Radio wave propagation

The open nature of the wireless medium makes the wireless communication
susceptible to eavesdropping attacks. In addition, fading and shadowing significantly
degrade the performance of the communication system in the wireless networks. A
versatile approach to circumvent the issues of eavesdropping attacks while exploiting the
physical properties of the wireless channel is the so-called physical layer-security. In this
work, we consider a model in which two legitimate users communicate in the presence of
an eavesdropper. We investigate the performance of the wireless network at the physical
layer that is subject to a variety of fading environments that may be modeled by the
Rayleigh, Nakagami-m, and Generalized-K distributions, to mention a few. We use the
secrecy outage probability (SOP) as the standard performance metrics to study the
performance of the wireless networks. We propose two different approaches to compute
the secrecy outage probability, and derive explicit expressions for the secrecy outage probability that allow us to characterize the performance of the wireless networks.
Specifically, we use a direct integration approach as well as a Taylor series base approach
to evaluate the secrecy outage probability. Finally, we use computer simulations, based
on MATLAB, to confirm the analytical results.

The rapid growth of satellite services using higher frequency bands such as the Ka-band has highlighted need for analyzing effects of different propagation phenomena. Since the wavelength of radiowaves is comparable with the size of rain drops, rain attenuation is the dominant propagation impairment at Ka frequencies. In addition, other impairments such as gaseous absorption, cloud and fog attenuation, tropospheric refractive effects, as well as depolarization become increasingly important with increasing operating frequency. Theoretical background of radiowave propagation principles, rain systems and gases in the atmosphere are presented to insure comprehension of propagation effects on space communication in Ka-band. Models for predicting rain attenuation and other propagation impairments along Earth-satellite path are provided in order to simplify design of communication systems. Propagation phenomena are explained on example of three propagation experiments performed in U.S., Europe and Japan. Whenever possible, mitigation techniques to overcome severe attenuations are introduced.

Wireless communication has become a significant part of our life. Bluetooth(TM) Radio system is one example of wireless communication, Wireless Local Area Network (WLAN) is another example of wireless technology. Both of systems operate in the same frequency band, the Industrial Scientific Medical (ISM) band, which use a 2.4 GHz carrier frequency. According characteristic of system, multi-path effect are major concern for indoor propagation. A frequency sounding technique is introduced to determine characteristics of the multi-path signal. However, multi-path can not be evaluated directly; some parameters are measured to determine the effect of multi-path. Angles of arrival can be used to facilitate the effect of multi-path signal. Using MatLab programming, Spatial Filter Periodogram (SPF) is introduced to estimate angles of arrival.

Body-proximate telecommunications devices are examined in both direct and multipath propagation. The study begins with a characterization of standard field strength sensitivity measurement methods for body-proximate telecommunications devices. Original measurements on a group of anthropometrically diverse people reveal that human adults, in a standard pose, are remarkably similar with respect to belt worn sensitivity performance, which motivates and justifies the use of an existing and a newly introduced light weight simulated human body device for testing, analysis and optimization of body worn telecommunications devices. Standard measurement methods using standard open air test ranges are established and validated by international transfers of measurements. The study extends to optimization of telecommunications devices in multipath, and particularly to the diversity reception of signals. A novel signal simulation model is introduced which includes multipath and shadowing, and is validated against both theoretical statistics and measurements. The signal simulation model is extended to characterize polarization randomization and cross-coupling based on an urban generalization of building height to street width ratio. The model is used to analyze measurements of polarization randomization of signals originating from an airborne transmitter flying a path whose geometry is consistent with low earth orbiting communications satellites.

In this dissertation, new semi-analytical expressions for the diversity bit error rate performance of asynchronous direct sequence-code division multiple access (DS-CDMA) systems in multipath fading channels are derived. Also, the PN acquisition time of a DS system with offset frequency periods greater than the code period in a AWGN channel is measured via laboratory experiments. In Part I we consider DS-CDMA systems operating in a cellular environment with multipath reception. Multipath propagation is exploited through the use of RAKE receivers. Coherent, differentially coherent and noncoherent binary demodulation schemes are considered. The multiple access interference is modeled as AWGN, conditioned on the fading statistics of the received signal. The mobile radio channel introduces selective fading, and is modeled as a tapped delay line. The amplitude of each resolvable path is statistically described by the Nakagami distribution, which is a general solution to the random vector problem that causes rapid fading. However, we assume independent but nonidentical fading along the RAKE branches. Therefore our analysis supports unequal mean powers and different amount of fading in the multipath components combined by the receiver. Also, the results can be easily extended to account for diversity from multiple antennas or coding in the generalized Nakagami multipath fading environment. In Part II we consider a land mobile satellite channel. First, a laboratory experiment is setup to evaluate the PN acquisition performance of a digital IF receiver in a AWGN channel with large Doppler offset. The digital conversion receiver uses the inherent aliasing property of sampling to realize the baseband conversion using a single analog-to-digital converter. Thereafter, digital signal processing on the I and Q samples enable for design trade-offs in the acquisition of the PN code with Doppler periods greater than the code period. Two code phase selection criterions, namely the maximum criterion and the threshold crossing criterion, are investigated and their acquisition time is measured for different frequency offsets and input IF signal to noise ratios. We also derive semi-analytical expressions for the BER performance of coherent and differentially coherent systems operating in a mobile satellite channel. In this case the channel is modeled as a multipath nonselective channel, but diversity gain can still be obtained through path diversity. This is the scenario when a signal is transmitted to all satellites in view and the received replicas are independently demodulated and combined at the receiver. Our analysis extends previous results to the case of unequal mean powers and Rice factors in the combined signals; a valid assumption if we consider that the satellites are in view at different elevation angles. Furthermore, the effect of imperfect power control in such mobile satellite DS-CDMA systems is also considered.