distributed channel assignment in multi-radio 802.11 mesh networks
DESCRIPTION
Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks Bong Jun Ko (IBM T.J. Watson Research) Vishal Misra (Columbia University) Jitendra Padhye (Microsoft Research) Dan Rubenstein (Columbia University). Wireless Mesh Networks. - PowerPoint PPT PresentationTRANSCRIPT
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Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks
Bong Jun Ko (IBM T.J. Watson Research)Vishal Misra (Columbia University)
Jitendra Padhye (Microsoft Research)Dan Rubenstein (Columbia University)
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Wireless Mesh Networks
WMN: Multi-hop wireless network infrastructure for local/residential area networks.
Goal: better channel utilization higher network capacity. For scalability and adaptability, light-weight distributed solution is desirable.
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Our PhilosophyWhy focus on channel assignment?
Decouple channel assignment and end-to-end routing.Routing protocols adapt to dynamic traffic load, link quality, and
even channel configuration (e.g., MR-LQSR1) .Channel assignment focuses on quickly-stabilizing channel
configuration based on physical topology.More scalable than centralized, joint-optimization approaches.
There are K channels, and assume (for now) every node can transmit and receive from all channels simultaneously.
Approach: For each node, minimize the number of other interfering nodes on the same channel.
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Node x’s interference range
1. R. Draves et al., “Routing in Multi-Radio, Multi-Hop Wireless Mesh Networks”, Mobicom 2004.
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Distributed Greedy Channel Selection
x y
Q : Will this process converge?
Let each node select its own channel.Whenever it is needed, each node changes to a channel that mi
nimizes the number of other nodes on the same channel in the interference range.
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Q : Will this process converge?
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YES!Proof :
•N(x): # of nodes on the same channel for node x.• xN(x) decreases monotonically.
Let each node select its own channel.Whenever it is needed, each node changes to a
channel that minimizes the number of nodes on the same channel in the interference range.
Distributed Greedy Channel Selection
>(-1) (+1)
Local optimization improves global optimization metric – Self-stabilizing!
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Experience with 802.11 Mesh NetworksPractical limitations
Current 802.11 transceivers can send or receive through only one channel at a time.
Neighboring nodes need to be at the same channel. Conflicting goals: connectivity vs better utilization.
Multi-radio stations1 common, default
channel for all nodesVariable channels
selected by channel assignment algorithm
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•Links of variable channels: express way •Links of common channel: local roads
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Performance Evaluation
Experiments on a 14-node testbed. A default channel from 802.11a Variable channels from 802.11g Interference range : 3 hops
Routing protocol : MR-LQSR (Multi-Radio Link Quality Source Routing) Aware of multi-radio, multi-channel environment Preference given to channel-diverse paths
Measure end-to-end throughput of multiple, concurrent TCP flows with random source-destination pairs
Compare to samech : all nodes are assigned the same channel for additional radio
rand : each node is assigned a channel uniformly at random for additional radio
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Testbed
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Individual TCP Throughput
•CDF of all TCP flow throughputs in all experiments.•Flows over longer paths benefit the most.
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Aggregate TCP Throughput
•Measured average TCP throughput of all flows in each experiment, and took median value of 5 experiments.•50% higher than samech / 20% higher than random.
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Conclusion
Developed a fully-distributed, self-stabilizing channel assignment algorithm for multi-hop wireless networks.
Experiments on multi-radio 802.11 mesh network testbed. Our mechanism shows improvements in network throughput
by 50% and 20% compared to homogeneous and random assignments, respectively.
Open ProblemsTheoretical running time and bounds of the distributed gr
eedy algorithm?Formal time-scale decomposition in radio resource contro
l (e.g., channel, power, rate, route control).
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Thank You
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Backup slides
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Other Results
Channel Utilization (in %) of 802.11g channels
Protocol Dynamics
samech rand DA10.1 15.1 22.7
# msgs 90.0Bytes 2080Time (sec)
32.4
Changes 0.22Requests 0.70
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Dealing with Delay and Asynchrony
Solution : a 3-way handshake protocol for distributed mutual exclusive operation.
REQUEST → ACCEPT or REJECT → UPDATE or ABORT
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3-way Handshake Protocol
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REQUEST
3-way Handshake Protocol
REQUEST specifies: Intended channel change Perceived channels of other nodes
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ACCEPT
3-way Handshake Protocol
x
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UPDATE
3-way Handshake Protocol
When a node ACCEPTed a REQUEST, it “freezes” its channel until corresponding response (UPDATE or ABORT) is received.
x
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xy
3-way Handshake Protocol
y
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yREQUEST
3-way Handshake Protocol
x
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REJECT
3-way Handshake Protocol
xy
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ABORT
3-way Handshake Protocol
xy
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yREQUEST
3-way Handshake Protocol
REQUEST
x
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REJECT
3-way Handshake Protocol
ACCEPTx
y
Break ties by predefined order of nodes- if x < y, y will be accepted to change.
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yABORT
3-way Handshake Protocol
UPDATE
x