Wireless Broadcast Environments Research Articles

Location-Based Data Dissemination for Spatial Queries in Wireless Broadcast Environments

Most current research on Location-Based Services (LBSs, for short) assumes point-to-point wireless communication, where the server processes a query and returns the query result to the user via a point-to-point wireless channel. However, LBSs via point-to-point wireless channel suffer from a tremendous amount of traffic and service requests from the user and thereby result in poor performance. In this paper, we present broadcast-based spatial query processing algorithms designed to support k-NN (k-Nearest Neighbor) and range queries via a wireless network. The task of the query processor is to selectively monitor the wireless broadcast channel, when the data items are disseminated by the server, according to their locations. Experiments are conducted to evaluate the performance of the proposed algorithms. Comprehensive experiments illustrate that the presented algorithms are highly scalable and are more efficient than the previous techniques in terms of both access time and energy consumption.

Energy and Latency Efficient Access of Wireless XML Stream

In this article, we address the problem of delayed query processing raised by tree-based index structures in wireless broadcast environments, which increases the access time of mobile clients. We propose a novel distributed index structure and a clustering strategy for streaming XML data that enables energy and latencyefficient broadcasting of XML data. We first define the DIX node structure to implement a fully distributed index structure which contains the tag name, attributes, and text content of an element, as well as its corresponding indices. By exploiting the index information in the DIX node stream, a mobile client can access the stream with shorter latency. We also suggest a method of clustering DIX nodes in the stream, which can further enhance the performance of query processing in the mobile clients. Through extensive experiments, we demonstrate that our approach is effective for wireless broadcasting of XML data and outperforms the previous methods.

Continuous Monitoring of Spatial Queries in Wireless Broadcast Environments

Wireless data broadcast is a promising technique for information dissemination that leverages the computational capabilities of the mobile devices in order to enhance the scalability of the system. Under this environment, the data are continuously broadcast by the server, interleaved with some indexing information for query processing. Clients may then tune in the broadcast channel and process their queries locally without contacting the server. Previous work on spatial query processing for wireless broadcast systems has only considered snapshot queries over static data. In this paper, we propose an air indexing framework that 1) outperforms the existing (i.e., snapshot) techniques in terms of energy consumption while achieving low access latency and 2) constitutes the first method supporting efficient processing of continuous spatial queries over moving objects.

An energy-efficient mobile transaction processing method using random back-off in wireless broadcast environments

Broadcast is widely accepted as an efficient technique for disseminating data to a large number of mobile clients over a single or multiple channels. Due to the limited uplink bandwidth from mobile clients to server, conventional concurrency control methods cannot be directly applied. There has been many researches on concurrency control methods for wireless broadcast environments. However, they are mostly for read-only transactions or do not consider exploiting cache. They also suffer from the repetitive aborts and restarts of mobile transactions when the access patterns of mobile transactions are skewed. In this paper, we propose a new optimistic concurrency control method suitable for mobile broadcast environments. To prevent the repetitive aborts and restarts of mobile transactions, we propose a random back-off technique. To exploit the cache on mobile clients, our method keeps the read data set of mobile transactions and prefetches those data items when the mobile transactions are restarted. As other existing optimistic concurrency control methods for mobile broadcast environments does, it works for both read-only and update transactions. Read-only transactions are validated and locally committed without using any uplink bandwidth. Update transactions are validated with forward and backward validation, and committed after final validation consuming a small amount of uplink bandwidth. Our performance analysis shows that it significantly decreases uplink and downlink bandwidth usage compared to other existing methods.

A scalable energy-efficient continuous nearest neighbor search in wireless broadcast systems

When the mobile environment consists of light-weight devices, the energy consumption of location-based services (LBSs) and the limited bandwidth of the wireless network become important issues. Motivated by this, we propose new spatial query processing algorithms to support Mobile Continuous Nearest Neighbor Query (MCNNQ) in wireless broadcast environments. Our solution provides a general client---server architecture for answering MCNNQ on objects with unknown, and possibly variable, movement types. Our solution enables the application of spatio-temporal access methods specifically designed for a particular type, to arbitrary movements without any false misses. Our algorithm does not require any conventional spatial index for MCNNQ processing. It can be adapted to static or moving objects, and does not require additional knowledge (e.g., direction of moving objects) beyond the maximum speed and the location of each object. Extensive experiments demonstrate that our location-based data dissemination algorithm significantly outperforms index-based solutions.

A concurrency control scheme for mobile transactions in broadcast disk environments

Broadcast disk technique has been often used to disseminate frequently requested data efficiently to a large volume of mobile clients over wireless channels. In broadcast disk environments, a server often broadcasts different data items with differing frequencies to reflect the skewed data access patterns of mobile clients. Previously proposed concurrency control methods for mobile transactions in wireless broadcast environments are focused on the mobile transactions with uniform data access patterns. These protocols perform poorly in broadcast disk environments where the data access patterns of mobile transactions are skewed. In broadcast disk environments, the time length of a broadcast cycle usually becomes large to reflect the skewed data access patterns. This will often cause read-only transactions to access old data items rather than the latest data items. Furthermore, updating mobile transactions will be frequently aborted and restarted in the final validation stage due to the update conflict of the same data items with high access frequencies. This problem will increase the average response time of the update mobile transactions and waste the uplink communication bandwidth. In this paper, we extend the existing FBOCC concurrency control method to efficiently handle mobile transactions with skewed data access patterns in broadcast disk environments. Our method allows read-only transactions to access the more updated data, and reduces the average response time of updating transactions through early aborts and restarts. Our method also reduces the amount of uplink communication bandwidth for the final validation of the update transactions. We present an in-depth experimental analysis of our method by comparing with existing concurrency control protocols. Our performance analysis shows that it significantly decreases the average response time and the amount of uplink bandwidths over existing methods.

Location-Based Spatial Query Processing with Data Sharing in Wireless Broadcast Environments

Location-based spatial queries (LBSQs) refer to spatial queries whose answers rely on the location of the inquirer. Efficient processing of LBSQs is of critical importance with the ever-increasing deployment and use of mobile technologies. We show that LBSQs have certain unique characteristics that traditional spatial query processing in centralized databases does not address. For example, a significant challenge is presented by wireless broadcasting environments, which have excellent scalability but often exhibit high-latency database access. In this paper, we present a novel query processing technique that, while maintaining high scalability and accuracy, manages to reduce the latency considerably in answering location-based spatial queries. Our approach is based on peer-topeer sharing, which enables us to process queries without delay at a mobile host by using query results cached in its neighboring mobile peers. We demonstrate the feasibility of our approach through a probabilistic analysis, and we illustrate the appeal of our technique through extensive simulation results.

An efficient nonuniform index in the wireless broadcast environments

Data broadcast is an efficient dissemination method to deliver information to mobile clients through the wireless channel. It allows a huge number of the mobile clients simultaneously access data in the wireless environments. In real-life applications, more popular data may be frequently accessed by clients than less popular ones. Under such scenarios, Acharya et al.’s Broadcast Disks algorithm ( BD) allocates more popular data appeared more times in a broadcast period than less popular ones, i.e., the nonuniform broadcast, and provides a good performance on reducing client waiting time. However, mobile devices should constantly tune in to the wireless broadcast channel to examine data, consuming a lot of energy. Using index technologies on the broadcast file can reduce a lot of energy consumption of the mobile devices without significantly increasing client waiting time. In this paper, we propose an efficient nonuniform index called the skewed index, SI, over BD. The proposed algorithm builds an index tree according to skewed access patterns of clients, and allocates index nodes for the popular data more times than those for the less popular ones in a broadcast cycle. From our experimental study, we have shown that our proposed algorithm outperforms the flexible index and the flexible distributed index.

Effective protocols for kNN search on broadcast multi-dimensional index trees

In a wireless mobile environment, data broadcasting provides an efficient way to disseminate data. Via data broadcasting, a server can provide location-based services to a large client population in a wireless environment. Among different location-based services, the k nearest neighbors ( kNN) search is important and is used to find the k closest objects to a given point. However, the kNN search in a broadcast environment is particularly challenging due to the sequential access to the data on a broadcast channel. We propose efficient protocols for the kNN search on a broadcast R-tree, which is a popular multi-dimensional index tree, in a wireless broadcast environment in terms of latency and tuning time as well as memory usage. We investigate how a server schedules the broadcast and provide the corresponding kNN search algorithms at the mobile clients. One of our kNN search protocols further allows a kNN search to start at an arbitrary time instance and it can skip the waiting time for the beginning of a broadcast cycle, thereby reducing the latency. The experimental results validate that our mechanisms achieve the objectives.

Better mobile client’s cache reusability and data access time in a wireless broadcast environment

Data broadcasting is an efficient data dissemination method in a wireless client–server system. A data server broadcasts data items periodically, and mobile clients cache data items to save communication bandwidth, resource usage, and data access time. The server also broadcasts invalidation reports (IRs) to maintain the consistency between server data and the clients’ cached data. Most existing cache invalidation policies in a wireless environment based on IRs simply purge the entire cache after a client has been disconnected long enough to miss a certain number (window size) of IRs. We present a cache invalidation scheme that provides better cache reusability and better data access time after a long disconnection. Our scheme attempts to increase cache reusability by respecting update rates at a server, broadcast intervals, the communication bandwidth, and data sizes, as well as disconnection time. Simulation results show that the increased cache reusability of our scheme can improve the data access time after a long disconnection.

Disseminating dependent data in wireless broadcast environments

In wireless mobile environments, data broadcasting is an effective approach to disseminate information to mobile clients. In some applications, the access pattern of all the data can be represented by a weighted DAG. In this paper, we explore how to efficiently generate the broadcast schedule in a wireless environment for the data set having a weighted DAG access pattern. Such a broadcast schedule not only minimizes the access latency but also is a topological ordering of the DAG. Minimized access latency ensures the quality of service (QoS). We prove that it is NP-hard to find an optimal broadcast schedule and provide some heuristics. After giving an analysis for these heuristics on the latency and complexity, we implement all the proposed heuristics to compare their performance.

Cooperation Strategy for Broadcast Scheduling and Base Station Caching in Hybrid Wireless Broadcast Environment

Cooperation Strategy for Broadcast Scheduling and Base Station Caching in Hybrid Wireless Broadcast Environment

Cooperation Strategy for Broadcast Scheduling and Base Station Caching in Hybrid Wireless Broadcast Environment

Recent advances in computer and wireless communication technologies have increased interest in combinations of various techniques such as pull-based data dissemination, data broadcasting, and data caching, as well as investigations into data management in hybrid data delivery systems. This paper proposes cooperative data management based on the Hybrid Wireless Broadcast (HWB) model to provide more efficient data delivery to mobile clients. Our cooperative strategy integrates broadcast scheduling with cache management of the base station, taking heterogeneous and homogeneous access of clients into consideration, by making effective use of HWB data dissemination, i.e., push-based broadcast, pull-based broadcast, and pull-based point-to-point wireless communication. Our simulation results confirmed that the strategy we propose can improve the performance of the system even further.

An Index Allocation Method for Data Access over Multiple Wireless Broadcast Channels

With the advent of mobile technology, broadcasting data over one or more wireless channels has been considered an excellent way to efficiently disseminate data to a large number of mobile users. In such a wireless broadcast environment, the minimization of both access and tuning times is an important problem because mobile devices usually have limited battery power. In this paper, we propose an index allocation method for data access over multiple channels. Our method first derives external index information from the scheduled data, and then allocates it over the channels, which have shorter broadcast cycles and hotter data items. Moreover, local exponential indexes with different parameters are built within each channel for local data search. Experiments are performed to compare the effectiveness of our approach with an existing approach. The results show that our method outperforms the existing method by 30% in average access time and by 16% in average tuning time when the data skew is high and data item size is much bigger than index node size.

EFFICIENT BROADCAST INDEXING SCHEME FOR LOCATION-DEPENDENT QUERIES IN MULTI CHANNELS WIRELESS ENVIRONMENT

Data dissemination scheme has been of great interest due to its scalability. In mobile environment, the advantage of such scheme is significant considering the inherent limitations of wireless environment. The application of broadcast indexing scheme in a wireless broadcast environment is necessary to help mobile clients to find the desired data instances efficiently. In this paper, we present a novel index structure called global indexing scheme for location-dependent queries. The proposed scheme is applied in a multi channel wireless environment and designed to serve queries efficiently in which the queries result depend on the mobile clients' current location. We develop a simulation model to find out the access time, tuning time and power consumption performance of global indexing scheme as compared to non-global indexing scheme. Additionally, we analyse the efficiency of valid scope used in the global index scheme as compared with an existing valid scope. It is found that global index performs substantially better than the existing indexing concept.