Wireless Communications

Mark BlunkHassan MirmotahariWei Min, ChengWing Kai, Cheng

1 - Wireless Spectrumhttp://et.nmsu.edu/~etti/spring97/techtips/spectrum.html

Physical Layer Transmission TypesInfrared light spectrum

Radio wave spectrum

Microwave spectrum

Infrared Light - Positive OptionsInexpensiveCompatible with fiber-optic linksNot bandwidth limitedNo licensing required (FCC)Transmissions may be aimed (1 to 2 kilometers)Transmissions may be omni-directional (30-60 feet)Amplitude driven little interferenceRange of 1-2 kilometers (approximately to 1 miles)Highest bandwidth and throughput

InfraLAN product with infrared transmission

Infrared Light Negative Aspects

Spectrum is shared with the sun and other lighting sources

LAN may become useless with enough interference

Signals will not permeate opaque objects (walls, dividers,etc)

Microwaves

Microwave - Positive Options

Higher throughput without spread spectrum

5.8ghz band using a narrow-band transmission

RadioLAN - product using microwave transmission

Microwave Negative Aspects

Expensive to build infrastructure

Must operate at less than 500 milliwatts (strict FCC regulations)

Not commonly used less available knowledge pool

Radio Waves - Spectrumhttp://www.heritage.org/library/categories/regulation/tp11c1.gif Pure tone 500.00Hz

1500.0Hz

Radio Waves - Positive Options

Commonly understood technologyNot subject to interference of light waves like infraredLess expensive than microwaveLong-range medium several architectures existCommonly used larger knowledge pool

WaveLAN, BreezeNet pro, Proxim Rangelan2, & RadioLAN

Radio Waves Negative Aspects

Spread spectrum technology high overhead

Lower rates of data transmissions due to overhead required

Subject to some interference causing delays in transmission

Radio Waves Spread Spectrum Methods

Direct Sequence Spread Spectrum (DSSS)

Transmission signal is spread over an allowed band

Frequency Hopping Spread Spectrum (FHSS)

Splits the band into subchannels signal then hops to transmit

Radio Waves Direct Sequence Spread Spectrum (DSSS)

Spreads signal over a band (Example, 50 MHz)

Random Binary String Modulates the Transmission Signal

String is known as a Spreading Code

Bits are mapped out as chips and mapped back as bits

Spreading Ratio The number of chips per bit

DSSS Spreading RatiosHigher Ratios Resist Interference BetterLower ratios allow for use of more bandwidth FCC dictates spreading ratios must be more than tenIEEE 802.1 standard requires a spreading ratio of elevenSender & Receiver must synchronize to the spreading codeOrthogonal spreading codes allow sharing of the band between LANsDSSS systems use wide subchannels, limiting LANs possibleRecovery is faster with DSSS due to ability to spread the signal over a wider band

Example Product = WaveLAN

Radio Waves Frequency Hopping Spread Spectrum (FHSS)

Splits the band into many subchannels (1-2MHz)Signal hops from subchannel to subchannelUses short bursts of data on each channel Bursts are within a dwell time (very short time)FCC requires at least 75 subchannelsFCC requires dwell time of no longer than 400msLess interference than DSSS due to hoppingSecurity is higher due to the hopping

Frequency Hopping Spread Spectrum (FHSS)(Continued)

Used by military and law enforcementJamming is very difficult as the whole band must be jammedOrthogonal hopping sequence allows for co-location of multiple LANsAllows for more co-located LANs than DSSSCommon new product method for wireless

Product Example = BreezeNet

Multipath Interference

Interference caused by signals bouncing off of physical objects and arriving at a receiver at differing times

Multipath is a problem for all wireless modesDHSS resists the issue by hopping to other frequenciesAnti-Multipath algorithms exist to resist the problemRayleigh fading is a subset of Multipath and can completely cancel out the signalInfrared resists Rayleigh fading due to small wavelengths

Wireless Types Information SourcesPinacor.comhttp://www.fcc.gov/oet/spectrum/http://www.ntia.doc.gov/

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2 -Examples of Wireless protocols and technologiesThe two main protocols and technologies discussed in this sections are:

Wireless ATM

Wireless Application protocol

Some background on ATMATM ( Asynchronous Transfer Mode) has been advocated as an important technology for the wide area interconnection of heterogeneous networksIn ATM networks, the data is divided into small, fixed length units called cells. The cell is 53 bytes.Each cell contain a 5 byte header which comprises of identification, control priority and routing information. The rest 48 bytes are the actual data.

Background continuedATM does not provide any error detection operations on the user payload inside the cell, and also provides no retransmission services, and only few operations are performed on the small headerATM switches support two kinds of interfaces: user-network interface (UNI) and network-node interface (NNI). UNI connects ATM end systems (hosts, routers etc.) to an ATM switch, while an NNI may be imprecisely defined as an interface connection of two ATM switches together

Why Wireless ATM?ATM provides end-to-end communication in a WAN environmentCompanies do not have to invest in extra equipment (i.e. routers, switches, etc.)ATM reduces the complexity, improves flexibility, while providing end-to-end connectivity

Why ATM Cont...Due to the recent advancement of fiber, next generation wireless networks should be designed so as to easily fit and co-exist with the Broadband ISDN (Integrated Services Digital Network). In order to avoid a serious mismatch between wireline and wireless networks, it is now timely to begin consideration of broadband wireless networks with similar service capabilities

Wireless ATM ChallengesBoth wireless networks technology, and ATM protocol are relatively new, and there are no fixed standards being defined for wireless ATM networksStill in research stage and the technology is being developedSome wireless LANs have lower speed and higher error rates

Modifications to ATMThe ATM cell size (53 bytes) may be too big for some wireless LANs ( due to lower speed and higher error rates), therefore wireless LANs may use 16 or 24 byte payload. The ATM header can also be compressed and be expanded to standard ATM at the base station An example of ATM header compression is to use 2 bytes containing 12-bit VCI (virtual channel identifier) and 4 bit control ( payload type, cell loss priority etc.)

WAP DefinedThe Wireless Application Protocol (WAP) is simply a protocola standardized way that a mobile phone/unit communicates to a server installed in the mobile phone networkMany advertising agencies and dot.coms have announced WAP servicesWAP takes a client-server approach. It incorporates a relatively simple microbrowser into the mobile phone, requiring only limited resources on the phone.

WAP Cont..This makes WAP suitable for thin clients and early smart phonesWAP puts the intelligence in the WAP Gateways while adding just a microbrowser to the phones themselvesMicrobrowser-based services and applications reside temporarily on servers, not permanently in phones

WAP Cont..WAP is aimed at turning a mass-market mobile phone into a network-based smart phoneA person with a WAP-compliant phone uses the built-in microbrowser to: 1. Make a request in wireless markup language (WML), a language derived from HTML especially for wireless network characteristics 2. This request is passed to a WAP Gateway, which then retrieves the information from an Internet server either in standard HTML format or WML 3. The requested information is then sent from the WAP Gateway to the WAP client, using whatever mobile network bearer service is available and most appropriate

WAP Cont.. WAP has also given a significant impetus for new players to add mobile as a new distribution channel for their existing products and services For example, CNN and Nokia teamed up to offer CNN Mobile, and Reuters and Ericsson teamed up to provide Reuters Wireless Services

Business ApplicationsCorporate applications that are being enhanced and enabled with a WAP interface include:Job Dispatch Remote Point Of Sale Customer Service Remote Monitoring Such As Meter Reading Vehicle Positioning Corporate Email

Business Applications Cont..Remote LAN Access File Transfer Web Browsing Document Sharing/Collaborative Working Audio Still Images Moving Images Home Automation

Consumer Applications Consumer Applications that are being enhanced and enabled with a WAP interface include:Simple Person to Person Messaging Voice and Fax Mail NotificationsUnified Messaging Internet Email Prepayment Mobile Commerce Mobile Banking Chat Information Services

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3 -Wireless LAN ConfigurationsA Peer-to-Peer NetworkClient and Access PointMultiple Access Points and RoamingUse of an Extension PointThe Use of Directional Antennas

A Wireless Peer-to-Peer Network

Client and Access Point

AP as Master

Multiple Access Points and Roaming

Use of an Extension Point

The Use of Directional Antennas

Factors to be ConsideredRange and CoverageThroughputIntegrity and ReliabilityCompatibility with the Existing NetworkInteroperability of Wireless DevicesInterference and Coexistence

Factors to be ConsideredLicensing IssuesSimplicity/Ease of UseSecurityCostScalabilityBattery Life for Mobile PlatformsSafety

EP: EP Roles as AP

EP: Preferred Master List

EP Topology: Single EP

EP Topology: Tree

EP Topology: Multi-hop Linear

EP Topology: combination

Building Environment

Recommended Test Equipment

Roaming Test

Site Survey Sample

Recommended TestFile TransferPrintingLoading Application over the NetworkRunning Client/Server Application

Special Tests for WLAN Microwave InterferenceNear/Far PhenomenonHidden Terminal

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4 - Wireless LAN - ProductsA flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN

Wireless EvolutionEthernet - the predominant LAN technology in the wired worldFirst wireless LAN technologies operated in the 900MHz band & low speed (1-2Mbps)1992, wireless LAN makers began developing products operating in the unlicensed 2.4 GHz frequency band1997 IEEE released the 802.11 standard for WLAN ( infrared light, FHSS, DSSS)

Geographic ScopeSOHO - set of PCs talk to each other(peer to peer WLAN)

Within a building or campus

Across buildings

BenefitsMobility - access to real-time information anywhere Installation - Simple, fastFlexibility - move, add, changeConnectivity - go where wire cannot goScalability - a few PCs to full infrastructure networks of thousands of users that allows roaming over a broad area.

Microwave spectrum

How WLAN works (1)Independent (or peer-to-peer) WLAN that connects a set of PCs with wireless adapters

How WLAN works (2)Access PointAccess Point(s) link wireless clients to the wired network

Product Considerations (1)Range / Coverage - 100 to 500+ ft (walls, metal)Throughput - 1 - 11+ Mbps (client #, range, multipath) Interference - unlicensed RF band ( wireless product)Coexistence - multi WLAN, multi vendor (interference)Ease of use - transparent to usersScalability - client #, coverage

Microwave spectrum

Product Considerations (2)Interoperability - wired & wireless infrastructureNetwork Management - add, delete, move, troubleshootSecurity - 40-bit keying standard not safeAdd-on security softwareStation enable capabilityBattery Life - extra power for transmit/receive Safety - stringent government and industry regulations

Microwave spectrum

Add-on security softwareby

ProductsPCMCIA slot II16-bit ISA32-bit PCIAccess pointAironet productsBridge

RF Product - client adaptersNetwork Architecture - Supports peer-to-peer networking and communication to wired networks via Access Points Range at 1Mbps 1600ft (490m) open environment; 325ft (100m) office Range at 11Mbps 425ft (130m) open environment; 110ft (35m) office Encryption 40-bit WEP / 128-bit WEP Antenna Integrated Internal antenna with diversity support, External 2dBi dipole antenna with RP-TNC connection

RF Product - client adapters(cont)Device Drivers Available NDIS2, NDIS3, NDIS4, NDIS5 ODI and Packet System Interface PCMCIA Type II slot, 32-bit PCI slot, 16-bit ISA slot Receive Sensitivity - 90dBm @ 1Mbps, - 88dBm @ 2Mbps, - 87dBm @ 5.5Mbps, - 84dBm @ 11Mbps Output Power 30mW (US, Canada, ETSI) Power Consumption Transmit: 350mA, Receive: 250mA, Sleep: under 10mA

RF Product - Access pointsNetwork Architecture Types Complies with IEEE 802.3 and Ethernet Blue Book Range at 1Mbps 1800ft (550m) open environment; 350ft (105m) office Range at 11Mbps 400ft (120m) open environment; 100ft (30m) office Encryption 40-bit WEP No. of Clients 10 - 2048

RF Product - Access points (Cont)Local Configuration Direct console port (Serial EIA-232 DB-9 female) Remote Configuration HTTP, Telnet, FTP, SNMPAutomatic Configuration BOOTP and DHCP Receive Sensitivity -90dBm @ 1Mbps, -88dBm @ 2Mbps, -87dBm @ 5.5Mbps, -84dBm @ 11Mbps s Output Power 30mW (US, Canada, ETSI) SNMP Compliance MIB I, MIB II

RF Product - client adaptersDevice Drivers Available NDIS2, NDIS3, NDIS4, NDIS5 ODI and Packet System Interface PCMCIA Type II slot, 32-bit PCI slot, 16-bit ISA slot Receive Sensitivity - 90dBm @ 1Mbps, - 88dBm @ 2Mbps, - 87dBm @ 5.5Mbps, - 84dBm @ 11Mbps Output Power 30mW (US, Canada, ETSI) 4.5mW/MHz (EIRP, Japan) Power Consumption Transmit: 350mA, Receive: 250mA, Sleep: under 10mA

RF Product - Wireless bridgesData Rates Supported 1, 2, 5.5 and 11 Mbps Range* Up to 8 Miles (13km) at 11 Mbps Frequency Band 2400-2483.5 Mhz Wireless Medium Direct Sequence Spread Spectrum Media Access Protocol Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)Network Protocols Supported IEEE 802.3 and Ethernet Blue Book

RF Product - Wireless bridges (cont)Modulation DBPSK @ 1 Mbps, DQPSK @ 2 Mbps, CCK @ 5.5 and 11 Mbps Operating Channels 11 channels Simultaneous Channels ThreeSNMP Compliance MIB I, MIB II Routing Protocol RIP II IP Bridging Protocol IEEE 802.1d Spanning Tree support Wireless Bridges per LAN Unlimited Maximum Users per Bridge 2048 (wireless)

Future TrendFaster, Better and CheaperIEEE 802.11b standard 11Mbps WLANs at 2.4GHz band. With optional modulation technique within the 802.11b specification, it is possible to double the current data rate.900MHz to 2.4GHz to 5.7GHz. (802.11a) for equipment operating at 5.7GHz that supports a 54Mbps data rateLonger key length and authentication will improve through the use of x.509 certificates

Wireless Information Sourceshttp://www.wlana.comhttp://www.dcbnet.com/apnotes.html#wirelesshttp://www.nwn.com (NoWiresNeeded)http://www.aironet.com

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