Wireless Services

1
Wireless Services

• Available for 10 years
• Paging
• Analog cellular
• New
• Digital cellular
• LEOs
• 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
• 1930s more widespread use to other public
  safety agencies, fire departments
• Now aviation, trucking, taxis, marine

6
Analog Cellular

• Developed in the 70s by ATT
• provided by local telcos
• implemented in the 80s
• 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 areas
• 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 areas
• 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 areas to have two providers
• rural areas 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
  areas

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
• Users 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 Telcos 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 areas unlike
  digital telephone service
• Nationwide service available

34
Leos

• 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 (GTEs)

42
Wireless for Local Telephone

• Fixed wireless fixed antenna on premise
• 1,000 wireless -vs- 2,000 landwire
• neighborhood antennas 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