Wimax

WiMAX A Killer Technology or Another Hype James T. Yu, Ph.D. [email protected] School of CTI DePaul University 11/07/2005

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Outline „

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Introduction Broadband Wireless Access (BWA) WiMAX Applications/Market • • •

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IEEE 802.16 • • • •

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Analysis Service Providers Equipment Vendors Physical Layer MACMAC-CPS MACMAC-SSCS QoS and Security

Summary

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2.1 1

Wireless Puzzle 802.15

i ile - F b o M X MA i W 3G WiF i UMTS VSAT 11/07/2005

Antenna System

GPRS

LM DS

6 802.1 MMDS

FS O

®

tooth e u l B

HS DP A

80

CDMA 802.2 0 EV DO 3

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Broadband Wireless Access (BWA) CPE (modem)

LAN

Backbone Base Station 11/07/2005

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WiMAX „

WiMAX - Worldwide interoperability for Microwave Access • It is a forum of product certification for interoperability

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Standard: IEEE 802.16802.16-2004 Frequency Spectrum:

• 10 - 66 GHz (LOS) • 2 – 11 GHz (NLOS) – both licensed and unlicensed

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Last mile technology (MAN/WAN)

• Support pointpoint-toto-point communication • Support Quality of Service (QoS)

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Backhaul technology for wireless LANs (802.11) Up to 30 miles of range with cell radius: 44-6 miles Shared data rate up to 75 Mbps. • Support 50 customers with T1T1-rate wireless connections Los: line of sight

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http://www.wimaxforum.org/news/events/wca_jan_2005/RWG_WCA_Jan_2005.pdf 11/07/2005

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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

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

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WAN vs. LAN

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Licensed vs. Unlicensed

• Distance

• 2.5G (unlicensed), 5.8G (unlicensed), 3.5G (licensed)

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Line of Sight (LOS) vs. NonNon-LOS NLOS) HalfHalf-duplex vs. full duplex Point to Point (P2P), Point to MultiMulti-Point (P2MP), and Mesh Fixed, portable (nomadic), and mobile Carrier, Enterprise, SOHO, Residential

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WiMAX Applications „ „

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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/

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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) „

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AT&T WiMAX Trial

• • •

Atlanta, June 2005 40 towers and 30 trial customers pretrial test at New Jersey and Alaska

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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

BellSouth WiMAX Trial

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Sprint and British Telecom also showed interests in WiMAX trials

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WiMAX – a viable last mile solution? „

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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

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If ILEC lowers the T1 price, how will it change the landscape of the broadband access market? 11/07/2005

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WiMAX for places w/o wired infrastructure „

Advantages over DSL • Much longer distance

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Some suburban areas Rural areas developing countries Note: this is the same for other WBA technologies which all failed.

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WiMAX for 802.11 Backhaul

*TROPOS Networks whitepaper 11/07/2005

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WiMAX vs. 3G (which one is a better wireless technology?) „

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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 „ „ „

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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 (WiMAX forum) • Wireless service providers • Product vendor „

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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 InIn-Stat/MDR, 2005). What is your projection?

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WiMAX Technology

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Wireless Frequency Band Technology Cellular

Frequency Band 824824-894M

Applications Cellular

PCS

1.8501.850-1.990G

Cellular

MMDS

2.52.5-2.7G

MAN/WAN

ISM (802.11b)

2.42.4-2.48G

LAN

U-NNI (802.11a)

5.7255.725-5.875G

LAN

802.16802.16-2004

2-11 and 1010-66 GHz MAN/WAN

LMDS

27.527.5-31.3GHz

MAN/WAN

http://www.ntia.doc.gov/osmhome/allochrt.pdf 11/07/2005

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WiFi and WiMAX

Speed (bps) Max Distance QoS Multiple Access

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

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

Connection type

Connectionless

ConnectionConnection-oriented

NO

TDD/FDD

Standard Frequency band

Full Duplex 11/07/2005

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Performance vs. Mobility 50M

20M

802.16 WiMAX

802.1x 802.16e

10M 802.20

1M fixed 11/07/2005

nomadic

3G

EVDO/HSDPA

mobile

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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 11/07/2005

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IEEE Wireless Standards WAN (Mobile) 802.20

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

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WiFi: 802.11b/g WiMAX: 802.16

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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

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High degree of flexibility for cost, capability, services, capacity FFT: Fast Fourier Transform

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Physical Layer (cont.) „

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PHY is point-to-multipoint and mesh topology LOS and NLOS • Multipath may be significant (NLOS)

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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)

• BS and SS are stationary • SS typically serves a building (business or residence)

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Provide SS with first-mile access to public networks Multiple services, with different QoS priority, simultaneously

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Mesh Architecture optional architecture for WiMAX

c.f. 802.11s 11/07/2005

Source: GWEC 29

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

Ref: WiMAX Forum 11/07/2005

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Multipath Signal „

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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

• Forward Error Correction (FEC)

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Spread Spectrum

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

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Advanced antenna System Power control.

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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)

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Binary Phase Shift Keying (BPSK): 1 bit/Hz • for reference, not used

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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

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Error Correction Techniques „

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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.

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Orthogonal Frequency Division Multiplexing (OFDM) „

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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

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OFDM

When A is at the peak, B, C, D and E are all zero. Ref. http://www.iec.org/online/tutorials/ofdm/ 11/07/2005

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Adaptive Antenna System (AAS) „ „

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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 „ „

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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) „

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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 „ „

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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 multiplemultiple-access procedure in the uplink is implemented using • unsolicited bandwidth grants, • polling, and • contention procedures. Vendors can have different implementations to optimize system performance 11/07/2005

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MAC-CPS: Duplex Scheme Support „

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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

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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 fullfull-duplex SS

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Framed FDD - downlink in bursts

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IEEE 802.16 (Figure 37) 11/07/2005

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TDD Frame

(physical slot)

asymmetric DL/UL

Source: IEEE 802.16 (Figure 38) 11/07/2005

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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)

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QoS

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Medium Access Control (MAC) „

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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

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Connection ID (CID) • 16 bit • Used in MAC PDU • Note that MAC PDU does not have SS MAC address or BS ID „

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why? connectionconnection-oriented service IEEE Communications Society - Chicago Chapter

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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

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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 „

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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

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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

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Requests and Grants „ „

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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.

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Privacy Sublayer „

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

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Protection from theft of services

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Privacy key management (PKM) protocol „ „

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Authorization Periodic re-authorization is required. (why?) X.509 digital certificates. Keys and age must be refreshed. Two sets of keys are always active.

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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 „

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Fixed wireless does NOT have a successful story in US, yet. WiMAX is a very complex protocol. • No analogy between WiFi and WiMAX, WiMAX, except 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, WiMAX, but … There are more questions than answers.

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