Discontinuous Transmission
/GSM:06.42/ Voice Activity Detection (half rate speech)
/GSM:06.81/ Overall DTX Operation (enhanced full
rate speech)
The downlink DTX function is supported for channel modes:
• TCH speech, full rate
• TCH speech, half rate
• TCH data, full rate, 9.6 kbit/s, non-transparent
• TCH data, half rate, 4.8 kbit/s, non-transparent
Channel combinations supported /GSM:05.02:6.4/:
• (i) TCH/F + FACCH/F + SACCH/TF
• (ii) TCH/H(0,1) + FACCH/H(0,1) + SACCH/TH(0,1)
The downlink DTX function is enabled when a
CHANNEL_ACTIVATION message, or a MODE_MODIFY message
with the DTX downlink indicator set, is received from the BSC.
The downlink DTX function for speech is initiated when a speech
frame containing comfort noise parameters, is received from the RTC
(Remote Transcoder).
The downlink DTX function for non-transparent data is initiated when a
complete RLP (Radio Link Protocol) frame, with all E1-bits /
GSM:04.21/ set to 1, is received from the RTC.
DTX handling speech
The usage of downlink DTX (on/off) is indicated in the speech frames
and in the idle speech frames to the RTC. To detect if a speech frame
received from the RTC contains speech or comfort noise parameters /
GSM:06.32 / or /GSM:06.42/, the RBS analyses the SID code word /
GSM:06.12:2.2/ or /GSM:06.22:2.2/.
SID frames (including comfort noise parameters) are scheduled in
TDMA frames according to /GSM:05:08:8.3/. When a SID frame is
stolen for signalling (FACCH) purposes, the scheduling in TDMA
frames is carried out according to /GSM:06.31:2.1.2/GSM:06.41:2.1.2/
or /GSM:06.81:2.1.2/ instead.
The output power is turned off during periods of silence, except in the
following cases:
• Transmission of SID frames (comfort noise parameters)
• Transmission of signalling (FACCH)
• Transmission on a C0 carrier (dummy bursts)
• Transmission on a transmitter configured for filling (dummy
bursts)
106 (306)
EN/LZT 123 2697 R5A
1998-08-13
© Ericsson Radio Systems AB
— All Rights Reserved —
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