IEEE 802'16 Air Interface for Fixed Broadband Wireless Access Systems

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 function2

• 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

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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

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Table 1 End-user Performance Expectations
Conversational/Real-time Services
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Table 2 End-user Performance Expectations
Interactive Services
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Table 3 End-user Performance Expectations
Streaming Services
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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.

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MAC Frame MAC Frame MAC Frame
Movable boundary
Broadcast Phase Downlink
Phase
DownlinkCarrier
Broadcast
Reserved
Movable boundary
Uplink Carrier
Uplink Phase Random
Access Phase
Reserved
Contention
Figure 4. FDD based 802.16 MAC Protocol
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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

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Contention free period repetition interval
(super frame)
Contention free period
Contention period
SIFS
SIFS
SIFS
SIFS
SIFS
SIFS
D2ack poll
D3ack poll
Beacon
D1poll
CF_End
U1ack
U2ack
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)

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WRR

• It is an extention of round robin scheduling

based on the static weight.
Counter Reset Cycle
1
1
1
VCC 1 (Source 1)
2
1
1
2
3
1
1
1
2
3
3
3
3
3
2
2
VCC 2 (Source 2)
3
WRR scheduler
3
3
3
VCC 3 (Source 3)
3
3
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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
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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 system4

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• 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 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

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Connection 1
Connection 1
Connection 2


Connection 11
WFQ Service Order
WFFQ Service Order
Figure 6. WFQ and WFFQ
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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,

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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
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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 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 a packet.
• Once the transmission is completed DCi is
  decremented by Li.

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• Deficit Round Robin Scheme

Qi
3500
initializing
(1st round)
DCi
3500
2800
7800
2000
serviced
1500
2800
7800
2000
Not serviced
(2nd round)
5000
2800
7800
2000
serviced
(3rd round)
700
2800
7800
2000
serviced
(4th round)
1400
2800
7800
2000
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Distrubuted Deficit Round Robin6

• Each connection is assigned a state variable
  called the DC(Deficit Counter)
• If the 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)

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• Distributed Deficit Round Robin Scheme

Qi
3500
initializing
(1st round)
DCi
3500
2800
7800
2000
serviced
1500
2800
7800
2000
serviced
-6300
2800
7800
2000
Not serviced
(2nd round)
-2800
2800
7800
2000
Not serviced
700
2800
7800
2000
(3rd round)
serviced
-2100
2800
7800
2000
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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

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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

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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.

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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.

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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.

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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 users 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

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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

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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/Bryan20Larish.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.