1. EECS 228a, Spring 2006 Shyam Parekh
802.16/WiMAX
EECS 228a, Spring 2006
Shyam Parekh

2. References IEEE 802.16-2004 (802.16REVd) IEEE 802.16-2005 (802.16e)
Intel’s Whitepapers, 2004 (
“IEEE Standard : 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 /WiMax: Current Performance Benchmarks and Future Potential,” A. Ghosh et al., IEEE Communication Magazine, Feb 2005
“Wireless Communication Standards: A Study of IEEE , , and ,” T. Cooklev, 2004

3. Electromagnetic Spectrum
Source: LBL

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

5. Applications of 802.16 Standards

6. Network Architecture

7. 802.16 Network Architecture (2)

8. Scope of Standards

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

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
Narrow bandwidth  long symbol times  all significant multipaths arrive within a symbol time minimizing ISI  no equalization  low complexity
Tx Signal
Rx Signal
Note: All signals & multipath over a useful symbol time are from the same symbol & add constructively (no ISI)
time
Cyclic Prefix Useful Symbol Time
time
Note: dashed lines represent multipath
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 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
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 e 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 in South Korea (Dec 2005)
Demonstrates 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 /WiMAX network level simulation
Contact
Technical contributions characterizing performance and network capacity are much needed