802.16/WiMAX

1
802.16/WiMAX

• EECS 228a, Spring 2006
• Shyam Parekh

2
References

• IEEE 802.16-2004 (802.16REVd)
• IEEE 802.16-2005 (802.16e)
• Intels Whitepapers, 2004 (http//www.intel.com/te
  chnology/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

• First standard based on proprietary
  implementations of DOCSIS/HFC architecture
  in wireless domain

• Original fixed wireless broadband air Interface
  for 10 66 GHz Line-of-sight only,
  Point-to-Multi-Point applications

• Extension for 2-11 GHz Targeted for
  non-line-of-sight, Point-to-Multi-Point
  applications like last mile broadband access

802.16 Amendment WiMAX System Profiles 10 - 66 GHz

• Adds WiMAX System Profiles and Errata for 2-11 GHz

• MAC/PHY Enhancements to support subscribers
  moving at vehicular speeds

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
WirelessMAN-OFDM 2-11 GHz License-exempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD
WirelessMAN-OFDMA 2-11 GHz Licensed Basic, (ARQ), (STC), (AAS) TDD, FDD
WirelessMAN-OFDMA 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
Narrow bandwidth ? long symbol times ? all
significant multipaths arrive within a symbol
time minimizing ISI ? no equalization ? low
complexity
Note All signals multipath over a useful
symbol time are from the same symbol add
constructively (no ISI)
Tx Signal Rx Signal
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/? 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.HHT/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
• Contact sparekh_at_lucent.com
• Technical contributions characterizing 802.16
  performance and network capacity are much needed