1. Wireless LAN Technology Lecture 32

2. Wireless LAN Introduction The proliferation of laptop computers and other mobile devices (PDAs and cell phones) created an obvious application level demand for wireless Local Area Networking. Companies jumped in, quickly developing incompatible wireless products in the 1990’s. Industry decided to entrust standardization to IEEE committee that dealt with wired LANs IEEE 802 committee!! 2

3. Defining a WLAN (Wireless Local Area Network) A communications network that provides connectivity to wireless devices within a limited geographic area. "Wi-Fi" is the universal standard for wireless networks and is the wireless equivalent of wired Ethernet networks. In the office, Wi-Fi networks are adjuncts to the wired networks. At home, a Wi-Fi network can serve as the only network since all laptops and many printers come with Wi-Fi built in, and Wi-Fi can be added to desktop computers via USB. Wi-Fi is achieved with a wireless base station, called an "access point." Its antennas transmit and receive a radio frequency within a range of 30 to 150 feet through walls and other non- metal barriers. 3

4. WLAN Design Goals Global, seamless operation Low power for battery use No special permissions or licenses needed to use the LAN Robust transmission technology Simplified spontaneous cooperation at meetings Easy to use for everyone, simple management Protection of investment in wired networks Security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation) Transparency concerning applications and higher layer protocols, but also location awareness if necessary 4

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6. Early Wireless LANs Many standards = No standards Limited or no encryption.5 to 2 Mbps throughput High NIC cost High AP cost Limited roaming 6

7. Modern Wireless LANs IEEE standards based 128 bit encryption ≥ 11 Mbps throughput Low NIC cost Low AP cost Integrated roaming 7

8. Pro and Cons of WLAN Advantages Very flexible within the reception area Ad-hoc networks without previous planning possible (almost) no wiring difficulties (e.g. historic buildings, firewalls) More robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... Disadvantages Typically very low bandwidth compared to wired networks due to shared medium Many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11n) Products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions like, e.g., IMT-2000 8

9. WLAN Deployments Medical Professionals Education Temporary Situations Airlines Security Staff Emergency Centers 9

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11. Wireless LAN Applications LAN Extension Cross-building interconnect Nomadic Access Ad hoc networking 11

12. LAN Extension Wireless LAN linked into a wired LAN on same premises Wired LAN Backbone Support servers and stationary workstations Wireless LAN Stations in large open areas Manufacturing plants, stock exchange trading floors, and warehouses 12

13. Single Cell LAN Extension 13

14. Multiple-cell Wireless LAN 14

15. Cross-Building Interconnect Connect LANs in nearby buildings Wired or wireless LANs Point-to-point wireless link is used Devices connected are typically bridges or routers 15

16. 16 Cross-Building Interconnect Connect LANs in nearby buildings Wired or wireless LANs Point-to-point wireless link is used Devices connected are typically bridges or routers Cisco Aironet 1300 and 1400 Series Wireless Bridges http://www.cisco.com/en/US/products/ps5861/prod_brochure09186a0080230777.html

17. Nomadic Access Wireless link between LAN hub and mobile data terminal equipped with antenna Laptop computer or notepad computer Uses: Transfer data from portable computer to office server Extended environment such as campus users move around with portable computers access to servers on wired LAN 17

18. Nomadic Access – Example 18

19. Ad Hoc Networking Temporary peer-to-peer network set up to meet immediate need Example: Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting 19

20. Wireless LAN Requirements Throughput Number of nodes Connection to backbone LAN Service area Battery power consumption Transmission robustness and security Collocated network operation License-free operation Handoff/roaming Dynamic configuration 20

21. Wireless LAN Requirements Throughput. The medium access-control (MAC) protocol should make as efficient use as possible of the wireless medium to maximize capacity. Number of nodes. Wireless LANs may need to support hundreds of nodes across multiple cells. Connection to backbone LAN. In most cases, interconnection with stations on a wired backbone LAN is required. For infrastructure wireless LANs, this is easily accomplished through the use of control modules that connect to both types of LANs. There may also need to be accommodation for mobile users and ad hoc wireless networks. Service area. A typical coverage area for a wireless LAN has a diameter of 100 to 300 m. 21

22. Wireless LAN Requirements Battery power consumption. Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. This suggests that a MAC protocol that requires mobile nodes to monitor access points constantly or engage in frequent handshakes with a base station is inappropriate. Typical wireless LAN implementations have features to reduce power consumption while not using the network, such as a sleep mode. 22

23. Wireless LAN Requirements Transmission robustness and security. Unless properly designed, a wireless LAN may be interference-prone and easily eavesdropped. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping. 23

24. Wireless LAN Requirements Collocated network operation. As wireless LANs become more popular, it's quite likely that two or more wireless LANs will operate in the same area or in some area where interference between the LANs is possible. Such interference may thwart the normal operation of a MAC algorithm and may allow unauthorized access to a particular LAN. 24

25. Wireless LAN Requirements License-free operation. Users would prefer to buy and operate wireless LAN products without having to secure a license for the frequency band used by the LAN. Handoff/roaming. The MAC protocol used in the wireless LAN should enable mobile stations to move from one cell to another. Dynamic configuration. The MAC addressing and network management aspects of the LAN should permit dynamic and automated addition, deletion, and relocation of end systems without disruption to other users. 25

26. Wireless LAN Categories Infrared (IR) LANs Spread spectrum LANs Narrowband microwave 26

27. Wireless LANs spread spectrum WLANs mostly operate in ISM (industrial, scientific, and medical) bands no Federal Communications Commission (FCC) licensing is required in USA OFDM WLANs orthogonal frequency division multiplexing superior to spread spectrum operate in 2.4 GHz or 5 GHz band infrared (IR) WLANs individual cell of IR LAN limited to single room IR light does not penetrate opaque walls 27

28. Strengths of Infrared Over Microwave Radio Spectrum for infrared virtually unlimited Possibility of high data rates Infrared spectrum unregulated Equipment inexpensive and simple Reflected by light-colored objects Ceiling reflection for entire room coverage Doesn ’ t penetrate walls More easily secured against eavesdropping Less interference between different rooms 28

29. Drawbacks of Infrared Medium Indoor environments experience infrared background radiation Sunlight and indoor lighting Ambient radiation appears as noise in an infrared receiver Transmitters of higher power required Limited by concerns of eye safety and excessive power consumption Limits range 29

30. IR Data Transmission Techniques Directed Beam Infrared Ominidirectional Diffused 30

31. Directed Beam Infrared Used to create point-to-point links Range depends on emitted power and degree of focusing Focused IR data link can have range of kilometers Cross-building interconnect between bridges or routers 31

32. Ominidirectional Single base station within line of sight of all other stations on LAN Station typically mounted on ceiling Base station acts as a multiport repeater Ceiling transmitter broadcasts signal received by IR transceivers IR transceivers transmit with directional beam aimed at ceiling base unit 32

33. Diffused All IR transmitters focused and aimed at a point on diffusely reflecting ceiling IR radiation strikes ceiling Reradiated omnidirectionally Picked up by all receivers 33

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35. Spread Spectrum WLAN Configuration usually use multiple-cell arrangement adjacent cells use different center frequencies 35

36. Spread Spectrum WLANs Transmission Issues licensing regulations differ between countries USA FCC allows in ISM band: spread spectrum (1W), very low power (0.5W) 902 - 928 MHz (915-MHz band) 2.4 - 2.4835 GHz (2.4-GHz band) 5.725 - 5.825 GHz (5.8-GHz band) 2.4 GHz also in Europe and Japan Interference many devices around 900 MHz: cordless telephones, wireless microphones, and amateur radio fewer devices at 2.4 GHz; microwave oven little competition at 5.8 GHz 36

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38. Narrowband Microwave LANs Use of a microwave radio frequency band for signal transmission Relatively narrow bandwidth Licensed Unlicensed 38

39. Licensed Narrowband RF Licensed within specific geographic areas to avoid potential interference Motorola - 600 licenses in 18-GHz range Covers all metropolitan areas Can assure that independent LANs in nearby locations don ’ t interfere Encrypted transmissions prevent eavesdropping 39

40. Unlicensed Narrowband RF RadioLAN introduced narrowband wireless LAN in 1995 Uses unlicensed ISM spectrum Used at low power (0.5 watts or less) Operates at 10 Mbps in the 5.8-GHz band Range = 50 m to 100 m 40

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42. Original 802.11 Physical Layer-DSSS Direct-sequence spread spectrum (DSSS) 2.4 GHz ISM band at 1 Mbps and 2 Mbps up to seven channels, each 1 Mbps or 2 Mbps, can be used depends on bandwidth allocated by various national regulations 13 in most European countries one in Japan each channel bandwidth 5 MHz encoding scheme DBPSK for 1-Mbps and DQPSK for 2- Mbps using an 11-chip Barker sequence 42

43. Original 802.11 Physical Layer-FHSS Frequency-hopping spread spectrum makes use of multiple channels signal hopping between multiple channels based on a pseudonoise sequence 1-MHz channels are used hopping scheme is adjustable 2.5 hops per second in United States 6 MHz in North America and Europe 5 MHz in Japan two-level Gaussian FSK modulation for 1 Mbps four-level GFSK modulation used for 2 Mbps 43

44. Original 802.11 Physical Layer-Infrared omnidirectional range up to 20 m 1 Mbps uses 16-PPM (pulse position modulation) 4 data bit group mapped to one of 16-PPM symbols each symbol a string of 16 bits each 16-bit string has fifteen 0s and one binary 1 2-Mbps has each group of 2 data bits is mapped into one of four 4-bit sequences each sequence consists of three 0s and one binary 1 intensity modulation is used for transmission 44

45. Comparison: infrared vs. radio transmission Infrared uses IR diodes, diffuse light, multiple reflections (walls, furniture etc.) Advantages simple, cheap, available in many mobile devices no licenses needed simple shielding possible Disadvantages interference by sunlight, heat sources etc. many things shield or absorb IR light low bandwidth Example IrDA (Infrared Data Association) interface available everywhere Radio typically using the license free ISM band at 2.4 GHz Advantages experience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.) Disadvantages very limited license free frequency bands shielding more difficult, interference with other electrical devices Example Many different products 45

46. Comparison: Infrastructure vs. ad-hoc Networks infrastructure network ad-hoc network AP wired network AP: Access Point 46

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48. In response to lacking standards, IEEE developed the first internationally recognized wireless LAN standard – IEEE 802.11 IEEE published 802.11 in 1997, after seven years of work Most prominent specification for WLANs Scope of IEEE 802.11 is limited to Physical and Data Link Layers. IEEE 802.11 Wireless LAN Standard 48

49. Appliance Interoperability Fast Product Development Stable Future Migration Price Reductions The 802.11 standard takes into account the following significant differences between wireless and wired LANs: Power Management Security Bandwidth Benefits of 802.11 Standard 49

50. IEEE 802 LAN Standards Family IEEE 802.3 Carrier Sense IEEE 802.4 Token Bus IEEE 802.5 Token Ring IEEE 802.11 Wireless IEEE 802.2 Logical Link Control (LLC) PHY OSI Layer 1 (Physical) Mac OSI Layer 2 (Data Link) 50

51. 802.11 Protocol Stack Part of the 802.11 protocol stack. 51

52. LiFi LiFi is transmission of data through illumination by taking the fiber out of fiber optics by sending data through a LED light bulb that varies in intensity faster than the human eye can follow. Li-Fi is the term some have used to label the fast and cheap wireless communication system, which is the optical version of Wi-Fi. The term was first used in this context by Harald Haas in his TED Global talk on Visible Light Communication. “At the heart of this technology is a new generation of high brightness light-emitting diodes 52

53. LiFi LIFI Solid-State Plasma Lighting 53

54. Comparison Between Current and Future Wireless Technology 54

55. Summary WLAN Applications Wireless Requirements WLAN Classifications DSSS and Frequency Hopping in WLANs IEEE Standardization 802.11 Physical Layer FHSS 802.11 Physical Layer DSSS Comparison of Infrared with Radio Transmission Infrastructure vs. ad-hoc Network 802.11 Benefits 802.11 Protocol Stack 55

56. 2 nd Part of the Lecture GNU Radio 56

57. 57  What is GNU Radio?  Basic Concepts  GNU Radio Architecture & Python  Dial Tone Example 57

58. What is GNU Radio?  Software toolkit for signal processing  Software radio construction  Rapid development  Cognitive radio  USRP (Universal Software Radio Peripheral)‏  Hardware frontend for sending and receiving waveforms 58

59. GNU Radio Components Hardware Frontend Host Computer RF Frontend (Daugtherboard)‏ ADC/DAC and Digital Frontend (USRP)‏ GNU Radio Software 59

60. GNU Radio Software  Opensource software (GPL)  Don't know how something works? Take a look!  Existing examples: 802.11b, Zigbee, ATSC (HDTV), OFDM, DBPSK, DQPSK  Features  Extensive library of signal processing blocks (C++/ and assembly)‏  Python environment for composing blocks (flow graph)‏ 60

61. GNU Radio Hardware  Sends/receives waveforms  USRP Features  USB 2.0 interface (480Mbps)‏  FPGA (customizable)‏  64Msps Digital to Analog converters (receiving)‏  128Msps Analog to Digital converteres (transmitting)‏  Daughterboards for different frequency ranges  Available Daughterboard  400-500Mhz, 800-1000Mhz, 1150-1450Mhz, 1.5- 2.1Ghz, 2.3-2.9Ghz 61

62. GNU Radio Hardware Schematic RX/TX Daughterboard ADC/DAC Host Computer FPGA USB Interface 62

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64. Basics: Blocks  Signal Processing Block  Accepts 0 or more input streams  Produces 0 or more output streams  Source: No input  noise_source, signal_source, usrp_source  Sink: No outputs  audio_alsa_sink, usrp_sink 64

65. Basics: Data Streams  Blocks operate on streams of data 153 379 412 65

66. Basics: Data Types  Blocks operate on certain data types  char, short, int, float, complex  Vectors  Input Signature:  Data types for input streams  Output Signature:  Data types for output streams Two streams of float One stream of complex 66

67. Basics: Flow Graph  Blocks composed as a flow graph  Data stream flowing from sources to sinks 67

68. 68 GNU Radio Architecture 68

69.  GNU radio has provided some useful APIs  What we are interested in at this time is how to use the existing modules that has been provided in GNU radio project to communicate between two end systems GNU Radio Architecture 69

70. GNU Radio Architecture - software  How these modules co-work?  Signal processing block and flow-graph  C++: Extensive library of signal processing blocks Performance-critical modules  Python: Environment for composing blocks Glue to connect modules Non performance-critical modules 70

71. GNU Radio Architecture – software(2)  Python scripting language used for creating "signal flow graphs“  C++ used for creating signal processing blocks An already existing library of signaling blocks  The scheduler is using Python’s built-in module threading, to control the ‘starting’, ‘stopping’ or ‘waiting’ operations of the signal flow graph. 71

72. GNU Radio Architecture – software(3) 72

73. GNU Radio Companion 73

74. GNU Radio Companion (Cont'd)  GNU Radio Companion  Design flow graphs graphically  Generate runnable code  Demonstration 74

75. Dial Tone Example Sine Generator (350Hz)‏ Sine Generator (440Hz) ‏ Audio Sink 75

76. Dial Tone Example #!/usr/bin/env python from gnuradio import gr from gnuradio import audio from gnuradio.eng_option import eng_option from optparse import OptionParser class my_top_block(gr.top_block): def __init__(self): gr.top_block.__init__(self)‏ parser = OptionParser(option_class=eng_option)‏ parser.add_option("-O", "--audio-output", type="string", default="", help="pcm output device name. E.g., hw:0,0")‏ parser.add_option("-r", "--sample-rate", type="eng_float", default=48000, help="set sample rate to RATE (48000)")‏ (options, args) = parser.parse_args ()‏ if len(args) != 0: parser.print_help()‏ raise SystemExit, 1 sample_rate = int(options.sample_rate)‏ ampl = 0.1 src0 = gr.sig_source_f (sample_rate, gr.GR_SIN_WAVE, 350, ampl)‏ src1 = gr.sig_source_f (sample_rate, gr.GR_SIN_WAVE, 440, ampl)‏ dst = audio.sink (sample_rate, options.audio_output)‏ self.connect (src0, (dst, 0))‏ self.connect (src1, (dst, 1))‏ if __name__ == '__main__': try: my_top_block().run()‏ except KeyboardInterrupt: pass 76

77. Summary  What is GNU Radio?  Basic Concepts  GNU Radio Architecture & Python  Dial Tone Example 77