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Wireless and Mobile Networks

Wireless and Mobile Networks. Ch2: Wireless Basics. Multiplexing Techniques. Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA ). Frequency Division Multiple Access (FDMA). Frequency. User n. …. User 2. User 1. Time.

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Wireless and Mobile Networks

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  1. Wireless and Mobile Networks Ch2: Wireless Basics

  2. Multiplexing Techniques Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA)

  3. Frequency Division Multiple Access (FDMA) Frequency User n … User 2 User 1 Time • Single channel per carrier • All first generation systems use FDMA

  4. FDMA f1’ f1 MS #1 f2’ f2 MS #2 … … … fn’ fn MS #n BS (Uplink) (Downlink)

  5. Time Division Multiple Access (TDMA) Frequency … User 1 User 2 User n Time • Sharing of the signal is accomplished by dividing available transmission time on a medium among users • Multiple channels per carrier • Most of second generation systems use TDMA

  6. TDMA Slot Frequency f ’ Frequency f #1 … #1 … … … … … #1 #1 MS #1 t t #2 … #2 … … … … #2 … #2 t MS #2 t … … … … #n #n … #n … … #n MS #n t t Frame Frame Frame Frame BS (Downlink) (Uplink)

  7. Code Division Multiplexing Also known as code division multiple access An advanced technique that allows multiple devices to transmit on the same frequencies at the same time

  8. CDMA Code Frequency Time

  9. Code Division Multiple Access (CDMA) Frequency f ’ Frequency f C1’ C1 MS #1 C2’ C2 MS #2 … … … Cn’ Cn MS #n BS (Uplink) (Downlink)

  10. CDMA Example

  11. Wireless networks in comparison to fixed networks • Higher loss-rates due to interference • emissions of, e.g., engines, lightning • Restrictive regulations of frequencies • frequencies have to be coordinated, useful frequencies are almost all occupied • Low transmission rates • local some Mbit/s, regional currently, e.g., 300kbit/s with UMTS • Higher delays, higher jitter • connection setup time with GSM in the second range, several hundred milliseconds for other wireless systems • Lower security, simpler active attacking • radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones • Always shared medium • secure access mechanisms important

  12. Wireless network types • Wireless personal area network (WPAN) is a personal, short distance area wireless network for interconnecting devices cantered around an individual person's workspace. Examples : IRDA, Bluetooth, RFID • Wireless local are network (WLAN) provide wireless network communication over short distances using radio signals instead of traditional network cabling (LAN).Example : 802.11b, 802.11a, 802.11g (Wi-Fi)

  13. Wireless network types • Wireless Metropolitan area network (WMAN) • Connects networks within a city or metropolitan-size area into a larger high-speed network • Examples : WiMAX

  14. Wireless network types • Wireless Wide area network (WAN) • Connects LANs and MANs between cities, across country, and around the world • Examples : GSM, UMTS (3G) • Wireless Global Networks (Satellite) • A WAN that crosses an international border • Examples : VSAT

  15. Overlay Networks - the global goal integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics regional vertical handover metropolitan area campus-based horizontal handover in-house

  16. Typical application: road traffic UMTS, WLAN, DAB, DVB, GSM, cdma2000, TETRA, ... ad hoc Personal Travel Assistant, PDA, Laptop, GSM, UMTS, WLAN, Bluetooth, ...

  17. Mobile devices • Pager • receive only • tiny displays • simple text messages • PDA • graphical displays • character recognition • simplified WWW • Laptop/Notebook • fully functional • standard applications Sensors, embedded controllers • Palmtop • tiny keyboard • simple versions of standard applications • Mobile phones • voice, data • simple graphical displays www.scatterweb.net performance

  18. Frequencies for communication VLF = Very Low Frequency UHF = Ultra High Frequency LF = Low Frequency SHF = Super High Frequency MF = Medium Frequency EHF = Extra High Frequency HF = High Frequency UV = Ultraviolet Light VHF = Very High Frequency Frequency and wave length: λ = c/f wave length λ, speed of light c ≅ 3x108m/s, frequency f

  19. Frequencies for communication Frequency Spectrum

  20. Frequencies for mobile communication • VHF-/UHF-ranges for mobile radio • simple, small antenna for cars • deterministic propagation characteristics, reliable connections • SHF and higher for directed radio links, satellite communication • small antenna, focusing • large bandwidth available • Wireless LANs use frequencies in UHF to SHF spectrum • some systems planned up to EHF • limitations due to absorption by water and oxygen molecules • (resonance frequencies)

  21. Bandwidth • Bandwidth – the absolute value of the difference between the lowest and highest frequencies of a signal • Width of the spectrum of frequencies that can be transmitted • if spectrum=300 to 3400Hz, bandwidth=3100Hz

  22. Bandwidth • Greater bandwidth leads to greater costs • Limited bandwidth leads to distortion • In digital communication Bandwidth • Data transmission rate • Measured in bits per second (bps)

  23. Components of communication System [Shannon’s model] Received Signal Message Signal Message Information Source Transmitter Receiver Destination Noise source

  24. Maximum Data Transfer Rates (channel Capacity ) • How do you calculate a maximum theoretical data rate? • Use Shannon’s equation S(f) = f x log2 (1 + S/N) Where f = signal frequency (bandwidth), S is the signal power in watts, and N is the noise power in watts

  25. Concepts Related to Channel Capacity • Data rate - rate at which data can be communicated (bps) • Bandwidth - the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz) • Noise - average level of noise over the communications path • Error rate - rate at which errors occur • Error = transmit 1 and receive 0; transmit 0 and receive 1

  26. Signal-to-Noise Ratio • Ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission • Typically measured at a receiver • Signal-to-noise ratio (SNR, or S/N) • A high SNR means a high-quality signal, low number of required intermediate repeaters • SNR sets upper bound on achievable data rate

  27. Channel Capacity Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions

  28. Channel Capacity Example 1 • For example, what is the data rate of a 3400 Hz signal with 0.2 watts of power and 0.0002 watts of noise? • S(f) = f x log2 (1 + S/N) S(f) = 3400 x log2 (1 + 0.2/0.0002) = 3400 x log2 (1001) = 3400 x 9.97 = 33898 bps

  29. Channel Capacity Example 2 Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB Using Shannon’s formula

  30. Signal Characteristics • Amplitude (A): signal value, measured in volts • Frequency (f): repetition rate, cycles per second or Hertz • Period (T): amount of time it takes for one repetition, T=1/f • Wavelength () - distance occupied by a single cycle of the signal or, the distance between two points of corresponding phase of two consecutive cycles

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