Sungbum Hong

A distributed algorithm for dynamic channel allocation

Recent demand for mobile telephone service has been growing rapidly while the electro-magnetic spectrum of frequencies allocated for this purpose remains limited. Any solution to the channel assignment problem is subject to this limitation, as well as the interference constraint between adjacent channels in the spectrum. Channel allocation schemes provide a flexible and efficient access to bandwidth in wireless and mobile communication systems. In this paper, we present an efficient distributed algorithm for dynamic channel allocation based upon mutual exclusion model, where the channels are grouped by the number of cells in a cluster and each group of channels cannot be shared concurrently within the cluster. We discuss the algorithm and prove its correctness. We also show that the algorithm requires at most (worst case) O(Ng⋅Nn log Nn) messages, where Ng is the number of groups and Nn is the number of neighbors. This is compared to Choys algorithm which requires O(Ng2⋅Nn), where Ng is the number of groups and Nn is the number of neighboring cells in the system. We report our algorithms performance with several channel systems using different types of call arrival patterns. Our results indicate that significant low denial rate, low message complexity and low acquisition time can be obtained using our algorithm.

An efficient synchronization scheme of multimedia streams in wireless and mobile systems

Recent advances in mobile computing and distributed multimedia systems allow mobile hosts (clients) to access wireless multimedia systems anywhere and at anytime, but not without creating a new set of issues and trade-offs. To the best of our knowledge, there has been very little research in dealing with the synchronization problem in wireless and mobile multimedia systems. In this paper, we propose an efficient distributed synchronization algorithm using quasi-sink for wireless and mobile multimedia systems to ensure and facilitate mobile client access to multimedia objects. We discuss the algorithm and provide its proof of correctness. We also present a set of simulation experiments to evaluate the performance of our scheme using message complexity and buffer usage at each frame arrival time. Our results indicate that our scheme exhibits a significant low message complexity and no underflow and overflow within the bounded delivery time.

Distributed dynamic channel allocation for mobile communication systems

We present an efficient distributed dynamic channel allocation algorithm for mobile communications systems. The algorithm is based upon the mutual exclusion model, where the channels are grouped by the number of cells in a cluster and each group of channels cannot be shared concurrently within the cluster. We discuss the algorithm and prove its correctness. We also show that the algorithm requires at most (worst case) O(N/sub g/*N/sub n/logN/sub n/) messages, where N/sub g/ is the number of groups and N/sub n/ is the number of neighbors. This is compared to Choys (1995) algorithm which requires O(N/sub g//sup 2/*N/sub n/), where N/sub g/ is the number of groups. Our simulation experiments indicate that the DDRA algorithm outperforms previous schemes. A 5% reduction in the denial rate, and a 10-30% reduction in the acquisition time channel were obtained using our algorithm when compared to the previous algorithm.

A performance study of a distributed algorithm for dynamic channel allocation

Recent demand for mobile telephone service have been growing rapidly while the electro-magnetic spectrum of frequencies allocated for this purpose remain limited. Any solution to the channel assignment problem is subject to this limitation, as well as the interference constraints between adjacent channels in the spectrum. Channel allocation schemes provide a flexible and efficient access to bandwith in wireless and mobile communication systems. In this paper, we present an efficient distributed algorithm for dynamic channel allocation based upon multual exclusion model, where the channels are grouped by the number of cells in a cluster and each group of channels can not be shared concurrently within the cluster. We describe the algorithm, and report its performance several channel systems using different types of call arrival patterns. Our results indicate that significant low denial rate, low message complexity and low acquisition time can be obtained using our algorithm.

Synchronization and handoff management schemes for wireless multimedia systems

This paper presents handoff management schemes for synchronization algorithms for wireless multimedia systems. The synchronization and handoff management schemes allow mobile hosts to receive time-dependant multimedia streams without delivery interruption while moving from one cell to another. They also maintain the correct ordering of the media components, through the execution of the wireless multimedia application by a means of timestamped messages passed among mobile hosts, base stations and servers. The timestamp values are used to compute the delay for each multimedia unit for each server. Furthermore, the proposed schemes always search for a quasi-receiver among the base stations with which the mobile hosts can communicate to synchronize multimedia units. We discuss the algorithms and present a set of simulation experiments that evaluate the performance of our schemes, using message complexity and buffer usage at each frame arrival time. Our results indicate that our schemes exhibit no underflow or overflow within the bounded delivery time.

A two-phase handoff management scheme for synchronizing multimedia units over wireless networks

This paper presents a two-phase handoff management scheme for synchronization algorithms of wireless multimedia systems. This scheme allows mobile hosts to receive multimedia units without delivery interruption while they are moving from one cell to another cell. The messages passing among mobile hosts, base station and servers include a time stamp to compute delay time for each multimedia unit for each server. The scheme always search for a Quasi-receiver among base stations with which mobile hosts are communicating to synchronize multimedia units. We discuss the algorithms and also present a set of simulation experiments to evaluate the performance of our scheme using message complexity and buffer usage at each frame arrival time. Our results indicate that our scheme exhibits no underflow within the bounded delivery time.

A soft-handoff management scheme for wireless multimedia systems using quasi-receivers

We propose a routing scheme to support synchronization of multimedia units (MMU) for mobile clients and wireless multimedia systems that makes use of base stations as quasi-receivers to control the MMU synchronization. Our scheme allow mobile hosts to receive multimedia units without delivering interruption while mobile hosts are moving from one cell to another cell. The proposed solution not only enhance the performance of MoSync, a synchronization mechanism for wireless multimedia systems, which we have developed earlier but also cope with network-jitter, end-system jitter clock drift, and changing network conditions during soft-handoff. Thus, our scheme is suitable both for synchronizing inter- and intra-streams during playback video and also for resynchronize streams in a wireless network. We present our soft hand-of management scheme, and provide their proof and correctness.

A performance evaluation of a temporally correct and optimistic concurrency control protocol

In this paper we focus on the temporary return of data values that are incorrect for given transactional semantics and could have catastrophic effects similar to those in parallel and discrete event simulation. In many applications using on-line transaction processing (OLTP) environments, for instance, it is best to delay the response to a transactions read request until it is either known or unlikely that a write message from an older update transaction will not make the response incorrect. Examples of such applications are those where aberrant behavior is too costly, and those in which precommitted data are visible to some reactive entity. In light of the avoidance of risk in this approach, we propose a risk-free multiversion temporally correct (RFMVTC) concurrency control algorithm. We discuss the algorithm, its implementation and report on the performance results of simulation models using a cluster of workstations.

A synchronization scheme for distributed multimedia servers and mobile clients using quasi-sink

The recent advances in mobile computing and distributed multimedia systems allow mobile hosts (clients) to access wireless multimedia systems anywhere and at anytime, but not without creating a new set of issues and trade-offs. To the best of our knowledge, there are very little research done that deal with the synchronization problem in wireless and mobile multimedia systems. In this paper, we propose an efficient distributed synchronization algorithm for wireless and mobile multimedia systems to ensure and facilitate mobile clients accessing multimedia objects. We discuss the algorithm and provide its proof of correctness in a wireless environment.