DECT Digital Enhanced Cordless Telecommunications

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DECTDigital Enhanced Cordless Telecommunications

• X32TSS
• Dominik Peklo Ondrej Caletka
• FEE CTU Prague

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Introduction

• European standard for digital cordless telephony
  data transmission
• Picocelluar infrastructure, low power, low
  interference, high capacity
• Easy to deploy no need for frequency planning
• Provides cordless access to various fixed or
  mobile networks via gateways

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History

• Early 1980s saw introduction of the first analog
  cordless telephone systems CT0/CT1 (mainly
  Sweden, UK)?
• Soon after, an inevitable shift to digital
  transmission followed. CT2 coexistence standard
  published in 1987 in UK
• Sweden pushing its TDMA/TDD in contrast to UKs
  FDMA/TDD
• 1988 DECT development initiated by ETSI based
  on TDMA/TDD/MC principles
• 1992 DECT is approved standard ETS300-175

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Specifications

• Modulation scheme GMSK
• Access method TDMA/TDD/MC
• Frequency band 1880-1900 MHz
• 10 carriers with 1728kHz span
• 24 timeslots per carrier (12 duplex)?
• total of 1152 Kbps per carrier
• maximum/mean Tx power 250/10 mW
• 32 Kbps ADPCM G.726 speech encoding

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Continuous DynamicChannel Selection

• DECT portable parts continuosly measure RSSI for
  all carrier and timeslot combinations and
  maintain an updated list in memory
• When setting up a call, the frequency/timeslot
  with the lowest measured RSSI is automatically
  selected

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Handover

• Support for seamless intracell or intercell
  handover as a means to escape from interfered
  channel and to support endpoint mobility
• Handover managed by the portable part based on
  the continuous RSSI measurement of available
  channels

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Security

• Subscription registering the portable to the
  network
• Authentication verifying portable's key
• Ciphering Encryption of audio data by per-call
  random key.

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Application Profiles

• GAP (Generic Access Profile) Basic telephony
  service, minimum set of mandatory features,
  insures mutual compatibility of different
  manufacturers equipment
• GIP (DECT/GSM Interworking Profile) Allows DECT
  portables to access GSM network DECT base
  station is directly connected to GSM MSC.
• IIP (ISDN Interworking Profile) DECT-based
  wireless bridge for ISDN S0 interface. Effective
  radio channel utilization.
• RAP (Radio Local Loop Access Profile) An
  alternative to laying cables on Last Mile. Cost
  efficient way to spread POTS in developing
  countries.

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Advantages/Disadvanatges

• No frequency planning needed
• Low transmitted power, low interference
• Easy to use, hard to eavesdrop (ciphering)
• Cordless access to other services (VoIP etc.)
• Speech quality comparable to ISDN
• Small area coverage
• High infrastructure cost
• Need to carry 2 phones (GSM DECT)?
• Low bandwidth for data (overtaken by 802.11)

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Conclusion

• The leading cordless telephony standard nowadays
• Encrypted for high security
• High quality speech
• Data transfer is possible
• Interference avoidance
• Being obsoleted by GSM boom

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Time for your questions...

• References
• http//en.wikipedia.org/wiki/DECT
• http//www.dectweb.com/
• http//www.dect.ch/pdf/TechnicalDocument.PDF
• http//www.dectweb.com/LearningZone/IEEE1992Articl
  e.pdf
• http//www.rdc.cz/prilohy/hardware/152_DECT.pdf
• http//mobil.idnes.cz/telefony.asp?rtelefonycA9
  81128_0002811_telefony