Load Balance Based Access Point Association
in Wireless Mesh Networks
Ma Tianze
Computer Network and Protocol Testing Laboratory,
Dept. of Computer Science & Technology, Tsinghua Univ.
Monday, April 10, 2023
Outline
Problem challenge
Related works
AP association algorithm
Indirect users balancing extension
Experiment
Monday, April 10, 2023
Problem challenge
WMN Characteristics
– Wireless Mesh Network is a multi-hop wireless network
– The data sent by a user will be transferred among the multi-hop path of the backbone to the mesh-router which has a back hole to the internet
– A new AP association mechanism is needed because conventional association method using signal strength as the only metric may be not quite suitable for WMN
Monday, April 10, 2023
WMN Characteristics
Internet
Mesh Router with Back Hole Mesh Router with Back Hole
Mesh Router Mesh Router
y
y
y
y
y
y
y
Mesh Routerwith AP
Mesh Routerwith AP
Which AP should the user be associated with?The left AP: Stronger signal, but heavy load and far from back holeThe right AP: Weaker signal, but light load and near to back hole
Monday, April 10, 2023
Problem challenge
Factors Considered in AP Association
– Signal strength: users would like to select an AP with good signal quality
– Quantity of AP’s users: If an AP serves too many users, the channel access delay of each user will be too large because of channel access competition.
– Multi-hop characteristic of WMN: Delay and congestion of the data path between AP and back holes
Monday, April 10, 2023
Related works
Dynamic Cross-Layer Association in 802.11-based Mesh Networks
– George Athanasiou, Thanasis Korakis, Ozgur Ercetin, Leandros Tassiulas
– IEEE INFOCOM 2007
– Defines an Airtime cost and make it the AP selection metric instead of 802.11 RSSRI
Monday, April 10, 2023
Related works
Joint Optimal Access Point Selection and Channel Assignment in Wireless Networks
– Koutsopoulos.I, Tassiulas.L
– Networking, IEEE/ACM Transactions
– Proposed a SCLB algorithm to assign users who stays in the overlap area of APs
Monday, April 10, 2023
AP association algorithm
Some Definitions
– A set of APs
– A set of users
– association coefficient
– The coefficient increases when the AP is appropriate for the user, which embodies the preference of users in AP association
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Monday, April 10, 2023
AP association algorithm
Network Model
– Each AP has an coverage
– The coverage of two or more APs is divided into several overlap areas
– The algorithm has several passes
– During a pass, all the overlap areas are traveled in turn
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AP1 AP2
AP3
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Monday, April 10, 2023
AP association algorithm
Algorithm Steps
– 1. All the overlap areas are traveled in turn
– 2. When it goes to a overlap area For each AP who forms this area, work out how many
users should be assigned to it Using a best-bipartite-matching algorithm to satisfy
above assignment and make the summation of association coefficient maximum
– 3. After all the areas have been traveled, if the association of users an APs is the same with last pass, the algorithm halts. Else go to step 1
Monday, April 10, 2023
AP association algorithm
work out how many users should be assigned to each AP
Purpose: After the assignment, the number of users of each AP can be balanced to the best of our abilities
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Monday, April 10, 2023
AP association algorithm
Using a best-bipartite-matching algorithm to satisfy above assignment
– We have already worked out how many users should be assigned to each AP in a overlap area
– The question is which user should be assigned to which AP
Purpose: make the summation of association coefficient maximum
Monday, April 10, 2023
AP association algorithm
best-bipartite-matching
– Nodes in left side are users
– Nodes in right side are APs split by number of users to be assigned to it in the area
– Weight of edges is association coefficientIf a best-bipartite-matching is found, the
summation of association coefficient maximum
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Monday, April 10, 2023
Indirect users balancing extension
Indirect Users
– An AP in WMN not only has direct users connected to it, but also has indirect users which would take it as a relay node of data transfer
– Indirect users can also be seen as load of AP
– If indirect users load of APs are not balanced, congestion may occurred on the data path
Monday, April 10, 2023
Indirect users balancing extension
As an extension to the above algorithm
– we define a load degree which summarizes the direct and indirect users to scale the load of APs
– The balancing of direct users will be replaced by the balancing of load degree.
Monday, April 10, 2023
Experiment
Tools
– C++ codes to implement the algorithmPerformance Metrics
– The overall throughput
– End-to-end delay
– Fairness of usersCompared with
– Pure IEEE 802.11
Monday, April 10, 2023
Thank you!