40 research outputs found
Slepian-Wolf Coding for Broadcasting with Cooperative Base-Stations
We propose a base-station (BS) cooperation model for broadcasting a discrete
memoryless source in a cellular or heterogeneous network. The model allows the
receivers to use helper BSs to improve network performance, and it permits the
receivers to have prior side information about the source. We establish the
model's information-theoretic limits in two operational modes: In Mode 1, the
helper BSs are given information about the channel codeword transmitted by the
main BS, and in Mode 2 they are provided correlated side information about the
source. Optimal codes for Mode 1 use \emph{hash-and-forward coding} at the
helper BSs; while, in Mode 2, optimal codes use source codes from Wyner's
\emph{helper source-coding problem} at the helper BSs. We prove the optimality
of both approaches by way of a new list-decoding generalisation of [8, Thm. 6],
and, in doing so, show an operational duality between Modes 1 and 2.Comment: 16 pages, 1 figur
Opportunistic Source Coding for Data Gathering in Wireless Sensor Networks
We propose a jointly opportunistic source coding and opportunistic routing (OSCOR) protocol for correlated data gathering in wireless sensor networks. OSCOR improves data gathering efficiency by exploiting opportunistic data compression and cooperative diversity associated with wireless broadcast advantage. The design of OSCOR involves several challenging issues across different network protocol layers. At the MAC layer, sensor nodes need to coordinate wireless transmission and packet forwarding to exploit multiuser diversity in packet reception. At the network layer, in order to achieve high diversity and compression gains, routing must be based on a metric that is dependent on not only link-quality but also compression opportunities. At the application layer, sensor nodes need a distributed source coding algorithm that has low coordination overhead and does not require the source distributions to be known. OSCOR provides practical solutions to these challenges incorporating a slightly modified 802.11 MAC, a distributed source coding scheme based on network coding and Lempel-Ziv coding, and a node compression ratio dependent metric combined with a modified Dijkstra's algorithm for path selection. We evaluate the performance of OSCOR through simulations, and show that OSCOR can potentially reduce power consumption by over 30% compared with an existing greedy scheme, routing driven compression, in a 4 x 4 grid network
Distributed Cooperative Spatial Multiplexing System
Multiple-Input-Multiple-Output (MIMO) spatial multiplexing systems can increase the spectral efficiency manyfold, without extra bandwidth or transmit power, however these advantages are based on the assumption that channels between different transmit antenna and receive antenna are independent which requires the elements in antenna array be separated by several wavelengths. For small mobile devices, the requirement is difficult to implement in practice. Cooperative spatial multiplexing (C-SM) system provides a solution: it organizes antennas on distributed mobile stations to form a virtual antenna array (VAA) to support spatial multiplexing.
In this thesis, we propose a novel C-SM system design which includes a transmitter with two antennas, a single antenna receiver and a relay group with two single antenna relays. In this design, we assume that the transmitter tries to transmit two coded independent messages to the receiver simultaneously but the transmitter-receiver link is too weak to support the transmission. Thus a relay group is introduced to help with the transmission. After relays receive the messages from the transmitter via a MIMO link, they first detect and quantize the received messages, then compress them independently according to the Slepian and Wolf theorem, the compressed messages are sent to the receiver simultaneously where de-compression and de-quantization are performed on the received messages. After that the resulting messages are combined to estimate the original coded messages. The estimated coded messages are decoded to produce the original messages.
The basic system structure is studied and an analytical bit error rate expression is derived. Several transmission protocols are also introduced to enhance the system BER performance.
The merit of this design is focus on the relay destination link. Because the Slepian and Wolf theorem is applied on the relay-destination link, messages at the relays can be compressed independently and de-compressed jointly at the receiver with arbitrarily small error probability but still achieve the same compression rate as a joint compression scheme does.
The Slepian and Wolf theorem is implemented by a joint source-channel code in this thesis. Several schemes are introduced and tested, the testing results and performance analysis are given in this thesis.
According to the chief executive officer (CEO) problem in the network information theory, we discover an error floor in this design. An analytical expression for this error floor is derived.
A feedback link is also introduced from the receiver to the relays to allow the relays to cooperatively adapt their compression rates to the qualities of the received messages.
Two combination schemes at the receiver are introduced, their performances are examined from the information theory point of view, the results and performance analysis are given in this thesis.
As we assume that the relay destination link is a multiple access channel (MAC) suffers from block Rayleigh fading and white Gaussian noise, the relationship between the MAC channel capacity and the Slepian and Wolf compression rate region is studied to analyse the system performance
A Critical Review of Physical Layer Security in Wireless Networking
Wireless networking has kept evolving with additional features and increasing capacity. Meanwhile, inherent characteristics of wireless networking make it more vulnerable than wired networks. In this thesis we present an extensive and comprehensive review of physical layer security in wireless networking. Different from cryptography, physical layer security, emerging from the information theoretic assessment of secrecy, could leverage the properties of wireless channel for security purpose, by either enabling secret communication without the need of keys, or facilitating the key agreement process. Hence we categorize existing literature into two main branches, namely keyless security and key-based security. We elaborate the evolution of this area from the early theoretic works on the wiretap channel, to its generalizations to more complicated scenarios including multiple-user, multiple-access and multiple-antenna systems, and introduce not only theoretical results but practical implementations. We critically and systematically examine the existing knowledge by analyzing the fundamental mechanics for each approach. Hence we are able to highlight advantages and limitations of proposed techniques, as well their interrelations, and bring insights into future developments of this area
Enabling Hardware Green Internet of Things: A review of Substantial Issues
Between now and the near future, the Internet of Things (IoT) will redesign the socio-ecological morphology of the human terrain. The IoT ecosystem deploys diverse sensor platforms connecting millions of heterogeneous objects through the Internet. Irrespective of sensor functionality, most sensors are low energy consumption devices and are designed to transmit sporadically or continuously. However, when we consider the millions of connected sensors powering various user applications, their energy efficiency (EE) becomes a critical issue. Therefore, the importance of EE in IoT technology, as well as the development of EE solutions for sustainable IoT technology, cannot be overemphasised. Propelled by this need, EE proposals are expected to address the EE issues in the IoT context. Consequently, many developments continue to emerge, and the need to highlight them to provide clear insights to researchers on eco-sustainable and green IoT technologies becomes a crucial task. To pursue a clear vision of green IoT, this study aims to present the current state-of-the art insights into energy saving practices and strategies on green IoT. The major contribution of this study includes reviews and discussions of substantial issues in the enabling of hardware green IoT, such as green machine to machine, green wireless sensor networks, green radio frequency identification, green microcontroller units, integrated circuits and processors. This review will contribute significantly towards the future implementation of green and eco-sustainable IoT
Multiple Multicasts with the Help of a Relay
The problem of simultaneous multicasting of multiple messages with the help
of a relay terminal is considered. In particular, a model is studied in which a
relay station simultaneously assists two transmitters in multicasting their
independent messages to two receivers. The relay may also have an independent
message of its own to multicast. As a first step to address this general model,
referred to as the compound multiple access channel with a relay (cMACr), the
capacity region of the multiple access channel with a "cognitive" relay is
characterized, including the cases of partial and rate-limited cognition. Then,
achievable rate regions for the cMACr model are presented based on
decode-and-forward (DF) and compress-and-forward (CF) relaying strategies.
Moreover, an outer bound is derived for the special case, called the cMACr
without cross-reception, in which each transmitter has a direct link to one of
the receivers while the connection to the other receiver is enabled only
through the relay terminal. The capacity region is characterized for a binary
modulo additive cMACr without cross-reception, showing the optimality of binary
linear block codes, thus highlighting the benefits of physical layer network
coding and structured codes. Results are extended to the Gaussian channel model
as well, providing achievable rate regions for DF and CF, as well as for a
structured code design based on lattice codes. It is shown that the performance
with lattice codes approaches the upper bound for increasing power, surpassing
the rates achieved by the considered random coding-based techniques.Comment: Submitted to Transactions on Information Theor
A Signal-Space Aligned Network Coding Approach to Distributed MIMO
© 2016 IEEE. This paper studies an uplink distributed MIMO (DMIMO) system that consists of users and K distributed base stations (BSs), where the BSs are connected to a central unit (CU) via independent rate-constrained backhaul (BH) links. We propose a new signal-space aligned network coding scheme. First, a network coding generator matrix is selected subject to certain structural properties. Next, distributed linear precoding is employed by the users to create aligned signal-spaces at the BSs, according to the pattern determined by the network coding generator matrix. For each aligned signal-space at a BS, physical-layer network coding is utilized to compute the corresponding network-coded (NC) messages, where the actual number of NC messages forwarded to the CU is determined by the BH rate-constraint. We derive an achievable rate of the proposed scheme based on the existence of the NC generator matrix and signal-space alignment precoding matrices. For DMIMO with two and three BSs, the achievable rates and degrees of freedom (DoF) are evaluated and shown to outperform existing schemes. For example, for DMIMO with two BSs where each user and BS have N and N antennas, respectively, the proposed scheme achieves a DoF of 2 min N,N-1, if the BH capacity scales like 2 min (N,N-1) log SNR. This leads to greater DoF compared to that utilizes the strategy for interference channel, whose DoF is min (N,N right). Numerical results demonstrate the performance advantage of the proposed scheme
Degraded Broadcast Diamond Channels with Non-Causal State Information at the Source
A state-dependent degraded broadcast diamond channel is studied where the
source-to-relays cut is modeled with two noiseless, finite-capacity digital
links with a degraded broadcasting structure, while the relays-to-destination
cut is a general multiple access channel controlled by a random state. It is
assumed that the source has non-causal channel state information and the relays
have no state information. Under this model, first, the capacity is
characterized for the case where the destination has state information, i.e.,
has access to the state sequence. It is demonstrated that in this case, a joint
message and state transmission scheme via binning is optimal. Next, the case
where the destination does not have state information, i.e., the case with
state information at the source only, is considered. For this scenario, lower
and upper bounds on the capacity are derived for the general discrete
memoryless model. Achievable rates are then computed for the case in which the
relays-to-destination cut is affected by an additive Gaussian state. Numerical
results are provided that illuminate the performance advantages that can be
accrued by leveraging non-causal state information at the source.Comment: Submitted to IEEE Transactions on Information Theory, Feb. 201
Lecture Notes on Network Information Theory
These lecture notes have been converted to a book titled Network Information
Theory published recently by Cambridge University Press. This book provides a
significantly expanded exposition of the material in the lecture notes as well
as problems and bibliographic notes at the end of each chapter. The authors are
currently preparing a set of slides based on the book that will be posted in
the second half of 2012. More information about the book can be found at
http://www.cambridge.org/9781107008731/. The previous (and obsolete) version of
the lecture notes can be found at http://arxiv.org/abs/1001.3404v4/
Distributed secrecy for information theoretic sensor network models
This dissertation presents a novel problem inspired by the characteristics of
sensor networks. The basic setup through-out the dissertation is that a set of sensor
nodes encipher their data without collaboration and without any prior shared secret
materials. The challenge is dealt by an eavesdropper who intercepts a subset of the
enciphered data and wishes to gain knowledge of the uncoded data. This problem
is challenging and novel given that the eavesdropper is assumed to know everything,
including secret cryptographic keys used by both the encoders and decoders. We
study the above problem using information theoretic models as a necessary first step
towards an understanding of the characteristics of this system problem.
This dissertation contains four parts. The first part deals with noiseless channels,
and the goal is for sensor nodes to both source code and encipher their data. We
derive inner and outer regions of the capacity region (i.e the set of all source coding
and equivocation rates) for this problem under general distortion constraints. The
main conclusion in this part is that unconditional secrecy is unachievable unless the
distortion is maximal, rendering the data useless. In the second part we thus provide
a practical coding scheme based on distributed source coding using syndromes (DISCUS)
that provides secrecy beyond the equivocation measure, i.e. secrecy on each
symbol in the message. The third part deals with discrete memoryless channels, and the goal is for sensor nodes to both channel code and encipher their data. We derive
inner and outer regions to the secrecy capacity region, i.e. the set of all channel coding
rates that achieve (weak) unconditional secrecy. The main conclusion in this part is
that interference allows (weak) unconditional secrecy to be achieved in contrast with
the first part of this dissertation. The fourth part deals with wireless channels with
fading and additive Gaussian noise. We derive a general outer region and an inner
region based on an equal SNR assumption, and show that the two are partially tight
when the maximum available user powers are admissible