1. Multimedia Communications QoS Support for Multimedia in IEEE 802.16 Networks A Survey of Scheduling Techniques Aadil Zia Khan Department of Computer Science Lahore University of Management Sciences Email: 06030004@lums.edu.pk

2. IEEE 802.16 Networks (Introduction) One of the most promising solutions for wireless broadband access IEEE Project 802 working group 16 working towards building its standards Commercial forum Worldwide Interoperability for Microwave Access (WiMAX) was founded which includes more than 300 member companies WiMAX will provide the last mile internet access to residential users Especially useful in regions where wire lined infrastructure does not exist or can not be setup WiMAX will create an economical alternative to expensive leased line solutions for small and medium enterprises December 2004 Tsunami in Aceh, Indonesia - a success story

3. IEEE 802.16 Networks (Evolution) Version 802.16  Operated between 10-66 GHz  Specified a single carrier  Provided only Point-to-Multipoint (PMP) communication Version, 802.16a  Extended the frequency band to below 11 GHz thus enabling non line of sight communication  Two air interfaces; 256-carrier Orthogonal Frequency Division Multiplex (OFDM) and 2048-carrier Orthogonal Frequency Division Multiple Access (OFDMA) were provided  Allowed mesh based topology in addition to the existing PMP communication Version 802.16d published in June 2004  Incorporates all the previous versions to provide fixed BWA Version 802.16e accepted in 2005  Supports full mobility at speed up to 70-80 m/s

4. IEEE 802.16 Networks (Benefits) High Speed Access Wireless Broad Coverage Mobility

5. IEEE 802.16 Networks (Operation & Architecture) Operation Two types of nodes Tower / Base Station Receiver / Subscriber Station Network Architecture Two types of networks Point-to-Mulitpoint All the Subscriber Stations communicate only through the Base Station Mesh All the Subscriber Stations can communicate through the Base Station as well as directly with other Subscriber Stations

6. IEEE 802.16 Networks (Phy. Layer Communication) Frequency Division Duplexing The uplink and downlink channels are on different frequencies Both the Half-Duplex and Full-Duplex modes are supported Time Division Duplexing The uplink and downlink channels are on same frequencies but occur at different time intervals TDD frame has a fixed duration and is divided into uplink and downlink subframes TDD framing is adaptive

7. IEEE 802.16 Networks ( MAC Layer Communication ) Connection oriented architecture  Each communication belongs to a particular connection and within that connection to a particular service flow class Channel access  UL-MAP and DL-MAP transmitted at the start of each frame  UL-MAP defines slots for uplink channel access as well as data burst profiles  DL-MAP defines downlink data burst profiles

8. IEEE 802.16 Networks (Bandwidth Allocation & Request) SS Bandwidth Request Use contention request opportunities when polled by the BS Send a bandwidth request in an allotted time slot Piggyback a bandwidth request on a data packet BS Bandwidth Allocation Grant per subscriber station Grant per connection Allocation decision based on available resources, bandwidth request and Quality of Service

9. IEEE 802.16 Networks (What is Qos ) Quality of Service, an architecture which treats packets differently One flow receives preferential treatment at the cost of other flows Guaranteed services are provided to the end users QoS guarantees can be for the following  Delay  Delay Jitter  Reserved Bandwidth  Error Rate

10. IEEE 802.16 Networks ( QoS Classes ) For transmission, give preference to packets according to the service class they belong to WiMAX defines four services classes  Unsolicited Grant Service  For real time traffic with fixed packet size  Provides fixed size unsolicited data grants periodically  Real Time Polling Service  For real time traffic with variable packet size  BS offers unicast polls  Contention isnt allowed but piggybacking is permissible  Non Real Time Polling Service  For non realtime flows requiring variable sized data grants  BS offers unicast polls.  Contention as well as piggybacking is allowed  Best Effort  BS doesn’t offer unicast polls  SS reserves bandwidth by contention and piggybacking

11. IEEE 802.16 Networks ( Scheduling Requirements ) A good scheduling algorithm must catered to the following:  Bandwidth utilization must be efficient. For example, resources shouldn’t be allocated to a bad link.  The scheduler should be able to cater to different QoS requirements with a guarantee on the long term throughput for all connections.  The scheduler should be fair in both the long run as well as the short run.  The scheduler should have a low complexity so that the decision making is rapid.  The system should be scalable.

12. IEEE 802.16 Networks (Some Existing Scheduling Techniques) WiMAX standard does not specify the type of scheduling algorithm to be used and instead leaves it to the discretion of the vendor Using Earliest Due Date for real time and Weighted Fair Queuing for non real time streams Token Bank Fair Queuing - Priority is the ratio of the number of tokens exchanged between the bank and that connection and the reserved rate. A negative ratio means that the connection has used more than the assigned number of tokens. The SSs are served based on their token generation rate to guarantee throughput and latency and the remaining bandwidth is distributed according to the priority ranking Frame Registry Tree Scheduler - This is a tree based approach. First level is taken to be the root. The second level represents time frames immediately after the current time frame. The third level represents the available modulation types. The fourth level organizes all the connections according to the SS each SS has one uplink node and one downlink node at this level. The fifth level organizes the connections according to their QoS. The last level consists of leaves for each active connection queue. The algorithm schedules each packet at the last time frame before its deadline. Changes in the connection characteristics like modulation type or service type of the channel can be easily updated

13. IEEE 802.16 Networks ( Contd. ) Maximum Delay Utility - Marginal utility functions with respect to the average waiting time for the corresponding QoS requirements are used. The function used should be able to meet the deadline requirements for real time traffic, as well as control greediness in non real time traffic. Opportunistic Fair Scheduling - The scheduler firstly computes the fair share weights for each connection based on the knowledge it has of the average gains of the channels. The associated data rate of each SS is calculated by the adaptive modulation process in BS. The scheduler then sorts in descending order each SS based on its achievable rate. Transmissions follow this order. … And many others which will be described in detail in the final paper.

14. References [1] C. Cicconetti, L. Lenzini, and E. Mingozzi, “Quality of Service Support in IEEE 802.16 Networks” [2] http://en.wikipedia.org/wiki/WiMAX [3] S. Ryu, B. Ryu, H. Seo, and M. Shin, “Urgency and Efficiency based Wireless Downlink Packet Scheduling Algorithm in OFDMA System” [4] W. Park, S.Cho, and S. Bahk, “Scheduler Design for Multiple Traffic Classes in OFDMA Networks” [5] K. Vinay, N. Sreenivasulul, D. Jayaraml, and D. Das, “Performance Evaluation of End-to-end Delay by Hybrid Scheduling Algorithm for QoS in IEEE 802.16 Network” [6] J. Sun, Y. Yao, and H. Zhu, “Quality of Service Scheduling for 802.16 Broadband Wireless Access Systems” [7] W. K. Wong, H. Tang, S. Guo, and V. C. M. Leung, “Scheduling Algorithm in a Point-to-Multipoint Broadband Wireless Access Network” [8] S. A. Xergias, N. Passas, and L. Merakos, “Flexible Resource Allocation in IEEE 802.16 Wireless Metropolitan Area Networks” [9] H. S. Alavi, M. Mojdeh, and N. Yazdani, “A Quality of Service Architecture for IEEE 802.16 Standards” [10] J. Chen, W. Jiao, and H. Wang “A Service Flow Management Strategy for IEEE 802.16 Broadband Wireless Access Systems in TDD Mode” [11] N. Liu, X. Li, C. Pei, B. Yang, “Delay Character of a Novel Architecture for IEEE 802.16 Systems” [12] M. Mehrjoo, M. Dianati, X. Shen, K. Naik “Opportunistic Fair Scheduling for the Downlink of IEEE 802.16Wireless Metropolitan Area Networks” [13] G. Song, Y. Li, “Utility-Based Resource Allocation and Scheduling in OFDM-Based Wireless Broadband Networks” [14] F. De Pellegrini, D. Miorandi, E. Salvadori and N. Scalabrino. “QoS Support in WiMAX Networks: Issues and Experimental Measurements” [15] Christian Müller, Anja Klein, Frank Wegner, “Coverage Extension of WiMax Using Multihop in a Low User Density Environment” [16] D. Tarchi, R. Fantacci, and M. Bardazzi, “Quality of Service Management in IEEE 802.16 Wireless Metropolitan Area Networks” [17] X. Meng, “An Efficient Scheduling For Diverse QoS Requirements in WiMAX”

15. Q & A