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Fundamental of Wireless LAN

This article provides an overview of the fundamental concepts of wireless LAN and radio waves, focusing on the IEEE 802 families. It covers topics such as infrared and carrier currents LANs, wireless LAN configuration, spread spectrum modulation, and forms of radio-based wireless LAN.

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Fundamental of Wireless LAN

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  1. Fundamental of Wireless LAN Radio Waves IEEE 802 Families Appenidx (Infrared and Carrier Currents LANs)

  2. Wireless LAN Configuration

  3. 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

  4. 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.

  5. 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.

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

  7. Spread Spectrum Modulation • Definition: “spread” a signal’s power over a wider band of frequency.

  8. 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)

  9. 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. Direct Sequence Spread Spectrum (DSSS)

  10. 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.

  11. 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.

  12. Forms of Radio-based Wireless LAN • Wireless Local Bridge • Infrastructure • Ad Hoc

  13. IEEE 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.

  14. Task groups of 802.11 • 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

  15. Task groups of 802.11 • 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。

  16. Appendix:(for your reference)

  17. 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

  18. 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. Diffused Infrared-based LAN

  19. “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

  20. Carrier 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.

  21. Power 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

  22. 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 power line Ethernet broadband over power lines(BLP)

  23. Medium frequency (≥ 1 kHz) • Home control (narrowband) • Use the household electrical power wiring as a transmission medium • Low-speed narrow-band communication • Control 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 ZigBee X10 Automatic meter reading

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