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Wireless Networking Spread Spectrum Technologies Module-04

Wireless Networking Spread Spectrum Technologies Module-04. Jerry Bernardini Community College of Rhode Island . Presentation Reference Material. CWNA Certified Wireless Network Administration Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett Chapter-3. OSI Model.

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Wireless Networking Spread Spectrum Technologies Module-04

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  1. Wireless NetworkingSpread Spectrum TechnologiesModule-04 Jerry Bernardini Community College of Rhode Island Wireless Networking J. Bernardini

  2. Presentation Reference Material • CWNA Certified Wireless Network Administration Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett • Chapter-3 Wireless Networking J. Bernardini

  3. OSI Model Wireless Networking J. Bernardini

  4. Telecommunication Channel • Channel - a path along which information in the form of an electrical signal passes. Usually a range of contiguous frequencies involved in supporting information transmission. Center Channel Frequency Amplitude Bandwidth Frequency Channel

  5. Narrow and Wide Band • Narrow and Wide Band – a relative comparison of a group or range of frequencies used in a telecommunications system. Narrow Band would describe a small range of frequencies as compared to a larger Wide Band range. Amplitude NB WB Frequency Freq. Range fL fH

  6. Noise Floor • Noise –A disturbance, especially a random and persistent disturbance, that obscures or reduces the clarity of a signal. Anything you don’t want. Amplitude Channel Signal Noise Floor Shot Thermal Freq.

  7. Signal to Noise Ratio dBm.VRMS 100 V -60 dBm Signal SNR-2 SNR-1 10 V -91 dBm SRX -95 dBm Noise Time SNRdB = 20 log (100 V/ 10 V) = 20 dB SNRdB = -60 dBm – (-95 dBm) = 35 dB

  8. Signal to Noise Ratio Orinoco Client NetStumbler AirMagnet

  9. Windows XP Wireless 802.11b

  10. Introduction to Spread Spectrum • Spread Spectrum – a telecommunications technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. Narrowband Amplitude Wideband Frequency

  11. 4-Types Spread Spectrum • Time Hopping, (THSS) • Frequency Hopping, (FHSS) • Direct Sequence Spread Spectrum, (DSSS) • Hybrid, DSSS/FHSS

  12. Uses of Spread Spectrum • Military - For low probability of interception of telecommunications. • Civil/Military - Range and positioning measurements. GPS – satellites. • Civil Cellular Telephony. • Civil Wireless Networks – 802.11 and Bluetooth.

  13. Frequency Hopping • Hedy Lamarr and composer George Antheil, patent number 2,292,387 circa 1942

  14. FHSS • FHSS - Acronym for frequency-hopping spread spectrum. 802.11,Bluetooth, & HomeRF. Amp. 1 3 2 4 Freq. Channel Wide Band Frequency Hop Sequence: 1, 3, 2, 4

  15. Frequency Hopping Spread Spectrum – Simplistic View CWNA Guide to Wireless LANs, Second Edition

  16. FHSS Timing Time Data Amplitude Hop Time Dwell Time Hop Sequence 1 2 3 4 Channels Frequency

  17. FHSS System Block Diagram Antenna FHSS Data Buffer Mixer Mod 1 3 2 4 Carrier Frequency Sequence Generator 1 3 2 4 Frequency Synthesizer

  18. FHSS Channel Allocation 2.480 GHz 2.403 GHz 2.479 GHz 2.402 GHz CH 79 CH 80 CH 2 CH 3 Amplitude 1 MHz 1 MHz 2.401.5 GHz 2.401.5 GHz 2.402.5 GHz 2.402.5 GHz Freq. 2.4835 GHz 2.400 GHz

  19. DSSS • DSSS - Acronym for direct-sequence spread spectrum. WLAN, 802.11. Amp. Signal 1 1 3 2 4 Freq. Channel DSSS Band

  20. DSSS USA Channel Allocation Amplitude Channels 1 2 3 4 5 6 7 8 9 10 11 Freq. 2.401 GHz 2.473 GHz

  21. DSSS 3 Non-overlap Channels Amplitude Ch 1 Ch 6 Ch 11 (2.412 GHz) (2.437GHz) (2.462 GHz) Freq. 22 MHz 2.473 GHz 3MHz 2.401 GHz 2401 MHz 2423 MHz 2426 MHz

  22. DSSS System Block Diagram Carrier Frequency Antenna DSSS Mixer Carrier Generator Mod 11-bit Barker Code Pseudo – Noise Generator Data Buffer Encoder Chipping Code 10110111000

  23. Comparing FHSS & DSSS

  24. OFDMOrthogonal Frequency Division Multiplexing • Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system. • Orthogonal means to establish right angle relationships between frequencies • OFDM spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies and null out of channel sidebands f2 f3 f1 f4 Wireless Networking J. Bernardini

  25. IEEE 802.11nDraft Modulation • Uses three modes of OFDM • 20MHz and 40 MHz bands • Data rates up to 600 Mbps • Non-HT mode • OFDM • Backward compatibility to a, b, g • HT mixed mode • Supports OFDM and ERP-OFDM • Greenfield mode • Only ERP-OFDM • Highest data rates Wireless Networking J. Bernardini

  26. Encoding and Modulation • Encoding - To change or translate one bit stream into another. Barker Code, Complementary Code Keying • Modulation – Appling information on a carrier signal by varying one or more of the signal's basic characteristics - frequency, amplitude and phase. DBPSK (Differential Binary Phase Shift Keying) DQPSK (Differential Quaternary PSK)

  27. Convolution Coding • Convolution coding is a method of channel coding by adding additional redundant information to provide error correction. Convolution codes operate on serial data, one or a few bits at a time and may use Exclusive-Or logic and shift registers. This type of error correction is used in wireless OFDM schemes.

  28. FCC Rules for FHSS • Prior to 8-31-00 • Use 75 of the 79 channels • Output Powermax = 1 Watt • Bandwidthmax = 1 MHz • Data Ratemax = 2 Mbps • After 8-31-00 • Only 15 of the 79 channels required • Output Powermax = 125 mW • Bandwidthmax = 5 MHz • Data Ratemax = 10 Mbps

  29. Co-location • Co-location is the ability to place multiple devices in a frequency space minimal interference • FHSS has many more frequencies / channels then DSSS which only has 3 co-location channels. • However 3 DSSS access points co-located at 11 Mbps each would result in a maximum throughput of 33 Mbps. It would require 16 access points co-located for FHSS to achieve a throughput of 32 Mbps.

  30. Orinoco Gold 802.11b

  31. Orinoco 802.11 abg

  32. Modulation • Carrier signal is a continuous electrical signal • Carries no information • Three types of modulations enable carrier signals to carry information • Height of signal • Frequency of signal • Relative starting point • Modulation can be done on analog or digital transmissions CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  33. Analog vs. Digital Transmissions Analog Signal = A signal that has continuously varying voltages, frequencies, or phases. All amplitude values are present from minimum to maximum signal levels. Digital Signal = A signal in which information is carried in a limited number of different discrete states or levels; High/Low, One/Zero, 1/0 CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  34. Analog and Digital Modulation • Analog Transmission use analog carrier signals and analog modulation. • Digital Transmission use analog carrier signals and digital modulation. • Modem (MOdulator/DEModulator): Used when digital signals must be transmitted over analog medium • On originating end, converts distinct digital signals into continuous analog signal for transmission • On receiving end, reverse process performed • WLANs use digital modulation of analog signals (carrier signal) CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  35. Frequency and Period CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  36. Analog Modulation • Amplitude: Height of carrier wave • Amplitude modulation (AM): Changes amplitude so that highest peaks of carrier wave represent 1 bit while lower waves represent 0 bit • Frequency modulation (FM): Changes number of waves representing one cycle • Number of waves to represent 1 bit more than number of waves to represent 0 bit • Phase modulation (PM): Changes starting point of cycle • When bits change from 1 to 0 bit or vice versa CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  37. Analog Modulation Amplitude modulation (AM) – Carrier frequency varies in amplitude Frequency modulation (FM) – Carrier frequency varies in frequency Phase modulation (PM) –Carrier varies in phase CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  38. Digital Modulation • Advantages over analog modulation: • Better use of bandwidth • Requires less power • Better handling of interference from other signals • Error-correcting techniques more compatible with other digital systems • Unlike analog modulation, changes occur in discrete steps using binary signals • Uses same three basic types of modulation as analog Amplitude shift keying (ASK) CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  39. Digital Modulation Frequency shift keying (FSK) Phase shift keying (PSK) CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

  40. Quadrature phase shift keying (QPSK) CWNA Guide to Wireless LANs, Second Edition

  41. Physical Layer Standards (continued) Figure 4-21: 16-level quadrature amplitude modulation (16-QAM) CWNA Guide to Wireless LANs, Second Edition

  42. Physical Layer Standards (continued) Figure 4-22: 64-level quadrature amplitude modulation (64-QAM) CWNA Guide to Wireless LANs, Second Edition

  43. Summary Wireless Networking J. Bernardini

  44. Throughput vs. Data Rate • Data Rate = Total Data Rate through system • Throughput = Data Payload Rate • Data Rate = Data Payload Rate + Overhead • Overhead = Coding + Modulation+ Bandwidth + Hardware + Software + Retransmission(errors) 5 Mbps Throughput 11 Mbps Data Rate 5 Mbps Throughput Wireless Networking J. Bernardini

  45. Data Rates and Throughput Estimates Wireless Networking J. Bernardini

  46. Bandwidths • Analog Bandwidth – Frequency in Khz,Mhz (1 Mhz) • Digital Bandwidth – bits per second (11 Mbps) • Wireless Bandwidth – Frequency Space made available to network devices (22 Mhz) Digital Bandwidth (Average Bit Rate) Bandwidth Amplitude Frequency Wireless Networking J. Bernardini

  47. Communication Resilience • Resistance to interference • FHSS best resilience but lowest throughput • OFDM next best resilience and higher throughput • HT-OFDM in IEEE 802.11n will provide the best resilience and the best throughput Wireless Networking J. Bernardini

  48. Key Terms and Concepts • bandwidth • coding • colocation • data rate • DSSS • ERP • FHSS • HR/DSSS • modulation • OFDM • throughput Wireless Networking J. Bernardini

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