Arash Behzad

On the performance of graph-based scheduling algorithms for packet radio networks

Many published algorithms used for scheduling transmissions in packet radio networks are based on finding maximal independent sets in an underlying graph. Such algorithms are developed under the assumptions of variations of the protocol interference model, which does not take the aggregated effect of interference into consideration. We provide a probabilistic analysis for the throughput performance of such graph based scheduling algorithms under the physical interference model. We show that in many scenarios a significant portion of transmissions scheduled based on the protocol interference model result in unacceptable signal-to-interference and noise ratio (SINR) at intended receivers. Our analytical as well as simulation results indicate that, counter intuitively, maximization of the cardinality of independent sets does not necessarily increase the throughput of a network. We introduce the truncated graph based scheduling algorithm (TGSA) that provides probabilistic guarantees for the throughput performance of the network.

Impact of power control on the performance of ad hoc wireless networks

An ad hoc wireless network with n nodes and m source-destination pairs, using a scheduling based medium access control (MAC) protocol such as time division multiple access (TDMA), and a routing mechanism that may be unicast or multicast based, is considered. Under a given nodal transmit power vector, we define the source-destination throughput vector to be achievable if there exists an associated temporal (based on the channel sharing MAC protocol) and spatial (based on the underlying routing mechanism) joint scheduling-routing scheme that yields the throughput vector. In this paper, we analyze and investigate the effect of nodal transmit power vector on the maximum (or supreme) level of a general (real-valued) function of the source-destination throughput levels. We represent the latter supreme level attained under power vector. We also derive a linear programming (LP) formulation for obtaining the exact solution to the optimization problem that yields the throughput capacity of finite ad hoc wireless networks. Our LP based performance evaluation results identify the magnitude of capacity upgrade that can be realized for networks with random topologies and traffic patterns.

Optimum integrated link scheduling and power control for ad hoc wireless networks

In this paper, we develop a new mathematical programming formulation for minimizing the schedule length in ad hoc wireless networks based on the optimal joint scheduling of transmissions across the multi-access communication links and allocation of transmit power levels, while meeting the requirements on the signal-to-interference and noise ratio (SINR) at intended receivers. We prove that the problem can be represented as a mixed integer linear programming (MILP) and show that the latter yields a solution that consists of transmit power levels that are strongly Pareto optimal. We demonstrate that our MILP formulation can be used effectively to derive optimal scheduling and power levels for networks with as many as 30 designated communication links. We exhibit that the MILP formulation can be also effectively solved to provide tight upper and lower bounds (corresponding to an approximation factor /spl Delta/) for the optimum schedule length of networks with as many as 100 designated links. We prove that the integrated link scheduling and power control problem is NP-complete. Consequently, we develop and investigate a heuristic algorithm of polynomial complexity (O|LO|/sup 5/) for solving the problem in a timely and practical manner. Our algorithm is based on the properties of a novel interference graph (the power-based interference graph) that we have introduced. We demonstrate that the frame length of schedules realized by our heuristic schemes reside in the 25 percentile of those attained by the optimal mechanism for randomly generated topologies.

Integrated Power Controlled Rate Adaptation and Medium Access Control in Wireless Mesh Networks

In this paper, a new mathematical programming model and assignment algorithms are developed for minimizing the schedule length in adaptive power and adaptive rate link scheduling in spatial-TDMA wireless networks. The underlying problem entails the optimal joint scheduling of transmissions across multi-access communication links combined with the simultaneous allocation of transmit power levels and data rates across active links, while meeting required Signal-to-Interference-plus-Noise Ratio (SINR) levels at intended receivers. We prove that the problem can be modeled as a Mixed Integer-Linear Programming (MILP) and show that the latter yields a solution that consists of transmit power levels that are strongly Pareto Optimal. We note this problem to be NP-complete. For comparison purposes, we employ the MILP formulation for computing the optimal schedule for networks with small number of designated links and limited number of data rate levels. We proceed to develop and investigate a heuristic algorithm of polynomial complexity for solving the problem in a computationally effective manner. The algorithm is based on the construction of a Power Controlled Rate adaptation Interference Graph. The desired schedule is then derived by using a greedy algorithm to construct an independence set from this graph. Based on system analyses, we show, for smaller illustrative networks, the performance behavior realized by the heuristic algorithms to generally be in the 75 percentile of those attained by the optimal schedule. We also show that performance of our heuristic algorithm is on average 20% better than that attained under prior algorithms that were developed for use under fixed transmit power and fixed rate link scheduling.

On the domination number of the generalized Petersen graphs

Graph domination numbers and algorithms for finding them have been investigated for numerous classes of graphs, usually for graphs that have some kind of tree-like structure. By contrast, we study an infinite family of regular graphs, the generalized Petersen graphs G(n). We give two procedures that between them produce both upper and lower bounds for the (ordinary) domination number of G(n), and we conjecture that our upper bound @?3n/5@? is the exact domination number. To our knowledge this is one of the first classes of regular graphs for which such a procedure has been used to estimate the domination number.

Distributed power controlled medium access control for ad-hoc wireless networks

We develop and investigate a new medium access control (MAC) algorithm and protocol for ad-hoc wireless networks that employs power control spatial-reuse scheduling techniques. We. introduce a novel interference graph (the power-based interference graph), whose independence and chromatic numbers provide fundamental bounds for the integrated scheduling-power control problem. Based on the properties of the power-based interference graph, we develop two distributed algorithms (the distributed power controlled scheduling algorithms, DPCSs), which merely utilize the local information in the process of time slot allocation and power control. We show that both algorithms lead to a significant increase in the network throughput level through-spatial reuse of the communications resources while (Pareto) optimizing the power consumption.

Delay-throughput performance of load-adaptive power-controlled multihop wireless networks with scheduled transmissions

The majority of current research on power control in ad-hoc wireless networks concentrates on enhancing throughput performance while disregarding delay requirements. Under such cases, the throughput enhancement is achieved at the expense of increased packet delay that would not be acceptable in many practical situations. In this paper, we study the performance of a load-adaptive power-controlled demand-assigned time division multiple access (DA/TDMA) wireless network, where a central controller may be employed to schedule transmissions under varying network load. We show that multi-hopping is not necessarily the optimal routing strategy to follow in every circumstance. In fact, even though multi-hopping, or alternatively the strategy to transmit at minimum required power levels, may contribute to increased spatial reuse, it causes substantial delay increase when compared to single hop transmissions, especially under light network loads. We thus propose a load adaptive power control protocol for integrated medium access control (MAC) and routing that requires the nodes to transmit at high power under light network load (resulting in a direct transmission between the source and the destination) and switch to multi-hop low power transmissions under heavy network load.

On the performance of randomized power control algorithms in multiple access wireless networks

In this paper, we develop and investigate a novel power control algorithm (the fair randomized power control algorithm; FRPC) to enhance the throughput level of the slotted Aloha medium access control mechanism. FRPC is developed based on the analysis of the capture effect for which the transmitter captures the channel only if the observed signal-to-interference and noise ratio (SINR) at the receiver is above a certain threshold. We first analyze the sensitivity of the generic randomized power control algorithm with respect to expected value and standard deviation of the power density function. In particular, based on the one-tailed version of Chebyshevs inequality, we derive a closed-form expression for an upper bound on the probability of capture (and an upper bound on the aggregate throughput) in the network. We then apply the latter result to the process of designing the FRPC algorithm for the slotted Aloha MAC mechanism. Our simulation results indicate that the FRPC algorithm leads to significant throughput gain while providing fairness for different mobile users in the system.

Power controlled multiple access control for wireless access nets

In this paper, we develop and investigate a new joint power controlled medium access control (MAC) algorithm for wireless access nets (ANets). In an ANet, the user nodes are associated with a single central node (backbone node) that serves to allocate and manage their resources. Under our new protocol, the net backbone node (BN) instructs the ANet nodes to make power control adjustments while simultaneously allocating to them slots for the requested transmission of their packets. Our algorithm leads to significant increase in the net throughput level by attaining high spatial reuse while striving to reduce power consumption in that nodes only employ the power levels required to reach their designated destinations. By introducing fair queuing and scheduling elements, we demonstrate the ability of our algorithm to support fairness in our scheduling. Two different methodologies for incorporation of fairness are proposed. We demonstrate the throughput and delay vs. fairness trade-off behavior of our new protocol.

ADHOC Wirless Networking Using Mobile Backbones

We introduce an adhoc wireless mobile network that employs a hierarchical networking architecture. The network nodes have different capabilities, and are thus divided into high and low capacity classes. We present a topological synthesis algorithm that selects a subset of the high capacity nodes to form a backbone network (Bnet). The latter consists of interconnected backbone nodes that intercommunicate across higher power (or regular) links, and may also make use of unmanned vehicles (UVs), including airborne UAVs orbiting at multiple altitudes, as well as ground based UGVs, to form a multi-tier backbone. Each backbone node controls the allocation of communications resources associated with client nodes that reside in its managed cluster of nodes (forming its Access Net - Anet). We introduce the Mobile Backbone Network Protocol (MBNP) to implement the key networking schemes for such a Mobile Backbone Network (MBN). Our description of this protocol involves the following procedures: backbone network topological synthesis; on-demand and/or proactive routing mechanisms; power control based MAC layer protocols; and network/MAC cross-layer resource allocation schemes. The MBNP serves to allocate resources across the network to ensure that user applications are granted acceptable quality-of-service (QoS) performance, while striving to ensure a highly survivable and robust backbone-oriented networking architecture. We include in MBNP a new class of on-demand routing algorithms, identified as MBNR, that employ the backbone network for selective forwarding of routerequest messages, while striving to achieve an efficient MAC layer operation. We enhance these new routing algorithms by incorporating link stability estimates to attain a robust routing operation. For this purpose, links that are determined by a node to be in an unstable state are dynamically eliminated from the backbone subnetwork that is used for establishing new routes. To ensure service quality for admitted flows, including the attainment of low delay jitter performance levels for supported realtime streams, we introduce flow admission control mechanisms into our MBN based on-demand routing