load balance based access point association in wireless mesh networks

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.

Thursday, April 20, 2023

Outline

Problem challenge

Related works

AP association algorithm

Indirect users balancing extension

Experiment


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


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


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


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


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



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

1 2{ , ,..., }MA a a a

1 2{ , ,..., }NU u u u

( , )i j ij ijw u a P e



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

45

3

2

1

AP1 AP2

AP3

AP4



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



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

2 2 21 1 2 2min( ( ( ) ) ( ( ) ) ... ( ( ) ) )k k l l kN a s N N a s N N a s N

1

( )l

k k ii

N M N a

1 2 ... l ks s s M



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



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

u1

u2

u4

u3

a1

a2

a2

a3

w11

w23w32

w42



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



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.


Experiment

Tools

– C++ codes to implement the algorithmPerformance Metrics

– The overall throughput

– End-to-end delay

– Fairness of usersCompared with

– Pure IEEE 802.11


Thank you!

load balance based access point association in wireless mesh networks

Documents

association of users

ap association algorithmusing

ap association algorithmwork

association coefficientif

access point association

ap selection metric

ap associationsignal

number of users