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Dynamic Channel Assignment and Routing in MultiRadio Wireless Mesh Networks Neil Tang 3102009

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Title: Dynamic Channel Assignment and Routing in MultiRadio Wireless Mesh Networks Neil Tang 3102009


1
Dynamic Channel Assignment and Routing in
Multi-Radio Wireless Mesh NetworksNeil
Tang3/10/2009
2
Outline
  • References
  • Channel Assignment Methods
  • Problem Definition
  • Link Layer (Channel Assignment) Protocol
  • Routing metric and protocol
  • Simulation Results

3
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 multi-radio, multi-hop wireless
    mesh networks, ACM Mobicom2004, pp. 114-128.

4
Channel Assignment Methods
  • Static
  • Dynamic
  • Hybrid

5
Assumptions
  • MAC layer 802.11
  • 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.
  • Channel switching delay a few millisecond.
  • Node each node has multiple radios (NICs), each
    of which can be tuned to one of the available
    channels.
  • Traffic Unicast communications and a connection
    request with a source-destination pair may arrive
    at any time.

6
Problem Definition
  • Problem A source-destination route and a
    corresponding channel assignment.
  • Optimization goals
  • 1) High channel utilization.
  • 2) Network connectivity is ensured.
  • 3) Allow implementation on existing 802.11
    hardware.

7
Interface Assignment
  • Fixed interfaces Some K out of M interfaces at
    each node are assigned for long intervals of time
    to some K channels.
  • 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.

8
Link Layer Protocol
  • Each node maintains a NeighborTable containing
    the fixed channels being used by its neighbors.
  • 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.
  • Broadcast (e.g., route discovery, Hello) is
    conducted over every channel.

9
Link Layer Protocol
  • When the switchable interface is switched to a
    new channel, it is always switched to the channel
    with the oldest queued data.
  • 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.

10
Link Layer Protocol
  • Nodes also maintain a ChannelUsageList containing
    a count of the number of nodes in its two-hop
    neighborhood using each channel.
  • 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.
  • 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.

11
Strength and Weakness
  • Transmitter-receiver synchronization is not
    needed.
  • High channel utilization and low interference.
  • Scalable.
  • High broadcast overhead.
  • Interface utilization and throughput?

12
Switching Cost
13
Switching Cost
  • InterfaceUsage(j) the fraction of the time a
    switchable interface was transmitting on channel
    j.
  • ps(j) the probability the switchable interface
    will be on a different channel (i ? j) when a
    packet arrives on channel j.
  • Switching cost

14
Routing Metric
For hop i, channel j
15
Measure ETX
16
Routing Protocol
  • DSR is the baseline solution.
  • 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.
  • 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.
  • 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.

17
Simulation Results
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