Advances in Wireless Networks:Advances in Wireless Networks:IEEE 802.16(WiMAX)IEEE 802.16(WiMAX)

Vinh Do

Comp 529

California State University of Northridge

OutlineOutline Background IEEE 802.15: PAN IEEE 802.11: Wireless LANs 802.11 last-mile network Mesh network IEEE 802.16

-Standards

-Physical layer

-MAC layer IEEE 802.20(proposed)

Elements of a wireless networkElements of a wireless network

network infrastructure

wireless hosts laptop, PDA, IP phone run applications may be stationary (non-

mobile) or mobile– wireless does not

always mean mobility

Elements of a wireless networkElements of a wireless network

network infrastructure

base station typically connected to wired

network relay - responsible for

sending packets between wired network and wireless host(s) in its “area”– e.g., cell towers

802.11, 802.16 access points

Elements of a wireless networkElements of a wireless network

network infrastructure

wireless link typically used to connect

mobile(s) to base station also used as backbone link multiple access protocol

coordinates link access various data rates,

transmission distance

Characteristics of selected wireless link Characteristics of selected wireless link standardsstandards

384 Kbps384 Kbps

56 Kbps56 Kbps

54 Mbps54 Mbps

5-11 Mbps5-11 Mbps

1 Mbps1 Mbps

802.15

802.11b

802.11{a,g}

IS-95 CDMA, GSM

UMTS/WCDMA, CDMA2000

.11 p-to-p link

2G

3G

Indoor

10 – 30m

Outdoor

50 – 200m

Mid rangeoutdoor

200m – 4Km

Long rangeoutdoor

5Km – 20Km

Elements of a wireless networkElements of a wireless network

network infrastructure

infrastructure mode base station connects

mobiles into wired or mesh network

handoff: mobile changes base station providing connection into wired network

Elements of a wireless networkElements of a wireless networkAd hoc mode no base stations nodes can only transmit to

other nodes within link coverage

nodes organize themselves into a network: route among themselves

Wireless Link CharacteristicsWireless Link Characteristics

Differences from wired link ….

– decreased signal strength: radio signal attenuates as it propagates through matter (path loss)

– interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well

– multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times

…. make communication across (even a point to point) wireless link much more “difficult”

Wireless network characteristicsWireless network characteristicsMultiple wireless senders and receivers create additional

problems (beyond multiple access):

AB

C

Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each othermeans A, C unaware of their

interference at B

A B C

A’s signalstrength

space

C’s signalstrength

Signal fading: B, A hear each other B, C hear each other A, C can not hear each other

interferring at B

Mradius ofcoverage

S

SS

P

P

P

P

M

S

Master device

Slave device

Parked device (inactive)P

replacement for cables (mouse, keyboard, headphones)

ad hoc: no infrastructure master/slaves:

– slaves request permission to send (to master)

less than 10 m diameter– master grants requests

802.15: evolved from Bluetooth specification

– 2.4-2.5 GHz radio band– up to 721 kbps

802.15: personal area network(PAN)802.15: personal area network(PAN)

IEEE 802.11 Wireless LANIEEE 802.11 Wireless LAN

802.11b

– 2.4-5 GHz unlicensed radio spectrum

– up to 11 Mbps

– direct sequence spread spectrum (DSSS) in physical layer

• all hosts use the same chipping code

– widely deployed, using base stations

802.11a

– 5-6 GHz range

– up to 54 Mbps

– Orthogonal frequency division multiplexing(OFDM)

802.11g

– 2.4-5 GHz range

– up to 54 Mbps

– Orthogonal frequency division multiplexing(OFDM)

All use CSMA/CA for multiple access

All have base-station and ad-hoc network versions

Wi-Fi with directional antennasWi-Fi with directional antennas

Increase range of 802.11 Fixed access/ Last mile usage-802.11 with high speed antennas 802.11g is often selected

-speed

-ability to handle interference(OFDM)

-interoperability with 802.11b-based devices Limitation

-efficiency of the network decreases as the number of users on 802.11

increases due to the overhead of managing additional subscriber

-CSMA/CA contributed to network traffic

Wi-Fi with directional antennasWi-Fi with directional antennas

802.11 Mesh network as MANs802.11 Mesh network as MANs Interconnect 802.11x based nodes by wireless 802.11 links 802.11a standard commonly used in AP to AP links (performance and non-

chanel overlapped with 802.11b/g) Properties

– 2.4GHz or 5 GHz unlicensed spectrum

– up to 54 Mbps

– Portable access Automatic learn and maintain dynamic path configuration Small nodes act as a simple router Connection is shared across nodes Based on propriety solutions

– May provide VoIP and QoS

– Coverage range can be over 10km

– Performance up to 100Mbps Better suited to blanket large areas with 802.11 access

Mesh network topology

Limitations

– A large subscriber base is needed to cover large areas

– Using omni-directional antennas produces noise into network– Shared bandwidth: more users translate into less banwidth

– Latency: latency increases with every hop

– Lack of standardization leads to unavailability of QoS.

Benefits

– Lower costs to the operator due to product availability

– Balanced traffic

– Flexibility over wired installations can be achieved

Advantages over single hop and directional last-mile alternatives

– Robustness and resiliency

– The shorter transmission range limit interference allowing simultaneously, spatially separated data flows

802.11 Mesh network(Cont.)802.11 Mesh network(Cont.)

IEEE 802.16 standardsIEEE 802.16 standards 802.16.1

– 10-66GHz unlicensed band

– LOS

– Up to 134Mbps

802.16.2: minimizing interference between coexisting WMANs

802.16-2004 (replace 802.16a/REVd)

– 2.5GHz, 3.5GHz licensed bands

– 5.8GHz licensed exempt band

– NLOS

– up to 75 Mbps

– Fixed end point

– 3 to 5 miles; Maximum range 30 miles based on tower height, antenna gain and transmit power.

IEEE 802.16 standards(Cont.)IEEE 802.16 standards(Cont.) 802.16e

– 2-6 GHz license band

– NLOS

– up to 15 Mbps

– Mobility, regional roaming

– Support mobile user traveling at speeds up to 95 miles/hr

– 1 to 3 miles Interoperability Built in QoS High performance Smart antennas Intelligent APs to monitor traffic

Point to Multipoint Wireless MANPoint to Multipoint Wireless MAN

Base Station(BS) connected to public networks BS serves Subscriber Stations(SSs)

– SS typically serves a building(business or residence)– Provide SS with first-mile access to public networks

Multiple services with different QoS Compare to a wireless LAN

– Many more users– Multimedia QoS– Longer distance– Higher data rate

WIMAX network topology(fixed endpoints)

WIMAX backhaul for a Wi-Fi mesh topology

WIMAX as an intra mesh backhaul option

WIMAX as a client connection option

IEEE 802.16 standardsIEEE 802.16 standards

Physical layer characteristicsPhysical layer characteristics

Line of sight(LOS)- because of 10-66GHz Broadband chanels

– Wide channels(20,25 or 28 MHz)– High capacity(down and up links)

Multiple Access– TDM/TDMA– High rate burst modems

Adaptive burst profile on both uplink and downlink Multiple duplex schemes

– Time division Duplex (TDD)– Frequency division duplex (FDD)-including burst FDD

• Support for half duplex terminals Adaptive modulation

– QPSK, QAM16, QAM64

Adaptive ModulationAdaptive Modulation

Allow a wireless system to choose the higher modulation depending on the channel conditions

– Lower modulation(QPSK) for higher range– Higher modulation(QAM) for lower range(increase throughput)

Baud Rate and Channel Size(10-66 GHz)Baud Rate and Channel Size(10-66 GHz)

Flexible plan--allowing manufacturers to choose according to spectrum requirements

Channel

Width

(MHz)

20

25

28

QPSK

Bit Rate

(Mbits/s)

32

40

44.8

16-QAM

Bit Rate

(Mbits/s)

64

80

89.6

64-QAM

Bit Rate

(Mbits/s)

96

120

134.4

Adaptive Burst profileAdaptive Burst profile

Burst profile– Modulation– Reed Solomon FEC(forward error correction)

• to recover error frame lost due to frequency selective fading or burst error

• Automatic repeat request (ARQ) is used to correct errors that can not be corrected by FEC

Dynamically assigned according to link conditions– Burst by burst, per subscriber station– Trade-off capacity vs robustness in real time

Roughly double capacity for the same cell area Burst profile for downlink channel is well known and robust

– Up to 12 burst profiles can be defined– The parameters of each are communicated to the SSs via MAC

messages during the frame control section of the downlink frame

Duplex scheme Duplex scheme The downlink channel is time division multiplex(TDM)

– Information for each SS multiplexed onto a single stream of data and received by all SSs within the same sector

The uplink is time division multiple access(TDMA)– Channel is divided into a number of time slots which are assigned various

uses(registration, user traffic) Frequency division duplex(FDD)

– DL and UL on the separate RF channel– Support half-duplex SSs (SS does not transmit/receive simultaneously)

Time division duplex(TDD)– DL and UL time-shared the same RF channel– SS does not transmit/receive simultaneously

TDD Frame(10-66GHz)TDD Frame(10-66GHz)

Frame duration: .5ms, 1ms, 2msFrame duration: .5ms, 1ms, 2msPhysical slot(PS) = 4 QAM symbols(1QAM symbol = 4bits)Physical slot(PS) = 4 QAM symbols(1QAM symbol = 4bits)

TDD downlink subframeTDD downlink subframe

DIUC: Downlink interval usage code

Tr/Rx: gap between the downlink burst and subsequent uplink bust

– Allows time for the BS to switch from transmit to receive mode and SSs to switch from receive to transmit mode

FDD framingFDD framing

Example of FDD bandwidth allocation

FDD downlink subframeFDD downlink subframe

TDMA portion: transmit data to some half-duplex SSs(the ones scheduled to transmit earlier in the frame than they receive)

-Need preamble to re-sync(carrier phase)

Uplink subframeUplink subframe

Uplink subframe descriptionsUplink subframe descriptions

Initial maintenance opportunities

– Ranging

– To determine network delay or to request power or profile change

– Collisions may occur in this interval Request contention opps

– SSs request bandwith in response to polling from BS.

– Collisions may occur in this interval Schedule data

– SSs transmit data bursts in the intervals granted by the BS

– Transition gaps between data intervals for synchronization purposes.

MAC LayerMAC Layer

Designed for Point-to-multipoint broadband wireless access apps

Support difficult user environments– High bandwidth, hundreds of user per channel– Continuous and burst traffic– Very efficient use of spectrum

Protocol independent core– ATM, IP, Ethernet,…

Flexible QoS offerings– Best Effort(BF), rt-VBR,nrt-VBR, ATM CBR

Security Support PHY alternatives

– Adaptive mod, TDD/FDD, single-carrier, OFDM/OFDMA

Service-specific convergence sublayersService-specific convergence sublayers

ATM convergent sublayer defined for ATM services Packet convergent sublayer

– Defined for mapping services such as IPv4, IPv6, Ethernet

Preserve or enable QoS Enable bandwidth allocation Classify service data units(SDUs) to the proper MAC

connection

MAC addressingMAC addressing

SS has 48bits IEEE MAC address– Use mainly as equipment id

16-bit Connection ID(CID)– Used in MAC PDUs

MAC PDU formatMAC PDU format

The Generic MAC header has fixed format One or more MAC sub-headers may be part of the payload The presence of sub-headers is indicated by a Type field in the

Generic MAC header

Generic MAC headerGeneric MAC header

LEN: PDU length in bytes(2048 max) HT: header Type Type: subheader, …

CID: Connection ID EC: Encryption Control HCS: Header Check

EKS: Encryption Key Sequence CI: CRC indicator Sequence

MAC PDU TransmissionMAC PDU Transmission

MAC PDUs are transmitted in PHY burst A single burst can contain multiple Concatenated MAC PDUs The PHY burst can contain multiple FEC blocks MAC PDUs may span FEC block boundaries The TC(Transmission convergence) layer between the MAC

and PHY allows for capturing the start of the next MAC PDU in case of erroneous FEC blocks

Downlink TransmissionsDownlink Transmissions

Two kinds of bursts: TDM and TDMA TDMA bursts have resync preamble Each terminal listens to all bursts at its operational IUC or a

more robust one Each burst may contain data for several terminals SS must recognize the PDUs with known CIDs DL-MAP message signals downlink usage

Burst profilesBurst profiles

Each burst profile has mandatory exit threshold and minimum entry threshold

SS allowed to request a less robust DIUC once above the minimum entry level

SS must request fall back to more robust DIUC once at mandatory exit threshold

Requests to change DIUC done with Downlink burst profile change REQ(DBPC-REQ) or RNG-REG messages

Transition to more robust burst profileTransition to more robust burst profile

Transition to less robust burst profileTransition to less robust burst profile

Uplink TransmissionsUplink Transmissions

Transmissions in contention slots– Bandwidth requests– Contention resolved using truncated exponential backoff

Transmissions in initial ranging slots– Ranging requests(RNG-REQ)– Contention resolved using truncated exponential backoff

Bursts defined by UIUCs Transmissions allocated by the UL-MAP message All transmissions have synchronization preamble

Uplink ServicesUplink Services

Unsolicited Grant Services (UGS)– Used for constant-bit-rate (CBR) service flows (SFs)

Best Effort (BE)– For best-effort traffic

Real time Polling Services (rtPS)– For rt-VBR SFs such as MEPEG video

None Real time Polling Services (nrtPS)– For nrt SFs with better than BE service such as bandwidth-intensive file

transfer

Request/Grant schemeRequest/Grant scheme

Bandwidth Requests are always per Connection Self Correcting

– No acknowledgement Grants are either per Connection (GPC) or per SS (GPSS)

– Grants (given as durations) are carried in the UL-MAP messages– SS needs to convert the time(durations) to amount of data using

information about the UIUC Bandwidth Grant per Subscriber Station (GPSS)

– BS grants bandwidth to the SS– SS may re-distribute bandwidth among its connections– Suitable for many connections per terminal– Low overhead but requires intelligent SS

Bandwidth Grant per Connection (GPC)– BS grants bandwidth to a connection– Mostly suitable for few users per SS– High overhead, but allows simpler SS

Bandwidth RequestsBandwidth Requests

Come from the Connection Implicit requests (UGS)

– No actual messages, negotiated at connection setup

BW request messages – Uses special BW request header – Requests up to 32 KB with a single message

Maintaining QoS in GPSSMaintaining QoS in GPSS

BS sees the requests for each connection; based on this, grants bandwidth to the SSs (maintaining QoS and fairness)

SS scheduler maintains QoS among its connections and is responsible to share the BW among the connections (maintaining QoS and fairness)

Algorithm in BS and SS can be very different

SS InitializationSS Initialization

Channel Acquisition– Scan frequency list to find an operation channel

– Establish synchronization with the BS

– Obtains the modulation and FEC schemes used on the carrier via Uplink Channel Description (UDC)

Perform ranging and Capabilities Negotiation – SS send a RNG_REQ in the ranging window

– BS measures arrival time and signal power; calculates timing advance and power adjustment

– BS send adjustment in RNG-RSP

– SS adjusts timing advance and power; sends new RNG-REQ

– Continue until power and timing is ok Authorize SS and perform key exchange

SS Initialization(Cont.)SS Initialization(Cont.)

Perform registration– SS send a list of capabilities and parts of the configuration file to the BS

in the REG-REG message– BS replies with the REG-RSP message(indicates with capabilities are

supported/allowed– SS acknowledges the REG-RSP with REG-ACK message

Establish ID connectivity (via DHCP) Set up connections

– BS passes Service Flow Encodings to the SS in multiple Dynamic Service Addition Request (DSA-REQ) messages

– SS replies with DSA-RSP messages– Service Flow Encodings contain either

• Full definition of service attributes• Service class name (ASCII string which is known at the BS and

which indirectly specifies a set of QoS parameters such as jitter and latency)

SS Authentication and RegistrationSS Authentication and Registration

Trust relation assumed between equipment manufacturer and network operator

Each SS contains both the manufacturer’s X.509 certificate and the the manufacturer’s certificate.

SS sent both certificates to the BS in the Authorization Request and Authentication Information messages

BS verifies the identity of the SS by checking the certificates and level of authentication of the SS

BS response with an Authorization Reply containing the Authorization key (AK) encrypted with the SS’s public key if the SS is authorized to join the network

The SS registers with the network upon successful authorization

Privacy and EncryptionPrivacy and Encryption

Secures over-the-air transmissions Protocol based on Privacy Key Management (PKM) from

DOCSIS(Data over Cable Service Interface Specification) Designed to allow new/multiple encryption algorithms Data encryption

– Currently 56-DES (Data Encryption Standards) in CBC (cipher block chaining) mode

– Initialization Vector (IV) based on frame number

Authentication– X.509 certificates with RSA public key encryption– Strong authentication of SSs (prevents theft of service)– Prevents cloning

Message authentication– Most important MAC management messages authenticated with one-way

hashing using Hashed Message Authentication Code(HMAC) with SHA-1

Security AssociationsSecurity Associations

A set of privacy information– Shared by a BS and one or more of its client SSs in order to support

secured communications– Includes Traffic Encryption Keys (TEKs) and CBC IVs

Security Association Establishment– Primary SA established during initial registration– Other SAs may be provisioned or dynamically created within the BS

IEEE 802.20 Wireless WANs( proposed)IEEE 802.20 Wireless WANs( proposed)

Similar to 802.16e, 3G

– Mobility, regional roaming

Differences

– < 3.5 GHz

– Cell ranges up to 8 miles

– Support mobile user traveling at speeds up to 155miles/hr

References

1. IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access

2. IEEE 802.16-2001, “IEEE Standard for local and Metropolitan Area Networks—Part 16: Air Interface for Fixed Broadband Wireless Access Systems”

3. WiMAX: The Critical Wireless Standard, Carolyn Gabriel

4. Understanding Wi-Fi and WiMAX as Metro-Access Solutions,

5. 802.16: A Look Under the Hood by Beth Cohen and Debbie Deutsch (www.wi-fiplanet.com)

6. WiMAX Anticlimax by Andy Dornan (www.networkmagazine.com)