| Summary: | Optical wireless communication is an attractive solution to the "last
mile" bottleneck problem with additional benefits of having rapid deployment,
enhanced security, protocol transparency, and unlicensed transmission
bandwidth. However, atmospheric turbulence induced signal fading is
a major performance degrading factor for any outdoor optical wireless communication
systems. Since the atmospheric turbulence induced fading varies
slowly, adaptive transmission is an effective fading mitigation solution for
an outdoor optical wireless communication system. In this thesis, we primarily
focus on the performance analysis of optical wireless communication
systems employing different adaptive transmission schemes.
We first study the average symbol error rate for a nonadaptive subcarrier
intensity modulated optical wireless communication systems employing
general order rectangular quadrature amplitude modulation. We consider
three different turbulence channel models, i.e., the Gamma-Gamma channel,
the K-distributed channel, and the negative exponential channel with
different levels of turbulence. Exact average symbol error rate expressions
are derived using a series expansion of the modified Bessel function. In addition,
detailed truncation error analysis and asymptotic error rate analysis
are also presented. Numerical results demonstrate that our series solutions
are highly accurate and efficient. Next we investigate a variable-rate, constant-power adaptive subcarrier
intensity modulation employing M-ary phase shift keying and rectangular
quadrature amplitude modulation for optical wireless communication
over the Gamma-Gamma turbulence channels. The adaptive schemes offer
efficient utilization of optical wireless communication channel capacity
by adapting the modulation order according to the received signal-to-noise ratio and a pre-defined target bit-error rate requirement. Highly accurate
series solutions are presented for the achievable spectral efficiency, average
bit-error rate, and outage probability using a series expansion approach of
the modified Bessel function. In addition, asymptotic bit-error rate and
outage probability analyses are presented. Our asymptotic bit-error rate
analysis shows that the diversity order of both non-adaptive and adaptive
systems depends only on the smaller channel parameter of the Gamma-
Gamma turbulence. Numerical results demonstrate high accuracy of our
series solutions with a nite number of terms and an improved spectral efficiency achieved by the adaptive systems without increasing the transmitter
power or sacrificing bit-error rate requirements. Finally, ergodic capacity is investigated for the optical wireless communications
employing subcarrier intensity modulation with direct detection,
and coherent systems with and without polarization multiplexing over the
Gamma-Gamma turbulence channels. We consider three different adaptive
transmission schemes: (i) variable-power, variable-rate adaptive transmission,
(ii) complete channel inversion with fixed rate, and (iii) truncated channel
inversion with fixed rate. For the considered systems, highly accurate
series expressions for ergodic capacity are derived using a series expansion of
the modified Bessel function and the Mellin transformation of the Gamma-
Gamma random variable. Our asymptotic analysis reveals that the high
SNR ergodic capacities of coherent, intensity modulated, and polarization
multiplexing systems gain 0:33 bits/s/Hz, 0:66 bits/s/Hz, and 0:66 bits/s/Hz
respectively with 1 dB increase of average transmitted optical power. Numerical
results indicate that a polarization control error less than 10 [degree] has a little influence on the capacity performance of polarization multiplexing systems. === Applied Science, Faculty of === Engineering, School of (Okanagan) === Graduate
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