Reference Manual

Call Control
later and later. The answer from the MS also arrives later and later at
the RBS. This function prevents the delay becoming so long as to cause
TS3 to overlap onto TS4, thus disturbing another call.
The function is terminated when the dedicated Resource Channels enter
state IDLE.
There are three different kinds of Adaptive Frame Alignment:
1. Access Delay Measurement
From the start of normal burst reception on a dedicated channel, the
RBS measures the Access Delay on all received bursts. These values
are used at the calculation of a new ordered TA value to the MS, see
Dynamic Time Alignment.
2. Initial Time Alignment
At start of downlink SACCH transmission, an initial ordered TA value
(received at channel activation) is used in the L1 header of the SACCH
block.
3. Dynamic Time Alignment
Three inputs are used to calculate the new/next TA order value included
in the L1 header of the downlink SACCH block /GSM 04.04:7.1/:
• The access delay measurements on all normal bursts that are
received since the last calculation (one SACCH reporting period)
•
The actual used (by MS) TA value which is received in L1 header
/GSM 04.04:7.2/ of the uplink SACCH block
• The previous/unit ordered TA value to MS
The ordered TA value must not be changed more than 1 step from the
TA /GSM 05.10:5/ previously ordered.
20.4 Asynchronous Handover Detection
Purpose
To detect access bursts (in a handover situation).
Preconditions and Initiation
See Channel Activation above.
Description
When the RBS is taking over the communication, in a handover
situation, it has no information of the distance to the MS and
consequently no Timing Advance information. The MS transmits access
bursts. These burst are kept very short (only 8 bits of information) in
order to prevent disturbing another call. This function measures the
delay of handover access burst received by the RBS and sets the
Timing Advance. The information is included in the
EN/LZT 720 0008 R1A
2001-06-26
195 (421)
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