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How Wireless Works…

How Wireless Works…. Matthew C. Valenti Lane Department of CSEE. And Why Sometimes it Doesn’t…. Wireline access lines. 231.8 million Feb. 07. Wireless subscribers (cellular and PCS). 3 rd generation. 2 nd generation. 1 st generation Analog (FM). 1000.

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How Wireless Works…

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  1. How Wireless Works… Matthew C. Valenti Lane Department of CSEE

  2. And Why Sometimes it Doesn’t…

  3. Wireline access lines 231.8 million Feb. 07 Wireless subscribers (cellular and PCS) 3rd generation 2nd generation 1st generation Analog (FM) 1000 The Wireless Revolution 100 Millions of Subscribers 10 1 0.1 2004 2007 1983 1986 1989 1992 1995 1998 2001 wireless growth in US alone Source: www.ctia.org

  4. Wireless Is BIG Business • In 2006, Americans used 857 billion minutes of talktime. • 1.6 million years total. • Average of 10 minutes/day/customer. • 42% of Americans use wireless as their primary phone. • U.S. Revenues and Industry • Average bill of $49.30/month/customer. • Over $135 billion/year industry. • 2.5% of US workforce in wireless industry • In the next 5 years, wireless will be a bigger US industry than automotive or agriculture. • Worldwide Usage • 2.3 billion wireless subscribers worldwide • 986 million handsets sold in 2006.

  5. Worldwide Wireless

  6. PCS: 1.85-2.0 GHz Cellular: 824-894 MHz

  7. How Crowded is the Spectrum? • Wireless Spectrum • 231 million subscribers in US • 220 MHz available for Wireless (110 each direction) • So just give each subscriber about 1 Hz of dedicated bandwidth (0.5 Hz each direction), right? • Problem: cellular signal occupies: • 200 kHz (GSM) • 550 distinct channel pairs. • Time division multiple access divides channels into 8 subchannels. • So 4400 “conversations” • 1.25 MHz (CDMA) • 88 distinct channel pairs. • Code division multiple access divides each channel into 64 subchannels • So 5632 “conversations”

  8. Something’s Got to Give…

  9. The Cellular Concept • Transmit power drops off with distance. • When you are far-enough away you can re-use the channel. • Similar concept to frequency re-use for radio and television stations. Ch #1 Ch #2 Ch #3 Ch #1 Low power transmitter, Frequency is re-used

  10. The Cellular Concept Set #1 Set #2 Set #3 Set #2 Set #3 Ch #1 Set #4 Set #1 Lower power transmitters provide coverage to a small portion of the service area. Frequency is reused

  11. Cell Patterns Idealized Cells Idealized Coverage Footprint Reality!

  12. Break the metropolitan area into small areas Each area is approximated with a hexagonal cell. A base station is located at the center of each cell. Each cell is assigned only a fraction of the total number of channels. Cells that are sufficiently far apart can reuse the same frequency. In the US, there are currently 200,000 base stations (cells). The Cellular Concept Cluster #1 Cluster #2 A F B A B G F E C G E D C A D F B G E C D Cluster #3

  13. Sectorized Antennas • Further interference reduction by using sectorized antennas.

  14. Hand Off Ch #2 Ch #1 • Mobile must be transferred between cells as it moves • Hard handoff • Soft handoff (CDMA) • Softer handoff (sectorized antennas) • Possibility for a dropped call.

  15. The Challenges ofWireless • Fading • Due to relative motion between TX and RX. • Multipath • Due to signal reflections. • Diffraction • Signal bending around objects (mountain, buildings) • Shadowing • Obstructions that attenuate signal (foliage) • Interference • Other signals • Main limitation in built-up areas. • Noise • Thermal excitement of electrons in receiver. • Background noise in space.

  16. Facing the Challenges • Source Coding • Companding: Reduces BW needed by voice. • Channel Coding • Forward Error Correction Coding. • By adding parity bits to transmitted data, errors can be corrected. • Spread Spectrum Communication • Use of Multiple Antennas • Advanced Receiver Processing • Equalizer: Undoes multipath • This is the type of stuff that EE’s working in the communications industry work on!

  17. To Learn More (A Lot More)… • Wireless Networking • CPE 462 • 11:00 AM – 12:15 PM, Tues-Thur. • Woerner • EE 327 and STAT 215 prereq’s. • Wireless Communication Systems • EE 562 • 2:00 - 3:15 PM, Tues-Thur. • Valenti • EE 461 and/or EE 513 prereq’s.

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