realistic and efficient multi-channel communications in...
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23-05-2011 | Real Time Networks
Realistic and Efficient Multi-Channel Communications in WSN
Miji Kim
Andreas Schädeli
Silvia Dorotheea Rus
Cievoloth Gilber Coca Olmos
223-05-2011 | Real Time Networks
Introduction
Problem description
Interference problems
Time synchronization problems
Description of solution
TCMP
Channel assignment
Test settings
Results
Performance Evaluation
Strengths and drawbacks
Paper Analysis
Conclusion
Content
323-05-2011 | Real Time Networks
Introduction
WSN: ad-hoc, multi-hop routing
Single-Channel vs. Multi-Channel communication
Single-Channel problem: Interferences
Multi-Channel problem: Synchronization
423-05-2011 | Real Time Networks
Only use orthogonal channels (no interference)
We are not alone!
Introduction
523-05-2011 | Real Time Networks
Channel Detection (CD)
Channel Assignment (CA)
Data Communication (DC)
Tree Based Multi-Channel Protocol (TMCP)
623-05-2011 | Real Time Networks
Channel Detection (CD)
Find usable channels
2 motes sample the link quality of each channel in different positions
Select non-adjacent channels (eliminates inter-tree interference)
Communication Range (CR)
Interference Range (IR)
Tree Based Multi-Channel Protocol (TMCP)
Pass through all frequencies..
Then find theones that suit
us!IR= 1,5 * CR
723-05-2011 | Real Time Networks
Channel Detection (CD)
Channel Assignment (CA) Partition the network into k subtrees
Assign a unique channel to each subtree
Minimal intra-tree interference
Tree Based Multi-Channel Protocol (TMCP)
Now, we areall partitionedinto subtrees.
823-05-2011 | Real Time Networks
Channel Detection (CD)
Channel Assignment (CA) Partition the network into k subtrees
Assign a unique channel to each subtree
Minimal intra-tree interference
Tree Based Multi-Channel Protocol (TMCP)
And we all chosea channel with
minimal interference!
923-05-2011 | Real Time Networks
Channel Detection (CD)
Channel Assignment (CA)
Data Communication (DC) No time synchronization needed
Base-station is equipped with
multiple tranceivers
Data reception and
dissemination is possible
Tree Based Multi-Channel Protocol (TMCP)
Communication can go on!
1023-05-2011 | Real Time Networks
Goal
Minimize intra-tree interferences.
Assumption
The network is static
Define
Node interference
Number of nodes by which the reception
can be disturbed at a given node
Tree interference
Maximum interference value among all
non-leaf nodes
Minimum interference Channel Assignment
1123-05-2011 | Real Time Networks
Algorithm
All interference values are known
Build shortest-path tree
Channel allocation
From top to bottom level of the tree
Process nodes with fewer parents first
Connect the node to the subtree where
adding the node brings the
least interference to the subtree
Select parent with least
interference value among
all parents
Assign nodes with large interference
as leaves
Minimum interference Channel Assignment
1223-05-2011 | Real Time Networks
Graph simulation in Java
200mX200m field 250 nodes uniformly distributed Communication range 10 to 35m Interference range is 1.5 times the communication range.
Since no other PMIT algorithms exists
Prim's algorithms to construct spanning trees (base schema with a single channel)
Eavesdropping channel assignment(used by node-base protocols MMSN).
lowest bound Maximum interference value/number of channels
Test Settings
1323-05-2011 | Real Time Networks
PMIT algorithm 1/3 of Prim’s interference
PMIT vs Eavesdropping.- when density is high PMIT has less interference.
Reason: Eavesdropping.- not enough channels for
nodes within two hops neighbors
PMIT looks for the local optimal.
higher density PMIT assign nodes with large interference as leaves.
PMIT - Lower Bound.
Algorithm is scalable with different densities.
With 8 channels Eavesdropping has 18% less interference. (no explanation why)
Results PMIT Performance
1423-05-2011 | Real Time Networks
Simulation - Same settings as before
TMCP vs. Spanning tree routing (protocol with a single channel).
Different network workloads
TMCP splits heavy workload into different trees.
More tolerant to systems load variations than spanning tree.
TMPC performance is unstable.
Flow congestion occurs on sub trees
TMCP Performance Evaluation
1523-05-2011 | Real Time Networks
Performances very close when number of channels is small.
TMCP achieves 10% higher throughput with less than 5 channels.
When the number of channels increases MMSN outperforms TMCP.
TMCP Performance Evaluation
1623-05-2011 | Real Time Networks
Strengths The algorithm doesn't do channels switching so doesn't need time
synchronization Every node keeps the shortest path to the base station, partitioning algorithm
doesn't require extra transmission and no extra energy consumption. Interference can be reduced by setting nodes with higher interference rate
as a leaf nodes
Drawbacks
The algorithm is not dynamic, what if we add a new node? The solution is not necessarily the best one since is an heuristic, maybe a
better one can be implemented (i.e. combination between tree base and node base).
(hardware Limitation) base station with multiple radio transceiver limitation Intra sub tree interference(proven to be a problem even in the test flow
congestions in sub trees).
Strengths and Drawbacks of TMCP
1723-05-2011 | Real Time Networks
Paper Analysis
Strengths
Few unstated assumptions
Presents realistic scenarios
Algorithm well understandable
Weaknesses
No details about other protocols
Very optimistic conclusion based on few results
Orthographic faults and bad graph labeling in one case
1823-05-2011 | Real Time Networks
What the paper says:
“It can be seen that without time errors, the node-based scheme always has higher packet reception ratios than the single channel scheme.”
What the figure says:
Paper Analysis
1923-05-2011 | Real Time Networks
Tree-based algorithm improves the throughput of the WSN.
Performed tests are not necessarily the best, Some real tests should be performed(existents are not relevant).
Maybe a combination of “tree-based – Node–based” could be implemented to improve the sub-tree flow congestion problem.
Fast Data Collection in Tree-Based Wireless Sensor Networks Paper makes comparisons of TMCP with other algorithms.
Conclusions
2023-05-2011 | Real Time Networks
Thank you for your attention!