined. Via examples, it is observed that the optimized codes using BPSK or QPSK with Gray coding operate close to the capacity boundary for strong interference. For the case of weak interference, it is shown that nontrivial rate pairs are achievable via the newly designed codes, which are not possible by single user codes with time sharing. Performance of the designed codes is also studied for finite block lengths through simulations of specific codes picked with the optimized degree distributions with random constructions, where, for one instance, the results are compared with those of some structured designs. © 1972-2012 IEEE.
Open Access
LDPC code design for fading interference channels
(IEEE, 2019-03) Shakiba-Herfeh, Mahdi; Tanc, A. K.; Duman, Tolga M.
We focus on the two-user Gaussian interference channel (IC) with fading 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 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 chart analysis based on binary erasure channel 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 optimal ones are demonstrated via both asymptotic and finite block length simulations.
Open Access
LDPC code design for fast fading interference channels
(IEEE, 2018-05) Shakiba-Herfeh, Mahdi; Tanc, A. K.; Duman, Tolga M.
We focus on two-user Gaussian interference channels (ICs) with fast fading and study implementation of explicit all public and Han- Kobayashi (HK) coding schemes with low-density parity-check (LDPC) codes. Stability conditions for the coding schemes are derived, and a modified form of the EXIT chart analysis is proposed to estimate the decoding threshold of LDPC code ensembles. The proposed code design is employed in several examples and the obtained rate pairs are compared with the achievable rate region (ARR) boundaries demonstrating that rate pairs very close to the ARR boundaries are attained. Performance of finite block length codes are also studied through simulations of specific codes picked from the optimized LDPC code ensembles in order to verify the analysis.
Open Access
LDPC code design for the two-user Gaussian multiple access channel
(Institute of Electrical and Electronics Engineers Inc., 2016) Sharifi S.; Tanc, A. K.; Duman, T. M.
We study code design for two-user Gaussian multiple access channels (GMACs) under fixed channel gains and under quasi-static fading. We employ low-density parity-check (LDPC) codes with BPSK modulation and utilize an iterative joint decoder. Adopting a belief propagation (BP) algorithm, we derive the PDF of the log-likelihood-ratios (LLRs) fed to the component LDPC decoders. Via examples, it is illustrated that the characterized PDF resembles a Gaussian mixture (GM) distribution, which is exploited in predicting the decoding performance of LDPC codes over GMACs. Based on the GM assumption, we propose variants of existing analysis methods, named modified density evolution (DE) and modified extrinsic information transfer (EXIT). We derive a stability condition on the degree distributions of the LDPC code ensembles and utilize it in the code optimization. Under fixed channel gains, the newly optimized codes are shown to perform close to the capacity region boundary outperforming the existing designs and the off-the-shelf point-to-point (P2P) codes. Under quasi-static fading, optimized codes exhibit consistent improvements upon the P2P codes as well. Finite block length simulations of specific codes picked from the designed ensembles are also carried out and it is shown that optimized codes perform close to the outage limits. © 2015 IEEE.
Open Access
LDPC codes for interference channels in the primary decodes cognitive regime
(Institute of Electrical and Electronics Engineers Inc., 2019) Shakiba-Herfeh, Mahdi; Tanç, A. K.; Duman, Tolga M.
We investigate cognitive interference channels (CICs), a variant of two-user ICs in which one of the transmitters (called the 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 this 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.
Open Access
Short length trellis-based codes for gaussian multiple-access channels
(Institute of Electrical and Electronics Engineers Inc., 2014) Ozcelikkale, A.; Duman, T. M.
We focus on trellis-based joint code design for two-user Gaussian multiple-access channel (MAC) in the short block length regime. We propose a design methodology, provide specific code designs and report numerical performance results. We compare the performance of the jointly designed codes with the performance of the codes designed for point-to-point (P2P) channels including optimum (in terms of minimum distance) convolutional codes. Our results show that the proposed codes achieve superior performance compared to these alternatives especially in the high signal-to-noise (SNR) regime in equal power scenarios.