## About

111

Publications

5,053

Reads

**How we measure 'reads'**

A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more

1,027

Citations

Introduction

**Skills and Expertise**

Additional affiliations

October 2008 - present

## Publications

Publications (111)

We study the information leakage to a guessing adversary in index coding with a general message distribution. Under both vanishing-error and zero-error decoding assumptions, we develop lower and upper bounds on the optimal leakage rate, which are based on the broadcast rate of the subproblem induced by the set of messages the adversary tries to gue...

Information leakage to a guessing adversary in index coding is studied, where some messages in the system are sensitive and others are not. The non-sensitive messages can be used by the server like secret keys to mitigate leakage of the sensitive messages to the adversary. We construct a deterministic linear coding scheme, developed from the rank m...

In the pliable variant of index coding, receivers are allowed to decode any new message not known a priori. Optimal code design for this variant involves identifying each receiver's choice of a new message that minimises the overall transmission rate. This paper proposes a formulation that further relaxes the decoding requirements of pliable index...

In this work, we study the secure index coding problem where there are security constraints on both legitimate receivers and eavesdroppers. We develop two performance bounds (i.e., converse results) on the symmetric secure capacity. The first one is an extended version of the basic acyclic chain bound (Liu and Sadeghi, 2019) that takes security con...

We study the information leakage to a guessing adversary in zero-error source coding. The source coding problem is defined by a confusion graph capturing the distinguishability between source symbols. The information leakage is measured by the ratio of the adversary's successful guessing probability after and before eavesdropping the codeword, maxi...

Establishing code equivalences between index coding and network coding provides important insights for code design. Previous works showed an equivalence relation between any index-coding instance and a network-coding instance, for which a code for one instance can be translated to a code for the other instance with the same decoding-error performan...

We characterise the optimal broadcast rate for a few classes of pliable-index-coding problems. This is achieved by devising new lower bounds that utilise the set of absent receivers to construct decoding chains with skipped messages. This work complements existing works by considering problems that are not complete-S, i.e., problems considered in t...

This paper studies pliable index coding, in which a sender broadcasts information to multiple receivers through a shared broadcast medium, and the receivers each have some message a priori and want any message they do not have. An approach, based on receivers that are absent from the problem, was previously proposed to find lower bounds on the opti...

For communications in the presence of eavesdroppers, random components are often used in code design to camouflage information from eavesdroppers. In broadcast channels without eavesdroppers, Marton coding comprises random components which allow correlation between auxiliary random variables representing independent messages. In this paper, we stud...

We consider a Multi-Sender Unicast Index-Coding (MSUIC) problem, where in a broadcast network, multiple senders collaboratively send distinct messages to multiple receivers, each having some subset of the messages a priori. The aim is to find the shortest index code, which minimizes the total number of coded bits sent by the senders. In this work,...

We provide a correction to
[1]
in response to an error reported by Vaddi and Rajan
[2]
. To this effect, we add one extra condition for the definition of an
$\mathsf {IC}$
structure on page 3696.

This paper studies the problem of secure communcation over the two-receiver discrete memoryless broadcast channel with one-sided receiver side information and with a passive eavesdropper. We proposed a coding scheme which is based upon the superposition-Marton framework. Secrecy techniques such as the one-time pad, Carleial-Hellman secrecy coding a...

A code equivalence between index coding and network coding was established, which shows that any index-coding instance can be mapped to a network-coding instance, for which any index code can be translated to a network code with the same decoding-error performance, and vice versa. Also, any network-coding instance can be mapped to an index-coding i...

We address centralized caching problem with unequal cache sizes. We consider a system with a server of files connected through a shared error-free link to a group of cache-enabled users where one subgroup has a larger cache size than the rest. We investigate caching schemes with uncoded cache placement which minimize the load of worst-case demands...

This paper simplifies an existing coding scheme for the two-receiver discrete memoryless broadcast channel with complementary receiver side information where there is a passive eavesdropper and individual secrecy is required. The existing coding scheme is simplified in two steps by replacing Wyner's secrecy coding with Carleial-Hellman's secrecy co...

This paper considers the downlink of a cache-enabled fog radio access network (F-RAN) with limited fronthaul capacity, where user association (UA), data delivery rate (DDR) and signal precoding are jointly optimized. We formulate a mixed-integer nonlinear programming problem in which the weighted difference of network throughput and total power con...

This paper studies index coding with two senders. In this setup, source messages are distributed among the senders (possibly with overlapping of messages). In addition, there are multiple receivers, where each receiver having some messages a priori, known as side-information, is requesting one unique message such that each message is requested by o...

We consider two-receiver broadcast channels where each receiver may know a priori some of the messages requested by the other receiver as receiver message side information (RMSI). We devise a general approach to leverage RMSI in these channels. To this end, we first propose a pre-coding scheme considering the general message setup where each receiv...

We consider the three-receiver Gaussian multipleinput multiple-output (MIMO) broadcast channel with an arbitrary number of antennas at the transmitter and the receivers. We investigate the degrees-of-freedom (DoF) region of the channel when each receiver requests a private message, and may know some of the messages requested by the other receivers...

The maximum operational range of continuous variable quantum key distribution protocols has shown to be improved by employing high-efficiency forward error correction codes. Typically, the secret key rate model for such protocols is modified to account for the non-zero word error rate of such codes. In this paper, we demonstrate that this model is...

In this paper, we represent Raptor codes as multi-edge type low-density parity-check (MET-LDPC) codes, which gives a general framework to design them for higher-order modulation using MET density evolution. We then propose an efficient Raptor code design method for higher-order modulation, where we design distinct degree distributions for distinct...

In this paper, we establish new capacity bounds for the multi-sender unicast index-coding problem. We first revisit existing outer and inner bounds proposed by Sadeghi et al. and identify the suboptimality of their inner bounds in general. We then present an alternative multi-sender maximal-acyclic-induced-subgraph outer bound that simplifies the e...

The focus of this paper is on the analysis and design of Raptor codes using a multi-edge framework. In this regard, we first represent the Raptor code as a multi-edge type low-density parity-check (METLDPC) code. This MET representation gives a general framework to analyze and design Raptor codes over a binary input additive white Gaussian noise ch...

This study considers the optimisation of multi-edge type low-density parity-check (MET-LDPC) codes to maximise the decoding threshold. The authors propose an algorithm to jointly optimise the node degree distribution and the multi-edge structure of MET-LDPC codes for given values of the maximum number of edge-types and maximum node degrees. This jo...

We extend the equivalence between network coding and index coding by Effros, El Rouayheb, and Langberg to the secure communication setting in the presence of an eavesdropper. Specifically, we show that the most general versions of secure network-coding setup by Chan and Grant and the secure index-coding setup by Dau, Skachek, and Chee, which also i...

Consider a communication scenario over a noiseless channel where a sender is required to broadcast messages to multiple receivers, each having side information about some messages. In this scenario, the sender can leverage the receivers' side information during the encoding of messages in order to reduce the required transmissions. This type of enc...

We consider the three-receiver Gaussian multiple-input multiple-output (MIMO) broadcast channel with an arbitrary number of antennas at each of the transmitter and the receivers. We investigate the degrees-of-freedom (DoF) region of the channel when each receiver requests a private message, and may know some of the messages requested by the other r...

Index coding models broadcast networks in which a sender sends different messages to different receivers simultaneously, where each receiver may know some of the messages a priori. The aim is to find the minimum (normalised) index codelength that the sender sends. This paper considers unicast index coding, where each receiver requests exactly one m...

This paper considers density evolution for lowdensity
parity-check (LDPC) and multi-edge type low-density
parity-check (MET-LDPC) codes over the binary input additive
white Gaussian noise channel. We first analyze three singleparameter
Gaussian approximations for density evolution and
discuss their accuracy under several conditions, namely at low
r...

This paper considers the optimization of multi-edge type low-density parity-check (METLDPC) codes to maximize the decoding threshold. We propose an algorithm to jointly optimize the node degree distribution and the multi-edge structure of MET-LDPC codes for given values of the maximum number of edge-types and maximum node degrees. This joint optimi...

A low-density parity-check (LDPC) code is a linear block code described by a sparse parity-check matrix, which can be efficiently represented by a bipartite Tanner graph. The standard iterative decoding algorithm, known as belief propagation, passes messages along the edges of this Tanner graph. Density evolution is an efficient method to analyze t...

The maximum operation range of continuous variable quantum key distribution systems is constrained by the efficiency of the forward error correction post processing step. In this paper, we show that the current definition of this forward error correction efficiency can exceed unity when employing fixed-rate error correction codes operating at high...

We consider a graphical approach to index coding. While cycles have been shown to provide coding gain, only disjoint cycles and cliques (a specific type of overlapping cycles) have been exploited in existing literature. In this paper, we define a more general form of overlapping cycles, called the interlinked-cycle (IC) structure, that generalizes...

We investigate the construction of secure index codes for a sender transmitting to multiple receivers with side information in the presence of an eavesdropper. We derive a sufficient and necessary condition for the existence of index codes that are secure against an eavesdropper with access to any subset of messages of cardinality $t$, for any fixe...

We consider the two-receiver memoryless broadcast channel with states where
each receiver requests both common and private messages, and may know part of
the private message requested by the other receiver as receiver message side
information (RMSI). We address two categories of the channel (i) channel with
states known causally to the transmitter,...

We consider a joint source-channel coding problem on a finite-field multiway relay channel, and we give closed-form lower and upper bounds on the optimal source-channel rate. These bounds are shown to be tight for all discrete memoryless sources in a certain class ${mathcal{P}^ast}$, and we demonstrate that strict source-channel separation is optim...

This paper investigates the capacity region of the three-receiver AWGN broadcast channel where the receivers (i) have private-message requests, and (ii) may know some of the messages requested by other receivers as side information. We first classify all 64 possible side information configurations into eight groups, each consisting of eight members...

A source coding problem over a noiseless broadcast channel where the source
is preinformed the contents of the cache of all receivers is an index coding
problem. Furthermore, if each receiver is interested in only one unique message
packet, we call this the index coding problem with the unicast message setting.
This problem can be represented by a...

We study the index coding problem in the unicast message setting, i.e., where
each message is requested by one unique receiver. This problem can be modeled
by a directed graph. We propose a new scheme called interlinked cycle cover,
which exploits interlinked cycles in the directed graph, for designing index
codes. This new scheme generalizes the e...

This paper investigates the capacity regions of two-receiver broadcast
channels where each receiver (i) has both common and private-message requests,
and (ii) knows part of the private message requested by the other receiver as
side information. We first propose a transmission scheme and derive an inner
bound for the two-receiver discrete memoryles...

Index coding studies multiterminal source-coding problems where a set of
receivers are required to decode multiple (different) messages from a common
broadcast, and they each know some messages a priori. In this paper, we
consider a class of index-coding problems, which we term single uniprior, where
at the receiver end, each receiver knows one of...

A low-density parity-check (LDPC) code is a linear block code described by a sparse parity-check matrix, which can be efficiently represented by a bipartite Tanner graph. The standard iterative decoding algorithm, known as belief propagation, passes messages along the edges of this Tanner graph. Density evolution is an efficient method to analyze t...

This paper considers the three-receiver AWGN broadcast channel where the
receivers (i) have private-message requests and (ii) know some of the messages
requested by other receivers as side information. For this setup, all possible
side information configurations have been recently classified into eight groups
and the capacity of the channel has bee...

This paper investigates the capacity region of three-receiver AWGN broadcast
channels where the receivers (i) have private-message requests and (ii) know
the messages requested by some other receivers as side information. We classify
these channels based on their side information into eight groups, and construct
different transmission schemes for t...

We study zero-error unicast index-coding instances, where each receiver must
perfectly decode its requested message set, and the message sets requested by
any two receivers do not overlap. We show that for all these instances with up
to five receivers, linear index codes are optimal. Although this class contains
9847 non-isomorphic instances, by us...

This letter investigates the role of index coding in the capacity of AWGN
broadcast channels with receiver message side information. We first show that
index coding is unnecessary where there are two receivers; multiplexing coding
and superposition coding are sufficient to achieve the capacity region. We next
show that, for more than two receivers,...

We study index-coding problems (one sender broadcasting messages to multiple
receivers) where each message is requested by at most one receiver. This type
of index-coding problems can be fully described by directed graphs. The aim is
to find the minimum codelength the sender needs to transmit. For any directed
graph, we show that if a maximum acycl...

We focus on the following instance of an index coding problem, where a set of
receivers are required to decode multiple messages, whilst each knows one of
the messages a priori. In particular, here we consider a generalized setting
where they are multiple senders, each sender only knows a subset of messages,
and all senders are required to collecti...

We consider a multi-way relay network with an orthogonal uplink and correlated sources, and we characterise reliable communication (in the usual Shannon sense) with a single-letter expression. The characterisation is obtained using a joint source-channel random-coding argument, which is based on a combination of Wyner et al.'s Cascaded Slepian-Wolf...

The capacity region of the finite-field multi-way relay channel (FFMWRC) with
independent private messages was established by Ong, Johnson, and Kellett
(IT-2011). In this paper, we extend the capacity results to include pairwise
common messages (each known to two nodes) in addition to private messages
(known to only one node). We first show that th...

This paper compares the partial-decode-forward and the
complete-decode-forward coding strategies for the half-duplex Gaussian
single-relay channel. We analytically show that the rate achievable by
partial-decode-forward outperforms that of the more straightforward
complete-decode-forward by at most 12.5%. Furthermore, in the following
asymptotic ca...

We study the half-duplex multiple-relay channel (HD-MRC) where every node can
either transmit or listen but cannot do both at the same time. We obtain a
capacity upper bound based on a max-flow min-cut argument and achievable
transmission rates based on the decode-forward (DF) coding strategy, for both
the discrete memoryless HD-MRC and the phase-f...

The $L$-user additive white Gaussian noise multiway relay channel is investigated, where $L$ users exchange information at the same rate through a single relay. A new achievable rate region, based on the functional-decode-forward coding strategy, is derived. For the case where there are three or more users, and all nodes transmit at the same power,...

This paper considers the three-way channel, consisting of three nodes, where
each node broadcasts a message to the two other nodes. The capacity of the
finite-field three-way channel is derived, and is shown to be achievable using
a non-cooperative scheme without feedback. The same scheme is also shown to
achieve the equal-rate capacity (when all n...

This paper considers the multi-way relay channel (MWRC) where multiple users exchange messages via a single relay. The capacity region is derived for a special class of MWRCs where (i) the uplink and the downlink are separated in the sense that there is no direct user-to-user links, (ii) the channel is restricted in the sense that each user's trans...

The multi-way relay channel (MWRC) models cooperative communication networks
in which many users exchange messages via a relay. In this paper, we consider
the finite field MWRC with correlated messages. The problem is to find all
achievable rates, defined as the number of channel uses required per reliable
exchange of message tuple. For the case of...

This paper studies a special class of multicast index coding problems where a
sender transmits messages to multiple receivers, each with some side
information. Here, each receiver knows a unique message a priori, and there is
no restriction on how many messages each receiver requests from the sender. For
this class of multicast index coding problem...

This paper considers the two-way relay channel (TWRC) where two users
communicate via a relay. For the restricted TWRC where the uplink from
the users to the relay is any deterministic function and the downlink
from the relay to the users is any arbitrary channel, the capacity
region is obtained. The TWRC considered is restricted in the sense that...

This paper studies the three-user finite-field multi-way relay channel, where
the users exchange messages via a relay. The messages are arbitrarily
correlated, and the finite-field channel is linear and is subject to additive
noise of arbitrary distribution. The problem is to determine the minimum
achievable source-channel rate, defined as channel...

The capacity of a class of multi-way relay channels, where L users
communicate via a relay (at possibly different rates), is derived for the case
where the channel outputs are modular sums of the channel inputs and the
receiver noise. The cut-set upper bound to the capacity is shown to be
achievable. More specifically, the capacity is achieved usin...

We investigate joint network and channel coding schemes for networks when
relay nodes are not capable of performing channel coding operations. Rather,
channel encoding is performed at the source node while channel decoding is done
only at the destination nodes. We examine three different decoding strategies:
independent network-then-channel decodin...

The three-user finite field multi-way relay channel with correlated sources is considered. The three users generate possibly correlated messages, and each user is to transmit its message to the two other users reliably in the Shannon sense. As there is no direct link among the users, communication is carried out via a relay, and the link from the u...

This paper investigates the additive white Gaussian noise two-way relay channel, where two users exchange messages through a relay. Asymmetrical channels are considered where the users can transmit data at different rates and at different power levels. We modify and improve existing coding schemes to obtain three new achievable rate regions. Compar...