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Synchronisation
Different UTRAN synchronisation required in a 3G network:
Network synchronisation
Node synchronisation
Transport channel synchronisation
Radio interface cynchronisation
Time alignment handling
Synchronisation Issues Model
Network Synchronisation relates to the distribution of synchronisation references to the UTRAN Nodes and the stability of the clocks in the UTRAN (and performance requirements on UTRAN internal interfaces). The distribution of an accurate frequency reference to the network elements in the UTRAN is related to several aspects. One main issue is the possibility to provide a synchronisation reference with a frequency accuracy better than 0.05 ppm at the Node B in order to properly generate signals on the radio interface.
Node Synchronisation relates to the estimation and compensation of timing differences among UTRAN nodes. FDD and TDD modes have different requirements on the accuracy of the timing difference estimation and on the necessity to compensate for these differences. Positioning / Localisation functions may also set requirements on Node Synchronisation.
The Transport Channel Synchronisation mechanism defines synchronisation of the frame transport between RNC and Node B, considering radio interface timing.
The Radio Interface Synchronisation relates to the timing of the radio frame transmission (either in downlink [FDD] or in both directions [TDD]). FDD and TDD have different mechanisms to determine the exact timing of the radio frame transmission and also different requirements on the accuracy of this timing. In FDD Radio Interface Synchronisation is necessary to assure that the UE receives radio frames synchronously from different cells, in order to minimise UE buffers.
The Time Alignment Handling procedure over Iu relates to the control of DL transmission timing in the CN nodes in order to minimise the buffer delay in SRNC. This procedure is controlled by SRNC.
Further reading: 3GPP TS 25.402
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