1. MASNET GroupXiuzhen ChengFeb 8, 2006 Terms and Concepts Behind Wireless Communications

2. MASNET GroupXiuzhen ChengFeb 8, 2006 Basic Wireless Terms n Electromagnetic waves n Frequency n Spectrum n Bandwidth n Capacity

3. MASNET GroupXiuzhen ChengFeb 8, 2006 Electromagnetic (EM) Radiation n A natural phenomenon that allows information to be carried from transmitter to a receiver via a medium such as the air or fiber optic cable n Wireless devices, such as cell phones, produce electromagnetic waves of different frequencies that move through space

4. MASNET GroupXiuzhen ChengFeb 8, 2006 Frequency n Frequency is the number of times that a wave's peak passes a fixed point in a specific period of time Point A 10 Cycles / 1 Second = 10 Hertz 1 Second

5. MASNET GroupXiuzhen ChengFeb 8, 2006 Frequency (cont.) n Frequency is measured in cycles per second, or Hertz (Hz) n Cellular phones, for example, produce radio waves with frequencies around 800 MHz n “Frequency” and “Spectrum” are used interchangeably by some people, although they are not the same 1,000 Hz = 1 KiloHertz (kHz) 1,000,000 Hz = 1 MegaHertz (MHz) 1,000,000,000 Hz = 1 GigaHertz (GHz)

6. MASNET GroupXiuzhen ChengFeb 8, 2006 n The set of all possible frequencies (an infinite number) is called the "electromagnetic spectrum" n The subset of frequencies from 3 kHz to 300 GHz is known as the "radio spectrum" Electromagnetic Spectrum Spectrum

7. MASNET GroupXiuzhen ChengFeb 8, 2006 Frequency vs. Bandwidth n Frequency is a specific location on the electromagnetic spectrum n Bandwidth is the range between two frequencies u Bandwidth is measured in Hertz u A cellular operator may transmit signals between 824-849 MHz, for a total bandwidth of 25 MHz

8. MASNET GroupXiuzhen ChengFeb 8, 2006 Bandwidth vs. Capacity n Capacity is usually measured by Mega bits per second (Mbps) n Bandwidth for a particular service is fixed, but the number of calls and the rate of data transmission is not (capacity)

9. MASNET GroupXiuzhen ChengFeb 8, 2006 An example: IEEE 802.11b (WiFi) n Operating center frequency: 2.4 GHz. u There are 11 channels in 802.11b. Starting from 2.412 GHz to 2.462 GHz. n Spectrum: 2.412 GHz ~ 2.462 GHz n Bandwidth: 40 MHz. n Capacity: 1, 2, 5.5, and11Mbps. Typical data rate is about 6.5Mbps.

10. MASNET GroupXiuzhen ChengFeb 8, 2006 Parameters that determine the capacity n Capacity is the fundamental concern in wireless networks. n The capacity of a particular bandwidth is determined by following parameters: u Signal strength u Interference u Path loss u Lower or higher frequencies u Etc

11. MASNET GroupXiuzhen ChengFeb 8, 2006 Signal strength n The ability of an electromagnetic wave to persist as it radiates out from its transmitter n Signal strength, or power, is measured in Watts, or more conveniently expressed in decibels (dB)

12. MASNET GroupXiuzhen ChengFeb 8, 2006 Power and Interference n Power can increase the strength of a signal, but it can also cause the signal to “bleed” into other frequencies, resulting in interference with other transmissions

13. MASNET GroupXiuzhen ChengFeb 8, 2006 Path loss (path attenuation) n Decrease in signal strength over distance due to: u Absorption u Reflection u Diffusion u Scattering u Free-space loss

14. MASNET GroupXiuzhen ChengFeb 8, 2006 Lower frequencies are n Better for mobile services u Low powered signals go farther at lower frequencies, resulting in F lower-powered handsets = smaller handsets F less interference

15. MASNET GroupXiuzhen ChengFeb 8, 2006 Higher Frequencies n Path Loss is greater at higher frequencies n Higher frequency signals have difficulty penetrating buildings and traveling around objects n Radio components are more expensive for higher frequencies n Frequency stability (staying in your allocated bandwidth) more difficult at higher frequencies As you increase the frequency, the coverage area decreases – but potential data rates increase (why?).

16. MASNET GroupXiuzhen ChengFeb 8, 2006 Propagation Characteristics n 900MHz u Multipath: High u Foliage: Pine (Absorb Radiation) n 2.4GHz u Multipath: Very High (Concrete, Brick, Steel) u Foliage: Any Absorbs Radiation (water resonance) n 5GHz u Multipath: Very High (Concrete, Brick, Steel, Foliage) u Foliage: Limited Absorption

17. MASNET GroupXiuzhen ChengFeb 8, 2006 More details will be coved in n The section named “Antennas and Propagations”.

18. MASNET GroupXiuzhen ChengFeb 8, 2006 Digital Technology n Transfers information in digital format (binary 0’s and 1’s) versus analog (continuous values) u Significant improvement in wireless systems (why?) u Reduces many problems associated with decrease in signal strength n We will see more of digital technology in the section named “Encoding, Spread Spectrum Technology”

19. MASNET GroupXiuzhen ChengFeb 8, 2006 Wireless technologies/standards n 802.11a n 802.11b (Wi-Fi) n 802.11g (Wi-Fi) n 802.11i (Security) n 802.16 2004, e & f (WiMAX) n Bluetooth (802.15) n 1G: CDPD (Cellular Digital Packet Data) n 2G: GSM (Global System for Mobile Communications) GPRS (General Packet Radio Service) n 3G: CDMA2000, WCDMA n EvDO (Evolution Data Only)

20. MASNET GroupXiuzhen ChengFeb 8, 2006 IEEE 802.11a/b/g (Wi-Fi) 802.11a802.11b802.11g 5 GHz2.4 GHz 54 Mbps11 Mbps54 Mbps Less interference, more bandwidth Best over-all coverage range Faster than 802.11b and better range than 802.11a Not as widely implemented, shorter range Not as fast as other technologies Less range than 802.11b

21. MASNET GroupXiuzhen ChengFeb 8, 2006 IEEE 802.16 (WiMAX) n 802.16d – A.K.A 802.16-2004 u Intended for "last mile" connectivity at high data rates. u Point-to-multipoint only implementation n 802.16e – Adds mobility u approved in December 2005.

22. MASNET GroupXiuzhen ChengFeb 8, 2006 IEEE 802.20 (MBWA) n Mobile Broadband Wireless Access (MBWA) Working Group u 1 Mbps u Mobile speeds of 100mph u Could compete with 3G cellular u Licensed band use only

23. MASNET GroupXiuzhen ChengFeb 8, 2006 IEEE 802.11i (WPA2) n Provide improvements to WiFi security n Address security short comings in WEP n Add user authentication

24. MASNET GroupXiuzhen ChengFeb 8, 2006 Evolution Data Only (EvDO) n Available in Larger Metro Areas u Offered by Sprint, Verizon, Other u 700Mbps n Supports Streaming Video

25. MASNET GroupXiuzhen ChengFeb 8, 2006 Elements of a wireless network network infrastructure r wireless hosts r base station r wireless link r Network infrastructure

26. MASNET GroupXiuzhen ChengFeb 8, 2006 Elements of a wireless network Ad hoc mode n no base stations n nodes can only transmit to other nodes within link coverage n nodes organize themselves into a network: route among themselves

27. MASNET GroupXiuzhen ChengFeb 8, 2006 Why a wireless network is more subjected attacks?