Microsoft PowerPoint - wireless-lan.ppt

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1 Fundamental of Wireless LAN Radio Waves IEEE 802 Families Appenidx (Infrared and Carrier Currents LANs) Ch2:1

2 Wireless LAN Configuration Ch2:2

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 Ch2:3

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. Ch2:4

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. Ch2:5

6 ISM Spectrum Availability Only 2.4 GHz is the world-accepted ISM band. 902 MHz is easier in manufacturing. Ch2:6

7 Spread Spectrum Modulation Definition: spread a signal s power over a wider band of frequency. Ch2:7

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) Ch2:8

9 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 uses 11 chips per data bit. Ch2:9

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. Ch2:10

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. Ch2:11

12 Forms of Radio-based Wireless LAN Wireless Local Bridge Infrastructure Ad Hoc Ch2:12

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, Ethernet, 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. Ch2:13

14 Task groups of a: Specification enabling up to 54 Mb/s to be achieved in the 5 GHz unlicensed radio band by utilizing OFDM b: Specification enabling up to 22 Mb/s to be achieved in the 2.4 GHz unlicensed radio band by utilizing DSSS c: Provides required information to ensure proper bridge operations, which is required when developing access points d: 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 Ch2:14

15 Task groups of e: Covers issues of MAC enhancements for QoS, such as EDCF service differentiation and HCF f: Provides interoperability for users roaming from one access point to another of different vendor g: Specification enabling up to 54 Mb/s to be achieved in the 2.4 GHz unlicensed radio band h: Dynamic channel selection and transmission power control i: Specification for WLAN security to replace the weak Wired Equivalent Privacy (WEP) k: Radio resource measurement for specifications so that a wireless network can be used more efficiently p: 又稱 WAVE;Wireless Access in the Vehicular Environment) 是一個由 IEEE 標準擴充的通訊協定通訊協定這個通訊協定主要用在車用電子的無線通訊無線通訊上它設定上是從 IEEE 來擴充延伸, 來符合智慧型運輸系統 (Intelligent Transportation Systems,ITS) 的相關應用 Ch2:15

16 Appendix: (for your reference) Ch2:16

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 Ch2:17

Diffused 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.

18 Diffused 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. Ch2:18

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 token ring board. data rate: 4 and 16 Mbps); Good security: Resilient to electrical noise. No mobility, little fault-tolerant capability Ch2:19

Carrier Current LANs Use power line as a medium to transmit data. Fig. 2.

20 Carrier Current LANs Use power line as a medium to transmit data. Fig 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. Ch2:20

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

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 Ch2:21

Ultra-High-frequency communication ( 100 MHz) High-frequency communication ( 1 MHz) Home networking (broadband) Used to interconnect home computers, peripherals or other networked consumer

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 Ethernet power line broadband over power lines(blp) Ch2:22

Medium frequency ( 1 khz) Home control (narrowband) Use the household electrical power

telemetry of electrical equipment such as meters, switches, heaters and domestic

technologies used in the automatic meter reading industry Remote control of lighting

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 Automatic meter reading X10 Ch2:23

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