WIreless Sensor Network

1. TDMA Scheduling Algorithm for Wireless Sensor
Networks
Neha Agarwal
Reg No.– 2011CS03
Motilal Nehru National Institute of Technology Allahabad
March 27, 2012
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

2. Outline
Motivation for TDMA Scheduling
Introduction
TDMA Scheduling
Node-based Scheduling Algorithm
Level-based Scheduling Algorithm
Scalability and Distributed Implementation
Conclusion
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

3. Motivation for TDMA Scheduling
More power consumption in IEEE 802.11 MAC protocol
1. Idle listening
2. Wastage of energy in collision
No delay guarantee
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

4. Introduction
TDMA protocols are more energy efficient
Nodes can enter inactive states until their alloted time slots
TDMA eliminate collisions and bound the delay
e.g. TDMA protocol for a traffic monitoring network has a
lifetime of 1200 days compared with 10 days using the IEEE
802.11 protocol
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

5. TDMA Scheduling
Allocation of time slots depending upon the topology and the
node packet generation rates
One-hop or multi-hop scheduling
One-hop: Allocation of time slots is done depending on the
allocation request and deadline of the nodes
Multi-hop: More than one node can transmit at the same time
slot if their receivers are in non-conflicting parts of the network
Two types of conflicts:
1. Primary conflict
2. Secondary conflict
Find the smallest length conflict free assignment of slots
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

6. Network and Transmission Model
Network is represented by graph G=(V,E),where V is a set of
nodes including the access point AP and E are the
transmission links to be scheduled
Interference graph C=(V,I)is known where I ,subset of VXV,
is the set of edges such that (u,v) belongs to I if either u or v
can hear each other or one of them can interfere with a signal
intended for the other
If u is transmitting ,v should not be scheduled to receive from
other node at the same time
Conflict graph GC=(V,EC) corresponding to graph G=(V,E)
and C=(V,I) EC comprises of edges between node pair in G
that should not transmit at the same time,and is generated by
taking into account primary and secondary conflicts
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

7. Scheduling Problem
Given the interference graph , the scheduling problem is to
find a minimum frame during which all nodes can send their
packets to AP
So we reduce the problem of finding the chromatic number of
a graph to the scheduling problem
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

8. Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

9. Node-based Scheduling Algorithm
Adapted from classical multi-hop scheduling algorithm with
the idea of scheduling as many non-conflicting set of nodes as
possible in each time slot
Algorithm has two parts:
1. Coloring the network: Nodes are ordered in non-increasing
order of degree,the algorithm then assign smallest color to the
nodes in such a way that none of the nodes of the same color
have an edge in the conflict graph
2. Scheduling the network: A superslot is collection of
consecutive time slots such that each node with at least one
packet at the beginning of the superslot transmits at least one
packet during the superslot
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

10. Example:Schedule for Node-based Scheduling Algorithm
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

11. Level-based Scheduling Algorithm
Algorithm has three parts:
1. Obtain a linear network: If the original tree network has
depth N, the linear network GL = (VL,EL) has nodes VL =
v1,..., vN with node vl corresponding to all nodes at level l in
the original network and edges . The interference graph CL =
(VL, IL) includes edge (vj, vl) . The resulting conflict graph
GCL = (VL, ECL) includes edge (vj, vl) if the transmissions of
a node at level j and a node at level l conflict in the original
network.
2. Color this linear network
3. Schedule the original network:If nodes vi, vj in the linear
network are assigned the same color, they do not interfere. By
construction of the linear network any two nodes in the
original network, one chosen from level i and the other from
level j, can transmit at the same time
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

12. contd..
A superslot is a collection of consecutive time slots such that
each level of the tree with at least one packet at the
beginning of the superslot forwards at least one packet to the
lower level during the superslot.
Number of slots in a superslot is at most equal to the total
number of colors used for coloring the linear network
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

13. Example: Schedule for Level-based Scheduling Algorithm
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

14. Scalability and Distributed Implementation
Clustering the nodes
The central controller corresponding to each cluster should
take into account the interferers that are outside their range
while generating schedules
Central controllers are assigned colors so that no two
conflicting controllers are assigned the same color
Distributed algorithms
Schedules of the nodes are generated based on the local
topology information of the nodes
Color assignment is performed in two stages
Each node picks one slot for transmission in the order of the
traversal DFS of the graph G
DFS is repeated and now each node picks as many of the
remaining colors as it can for transmission
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

15. Scalability and Distributed Implementation
The DFS traversal starts with a token message generated at
the AP
Upon receipt of the token, the node performs the color
assignment and then sends this information to its one-hop and
two-hop neighbors. It then sends the token to each of its
neighbors in G who have not received the token yet.
Once it finds that all its neighbors have received the token, it
sends the token back to its parent
At the end of the traversal, the token carries the information
of the number of colors used in the network
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

16. Example: Schedule for Distributed Scheduling Algorithm
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

17. Example 2
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

18. Conclusion
Scheduling problem is to determine the smallest length
conflict-free assignment of slots
Two centralized algorithms has been proposed
In node based scheduling the schedule is obtained based on
the coloring of the original network
In level-based scheduling firstly linear network is obtained then
schedule is obtained based on the coloring of the linear
network
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

19. References
TDMA scheduling algorithms for wireless sensor networks by
Sinem Coleri Ergen Pravin Varaiya
Ephremides, A., Truong, T. V. (1990). Scheduling broadcasts
in multihop radio networks. IEEE Transactions on
Communica- tions, 38(4), 456460.
Tavli, B., Heinzelman, W. B. (2004). MH-TRACE: Multihop
time reservation using adaptive control for energy
efficiency.IEEE Journal on Selected Areas in Communications,
22(5), 942 953.
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks

20. Thank You
Neha Agarwal Reg No.– 2011CS03 Motilal Nehru National Institute of Technology Allahabad
TDMA Scheduling Algorithm for Wireless Sensor Networks