Abstract-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. We establish tight bounds that relate the outage probability caused by channel fading to the signal-to-interference margin calculated when the statistical variation of the signal and intereference powers is ignored. This allows us to show that well-known methods for allocating power, based on Perron-Frobenius eigenvalue theory, can be used to determine power allocations that are provably close to achieving optimal (i.e., minimal) outage probability. We show that the problems of minimizing transmitter power subject to constraints on outage probability and minimizing outage probability subject to power constraints can be posed as a geometric program (GP). A GP is a special type of optimization problem that can be transformed to a nonlinear convex optimization problem by a change of variables and therefore solved globally and efficiently by recently developed interior-point methods. We also give a fast iterative method for finding the optimal power allocation to minimize outage probability.

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We introduce a novel formulation of the power control problem in wireless networking, which is especially appropriate for packet-based wireless communication, capturing the fundamental packet delay vs. transmission power tradeoff. Model analysis under simple, yet natural, assumptions yields ubiquitous structural properties of optimal power control schemes, which are then leveraged in the design of a new family of distributed algorithms for power-controlled multiple access (PCMA). Their experimental evaluation by simulation demonstrates performance gains over standard approaches. This is a first step toward designing efficient PCMA protocols for shared channel access in wireless packet networks.

We consider a wireless multimedia CDMA system, where the different mobiles transmit at different rates. We devise a method of simultaneously optimizing the power and rate at which the different terminals transmit for achieving their required Quality of Service (QoS). The QoS is defined to be the effective data rate which is different from the transmission rate. Optimization of power enhances battery life and optimization of data transmission rates facilitates in building cheaper and power efficient mobile systems. The joint optimization problem is formulated so that for a specified Q o S , the total power transmitted by all the mobiles, and the sum of the transmitting rates of different mobiles can be minimized. The optimization problem is shown to be a non-linear and non-convex problem, but is solved to get a globally optimal solution using geometric programming. Results show that with optimized rates and powers, we can obtain better QoS than that obtained by present systems which use higher power.

We investigate novel channel access schemes for packetized wireless networks, which can dynamically switch between distinct transmission modes in order to better match the channel state and deliver packets to the receiver with higher success probability (rate). We call them Multimodal Dynamic Multiple Access -MDMA schemes. Based on the observed channel impairment state (typically a combination of interference, fading, multipath etc.) and the transmitter queue packet backlog at any time instant (slot), each user autonomously selects the best transmission mode to activate and power level to transmit at. First, a general formulation of the MDMA problem is introduced in several methodological steps of progressive complexity. It is based on dynamic programming and captures the basic tradeoffs. Analytical issues are not pursued in detail here, but instead several ubiquitous structural properties of MDMA schemes are identified and explored. Based on those, a novel suite of MDMA algorithms is designed and evaluated. On a simulated baseline scenario, MDMA is shown to achieve over 30% higher throughput than previously studied raw PCMA [5] schemes and even higher performance gains over other standard benchmark ones. This indicates that MDMA schemes can release 'latent' network capacity which is suppressed by others, and should be further explored. This study is a first step towards designing full MDMA protocols for high-performance wireless packet networks.