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Fundamental of Wireless LANFundamental of Wireless LAN

Radio Waves IEEE 802 Families Appenidx (Infrared and Carrier Currents LANs)

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Wireless LAN Configuration

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Radio-Based Wireless LANs

Most widely used method Adv: penetrating walls and other obstacles with little

attenuation. Disadv: security, interference, etc.

2 approaches: Narrow band ISM band and Spread spectrum

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Narrow Band Modulation

Concentrate all transmission power in a narrow range of frequency.

Efficient use of radio spectrum; save bandwidth. ex: television, AM, FM Adv: for long distance transmission (e.g. metropolitan

area) Disadv: noise can easily corrupt the signals Need to obtain FCC licenses to coordinate the use.

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ISM Bands In 1985, FCC modified part 15 to stimulate the use of

wireless networks. ISM=Industrial, Scientific, and Medical Unlicensed, you can freely install and move.

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ISM Spectrum Availability

Only 2.4 GHz is the world-accepted ISM band. 902 MHz is easier in manufacturing.

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Spread Spectrum Modulation

Definition: “spread” a signal’s power over a wider band of frequency.

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Spread Spectrum

Disadv: This contradicts with the goal of conserving bandwidth.

Adv: less susceptible to electrical noise (especially from narrow band sources) In World War II, US Army uses spread spectrum to avoid

hostile jamming. (invented by Hedy Lamarr, an actress) To spread a signal, there are two ways:

direct sequence (DSSS) frequency hopping (FHSS)

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Direct Sequence Spread Spectrum (DSSS)

Use bit sequence to represent “zero” and “one” (Fig. 2-5)

Also referred to as “chipping code”.

Longer chipping codes are more resilient to noise.

Minimum length = 10 (by FCC)

IEEE 802.11 uses 11 chips per data bit.

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Frequency Hopping Spread Spectrum (FHSS)

Data is modulated by carrier signals that hop from frequency to frequency as a function of time, over a wide band of frequencies.

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FHSS (cont.)

Hopping Code: to determine the order of hopping frequencies

The receiver must “listen” to incoming signals at the right time at the right frequency.

FCC regulation: at least 75 frequencies, with max. dwell time 400ms.

Adv.: very resilient to noise. Orthogonal hopping codes: a set of hopping codes that

never use the same frequencies at the same time (can be on-line adjusted by software).

Allow multiple wireless LANs to co-exist.

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Forms of Radio-based Wireless LAN

Wireless Local Bridge Infrastructure Ad Hoc

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IEEE 802 FamiliesIEEE 802 Families

IEEE? a non-profit professional org. founded in 1884; now has

320,000 members in 150 countries;

Most notable standards: IEEE 802 family (802.2 LLC, 802.3 Ethernet, 802.5 Token

Ring, etc.)

IEEE membership info: Open to anyone. It’s FREE!! Must pay meeting fees. Membership Category: voting member, nearly member,

aspirant member, sleeping member.

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802.11a: Specification enabling up to 54 Mb/s to be achieved in the 5 GHz unlicensed radio band by utilizing OFDM

802.11b: Specification enabling up to 22 Mb/s to be achieved in the 2.4 GHz unlicensed radio band by utilizing DSSS

802.11c: Provides required information to ensure proper bridge operations, which is required when developing access points

802.11d: Covers additional regulatory domains, which is especially important for operation in the 5 GHz bands because the use of these frequencies differ widely from one country to another

Task groups of 802.11

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802.11e: Covers issues of MAC enhancements for QoS, such as EDCF service differentiation and HCF

802.11f: Provides interoperability for users roaming from one access point to another of different vendor

802.11g: Specification enabling up to 54 Mb/s to be achieved in the 2.4 GHz unlicensed radio band

802.11h: Dynamic channel selection and transmission power control 802.11i: Specification for WLAN security to replace the weak Wired

Equivalent Privacy (WEP) 802.11k: Radio resource measurement for 802.11 specifications so that a

wireless network can be used more efficiently 802.11p:又稱WAVE ； Wireless Access in the Vehicular

Environment）是一個由 IEEE 802.11標準擴充的通訊協定。這個通訊協定主要用在車用電子的無線通訊上。它設定上是從 IEEE 802.11來擴充延伸，來符合智慧型運輸系統（ Intelligent Transportation Systems ， ITS）的相關應用。

Task groups of 802.11

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Appendix:(for your reference)

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Infrared Light-based Wireless LAN

Wavelength range: 0.75 ~ 1000 u ultraviolet < visible lights < infrared < radio typically operating at 0.82u

Adv: higher security: does not propagate through opaque objects,

keeping signals within rooms and building no interference from microwave ovens and radio transmitters

Disadv: directional, not suitable for mobile applications

Two types of infrared light LANs: Diffused Point-to-point

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Diffused Infrared-based LANDiffused Infrared-based LAN

Example: TV remote controller

Example: three stations using a ceiling Just like using a flashlight,

and talking to people using Morse Code.

A person wants to send must look at the ceiling to make sure that no other people are sending.

The receiver looks at the packet header to check for incoming packets.

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“Point-to-Point” Infrared LAN System Each link has a pair of transducers (uni-directional):

up to 75 ft.

connect as a token ring (what is token ring??)Each transducer can talk with a IEEE 802.5 token ring board.

data rate: 4 and 16 Mbps); Good security:

Resilient to electrical noise.

No mobility, little fault-tolerant capability

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Carrier Current LANsCarrier Current LANs

Use power line as a medium to transmit data. Fig. 2.15

The electrical power companies provide 110V, 60Hz alternating current; the signal can support 1~2 Mbps data signals.

Adv: adopt already-existing cables Products are being seen/proposed in the market.

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Power Line CommunicationPower Line Communication

Power line communication or power line carrier (PLC) is a system for carrying data on a conductor also used for electric power transmission Different types of power line communications use different frequency

bands, depending on the signal transmission characteristics of the power wiring used

Ultra-High-frequency communication (≥ 100 MHz) High-frequency communication (≥ 1 MHz)

Home networking (broadband)Used to interconnect home computers, peripherals or other

networked consumer peripherals

Internet access (broadband over power lines)The use of PLC technology to provide broadband Internet

access through ordinary power lines

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broadband over power lines(BLP)

power line

Ethernet

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Medium frequency (≥ 1 kHz) Home control (narrowband)

Use the household electrical power wiring as a transmission medium

Low-speed narrow-band communicationControl and telemetry of electrical equipment such as meters,

switches, heaters and domestic appliances

Transmitting radio programs Low frequency (< 1 kHz)

PLC is one of the technologies used in the automatic meter reading industry

Remote control of lighting and appliances without installation of

additional control wiring

Automatic meter reading X10

ZigBee