Prathima Agrawal

A Survey of Energy Efficient Network Protocols for Wireless Networks

Wireless networking has witnessed an explosion of interest from consumers in recent years for its applications in mobile and personal communications. As wireless networks become an integral component of the modern communication infrastructure, energy efficiency will be an important design consideration due to the limited battery life of mobile terminals. Power conservation techniques are commonly used in the hardware design of such systems. Since the network interface is a significant consumer of power, considerable research has been devoted to low-power design of the entire network protocol stack of wireless networks in an effort to enhance energy efficiency. This paper presents a comprehensive summary of recent work addressing energy efficient and low-power design within all layers of the wireless network protocol stack.

Adapting packet fair queueing algorithms to wireless networks

Parames~varan Ramana.tllan Pratbinla t\graIval Dept. of Elect. & Comp. Engr. I[)ter]~et. ArcIl. Research Lab University of Wisconsin Bellcore, hIorristotvn Nladison, WI 53706 Ne\v .Jersey 07960. parmesll!@ece.\visc.edu pagra~val(~bellcore. com Bit errors are fairly common during transmission in a wireless network. As a result, a straight-forwarcl application of existing packet fair queueing (PFQ) algorithms from wireIine to wireless networks results in an ine~cient use of ~he Kmited wireless bandwidth. In this paper, we propose a simple approach for adapting the existing PFQ algorithms for the wire]ine networks to provide the same kind of long-term fairness guarantees while making efficient use of the wireless bandwidth. In the proposed approach, long-term fairness guarantees are provided by supplementing the bandwidth given to sessions which have not received satisfactory service in the short -term due to poor quahty of their wireless channel. To efficiently keep track of the amount of supplemental bandwidth for each session, the paper introduces the concept of a long-term fairness server. This concept. also allows one to easily integrate the proposed approach with any of the existing PFQ algorithms.

Dynamic resource allocation schemes during handoff for mobile multimedia wireless networks

User mobility management is one of the important components of mobile multimedia systems. In a cell-based network, a mobile should be able to seamlessly obtain transmission resources after handoff to a new base station. This is essential for both service continuity and quality of service assurance. In this paper, we present strategies for accommodating continuous service to mobile users through estimating resource requirements of potential handoff connections. A diverse mix of heterogeneous traffic with diverse resource requirements is considered. The investigate static and dynamic resource allocation schemes. The dynamic scheme probabilistically estimates the potential number of connections that will be handed off from neighboring cells, for each class of traffic. The performance of these strategies in terms of connection blocking probabilities for handoff and local new connection requests are evaluated. The performance is also compared to a scheme previously proposed by Yu and Leung (see IEEE J. Select. Areas Commun., vol.15, p.1208-25, 1997). The results indicate that using dynamic estimation and allocation, we can significantly reduce the dropping probability for handoff connections.

TeleMIP: telecommunications-enhanced mobile IP architecture for fast intradomain mobility

This article first surveys existing protocols for supporting IP mobility and then proposes an extension to the mobile IP architecture, called TeleMIP. Our architecture attempts to achieve smaller handoff latency by localizing the scope of most location update messages within an administrative domain or a geographical region. TeleMIP is intended for use in evolving third-generation wireless networks, and introduces a new logical entity, called the mobility agent, which provides a mobile node with a stable point of attachment in a foreign network. While the MA is functionally similar to conventional foreign agents, it is located at a higher level in the network hierarchy than the subnet-specific FAs. Location updates for intradomain mobility are localized only up to the MA; transmission of global location updates are necessary only when the mobile changes administrative domains and/or geographical regions. By permitting the use of private or locally scoped addresses for handling intradomain mobility, TeleMIP allows efficient use of public address space. Also, by reducing the frequency of global update messages, our architecture overcomes several drawbacks of existing protocols, such as large latencies in location updates, higher likelihood of loss of binding update messages, and loss of inflight packets, and thus provides better mobility support for real-time services and applications. The dynamic creation of mobility agents (in TeleMLP) permits the use of load balancing schemes for the efficient management of network resources.

An adaptive power control and coding scheme for mobile radio systems

We propose a dynamic combined power control and forward error correction control (FEC) algorithm for mobile radio systems that can minimize the power consumed by wireless transmitters while increasing the number of simultaneous connections. This algorithm is distributed, where individual transmitter-receiver pairs determine the minimal power and FEC to satisfy specified quality-of-service (QOS) constraints. We present simulation results showing that this algorithm outperforms previous algorithms that use only power control.

Delay reduction techniques for playout buffering

Receiver synchronization of continuous media streams is required to deal with delay differences and variations resulting from delivery over packet networks such as the Internet. This function is commonly provided using per-stream playout buffers which introduce additional delay in order to produce a playout schedule which meets the synchronization requirements. Packets which arrive after their scheduled playout time are considered late and are discarded. In this paper, we present the Concord algorithm, which provides a delay-sensitive solution for playout buffering. It records historical information and uses it to make short-term predictions about network delay with the aim of not reacting too quickly to short-lived delay variations. This allows an application-controlled tradeoff of packet lateness against buffering delay, suitable for applications which demand low delay but can tolerate or conceal a small amount of late packets. We present a selection of results from an extensive evaluation of Concord using Internet traffic traces. We explore the use of aging techniques to improve the effectiveness of the historical information and hence, the delay predictions. The results show that Concord can produce significant reductions in buffering delay and delay variations at the expense of packet lateness values of less than 1%.

Voice performance in WLAN networks - an experimental study

In this work, we measure wireless local area network (WLAN) voice performance and capacity. While most WLAN applications today are data centric, the growing popularity of Voice over IP (VoIP) applications and the escalating trend towards convergence with cellular networks will catalyze an increased mix of voice traffic. Since voice applications must compete with each other and with simultaneous data applications for WLAN bandwidth, quantifying voice performance and capacity in the presence of background data traffic is an important issue. We offer a practical investigation into the ability of 802.11b MAC layer to support simultaneous voice and data. We quantify VoIP capacity for standard WLAN networks, indicative of those already in the field, as well as evaluate the practical benefits of implementing backoff control and priority queuing at the access point. Conclusions are drawn based on an extensive set of real-world measurements conducted using off-the-shelf equipment in a commercial testbed.

Fault coverage requirement in production testing of LSI circuits

A technique is described for evaluating the effectiveness of production tests for large scale integrated (LSI) circuit chips. It is based on a model for the distribution of faults on a chip. The model requires two parameters, the average number (n/SUB 0/) of faults on a faulty chip and the yield (y) of good chips. It is assumed that the yield either is known or can be calculated from the available formulas. The other parameter, n/SUB 0/, is determined from an experimental procedure. Once the model is fully characterized, it allows calculation of the field reject rate as a function of the fault coverage. The technique implicitly takes into account such variables as fault simulator characteristics, the feature size, and the manufacturing environment. An actual LSI circuit is used as an example.

Minimizing cellular handover failures without channel utilization loss

In cellular systems, a primary goal is the reduction of handover failures in the system. Channel allocation policies that address this by setting aside guard channels for the exclusive use of handover requests suffer from a lower utilization of the scarce channel resources. We define a class of non-reserving policies that efficiently utilize the channels. Within this class, we identify a most critical first policy that is optimal with respect to handover failure probability. Moreover, this policy is shown to have the best channel utilization in its class as well. The proofs of optimality are accompanied by the description of a technique to realize the policy in practice. Simulation results that demonstrate its improvement over previous policies are presented as well.

Concurrency and Communication in Hardware Simulators

This paper describes models for concurrency and interpartition communication in a hardware logic simulator implemented using multiprocessors. Software simulation data from production VLSI chips were analyzed in the context of a multiprocessor environment to obtain experimental values for concurrency and communication. The VLSI chips were randomly partitioned in the above experiments. The concurrency observed is significantly lower than the maximum achievable theoretically. This effect was more pronounced for circuits with lower activity. The effect of different simulators (unit and multiple delay), on concurrency and communication, is explained. Finally, a partitioning heuristic whose objective is to enhance concurrency and minimize communication is proposed. It makes use of the circuit topology and the delay information in a simulation database.