A Bandwidth Scheduling Algorithm Based on Minimum Interference

Traffic in Mesh Mode

Xu-Yajing, Li-ZhiTao, Zhong-XiuFang and Xu-HuiMin

International Conference on Wireless Communications, NetInternational Conference on Wireless Communications, Networking and Mobile Computing, 2007. working and Mobile Computing, 2007.

WiCom 2007.WiCom 2007.

Mei-jhen ChenMei-jhen Chen

OutlineOutline

IntroductionIntroduction Overview of WiMax MeshOverview of WiMax Mesh Proposed Scheduling AlgorithmProposed Scheduling Algorithm SimulationsSimulations ConclusionConclusion

IntroductionIntroduction

IEEE 802.16 defines two different air-interfaces: Point-to-Multi-Point (PMP) and Mesh.

Introduction Introduction (cont.)(cont.)

Related work: (consider points)

To built collision Matrix of nodes Finding a path with least links finding a path with minimal blocking nodes

These papers have not discussed the traffic of interference links which will influence on transmission efficiency in Mesh mode.

In this paper a bandwidth scheduling algorithm is proposed based on minimum interference traffic.

Overview of WiMax MeshOverview of WiMax Mesh

new node joins mesh network

BS SSs

MSH-NENT

MSH-NCFG

New SS

MSH-NCFG

broadcast

connect one as its response node

MSH-NENT

Finish the process

MSH-NENT

Overview of WiMax Mesh Overview of WiMax Mesh (cont.)(cont.)

Centralized scheduling BS maintains the routing tree of entire network, and control

s all the channel access. If one SS wants to transmit, it has to wait the grant of BS.

Distributed scheduling SSs can communicate directly on scheduling strategies wit

hout BS’s grant.

Overview of WiMax Mesh Overview of WiMax Mesh (cont.)(cont.)

There are two control messages in centralized scheduling:

Mesh Centralized Scheduling Configuration Message (MSH-CSCF)

• contains the channel configuration and routing tree Mesh Centralized Scheduling Message (MSH-CSCH)

• contains bandwidth request and grant, and updates routing tree.

Overview of WiMax MeshOverview of WiMax Mesh (cont.)(cont.)

BS SSs

MSH-CSCF

(broadcast)

MSH-CSCH

(Request message)

MSH-CSCH

(Grant message)

Maintain a routing treeForward to SSs

Determine the amount of granted resources for each link

Proposed Scheduling AlgorithmProposed Scheduling Algorithm

A bandwidth scheduling algorithm based on minimum interference traffic to maximize the network throughput

Authors analyze the algorithm as following steps. Calculate every uplink and downlink traffic. Find the collection of links and then compute the total

traffic of this collection. Select a path from SS to BS, and compute the whole traffic

which the path impacts. Make a collision-free scheduling according to routing tree

and link interference collections.

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Calculation of the links’ traffic-Calculation of the links’ traffic

Wireless links in Mesh are divided into uplinks and downlinks.

: the average bandwidth in every frame of uplinks which BS allocates for node i. : the average bandwidth in every frame of downlinks which BS allocates for node i. f : the index of current frame. Bui(j) : the bandwidth which node i was assigned in frame j of uplinks. Bdi(j) : the bandwidth which node i was assigned in frame j of downlinks. N : the number of frames.

uiB

)1(

1

N

jB

B

f

Nfjui

ui

)2(

1

N

jB

B

f

Nfjdi

di

diB

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Calculation of the links’ traffic-Calculation of the links’ traffic

The total bandwidth used by a particular node per frame is recorded in a local database.

For each frame passing, the BS updates the database by removing the least recent entry and adding the latest bandwidth usage.

BS can compute the usage of bandwidth for all the nodes.

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Calculation of the links’ traffic-Calculation of the links’ traffic

:the average uplink flow of every wireless link.

:the average downlink flow of every wireless link.

)3(}{

,

jCk

ukuiji BBUS

)4(}{

,

jCk

dkdiji BBDS

jiUS ,

jiDS ,

Cj : the child nodes of node j.node i is the response node of node j .

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree-Construction of Routing tree

This algorithm is looking for a path from current node to BS, if the whole traffic which is interfered by the path is lowest, it is the optimal path.

In a single-channel TDD network, any unicast transmission follows the principle.

No node may simultaneously transmit and receive data No neighbor of a sending node may receive data except rec

eiver No neighbor of a receiving node may transmit data except s

ender

0

1

5

6

4

2

37

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree-Construction of Routing tree

Interference modelInterference model

BS

Link

Range

DL4,7 UL0,4

DL0,4

UL0,1

DL0,1

UL0,2

DL0,2

DL0,3

DL1,5UL1,5 DL1,5UL1,5

UL0,3

UL4,7

Figure 2. Interference model of routing tree

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree-Construction of Routing tree

When node i communicates with node j, it can calculate the total interference traffic ISi, j :

)5(

}{},{

,

}{},{

,,

,,

,,

,,

,,

jiyx

jiyx

jiyx

jiyxDIDLUIDL

yx

DIULUIUL

yxji DSUSIS

)6(, jkjk PSISPS

{UIx,y} :the collection of links that ULx,y interferes{DIx,y} :the collection of links that DLx,y interferesPSk : the total interference traffic which the path impacts

0

i

j

k

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree-Construction of Routing tree

exampleexample

8

0

1

5

6

4

2

37

new

PS8=IS2,8+PS2

PS8=IS5,8+PS5

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree -Construction of Routing tree --reconstruct

Network flow changes with time, therefore PSk of any node k changes continuously.

To reconstruct the routing tree as the following principles:

Only adjust the leaf node after finishing the communications

Adjust leaf node as discerning interference traffic.

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree -Construction of Routing tree --reconstruct

Process 1Process 1

i

j

PSi

optimal response node

PSi’= ISj,i + PSj (excludes the traffic that SSi generated)

PSj

r

0 BS

select

)7(*,'

diuijiji BBkPSISPS

k : the time that every link in Pi

leaf node

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Construction of Routing tree -Construction of Routing tree --reconstruct

Process 2Process 2 If the difference between PSi and PS’i is little, then small flo

w fluctuation will cause adjustment repeatedly. Let confidence factor M (0,1) as the threshold.∈

Update interference traffic table and response node of current node.

otherwise, continue to compute next leaf node in the interference traffic table.

)8(*)1('ii PSMPS

Proposed Scheduling AlgorithmProposed Scheduling Algorithm -Collision-free scheduling algorithm-Collision-free scheduling algorithm

Simulations Simulations -assumptions-assumptions

Assume a single channel network with no bit errors. SSs ranges from 20 to 120. Random topology is generated in an L*L square.

2ndL n : the number of SSsd : the maximal transmission range between two nodes

Simulations Simulations -results-results

ConclusionConclusion

This paper proposes a bandwidth scheduling mechanism in WiMAX Mesh network based on minimum interference traffic.

It can adjust network topology with the change of flow, reduce the interference among the links, and make traffic of entire Mesh network load balance.