WiMAX

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WiMAX A Killer Technology or Another Hype
James T. Yu, Ph.D. [email protected] School of CTI DePaul University
11/07/2005 IEEE Communications Society - Chicago Chapter 1

Outline
Introduction Broadband Wireless Access (BWA) WiMAX Applications/Market
• • • • • • • Analysis Service Providers Equipment Vendors Physical Layer MAC-CPS MACMAC-SSCS MACQoS and Security

IEEE 802.16

Summary
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80

-F i obile M
X iMA W 3G WiF i
UMTS
VSAT
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2.1 1

Wireless Puzzle
802.15

LM DS

GPRS

MMDS

FS O

oth lueto B

®

CDMA 802.2 0 EV DO
3

IEEE Communications Society - Chicago Chapter

Antenna System

Broadband Wireless Access (BWA)
CPE (modem)

Backbone Base Station
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LAN

HS DP A
4

6 802.1

WiMAX
WiMAX - Worldwide interoperability for Microwave Access Standard: IEEE 802.16-2004 802.16Frequency Spectrum:
• It is a forum of product certification for interoperability • 10 - 66 GHz (LOS) • 2 – 11 GHz (NLOS) – both licensed and unlicensed

Last mile technology (MAN/WAN)

Backhaul technology for wireless LANs (802.11) Up to 30 miles of range with cell radius: 4-6 miles 4Shared data rate up to 75 Mbps. • Support 50 customers with T1-rate wireless T1connections
Los: line of sight

• Support point-to-point communication point- to• Support Quality of Service (QoS)

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http://www.wimaxforum.org/news/events/wca_jan_2005/RWG_WCA_Jan_2005.pdf
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Technologies vs. Problems
WiMAX is a wonderful technology, but what is the problem?
• Internet: How do we use wireless (and which one?) to surf the Internet? • Intranet: Is wireless (and which one) a viable technology for the intranet application?

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Technology Consideration
Price/performance
• Throughput/Speed • Distance

WAN vs. LAN

max throughput = channel bandwidth (Hz) × bits/Hz

Licensed vs. Unlicensed

Line of Sight (LOS) vs. Non-LOS NLOS) NonHalf-duplex vs. full duplex HalfPoint to Point (P2P), Point to Multi-Point (P2MP), Multiand Mesh Fixed, portable (nomadic), and mobile Carrier, Enterprise, SOHO, Residential
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• 2.5G (unlicensed), 5.8G (unlicensed), 3.5G (licensed)

WiMAX Applications
Last Mile (T1 replacement) Broadband Access for rural areas where there is a lack of wired infrastructure WiFi Backhaul Evolution: 3G to 4G

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Case Studies - Wireless ISP
TowerStream
• http://www.towerstream.com/

WiMAX services in Boston, Chicago, LA, NYC, and bay area. Product vendor: Aperto Networks a profitable company 5-for-5 plan, 5M at $500/month
• a better deal than T1 and DSL (today!)
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WISP Case Studies (others)
• • • •

AT&T WiMAX Trial

BellSouth WiMAX Trial

Atlanta, June 2005 40 towers and 30 trial customers pretrial test at New Jersey and Alaska Athens, GA (targeting college students) and a few rural sites in Florida 1.5M (down) and 256K (up) for $39.95/mm Strategy: 100% coverage of service area with 80% DSL and 20% WiMAX

• •

Sprint and British Telecom also showed interests in WiMAX trials
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WiMAX – a viable last mile solution?
What is the price for T1 (internet) today? (~$600/month) What is the cost of T1 for ILEC today?
• T1: 2-wire (HDSL2) and 4-wire (HDSL) • local loop: 2-wire, $10/month

If ILEC lowers the T1 price, how will it change the landscape of the broadband access market?
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WiMAX for places w/o wired infrastructure
Advantages over DSL
• Much longer distance

Some suburban areas Rural areas developing countries Note: this is the same for other WBA technologies which all failed.
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IEEE Communications Society - Chicago Chapter

WiMAX for 802.11 Backhaul

*TROPOS Networks whitepaper
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WiMAX vs. 3G
(which one is a better wireless technology?)
Some studies position WiMAX as a 4G technology due to its higher speed (throughput) than 3G. WiMAX (w/ 802.16e) offers mobility and has some advantages over 3G (higher performance). Is there any major wireless carrier considering? If not, what is migration path from 3G to 4G (if there is one)?

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WiMAX Equipment and Vendors
Base Station: ~$50K CPE: ~$500 Price is expected to go down significantly after the interoperability certification in 2006? Vendors:
• • • • • • AirSpan Networks (AS4030) Alvarion (BreezaMAX) BreezaMAX) Tropos Networks Aperto Networks Navini Networks Others (Motorola, Nokia, etc.)

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Future of WiMAX
How is WiMAX different from those failed wireless technologies
• standards, interoperability (WiMAX forum) (WiMAX • Wireless service providers • Product vendor
INTEL (>$500M invested), more players, etc

Broadband wireless access (BWA) market is projected to reach $1.2B (worldwide) by 2007, and WiMAX is expected to be a key player. (by In-Stat/MDR, 2005). InWhat is your projection?
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WiMAX Technology

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Wireless Frequency Band
Technology
Cellular PCS MMDS ISM (802.11b) U-NNI (802.11a) 802.16-2004 802.16LMDS

Frequency Band
824-894M 8241.850-1.990G 1.8502.5-2.7G 2.52.4-2.48G 2.45.725-5.875G 5.72527.5-31.3GHz 27.5-

Applications
Cellular Cellular MAN/WAN LAN LAN MAN/WAN

2-11 and 10-66 GHz MAN/WAN 10-

http://www.ntia.doc.gov/osmhome/allochrt.pdf
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WiFi and WiMAX
Standard Frequency band Speed (bps) Max Distance QoS Multiple Access
Connection type

WiFi 802.11b/g 2.4GHz (unlicensed) 11M/54M 300 ft NO CSMA/CA
Connectionless

WiMAX 802.16 2-11GHz* (both) up to 75M >10 miles YES TDM/TDMA/OFDMA
Connection-oriented Connection-

Full Duplex
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NO
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TDD/FDD
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Performance vs. Mobility
50M 802.16 WiMAX

20M 10M

802.1x 802.16e

1M fixed
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802.20 nomadic

EVDO/HSDPA

3G

mobile
21

IEEE Communications Society - Chicago Chapter

IEEE Standards
1. IEEE 802.16-2001 (10-66GHz)
Air Interface for Fixed Broadband Wireless Access System

2. IEEE 820.16a-2003 (2-11GHz) – WiMAX 3. IEEE 802.16-2004: (1) + (2) 4. IEEE 802.16.2 – Coexistence 5. IEEE 802.16c – System Profile for 1066GHz 6. IEEE 802.16e (draft) - mobility
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IEEE Wireless Standards
WAN (Mobile) 802.20

MAN (Metro) 802.16 LAN (Local) 802.11 PAN (personal) 802.15

WiFi: 802.11b/g WiMAX: 802.16
23

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Reference Model of 802.16

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Source: IEEE 802.16 (Figure 1)
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802.16 Physical Layer
Several PHYs are standardized:
• Single-carrier (SC) for 10-66 GHz • Single-carrier (SC2) for 2-11 GHz • OFDM for 2-11 GHz – 256 FFT • OFDMA for 2-11 GHz – 2048 FFT

High degree of flexibility for cost, capability, services, capacity
FFT: Fast Fourier Transform
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Physical Layer (cont.)
PHY is point-to-multipoint and mesh topology LOS and NLOS
• Multipath may be significant (NLOS)

Channel BW – 1.5 to 14 MHz Advanced power management Interference mitigation AAS and sectored Antenna ARQ on a per-connection basis
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WiMAX Architecture (P2MP)
BS: Base Station SS: Subscriber Station RS: Repeater Station TE: Terminal Equipment

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Source: GWEC

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Point-to-Multipoint (P2MP)
Wireless MAN: not a LAN Base Station (BS) connected to public networks BS serves Subscriber Stations (SS)

Provide SS with first-mile access to public networks Multiple services, with different QoS priority, simultaneously
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• BS and SS are stationary • SS typically serves a building (business or residence)

Mesh Architecture
optional architecture for WiMAX

c.f. 802.11s
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Source: GWEC
29

LOS vs. NLOS
In general, >10GHz is LOS, and <10G can be either LOS or NLOS.

Ref: WiMAX Forum
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Multipath Signal
Multipath is the composition of a primary signal plus duplicate or echoed images caused by reflections of signals off objects between the transmitter and the receiver. The echoed signal is delayed in time and reduced in power, and it causes intersymbol interference (ISI) or distortion of the received signal. Not an issue for LOS, but a major issue for NLOS. What are the solutions to Multipath signal in NLOS?

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NLOS Technology Solutions
(to address the issue of multipath)
Adaptive modulation Error correction techniques Spread Spectrum
• Forward Error Correction (FEC)

Advanced antenna System Power control.
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• Orthogonal Frequency Division Multiplexing (OFDM) • Sub-Channelization – divide into many subchannels and mux them together for a bigger pipe

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Adaptive Modulation
Adjust the signal modulation scheme depending on the signal to noise ratio (SNR) condition of the radio link.
• a fixed scheme that is budgeted for the worst case conditions. • Qadrature Amplitude modulation (QAM) • Phase Shift Keying (PSK) • for reference, not used

Binary Phase Shift Keying (BPSK): 1 bit/Hz Quadrature PSK (QPSK): 2 bits/Hz, low SNR 16-QAM (4 phases × 4 amplitudes): 4 bit/Hz 64-QAM: 6 bit/Hz 256-QAM: 8 bit/Hz, high SNR
Q: In a very noisy channel, which modulation scheme is selected?
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Adaptive Physical Layer
256-QAM 64-QAM 16-QAM

QPSK distance

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Modulation and BER (Bit Error Rate)
QPSK

QPSK achieves same BER at lower SNR

256-QAM requires high SNR

SNR (dB)
Ref: Cisco Interoworking book
11/07/2005 IEEE Communications Society - Chicago Chapter 35

Error Correction Techniques
Error correction techniques have been incorporated into WiMAX to reduce the system signal to noise ratio (SNR) requirements. Forward Error Correction (FEC): Advanced algorithms to detect and recover from erroneous frames. Automatic repeat request (ARQ) to request frame retransmission for frames that cannot be corrected by FEC. Improve the bit error rate (BER) performance for a similar threshold level.
11/07/2005 IEEE Communications Society - Chicago Chapter 36

Orthogonal Frequency Division Multiplexing (OFDM)
It is a technique to increase transmission speed by multiplexing. It uses one wide frequency channel by breaking it up into several sub-channels. All small sub-channels are multiplexed into one “fat” channel. Orthogonal: overlapping but distinguishable
11/07/2005 IEEE Communications Society - Chicago Chapter 37

OFDM

When A is at the peak, B, C, D and E are all zero. Ref. http://www.iec.org/online/tutorials/ofdm/
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Adaptive Antenna System (AAS)
Optional in 802.16 Use multiple antennas to improve the coverage and the system capacity. The spectral efficiency is increased linearly with the number of antenna elements. AAS is able to improve the SNR gain by combining multiple signals. AAS also reduces the frequency interference between users.

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Power Control
Power control is used to improve the overall performance of the system. It is implemented by the base station (BS) sending power control information to subscriber stations (SS) to regulate the transmit power level so that the level received at the base station is at a pre-determined level. The SS transmits only enough power (as specified by the BS). The power control reduces the overall power consumption of the SS and the potential interference with other colocated base stations. For LOS the transmit power of the SS is approximately proportional to it’s distance (square) from the base station. For NLOS it is heavily dependant on the interference.

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Dynamic Frequency Selection (DFS)
Optional procedure, but required in unlicensed bands DFS consists of • Requesting and reporting measurements • Testing channels for the presence of primary users • Detecting primary users • Ceasing operation on a channel after primary users have been found • Selecting and advertising a new channel
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MAC Common Part Sublayer
Supporting multiple access In the downlink, BS does not have to coordinate its transmissions, except for TDD (Time Division Duplex). The uplink is shared on a demand basis. The multiple-access procedure in the uplink is multipleimplemented using • unsolicited bandwidth grants, • polling, and • contention procedures. Vendors can have different implementations to optimize system performance
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MAC-CPS: Duplex Scheme Support
On downlink, SS is associated with a specific burst. On uplink, SS is allotted a variable length time slot , for their transmissions MAC support for duplex schemes Time-Division Duplex (TDD)
• Downlink & Uplink time share the same RF channel • Dynamic asymmetry

Frequency-Division Duplex (FDD)
• Downlink & Uplink on separate RF channels • Static asymmetry

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Frequency-division duplexing (FDD)
Separated frequency channel for DL and UL. Unframed FDD for full-duplex SS fullFramed FDD - downlink in bursts

IEEE 802.16 (Figure 37)
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TDD Frame

(physical slot)

asymmetric DL/UL

Source: IEEE 802.16 (Figure 38)
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Service Specific Convergence Sublayer (SSCS)
Accepting higher-layer data Classification (and processing) of data Delivering data to the MAC layer Receiving data from the peer entity Two convergence sublayers:
• ATM CS • Packet CS (Ethernet and IP)

QoS
11/07/2005 IEEE Communications Society - Chicago Chapter 46

Medium Access Control (MAC)
A MAC frame consists of header, payload, and CRC Frames can be concatenated, fragmented, or packed One SS may serve multiple tenants

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MAC Addressing
SS has 48-bit 802.3 MAC address BS has 48-bit base station ID
• Not a MAC address

Connection ID (CID)
• 16 bit • Used in MAC PDU • Note that MAC PDU does not have SS MAC address or BS ID
why? connection-oriented service connection11/07/2005 IEEE Communications Society - Chicago Chapter 48

Generic MAC Header

Q: do you see source and destination MAC address? Q: How does SS and BS accept MAC frames sent to them?
11/07/2005 IEEE Communications Society - Chicago Chapter 49

MAC PDU Transmission
PDU 1 PDU 2 PDU 3 PDU 4 PDU 5
Burst

P

FEC 1

FEC 2

FEC 3

P: Preamble FEC Block: MAC PDUs + FEC Code

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SS Operation: Network Entry and Initialization
1.

2. 3. 4. 5. 6. 7. 8.

Scan for downlink channel; synchronize with BS Obtain uplink transmission parameters Perform ranging (acquire timing offset) Negotiate capabilities Establish connectivity (for upper layer) Establish time of day Transfer operational parameters Set up connections
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Channel Access and QoS
Packets are associated with a service flow A service flow has associated QoS parameters: bandwidth, latency, jitter, and throughput Service flows can be static (preconfigured) or dynamically established The BS includes authorization module that approves or denies every change to the QoS parameters
11/07/2005 IEEE Communications Society - Chicago Chapter 52

QoS Mechanism
Scheduling services
• Unsolicited grant service (UGS) - for real-time fixed-size packets (VOIP, T1/E1) • Real-time polling service (rtPS) - for variable-size packets (MPEG video) • Non-real-time polling service (nrtPS) – non-real-time data with variable-sized packets (FTP) • Best effort service
11/07/2005 IEEE Communications Society - Chicago Chapter 53

Requests and Grants
SSs can request bandwidth During these requests, collisions can happen (CSMA). If the request is successful, the SS will receive a data grant. There are incremental and aggregated requests. Requests are per connections, but grants are per SS only.
11/07/2005 IEEE Communications Society - Chicago Chapter 54

Privacy Sublayer
Privacy - encrypting connections SS/BS Encryption has two component protocols
• Encapsulation protocol for encrypting packet data • Privacy key management (PKM) protocol.

Protection from theft of services
11/07/2005 IEEE Communications Society - Chicago Chapter 55

Privacy key management (PKM) protocol
Authorization Periodic re-authorization is required. (why?) X.509 digital certificates. Keys and age must be refreshed. Two sets of keys are always active.
11/07/2005 IEEE Communications Society - Chicago Chapter 56

Current projects within 802.16
802.16e – mobility Physical layer below 2 GHz MAC modification to support pointto-point (P2P) systems

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Summary
Fixed wireless does NOT have a successful story in US, yet. WiMAX is a very complex protocol. • No analogy between WiFi and WiMAX, except WiMAX, for wireless WiMAX is great for T1 users today, but … WiMAX is better than 3G, but … WiMAX can be used for WiFi backhaul, but … WiMAX is attractive in urban and developing countries. There are market windows for WiMAX, but … WiMAX, There are more questions than answers.
11/07/2005 IEEE Communications Society - Chicago Chapter 58

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