Continuous Monitoring of Spatial Queries in Wireless Broadcast Environments(2009)

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Abstract

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.

SYSTEM ANALYSIS

 Existing System:

The use of repetitive broadcast as a way of augmenting the memory hierarchy of clients in an asymmetric communication environment. We describe a new technique called “Broadcast Disks” for structuring the broadcast in a way that provides improved performance for non-uniformly accessed data. The Broadcast Disk superimposes multiple disks spinning at different speeds on a single broadcast channel—in effect creating an arbitrarily fine-grainedmemoryhierarchy. In addition to proposing and defining the mechanism, a main result of this work is that exploiting the potential of the broadcast structure requires a reevaluation of basic cache management policies. We examine several “pure” cache management policies and develop and measure implementable approximations to these policies.

Proposed System:

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.

Modules:

1.    Network Module

2.    Wireless Broadcasting

3.    Air Indexing

4.    Spatial Query Processing

5.    Continuous kNN Queries 

Module Description:

]1.    Network Module

        Client-server computing or networking is a distributed application architecture that partitions tasks or workloads between service providers (servers) and service requesters, called clients. Often clients and servers operate over a computer network on separate hardware. A server machine is a high-performance host that is running one or more server programs which share its resources with clients. A client also shares any of its resources; Clients therefore initiate communication sessions with servers which await (listen to) incoming requests.

2.    Wireless Broadcasting

      The transmission schedule in a wireless broadcast system consists of a series of broadcast cycles. Within each cycle the data are organized into a number of index and data buckets. A bucket (which has a constant size) corresponds to the smallest logical unit of information, similar to the page concept in conventional storage systems. A single bucket may be carried into multiple network packets (i.e., the basic unit of information that is transmitted over the air). However, they are typically assumed to be of the same size (i.e., one bucket equals one packet).

3.    Air Indexing

The main motivation behind air indexes is to minimize the power consumption at the mobile client. Although in a broadcast environment, the uplink transmissions are avoided, receiving all the downlink packets from the server is not energy efficient. For instance, the Cabletron 802.11 network card (wireless LAN) was found to consume 1,400 mW in the transmit, 1,000 mW in the receive, and 130 mW in the sleep mode. Therefore, it is imperative that the client switches to the sleep mode (i.e., turns off the receiver) whenever the transmitted packets do not contain any useful information.

4.    Spatial Query Processing

Spatial queries have been studied extensively in the past and numerous algorithms exist for processing snapshot queries on static data indexed by a spatial access method. Subsequent methods focused on moving queries (clients) and/or objects. The main idea is to return some additional information (e.g., more NNs, expiry time, and validity region) that determines the lifespan of the result. Thus, a moving client needs to issue another query only after the current result expires. These methods focus on single query processing, make certain   assumptions about object movement (e.g., static in, linear in), and do not include mechanisms for maintenance of the query results (i.e., when the result expires, a new query must be issued).

The possibility of broadcasting spatial data together with a data partitioning index. They present several techniques for spatial query processing that adjust to the limited memory of the mobile device. The authors evaluate their methods experimentally for range queries (using the R-tree as the underlying index) and illustrate the feasibility of this architecture.

5.    Continuous kNN Queries 

Consider, for instance, a user (mobile client) in an unfamiliar city, who would like to know the 10 closest restaurants. This is an instance of a k nearest neighbor (kNN) query, where the query point is the current location of the client and the set of data objects contains the city restaurants. Alternatively, the user may ask for all restaurants located within a certain distance, i.e., within 200 meters. This is an instance of a range query.

Hardware Requirements:

•         System                : Pentium IV 2.4 GHz.

•         Hard Disk           : 40 GB.

•         Floppy Drive      : 1.44 Mb.

•         Monitor               : 15 VGA Colour.

•         Mouse                 : Logitech.

•         Ram                     : 256 Mb.

Software Requirements:

•         Operating system         : - Windows XP Professional.

•         Coding Language         : - Java.

•         Tool Used                     : - Eclipse.

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