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Feature #1545
opencontinuous timing advance loop using PTCCH
Start date:
02/23/2016
Due date:
% Done:
60%
Spec Reference:
44.004 7.8 + 7.9 | 44.018 3.5.3.1 | 45.010 6.5.2 | 45.002 7 Mapping Table 6
Description
We currently only implement the "initial TA" where the TA of a MS is determined at time the TBF is established. If the MS moves more than 1 TA during a TBF being active, this leads to problems.
GPRS has the PTCCH for this, a special channel in the PDCH channel combination multiplex, using which we can instruct a sub-set of 16 MS (whether TBFs are active or not) to adjust their timing advance continuously. What needs to be done is- code to generate the PTCCH/D messages
- code to parse the PTCCH/U messages
- code to determine which 16 MS will be part of the current PTCCH subset
- unit tests for the above
We also need to see how we can test this with actual hardware, in a way that TA exists (and changes) over time. Unfortuantely we don't have a MS-side GPRS implementation for OsmocomBB, because then we could simply artificially delay the transmit burst timing to make the network determine a higher TA.
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