Infotech Oulu Lecture Series
Date: January 21, 2015
A Soft Network Coded Multilevel Forwarding Scheme for Multiple Access Relay Systems
Lecturer: Dr. Nalin Jayakody, University of Tartu, Estonia
Many wireless relay protocols have been proposed in the literature to reap the benefits promised by cooperative wireless communication. The two most frequently used relaying protocols are decode-and-forward (DF) and amplify and forward (AF). The main performance degradation in a DF protocol arises from error propagation during retransmission when decoding errors occur at the relay in the low SNR regime of the source-relay channel. In the AF relay protocol, the signal received by the relay is amplified and re-transmitted to the destination. Different amplifying factors may be used. In contrast to DF, the AF protocol suffers from noise amplification, but AF precludes premature decisions and thus preserves the soft information content of the received signal. DF lacks the main advantages of AF and vice versa. One way of avoiding the error propagation and noise amplification is to calculate and forward the corresponding soft information instead of making a premature decision based on the transmitted information symbols at the relay. Soft information indicates the reliabilities or probabilities of the underlying symbols. We refer to such a protocol as soft information relaying (SIR).
In this talk we propose a novel technique of multilevel threshold based soft quantization (MLT-SQ) scheme for a multiple access relay system (MARS). The scheme is suitable for systems using binary phase-shift keying (BPSK) and network coding at the relay. In the proposed MLT-SQ protocol, the relay evaluates the reliabilities, expressed as log-likelihood ratios (LLRs), of the received signals from the two sources. It then computes the LLRs of the network-coded packet and quantizes these using a set of optimized multilevel thresholds, forwarding the resulting “quantized soft symbols” to the destination. We provide the derivation for the bit error rate (BER) at the destination, based on which we optimize the multilevel thresholds to minimize the BER. Simulation results are provided for the proposed MLT-SQ system, both without coding and for the case where low-density parity-check (LDPC) coding is employed. The proposed system achieves full diversity order. The performance of our system is superior in terms of BER when compared to other relevant competing schemes.
Dr. Nalin Jayakody received the BEng degree in Electronics Engineering (with first class honours) from the Mehran University of Engineering and Technology, Pakistan in 2009. He received his MSc degree in Electronics and Communication Engineering from the department of Electrical and Electronics Engineering, Eastern Mediterranean University, Turkey in 2010. He received the PhD degree in Electronics and Communication Engineering in 2014, from the University College Dublin, Ireland. Since Oct 2014, he holds a postdoctoral position with the Institute of Computer Science, University of Tartu, Estonia. Dr. Jayakody is a Member of the IEEE. He has served as a session chair or a technical program committee member for various international conferences, such as IEEE WCNC 2013, PIMRC 2014.
Index Coding for Broadcast Channel with Side Information
Lecturer: Dr. Vitaly Skachek, University of Tartu, Estonia
Based on joint works with Son Hoang Dau and Yeow Meng Chee.
In this talk, we discuss the problem of Index Coding with Side Information. This problem considers a broadcast communication scenario with one transmitter and several receivers. Each receiver has partial data in its possession, and it requests some additional data. The transmitter has to deliver all the requested data, while using a minimum number of transmissions.
In the first part of the talk, we consider the case where transmitted symbols are subject to errors. Our results include bounds on the optimal length of a linear error-correcting index code (ECIC). For large alphabets, a construction based on concatenation of an optimal index code with a classical MDS code is shown to be optimal. We also analyze a random construction, which yields another bound on the length of an optimal linear ECIC.
In the remaining part of the talk we discuss security aspects of the index coding problem. In particular, we generalize the notion of weak security (Bhattad and Narayanan, 2005) to block security, applicable to the index coding problem.
Vitaly Skachek received the B.A., M.Sc. and Ph.D. degrees from the Technion---Israel Institute of Technology. In the summer of 2004, he visited the Mathematics of Communications Department at Bell Laboratories. During 2007--2012, Dr. Skachek held post-doctoral/research positions with the Claude Shannon Institute, University College Dublin, Ireland, with the School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, with the Coordinated Science Laboratory, University of Illinois at Urbana-Champaign and with McGill University, Montreal, Canada. He is now a Senior Lecturer with the University of Tartu, Estonia.
Last updated: 12.1.2015