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Wireless Service Engineering

Properties of Communication technologies

  • Communication range
    • Lower frequency → less power required to gain longer distance,
  • Latency
  • Data transfer rate
  • Architecture
  • Price for creating network

Cellular Technologies

  • aka Mobile phone technologies
    • TDMA, GSM, GPRS, EDGE, UMTS …
  • Supported mainly by mobile phones
    • Adding the capability to the device
      • PCMCIA cards
      • CF cards
    • Connection through mobile phone
      • Serial connection over wire
      • Wireless Bluetooth connection
  • Different cellular standards are supported in different areas of the world
    • Some standards use different frequencies on different areas
    • Compatibility problems for mobile terminals
    • Created solution may require some conversion in order to work in different areas.
  • Topology
    • Terminals connected to base stations at fixed location.
    • Base stations are connected to each other usually with wires.
  • Base stations
    • In other technologies these are called access point
    • Base station coverage area is called cell
    • Cell sizes vary
    • Base stations are connected to each other with dedicated lines
  • Regulated radio frequency
    • Creating own network requires license

Connectivity

  • Two types of connections

1. Voice connections

2. Data connections

  • Connection oriented (GSM Data, IP connections)
  • Connectionless messaging (SMS,MMS)
  • Two separate logical channels
  • Control channels (CCH) for signaling (CCH)
    • handling connections
    • messaging capabilities.
  • traffic channels (TCH) for payload, speech or data
  • Connection forming between BS and mobile
    • Mobile requests free channel for signalling
    • BS allocates the signalling channel
    • MS requests call setup and gains traffic channel from BS
  • Authentication of Mobile is based on Subscriber Identity Module (SIM)
    • Contains
      • International Mobile Subscriber Identity (IMSI)
      • Personal Identification Number (PIN)
      • Identifying key
      • Cryptograhic algorithms
  • Latency
    • From hundreds of milliseconds up to seconds.
    • Processing the connections increase latency
      • The more there is users the higher the latency
  • Good support for mobility
    • Handovers and roaming.

Messaging

  • Connectionless transfer of messages
  • One messages can contain maximum of 140 octets (bytes)
    • GSM alhabet is 7-bit → 160 characters maximum
    • SMS concatenation allows multiple smaller messages to be used to deliver one long message.
    • Can also be used to deliver binary content.
  • Message delivery is not guaranteed
    • Best effort delivery
  • Class 1 messages pop on screen when arriving
    • Meant for urgent information
  • Billing is message based

GSM DATA

  • Mobile phone used as a modem
  • Circuit-switched
  • Bandwidth 9600 bit/s
  • High-Speed Circuit-Switched Data (HSCSD) allocates several data channels into one logical link
    • Bandwidths up to 43.3 kbit/s
    • Realistic bandwidth is usually about 30 Kbit/s when stationary and 10 Kbit/s when moving.
  • Billing is time based

GPRS

  • Enhancement to GSM
    • Seperate GPRS network added behind Base Station Controller (BSC)
    • BTS, BSC and databases require software update
    • BSC requires Packet control unit.
    • New mobile terminal required (terminals backward compatible)
  • Packet based communication
  • Support typically up to 100 users
    • User may utilize 1-8 channels
  • Support for IP and X.25 packets
    • TCP over X.25
    • UDP and TCP over IP
    • Applications can be created on top of TCP or UDP
  • GPRS connection
    • Mobile has to activate the packet data address
    • Mobile initiates connection to the service
  • Billing is based on the amount of data transfered.

EDGE

  • Enhanced Data rates for GSM Evolution (EDGE) (EGPRS)
    • Enhancement of GPRS
    • Can utilize existing GSM core network
      • Only software uogrades required.
  • Data rates up to 384 kbit/s
    • Achieved by using 8PSK (8 Phase Shift Keying)in addition to GMSK (Gaussian minimum-shift keying)
    • 3bit word for every change in carrier phase

UMTS

  • Standardized by 3GPP
  • Uses WCDMA
  • Supports up to 1920 kbit/s data transfer rates
    • Currently reality: 384 kbit/s
  • Currently very limited area covered

Things to consider

  • The network is owned by network operator
    • Operator charges on the network use
    • Messaging based service can use operators charging infrastructure.
      • The use of service is charged in phone bill.
  • Peer-to-Peer communication problematic

Do it yourself: SMS based service

  • Details with c-code can be acquired : Ikonen, Porras, Hämäläinen: Mobile Network Services with Linux, Embedded linux journa,l march/april ,2001
  • Parts:
    • Desktop computer running Linux operating system
    • Nokia Communicator
    • Serial cable between communicator and desktop computer
      • Communicator is shown in /dev/TTYSx where x depends on the communication port used.
  • Communicator is controlled using AT commands
    • Communicator has to be set to “fax modem” mode to accept these commands and activate
    • Connect communicator with terminal program
    • Set the number to message center: AT+CSCA=“number”, 145
  • Receiving message
    • Set communicator to online mode: AT+CNMI=1,2
      • messages are given directly to the serial line
    • Listen the serial port
  • Sending message
    • AT+CMGS=“number”
    • write message and press ctrl-Z to sent the message
  • Combining these methods, dierenr kind of services can be created.
Last modified: 2013/07/01 14:41