Page 1036 - 5G Basics - Core Network Aspects

2 Transport aspects

For a given Mds, the value of Mus results from the following equation:

Mus = MF – 1 – Mds
X.6.4 The TDD frame prior to and after a DTA update

The DTA procedure modifies the number of downstream symbol periods Mds in a TDD frame, and
correspondingly the number of upstream symbol periods Mus, while the duration of the TDD frame
MF = Mds + Mus +1 and all other parameters of the TDD frame remain unchanged. The RMC symbol offsets
(DRMCds and DRMCus) and the downstream and upstream ACK window shifts (DS_ACK_WINDOW_SHIFT and
US_ACK_WINDOW_SHIFT) shall also remain unchanged by the DTA update.
If DTA is enabled, the RMC symbol offsets DRMCds and DRMCus shall be selected during initialization such that
just prior to and immediately after any DTA update, the following conditions are met (see Figure X.2):
Mus – DRMCus – 1 + DRMCds ≥ 4 (1)
Mds – DRMCds – 1 + DRMCus ≥ DTA_min_DRMCds2us (2)

where DTA_min_DRMCds2us is indicated by the FTU-R during initialization (see the NPar(3) field
'DTA_min_DRMCds2us' in Table X.13 in clause X.7.1), with valid values being 4 and 5.
NOTE – Equation (1) and (2) ensure that:
• The time period between the US RMC to the DS RMC (sent in the following TDD frame) is at least 4 symbols;
• The time period between the DS RMC to the US RMC (of the same TDD frame), is at least
DTA_min_DRMCds2us symbols.

Figure X.2 – TDD frame structure before and after a DTA update
NOTE – As explained above, the only parameter of the TDD frame that is changed by a DTA update is Mds (and Mus as a
result), while the other parameters of the TDD frame such as the duration of the TDD frame, the RMC symbol offsets
and the ACK window shifts are unchanged. As a result, the size of the downstream ACK window, associated with the
first TDD frame that is using the new Mds value:
• will be greater than the downstream ACK window size of the previous TDD frame if Mds increased due to
the DTA update.
• will be less than the downstream ACK window size of the previous TDD frame if Mds decreased due to the
DTA update.
The upstream ACK window size will not be affected by a DTA update. A few examples to illustrate this are
given in Figure X.3.

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