Terms and Concepts Behind Wireless Communications

1. Terms and Concepts Behind Wireless Communications

2. Basic Wireless Terms • Electromagnetic waves • Frequency • Spectrum • Bandwidth • Capacity

3. Electromagnetic (EM) Radiation • 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 • Wireless devices, such as cell phones, produce electromagnetic waves of different frequencies that move through space

4. Point A 1 Second 10 Cycles / 1 Second = 10 Hertz Frequency • Frequency is the number of times that a wave's peak passes a fixed point in a specific period of time

5. Frequency (cont.) • Frequency is measured in cycles per second, or Hertz (Hz) • Cellular phones, for example, produce radio waves with frequencies around 800 MHz • “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. Spectrum • The set of all possible frequencies (an infinite number) is called the "electromagnetic spectrum" • The subset of frequencies from 3 kHz to 300 GHz is known as the "radio spectrum" Electromagnetic Spectrum

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

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

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

10. Parameters that determine the capacity • Capacity is the fundamental concern in wireless networks. • The capacity of a particular bandwidth is determined by following parameters: • Signal strength • Interference • Path loss • Lower or higher frequencies • Etc

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

12. Power and Interference • 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. Path loss (path attenuation) • Decrease in signal strength over distance due to: • Absorption • Reflection • Diffusion • Scattering • Free-space loss

14. Lower frequencies are • Better for mobile services • Low powered signals go farther at lower frequencies, resulting in • lower-powered handsets = smaller handsets • less interference

15. Higher Frequencies • Path Loss is greater at higher frequencies • Higher frequency signals have difficulty penetrating buildings and traveling around objects • Radio components are more expensive for higher frequencies • 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. Propagation Characteristics • 900MHz • Multipath: High • Foliage: Pine (Absorb Radiation) • 2.4GHz • Multipath: Very High (Concrete, Brick, Steel) • Foliage: Any Absorbs Radiation (water resonance) • 5GHz • Multipath: Very High (Concrete, Brick, Steel, Foliage) • Foliage: Limited Absorption

17. More details will be coved in • The section named “Antennas and Propagations”.

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

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

20. IEEE 802.11a/b/g (Wi-Fi)

21. IEEE 802.16 (WiMAX) • 802.16d – A.K.A 802.16-2004 • Intended for "last mile" connectivity at high data rates. • Point-to-multipoint only implementation • 802.16e – Adds mobility • approved in December 2005.

22. IEEE 802.20 (MBWA) • Mobile Broadband Wireless Access (MBWA) Working Group • 1 Mbps • Mobile speeds of 100mph • Could compete with 3G cellular • Licensed band use only

23. IEEE 802.11i (WPA2) • Provide improvements to WiFi security • Address security short comings in WEP • Add user authentication

24. Evolution Data Only (EvDO) • Available in Larger Metro Areas • Offered by Sprint, Verizon, Other • 700Mbps • Supports Streaming Video

25. network infrastructure Elements of a wireless network • wireless hosts • base station • wireless link • Network infrastructure

26. Elements of a wireless network Ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves

27. Why a wireless network is more subjected attacks?