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

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

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

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

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)

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

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 MHz, for a total bandwidth of 25 MHz

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)

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

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

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)

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

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

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

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?).

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

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

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”

MASNET GroupXiuzhen ChengFeb 8, 2006 Wireless technologies/standards n a n b (Wi-Fi) n g (Wi-Fi) n i (Security) n , 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)

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

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

MASNET GroupXiuzhen ChengFeb 8, 2006 IEEE (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

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

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

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

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

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