Improving Capacity and Flexibility of Wireless Mesh
Networks by Interface Switching
Yunxia Feng, Minglu Li and Min-You Wu
Presented by: Yunxia Feng
Dept. of Computer Science & Engineering Shanghai Jiao Tong University
Shanghai, China
Outlines
Problem Description
Hybrid Channel Assignment Protocol (HCAP) The Interface Assignment Strategies
Coordination Policy of HCAP
The Channel Assignment Algorithm
Evaluation Results
Conclusions and Future Works
Problem Description
Fig. 1 The I-WMN ArchitectureGateways (GAs): The routers that connect to wired networks via wired links;
SNs: The mesh routers within the transmission range of GAs;
GNs: All of the mesh routers except GAs and SNs.
Problem Description (cont.)
Interference in I-WMNs is serious Heavy traffic loads; Multiple hops between the source and destination nodes; One interface can only fix on one channel at the same time.
Possible Resolutions Equipping each node with multiple interfaces;
Fix interfaces on different channels. However, it is difficult to equip each node with the same
number of interfaces as available channels. Dynamic channel assignment (DCA)
Co-channel interference is minimized; Improves the network capacity; Enhances the scalability of WMNs.
Components of Multi-interface DCA
Interface assignment strategy: Decides the interface switching mode of nodes;
Coordination scheme: Provides methods to implement communications
between nodes under given interface assignment strategy.
Problems Induced by DCA
Switching Overheads switching delay
Dependence Problems Connection dependence
Nodes cannot communicate with each other due to switching to different channels.
Channel dependence Changing the channel of a particular link may result in
changing allocated channels of many other links in the network.
Hybrid Channel Assignment Protocol (HCAP)
Premises GAs distribute across the network, and any two GAs do not
interfere with each other even if they are assigned the same channel;
One SN node can only establish one routing path to the GA nodes at a time;
HCAP adopts one of current synchronization protocols; If each node is equipped with only two interfaces, then,
A SN is within the transmission range of only one GA. If each node is equipped with more than two interfaces, then
A SN is within the transmission range of the same number of GAs as the number of its interface that adopt static strategy.
The Interface Assignment Strategies
GA Nodes: Static interface assignment strategy to avoid frequent
interface switching. All the Other Nodes (SN and GN nodes):
Hybrid strategy to keep flexible fixed interface (FI): the interface that adopts static strategy; switching interface (SI): the interface that dynamically switch
channels.
The Interface Assignment Strategies (cont.)
Declaration & Definitions The channel assigned to every FI is different from that
of nodes within its interference range as possible. The channel is referred to the node’s receiving channel
(CRec);
The corresponding interface is referred to its receiving interface (IRec).
Dynamic links: links between hybrid nodes Static links: links between GA nodes and SN nodes
within their transmission range.
Questions in Implementing HCAP
Which interface should a CRec be assigned to? CRec is assigned to the FI of GN nodes; CRec is assigned to the SI of SN nodes.
Reasons The FI of every SN node should fix on one channel of the GA
within its transmission range. Every SN node should fix its FI on one channel of the GA within
its transmission range to communicate with the GA since none interface on GA nodes can switch interfaces dynamically.
The assigned channels of GAs should be shared among the fewest nodes to minimize the interference level on them due to the heaviest loads.
The sketch of HCAP
(a) Network topology (b) Sketch of HCAP
Fig. 2 A simple example of HCAP
Coordination Policy of HCAP
Divide the time of hybrid nodes into slots, whereas several slots compose one Cycle.
Connection dependency problem in HCAP Suppose that B is transmitting packets to node G on link at
present. If node C wants to send some packets to B, there is connection dependency problem.
Resolution Designate several slots in every Cycle for the SI of every SN
node to fix on its CRec. We denote these slots by Receiving Slots (RS) to differentiate with other slots. The number and positions of RSs in a Cycle are determined by the settings of each specific network.
Broadcast Problem
Description: There is no permanent links between hybrid nodes
The FIs of hybrid nodes are assigned different channels, whereas their SIs switch to different channels dynamically.
Resolution: Take several slots from the left slots of every Cycle as
Broadcast Slots (BS), during which the SI of all hybrid nodes switch to a predefined channel to only transfer broadcast packets. The number and positions of RSs in a Cycle are determined by the settings of each specific network.
Channel Assignment Algorithm
Three Phases In the first phase, the algorithm assigns channels to both
interfaces of GA nodes. In the second phase, the algorithm assigns channels to the FI of
SN nodes. At last, the algorithm assigns CRec to hybrid nodes.
Channel Assignment Sequence The algorithm always assigns channel to the node that has the
biggest η. If multiple nodes have the biggest η, they are assigned channels in a random order. This sorting gives higher priority for nodes that have more restrictions.
Default Simulations Settings
A 36-node I-WMN, where each node is equipped with two half-duplex interfaces.
The 36 nodes randomly distribute in a 6×6 square grid network, and the distance between two neighboring nodes equals to transmission range.
Four nodes are designated as GA nodes and connected to the wired network.
The ratio between interference range and transmission range is set to 2.
The simulation period is between 24-58 seconds. Utilize the DSR protocol for route selection.
Evaluation Results
Fig.3 Throughput Comparison Fig. 4 Adaptation to Flow changes
8 12 16 20 24100
200
300
400
500
Thr
ough
put
(Mbp
s)
Number of traffic flows
HCAP HYBRID STATIC
Evaluation Results
Fig. 5 Throughputs vs. traffic fairness Fig. 6 Impact of broadcast slot
0 50 100 150 200 250 300 350 400
0
10
20
30
40
50
60
70
80
90
100
Suc
cess
ful t
raffi
c flo
ws
ratio
(%)
Throughput (Mbps)
HCAP HYBRID STATIC
1 2 3 4 5 6 7 8 9 10300
325
350
375
400
425
450
475
500
525
550
Ag
gre
ga
te T
hro
ug
hp
ut
(Mb
ps)
Broadcast Slot Time (ms)
Conclusions & Future Works
We have presented a hybrid channel assignment protocol to improve the capacity and flexibility of WMNs.
The protocol does not depend on prior information on the traffic loads, whereas it can adapt automatically to the changes in the network.
Extensive simulations show that the protocol improves the network capacity and flexibility. It also achieves better per-flow fairness, whereas it keeps both interface switching overheads and coordination complexity under tolerable range.
As future work, we will provide analyses results and describe how to the algorithm in details.
Thank You
Q & A ?