UK Aerial Robotics Team

1
Cell Phone Technologies

• Overview of Cellular Phone Technologies
• Technology Generations
• Cellular Networks
• Messaging Services
• By Matt Smith

2
Cell Phone Technologies

• The Gs
• Cellular networks are broken up into three
  generations of technologies
• 1G Analogue cell phone standards introduced in
  the 1980s
• Analogue signal was modulated to higher
  frequencies (150MHz and up)
• Required more bandwidth and poor noise rejection
• 2G The call is encoded into digital signal
• Can be compressed and multiplexed more
  effectively for better use of bandwidth
• More susceptible to drop outs and loss of
  tonality in someone's voice
• 3G The second generation digital technology
• Increased bandwidth to allow for the transfer of
  voice and non-voice data simultaneously

3
Cell Phone Technologies

• The popular 2G cellular networks
• GSM Developed by an international association
  (Cingular)
• Advantages Better international coverage, and
  battery life
• CDMA Proprietary network developed by Qualcomm
  (Sprint/Verizon)
• Advantages Better U.S coverage and higher data
  transfer rates

4
GSM Network

• Basic diagram of a GSM network

5
Accessing the GSM network

• Subscriber Identity Module (SIM) card Programmed
  with the users phone identity and personal
  information
• Base Transceiver Station The mobile phone mast
  that mobile phones attempt to establish a
  connection
• Home Resource Locator SIM record is stored in
  database by the home phone company
• Visitor Resource Locator Contact the HRL to
  retrieve information about services available to
  the user

6
After Establishing a Connection

• Once a connection to the network has been
  established a number of services are open to the
  end user including
• Voice calls Encodes audio signals in a digital
  form and routes the audio data to the Public
  Switched Telephone Network via a message
  switching center
• Direct Data Services Several services
  implemented to deal with digital data directly
  without inefficient conversions to and from audio

7
Direct Data Services

• Established connection data services
• Circuit Switched Data (CSD)
• General Packet Radio Service (GPRS)
• Enhanced Data Rates for GSM Evolution (EDGE)

8
Communication Paradigms

• Circuit switching When the connection is
  established the full bandwidth is reserved for
  the duration of the connection.
• Generally charged for by the minute because
  bandwidth is be used even if nothing is being
  transferred
• Packet switching Users share the same channel
  and bandwidth is only used during transfers
• Generally charged by data transferred because
  bandwidth is not reserved during the connection

9
Data Transfer Service

• Circuit Switched Data GSM first data
  transmission
• CSD reserved one time slot for data rates up to
  9.4 kbps
• High Speed Circuit Switched Data Based off of
  CSD, it provide faster data rates through better
  coding and by reserving up to four time slots

10
Data Transfer Services (cont.)

• General Packet Radio Service Packet switching
  service that take advantage of unused time slots.
  Data transfer rates of about 40 kbps.
• EDGE Defines a new hardware layer for GSM
  network and triples the gross data rate offered
  by the network

11
Connecting to GPRS

• Mobile device must attach to the GPRS network
  then activate a PDP context
• Packet Data Protocol Data structure allocated
  that contains subscribers session information
• Once the context has been activated the device
  can transmit packets of its supported packet data
  protocol type
• Generally IP is the only supported data protocol

12
Short Message Service

• SMS uses a store and forward approach to send
  messages
• Messages are sent to a short message service
  center (SMSC)
• The SMSC will attempt to send the message to the
  recipient, if the recipient cannot be reached the
  message is stored and the SMSC will retry
  delivery when the destination is reachable
• Message delivery is best effort. There are no
  guarantees the message will be delivered. Delays
  and complete message loss is not uncommon
• Payload is limited to 140 bytes
• Long SMS is segmented over multiple messages. In
  this case a user data header (UDH) is defined
  lowering the effective payload to 134 bytes

13
Final Notes

• GPRS compatibility classes
• Three classes exist
• Most devices are class B
• The device can be connected to GPRS service or
  GSM service. If the device needs to use a GSM
  service (voice, SMS) the GPRS service is
  suspended and automatically resumed when the GSM
  service completes
• Most mobile devices have a defined AT command set
  that allows an external device to use the mobile
  device
• Command State the mobile device receives AT
  commands
• Data State Once PDP context has been activated
  the mobile device enters a data state to send and
  receive data packets. The device stays in this
  state until the layer 2 termination procedure has
  been completed successfully.