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K. Swathi et al Int. Journal of Engineering Research and Applications
ISSN : 2248-9622, Vol. 3, Issue 6, Nov-Dec 2013, pp.942-946

RESEARCH ARTICLE

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Novel Approach for Dynamic Data Collection in Tree Based
Wireless Sensor Networks
K. Swathi1, Sk. Abdul Ali2
1.
2.

M.Tech Scholar, Nimra Institute Of Engineering & Technlogy
Associate Professor, Nimra Institute Of Engineering & Technlogy

ABSTRACT
In the wireless sensor networks the energy of the nodes present in the network is limited. Due to the low
manufacturing costs of sensor nodes, they can be organized in large numbers and containing more challenges in
routing, topology and data management protocols. These challenges are complicated by severe energy
constraints and the inherently unreliable nature of wireless communications which have yielded work in
increasing network efficiency. Our main objective is to increase the tolerance level and decrease the complexity
of the wireless sensor network. In this primarily visualize time scheduling on a single frequency channel with
the aim of reducing the number of time slots necessary to entire a convergecast. After we mingle scheduling
with communication power control to moderate the effects of interference, and demonstrate that while power
control helps in reducing the schedule length under a on its own frequency, forecast transmissions using several
frequencies is more capable. We present lower bounds on the schedule length when interference is completely
removed, and recommend algorithms that achieve these bounds. We also estimate the performance of different
channel assignment methods, the use of multi-frequency scheduling can sufficient to eliminate most of the
interference. After that the data collection rate increases by reducing the interference by the topology of the
routing tree.
Index Terms: Convergecast, Data Collection, Degree constrained spanning tree, Hybrid convergecast tree,
Minimal Spanning Tree Time Division Multiple Access Scheduling

I.

INTRODUCTION

Wireless sensor networks consist of
distributed self-governing sensor nodes which are
used in various applications areas such as health,
home, military. Each node receives data from
surroundings and it will forward the data to its base
station. The location of each sensor node is not
predetermined and each sensor nodes contains its
own self organizing capabilities. The unique feature
of sensor nodes is the cooperative effort of sensor
nodes. As an unconventional of sending the raw data
to the nodes responsible for the synthesis, sensor
nodes make use of their processing capabilities to
locally carry out simple computations and it will
transmit only the required and partially processed
data. Sensor nodes are used for continuous sensing,
detecting events, event ID, and sensing the location.
The sensor nodes are scattered in the sensor
network. Each scattered sensor nodes has the ability
to collect and route data to the sink.

Fig.1: Self forming Wireless Sensor Networks
Convergecast is the collection of data from
a set of sensors toward a general sink over a tree
based routing topology, is a primary operation in
wireless sensor networks. In many applications, it is
critical to offer a guarantee on the delivery time as
well as increase the rate of such data collection. For
example, in security and mission-critical
applications where sensor nodes are organized to

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detect oil/gas leak or structural damage, the
actuators and controllers need to take delivery of
data from all the sensors within an exact deadline,
failure of which might lead to unpredictable and
catastrophic events. The other applications such as
permafrost monitoring require periodic and fast data
delivery over long periods of time, which falls
beneath the grouping of permanent data collection.
For periodic traffic, it is well known that contention
free medium access control (MAC) protocols such
as Time Division Multiple Access are better fit for
fast data collection, since they can reduce collisions
and retransmissions and provide guarantee on the
completion time as divergent to contention-based
protocols. The problem of building conflict free
Time Division Multiple Access schedules even
under the simple graph-based interference model
has been proved to be NP-complete. In this work,
we consider a DMA framework and design
polynomial-time heuristics to minimize the schedule
length for both types of convergecast. We
furthermore find lower bounds on the achievable
schedule lengths and compare the performance of
our heuristics with these bounds.
In Time Division Multiple Access
schedule, time slotted and each slot is long enough
to transmit and receive of a single packet. Hence the
time slots are grouped as a non – overlapping frames
and the schedule for each frame is repeated when
the data collection is periodic. The main objective of
Time Division Multiple Access design is to
minimize schedule length, minimize Latency,
minimizing energy consumption, maximizing
capacity,
maximizing
fairness,
minimizing
communication costs, maximizing the parallel
transmission, meeting deadlines, and minimizing
interference. A Wireless sensor networks has small
or no infrastructure. It contains of a number of
sensor nodes which works together to monitor a
region and it is used to obtain data about the
environment. The Wireless sensor networks are
classified into two types such as structured and
unstructured. An unstructured WSN contains the
dense collection of sensor nodes. The Sensor nodes
are deployed in an ad hoc manner into the field.
Once deployed, the network is kept unattended to
perform monitoring and reporting functions. Hence
network maintenance and failure detection is
difficult since there are so many nodes. In structured
network, all or some of the nodes are deployed in a
pre planned manner. Due to small number of nodes
network maintenance is easy and management cost
is reduced.

II.

RELATED WORK

Collecting data is the basic operation in
wireless sensor networks. Collecting those data in a
well-organized manner is more critical when
compared to the performance of sensor networks.
Each sensor will measure the values at regular time
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intervals and it will send that to sink node. The total
collection of data is called as snapshot. Here the
sensor network is a Time Division Multiple Access
based network. In the past, the data collection
capacity is based on large scale random networks,
though most of the sensors are not deployed
uniformly and the available sensors will not be as
huge as in theory. For this purpose we have to know
about the capacity of data collection in a network.
The capacity of data collection shows how the sink
collects data from sensor nodes quickly by
considering its interference conditions. The upper
and lower bounds for data collection capacity are
constructed based on the protocol interference and
disk graph models. A simple BFS tree based method
is used to achieve the collection capacity which
matches the upper bound.
In sensor networks the packets generated
by each and every node have to reach the sink. This
many – to –one communication is known as
convergecast. A Time Division Multiple Access
schedule is used which minimizes the total time
required to complete the convergecast. A simple
version of problem is considered where every node
generates exactly one packet. Yiin Zhang
constructed a distributed scheduling algorithm for
the tree networks that requires at most max(3nk –
1,N) time slots for convergecast, where nk
corresponds to the maximum number of nodes in
any sub tree and N represents the number of nodes
in network. The Distributed scheduling algorithm
requires at most 3N time slots in any network. The
proposed simulation shows that the number of time
slots required is about 1.5 N. Two bounds are
required for the packets to be buffered at the node
during convergecast. Sleep schedules for nodes are
considered for conserve energy. It reduces the
energy consumption by at least 50% Breadth first
search tree is considered for convergecast
scheduling. The problem of minimizing the schedule
length for raw-data convergecast on single channel
is shown to be NP-complete on general graphs.
Maximizing the throughput of convergecast by
finding a shortest-length, conflict-free schedule is
studied, where a greedy graph coloring strategy
assigns time slots to the senders and prevents
interference and also discussed the impact of routing
trees on the schedule length and proposed a routing
scheme called disjoint strips to transmit data over
different shortest paths. Though the sink remains as
the restricted access, sending data over different
paths does not reduce the schedule length. The
improvement due to the routing structure comes
from using capacitated minimal spanning trees for
raw-data convergecast, where the number of nodes
in a sub tree is no additional than half the total
number of nodes in the remaining sub trees.

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III.

TDMA SCHEDULING OF
CONVERGECASTS

3.1 Periodic Aggregated Convergecast
In this consider the scheduling problem
where packets are aggregated. Data aggregation is a
frequently used technique in Wireless Sensor
Networks that can eliminate redundancy and
minimize the number of transmissions, thus
reduction energy and humanizing network lifetime.
Aggregation can be achieved in a lot of ways, such
as by restraining carbon copy messages; using data
compression and packet merging techniques; or
taking advantage of the correlation in the sensor
readings. We reflect on continuous monitoring
applications where perfect aggregation is possible
and each node is capable of aggregating all the
packets received from its children in addition to that
produced by itself into a single packet before
transmitting to its parent. The amount of aggregated
data transmitted by each node is constant and does
not depend on the size of the raw sensor readings.
Usual examples of such aggregation functions are
MIN, MEDIAN, MAX, AVERAGE, COUNT, etc.

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that at the last part of frame 1, the sink does not
contain packets from nodes 5 and 6; however, as the
schedule is repeated, it accepts aggregated packets
from 2, 5, and 6 in slot 2 of the next frame. In the
same way, the sink also receives aggregated packets
from nodes 1 and 4 opening from slot 1 of frame 2.
The entries {1, 4} and {2, 5, 6} in the table represent
single packets including aggregated data from nodes
1 and 4, and from nodes 2, 5, and 6,
correspondingly. Thus, a pipeline is recognized
from frame 2, and the sink goes on to receive
aggregated packets from all the nodes once every 6
time slots. Thus, the minimum schedule length is 6.
3.2. Assignment of Timeslots
In every iteration of BFS-TIMESLOT
ASSIGNMENT (lines 2-6), an edge e is chosen in
the Breadth First Search (BFS) order starting from
any node, in addition to is allocated the minimum
time slot that is different from all its adjacent edges
respecting intrusive restrictions. Note that, since we
calculate the performance of this algorithm also for
the case when the interfering links are present, we
make sure for the corresponding constraint in line 4;
on the other hand, when interference is removed this
check is redundant. The algorithm runs in O(|ET |2)
time and minimizes the schedule length when there
are no intrusive links and demonstrate the same
network of 1(a) in 1(c) with all the interfering links
removed, and so the network is scheduled in 3 time
slots.

Fig.2: Aggregated convergecast and pipelining:
(a) Schedule length of 6 in the presence of
interfering links.
(b) Node ids from which (aggregated) packets are
received by their corresponding parents in each
time slot over different frames.
(c) Schedule
length
of
3
using
BFSTIMESLOTASSIGNMENT when all the
interfering links are eliminated.
In above Fig. 1(a) and 1(b), illustrates the
notion of pipelining in aggregated convergecast and
that of a schedule length on a network of 6 source
nodes. The hard lines correspond to tree edges, and
the scattered lines represent interfere links. The
numbers nearby the links correspond to the time
slots at which the links are programmed to
broadcast, and the numbers within the circles
represent node ids. The accesses in the table list the
nodes from which packets are received by their
corresponding receivers in each time slot. We note
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IV.

MULTI-CHANNEL SCHEDULING

Multi-channel communication is an
efficient method to eliminate interference by
enabling concurrent transmissions over different
frequencies. Although typical Wireless Sensor
Networks radios operate on a limited bandwidth,
their working frequencies can be in the swing of
things, thus allowing
more
simultaneous
transmissions and faster data delivery. At this time,
we think about fixed-bandwidth channels, which are
typical of Wireless Sensor Networks radios, as
opposed to the possibility of improving link
bandwidth by consolidating frequencies. We explain
three channel assignment methods that consider the
problem at different levels allowing us to study their
pros and cons for both types of convergecast. These
methods regard as the channel assignment problem
at different levels: the link level (JFTSS), node level
(RBCA), or cluster level (TMCP).
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4.1 Joint Frequency Time Slot Scheduling
(JFTSS)
Joint Frequency Time Slot Scheduling
presents a greedy combined solution for
constructing a maximal schedule, such that a
schedule is called to be maximal if it meets the
adjacency and inquisitive constraints, and no more
links can be scheduled for synchronized
transmissions on any time slot and channel
exclusive of breaching the constraints. Joint
Frequency Time Slot Scheduling schedules a
network starting from the link that has the highest
number of packets (load) to be transmitted. While
the connection loads are equal, while in aggregated
convergecast, the most inhibited ink is measured
first, i.e., the link for which the number of other
links breaching the interfering and adjacency
restriction when scheduled at the same time is the
highest. The algorithm starts with an empty
schedule and first sorts the links according to the
loads or constraints. The mainly loaded or unnatural
link in the first accessible slot-channel pair is
scheduled first and added to the schedule. All the
links that have an adjacency restriction with the
programmed link are expelled from the list of the
links to be scheduled at a given slot. The links with
the purpose of do not have an interfering restriction
with the scheduled link can be programmed in the
same slot and channel while the links that have an
inquisitive constraint should be scheduled on
dissimilar channels, if achievable. The algorithm
continues to schedule the links according to the
most loaded (or most constrained) metric.

nodes with the BFSTimeSlot Assignment algorithm.
The advantage of TMCP is that it is designed to
support convergecast traffic and does not require
channel switching. Though, disputation inside the
branches is not determined since all the nodes on the
same branch communicate on the same channel.
4.3. Receiver-Based Channel Assignment (RBCA)
In Receiver-Based Channel Assignment,
the children of a common parent transmit on the
same channel. Each node in the tree, consequently,
operates on at most two channels, therefore avoiding
pair-wise, per-packet, channel negotiation expenses.
The algorithm initially assigns the same channel to
all the receivers. Then, for each receiver, it creates a
set of interfering parents based on SINR thresholds
and iteratively assigns the next available channel
starting from the most interfered parent (the parent
with the highest number of interfering links).
However, due to adjacent channel overlaps, SINR
values at the receivers may not always be high
enough to tolerate interference, in which case the
channels are assigned according to the ability of the
transceivers to reject interference. We proved
approximation factors for Receiver-Based Channel
Assignment when used with greedy scheduling in.
Initially all nodes are on frequency F1. ReceiverBased Channel Assignment starts with the most
interfered parent, node 2 in this example, and
assigns F2. Then it continues to assign F3 to node 3
as the second most interfered parent. Since all
interfering parents are assigned different frequencies
sink can receive on F1.

V.

Fig.3: Scheduling with multi-channels for
aggregated convergecast:
(a) Schedule generated with JFTSS. (b) Schedule
generated with TMCP. (c) Schedule generated with
RBCA. (b) Schedule generated with RBCA.
4.2 Tree-Based Multi-Channel Protocol (TMCP)
Tree-Based Multi-Channel Protocol is a
greedy, tree-based, multi-channel protocol for data
collection applications. It separation the network
into several sub trees and minimizes the intra tree
interference by assigning dissimilar channels to the
nodes residing on unlike branches starting from the
top to the bottom of the tree. The nodes on the
leftmost branch is allocated frequency F1,
subsequent branch is allocated frequency F2 and the
last branch is allocated frequency F3 and after the
channel assignments, time slots are allocated to the
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EVALUATION

We deploy nodes randomly in a region
whose dimensions are varied between 20 × 20 m2
and 300 × 300 m2 to simulate different levels of
density. The number of nodes is kept fixed at 100.
For different parameters, we average each point
over 1000 runs. We use an exponential path-loss
model for signal propagation with the path-loss
exponent α varying between 3 and 4, which is
typical for indoor environments. We also use the
physical interference model and simulate the
behavior of CC2420 radios that are used on Telosb
and TmoteSky motes and are capable of operating
on 16 different frequencies. The transmission power
can be adjusted between −24 dBm and 0 dBm over
8 different levels, and the SINR threshold is set to β
= −3 dB1. We first evaluate the schedule length for
single-channel TDMA, and then its improvement
using transmission power control, multiple channels,
and routing trees.
5.1. Aggregated Convergecast
It shows the variation of schedule length
with density for different values of α on minimumhop tree. We observe that the schedule length
decreases as the deployment gets sparser. This
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happens because at low densities the interference is
less, and so more concurrent transmissions can take
place. In the densest deployment (L = 20) when all
the nodes are within the range of each other, the sink
is the only parent, and the network is scheduled in
99 time slots regardless of power control. However,
in sparser scenarios, using power control the
network can be scheduled with fewer time slots as
the level of interference goes down. We achieve a
10 − 20% reduction in schedule length for the best
case.

Fig.4: Scheduling on minimum-hop trees with
multiple channels: (a) Aggregated convergecast.
(b) Raw-data convergecast.
5.2. Raw Data Convergecast
It shows the variation of schedule length on
CMST. The impact of such routing trees is more
prominent in sparser networks (L ≥ 200) than
routing over minimum-hop spanning trees. When L
< 200, the length is bounded by N. Beyond this
point, it is almost always not possible to construct
trees where the constraint 2nk−1 < N holds. In such
cases, the schedule length is some degree of by 2nk
− 1.

VI.

CONCLUSION

Wireless sensor networks can be used in
various applications areas. A sensor networks
consists of large number of nodes and the location
of each sensor nodes is predetermined. By using
TDMA, the nodes communicate on different time
slots in order to prevent conflicts. In order to
improve the data collection the capacity at each
node is adjusted whenever the packet moves from
one sensor node to another sensor node. . A hybrid
convergecast tree is projected for transmitting the
packets with minimum cost for long suited nodes.
Fast convergecast in Wireless Sensor Networks
where nodes communicate using a TDMA protocol
minimize the schedule length. We deal with the
fundamental limitations due to interference and halfduplex transceivers on the nodes and explored
techniques to overcome the same. We set up that
while transmission power control helps in reducing
the schedule length, multiple channels are more
effective and also observed that node-based (RBCA)
and link-based (JFTSS) channel assignment
schemes are more efficient in terms of eliminating
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interference as compared to assigning different
channels on different branches of the tree (TMCP).

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