This document provides an overview of the 802.16/WiMAX standards for broadband wireless access. It describes the history and applications of the standards, the network architecture including frame structure, scheduling types, and quality of service mechanisms. Key physical layer technologies like OFDM, OFDMA and management messages are summarized. Early large-scale deployments like WiBro in South Korea are also mentioned.

1. 802.16/WiMAX
EECS 228a, Spring 2006

2. References
• IEEE 802.16-2004 (802.16REVd)
• IEEE 802.16-2005 (802.16e)
• Intel’s Whitepapers, 2004 (
http://www.intel.com/technology/itj/2004/volume08issue03/)
• “IEEE Standard 802.16: A Technical Overview of the
WirelessMAN Air Interface for Broadband Wireless Access,”
C. Eklund et al., IEEE Communication Magazine, June 2002
• “Broadband Wireless Access with 802.16/WiMax: Current
Performance Benchmarks and Future Potential,” A. Ghosh et
al., IEEE Communication Magazine, Feb 2005
• “Wireless Communication Standards: A Study of IEEE
802.11, 802.15, and 802.16,” T. Cooklev, 2004

3. Electromagnetic Spectrum
Source: LBL

4. 802.16 Standards
History
802.16a
(Jan 2003)
• Extension for 2-11 GHz: Targeted for non-
line-of-sight, Point-to-Multi-Point applications
like “last mile” broadband access
802.16
(Dec 2001)
• Original fixed wireless broadband air Interface
for 10 – 66 GHz: Line-of-sight only, Point-to-
Multi-Point applications
802.16c
(2002)
802.16 Amendment
WiMAX System Profiles
10 - 66 GHz
802.16REVd
(802.16-2004)
(Oct 2004)
• Adds WiMAX System Profiles and Errata for
2-11 GHz
802.16e
(802.16-2005)
(Dec 2005)
• MAC/PHY Enhancements to support
subscribers moving at vehicular speeds
• First standard based on proprietary implementations of DOCSIS/HFC
architecture in wireless domain

5. Applications of 802.16
Standards

6. 802.16 Network Architecture

7. 802.16 Network Architecture (2)

8. Scope of 802.16 Standards

9. Physical Layer Summary
Designation Applicability MAC Duplexing
WirelessMAN-SC 10-66 GHz Licensed Basic TDD, FDD, HFDD
WirelessMAN-SC 2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
WirelessMAN-OFDM
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
WirelessMAN-OFDMA
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD

10. Channel Characteristics
• 10-66 GHz
– Very weak multipath components (LOS is
required)
– Rain attenuation is a major issue
– Single-carrier PHY
• 2-11 GHz
– Multipath
– NLOS
– Single and multi-carrier PHYs

11. Wireless Performance
(as of 2003)
Source: S. Viswanathan, Intel

12. OFDMA Subchannels
• A subset of subcarriers is grouped together to form a subchannel
• A transmitter is assigned one or more subchannels in DL direction
(16 subchannels are supported in UL in OFDM PHY)
• Subchannels provide interference averaging benefits for aggressive frequency
reuse systems

13. OFDM Basics
Orthogonal Subcarriers
Cyclic Prefix in Frequency Domain Cyclic Prefix in Time Domain

14. Equalizers are avoided in
OFDM
time
Cyclic Prefix Useful Symbol Time
time
Note: All signals & multipath over a
useful symbol time are from the same
symbol & add constructively (no ISI)
Note: dashed lines
represent multipath
Narrow bandwidth  long symbol times  all significant multipaths arrive within a symbol
time minimizing ISI  no equalization  low complexity
Tx Signal
Rx Signal
Source: Lucent

15. Tradeoffs of FFT size
• The FFT size determines the number of sub-
carriers in the specified bandwidth
• Larger FFT sizes lead to narrower subcarriers and
smaller inter-subcarrier spacing
–More susceptibility to ICI, particularly in high Doppler
(Note: Doppler shift for 125 km/hr for operation at 3.5
GHz is v/λ = 35 m/sec/0.086 m = 408 Hz)
–Narrower subcarriers lead to longer symbol times 
less susceptibility to delay spread
• Smaller FFT sizes the opposite is true
Source: Lucent

16. OFDMA Scalability
• Supports s wide range of frame sizes (2-20 ms)
Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”

17. Time Division Duplexing (TDD)

18. General Downlink Frame
Structure
• Downlink Interval Usage Code (DIUC) indicates burst profile

19. General Uplink Frame
Structure
• Uplink Interval Usage Code (UIUC) indicates burst profile

20. OFDMA TDD Frame Structure
• DL-MAP and UL-MAP indicate the current frame structure
• BS periodically broadcasts Downlink Channel Descriptor (DCD) and Uplink
Channel Descriptor (UCD) messages to indicate burst profiles (modulation and
FEC schemes)

21. Frame Structure – Another View

22. Network Entry Process

23. SDU and PDU

24. Connections
• 802.16/WiMAX is connection oriented
• For each direction, a connection
identified with a 16 bit CID
• Each CID is associated with a Service
Flow ID (SFID) that determines the
QoS parameters for that CID

25. PDU Transmission
Source: R. Marks (NIST) IEEE Presentation

26. QoS Mechanism

27. Generic MAC Frame

28. Generic MAC Header

29. Generic Bandwidth Request

30. Management Messages
• Management messages are broadcast
or sent on three CIDs in each direction:
Basic, Primary, and Secondary
– Uplink Channel Descriptor
– Downlink Channel Descriptor
– UL-MAP
– DL-MAP
– DSA-REQ
– DSA-RSP

31. Key Management Messages (1)

32. Key Management Messages (2)

33. Scheduling Types and QoS
Scheduling Type Parameters
Unsolicited Grant Service
(UGS)
Max Sustained Traffic Rate,
Maximum Latency,
Tolerated Jitter
Real-Time Polling Service
(rtPS)
Max Sustained Traffic Rate,
Min Reserved Traffic Rate,
Committed Burst Size,
Maximum Latency, etc.
Non-real-time Polling Service
(nrtPS)
Committed Information Rate,
Maximum Information Rate
Best Effort (BE) Maximum Information Rate
• Extended rtPS was introduced in 802.16e that combines UGS and rtPS: This has
periodic unsolicited grants, but the grant size can be changed by request

34. Scheduling Classes

35. Advanced 802.16 Features
• Multiple Input and Multiple Output (MIMO)
– MIMO channel capacity is given by
C = B log2 det(I + SNR.HH*T
/N)
where H is MxN channel matrix with M and N are
receive and transmit antennas, resp.
• Hybrid-ARQ
– For faster ARQ, combines error correction and
detection and makes use of previously received
versions of a frame
• Adaptive Antenna System (AAS)
– Enables directed beams between BS and SSs

36. WiBro (Wireless Broadband)
• WiBro is an early large-scale
deployment of 802.16 in South Korea
(Dec 2005)
• Demonstrates 802.16 performance as
compared to 3G/4G cellular
alternatives
• 3 operators have been licensed by the
government (each spending ~$1B)

37. WiMAX Opportunities
• There is a work opportunity to
create/enhance 802.16/WiMAX
network level simulation
• Technical contributions characterizing
802.16 performance and network
capacity are much needed

38. Thanks