Transcript Mobile Ad Hoc Network (MANET) Neil Tang 1/22/2007

Dynamic Channel Assignment and Routing
in Multi-Radio Wireless Mesh Networks
Neil Tang
3/10/2009
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Outline
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References
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Channel Assignment Methods
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Problem Definition
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Link Layer (Channel Assignment) Protocol
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Routing metric and protocol
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Simulation Results
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References
Kyasanur-MC2R06: P. Kyasanur and N. H. Vaidya, Routing and link-layer
protocols for multi-channel multi-interface ad hoc wireless networks, ACM
SIGMOBILE Mobile Computing and Communications Review, Vol.10,
No.1, 2006, pp. 31 – 43.
Draves-MobiCom06: R. Draves, J. Padhye, and B. Zill, Routing in multiradio, multi-hop wireless mesh networks, ACM Mobicom’2004, pp. 114-128.
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Channel Assignment Methods
 Static
 Dynamic
 Hybrid
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Assumptions
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MAC layer: 802.11
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Multiple available channels: IEEE 802.11a and 802.11b standard
specify 12 and 3 non-overlapping channels respectively. The number
of available channels is larger than the number of radios in a node.
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Channel switching delay: a few millisecond.
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Node: each node has multiple radios (NICs), each of which can be
tuned to one of the available channels.
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Traffic: Unicast communications and a connection request with a
source-destination pair may arrive at any time.
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Problem Definition
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Problem: A source-destination route and a corresponding channel
assignment.
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Optimization goals:
1) High channel utilization.
2) Network connectivity is ensured.
3) Allow implementation on existing 802.11 hardware.
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Interface Assignment
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Fixed interfaces: Some K out of M interfaces at each node are
assigned for long intervals of time to some K channels.
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Switchable interfaces: The remaining M − K interfaces are dynamically
assigned to any of the remaining M − K channels (over short time
scales), based on data traffic.
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Link Layer Protocol
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Each node maintains a NeighborTable containing the fixed channels being
used by its neighbors.
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Each channel is associated with a packet queue. If an unicast packet is
received at the link layer for transmission, the fixed channel of the destination
of the packet is looked up in the NeighborTable, and the packet is added to the
corresponding channel queue.
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Broadcast (e.g., route discovery, Hello) is conducted over every channel.
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Link Layer Protocol
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When the switchable interface is switched to a new channel, it is
always switched to the channel with the oldest queued data.
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The switchable interface changes channels only when there are
packets queued for another channel, and one of the following two
conditions hold: 1) The switchable interface is on a channel with an
empty queue. 2) The switchable interface has been on a channel for
more than MaxSwitchTime duration.
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Link Layer Protocol
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Nodes also maintain a ChannelUsageList containing a count of the
number of nodes in its two-hop neighborhood using each channel.
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Periodically, each node broadcasts a “Hello” packet on every channel.
The Hello packet contains the fixed channel being used by the node,
and its current NeighborTable.
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If the number of other nodes using the same fixed channel as itself is
large, then a node with some probability p (set to 0.4 in simulations)
changes its fixed channel to a less used channel.
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Strength and Weakness
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Transmitter-receiver synchronization is not needed.
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High channel utilization and low interference.
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Scalable.
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High broadcast overhead.
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Interface utilization and throughput?
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Switching Cost
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Switching Cost
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InterfaceUsage(j): the fraction of the time a switchable interface was
transmitting on channel j.
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ps(j): the probability the switchable interface will be on a different
channel (i ≠ j) when a packet arrives on channel j.
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Switching cost:
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Routing Metric
For hop i, channel j :
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Measure ETX
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Routing Protocol
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DSR is the baseline solution.
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The RREQ packet sent by a node X over a channel i contains the ETT,
switching cost, and channels used on all previous hops, as well as the
switching cost of channel i at node X.
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An intermediate node re-broadcasts the RREQ if 1) The sequence number in
the RREQ is being seen for the first time. 2) The cost of the already
discovered (partial) path in the RREQ is smaller than the cost seen in all
earlier RREQs with the same sequence number, if any.
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When the destination receives an RREQ, it responds with a route reply (RREP)
only if the cost of the received RREQ is smaller than other RREQs (containing
the same sequence number) seen till then.
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Simulation Results
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