1. 1 Wireless Networks Lecture 42 IEEE 802.16 Dr. Ghalib A. Shah

2. 2 WiMAX Basics  WiMAX or 802.16 is an effort by the IEEE to develop a standards based air interfaces for the licensed and unlicensed radio frequencies from 2 to 66 GHz  The approach they have taken is to develop a common MAC – Media Access Control sub layer of the data link layer  Then to offer differing physical layers to accommodate the needs of the different frequencies and regulatory environments  The IEEE believes that the existing approaches to delivering wireless data services do have the potential for long term growth when used outside of the local area network 2

3. 3 IEEE 802.16 Overview  Family of standards for wireless metropolitan area networks (WMAN)  Provide broadband (i.e., voice, data, video) connectivity  Specifies the air interface, including the medium access control (MAC) layer and multiple physical layer specifications  802.16e is an amendment to 802.16d (fixed or nomadic wireless broadband) to support mobility ►Vehicular speeds up to 75 mph

4. 4 WiMAX Forum  Formed in June 2001 to promote conformance and interoperability of the 802.16 standard  Develops “system profiles” that define mandatory and optional features of standard [1] IEEE® 802.16e Mobile Broadband Wireless Amendment IEEE® 802.16-2004 Fixed Broadband Wireless Standard Mobile WiMAX System Profile Release-1 Mandatory and Optional Features

5. 5 802.16 Evolution Extension for 2-11 GHz Non-line-of-sight Point-to-Multi-Point applications Original fixed wireless broadband air Interface for 10 – 66 GHz Line-of-sight only Point-to-Multi-Point applications Revised and replaced previous versions WiMAX System Profiles MAC/Physical layer enhancements to support subscribers moving at vehicular speeds 802.16 Dec 2001 802.16a Jan 2003 802.16d Oct 2004 802.16e Dec 2005 [2]

6. 6 Characteristics of 802.16 Frequency Ranges  10 - 66 GHz ►Short wavelength ►Line-of-sight (LOS) required ►Negligible multipath ►The commonly used frequencies in this range are 10.5, 25, 26, 31, 38, and 39 GHz  2 – 11 GHz ►Longer wavelength ►LOS not required ►Improved range and in-building penetration ►Multipath effects may be significant

7. 7 IEEE 802.16 Standard 802.16802.16d/HiperMAN802.16e Completed December 2001June 2004 (802.16d)Estimate 2005 Spectrum 10 - 66 GHz< 11 GHz< 6 GHz Channel Conditions Line of Sight OnlyNon Line of Sight Bit Rate 32 – 134 Mbps in 28MHz channel bandwidth Up to 75 Mbps in 20MHz channel bandwidth Up to 15 Mbps in 5MHz channel bandwidth Modulation QPSK, 16QAM and 64QAM OFDM 256 FFT QPSK, 16QAM, 64QAM Scalable OFDMA 128 to 2048 FFT Mobility Fixed Portable Channel Bandwidth s 20, 25 and 28 MHz1.75 to 20 MHz

8. 8 Why do we need broadband wireless access?  Fill the gap between high data rate wireless LAN and very mobile cellular networks.  Wireless alternative to cable and DSL for last- mile broadband access ►Developing countries ►Rural areas  Provide high-speed mobile data and telecommunications services

9. 9 802.11 v 802.16 ►802.11’s media access control protocol is optimized for shorter- range topologies ►It also was not designed to serve a large number of users ►Wireless MAN, on the other hand, was designed to solve the problems of delivering wireless broadband networks over longer distances and through more difficult environments, such as heavily wooded areas 9

10. 10 Comparison 802.11 and 802.16 802.11 < 300 feet Optimized for indoor short range 2.7 bps/Hz peak. <= 54Mbps in 20MHz 1-10 CPE CSMA/CA No QOS Technology Range Coverage Data rate Scalability QOS 802.16 < 30 Mile ( typical 3~4) Outdoor LOS & NLOS 5bps/Hz peak, <100Mbps in 20 MHz 1- hundreds CPE TDMA On demand BW  voice Video, data

11. 11 Network Architecture Source: WiMAX Nuts and Bolts – Steve Hilton [3]

12. 12 Physical Layer  Five physical layer modes 802.16d 802.16e DesignationApplicability WirelessMAN-SC10 -66 GHz WirelessMAN-SCaBelow 11GHz Licensed bands WirelessMAN-OFDMBelow 11GHz Licensed bands WirelessMAN-OFDMABelow 11GHz Licensed bands WirelessHUMANBelow 11GHz Licensed-exempt bands

13. 13 Orthogonal Frequency Division Multiplexing (OFDM)  Multiplexing technique that divides the channel into multiple orthogonal sub channels  Input data stream is divided into several substreams of a lower data rate (increased symbol duration) and each substream is modulated and simultaneously transmitted on a separate sub channel  High spectral efficiency, resilient to interference, and low multi-path distortion

14. 14 Conventional FDM and OFDM Source: Broadband Wireless Access (W-PAN, W-LAN, WiMAX, Wi-Mob) (including OFDM concepts) - A. K. Seth [4]

15. 15 Orthogonal Frequency Division Multiple Access (OFDMA)  Multiple-access/multiplexing scheme ►a multiple-access/multiplexing scheme that provides multiplexing operation of data streams from multiple users onto the downlink sub-channels and uplink multiple access by means of uplink sub-channels. ►Dynamically assign a subset of subchannels to individual users  WirelessMAN-OFDMA based on scalable OFDMA (SOFDMA) ►Support scalable channel bandwidths from 1.25 to 20 MHz

16. 16 Other Physical Layer Features  Hybrid automatic repeat request (HARQ) ►Adjusts automatically to channel conditions ►Receiver saves failed transmission attempts to help future decoding Every transmission helps increase probability of success  Multiple-in Multiple-out (MIMO) ►Multiple antennas on sender and receivers ►Takes advantage of multi-path ►Increased spectral efficiency

17. 17 TDD  The 802.16e PHY supports TDD and Full and Half- Duplex FDD operation;  To counter interference issues, TDD does require system-wide synchronization;  TDD is the preferred duplexing mode for the following reasons: ►TDD enables adjustment of the downlink/uplink ratio to efficiently support asymmetric downlink/uplink traffic, ►Unlike FDD, which requires a pair of channels, TDD only requires a single channel for both downlink and uplink providing greater flexibility ►Transceiver designs for TDD implementations are less complex and therefore less expensive.

18. 18 MAC Layer  Connection-oriented  A fundamental premise of the MAC architecture is quality of service (QoS)  QoS provided via service flows

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20. 20 MAC Layer Service Specific Convergence Sublayer MAC Common Part Sublayer Privacy Sublayer Interface to higher layer protocols, classifies incoming data, etc. Core MAC functions (i.e., scheduling, connection maintenance,fragmentation), QoS control Encryption, authentication, secure key exchange