Page 921 - 5G Basics - Core Network Aspects

Transport aspects 2

The FTU-O determines the duration of the VECTOR 2 stage and indicates the completion of this stage by
sending an O-P-SYNCHRO 4 signal. After completion of this stage, any joining lines can transmit
downstream and upstream data symbols without disturbing transmission over active lines and with
crosstalk from active lines and other joining lines cancelled.

12.3.3.1.8 PARAMETER UPDATE stage

The FTU-O transmits sync symbols modulated by probe sequence and SOC symbols over the first sds symbol
positions of each downstream logical frame. The FTU-R transmits sync symbols modulated by probe
sequence and SOC symbols over the first sus symbol positions of each upstream logical frame. The stage is
divided into two sub-stages using signals O/R-P-PRM-UPDATE 1 and O/R-P-PRM-UPDATE 2. Division into
two stages allows applying different downstream SOC settings before and after SNR measurements.

The SOC channel is active in both directions. First, both FTU-O and FTU-R transmit O-IDLE and R-IDLE,
respectively, and then FTU-O and FTU-R exchange SOC messages O-SNR, R-SNR followed by SOC messages
O-PRM, R-PRM to update transmission parameters of FTU-O and FTU-R that includes final set of active
subcarriers (MEDLEYus, MEDLEYds), final PSDs for upstream and downstream (MREFPSDus and
MREFPSDds), final set of blackout subcarriers, number of pilot symbols, and other parameters (see clause
12.3.3.2).
NOTE – During this stage, the VCE may compute the necessary updates of PSD and gains for both active lines and
joining lines to perform downstream spectrum optimization. For spectrum optimization the VCE may use the channel
estimation, precoder coefficients, and SNR values received from the FTU-R. The VCE may also compute the
corresponding adjustments in bit loading for all active lines. Implementation of these adjustments may require an OLR
in active lines. A time period is assigned at the beginning of the stage for accurate SNR measurement and later for
downstream PSD optimization.
The FTU-O terminates this phase by sending O-P-SYNCHRO 5 signal.

12.3.3.2 SOC messages transmitted during channel discovery phase
The SOC message exchange during the channel discovery phase is presented in Figure 12-10, which also
shows the main content/tasks of each message. The detailed definition of each message is presented in
clauses 12.3.3.2.1 to 12.3.3.2.10.

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