22,253 research outputs found
Cooperative communication in wireless local area networks
The concept of cooperative communication has been proposed to improve link capacity, transmission reliability and network coverage in multiuser
wireless communication networks. Different from conventional point-to-point and point-to-multipoint communications, cooperative communication
allows multiple users or stations in a wireless network to coordinate
their packet transmissions and share each other’s resources, thus achieving
high performance gain and better service coverage.
According to the IEEE 802.11 standards, Wireless Local Area Networks
(WLANs) can support multiple transmission data rates, depending
on the instantaneous channel condition between a source station and
an Access Point (AP). In such a multi-rate WLAN, those low data-rate stations
will occupy the shared communication channel for a longer period
for transmitting a fixed-size packet to the AP, thus reducing the channel
efficiency and overall system performance.
This thesis addresses this challenging problem in multi-rate WLANs
by proposing two cooperative Medium Access Control (MAC) protocols,
namely Busy Tone based Cooperative MAC (BTAC) protocol and Cooperative
Access with Relay’s Data (CARD) protocol. Under BTAC, a low
data-rate sending station tries to identify and use a close-by intermediate
station as its relay to forward its data packets at higher data-rate to the AP through a two-hop path. In this way, BTAC can achieve cooperative
diversity gain in multi-rate WLANs. Furthermore, the proposed CARD
protocol enables a relay station to transmit its own data packets to the AP
immediately after forwarding its neighbour’s packets, thus minimising the
handshake procedure and overheads for sensing and reserving the common
channel. In doing so, CARD can achieve both cooperative diversity
gain and cooperative multiplexing gain. Both BTAC and CARD protocols
are backward compatible with the existing IEEE 802.11 standards.
New cross-layer mathematical models have been developed in this
thesis to study the performance of BTAC and CARD under different channel
conditions and for saturated and unsaturated traffic loads. Detailed simulation
platforms were developed and are discussed in this thesis. Extensive
simulation results validate the mathematical models developed and show
that BTAC and CARD protocols can significantly improve system throughput,
service delay, and energy efficiency for WLANs operating under realistic
communication scenarios
Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage
With the rapid growth of demand for ever-increasing data rate, spectrum
resources have become more and more scarce. As a promising technique to
increase the efficiency of the spectrum utilization, cognitive radio (CR)
technique has the great potential to meet such a requirement by allowing
un-licensed users to coexist in licensed bands. In conventional CR systems, the
spectrum sensing is performed at the beginning of each time slot before the
data transmission. This unfortunately results in two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. To tackle these problems, in this paper we present a
new design paradigm for future CR by exploring the full-duplex (FD) techniques
to achieve the simultaneous spectrum sensing and data transmission. With FD
radios equipped at the secondary users (SUs), SUs can simultaneously sense and
access the vacant spectrum, and thus, significantly improve sensing
performances and meanwhile increase data transmission efficiency. The aim of
this article is to transform the promising conceptual framework into the
practical wireless network design by addressing a diverse set of challenges
such as protocol design and theoretical analysis. Several application scenarios
with FD enabled CR are elaborated, and key open research directions and novel
algorithms in these systems are discussed
Spectrum Sharing in Dynamic Spectrum Access Networks: WPE-II Written Report
A study by Federal Communication Commission shows that most of the spectrum in current wireless networks is unused most of the time, while some spectrum is heavily used. Recently dynamic spectrum access (DSA) has been proposed to solve this spectrum inefficiency problem, by allowing users to opportunistically access to unused spectrum. One important question in DSA is how to efficiently share spectrum among users so that spectrum utilization can be increased and wireless interference can be reduced. Spectrum sharing can be formalized as a graph coloring problem. In this report we focus on surveying spectrum sharing techniques in DSA networks and present four representative techniques in different taxonomy domains, including centralized, distributed with/without common control channel, and a real case study of DSA networks --- DARPA neXt Gen- eration (XG) radios. Their strengths and limitations are evaluated and compared in detail. Finally, we discuss the challenges in current spectrum sharing research and possible future directions
Telecommunications requirements study for the electric membership corporations of Georgia
Issued as Monthly letter report no. 1-3, and Final report, Project no. A-192
Performance evaluation of channel selection algorithm for multi-channel MAC protocol in ad hoc networks
This thesis aims to provide an approach that is to investigate channel selection algorithm
for increasing the performance of ad hoc networks. Although our channel selection algorithms are very simple, multi-channel MAC protocol that employs our channel selection algorithms are effective for increasing the performance of ad hoc networks.学位記番号:工博甲47
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