Traditionally, ad hoc networks have been viewed as a connected graph over which end-to-end routing paths had to be established. Mobility was considered a necessary evil thatinvalidatespathsandneedstobeovercomeinanintelligent way to allow for seamless communication between nodes. However, it has recently been recognized that mobility can be turned into a useful ally, by making nodes carry data around the network instead of transmitting them. This model of routing departs from the traditional paradigm and requires new theoretical tools to model its performance. A mobility-assisted protocol forwards data only when appropriate relays encounter each other, and thus the time between such encounters, called hitting or meeting time, is of high importance. In this paper, we derive accurate closed form expressions for the expected encounter time between different nodes, under commonly used mobility models. We also propose a mobility model that can successfully capture some important real-world mobility characteristics, often ignored in popular mobility models, and calculate hitting times for this model as well. Finally, we integrate this results with a general theoretical framework that can be used to analyze the performance of mobility-assisted routing schemes. We demonstrate that derivative results concerning the delay of various routing schemes are very accurate, under all the mobility models examined. Hence, this work helps in better understanding the performance of various approaches in different settings, and can facilitate the design of new, improved protocols.

We propose a new method of power control for interference limited wireless networks with Rayleigh fading of both the desired and interference signals. Our method explictly takes into account the statistical variation of both the received signal and interference power, and optimally allocates power subject to constraints on the probability of fading induced outage for each transmitter/receiver pair. We establish several results for this type of problem.

Cellular frequency reuse is known to be an efficient method to allow many wireless telephone subscribers to share the same frequency band. However, for wireless data and multi-media communications optimum cell layouts differ essentially from typical solutions for telephone systems. We argue that wireless radio systems for bursty message traffic preferably use the entire bandwidth in each cell. Packet queuing delays are derived for a network with multipath fading channels, shadowing, path loss and discontinuously transmitting base stations. Interference between cells can be reduced by appropriately scheduling transmissions or by `spatial collision resolution'.

We present a game-theoretic treatment of distributed power control in CDMA wireless systems using outage probabilities. We prove that the noncooperative power control game considered admits a unique Nash equilibrium (NE) for uniformly strictly convex pricing functions and under some technical assumptions on the SIR threshold levels. We analyze global convergence of continuous-time as well as discretetime synchronous and asynchronous iterative power update algorithms to the unique NE of the game. Furthermore, a stochastic version of the discrete-time update scheme, which models the uncertainty due to quantization and estimation errors, is shown to converge almost surely to the unique NE point. We further investigate and demonstrate the convergence and robustness properties of these update schemes through simulation studies.

In this paper the performance of a cellular mobile radio system with frequency reuse is evaluated, in terms of outage probability. Deterministic path loss, log-normal shadowing and Ricean fading are accounted for, and the use of diversity and power control is considered in order to enhance the system performance. Both hexagonal and lineal cells are considered. Particular attention is given to the sensitivity of the outage probability to the system parameters, especially those related to the propagation model (fading, shadowing and path loss). It is seen that diversity and power control can improve the system behavior. The performance is sensitive to the fading parameter (i.e., the Rice factor) of the intended user, but is relatively independent of that of the interferers; also, a significant dependence is observed on the shadowing parameter, whereas a limited dependence is seen on the outage threshold and on the channel utilization. Finally, the presence of a dual path loss law degrade...

Abstract—Physical Carrier Sensing plays a crucial role in the effectiveness of CSMA-based MAC protocols, yet its properties and impact on the system performance under slow fading channel have not been well understood. We demonstrate that carrier sensing can be highly unreliable even within the “carrier sensing range ” and the channel is largely stable during a transmission between slowly moving mobile stations. Then we formulate the carrier sensing outage probability between competing mobile stations and propose a model to estimate the frame error rate and normalized throughput of a saturated IEEE 802.11 DCF single-hop ad-hoc network. Our model is validated via extensive simulations using Qualnet. The numerical and simulation results reveal substantial degradation in system performance with a small amount of carrier sensing outage. I.

Noncooperative game theory is used as a basis for analyzing, developing, and implementing decision, control, and resource allocation schemes to address various network control problems such as congestion control, code division multiple access (CDMA) power control, and network intrusion detection and response. In the cases of CDMA power control and congestion control, a fairly general, distributed, market-based resource allocation framework is developed and analyzed. The applicability of the underlying noncooperative network game's principles to both network control problems can be considered as an indicator of the generality and usefulness of this approach. Based on this general framework, various algorithms customized according to the specific nature of the network at hand are developed. Making use of a variety of control theoretic tools such as Lyapunov and hybrid system theories, stability and robustness properties of these algorithms are studied rigorously. An analysis of robustness with respect to feedback delays, which is of particular importance, is provided for most of the algorithms considered. In the case of network intrusion detection, dynamic noncooperative games are utilized to model the decision and analysis processes in an IDS. Again, both generic and system-specific schemes and models are considered. In addition to the theoretical analysis of the network control problems addressed, implementation related aspects of the schemes developed are investigated. For each algorithm, theoretical results obtained are supported and demonstrated either via high-level MATLAB simulations or using the NS-2 packet level network simulator. Through extensive simulations, applicability and underlying assumptions of the theoretical models are verified.

Abstract Cellular frequency reuse is known to be an efficient method to allow many wireless telephone subscribers to share the same frequency band. However, frequency reuse laeds to mutual interference among co-channel cells. We review the technique for computing and modelling link performance in cellular networks. 1

Abstract—In a slow fading environment, the carrier sense range is not constant, so there is not a constant set of hidden terminals for a mobile station. The probability of capture with a set of interferers is not a fixed value either, and it fundamentally affects the loss rate and throughput of the whole network. We estimate the expectation of the capture probability in a single hop ad hoc network and incorporate it with our previously proposed model for 802.11 DCF that considers the time-varying nature of carrier sensing. The system throughput is then derived from an individual station’s point of view. The model is verified against simulations, and extensive numerical experiments are performed to demonstrate its application. I.

Abstract—We present a model that predicts the saturated single-hop performance of IEEE 802.11 ad hoc network in the face of the physical capture effect under a block-fading Rayleigh channel. Based on an estimate of the frame delivery rate and a fixed point iteration algorithm, we devise an efficient control on the rate of convergence and a wise selection of the interferer sets that significantly affect the final results, so as to overcome the explosive time complexity of the iteration algorithm. These enhancements achieve up to two orders of magnitude speedup for large ad hoc networks with minimal and controllable prediction error, so that large scale monte carlo experiments for various distributions are made possible. I.