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IEEE 802.16 Air Interface for Fixed Broadband Wireless Access Systems

IEEE 802.16 Air Interface for Fixed Broadband Wireless Access Systems. Kwangho Kook. IEEE 802 Standard. 802.3 : CSMA/CD (Ehernet) 802.4 : Token Bus 802.5 : Token Ring 802.6 : MAN 802.11 : Wireless LAN 802.12 : Gigabit LAN 802.16 : Fixed Broadband Wireless Access System.

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IEEE 802.16 Air Interface for Fixed Broadband Wireless Access Systems

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  1. IEEE 802.16Air Interface for Fixed Broadband Wireless Access Systems Kwangho Kook

  2. IEEE 802 Standard • 802.3 : CSMA/CD (Ehernet) • 802.4 : Token Bus • 802.5 : Token Ring • 802.6 : MAN • 802.11 : Wireless LAN • 802.12 : Gigabit LAN • 802.16 : Fixed Broadband Wireless Access System

  3. 802.2 Logical Link Data Link Layer 802.1 Bridging 802.3 Medium Access 802.3 Physical 802.4 Medium Access 802.4 Physical 802.5 Medium Access 802.5 Physical 802.6 Medium Access 802.6 Physical 802.11 Medium Access 802.11 Physical 802.12 Medium Access 802.12 Physical 802.16 Medium Access 802.16 Physical Physical Layer Fig. 1 The relationship between the standard and other members of the family

  4. IEEE 802.16 • 802.16 consists of the access point, BS(Base Station) and SSs(Subscriber Stations) • All data traffic goes through the BS, and the BS can control the allocation of bandwidth on the radio channel. • 802.16 is a Bandwidth on Demand system.

  5. SS SS BS SS Figure 1. Wireless Access Network

  6. IEEE 802.16 [1] • Scope : • Specifies the air interface, MAC (Medium Access Control), PHY(Physical layer) • Purpose : • to enable rapid worldwide deployment of cost-effective broadband wireless access products • to facilitate competition in broadband access by providing alternatives to wireline broadband access • Main advantage : • fast deployment, dynamic sharing of radio resources and low cost

  7. IEEE 802.16 • The spectrum to be used • 10 - 66 GHz licensed band • Due to the short wavelength • Line of sight is required • Multipath is negligible • Channels 25 or 28 MHz wide are typical • Raw data rates in excess of 120 Mbps • 2 -11 GHz • IEEE Standards Association Project P802.16a • Approved as an IEEE standard on Jan 29, 2003

  8. IEEE 802.16 MAC layer function[2] • Transmission scheduling : • Controls up and downlink transmissions so that different QoS can be provided to each user • Admission control : • Ensures that resources to support QoS requirements of a new flow are available • Link initialization • Scans for a channel, synchronizes the SS with the BS, performs registration, and various security issues. • Support for integrated voice/data connections • Provide various levels of bandwidth allocation, error rates, delay and jitter

  9. IEEE 802.16 MAC layer function • Fragmentation : • Sequence number in the MAC header is used to reassemble at the receiver • Retransmission : • Implement an ARQ(Automatic Repeat Request)

  10. Basic Services • UGS(Unsolicited Grant Service) • Supports real-time service flows that generate fixed size data packets on a periodic basis, such as T1/E1 and Voice over IP • The BS shall provide fixed size slot at periodic intervals. • rtPS(Real-Time Polling Service) • Supports real-time service flows that generate variable size data packets on a periodic basis, such as MPEG video

  11. Basic Services • nrtPS(Non-Real-Time Polling Service) • Supports non real-time service flows that generate variable size data packets on a regular basis, such as high bandwidth FTP. • BE(Best Effort service) • Provides efficient service to best effort traffic

  12. Table 1 End-user Performance Expectations – Conversational/Real-time Services

  13. Table 2 End-user Performance Expectations – Interactive Services

  14. Table 3 End-user Performance Expectations – Streaming Services

  15. FDD based MAC protocol [3] • Downlink • Broadcast phase : The information about uplink and downlink structure is announced. • DL-MAP(Downlink Map) • DL-MAP defines the access to the downlink information • UL-MAP(Uplink Map) • UL-MAP message allocates access to the uplink channel • Uplink • Random access area is primarily used for the initial access but also for the signaling when the terminal has no resources allocated within the uplink phase.

  16. MAC FrameMAC Frame MAC Frame Movable boundary DownlinkCarrier Broadcast PhaseDownlink Phase Broadcast Reserved Movable boundary Uplink Carrier Uplink PhaseRandom Access Phase Reserved Contention Figure 4. FDD based 802.16 MAC Protocol

  17. Frame n-1 Frame n DL-MAP n-1 UL-MAP n-1 Downlink Subframe Uplink Subframe Round trip delay + T_proc Bandwidth request slots Figure 3. Time relevance of PHY and MAC control information

  18. 802.11 • Wireless LAN Medium Access Control (MAC) and Physical Layer(PHY) Specifications • 802.11a : up to 54 Mbps in 5GHz band • 802.11b : up to 11 Mbps in 2.4GHz band • 802.11 MAC protocol supports two kinds of access method • PCF(Point Coordinated Function) • Based on the polling controlled by AP(Access Point) • Intended for transmission of real-time traffic as well as that of asynchronous data traffic • DCF(Distributed Coordinated Function) • Designed for asynchronous data transmission • Based on CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance

  19. Contention free period repetition interval (super frame) Contention free period Contention period SIFS SIFS SIFS SIFS SIFS SIFS D2+ack +poll D3+ack +poll Beacon D1+poll CF_End U1+ack U2+ack PICF Figure 5. Point Coordinator Function in IEEE 802.11 Standard

  20. Downlink/Uplink Scheduling • Radio resources have to be scheduled according to the QoS(Quality of Service) parameters • Downlink scheduling: • the flows are simply multiplexed • the standard scheduling algorithms can be used • WRR(Weighted Round Robin) • VT(Virtual Time) • WFQ(Weighted Fair Queueing) • WFFQ(Worst-case Fair weighted Fair Queueing) • DRR(Deficit Round Robin) • DDRR(Distributed Deficit Round Robin)

  21. WRR • It is an extention of round robin scheduling based on the static weight. Counter Reset Cycle VCC 1 (Source 1) 1 1 1 2 1 3 3 1 3 2 1 3 3 1 3 2 1 VCC 2 (Source 2) 2 2 3 WRR scheduler VCC 3 (Source 3) 3 3 3 3 3

  22. VT • VT : aims to emulate the TDM(Time Division Multiplexing) system [4] • connection 1 : reserves 50% of the link bandwidth • connection 2, 3 : reserves 20% of the link bandwidth Connection 1 Average inter-arrival : 2 units Connection 1 Average inter-arrival : 2 units Connection 2 Average inter-arrival : 5 units Connection 3 Average inter-arrival : 5 units First-Come-First-Served service order Virtual times Virtual Clock service order

  23. WFQ and WFFQ • FFQ(Fluid Fair Queue) : head-of-the line processor sharing service discipline • : guaranteed rate to connection i • C : the link speed • : the set of non-empty queue • The service rate for a non-empty queue i • WFQ : picks the first packet that would complete service in the corresponding FFQ system[4]

  24. WFFQ : picks the first packet that would complete service among the set of packets that have started service in the corresponding FFQ system[4] • Example • All packets have the same size 1 and link speed is 1 Guaranteed rate for connection 1 : 0.5 Guaranteed rate for connection 2-11 : 0.05 Connection 1 sends 11 back-to-back packets at time 0 Connection 2-11 sends 1 packet at time 0 • The completion time of connection 1 : 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22 • The completion time of connection 2 – 11 : 20

  25. Connection 1 Connection 1 Connection 2 … … Connection 11 WFQ Service Order WFFQ Service Order Figure 6. WFQ and WFFQ

  26. VT and WFQ • All packets are fixed size and require exactly one second to service • Starting at time zero, 1000 packets from connection 1 arrive at a rate of 1 packet/second • Starting at time 900, 450 packets from connection 2 arrive at a rate of 1 packet/second • The completion times of the 901, 902, 903, … packets of connection 1 in FFQ system are 1802, 1904, 1806, … • The completion times of the 1, 2, 3, … packets of connection 2 in FFQ system are 901, 902, 903, …

  27. Connection 1 Connection 1 Connection 2 Virtual Clock Service Order 898 900 902 904 WFQ Service Order 898 900 902 904 Figure 7. WFQ and Virtual Clock

  28. Deficit Round Robin[5] • Each connection is assigned a state variable called the DC(Deficit Counter). • At the start of each round, DCi of queue i is incremented by a specific service share(quantum) • If the length of the head of the line packet, Li, is less than or equal to DCi,, the scheduler allows the ith queue to send apacket. • Once the transmission is completed DCi is decremented by Li.

  29. Qi 3500 initializing (1st round) DCi 3500 2800 7800 2000 • Deficit Round Robin Scheme serviced 2800 7800 2000 1500 Not serviced (2nd round) 2800 7800 2000 5000 serviced (3rd round) 2800 7800 2000 700 serviced (4th round) 2800 7800 2000 1400

  30. Distrubuted Deficit Round Robin[6] • Each connection is assigned a state variable called the DC(Deficit Counter) • If the value of the DCiis positive then the scheduler allows the ith queue to send apacket. • Once the transmission is completed DCi is decremented by Li, the length of the transmitted packet . • At the start of the subsequent rounds, DCi is incremented by a specific service share(quantum)

  31. Qi 3500 initializing (1st round) DCi 3500 2800 7800 2000 • Distributed Deficit Round Robin Scheme serviced 2800 7800 2000 1500 serviced 2800 7800 2000 -6300 Not serviced (2nd round) 2800 7800 2000 -2800 Not serviced 2800 7800 2000 700 (3rd round) serviced 2800 7800 2000 -2100

  32. Downlink/Uplink Scheduling Uplink scheduling: • Responsible for the efficient and fair allocation of the resources(time slots) in the uplink direction • Uplink carrier : • Reserved slots • contention slots(random access slots) • The standard scheduling algorithms can be used

  33. Bandwidth allocation and request mechanisms • The method by which the SS(Subscriber Station) can get the bandwidth request message to the BS(Base Station) • Unicast • When an SS is polled individually, no explicit message is transmitted to poll the SS. • The SS is allocated, in the UP-MAP(Uplink Map), bandwidth sufficient for a bandwidth request. • Multicast • Certain CID(Connection Identifier) are reserved for multicast groups and for broadcast messages. • An SS belonging to the polled group may request bandwidth during any request interval allocated to that CID in the UP-MAP • Broadcast

  34. Bandwidth allocation and request mechanisms • UGS : • The BS provides fixed size bandwidth at periodic intervals to the UGS. • The SS is prohibited from using any contention request opportunities. • The BS shall not provide any unicast request opportunities. • rtPS • The BS provides periodic unicast request opportunities. • The SS is prohibited from using any contention request opportunities.

  35. Bandwidth allocation and request mechanisms • nrtPS • The BS provides timely unicast request opportunities. • The SS is allowed to use contention request opportunities. • BE • The SS is allowed to use contention request opportunities.

  36. Contention Resolution • Collisions may occur during Request intervals. • Contention resolution is based on a truncated binary exponential backoff, with the initial backoff window and the maximum backoff window controlled by the BS. • A truncated binary exponential backoff • The SS shall randomly select a number within its backoff window. • This value indicates the number of contention transmission opportunities that the SS shall defer before transmitting • If the contention transmission fails, the SS increases its backoff window by a factor of two.

  37. The 4Gmobile system • 4Gmobile system : Fourth-generation mobile wireless communications • The vision of the 4Gmobile system • Providing broadband wireless access • Providing Internet-based communications • Ensuring seamless services provisioning across a multitude of wireless systems and networks • Providing optimum delivery of the user’s wanted service via the most appropriate network available • IEEE 802.16e • Air interface for Fixed and Mobile Broadband Wireless Access Systems • Started at December 11, 2002

  38. Future Study • Study on the scheduling method • Downlink scheduling method • Uplink scheduling method • Study on the relevant Fragment Size • Study on the criteria whether packing or non-packing

  39. References [1] IEEE Std 802.16-2001. [2] B. Larish, “The MAC layer in Broadband Wireless Access Networks,” http://www.eas.asu.edu/trace/eee459/Bryan%20Larish.doc [3] J. Bostie, G. Kandus, “MAC Scheduling for Fixed Broadband Wireless Access Systems, COST263_v0_0.doc [4] Hui Zhang, “Service disciplines for guaranteed performance service in packet-switching networks,” Proc. IEEE, vol. 83, Oct. 1995. [5] M. Shreedhar and G. Varghese, “Efficient Fair Queueing using deficit round robin,” IEEE/ACM Transactions on Networking, Vol. 4, No. 3, June 1996, pp. 375-385. [6] R.S. Ravindra, D. Everitt, and L.L.H. Andrew, “Fair Queueing Scheduler for IEEE 802.11 Based Wireless Multimedia Networks, http://www.ee.mu.oz.au/staff/lha/abstract/wlan_mmt99.html [7] S. Lu, V. Bharghavan, and R. Srickant, “Fair Scheduling in Wireless Packet Networks,” IEEE Trans. on Networking, Vol. 7, No. 4 August 1999. [8] Y. Cao and V.O.K. Li, “Scheduling Algorithms in Broad-band Wireless Networks,” Proc. IEEE, Vol. 89, No.1, January 2001, pp 76-87.

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