95 research outputs found
Asymptotic Capacity of Large Relay Networks with Conferencing Links
In this correspondence, we consider a half-duplex large relay network, which
consists of one source-destination pair and relay nodes, each of which is
connected with a subset of the other relays via signal-to-noise ratio
(SNR)-limited out-of-band conferencing links. The asymptotic achievable rates
of two basic relaying schemes with the "-portion" conferencing strategy are
studied: For the decode-and-forward (DF) scheme, we prove that the DF rate
scales as ; for the amplify-and-forward (AF) scheme, we
prove that it asymptotically achieves the capacity upper bound in some
interesting scenarios as goes to infinity.Comment: submitted to IEEE Transactions on Communication
The Gaussian Multiple Access Diamond Channel
In this paper, we study the capacity of the diamond channel. We focus on the
special case where the channel between the source node and the two relay nodes
are two separate links with finite capacities and the link from the two relay
nodes to the destination node is a Gaussian multiple access channel. We call
this model the Gaussian multiple access diamond channel. We first propose an
upper bound on the capacity. This upper bound is a single-letterization of an
-letter upper bound proposed by Traskov and Kramer, and is tighter than the
cut-set bound. As for the lower bound, we propose an achievability scheme based
on sending correlated codes through the multiple access channel with
superposition structure. We then specialize this achievable rate to the
Gaussian multiple access diamond channel. Noting the similarity between the
upper and lower bounds, we provide sufficient and necessary conditions that a
Gaussian multiple access diamond channel has to satisfy such that the proposed
upper and lower bounds meet. Thus, for a Gaussian multiple access diamond
channel that satisfies these conditions, we have found its capacity.Comment: submitted to IEEE Transactions on Information Theor
Cooperative Protocols for Relay and Interference Channels with Half-Duplex Constraint
Enabling cooperation among nodes of a wireless network can significantly reduce the required
transmit power as well as the induced intra-network interference. Due to the practical
half-duplexity constraint of the cooperating nodes, they are prohibited to simultaneously
transmit and receive data at the same time-frequency resource. The purpose of this
dissertation is to illustrate the value of cooperation in such an environment. To understand
how to cooperate efficiently, information theory is employed as a useful tool, which not only
determines the fundamental limits of communication (i.e., capacity) over the considered
network, but also provides insights into the design of a proper transmission scheme for that
network.
In this thesis, two simple but yet important types of wireless networks, namely Relay
Channel, and Interference Channel are studied. In fact, these models constitute building
blocks for larger networks. The first considered channel is a diamond-shaped relay channel
consisting of a source, a destination, and two parallel relays. The second analyzed channel
is an interference channel composed of two transmitter-receiver pairs with out-of-band
transmitter cooperation, also referred to as conferencing encoders. While characterizing
the capacity of these channels are difficult, a simpler and a more common approach is to
find an achievable scheme for each channel that ensures a small gap from the capacity for
all channel parameters.
In chapter 2, the diamond relay channel is investigated in detail. Because of the half-duplex
nature of the relays, each relay is either in transmit or receive mode, making
four modes possible for the two-relay combination, specifically, 1) broadcast mode (both
relays receive) 2,3) routing modes (one relay transmits, another receives) 4) multiple-access
mode (both relays transmit). An appropriate scheduling ( i.e., timing over the modes) and
transmission scheme based on the decode-and-forward strategy are proposed and shown
to be able to achieve either the capacity for certain channel conditions or at most 3.6 bits below the capacity for general channel conditions. Particularly, by assuming each
transmitter has a constant power constraint over all modes, a parameter Δ is defined,
which captures some important features of the channel. It is proven that for Δ=0 the
capacity of the channel can be attained by successive relaying, i.e., using modes 2 and 3
defined above in a successive manner. This strategy may have an infinite gap from the
capacity of the channel when Δ≠0. To achieve rates as close as 0.71 bits to the capacity,
it is shown that the cases of Δ>0 and Δ<0 should be treated differently. Using new
upper bounds based on the dual problem of the linear program associated with the cut-set
bounds, it is proven that the successive relaying strategy needs to be enhanced by an
additional broadcast mode (mode 1), or multiple access mode (mode 4), for the cases of Δ0, respectively. Furthermore, it is established that under average power
constraints the aforementioned strategies achieve rates as close as 3.6 bits to the capacity
of the channel.
In chapter 3, a two-user Gaussian Interference Channel (GIC) is considered, in which
encoders are connected through noiseless links with finite capacities. The setup can be
motivated by downlink cellular systems, where base stations are connected via infrastructure
backhaul networks. In this setting, prior to each transmission block the encoders
communicate with each other over the cooperative links. The capacity region and the
sum-capacity of the channel are characterized within some constant number of bits for
some special classes of symmetric and Z interference channels. It is also established that
properly sharing the total limited cooperation capacity between the cooperative links may
enhance the achievable region, even when compared to the case of unidirectional transmitter
cooperation with infinite cooperation capacity. To obtain the results, genie-aided upper
bounds on the sum-capacity and cut-set bounds on the individual rates are compared with
the achievable rate region. The achievable scheme enjoys a simple type of Han-Kobayashi
signaling, together with the zero-forcing, and basic relaying techniques
Capacity Results for Wireless Cooperative Communications with Relay Conferencing
In this dissertation we consider cooperative communication systems with relay conferencing, where the relays own the capabilities to talk to their counterparts via either wired or wireless out-of-band links. In particular, we focus on the design of conferencing protocols incorporating the half-duplex relaying operations, and study the corresponding capacity upper and lower bounds for some typical channels and networks models, including the diamond relay channels (one source-destination pairs and two relays), large relay networks (one source-destination pairs and N relays), and interference relay channels (two source-destination pairs and two relays).
First, for the diamond relay channels, we consider two different relaying schemes, i.e., simultaneous relaying (for which the two relays transmit and receive in the same time slot) and alternative relaying (for which the two relays exchange their transmit and receive modes alternatively over time), for which we obtain the respective achievable rates by using the decode-and-forward (DF), compress-and-forward (CF), and amplify-and-forward (AF) relaying schemes with DF and AF adopted the conferencing schemes. Moreover, we prove some capacity results under some special conditions.
Second, we consider the large relay networks, and propose a "p-portion" conferencing scheme, where each relay can talk to the other "p-portion" of the relays. We obtain the DF and AF achievable rates by using the AF conferencing scheme. It is proved that relay conferencing increases the throughput scaling order of the DF relaying scheme from O(log(log(N ))) for the case without conferencing to O(log(N )); for the AF relaying scheme, it achieves the capacity upper bound under some conditions.
Finally, we consider the two-hop interference relay channels, and obtain the AF achievable rates by adopting the AF conferencing scheme and two different decoding schemes at the destination, i.e., single-user decoding and joint decoding. For the derived joint source power allocation and relay combining problem, we develop some efficient iterative algorithms to compute the AF achievable rate regions. Moreover, we compare the achievable degree-of-freedom (DoF) performance of these two decoding schemes, and show that single-user decoding with interference cancellation at the relays is optimal
Capacity Bounds For Multi-User Channels With Feedback, Relaying and Cooperation
Recent developments in communications are driven by the goal of
achieving high data rates for wireless communication devices. To
achieve this goal, several new phenomena need to be investigated
from an information theoretic perspective. In this dissertation,
we focus on three of these phenomena: feedback, relaying and
cooperation. We study these phenomena for various multi-user
channels from an information theoretic point of view.
One of the aims of this dissertation is to study the performance
limits of simple wireless networks, for various forms of feedback
and cooperation. Consider an uplink communication system, where
several users wish to transmit independent data to a base-station.
If the base-station can send feedback to the users, one can expect
to achieve higher data-rates since feedback can enable cooperation
among the users. Another way to improve data-rates is to make use
of the broadcast nature of the wireless medium, where the users
can overhear each other's transmitted signals. This particular
phenomenon has garnered much attention lately, where users can
help in increasing each other's data-rates by utilizing the
overheard information. This overheard information can be
interpreted as a generalized form of feedback.
To take these several models of feedback and cooperation into
account, we study the two-user multiple access channel and the
two-user interference channel with generalized feedback. For all
these models, we derive new outer bounds on their capacity
regions. We specialize these results for noiseless feedback,
additive noisy feedback and user-cooperation models and show
strict improvements over the previously known bounds.
Next, we study state-dependent channels with rate-limited state
information to the receiver or to the transmitter. This
state-dependent channel models a practical situation of fading,
where the fade information is partially available to the receiver
or to the transmitter. We derive new bounds on the capacity of
such channels and obtain capacity results for a special sub-class
of such channels.
We study the effect of relaying by considering the parallel relay
network, also known as the diamond channel. The parallel relay
network considered in this dissertation comprises of a cascade of
a general broadcast channel to the relays and an orthogonal
multiple access channel from the relays to the receiver. We
characterize the capacity of the diamond channel, when the
broadcast channel is deterministic. We also study the diamond
channel with partially separated relays, and obtain capacity
results when the broadcast channel is either semi-deterministic or
physically degraded. Our results also demonstrate that feedback to
the relays can strictly increase the capacity of the diamond
channel.
In several sensor network applications, distributed lossless
compression of sources is of considerable interest. The presence
of adversarial nodes makes it important to design compression
schemes which serve the dual purpose of reliable source
transmission to legitimate nodes while minimizing the information
leakage to the adversarial nodes. Taking this constraint into
account, we consider information theoretic secrecy, where our aim
is to limit the information leakage to the eavesdropper. For this
purpose, we study a secure source coding problem with coded side
information from a helper to the legitimate user. We derive the
rate-equivocation region for this problem. We show that the helper
node serves the dual purpose of reducing the source transmission
rate and increasing the uncertainty at the adversarial node. Next,
we considered two different secure source coding models and
provide the corresponding rate-equivocation regions
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