1、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,802.3 Medium Access802.3 Physical
2、,802.2 Logical Link,802.1 Bridging,802.4 Medium Access802.4 Physical,802.5 Medium Access802.5 Physical,802.6 Medium Access802.6 Physical,802.11 Medium Access802.11 Physical,802.12 Medium Access802.12 Physical,802.16 Medium Access802.16 Physical,Data Link Layer,Physical Layer,Fig. 1 The relationship
3、between the standard and other members of the family,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.,IEEE 802.16,S
4、S,SS,SS,BS,Figure 1. Wireless Access Network,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 provid
5、ing alternatives to wireline broadband access Main advantage : fast deployment, dynamic sharing of radio resources and low cost,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 d
6、ata rates in excess of 120 Mbps 2 -11 GHz IEEE Standards Association Project P802.16a Approved as an IEEE standard on Jan 29, 2003,IEEE 802.16,IEEE 802.16 MAC layer function2,Transmission scheduling : Controls up and downlink transmissions so that different QoS can be provided to each user Admission
7、 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 al
8、location, error rates, delay and jitter,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),Basic Services,UGS(Unsolicited Grant Service) Supports real-time service flows th
9、at 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,Basic
10、 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,Table 1 End-user Performance Expectations Conversatio
11、nal/Real-time Services,Table 2 End-user Performance Expectations Interactive Services,Table 3 End-user Performance Expectations Streaming Services,FDD based MAC protocol 3,Downlink Broadcast phase : The information about uplink and downlink structure is announced. DL-MAP(Downlink Map) DL-MAP defines
12、 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.,MAC Frame MAC Frame MAC
13、 Frame,Broadcast Phase Downlink Phase,Movable boundary,DownlinkCarrier,Uplink Carrier,Uplink Phase Random Access Phase,Broadcast,Reserved,Movable boundary,Reserved,Contention,Figure 4. FDD based 802.16 MAC Protocol,Downlink Subframe,Uplink Subframe,DL-MAP n-1,UL-MAP n-1,Frame n-1,Frame n,Round trip
14、delay + T_proc,Bandwidth request slots,Figure 3. Time relevance of PHY and MAC control information,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
15、 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
16、 Sense Multiple Access with Collision Avoidance,Beacon,D1+poll,U1+ack,D2+ack +poll,U2+ack,SIFS,SIFS,SIFS,SIFS,SIFS,SIFS,D3+ack +poll,CF_End,PICF,Contention free period,Contention period,Contention free period repetition interval (super frame),Figure 5. Point Coordinator Function in IEEE 802.11 Stand
17、ard,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(Wor
18、st-case Fair weighted Fair Queueing) DRR(Deficit Round Robin) DDRR(Distributed Deficit Round Robin),1,1,1,VCC 1 (Source 1),2,2,VCC 2 (Source 2),3,3,3,VCC 3 (Source 3),3,3,2,1,3,1,2,3,1,1,1,2,3,3,3,3,3,WRR scheduler,Counter Reset Cycle,It is an extention of round robin scheduling,based on the static
19、weight.,WRR,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
20、-arrival : 5 units,Connection 3 Average inter-arrival : 5 units,First-Come-First-Served service order,Virtual times,Virtual Clock service order,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 n
21、on-empty queueThe service rate for a non-empty queue i WFQ : picks the first packet that would complete service in the corresponding FFQ system4,WFFQ : picks the first packet that would complete service among the set of packets that have started service in the corresponding FFQ system4 Example All p
22、ackets have the same size 1 and link speed is 1Guaranteed rate for connection 1 : 0.5Guaranteed rate for connection 2-11 : 0.05Connection 1 sends 11 back-to-back packets at time 0Connection 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
23、completion time of connection 2 11 : 20,Connection 1,Connection 1,Connection 2,WFQ Service Order,Connection 11,WFFQ Service Order,Figure 6. WFQ and WFFQ,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 r
24、ate 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, 90
25、2, 903, ,Connection 1,Connection 1,Connection 2,Virtual Clock Service Order,WFQ Service Order,898,900,902,904,Figure 7. WFQ and Virtual Clock,898,900,902,904,Deficit Round Robin5,Each connection is assigned a state variable called the DC(Deficit Counter). At the start of each round, DCi of queue i i
26、s 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 a packet. Once the transmission is completed DCi is decremented by Li.,Deficit Round Robin Scheme,Qi,DCi,3500,3500,2800,7800,2
27、000,1500,5000,700,1400,2800,7800,2000,2800,7800,2000,2800,7800,2000,2800,7800,2000,initializing,(1st round),serviced,Not serviced,serviced,(2nd round),serviced,(3rd round),(4th round),Distrubuted Deficit Round Robin6,Each connection is assigned a state variable called the DC(Deficit Counter) If the
28、value of the DCi is positive then the scheduler allows the ith queue to send a packet. 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),Distributed Defici
29、t Round Robin Scheme,Qi,DCi,3500,3500,2800,7800,2000,1500,-6300,-2800,700,-2100,2800,7800,2000,2800,7800,2000,2800,7800,2000,2800,7800,2000,2800,7800,2000,initializing,(1st round),serviced,serviced,Not serviced,(2nd round),Not serviced,(3rd round),serviced,Uplink scheduling: Responsible for the effi
30、cient 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,Downlink/Uplink Scheduling,Bandwidth allocation and request mechanisms,The method by which the SS(Subscr
31、iber 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 Ide
32、ntifier) 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,Bandwidth allocation and request mechanisms,UGS : The BS provides fixed size bandwidth at periodi
33、c 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.,Bandwidth alloc
34、ation 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.,Contention Resolution,Collisions may occur during Request intervals. Contention resolution
35、 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
36、 opportunities that the SS shall defer before transmitting If the contention transmission fails, the SS increases its backoff window by a factor of two.,The 4Gmobile system,4Gmobile system : Fourth-generation mobile wireless communications The vision of the 4Gmobile system Providing broadband wirele
37、ss access Providing Internet-based communications Ensuring seamless services provisioning across a multitude of wireless systems and networks Providing optimum delivery of the users wanted service via the most appropriate network available IEEE 802.16e Air interface for Fixed and Mobile Broadband Wi
38、reless Access Systems Started at December 11, 2002,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,References,1 IEEE Std 802.16-2001. 2 B. Larish, “The MAC layer i
39、n 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.
40、 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 Multimed
41、ia 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.,
