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Wireless Transmission and Services

Wireless Transmission and Services. Objectives. Associate electromagnetic waves at different points on the wireless spectrum with their wireless services Identify characteristics that distinguish wireless transmission from wire-bound transmission

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Wireless Transmission and Services

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  1. Wireless Transmission and Services

  2. Objectives • Associate electromagnetic waves at different points on the wireless spectrum with their wireless services • Identify characteristics that distinguish wireless transmission from wire-bound transmission • Explain the architecture and access methods used in cellular networks and services • Understand the differences between wireless and wireline local loops

  3. Objectives • Describe the most popular WLAN standards, including their advantages, disadvantages, and uses • Identify the major satellite positioning schemes and list several telecommunications services that rely on satellite transmission

  4. The Wireless Spectrum http://www.fcc.gov/Bureaus/OPP/working_papers/oppwp38chart.pdf f

  5. The Wireless Spectrum

  6. The Wireless Spectrum

  7. Unlicensed Frequency Bands

  8. Characteristics of Wireless Transmission

  9. Antennas • Radiation pattern - the relative strength over a three dimensional area of all the electromagnetic energy the antenna sends or receives. • Directional antenna - issues wireless signals along a single direction

  10. Antennas • Omni-directional antenna - issues and receives wireless signals with equal strength and clarity in all directions.

  11. Signal Propagation • Reflection - the wave encounters an obstacle and bounces back towards its source. • Diffraction - a wireless signal splits into secondary waves when it encounters an obstruction. • Scattering - the diffusion, or the reflection in multiple different directions of a signal.

  12. Signal Propagation

  13. Signal Propagation • Fading and Delay • Fading: a change in signal strength as result of some of the electromagnetic energy being scattered, reflected, or diffracted after being issued by the transmitter. • Diversity - the use of multiple antennas or multiple signal transmissions to compensate for fading and delay.

  14. Signal Propagation • Attenuation - after a signal has been transmitted, the farther it moves away from the transmission antenna, the more it weakens. • Interference - because wireless signals are a form of electromagnetic activity, they can be hampered by other electromagnetic energy, resulting in interference.

  15. Narrowband, Broadband, and Spread Spectrum Signals • Narrowband - a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies. • Broadband- a type of signaling that uses a relatively wide band of the wireless spectrum. • Spread spectrum - the use of multiple frequencies to transmit a signal.

  16. Fixed vs. Mobile

  17. Fixed vs. Mobile

  18. Cellular Communications • Mobile telephone service - a system for providing telephone services to multiple, mobile receivers using two-way radio communication over a limited number of frequencies. • Mobile wireless evolution: • First generation • Second generation • 3G - Third generation • 4G - Fourth generation (next)

  19. Principles of Cellular Technology

  20. Cells

  21. 1 6 2 7 5 3 1 4 1 6 2 6 2 7 5 3 7 5 3 4 4 Figure Radio frequency reuse for cellular towers

  22. Cellular Call Completion • Components of a signal: • MIN (Mobile Identification Number) - an enclosed representation of the mobile telephone’s 10-digit telephone number. • ESN (Electronic Serial Number) - a fixed number assigned to the telephone by the manufacturer. • SID (System Identification Number) - a number assigned to the particular wireless carrier to which the telephone’s user has subscribed.

  23. Cellular Call Completion Mobile telephone switching office

  24. Mobile Switching Office BTS BSC BTS BTS BTS BTS Central Office BSC – Base Station Controller BTS – Base Transceiver Stations BH – Backhaul Figure 10-4

  25. Call Completion

  26. Figure 10-5

  27. Figure 10-6

  28. AMPS (Advanced Mobile Phone Service) • A first generation cellular technology that encodes and transmits speech as analog signals.

  29. TDMA (Time Division Multiple Access)

  30. CDMA (Code Division Multiple Access) • Each voice signal is digitized and assigned a unique code, and then small components of the signal are issued over multiple frequencies using the spread spectrum technique.

  31. GSM (Global System for Mobile Communications) • A version of TDMA (time division multiple access) technology, because it divides frequency bands into channels and assigns signals time slots within each channel. • Makes more efficient use of limited bandwidth than the IS-136 TDMA standard common in the United States. • Makes use of silences in a phone call to increase its signal compression, leaving more open time slots in the channel.

  32. 3G (Third Generation) Technologies • In this emerging technology a user can access all telecommunication services from one mobile phone. • CDMA2000 - a packet switched version of CDMA. Maximum throughput is 2.4 Mbps. • W-CDMA (Wideband CDMA) - based on technology developed by Ericson, is also packet-based and its maximum throughput is also 2.4 Mbps.

  33. WLL (Wireless Local Loop) • WLL is a generic term that describes a wireless link used in the PSTN to connect LEC central offices with subscribers. • Acts the same as a copper local loop. • Used to transmit both voice and data signals.

  34. LMDS (Local Multipoint Distribution Service) • A point-to-multipoint, fixed wireless technology that was conceived to supply wireless local loop service in densely populated urban areas to issue television signals. • A disadvantage is that its use of very high frequencies limits making its transmission distance to no more than 4km between antennas.

  35. MMDS (Multipoint Multichannel Distribution System) • Uses microwaves with frequencies in the 2.1 to 2.7 GHz range of the wireless spectrum. • One advantage is its lower frequency range, MMDS is less susceptible to interference. • MMDS does not require a line-of-sight path between the transmitter and receiver.

  36. WLAN Architecture

  37. WLAN Architecture

  38. WLAN Architecture

  39. Wireless Networking Standards • 802.11 - IEEE’s Radio Frequency Wireless networking standard committee. • 802.11b - uses DSSS (direct sequence spread spectrum) signaling. Uses the 2.4-2.5 GHz frequency range and separates it into 14 overlapping 22-MHz channels – 11 mbps. Mbps 38 meters • 802.11g - designed to be just as affordable as 802.11b while increasing its maximum capacity from 11 Mbps through different encoding techniques to 54Mbps. Mbps 38 meters • 802.11a - uses multiple frequency bands in the 5 GHZ range. Like 802.11g, 802.11a provides a maximum throughput of 54 Mbps 35 meters • 802.11n - developed by the IEEE LAN/MAN Standards Committee (IEEE 802) in the 5 GHz and 2.4 GHz public spectrum bands. 300 Mbit/s (2 streams) 70 meters

  40. Bluetooth • A mobile wireless networking standard that uses DSS (direct sequence spread spectrum) signaling in the 2.4 GHz band to achieve a maximum throughput of less than 1 Mbps. Effective range up to 25 - 30 feet • Designed to be used on small networks composed of personal communications devices, also known as PANs (Personal Area Networks).

  41. Personal Area Networks

  42. Satellite Positioning • The original method for positioning satellites above the earth was in GEO (geosynchronous orbit). • Geosynchronous satellites are positioned approximately 35,800 km (22,300 miles) above the earth’s equator. • An alternative to GEO satellites are LEO (low earth orbiting) satellites.

  43. Satellite Positioning http://science.nasa.gov/realtime/jtrack/3d/JTrack3D.html

  44. Satellite Services • Digital broadcasting - To deliver content to subscribers, multimedia providers uplink their audio and video signals to a satellite, which then downlinks the signals, in a broadcast fashion, to earth. • Analog broadcasting - Traditional analog television and radio signals can be issued from a terrestrial transmitter to a satellite and then downlinked to another terrestrial location within seconds. • Mobile Wireless - Services such as cellular telephone, paging, and other PCS applications are well suited to LEO or MEO satellite transmission.

  45. Satellite Services • Tracking and monitoring - Two-way satellite communications can be used to monitor the whereabouts and condition of wildlife, mobile weather sensors, marine vessels, and so on anywhere in the world. • GPS (Global positioning service) - A service that expands on remote monitoring functions, GPS allows a mobile station on earth to exchange signals with a satellite to determine its precise location. • WANs (Wide area networks) - Private companies use satellite transmission to connect multiple locations on their WANs.

  46. Components & Technologies 46

  47. Cisco Aironet 802.11b Client Adapters 2.4 GHz • 802.11b • 11 Mbps Include • PC Card • PCI Card • LMC Card • Mini PCI

  48. 5 GHz/802.11a 54 Mbps Rate Shifting 6, 9, 12, 18, 24, 36, 48, or 54 Fixed data rates User configurable option 5 dBi Patch Antenna CardBus interface Transmit power settings: 20 mW, 10 mW, and 5 mW Example of wireless adapter Acoustical strength is measured relatively per the dBi scale.

  49. WLAN Topologies • A typical use of wireless technology as an add-on to a traditional LAN. • Building to building wireless connectivity can be more cost effective and can avoid obstacles faced by wired connections.

  50. WAN Solutions • Four main requirements for WLAN solution: • High availability • Through system redundancy • Redundant AP automatic rate negotiation • Scalability • using multiple APs per coverage area • using multiple frequencies • AP using load balancing • Manageability (diagnostic tools) • Open Architecture • 802.11a • 802.11b

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