Fair and Efficient multihop Scheduling Algorithm for IEEE BWA Systems Daehyon Kim and Aura Ganz International Conference on Broadband Networks 2005

Outline Introduction Overview of IEEE Mesh Mode Fair and Efficient Scheduling Algorithm Simulation Results Conclusion

Introduction Demand for last-mile broadband access networks has grown significantly due to the rapid for Internet access and multimedia services Fixed broadband wireless access system based on IEEE standard may become a viable alternative to wired system

Introduction IEEE standard defines two topologies –PMP (Point-to-Multipoint) Topology –Mesh Topology Only PMP mode network where all nodes are directly connected to a central node is not always physical feasible

Introduction Goal –Emphasis is placed on maximizing channel utilization and providing equal channel access (Fair Access) to all the nodes on multihop communication which enabled by the mesh mode

Overview of IEEE Mesh Mode Definition and Terminology –The base Station (BS) –The Subscriber Station (SS) –The Neighbor Node –The Neighborhood –The Extended neighborhood –The Sponsor Node

Overview of IEEE Mesh Mode

Fair and Efficient Scheduling Algorithm Goal –Maximize the network throughput –Provide equal bandwidth to each node in the network How –The First Phase ： Node Ordering Ensure that all nodes get their fair share of the bandwidth Executed by the BS –The Second Phase ： Link Allocation Ensure that multiple nodes in transmission without collisions Executed by the SSs

Fair and Efficient Scheduling Algorithm Ensure that all nodes get their fair share of the bandwidth Ensure that multiple nodes in transmission without collisions

Node Ordering Algorithm Motivation –In the current standards, there is no specific algorithm for the node ordering. Purpose –Define a new ordering algorithm to ensure that all nodes get their fair share of the bandwidth

Node Ordering Algorithm Weight value W i of a node –Assigned by the BS during the network initialization –Reflect the priority of the node The weight can reflect the user’s QoS classes as defined in the service-level agreement –Definition The weight value of Node i The weight value of Child Nodes

Node Ordering Algorithm Satisfaction Index S i (x) –The ratio of the average bandwidth allocated in a given number of frames to the node’s weight –Definition

Link Allocation Algorithm Each SS computes the entire schedule by taking as inputs –The Order List Broadcast by the BS through the MSH-CSCF messages –The Bandwidth Requirement of each node Broadcast by the BS through the MSH-CSCH messages Therefore,each SS already complete information on the topology of the entire network

Link Allocation Algorithm Two Matrices –Schedule Matrix Contains a list of all nodes scheduled to transmit in a given timeslot Format ： –Collision Matrix Contains a list of all the neighbors and extended neighbors of the nodes that are scheduled to transmit i in that slot Format: the same to Schedule Matrix Time SlotNode ID

Link Allocation Algorithm –Input Information OrderList,Topology,# of timeslots for Node –For the timeslots that are allocated for transmission by a node The sending node is added to the Schedule Matrix All the nodes in its extended neighbor are added to the Collision Matrix –This Process is repeated until the SS finds its own timeslots or until no more nodes are left –Output Information Schedule Matrix

Example Network Topology –The vertex represents a node in the mesh network –The edge represents the relationship of the sponsor node or child

Example Order List = { 16, 17, 18, 19 } –Each Node require 2,3,1,2 timeslots, respectively Suppose the Schedule and Collision Matrices are initially empty –Node 16 is immediately added to the schedule Matrix for timeslot 0 and 1 –All the nodes in the extended neighborhood of node 16 are added to the Collision Matrix for the same timeslot Time SlotNode ID Time SlotNode ID 0BS,5,6,7,8,15,17,18,20,21 1 Schedule Matrix after scheduling node 16 Collision Matrix after scheduling node 16 All the nodes in the extended neighborhood of node 16 Node 16

Example Node 17 is scheduled in the timeslots 2, 3 and 4 –Node 17 is in the Collision Matrix for both 0 and 1 Node 18 is scheduled in the timeslot 5 –Node 18 is in the Collision Matrix for slots 0 to 4 Node 19 is scheduled in the timeslots 0 and 1 –Node 19 is not in the Collision Matrix Collision Matrix

Example Final Schedule MatrixFinal Collision Matrix

Simulation Results Simulation Tool ： C++ Packets were randomly generated by the mesh SSs and transmitted toward the BS in the upstream direction

Simulation Results

The Maximum throughput at the BS is 52.4 Mbps

Simulation Results Fairness Index = (the node ’ s throughput) ÷ (the average throughput) The Low variance indicates fair allocation of the channel resource

Conclusion This paper proposed a scheduling algorithm for mutlihop mesh IEEE fixed wireless network This algorithm is compatible with the standard