cellular telephone by L0Oho6

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									           CELLULAR MOBILE
           COMMUNICATIONS
o A cellular mobile communications system
  provides voice, data and multimedia services.
o Used large numbers of low power
  transmitter/receiver (Tx/Rx) known as cell.
o Cell size depends on subscribers density.
o Cell can be split into small cell to
  accommodate growth.
                            CELL
• A cell is the geographical area covered by a cellular telephone
  transmitter.
• A city is divided into small cells.
• Each cell is equipped with a low-powered radio
  transmitter/receiver or Radio Base Station (RBS).
• The cell provided by a RBS can be from one mile to twenty
  miles in diameter, depending on terrain, transmission power,
  and capacity demands.
• The hexagon shape was chosen because it is the most
  efficient and easily managed system.
                      Clusters
• A cluster is a group of
  cells.
• No channels are reused
  within a cluster.
• The figure illustrates a
  seven-cell cluster.
      CELLULAR SYSTEM COMPONENTS
•   Mobile Unit (MU)
•   Radio Base Station (RBS)
•   Mobile Telephone Switching Office (MTSO)
•   Public Switched Telephone Network (PSTN)
              Mobile Units (MU)
• The mobile unit consists
  of a control unit and a
  transceiver that
  transmits and receives
  radio transmissions to
  and from a cell site.
             Radio Base Station (RBS)
• RBS is the physical
  location of radio
  equipment that provides
  coverage within a cell.
• A list of hardware located
  at a cell site includes
  power sources, interface
  equipment, radio
  frequency transmitters
  and receivers, and
  antenna systems.
     Mobile Telephone Switching Office
                  (MTSO)
• The MTSO is the central switch that controls the entire
  operation of a cellular system.
• The MTSO is responsible for monitoring the relative signal
  strength of your cellular phone as reported by each of the cell
  towers, and switching your conversation to the cell tower
  which will give you the best possible reception.
• It houses the mobile switching center (MSC), field monitoring,
  and relay stations for switching calls from cell sites to PSTN.
• The MSC controls calls, tracks billing information, and locates
  cellular subscribers and arranges handoffs.
   Public Switched Telephone Network
                 (PSTN)
• The worldwide voice telephone network.
• The PSTN is made up of local networks, the
  exchange area networks, and the long-haul
  network that interconnect telephones and
  other communication devices on a worldwide
  basis.
          Radio Base Station (RBS)
• Radio interface between MSC and MU
• Consist of antenna, tower or building &
  equipment
• Two types of radio channel
   • Duplex voice channels
   • Duplex control channels
• Signal coverage from RBS depends on
   • Characteristic of the terrain
   • Height of antenna
              Voice Channels (VC)
• Voice Channel: A channel used for transmission of
  voice data from a base station to a cellular phone
  (forward voice channel) or from a cellular phone to a
  base station (reverse voice channel)
• Selected for conversation by MSC during call set up
• When conversation is finished, the channel became
  free for next conversation
• MSC kept a list of all voice channels and their status
  (free, busy, blocked etc)
• When VC free, the Tx of voice channel unit in RBS is
  switched OFF
• When VC is selected, the Tx is switched ON
             Control Channel (CC)
• Control Channel: A channel used for transmission of
  digital control information from a base station to a
  cellular phone (forward control channel) or from a
  cellular phone to a base station (reverse control
  channel).
• The CC is a special frequency that MU & RBS use to
  talk to one another for things like call set-up and
  channel changing.
• MU move from one cell to another will have to tune
  to new CC of that cell
Reverse
channel

     Forward
     channel
                        Antenna


    Transmitter


Frequency Synthesizer


      Receiver


      Logic Unit


     Control Unit
                        Antenna
• RBS used 2 types of
  antenna:
   – Directional
   – Omnidirectional
          Omnidirectional Antenna
• Radiates or receives
  equally well in all
  directions.
• Also called the "non-
  directional" antenna
  because it does not favor
  any particular direction.
• Can deliver very long
  communications
  distances, but has one
  drawback which is poor
  coverage below the
  antenna.
           Directional Antenna
• Focus the RF energy in a particular direction.
• Can divert the RF energy in a particular
  direction to farther distances.
              Cell-phone Codes
• All cell phones have special codes associated with
  them.
• These codes are used to identify the phone, the
  phone's owner and the service provider.
• Types of codes:
   – Electronic Serial Number (ESN)
   – Mobile Identification Number (MIN)
   – System Identification Code (SID)
• Electronic Serial Number (ESN) - a unique 32-bit
  number programmed into the phone when it is
  manufactured.
• Mobile Identification Number (MIN) - a 10-digit
  number derived from cell phone's number
• System Identification Code (SID) - a unique 5-digit
  number that is assigned to each carrier by the FCC.
• ESN is considered a permanent part of the phone,
  both the MIN and SID codes are programmed into
  the phone when you purchase a service plan and
  have the phone activated.
                        Paging
• Paging: The act of seeking a cellular phone when an
  incoming call is trying to reach the phone.
• When MU first power up the phone, it listens for an
  SID on the control channel.
• If the phone cannot find any control channels to
  listen to, it knows it is out of range and displays a "no
  service" message.
• When it receives the SID, the phone compares it to
  the SID programmed into the phone.
• If the SIDs match, the phone knows that the cell it is
  communicating with is part of its home system.
• Along with the SID, the phone also transmits a
  registration request, and the MTSO keeps track of
  MU phone's location in a database.
• This way, the MTSO knows which cell MU are in
  when it wants to ring the phone.
• The MTSO gets the call, and it tries to find MU.
• It looks in its database to see which cell MU are in.
• The MTSO picks a frequency pair that MU phone will
  use in that cell to take the call.
• The MTSO communicates with MU phone over the
  control channel to tell it which frequencies to use,
  and once MU phone and the tower switch on those
  frequencies, the call is connected.
• Now, MU are talking by two-way radio to a friend.
• As you move toward the edge of your cell, your cell's base
  station notes that your signal strength is diminishing.
• Meanwhile, the base station in the cell you are moving toward
  (which is listening and measuring signal strength on all
  frequencies, not just its own one-seventh) sees your phone's
  signal strength increasing.
• The two base stations coordinate with each other through the
  MTSO, and at some point, your phone gets a signal on a
  control channel telling it to change frequencies.
• This hand off switches your phone to the new cell.
                   Handoff
• Handoff: The process by which the MTSO
  passes a cellular phone conversation from
  one radio frequency in one cell to another
  radio frequency in another.
• Handoff occurs when the MTSO automatically
  transfers a call from radio channel to radio
  channel as a mobile crosses adjacent cells
• The handoff is performed so quickly that MU
  usually never notice.
• During a call, two parties are on one voice channel.
• When the mobile unit moves out of the coverage area
  of a given cell site, the reception becomes weak.
• At this point, the cell site in use requests a handoff.
• The system switches the call to a stronger-frequency
  channel in a new site without interrupting the call or
  alerting the user.
• The call continues as long as the user is talking, and
  the user does not notice the handoff at all.
              Frequency Re-use
• Frequency Reuse: The process of using the same
  carrier frequency (channel) in different cells that are
  geographically separated.
• A set of cells each operate on different channel in a
  group to form cluster.
• A cluster is repeated as many time as necessary to
  cover wide area.
• Adjacent cells are not allowed to operate at the same
  frequency since this causes interference between the
  cells.
• Since each cell is designed to use radio
  frequencies only within its boundaries, the
  same frequencies can be reused in other cells
  not far away with little potential for
  interference.
• Cells are assigned a group of channels that is
  completely different from neighboring cells.
                   Cell Splitting
• Cell Splitting - The process of creating more
  coverage and capacity in a wireless system by
  splitting/divide a single cell into smaller cells.
• As a service area becomes full of users, this
  approach is used to split a single area into
  smaller ones.
• In this way, urban centers can be split into as
  many areas as necessary to provide acceptable
  service levels in heavy-traffic regions, while
  larger, less expensive cells can be used to cover
  remote rural regions
       Signal-to-noise Ratio (SNR)
• Signal-to-noise ratio (SNR or S/N) is defined as
  the ratio of a signal power to the noise power.
• Measured in decibels (dB)
• SNR shows how much stronger/weaker the
  desired signal compared to unwanted noise.
• A higher value indicates less background
  noise.
                    Making a Call
• When a cellular user makes a call from a cellular phone, radio
  signals are transmitted to the cell site.
• The cell site alerts the MTSO switching station.
• The MTSO provides an open channel ( frequency ) and
  connects the call to the PSTN.
• The PSTN put the call through to the number to be reached.
• This process takes the same amount of time that it takes to
  make a call from a land line phone.
                  Receiving a Call
• A call placed to a cellular phone may come from either a land
  line phone or another cellular phone.
• Whichever the source, the MTSO is notified that a call has
  been placed to a specific cellular telephone number.
• At this point, the MTSO searches for the correct cellular
  phone by sending out data over the radio waves.
• Cellular phones that are in standby mode ( i.e., turned on but
  not being used in a call ) continuously scan the radio waves
  being transmitted by the MSTO.
• If a phone " hears " its telephone number, it sends back a
  signal that informs the closest cell site of its Electronic Serial
  Number ( ESN ) and its telephone number ( Mobile
  Identification Number or MIN ).
• The cell site passes this information to the MTSO, where the
  ESN and MIN are verified and a channel ( frequency ) is
  assigned for the call.
• The cellular phone receives the message directing it to tune to
  the correct voice channel.
• The cell site makes the voice channel available, and the call is
  completed.
               Call Termination
• If the land-based phone ends the call, the MTSO
  issues a release order.
• The phone responds by sending about two
  seconds of supervisory tone.
• If the mobile unit ends the call, it simply sends
  about two seconds of supervisory tone.
• In either case, the phone then turns off the
  transmitter, tunes to the strongest paging
  channel, and returns to the idle state, listening
  for a page.
                        WAP
• Wireless Application Protocol (WAP) is an open
  international standard for applications that use
  wireless communication.
• Its main use is to enable access to the Internet from
  a mobile phone or PDA.
• In 1997, Nokia, Motorola, Ericsson and Phone.com
  came together to create the WAP because they
  believed that a universal standard is critical to the
  successful implementation of wireless Internet.
• A mini-browser is an integral part of WAP enabled
  phones.
• WAP strips all but graphics for display on small screens, such
  as mobile phones.
• A WAP browser provides all of the basic services of a
  computer based web browser but simplified to operate within
  the restrictions of a mobile phone, such as its smaller view
  screen.
• WAP sites are websites written in WML (Wireless Markup
  Language) and accessed via the WAP browser.
• WAP allows mobile users to check Email by mobile phone,
  tracking of stock market prices, sports results, news headlines
  and music downloads
                         Amazon web WAP
Amazon web in Internet

								
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