A case study. Describing a street testbed we recently built for studying the use of wireless mesh network for adaptive traffic control system Discuss some initial measurement results regarding link characteristics of 802.11 900Mhz Ethernet over powerline and Unwired (a WiMax variant)
Turn green at t1 for 30sec
C=8 for the last 10 sec
Traffic server (Regional Computer)
Sensor data + ACK
to ensure that 90% (2500) nodes each has at least 3 neighbours (e.g. for fault tolerance) requires a radio range of at least 1km.
Link distance: 200m
+ increased spatial reuse and improved signal quality
+ less power consumption while maintaining a similar link quality
13 pairs: no lossIntersection selection (omni-directional, 11Mbps)
19 pairs: no lossIntersection selection (directional, 11Mbps)
Ubiquity SR2 (400mW)
w/ 8dBi omni-directional ant.
Ubiquity SR9 (700mW)
w/ 6dBi omni-directional ant.
Diamond digital router
Netgear powerLAN adapter
Roof for water/heat proof
Mosquito mesh for insect proofMesh node
One hop: 521-522
Two hop: 521-523
losses become burstier as the distance increases
Latency and its variation increase as the number of hops increase
Latency is not strongly correlated with distance
Loss is not completely correlated with distance: location-dependant
Antenna location makes a difference
900MHz has a lower loss rate but higher latency: due to retry?
Powerline communication works pretty well when distance is within
Its operation region
NICTALatency of Unwired link(round-trip delay from mesh node to unwired gateway)
Almost half of the delay happens on the Unwired wireless link
Self-forming and self-healing
SourceWhy WMN for traffic control?