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Design of a reliable communication system for grid-style traffic light networks. Junghoon Lee Dept. of Computer science and statistics Jeju National University Rep. of Korea. Song Han, Aloysius K. Mok Dept. of Computer sciences University of Texas Austin, Texas, USA. Contents. - PowerPoint PPT Presentation
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Design of a reliable communication system for grid-style traffic light net-
works
Junghoon LeeDept. of Computer science and statistics
Jeju National UniversityRep. of Korea
Song Han, Aloysius K. MokDept. of Computer sciences
University of TexasAustin, Texas, USA
Performance Evaluation
Background and Related Work
Conclusion
Introduction
Channel schedule and routing
Contents
<3>
Feedback control loop
consists of geographically distributed components. needs reliable and timely communication. can install wireless process control protocol. WirelessHART standard has Clear Channel Assessment and provides predictable network access.
Controller Actuators
Sensors
Controlledprocess
Current state
Current state
<4>
Controlled process
Jeju area is located in the southernmost part of Korea.
It hosts many pilot projects for the purpose of testing a sys-tem before its deployment.
Vehicular telematics system
Smart grid system
<5>
Traffic light network
The traffic light is secure place for wireless nodes. Traffic lights form a grid topology in urban area. Process control applications can run on this network.
Global control system
Level 1 network
Level 2 network
Performance Evaluation
Routing and Scheduling Scheme
Conclusion
Introduction
Background and Related Work
Contents
<7>
WirelessHART standard
IEEE 802.15.4 2.4 GHz radioband physical link supports mesh networking directly. 16 frequency channels with 5 MHz guard time Channel blacklisting and hopping The slot-based access scheme with time synchronization The size of a single time slot : 10 ms central network manager schedule provisioning and updating CCA (Clear Channel Assessment) to avoid interference
<8>
Slot organization
Setting the channel each time slot begins. 10 ms slots have CCA (Channel Condition Assessment). CCA and channel tuning just take several bit time. additional CCA and channel tuning for a slot
<9>
Protocol stack and mesh
From Jianping Song et al.’s paper in RTAS 2008 [5]
Performance Evaluation
Background and Related Work
Conclusion
Introduction
Routing and Scheduling Scheme
Contents
<11>
Motivation
The standard does not define what to do when the CCA result is not good.
If the CCA result is not good, can it be possible to take another route?
Primary and secondary receivers can solve this prob-lem.
Two receivers wait for the message and the sender se-lects the receiver (channel) according to CCA result.
The transmission paths can be easily split and merged over the grid topology.
<12>
System Model
Traffic Light Network The traffic lights, installed in the intersections, form a grid
network in the Manhattan-style road network. Each node can exchange messages directly with its verti-
cal and horizontal neighbors, but not its diagonal one, considering the directional antenna.
Control Loop ① reading state variables from sensors, ② deciding the
control action, and ③ sending the value of control vari-ables to the actuators
①, ③ : the network and the communication schedules
<13>
System Model
The controller node is located at the left-top. For N0,0 -> N1,1, H0,1->V1,1 and V1,0, H1,1 paths are available. N0,0 performs split and N1,1 runs merge op. over 2 slots. CCA result is always right.
Controllernode
Controllernode
Four 4 4 gridsⅹ
<14>
Split-merge operation
sender
Primary receiver
secondary receiver
receiver
Primary sender
secondary sender
<15>
Sample slot allocation table
Split op.
Merge op.
slot allocation for a 3 3 grid and downlink.
<16>
Route decision
Each rectangle can be considered to be a virtual link. Run the shortest path algorithm. The virtual link can be mapped to 2 slot transmissions.
[….Si,j,......]Primary [ …, Hi,j+1,Vi+1,j+1,…]Secondary [ …, Vi+1,j,Hi+1,j+1,…] F1 substitution
[….Si,j,......]Primary [ …, Vi+1,j,Hi+1,j+1,…]Secondary [ …, Hi,j+1,Vi+1,j+1,…] F2 substitution
<17>
Virtual link model
Success probabilities for the two paths in a rectangle, F1 and F2 Select the bigger of the two as the primary path Set the error rate of the virtual link (1 – F1) or (1- F2) Run the Dijkstra’s shortest path algorithm
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1,1,11,
1,11,1,1,,1
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Routing and Scheduling Scheme
Background and Related Work
Conclusion
Introduction
Performance Evaluation
Contents
<19>
Performance Evaluation
Simulation Environment using SMPL which provides discrete event scheduling For simplicity, only the downlink graph was considered. 500 sets of link error rates are generated. The success ratios are averaged.
Main metrics success ratio according to slot error rate, hop count. success ratio for the different routing schemes, dimen-
sion additional receive ratio effect of node failures
<20>
Performance Evaluation
Each link has the same error rate
Guilbert-Elliot error model
End-to-end messages to each node a round Overall success ratio a large performance
gap on the high slot er-ror rate
7.9 %
Effect of slot error rate
<21>
Performance Evaluation
11.4 %7.8 %5.5 %
Success ratio classified by hop counts
hop by hop success ratio no improvement for the
1 hop nodes The 6 hop node has 3
split-merge operations. SM shows stable suc-
cess ratio for the hop count change.
<22>
Performance Evaluation
Improvement by the routing scheme
6.69 %
Each link has its own error rate.
Enhance performance by the routing scheme based on the virtual link model
just 3.6 % loop length overhead
<23>
Performance Evaluation (4/4)
Effect of grid dimension
9.0 % average slot error rate
is set to 0.1. A larger grid has more
rectangles. Average hop length in-
creases. Performance gap in-
creases for a larger grid.
<24>
Performance Evaluation (4/4)
Overhead analysis Additional receive due
to the split operation total slots needed in a
control round
All nodes in the same row and column have the same SM opera-tions
)1(2
1
)1(n
i
iinn
1
1
}1)(2{n
i
in
<25>
Performance Evaluation (4/4)
Gap for diagonal nodes and other nodes Compare with a link
disjoint path Each link has the
same error rate Difference in average
success ratio is less than 6 %
For the diagonal case, the difference reaches up to 35 %
Performance Evaluation
Routing and Scheduling Scheme
Background & Related Work
Introduction
Conclusion
<27>
Conclusions
Summary
Process control for grid topology traffic light network Attempts two paths according to CCA by split-merge SM operation can be modeled as a virtual link Shortest path-based routing and slot allocation Enhances delivery ratio by up to 7.9 % on average
Future Work Apply the split-merge operation for data collection and
multicasting
Thank You
<29>
Performance Evaluation (4/4)
Effect of node failures 1 node failure makes 4
links unconnected A non-fringe node fail-
ure makes it difficult to run the SM operation.
outperforms grid for all node failure range.
4.7 %