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Wireless Services

Wireless Services

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Wireless Services

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  1. Wireless Services • Available for 10 years: • Paging • Analog cellular • New: • Digital cellular • LEO’s • PCS • SMR

  2. History Wireless • Mobile telephony first provided by two-way radio • 1946: first mobile service available in St. Louis, Missouri • $2,000 - $3,000 per phone • each city 1 transmitter/receiver • range limited

  3. History Wireless • one transmitter shared same channels • 25-35 calls could be handle at one time • quality spotty • static high • frequent breaking up of calls

  4. Early Service Area • Provided by wireline common carriers: • Bell company • independent • radio common carrier • High cost service • Many unserved customers • Untapped market solved by cellular service

  5. Mobile Radio • Closed system, was not connected to PSTN • taxicabs could only talk to taxicabs • police early pioneers of this service • 1921: Detroit police • 1930’s: more widespread use to other public safety agencies, fire departments • Now: aviation, trucking, taxis, marine

  6. Analog Cellular • Developed in the 70’s by ATT • provided by local telco’s • implemented in the 80’s • with standard format to work with PSTN • most important function was to add capacity to non-cellular mobile telephone service • more affordable telephones responsible growth

  7. Analog Cellular • As this service became more affordable • used in business • used as personal tool • Became extremely popular • now capacity constraints in metro area’s • digital cellular developed to add more capacity

  8. Spectrum Allocation • Different portions of the spectrum assigned to: • aviation • marine • public agencies • broken into bands assigned by FCC • residential cordless: 46-49 MHz • CB: 27, 462,467 MHz

  9. Spectrum • TV channels and mobile radio services are allocated very high frequency bands in the 30-300 MHz range • 30 MHz means that each wave has 30 million cycles or hertz per second • the higher the frequency, the shorter the radio wavelength • the smaller the wavelength the more susceptible to weather conditions • 3000 hertz longer wavelength than 3,000,000 hertz wave

  10. Wavelengths • Raindrops and other wind conditions can affect wavelengths • The smaller the wavelength the more it will be affected by the weather • Reason why high-frequency microwave systems are susceptible to weather conditions than low frequency systems

  11. PCS Services • Are allocated very high frequencies • Cannot be transmitted as far as lower frequencies • PCS towers and antennas are therefore placed closer together than lower frequency cellular services when covering the same area

  12. Spectrum Limitations • Spectrum is a limited resource • Goal of new wireless technologies is to do more with less and to be able to share the spectrum with increasing number of users • spectrum first stretched by setting up hexagonal shaped cells • digital adds capacity through multiplexing: CDMA or TDMA

  13. Background Cellular • Grew out of advanced mobile radio service • analog cell service available in metro area’s • only 25-35 conversations possible at a time in one metro area • cellular added capacity due to cells • reuse of frequencies by allowing each cell to carry up to 57 calls per cell • more  more capacity

  14. Cellular Service • 1983: first cells trialed in Chicago and Baltimore • FCC decisions: • allocate 825-890MHz spectrum to cellular • metro area’s to have two providers • rural area’s to have two providers • A (provider) & B blocks of frequencies assigned • non-metro frequencies given out by lottery • 1987: 200 cellular systems in place in 127 metro area’s

  15. Cellular Market • Slow to become popular in US, too expensive • 1990 finally showed large increase • due to decreases in charges 1988-1990 • 1990: 5 million users -vs- 1996 44 million • 88% increase • Europe higher penetration, higher use

  16. Cellular Market • Major challenges facing providers: • lack of uniform national cellular network and uneven quality in service • lack of multiplexing standards • PCS not fully built • service on cellular calls uneven

  17. Basic Principles Cellular • 50MHZ bandwidth in 800-900MHz radio band used to create 832 two-way radio channels • channels are reused by use of low-power radio transmitters, each serving a geographic area called a cell • 7 cells form a cluster, pattern of clusters repeated over and over

  18. Basic Principles Cellular • Cells are depicted as hexagons • In reality shape varies by geography/terrain served • cell configuration minimizes interference caused by reuse of a channel • Cells serving dense areas are assigned more channels

  19. Basic Principles Cellular • If congested  cells are further subdivided or split into smaller cells using lower powered transmitters • System can grow gradually • User’s mobility tracked from cell to cell in order to change radio channels appropriately

  20. Basic Principles Cellular • Handoff: tracking of user along with changes in channel usage • Handoff information sent to next cell in the downlink speech channel through in-band signaling • Paging: shared radio channel used to broadcast the numbers of mobile units being called

  21. Multipaths • High-frequency radio transmission is used in cellular telephony • These are highly susceptible to reflections that lead to multiple paths from the transmitter to the receiving antenna • Multiple signals may arrive out of phase • Cancel each other out

  22. Multipaths • Cancellations cause fast fading of the received signal as automobile travel • Signal processing used to minimize fading by filling in missing portions of signal

  23. D-AMPS • Digital-advanced mobile phone service • Digital cellular: • has more capacity per cell than analog cellular • developed to add capacity to system • reached limit on breaking cells up into smaller sizes (leads to dropped calls) • meant to compete with PCS (caller ID, call waiting, paging, short message, etc.) • improved privacy

  24. Digital Cellular • Offered over same frequencies as their analog cellular service • 3 to 10 more capacity than analog service

  25. Multiple Access • Overall capacity increased by sharing a radio channel among a number of voice channels • TDMA (time division multiple access) • CDMA (code division multiple access)

  26. TDMA • Same band of frequencies is shared by all the calls • Short bursts of digital data from each conversation are sent • Packets are reassembled at destination • A digital system assigns 10 time slots for each frequency channel • Originated in satellite communication

  27. CDMA • Also called spread spectrum • Each phone call combined with a code which only one phone plucks from the air • Dispersed signals are pulled out of the background noise by a receiver which knows the code • Developed by Qualcomm Inc.

  28. Limitations Analog Cellular • Change in signals and errors introduced during hand offs between base stations, wireless network, and land base stations • High error rate  delays due to retransmissions • slow speed 9600 Bps

  29. Digital Cellular • Digital multiplexing developed to add capacity • With digital multiplexing features added: • caller id • call forwarding • 3-way • handset with paging • short message servicing

  30. Digital Multiplexing • To be used on existing cellular airwave capacity as well as on new space provided by FCC • All digital services use multiplexing to offer diverse services • Softer handoff, calls are rarely dropped • Handsets use lower amount of power

  31. GSM • 1987: European Union choose GSM as standard for delivery of wireless channel • US: choose TDMA and later CDMA, Telecom Industry Association (TIA) settled on TDMA, however many Bell Telco’s decided to go with newer CDMA •  US started with two different standards different from Europe

  32. Digital Services US • Use different frequencies: • PCS • digital cellular • Both can: • utilize TDMA or CDMA, offer same features • both difficult to eavesdrop due to multiplexing • PCS: lower cost, lower towers, smaller

  33. Paging • Well established wireless service • Booming industry • Voice mail and two-way messaging being added • Can be reached in many remote area’s unlike digital telephone service • Nationwide service available

  34. Leo’s • Moterola, Hughes, Teledesic, Loral, TRW • Poured billions into purchase of airwaves and technology • To provide telephone, data communication, broadcast quality video and internet access • Outcome: bankrupt now repositioning

  35. SMR • Used originally for dispatch services • Field maintenance crews and delivery organizations • Best use for bursty information • New networks by Motorola and IBM: • ARDIS • RAM

  36. ARDIS/RAM • Packetized radio data only systems • slow speeds • trucking and dispatch systems • email to mobile workers • licensee look-up • tracking car rentals

  37. Nextel • Changed its analog data network services form all data communication to a voice and data network • Expanded use of lower spectrum used in SMR • Upgraded to all digital • Sells PCS like services

  38. PCS • Low cost, feature rich wireless phone service • Pricing to be low enough for wide audience • Handsets incorporate: • two-way paging • short messaging, voice messaging • LCD screen • Meant to combine mobile phone, pager, answering machine

  39. PCS • 1800 -1900 MHz range • Use of higher frequencies • Lower towers, but more towers required • Towers inexpensive to build • Still no multiplexing standards • Incompatible methods of digitizing calls • Multiple manufacturers

  40. PCS • Personal communication services • conceived to be a low cost, feature rich wireless phone service • pricing low to capture wide audience • handsets incorporate: • two-way paging - voice messaging • short messaging - LCD screen • meant to combine: mobile phone, pager, answering machine

  41. Wireless for Local Telephone • LEC may get into wireless to link directly into local loop • Pacific Telesis, copper/fiber at capacity • Offers low cost way to expand into other territories (GTE’s)

  42. Wireless for Local Telephone • Fixed wireless: fixed antenna on premise • $1,000 wireless -vs- $2,000 landwire • neighborhood antenna’s beam radio signal to homes (2000 homes serviced one antenna) • Debit cards for wireless calling • prepaid airtime • popular for those who have no credit • popular all over the world, just starting in US

  43. Private Networks over Mobile Frequency • 1970: transmission of data using RF networks • Federal Express • used for tracking of packages by scanning bar codes taped to each package, repeated at strategic points • scanner sends data to main processor • know where package is at all times

  44. CDPD • Cellular Digital Packet Data or IP wireless • Developed by IBM to transmit data over spare capacity in analog networks • Good for transmitting short, bursty messages: email, credit card information, alarm monitoring • Speeds slow, but the price is right • Not widely used