Data Retrieval Scheduling For Unsynchronized Channel in Wireless Broadcast System

A. Vergin Janani Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.51-54
www.ijera.com 51 | P a g e
Data Retrieval Scheduling For Unsynchronized Channel in
Wireless Broadcast System
A. Vergin Janani1
, K. Vigneshkumar2
1
Department of Computer Science and Engineering, Anna University Chennai, India
2
Assistant Professor, Department of Computer Science and Engineering, Muthayammal Engineering College,
Rasipuram, India
Abstract-Wireless data broadcast is a disseminating data into large number of mobile clients. In many
information services, the users may query multiple data items at a time. The environment under consideration is
asymmetric in that the information server has much more bandwidth available, as compared to the clients. To
maximize the number of downloads given a deadline. It defines a problem called largest number data retrieval
(LNDR). To prove the decision problem of LNDR is a NP hard, and to investigate approximation algorithm for
it. It also define another problem called minimum cost data retrieval (MCDR), which aims at downloading a set
of requested data items with the least response time and energy consumption. Data scheduling problem over
unsynchronized channel at server side. In proposed system LNDR and MCDR in push based and pull based
broadcast system are used. The proposed approximation algorithms efficiently schedule the data retrieval
process of downloading multiple data from multiple channels. Push based and pull based broadcast model are
used in unsynchronized channel. When the time needed for channel switching can be ignored, a Maximum
Matching optimal algorithm is exhibited for LNDR which requires only polynomial time. The switching time
cannot be neglected, finally to provide simulation results to demonstrate the practical efficiency of the proposed
algorithms.
Index Terms- Push based broadcast, pull based broadcast, unsynchronized channel, wireless broadcast system
I. INTRODUCTION
Wireless data broadcast has been a popular data
dissemination method in the mobile computing
environment. In a typical wireless data broadcast
system, a base station will broadcast information over
one or multiple broadcast channels repeatedly.
Clients will listen to the channels, wait for the
requested data and download them when they arrive.
Wireless data broadcast is especially suitable for
public information, such as weather, traffic, and stock
quote, because of its scalability and flexibility. Two
major performance concerns for a wireless data
broadcast system are the response time and the
energy efficiency. Response time is the time interval
between the moments a client tunes in a broadcast
system with a request of one or more data items to
the moment all requested data are downloaded. It is
obvious that shorter response time is more desirable.
On the other hand, in wireless communication
environments, most clients are mobile devices
operating on batteries. The smaller the amount of
energy consumed during retrieving data is, the longer
the battery life of a mobile device will be. Therefore,
saving energy is another important issue for
designing wireless data broadcast system.
To facilitate energy conservation, a mobile
device typically supports two operation modes: active
mode and doze mode. The device normally operates
in the active mode; it can switch to the doze mode to
save energy when the system becomes idle. For
example, a typical wireless PC card, Orinoco,
consumes 60 mW during the doze mode and 805-
1,400 mW during the active mode. In the literature,
two performance metrics, namely, access latency and
tuning time, have been used to measure access
efficiency and energy conservation, respectively.
Wireless transmission is error-prone. Data might be
corrupted or lost due to many factors like signal
interference, etc. The client access algorithm for the
exponential index under unreliable broadcast is
described. We also provide a performance analysis of
the exponential index in terms of the access latency
and tuning time under unreliable wireless broadcast
environments. Extensive experiments are conducted
to compare the exponential index with two state-of-
the-art air indexing schemes, i.e., the distributed tree
and the flexible index under various link error
probabilities. Simulation results show that the
proposed exponential index substantially outperforms
the existing indexing schemes. In particular, it is
more resilient to link errors and achieves more
performance advantages from index caching. The
results demonstrate its great flexibility in trading
access latency with tuning time.
The focus of our research is to discuss how to
schedule the retrieving process of a set of requested
data, given their time offset and resided channels,
using a client with multiple antennae. Our target is to
RESEARCH ARTICLE OPEN ACCESS

minimize the access latency and number of channels
switching’s for the client. In other words, by the
employing protocols proposed in this paper, a client
should be able to download a set of requested data
using multiple retrieving processes in parallel, with
short response time and minimum energy
consumption. We name this problem as Parallel Data
Retrieval Scheduling with MIMO Antennae. In this
paper, we present the communication model,
formally define the PADRS-MIMO problem, and
construct two greedy heuristics named Least Switch
Data Retrieval Protocol and Best First Data Retrieval
Protocol.
II. LITERATURE SURVEY
Besides single-channel model, there are a lot of
researches for scheduling data items over multiple
channels. In designed a broadcast system that has
multiple channels and multi-level caches. In
developed a dynamic programming algorithm to
allocate data items over multiple channels, assuming
no data item is replicated among different channels.
In push-based broadcast, the broadcast schedule
is fixed, which may result in a long response time for
some frequent request. In view of this, pull-based
broadcast was investigated as an alternative. In
several heuristic algorithms, such as first come first
served most requests first and longest wait first were
proposed.
Although there have been many works done on
data scheduling at the server side, there have been
few works done on data retrieval scheduling from the
client’s point of view. Several heuristic algorithms
for downloading multiple data items from parallel
channels. But they did not provide any theoretical
analysis on either the data retrieval scheduling or
their proposed algorithms. They also assumed the
data set is partitioned over multiple channels without
replications, which further restricts the applications
of their works. As pointed out popular data items
should be broadcasted more frequently than
unpopular ones. No algorithm designed for pull-
based data scheduling at the server side over multiple
unsynchronized channels. Wireless data broadcast is
an efficient technique of disseminating data
simultaneously to a large number of mobile clients.
In many information services, the users may query
multiple data items at a time. In this paper, we study
the data retrieval scheduling problem from the
client’s point of view. We formally define the Largest
Number Data Retrieval (LNDR) problem with the
objective of downloading the largest number of
requested data items in a given time duration, and the
Minimum Cost Data Retrieval problem which aims at
downloading a set of data items with the minimum
energy consumption. When the time needed for
channel switching can be ignored.
A Maximum Matching optimal algorithm is
exhibited for LNDR which requires only polynomial
time; when the switching time cannot be neglected,
LNDR is proven to be NP−hard and a greedy
algorithm with constant approximation ratio is
developed. We also prove that the MCDR problem is
NP−hard to be approximated within to any nontrivial
factor and a parameterized heuristic is devised to
solve MCDR non-optimally. In recent years, fast
development of wireless communication technology
such as OFDM makes efficiently broadcasting data
through multiple channels possible. How to allocate
the data onto multiple channels to minimize the
expected response time has become a hot research
topic and lots of scheduling algorithms are proposed.
III. METHODOLOGY
3.1 EXISTING METHODOLOGY
The single-channel model is a lot of researches
scheduling data items over multiple channels. In
designed a broadcast system that has multiple
channels and multi-level caches. The dynamic
programming algorithm to allocate data items over
multiple channels, assuming number of data item is
replicated among different channels. Push-based
broadcast, the broadcast schedule is fixed, which may
result in a long response time for some frequent
request. Heuristic algorithms are used first come first
served; most requests first and longest wait
first.FCFS (First Come First Server) algorithm the
mobile client can only access a single channel at any
particular time. So a client cannot download data
from two or more channels. These methods allow the
data dissemination processes that come first in the
data queue.MRF (Most Request First) algorithm the
mobile client can access two or more channels at any
particular time. So a client cannot download data in
the arrival time. The data broadcast is done who
continuously send the request to the server.LWF
(Longest Wait First) is the data send to server and
process will be waiting stages, after that packet will
be send to server. Heuristic algorithms for
downloading multiple data items from parallel
channels. But they did not provide any theoretical
analysis on either the data retrieval scheduling or
their proposed algorithms. It also assumed the data
set is partitioned over multiple channels without
replications, which further restricts the applications
of their works
3.2 PROPOSED SYSTEM
3.2 PROPOSED METHOD
3.2.1 PUSH BASED BROADCAST
Push-based system is the server will
broadcast the set of data items to the clients
periodically according to a fixed schedule. The
channels have uniform bandwidth ba and the data
items have uniform size si. All channels are

partitioned into distributed time slots, each of size
si/ba. The time slot is the smallest unit to download
data. Clients will retrieve all the necessary indices
before downloading data, which is not related to the
data retrieval scheduling. To avoid downloading
incomplete data, two data items being broadcasted at
time t and t1 md0 via different channels cannot be
both downloaded during time. When all the channels
share a global time, say the channels are
synchronized.
Fig 3.2 Proposed Method
The client have three types of working models:
doze mode, active mode and channel switching
mode. The energy consumed per time slot in the
active mode is much higher than that in the doze
mode. The clients will change the modes whenever
possible to reduce the energy consumption. When
switching among different channels, the clients have
to change their radio frequencies and synchronize
their clocks. Therefore, the energy consumption is
also related to the number of channel switching’s.
3.2.2 PULL BASED BROADCAST
Pull-based system is the clients will send
requests to the server and the server will provide
timely broadcast according to the requests received.
The down-link channels the clients will send requests
to the server through an up-link channel, and the
server will decide the broadcast schedule based on
the requests received. In a pull-based system, clients
do not know the index information for a requested
data item until it has been scheduled at the server
side. The rest of model assumptions for pull-based
broadcast are the same to that for push-based
broadcast and hence omitted for saving space.
3.3 MODULES DESCRIPTION
1. LNDR in Push Based System
2. LNDR in Pull Based System
3. MCDR in Push Based System
4. MCDR in Pull Based System
3.3.1 LNDR IN PUSH BASED SYSTEM
LNDR push based system select all the
schedules variables are equal to 1 and arbitrarily
choose one data item if it appears in multiple
schedules, which forms a valid retrieval schedule for
the whole time duration. This kind of situations, it
can add weights to data items and the objective is to
download a subset of requested data items with
maximum weight. Besides weighted model, in some
applications, the data items may have non-uniform
sizes and channels may have non-uniform
bandwidths. That is, a data item may require multiple
time slots to download. LNDR push based system
using approximation algorithm. Approximation
algorithm is a set of broadcast schedule with
requested data item and time duration between t1 and
t2.
Broadcast channel can partition the whole time
duration into disjoint intervals such that the number
of valid schedules in each interval is bounded. For
each time interval to construct the set of all local
retrieval schedules and first time slot obligated for
possible channel switching. Approximation algorithm
to apply pipage rounding algorithm (PRA) and
choose retrieval schedules for time interval. Pipage
rounding algorithm to select schedules for those time
intervals.
3.3.2 LNDR IN PULL BASED SYSTEM
Pull-based broadcast is different from push-
based broadcast in that data items are scheduled at
the server side in real time. After submitting a
request, a client at any particular time t may only get
the broadcast schedule for the next one or several
time slots. Assuming a client can get the broadcast
schedule for the next r time slots, it show that a
greedy data retrieval strategy can provide a 1/1+ (2/r)
factor approximation solution. LNDR Pull-based
broadcast system using greedy algorithm. Greedy
algorithm is a set of broadcast channel, request data
and deadline to be calculated. Approximation ratio to
LNDR in pull-based broadcast, where a client only
knows the broadcast schedule for the next r time slot.
The idea of this approach is also appropriate for
LNDR in push-based broadcast. The current time (t)
is completed in the given deadline to be download
large number of data.
3.3.3 MCDR IN PUSH BASED SYSTEM
The broadcast system is push based, the data
items are uniform in size and the channels are
uniform in bandwidth. The heuristic proposed in this

section can only be applied when the broadcast
schedule is known (the system is push-based). While
in the pull-based broadcast, since it only know the
broadcast schedule for the next several time
slots.MCDR in push based system using heuristic
algorithm. Heuristic is a set of triples selected and t is
the earliest possible time that all the requested data
items can be downloaded. Each time heuristic
searches for a channel broadcasting a significant
number of data items during a short time interval
before deadline. Heuristic can be applied for
downloading non-uniform size data items from non-
uniform bandwidth channels.
3.3.4 MCDR IN PULL BASED SYSTEM
The objective of MCDR is to reduce the
response time and energy consumption. The index
information is assumed to be obtained before data
retrieving; it combines the benefits of both channel
scheduling to reduce the energy consumption in
channel switching and data item scheduling to reduce
the response time and the energy consumption in the
doze mode.MCDR in pull based system using greedy
heuristic algorithm. Greedy heuristic broadcast
schedule searching the channel during the time
interval and if channel exist to download data items
in the given deadline.
Greedy heuristic algorithm minimum time to retrieve
the large number of data items.
IV. CONCLUSIONS
The server sends the information to the clients
periodically and different users may be listening to
the different number of broadcast channels, present
an algorithm to coordinate broadcasts over different
channels. The data retrieval scheduling over multiple
channels. LNDR in push-based broadcast is the MM
can download the maximum number of data items
when the channels are synchronized. Two
optimization problems occurs in the MCDR and
LNDR, are defined and a series of theoretical results,
such as NP−hardness, approximate and in-
approximate. The simulation results show that the
proposed approximation algorithms efficiently
schedule the data retrieval process of downloading
multiple data from multiple channels. It also
demonstrates the data allocation scheduling at the
server side by simulations with various parameters.
The pull based and pull based data scheduling at the
server side over multiple unsynchronized channels.
Data scheduling problem over for unsynchronized
channels from the server’s point of view. Finally
provide simulation results to demonstrate the
practical efficiency of the proposed algorithm.
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Data Retrieval Scheduling For Unsynchronized Channel in Wireless Broadcast System

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