Enabling decentralized wireless index coding in practice

Index coding is a problem in theoretical computer science and network information theory that studies the optimal coding scheme for transmitting multiple messages across a network to receivers with different side information. The ultimate goal of index coding is to reduce transmission time in a communication network by minimizing the number of messages based on shared information. Index coding theory extends to several key engineering problems in network communication including peer to peer communication, distributed broadcast networks, and interference alignment. Although the theoretical connection between index coding and wireless networks is valuable, we focus on finding index coding strategies for a realistic wireless network. More specifically, we investigate how index coding can be applied to an OFDMA downlink network during the retransmission phase. An orthogonal frequency-division multiple access (OFDMA) downlink network is a network where data is sent downward from a designated higher-level transmitter to a group of receiving nodes. In addition, receivers can often decode the other receivers' physical layer signals on the other sub-channels that can be exploited as side information. If this side information is sent back to the transmitter, it can then be coded to cancel the interference in subsequent retransmission phases resulting in fewer retransmission messages. In this report, we explain the coding model and characterize the benefits of index coding for retransmissions within an OFDMA downlink network. In addition, we demonstrate the results of applying this index coding scheme in such network in both simulation and in an active wireless mesh network.Electrical and Computer Engineerin

Coding theoretic methods for systems with side information

In real life, many communication system problems have side information due to the broadcasting nature of communication medium. By utilizing the side information, either the communication rate can be increased or the cost of transmission can be decreased. In this proposal, I am going to investigate three problems: index-coded retransmission for OFDMA downlink, decentralized framework for coded caching, and key generation using physically unclonable functions (PUFs). In the first part, we propose a novel index-coded retransmission scheme for OFDMA downlink. In OFDMA downlink, receivers can often decode the other users’ physical layer signals on the other sub-channels, which can be exploited as side information to cancel the interference in subsequent retrans- mission. In contrast to the original index coding formulation, its application to wireless networks has to deal with decoding error probabilities due to channel variations such as fading. We show the tradeoff between the transmission rate gain and the performance of index coding algorithm. We simulate the end to end system with a novel randomized greedy coloring index coding algorithm, and show non-trivial gain with a 100 nodes system. In the second part, we shift to the problem of coded caching: in this case instead of storing a whole file as side information, we can design the cache content to minimize the worst case transmission rate. We propose a novel framework that can translate any centralized coded caching scheme to decentralized scheme without transmission gain loss. We prove the performance of our algorithm is not degraded due to the dynamics introduced by decentralization. In the third part, we present an algebraic binning based coding scheme and its associated achievable rate for key generation using physically unclonable functions is determined. This achievable rate is shown to be optimal under the generated-secret (GS) model for PUFs. Furthermore, a polar code based polynomial-time encoding and decoding scheme that achieves this rate is also presented.Electrical and Computer Engineerin