1. Fen Hou and Pin-Han Ho Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario Wireless Communications and Mobile Computing, vol. 10, no. 7, July, 2010 An Efficient Scheduling Scheme with Diverse Traffic Demands in IEEE 802.16 Networks

2. Agenda Introduction System Model Weighted Proportional Fair (WPF) Scheduling Performance Analysis Simulations Conclusions

3. 1. Four QoS Types of Service Flows 2. Common Solutions for Four QoS Types 3. Motivations 4. Contributions Introduction

4. Four QoS Types of Service Flows QoS Types DescriptionsExamplesConstraints Unsolicited Grant Service (UGS) Real-time constant-bit-rate (CBR) applications VoIP without silence suppression Delay, Delay jitter Real-time Polling Service (rtPS) Real-time variable-bit-rate (VBR) applications IPTV, video conferences Delay, Min. throughput, max. sustained throughput Non-real-time Polling Service (nrtPS) Delay-tolerant variable-bit- rate (VBR)applications FTP, Internet web services Min. throughput Best Effort (BE) Delay-tolerant variable-bit- rate (VBR)applications E-mailNone IEEE 802.16 has attracted extensive attentions from both industry and academia Provide QoS satisfaction for different applications

5. Common Solutions for Four QoS Types Packet scheduling plays a key role in fulfilling service differentiation and QoS provisioning Contains the packet transmission order decisions and resource allocation mechanism Common solutions for four QoS types UGS: periodically grant a fixed amount of resources rtPS: Largest weighted delay first [7] nrtPS, BE: Proportional fairness scheduling [12] provide a good balance between the system throughput and fairness

6. Motivations Conventional scheduling schemes based on proportional fairness are focused on equivalently allocating the available resource among the users which are rather efficient when the traffic demand of each user is homogeneous Traffic demands and channel conditions should be taken into considerations Example: BE traffic load/demand for an SS of office building could be much higher than that for an SS of resident house during the day time

7. Contributions Weighted Fairness Scheduling scheme is proposed An analytical model is developed to quantify the relation The weight of each SS Channel conditions Performance metrics System spectral efficiency Resource utilization, Throughput Fairness

8. 1. Channel Model 2. Adaptive Modulation and Coding (AMC) System Model

9. Channel Model The strength of received signals are decided by two effects Large-scale path-loss attenuation Determined by the geographical environment and distance between the receiver and the transmitter Small-scale fading Caused by multiple versions of a transmitted signal with different delay and occurs spontaneously in the time span with a random duration and depth Common used channel model for NLOS: Rayleigh flat fading channel The channel condition of each SS varies on the frame basis

10. Adaptive Modulation and Coding (AMC) An advanced technique at the physical layer to achieve a high throughput by adaptively adjusting the sending rate based on the channel conditions Based on the perceived SNR of an SS, the BS selects a proper modulation level and coding scheme for each SS.

11. 1. Formal Definition of WPF 2. Examples of WPF 3. Implementations of WPF Weighted Proportional Fair (WPF) Scheduling

12. Formal Definition of WPF The WPF scheduling scheme selects SSs for service based on the weighted relative channel conditions of SSs Formal definition of WPF The weighted relative channel condition of SS i The weight of SS i Average channel condition for SS i Instance channel condition for SS i

13. Example Suppose that six SSs in the IEEE 802.16 networks SS IDswiwi Instance channel condition for SS i Average channel condition for SS i The weighted relative channel condition of SS i 1512dB3dB5*(12/4)=15 21024dB6dB10*(24/6)=40 31554dB9dB15*(54/9)=90 4206dB12dB20*(6/12)=10 5255dB15dB24*(5/15)=8.x 63036dB18dB30*(36/18)=60 Selection order: SS 3  SS 6  SS 2  SS 1  SS 4  SS 5

14. Implementations of WPF The weight value of SS i (w i ) is equal to its traffic demands D i The framework of the scheduling module at the BS

15. 1. Service Probability of SS i 2. Spectral Efficiency 3. Throughput Performance Analysis

16. Service Probability of SS i The service probability of SS i is defined as the probability that SS i is selected for service in an arbitrary frame when the system is stable Given SS i is selected for service when its weighted x

17. Spectral Efficiency The theoretical upper bound of spectral efficiency can be obtained based on Shannon’s channel capacity Given SS i is selected for service when its weighted x

18. Spectral Efficiency Spectral efficiency is defined as the amount of information bits transmitted over a unit bandwidth The probability that SS i is selected for service in an arbitrary frame The theoretical upper bound of spectral efficiency based on Shannon’s channel capacity Total spectral efficiency achieved by all SSs is the sum of spectral efficiency of each SS

19. Throughput Since BE service is the lowest priority among the multiple service types, it only takes the leftover resource Let α be the time ratio available for the downlink transmission of BE flows, and denote the throughput of SS i for BE service

20. 1. Main Simulation Parameters 2. Service Probability for Each SS 3. Throughput 4. System Efficeincy Simulations

21. Main Simulation Parameters Simulator: Matlab One BS and 12 SSs Rayleigh flat fading channels

22. Service Probability for Each SS

23. Throughput

24. System efficiency

25. Conclusion WPF scheduling scheme for BE service in IEEE 802.16 networks is proposed An analytical model has been developed for investigating the performance of the proposed scheme in terms of Service probability of each SS Spectral efficiency Achieved throughput