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The design of emergent wireless sensor networks operating near the ground requires channel models that account for previously unconsidered propagation phenomena. Most models used for link planning and radio design of the last century were designed for use in situations where the transmitters were at least tens of meters above the earth surface. However, near the earth surface, the specifics of the ground composition and atmospheric effects have been postulated to play a significant role. This dissertation describes the first set of investigations in this emergent environment. A novel computational electromagnetics model is presented that can calculate electromagnetic fields of a dipole embedded in planar-stratified propagation medium that represents the ground and near-surface atmosphere. It is the first available electromagnetic model to efficiently combine a spectral-domain solution in arbitrary multilayers of lossy-dielectric media with high-order quadrature routines to synthesize the fields of an impressed dipole. For the first time, high-order asymptotic quadrature is used to efficiently obtain solutions at arbitrary ranges from the dipole source. A measurements-based model of the near-ground atmosphere is derived, and results of modeling the atmosphere are used to predict the performance of an ultra-high-frequency radio system operating near the ground surface. Finally, a study is conducted to determine the effects of varying key parameters in the near ground channel, including atmospheric conditions, ground conditions, and frequency. The primary result is that ultra-high-frequency near-earth narrowband channels are largely insensitive to large-scale refractive effects that occur naturally on Earth; however, as the transmitter frequency increases into the super-high-frequency and millimeter wave regimes, refractive effects have significant effects on the radio propagation environment.

Future generation wireless networks are envisioned to provide ubiquitous networking to a wide number of mobile users, promising them the ability to access the various data networks anywhere and anytime. Such networks have motivated the research into efficient management and allocation of the wireless network's limited resources. Heterogeneity also exists amongst the subscribers, i.e. there are those who are willing to spend a little extra on their subscriptions in the prospect of obtaining a better level of service. This work proposes a framework for efficient resource management, while satisfying the heterogeneous QoS demands of the different subscribers. Part of the proposed framework was used to generate mathematical models for the purpose of analyzing the behavior of the system under two different resource management schemes.

Cognitive Radio (CR) is considered to be a novel approach to improve the underutilization of precious radio resources by exploiting the unused licensed spectrum in dynamically changing environments. Designing efficient resource allocation algorithms for dynamic spectrum sharing and for power allocation in OFDM-CR networks is still a challenging problem. In this thesis, we specifically deal with these two problems. Dynamic spectrum sharing for the unlicensed secondary users (SU)s with device coordination could minimize the wastage of the spectrum. But this is a feasible approach only if the network considers the fairness criterion. We study the dynamic spectrum sharing problem for device coordinated cognitive radio networks with respect to fairness. We propose a simple modified proportional fair algorithm for a dynamic spectrum sharing scenario with two constraints, time and utility. Utility is measured by the amount of data processed and time is measured as the duration of a slot. This algorithm could result in variable or fixed length time slots. We will discuss the several controls possible on the algorithm and the possible extension of this algorithm for multicarrier OFDM based CR systems. Traditional water-filling algorithm is inefficient for OFDM-CR networks due to the interaction with primary users (PU)s. We consider reliability/availability of subcarriers or primary user activity for power allocation. We model this aspect mathematically with a risk-return model by defining a general rate loss function. We then propose optimal and suboptimal algorithms to allocate power under a fixed power budget for such a system with linear rate loss. These algorithms as we will see allocate more power to more reliable subcarriers in a water-filling fashion with different water levels. We compare the performance of these algorithms for our model with respect to water-filling solutions. Simulations show that suboptimal schemes perform closer to optimal scheme although they could be implemented with same complexity as water-filling algorithm. We discuss the linearity of loss function and guidelines to choose its coefficients by obtaining upper bounds on them. Finally we extend this model for interference-limited OFDM-CR systems.

The research in this dissertation involves the computationally efficient decoding of multiple access systems and multiple antenna systems. / Thesis (PhDTelecommunications)--University of South Australia, 2004.

Thesis (PhD)--University of South Australia, 2003.

Thesis (PhD)--University of South Australia, 2003.

Thesis (PhDBusinessManagement)--University of South Australia, 2002.

Continuing advances in wireless communications and MEMS (Micro-Electro Mechan- ical Systems) technologies have fostered the construction of a wide variety of sensor and ad hoc networks. These networks have broad applications spanning wide ar- eas, such as environmental monitoring, infrastructure maintenance, traffic manage- ment, energy management, disaster mitigation, personal medical monitoring, smart building, as well as military and defence. While these applications require high per- formance from the network, they suffer from resource constraints (such as limited battery power, processing capability, buffer space, etc.) that do not appear in tra- ditional wired networks. The inherent infrastructure-less characteristic of the sensor and ad hoc networks creates significant challenges. This dissertation addresses these challenges with two protocol designs. The main contributions of this dissertation are the design and evaluation of CS- MAC (stands for CDMA Sensor MAC), a novel multi-channel media access control (MAC) protocol for direct sequence code division multiple access (DS-CDMA) wire- less sensor networks. Our protocol design uses combination of DS-CDMA and fre- quency division to reduce the channel interference and consequently improves system capacity and network throughput. We provide theoretical characterisation of the mean multiple access interference (MAI) at a given node in relation to the number of frequency channels. We show that by using only a small number of frequency chan- nels, the mean MAI can be reduced significantly. Through discrete event simulation (using UC Berkerly NS-2 simulator), we provide comparison of our proposed system to a pure DS-CDMA system as well as a contention based system. Simulation results reveal that our proposed system can achieve significant improvement in system efi ciency (measured in packet/second/channel) of a contention based system. When the same number of packets are transmitted in the network, our system consumes much less communication energy compared to the contention based system. A distributed channel allocation protocol is also proposed for the network forma- tion phase. We prove that our algorithm converges with correct channel assignments. Simulation results reveal that a much smaller number of channels is required than theoretical value when nodes are uniformly randomly deployed. The second contribution of this dissertation involves the design and evaluation of two location-aware select optimal neighbour (SON) algorithms for CSMA/CA based MAC protocol for wireless ad hoc networks. Both algorithms concentrate on the improvement of energy eficiency of the whole network through the optimisation of the number of neighbours of each node. Our algorithms not only consider radio electronic energy consumption (e.g., coding, decoding) and radio transmission energy consumption (e.g., power amplifier), but also the electronic energy consumption at those irrelevant receivers (those who are not addressed by the transmission) that are located within the transmission range. Through simulations, we show that our algorithms can achieve signi??cant energy savings compared to the standard IEEE 802.11.

Continuing advances in wireless communications and MEMS (Micro-Electro Mechan- ical Systems) technologies have fostered the construction of a wide variety of sensor and ad hoc networks. These networks have broad applications spanning wide ar- eas, such as environmental monitoring, infrastructure maintenance, traffic manage- ment, energy management, disaster mitigation, personal medical monitoring, smart building, as well as military and defence. While these applications require high per- formance from the network, they suffer from resource constraints (such as limited battery power, processing capability, buffer space, etc.) that do not appear in tra- ditional wired networks. The inherent infrastructure-less characteristic of the sensor and ad hoc networks creates significant challenges. This dissertation addresses these challenges with two protocol designs. The main contributions of this dissertation are the design and evaluation of CS- MAC (stands for CDMA Sensor MAC), a novel multi-channel media access control (MAC) protocol for direct sequence code division multiple access (DS-CDMA) wire- less sensor networks. Our protocol design uses combination of DS-CDMA and fre- quency division to reduce the channel interference and consequently improves system capacity and network throughput. We provide theoretical characterisation of the mean multiple access interference (MAI) at a given node in relation to the number of frequency channels. We show that by using only a small number of frequency chan- nels, the mean MAI can be reduced significantly. Through discrete event simulation (using UC Berkerly NS-2 simulator), we provide comparison of our proposed system to a pure DS-CDMA system as well as a contention based system. Simulation results reveal that our proposed system can achieve significant improvement in system efi ciency (measured in packet/second/channel) of a contention based system. When the same number of packets are transmitted in the network, our system consumes much less communication energy compared to the contention based system. A distributed channel allocation protocol is also proposed for the network forma- tion phase. We prove that our algorithm converges with correct channel assignments. Simulation results reveal that a much smaller number of channels is required than theoretical value when nodes are uniformly randomly deployed. The second contribution of this dissertation involves the design and evaluation of two location-aware select optimal neighbour (SON) algorithms for CSMA/CA based MAC protocol for wireless ad hoc networks. Both algorithms concentrate on the improvement of energy eficiency of the whole network through the optimisation of the number of neighbours of each node. Our algorithms not only consider radio electronic energy consumption (e.g., coding, decoding) and radio transmission energy consumption (e.g., power amplifier), but also the electronic energy consumption at those irrelevant receivers (those who are not addressed by the transmission) that are located within the transmission range. Through simulations, we show that our algorithms can achieve signi??cant energy savings compared to the standard IEEE 802.11.