Product manual

System description, DECT air interface

Technical Product Manual - DCT1800-GAP

TD 92093 (1/LZBNB 103 108 R4D) / 2006-03-09/ Ver.C

• Radio exchange number

• Base station number

• Cordless phone number

• Carrier number and time slot pair

• Antenna number

• Quality of received package

• Access rights indicator

Speech data field

This field contains the speech samples in Adaptive Differential Pulse Code Modulation (ADPCM) code.

CRC field

This field contains a Cyclic Redundancy Check (CRC) code to check if a packet was received correctly.

Z-field

This optional field is used to detect collisions between packages. Collisions are possible since DECT

supports uncoordinated system installation and so DECT systems may not be synchronized. Thus, if

DECT systems are physically located nearby each other there can be interference. The Z-field may

be used by the receiver for early detection of unsynchronised interference sliding into the end of the

physical packets. Unsynchronised interference sliding into the beginning of a packet can be detected

by bit errors in the sync-field. The Z-field is identical to the CRC-field. By constantly comparing the Z-

field with the CRC-field a cordless phone can detect when the Z-field becomes corrupted and then

request for a handover before data is corrupted.

Guard field

The guard field avoids the loss of information due to the overlap of time slots. Time slots overlap due

to the limited propagation speed of the radio waves and power ramp up/down of transceivers in both

cordless phones and base stations.

Fig. 29 Packet format in speech applications

Carrier

time slots:

TDMA frame: 10 ms

Sync Signalling

Speech data

CRC

32 64 320 4

Number of bits:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Base station transmits Cordless phone transmits

456

Guard

016