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 Δ<0 and Δ>0, 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.
| Identifer | oai:union.ndltd.org:WATERLOO/oai:uwspace.uwaterloo.ca:10012/5473 |
| Date | January 2010 |
| Creators | Bagheri, Hossein |
| Source Sets | University of Waterloo Electronic Theses Repository |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
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