A Fair Multiple-Slot Assignment Protocol for TDMA Scheduling in Wireless Sensor Networks K. Banerjee, P. Basuchaudhuri, D. Sadhukhan and N. Das
Dec 30, 2015
A Fair Multiple-Slot Assignment Protocol for TDMA Scheduling in Wireless Sensor Networks
K. Banerjee, P. Basuchaudhuri, D. Sadhukhan and N. Das
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WSN : Wireless Sensor Networks
Organization
Collision Avoidance : TDMA
Scheduling : Frame length minimization problem
Distributed Protocol
Performance Evaluation
Conclusion
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What is Sensor Network?
B
E
A
D
C
F
G
• A collection of sensor nodes• Engaged in data transmission, reception, aggregation and redirecting to a sink• An ad-hoc network
SINK
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Major Applications
• Environmental Monitoring• Habitat Monitoring • Precision Agriculture• Disaster Recovery• Natural Calamity Prediction• Defense Applications• Assisted Living for aged & disabled• Health Care
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Large number of nodes
Multi-hop network
Streaming data
No global knowledge about the network
Frequent node failure
Energy is the scarce resource
Limited memory
Autonomous
Unique Constraints
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Need to shutdown the radio if possible
SENSORS
Power consumption of node subsystems
0
5
10
15
20
Po
wer
(m
W)
CPU TX RX IDLE SLEEP
RADIOSLEEPIDLERXTX EEEE
Energy Consumers
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Communication uses a single channel over the same wireless medium
Communication in sensor network
.
A node broadcasts data packets and nodes within its transmission zone can receive those packets
Interference takes place when more than one transmission overlaps : Collision
Several collision avoidance methods are available while accessing the media-
• CSMA : listening also consumes energy
• FDMA : not suitable; generally single channel
• TDMA : best suited; nodes can sleep in idle times
Collision Avoidance
Collision causes retransmission : wastage of energy
Energy is the most scarce resource
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Slot: Smallest time slice, in which a node can either transmit or receive
Frame: A minimal sequence of slots is a frame
A matrix is used to represent a schedule
Slot, Frame and Schedule
Node→
R--R-5-R---4--R-R3R--R-2--R-R154321Slot
TDMA
Time is slotted : each node is assigned at least one collision-free slot in a frame; frames are repeated
TDMA: Periodic listen and sleep
–Turn off radio when sleeping–Reduce duty cycle to ~10% (e.g. 200 ms on/2s off)–Increased latency for reduced energy
How to reduce the latency?
sleeplisten listen sleeptransmit
Nodes within 1 hop neighborhood creates primary interference
Nodes within 2 hop neighborhood (but not in 1 hop neighborhood) creates secondary interference
So no two nodes within 2 hop neighborhood can be given same time slot for transmission
Slots can be reused for nodes at more than 2-hop distance
Unique Slots
Problem Definition
How to find a TDMA schedule with minimum frame length that assigns at least one conflict-free slot to
each node?
Can be modeled as a graph-coloring Problem
NP-Complete Problem [Ephremides et al, 1990]
Distributed solution is needed
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• WSN consists of N static nodes
• Each node is assigned a unique id i, 1< i<N
• No global knowledge about network topology: each node knows N, the total number of nodes in the network • A node can only be in one state at a time: broadcasting or receiving
• All the links are bi-directional
Assumptions Revisited
The easiest way to solve the problem is providing each node a particular time slot.But that leads to -
1. Frame length = Number of nodes.2. Wastage of time slots.
Assigning Slots
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Ephremides & Truong (IEEE Tr. Comm., 1990)
Table 1
RR
1 5 4 3 2
Node→
-
R---5-R---4--R-3
--R2--R154321Slot
R
R
-
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Improvements over Previous Works
Fairness – Even distribution of reserved slots
Compaction – Reduction of number of slots in the schedule matrix, wherever possible
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Table 2: The initial-schedule-matrixNode→
Step – I : Initial-Schedule-Matrix
R---5-R---4--R-3
--R2--R154321Slot
1 5 4 3 2
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Table 3: The contention matrix Node→
Step – II : Contention Matrix
Contention (Ci,j) = total number of 2-hop neighbors of nodei to which the slot Sj is available
XXX1X5XXXXX4XXXX132XXX22XX22X154321Slot
1 5 4 3 2
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Table 4: The complete-schedule-matrix after Fair-ReservationNode→
Step – III : Complete-Schedule-Matrix
R--R-5-R---4--R-R3R--R-2--R-R154321Slot
X
X
Parallel Execution
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Table 5: The compact-schedule-matrix Node→
Step – IV : Compact-Schedule-Matrix
-R---3R--R-2--R-R154321Slot
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Simulation Environment
Random graph generation
• Graph generation algorithms have been used
• Number of nodes may vary from 50-250
• Randomly generated each time in Unix Environment
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Comparison based on standard deviation of number of slots assigned to individual nodes
Performance Evaluation : Fairness
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Tr = avg. # of slots reserved per node / frame length
Comparison based on transmission rates (Tr)
Performance Evaluation : Throughput
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Conclusion
Proposed algorithm outperforms in terms of:
frame lengthfairness and throughput
Efficient for large networks with uniform trafficDistributed algorithm for compaction is to be
studied
References
1. A. Ephremides and T. V. Truong, “Scheduling Broadcasts in Multihop Radio Networks,” IEEE Transactions on Communications, Vol. 38, No. 4, April 1990, pp: 483-495.
2. I. F. Akyildiz, W. Su, Y. Sankarasubramaniam and E. Cayirci, “A Survey on Sensor Networks,” IEEE Communications Magazine, August 2002, pp: 102-114.
3. S. Ramanathan and E. L. Lloyd, “Scheduling Algorithms for Multihop Radio Networks,” IEEE/ACM Transactions on Networking, Vol. 1, No. 2, April 1993, pp: 166-177.
4. S. Ramanathan, “A Unified Framework and Algorithm for Channel Assignment in Wireless Sensor Networks,” Wireless Networks, Vol. 5, No. 2, 1999, pp: 81-94.
5. I. Rhee, A. Warrier, J. Min and L. Xu, “DRAND: Distributed Randomized TDMA Scheduling for Wireless Ad-hoc Networks,” Proc. of MobiHoc ’06, May 2006, pp: 190-201.
6. Y. Wang and I. Henning, “A Deterministic Distributed TDMA Scheduling Algorithm for Wireless Sensor Networks,” Proc. of International Conference on Wireless Communication, Networking and Mobile Computing, WiCOM 2007, pp: 2759-2762
7. S. Gandham, M. Dawande and R. Prakash, “Link scheduling in sensor networks: distributed edge coloring revisited,” Proc. of 24th Annual Joint Conference of the IEEE Computer and Communications Societies, INFOCOM 2005, pp: 2492- 2501.
8. S. Bhattacharjee and N. Das, “Distributed Time Slot Assignment in Wireless Ad Hoc Networks for STDMA,” Lecture Notes in Computer Science (Springer), No. 3618, Proc. of the 2nd International Conference on Distributed Computing and Internet Technology (ICDCIT 2005), Dec. 2005, pp. 93-104.
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