Transcript DECT Digital Enhanced Cordless Telecommunications X32TSS

DECT
Digital Enhanced Cordless
Telecommunications
X32TSS
Dominik Peklo & Ondřej Caletka
FEE CTU Prague
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
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 it‘s TDMA/TDD in contrast to
UK‘s FDMA/TDD
• 1988 – DECT development initiated by ETSI
based on TDMA/TDD/MC principles
• 1992 – DECT is approved standard ETS300-175
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
Continuous Dynamic
Channel 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
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
Security
• Subscription: registering the portable to the
network
• Authentication: verifying portable's key
• Ciphering: Encryption of audio data by per-call
random key.
Application Profiles
• GAP (Generic Access Profile): Basic telephony
service, minimum set of mandatory features,
insures mutual compatibility of different
manufacturer‘s 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.
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)
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
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/IEEE1992Article.pdf
•
http://www.rdc.cz/prilohy/hardware/152_DECT.pdf
•
http://mobil.idnes.cz/telefony.asp?r=telefony&c=A981128_0002811_telefony