Marwan Krunz

Node clustering in wireless sensor networks: recent developments and deployment challenges

The large-scale deployment of wireless sensor networks (WSNs) and the need for data aggregation necessitate efficient organization of the network topology for the purpose of balancing the load and prolonging the network lifetime. Clustering has proven to be an effective approach for organizing the network into a connected hierarchy. In this article, we highlight the challenges in clustering a WSN, discuss the design rationale of the different clustering approaches, and classify the proposed approaches based on their objectives and design principles. We further discuss several key issues that affect the practical deployment of clustering techniques in sensor network applications.

Multi-constrained optimal path selection

Providing quality-of-service (QoS) guarantees in packet networks gives rise to several challenging issues. One of them is how to determine a feasible path that satisfies a set of constraints while maintaining high utilization of network resources. The latter objective implies the need to impose an additional optimality requirement on the feasibility problem. This can be done through a primary cost function (e.g., administrative weight, hop count) according to which the selected feasible path is optimal. In general, multi-constrained path selection, with or without optimization, is an NP-complete problem that cannot be exactly solved in polynomial-time. Heuristics and approximation algorithms with polynomial and pseudo-polynomial-time complexities are often used to deal with this problem. However, existing solutions suffer either from excessive computational complexities that cannot be used for online network operation or from low performance. Moreover, they only deal with special cases of the problem (e.g., two constraints without optimization, one constraint with optimization, etc.). For the feasibility problem under multiple constraints, some researchers have proposed a nonlinear cost function whose minimization provides a continuous spectrum of solutions ranging from a generalized linear approximation (GLA) to an asymptotically exact solution. We propose an efficient heuristic algorithm for the most general form of the problem. We first formalize the theoretical properties of the above nonlinear cost function. We then introduce our heuristic algorithm (H MCOP), which attempts to minimize both the nonlinear cost function (for the feasibility part) and the primary cost function (for the optimality part). We prove that H MCOP guarantees at least the performance of GLA and often improves upon it. H MCOP has the same order of complexity as Dijkstras algorithm. Using extensive simulations on random graphs with correlated and uncorrelated link weights, we show that under the same level of computational complexity, H MCOP outperforms its (less general) contenders in its success rate in finding feasible paths and in the cost of such paths.

An overview of constraint-based path selection algorithms for QoS routing

Constraint-based path selection aims at identifying a path that satisfies a set of quality of service (QoS) constraints. In general, this problem is known to be NP-complete, leading to the proposal of many heuristic algorithms. We provide an overview of these algorithms, focusing on restricted shortest path and multi-constrained path algorithms.

Power controlled dual channel (PCDC) medium access protocol for wireless ad hoc networks

In this paper, we propose a comprehensive solution for power control in mobile ad hoc networks (MANETs). Our solution emphasizes the interplay between the MAC and network layers, whereby the MAC layer indirectly influences the selection of the next-hop by properly adjusting the power of route request packets. This is done while maintaining network connectivity. Directional and channel-gain information obtained mainly from overheard RTS and CTS packets is used to dynamically construct the network topology. By properly estimating the required transmission power for data packets, our protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving node. Simulation results indicate that compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in the channel utilization and end-to-end network throughput, and a significant decrease in the total energy consumption.

CDMA-based MAC protocol for wireless ad hoc networks

We propose a CDMA-based power controlled medium access protocol for mobile ad hoc networks (MANETs). Unlike previously proposed protocols, ours accounts for the multiple access interference (MAI), thereby addressing the notorious near-far problem that undermines the throughput performance in MANETs. Channel-gain information obtained from overheard RTS and CTS packets over an out-of-band control channel is used to dynamically bound the transmission power of mobile terminals in the vicinity of a receiver. By properly estimating the required transmission power for data packets, the proposed protocol allows for interference-limited simultaneous transmissions to take place in the neighborhood of a receiving terminal. Simulation results indicate that compared to the IEEE 802.11 approach, the proposed protocol achieves a significant increase in network throughput at no additional cost in energy consumption.

Transmission power control in wireless ad hoc networks: challenges, solutions and open issues

Recently, power control in mobile ad hoc networks has been the focus of extensive research. Its main objectives are to reduce the total energy consumed in packet delivery and/or increase network throughput by increasing the channels spatial reuse. In this article, we give an overview of various power control approaches that have been proposed in the literature. We discuss the factors that influence the selection of the transmission power, including the important interplay between the routing (network) and the medium access control (MAC) layers. Protocols that account for such interplay are presented.

POWMAC: a single-channel power-control protocol for throughput enhancement in wireless ad hoc networks

Transmission power control (TPC) has great potential to increase the throughput of a mobile ad hoc network (MANET). Existing TPC schemes achieve this goal by using additional hardware (e.g., multiple transceivers), by compromising the collision avoidance property of the channel access scheme, by making impractical assumptions on the operation of the medium access control (MAC) protocol, or by overlooking the protection of link-layer acknowledgment packets. In this paper, we present a novel power controlled MAC protocol called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 ad hoc MAC protocol but which achieves a significant throughput improvement over the 802.11 protocol. Instead of alternating between the transmission of control (RTS/CTS) and data packets, as done in the 802.11 scheme, POWMAC uses an access window (AW) to allow for a series of request-to-send/clear-to-send (RTS/CTS) exchanges to take place before several concurrent data packet transmissions can commence. The length of the AW is dynamically adjusted based on localized information to allow for multiple interference-limited concurrent transmissions to take place in the same vicinity of a receiving terminal. Collision avoidance information is inserted into the CTS packet and is used to bound/ the transmission power of potentially interfering terminals in the vicinity of the receiver, rather than silencing such terminals. Simulation results are used to demonstrate the significant throughput and energy gains that can be obtained under the POWMAC protocol.

Modeling video traffic using M/G//spl infin/ input processes: a compromise between Markovian and LRD models

Statistical evidence suggests that the autocorrelation function p(k) (k=0,1,...) of a compressed-video sequence is better captured by p(k)=e/sup -/spl beta//spl radic/k/ than by p(k)=k/sup -/spl beta//=e/sup -/spl beta/logk/ (long-range dependence) or p(k)=e/sup -/spl beta/k/ (Markovian). A video model with such a correlation structure is introduced based on the so-called M/G//spl infin/ input processes. In essence, the M/G//spl infin/ process is a stationary version of the busy-server process of a discrete-time M/G//spl infin/ queue. By varying G, many forms of time dependence can be displayed, which makes the class of M/G//spl infin/ input models a good candidate for modeling many types of correlated traffic in computer networks. For video traffic, we derive the appropriate G that gives the desired correlation function p(k)=e/sup -/spl beta//spl radic/k/. Though not Markovian, this model is shown to exhibit short-range dependence. Poisson variates of the M/G//spl infin/ model are appropriately transformed to capture the marginal distribution of a video sequence. Using the performance of a real video stream as a reference, we study via simulations the queueing performance under three video models: our M/G//spl infin/ model, the fractional ARIMA model (which exhibits LRD), and the DAR(1) model (which exhibits a Markovian structure). Our results indicate that only the M/G//spl infin/ model is capable of consistently providing acceptable predictions of the actual queueing performance. Furthermore, only O(n) computations are required to generate an M/G//spl infin/ trace of length n, compared to O(n/sup 2/) for an F-ARIMA trace.

On the characterization of VBR MPEG streams

We present a comprehensive model for variable-bit-rate MPEG video streams. This model captures the bit-rate variations at multiple time scales. Long-term variations are captured by incorporating scene changes, which are most noticeable in the fluctuations of I frames. The size of an I frame is modeled by the sum of two random components: a scene-related component and an AR(2) component that accounts for the fluctuations within a scene. Two random processes of i.i.d. rvs are used to model the sizes of P and B frames, respectively. The complete model is then obtained by intermixing the three sub-models according to a given GOP pattern. It is shown that the composite model exhibits long-range dependence (LRD) in the sense that its autocorrelation function is non-summable. The LRD behavior is caused by the repetitive GOP pattern which induces periodic cross-correlations between different types of frames. Using standard statistical methods, we successfully fit our model to several empirical video traces. We then study the queueing performance for video traffic at a statistical multiplexer. The results show that the model is sufficiently accurate in predicting the queueing performance for real video streams.

Statistical characteristics and multiplexing of MPEG streams

This paper presents a study of the statistical characteristics and multiplexing of variable-bit-rate (VBR) MPEG-coded video streams. Our results are based on 23 minutes of video obtained from the entertainment movie, The Wizard of Oz. The experimental setup which was used to capture, digitize, and compress the video stream is described. Although the study is conducted at the frame level (as opposed to the slice level), it is observed that the inter-frame correlation structure for the frame-size sequence involves complicated forms of pseudo-periodicity that are mainly affected by the compression pattern of the sequence. A simple model for an MPEG traffic source is developed in which frames are generated according to the compression pattern of the original captured video stream. The number of cells per frame is fitted by a lognormal distribution. Simulations are used to study the performance of an ATM multiplexer for MPEG streams.