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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.

26.4 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 P2A

2001-11-28

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Preliminary