Wireless networks become more and more important in modern information systems
as the last mile/meter solutions, thanks to the flexibility of mobile access to facilitate
Internet access anytime, anywhere. Given the limited resources, e.g., spectrum and
energy supplies, to meet the ever increasing demand for wireless data services, new approaches
are beckoned to enhance the spectrum and energy efficiency. We investigate
this problem from three important aspects, digital modulation, clock synchronization
and concurrent transmission scheduling. The contributions of this dissertation are
four-fold.
First, we employ the cross-layer design to explore the spatial diversity and broadcast
nature of wireless links and propose a novel network modulation scheme that
can superpose the information bits of different priorities into one symbol. It offers
a new dimension to improve the network throughput since we can flexibly configure
the transmission according to the channels among transceivers. Moreover, it is
compatible with the main-stream hardware and we just need a software upgrade to
implement the idea.
Second, we propose modulation schemes based on hexagonal tiling, which is known
to be the most compact way of two-dimensional regular tiling. In order to fully utilize
the advantage of hexagonal constellation, we employ the non-binary error controlcoding since the number of constellation points of hexagonal constellation is not necessarily
to be an integer power-of-two. The feasibility of these new modulation schemes
is verified by the prototype system based on the software defined radio platform
USRP2 and GNU Radio.
Third, to facilitate a wide range of wireless communications technologies and
protocols, clock synchronization among several wireless devices is a fundamental requirement.
We investigated this problem by tracing to the source of clock desynchronization,
which is the clock skew. However, as shown by measurement results, the
clock skew is not constant and related to the working temperature. We propose a
novel clock skew estimation algorithm that can leverage the temperature information
to accurately estimate the clock skew. Based on the estimation results, we propose
a clock synchronization scheme that can directly remove the clock skew according to
the working temperature.
Fourth, the traditional time-sharing based scheduling schemes usually schedule
one transmission within certain area. The emerging broadband wireless devices can
dynamically adjust the transmitted data rate according to the received signal to
interference and noise ratio (SINR). Allowing concurrent transmissions may be more
efficient, while optimal scheduling problem for concurrent transmissions is an NP-hard
problem. We propose simple yet effective heuristic algorithms that can significantly
improve the system throughput with moderate computational complexity. / Graduate / 0544 / yangzhe2007@gmail.com
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/4603 |
| Date | 08 May 2013 |
| Creators | Yang, Zhe |
| Contributors | Cai, Lin |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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