Balakrishnan Narendran

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%.

A network flow framework for online dynamic channel allocation

We present a framework based on network flows for dynamic channel allocation. The framework allows us to gracefully extend previously proposed heuristics, while avoiding the problems associated with the optimal packing schemes. The framework is shown to yield parametrizable algorithms that tradeoff the benefit of channel reassignments with the costs. Channel reassignments are allowed to be performed not just at new call arrivals, but also at various other trigger points like call terminations and channel quality deterioration.

Data distribution algorithms for load balanced fault-tolerant Web access

Describes the design and analysis of RobustWeb, a scalable and fault-tolerant World Wide Web server cluster that is based on HTTP redirection. The system consists of a set of N back-end document servers and one or more redirection servers which receive the HTTP requests and redirect them to the document servers. A load distribution algorithm is used for initial distribution of the documents on the servers. Given a specific degree of replication k, the distribution algorithm guarantees that at least k replicas of each document are present after document distribution is complete. The redirection servers redirect requests to one of the replicas with a pre-computed redirection probability. When a server fails, the redirection probabilities are recomputed using a novel algorithm based on network flow. Theis enables the load to be approximately balanced among the remaining servers, allowing for graceful degradation of the service in the event of failures. A preliminary prototype of RobustWeb has been implemented.

The Concord algorithm for synchronization of networked multimedia streams

Synchronizing different data streams from multiple sources simultaneously at a receiver is one of the basic problems involved in multimedia distributed systems. This requirement stems from the nature of packet based networks which can introduce end-to-end delays that vary both within and across streams. We present a new algorithm called Concord, which provides an integrated solution for these single and multiple stream synchronization problems. It is notable because it defines a single framework to deal with both problems, and operates under the influence of parameters which can be supplied by the application involved. In particular these parameters are used to allow a trade-off between the packet loss rates, total end-to-end delay and skew for each of the streams. For applications like conferencing this is used to reduce delay by determining the minimum buffer delay/size required.

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.

A testbed for mobile networked computing

The rapid deployment of wireless access technology, along with the emergence of high speed integrated service networks, promises to provide users with ubiquitous access to multimedia information in the near future. We are building an experimental testbed system, SWAN (Seamless Wireless ATM Network), to mimic this emerging networking environment. Our wireless access network is organized according to a nanocellular design with base stations serving as a gateway for communication between the wired network and the mobile hosts in a cell. Normally, a mobile host sends and receives traffic through the base station in its current cell. But SWAN also supports direct ephemeral networking between a limited number of cooperating mobile hosts within a small domain. The heart of the testbed is a networking subsystem, FAWN (Flexible Adapter for Wireless Networking) that interfaces the standard PCMCIA bus to an RF modem. The FAWN interface is used with a PC or workstation connected to a wired backbone network or a portable device such as a laptop or palmtop computer. In addition, a user interface consisting of an LCD display, audio I/O, and a bar code reader has been built. When interfaced with FAWN this results in a portable wireless multimedia terminal.

Optimal prioritization of handovers in mobile cellular networks

Investigates channel allocation policies that choose among incoming handover requests to a particular cell. Within a class of non-reserving policies that efficiently utilize the scarce channel resources, the authors identify a most critical first policy that is optimal with respect to handover failure probability. The proof of optimality is accompanied by the description of two techniques to realize the policy in practice. Simulation results that demonstrate its improvement over previous policies are presented as well.

Internet stream synchronization using Concord

Using packet networks to transport multimedia introduces delay variations within and across streams, necessitating synchronization at the receiver. This requires stream data to be buffered prior to presentation, which also increases its total end to end delay. Concord recognizes that applications may wish to influence the underlying synchronization policy in terms of its effect on quality of service. It provides a single framework for synchronization within and across streams and employs an application specific tradeoff between packet losses, delay and inter- stream skew. We present a new predictive approach for synchronization and a selection of results from an extensive evaluation of Concord for use in the Internet. A trace driven simulator is used, allowing a direct comparison with alternative approaches. We demonstrate that Concord can operate with lower maximum delay and less variation in total end to end delay, which in turn can allow receiver buffer requirements to be reduced.

Multi-way partitioning of VLSI circuits

Partitioning is one of the critical phases of hierarchical design processes like VLSI design. Good partitioning techniques can positively influence the performance and cost of a VLSI product. This paper proposes a partitioning algorithm with a new cost metric. viewed from a VLSI layout point of view our cost metric minimizes the average delay per net. It can also be interpreted as achieving the minimum number of vias per net. This paper highlights how the seemingly slight difference between our metric and others could cause partitions to be evaluated considerably differently. Experimental results show that in addition to the expected improvements we get on our metric, the proposed algorithm does well on the traditional nets cut metric as well.