Generation by generation, wireless communication has advanced in various ways and
provided reliable communication services at higher and higher data rates to the needs
of more and more advanced wireless applications. Two main issues towards future
wireless communications are high-speed transmission technique to provide high data
rate services and reliable communication to ensure the required performance. This
dissertation focuses on these two issues. Since orthogonal frequency division multiplexing
(OFDM) has emerged as an enabling technique for high-speed transmission
in dispersive environments, major and fundamental issues in OFDM, namely, synchronization,
channel estimation, and peak-to-average power ratio (PAPR) reduction
are addressed. For the required reliability, automatic repeat request (ARQ) schemes
must be applied. Due to large potential performance improvement, adaptive ARQ
schemes have recently attracted much attention and are also addressed here.
We propose two improved OFDM timing synchronization methods which overcome
the drawbacks of existing methods. We present a time-domain-based OFDM channel
estimation which outperforms the existing time-domain-based approach and has a
similar performance to the linear minimum mean square error estimator but with
less complexity. For OFDM systems with transmit diversity, we present a reduced
complexity channel estimation which has a comparable performance to the existing
method for channels with relatively small delay spreads, but achieves much complexity
saving. An approach to find the number of most significant channel taps is described
for diverse channel environments. We analyze the effect of non-sample-spaced channel
path on the channel estimation and propose a modification for further improvement.
Timing synchronization, frequency synchronization and channel estimation are
usually addressed separately. Since they can affect each other, the idea of jointly addressing
all of them together is much desirable and pursued here. This joint approach
reflects the actual performance and gives an opportunity to exploit some information
obtained from one task in another, hence promising more improvement. The proposed
training preamble-based joint timing and frequency synchronization utilizes some information
from the channel estimation. The sync detection is also considered. We
design the training symbol to achieve a better coarse timing synchronization. Methods
to suppress or circumvent the interference in the frequency estimation caused by
timing errors are presented. A new performance measure for OFDM timing synchronization
is proposed which leads to obtaining optimal timing estimation setting. Next,
we present a joint timing synchronization, frequency synchronization and channel estimation
based on training preamble based maximum likelihood realization. Further
complexity reduction by an adaptive scheme is also proposed.
We address some fundamental questions on peak factors, sampling theorem and
sampling series. We present several bounds of bandlimited functions and peak factor
ratio bound of a continuous signal and its sampled signal. Some discussion on the requirements
of sampling theorems and related aspects on sampling series are presented.
We study PAPR behavior of some Reed-Muller codes in OFDM systems in an attempt
to find a code with good error correction, low PAPR, efficient encoding/decoding and
reasonable code rate. Some regularities of the second and third-order cosets of first order
Reed-Muller codes with low PAPR are presented which indicates possibility of
finding such code for OFDM.
The main issues in adaptive ARQ schemes are how to design the adaptive system
parameters and how to effectively sense the channel conditions. We present an
approach for designing the adaptive ARQ system parameters based on the through put
calculation and optimization. An alternative approach which avoids the tedious
throughput calculation is also presented. An effective channel sensing algorithm which
utilizes the error correcting capability is proposed. Incorporation of the adaptive frequency
hopping concept into the ARQ scheme with adaptive error control is introduced
which has a significant throughput improvement in slow fading channels. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/10210 |
| Date | 30 October 2018 |
| Creators | Minn, Hlaing |
| Contributors | Bhargava, Vijay K. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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