1. Performance Evaluation of Scheduling in IEEE 802.16 based Wireless Mesh Networks Bo Han, Weijia Jia,and Lidong Lin Computer Communications, 2007 Mei-zhen Chen

2. Outline  Introduction  Background on IEEE 802.16 Mesh Mode  Our Scheduling Scheme Problem definitions and Modeling Problem definitions and Modeling ransmission-ree cheduling Algorithm Transmission-Tree Scheduling Algorithm Example Example Performance Analysis Performance Analysis  Simulation  Conclusion

3. Introduction (1/4)  Traditional broadband access is offered through digital subscriber line (xDSL), cable or T1 networks.  Each of these techniques has different cost, performance, and deployment trade-offs.   Fix Broadband Wireless Access (FBWA) systems are gaining extensive acceptance for wireless multimedia services with several advantages.

4. Introduction (2/4)  Compared with the traditional wireless ad hoc networks WMNs (Wireless Mesh Networks) are not isolated self- configured networks. WMNs (Wireless Mesh Networks) are not isolated self- configured networks.. WMNs serve as access networks that employ multihop forwarding to relay traffic. Traffic patterns may be asymmetric Traffic patterns may be asymmetric The links in WMNs have much longer duration times. The links in WMNs have much longer duration times. Most applications of WMNs are broadband services with various QoS requirements. Most applications of WMNs are broadband services with various QoS requirements.

5. Introduction (3/4)  In the mesh mode, scheduling will impact the system performance.  two kinds of scheduling Broadcast scheduling Broadcast scheduling The entities scheduled are the themselves.The entities scheduled are the nodes themselves. The transmission of a node is intended for, and must be received collision-free by all of its neighbors.The transmission of a node is intended for, and must be received collision-free by all of its neighbors. Link scheduling The between the nodes are scheduled.The links between the nodes are scheduled. The transmission of a node is intended for a particular neighbor, and it is required that there be no collision at this receiver.The transmission of a node is intended for a particular neighbor, and it is required that there be no collision at this receiver.

6. Introduction (4/4)  Authors proposed a collision-free centralized scheduling algorithm for IEEE 802.16 mesh mode.   The proposed scheme considers some distinct features of WMNs the function of access networks the inherent relay model  considers some important performance metrics Fairness Fairness channel utilization channel utilization transmission delay transmission delay

7. Background on IEEE 802.16 Mesh Mode (1/4)  P2MP a central Base Station (BS) a central Base Station (BS) the only transmitter operating in the downlink (from BS to SS)the only transmitter operating in the downlink (from BS to SS) a set of Subscriber Stations (SSs). a set of Subscriber Stations (SSs). share the uplink to the BS on a demand basisshare the uplink to the BS on a demand basis  Mesh mode Nodes are organized in an ad hoc fashion. Nodes are organized in an ad hoc fashion. Each node can traffic for other nodes and is provisioned. Each node can relay traffic for other nodes and QoS is provisioned. A direct connection to backhaul services outside the mesh network is termed the Mesh BS. A direct connection to backhaul services outside the mesh network is termed the Mesh BS. Uplinks and downlinks are defined as the directions to and from the Mesh BS, respectively.

8. Background on IEEE 802.16 Mesh Mode (2/4)  Mesh from P2MP mode  Mesh differs from P2MP mode Traffic can be routed through other SSs and can occur directly between the SSs Traffic can be routed through other SSs and can occur directly between the SSs Only supports Time Division Duplex (TDD) for uplink and downlink traffic. Only supports Time Division Duplex (TDD) for uplink and downlink traffic. For the transmission, several SSs share the channel in a TDMA (Time Division Multiple Access) fashion. For the transmission, several SSs share the channel in a TDMA (Time Division Multiple Access) fashion.

9. Background on IEEE 802.16 Mesh Mode (3/4)  A new SS(u) entering IEEE 802.16 based WMN obeys the following procedures: for MSH-NCFG (Mesh Network Configuration) messages u scans for MSH-NCFG (Mesh Network Configuration) messages establish coarse synchronization with the network shall build a physical neighbor list u shall build a physical neighbor list From this list, u select a Sponsoring Node (SN) From this list, u select a Sponsoring Node (SN) relays MAC messages to and from the BS for urelays MAC messages to and from the BS for u Registration Registration

10. Background on IEEE 802.16 Mesh Mode (4/4)

11. Our Scheduling Scheme -Problem definitions and modeling (1/4)  the of a link scheduling  the cycle of a link scheduling the time needed to transmit all the traffic to/from the BS in the WMN the time needed to transmit all the traffic to/from the BS in the WMN  the of a link scheduling  the length of a link scheduling the number of time slots in the cycle the number of time slots in the cycle  channel utilization ratio (CUR) the ratio between the number of occupied time slots and the number of available time slots the ratio between the number of occupied time slots and the number of available time slots  the average transmission delay the number of time slots between the time slot when a packet is transmitted by the source SS and the time slot when the same packet arrives at the destination the number of time slots between the time slot when a packet is transmitted by the source SS and the time slot when the same packet arrives at the destination

12. Our Scheduling Scheme -Problem definitions and modeling (2/4)  Scheduling problem how to assign time slots to transmission links in IEEE 802.16 based WMNs so as how to assign time slots to transmission links in IEEE 802.16 based WMNs so as ( 1) to reduce the length of scheduling (2) to improve the channel utilization ratio (3) to decrease the transmission delay

13. Our Scheduling Scheme -Problem definitions and modeling (3/4)  transmissions  transmissions may collide in two ways in wireless networks: Primary interference (the transmission/reception constraint) Primary interference (the transmission/reception constraint) occurs when a node has to do more than one thing in a single time slotoccurs when a node has to do more than one thing in a single time slot Secondary interference (the interference-free constraint) Secondary interference (the interference-free constraint) occurs when a receiver R tuned to a particular transmitter T

14. Our Scheduling Scheme -Problem definitions and modeling (4/4) Nei[u] ： the closed one-hop neighbor set of node u Sons(v) ： the set of node v’s sponsored nodes transmission link interference link interfered nodes ： (1) Nei[B]-{A} ： B,C,P Example ： uplink (2) Sons(Nei[A]-{B}) ： E,F,N

15. Our Scheduling Scheme -ransmission-ree cheduling Algorithm (1/4) Our Scheduling Scheme -Transmission-Tree Scheduling Algorithm (1/4)  A SS is assigned  A SS is assigned service token based on its traffic demand. allocate time slots to each link proportionally allocate time slots to each link proportionally fairness fairness no nodes will be starved no nodes will be starved   Each time after a link is assigned a time slot, the service token of the transmitter is decreased by one that service token of the receiver is increased by one

16. Our Scheduling Scheme -ransmission-ree cheduling Algorithm (2/4) Our Scheduling Scheme -Transmission-Tree Scheduling Algorithm (2/4)  Suppose totally n SSs totally n SSs tr i ： the traffic demand of SS i tr i ： the traffic demand of SS i g ： the greatest common divisor (GCD) of tr 1, tr 2, … tr n g ： the greatest common divisor (GCD) of tr 1, tr 2, … tr n token i ： the service token assigned to SS i token i ： the service token assigned to SS i {token i } ： ST {token i } ： ST

17. Our Scheduling Scheme -ransmission-ree cheduling Algorithm (3/4) Our Scheduling Scheme -Transmission-Tree Scheduling Algorithm (3/4)  k ： the length of the resulted scheduling  the inputs the scheduling tree the scheduling tree T the service token set the service token set ST  the output an n×k scheduling matrix S an n×k scheduling matrix S S ij = 1 ： node i is scheduled in time slot j S ij = 0 ： otherwise

18. Our Scheduling Scheme -ransmission-ree cheduling Algorithm (4/4) Our Scheduling Scheme -Transmission-Tree Scheduling Algorithm (4/4) available ： the service token of the transmitter of a link is nonzero idle ： otherwise scheduled ： selected link interfered ： all the conflicting neighboring links of selected link Selection criteria ： (1) random (2) min interference (3) nearest to BS (4) farthest to BS

19. Our Scheduling Scheme - Our Scheduling Scheme -Example CUR ： 10.5% CUR ： 11.8% Hops = 3 interfered

20. Our Scheduling Scheme -Performance Analysis(1/2) Proposition 1 ： Let hop i to be the hop count of SS i to BS, the length of scheduling k is at most O(n). Proof ： The total number of occupied time slots is get the BS shall gather traffic demands from all the SSs within a certain hop range HR threshold  hop i ≤ HR threshold  hop i ≤ HR threshold the traffic demand of each SS will also have the maximal value which should be a constant. Thus, k ≤O(n)

21. Our Scheduling Scheme -Performance Analysis(2/2) Proposition 2 ： The of the proposed scheduling algorithm is of O(n 2 ). The time complexity of the proposed scheduling algorithm is of O(n 2 ). Proposition 3 ： The channel utilization ratio CUR

22. Simulation -Performance metrics   Three parameters are set up for the performance evaluation ： the length of scheduling k CUR the average transmission delay

23. Simulation -setup  A C-coded custom simulator  selection criteria Random, Channel, Furthest, Nearest Random, Channel, Furthest, Nearest  a square simulation area of size ： 100 by 100 units.  A given number of SSs were randomly and uniformly distributed.  Each SS has a fixed transmission range r.  The BS is placed at the center of the simulation area  running these algorithms on 300 connected graphs  HR threshold is assigned to be 7.

24. Simulation –result(1/3)

25. Simulation –result(2/3)

26. Simulation –result(3/3)

27. Conclusion  Authors proposed a centralized scheduling algorithm for IEEE 802.16 based WMNs.  Authors proposed a collision-free centralized scheduling algorithm for IEEE 802.16 based WMNs.  The model is integrated into this scheduling algorithm.  The relay model is integrated into this scheduling algorithm.  The scheduling scheme takes, and into consideration.  The scheduling scheme takes fairness, channel utilization and transmission delay into consideration.   We use the length of scheduling, channel utilization ratio and transmission delay to evaluate the performance of the proposed scheduling algorithm. reduce the length of scheduling transmission delay improve the channel utilization ratio