05.103GPPRadio subsystem synchronizationTS
A.2.1 The pseudo‑synchronization scheme
If the pseudo‑synchronization scheme is supported, the BTS shall comply with the following requirements, in addition to those of the main part of the recommendations.
A.2.1.1 BTS a time difference estimate
The BTS shall maintain for each of a set of neighbouring BTS a time difference estimate encoded as in A 1.1. These time differences can be updated when a MS supporting the pseudo‑synchronization scheme enters the cell via a handover: the MS provides the observed time difference corrected for the propagation time with the previous BTS but not corrected for the propagation to the current BTS. When the adaptive frame alignment process in the new BTS has assessed the propagation time, it is used to correct the observed time difference given by the MS and the result is used (possibly after some unspecified processing) to update the value of the time difference with the previous BTS. Other means for maintaining the time difference estimates may be used.
A.2.1.2 The reception epoch criterion
The reception epoch criterion used for evaluating the MS time shift (see subclause 5.6) shall be as close as possible to line of sight path reception epoch, so that with MS supporting the pseudo‑synchronization scheme the timing advance for stationary MS is as close as possible to the double propagation delay.
A.2.1.3 Pseudo‑synchronized handover
When a handover is requested, if the MS supports pseudo‑synchronization, it may be chosen to order a pseudo‑synchronized handover. In that case, the time difference between the two BTS, memorized as specified in A.2.1 and encoded as specified in subclause A.1.1 must be sent to the MS.
A.2.2 The synchronization scheme
If the synchronization scheme is supported, the BTS shall comply with the following requirements, in addition to those of the main part of the specifications.
The BTS shall maintain synchronization with a set of neighbouring BTS. In this context, synchronization means that the timing of the TDMA frame at the BTSs is the same, i.e. the timeslot zeros from the BTS transmitted are synchronous with the timeslot zeros of the carriers on the set of neighbouring BTSs. However, the frame numbers need not be the same. All timings are to be referenced at the BTS.