A skewed distributed indexing for skewed access patterns on the wireless broadcast

Mobile technology is currently growing rapidly and mobile information services have also becoming more critical in the world of mobile technology. It allows mobile users to download useful data, possibly from multiple sources. In this paper, we propose several techniques in processing information downloaded from multiple non-collaborative servers onto a mobile device. The proposed techniques are divided into two main classifications: (i) mobile device side processing, and (ii) server side processing. We also introduce the extended versions utilizing a block-based processing that helps reducing transfer costs and adapts to the memory limitation of mobile devices. Each of these proposed techniques comes in various versions. Walkthrough examples are also illustrated. Implementation and performance evaluation of these various techniques are investigated and critically analyzed.

On-Mobile Query Processing Incorporating Multiple Non-Collaborative Servers

Acharya et al.'s broadcast disks (BD) are periodic dissemination architecture in the context of mobile systems. However, BD has the empty slot problem, resulting in the waste of bandwidth and the increase of access time. Therefore, in this paper, we propose an efficient broadcast program, the binary-number-based (BNB) approach, in which no empty slot is wasted with a restriction on the broadcast frequency. Next, we propose a generalized BNB (GBNB) approach in which no empty slot is wasted and the frequency of each disk is decided by the given access probabilities of pages on the disk. From our experimental results, we show that both our BNB and GBNB have shorter mean access time than BD.

A binary-number-based approach to data broadcasting in wireless information systems

Data delivery is through broadcast in wireless information systems due to the asymmetric communication property. However, broadcasting data easily wastes large access time because the large amount of data pages needs to be broadcast. In this paper we propose three compression-based strategies considering access order to reduce access time. Then, the expected access time of three proposed strategies is also derived by using the probability model. Our analytic and experimental results show that the compression-based broadcast strategies can dramatically reduce the access time for mobile users (MU).

Compression-based broadcast strategies in wireless information systems

The data-broadcast problem consists in finding an infinite schedule to broadcast a given set of messages so as to minimize the average response time to clients requesting messages, and the cost of the broadcast. This is an efficient means of disseminating data to clients, designed for environments, such as satellites, cable TV, mobile phones, where there is a much larger capacity from the information source to the clients than in the reverse direction. Previous work concentrated on scheduling indivisible messages. Here, we studied a generalization of the model where the messages can be preempted. We show that this problem is NP-hard, even in the simple setting where the broadcast costs are zero, and give some practical 2-approximation algorithms for broadcasting messages. We also show that preemption can improve the quality of the broadcast by an arbitrary factor.

The data broadcast problem with preemption

In this paper, we investigate the broadcasting scheduling over multiple channels for the case where a mobile client might need more than one page (i.e., a query set of data pages). Ke has proposed the SNV (Set-based version-Non-overlap Version) strategy for query set broadcast scheduling in multiple channels. In the SNV strategy, the data pages of the same query set are put together as much as possible, and the strategy tries to avoid scheduling two or more pages of one query set at the same time slot of different channels. However, there are two disadvantages with the SNV strategy: (1) a data page with high access frequency may be scheduled at a time slot near the end of the broadcast cycle, which will result in long access time for the whole query set; (2) it may increase the number of slots in a certain chain, which will result in a waste of bandwidth of the other channels. Therefore, in this paper, we propose an efficient broadcast scheduling strategy, a hybrid approach, to improve these two disadvantages. Basically, our hybrid approach combines the advantages of page-based and set-based strategies. Through our performance analysis and simulation, we show that our hybrid approach requires less total expected delay access time and creates a smaller number of slots and a smaller number of empty slots in one broadcast cycle compared to the SNV strategy.

Shih-Ying Chiu

Papers

A Hybrid Approach to Query Sets Broadcasting Scheduling for Multiple Channels in Mobile Information Systems