Page 871 - 5G Basics - Core Network Aspects

Transport aspects 2

remove the impact of the near-end receiver filter characteristics to achieve an accurate estimate of ALN(f),
assuming the receiving FTU presents a load impedance to the network of 100 Ohms resistive (see Note 1).
NOTE 1 – In actual implementations, the receiving FTU load impedance may deviate from 100 Ohms resistive.
NOTE 2 – The ALN is equivalent to the noise component used in calculation of the SNR test parameter referred back to
the U-reference point.
NOTE 3 – If FEXT cancellation is disabled on the line under test, the ALN includes the full crosstalk level from all the
other lines into the line under test.
NOTE 4 – ALN for upstream is not defined because of the presence of the post-canceller in the upstream receiver. A
post-canceller combines signals from multiple U-reference points.
The active line noise PSD ALN(f) per subcarrier group shall be measured by the FTU-R during showtime L0
link state only, and shall be updated during showtime L0 link state only on request in response to an update
test parameters request (see clause 7.1.9.1 of [ITU-T G.997.2]). The FTU-R FME shall send the ALN to the
FTU-O FME via eoc on request (see clause 11.2.2.6.2).

The ALN shall be measured only at time periods during reception of downstream RMC symbols or
downstream data symbols in the NOI at the symbol positions specified by the MNDSNOI value.

NOTE 5 – ALN(f) is measured on a line that is in the L0 link state, whilst the line state of other lines served by the same
DPU may stay in whatever line state they are in. Therefore, the ALN measurement results may be affected by the line
state of the other lines, e.g., the measured ALN could be lower due to the transmission of decimated RMC symbols in
low power link states.
The FTU-R shall average the measurements over Navg of at least 256 symbols (consecutive or non-
consecutive) and shall take at most 1 second. The FTU-R shall indicate the number of symbol periods used
for the measurement (represented as a 16-bit unsigned integer) together with the ALN update.
The ALN shall be represented by subcarrier groups. The number of subcarriers, G, in one subcarrier group
shall be equal to:
G ≤ max(1, 2 ceiling(log ((Θds+1)/512) )
2
where Θds is the highest subcarrier index of the MEDLEYds set, and 512 is the maximum number of
subcarrier groups. Valid values of G are 1, 2 and 4. The FTU shall indicate the group size G used for the
measurement (represented as an eight-bit unsigned integer) together with the ALN update.
The active line noise PSD ALN(k × G × fSC) shall be the average of the linear power values of active line noise
on the subcarriers k × G to ((k+1) × G) –1, where fSC is the subcarrier spacing in Hz defined in clause 10.4.2.
ALN shall be expressed in dBm/Hz. It shall be represented as an eight-bit unsigned integer n(k), where k = 0
to ceiling(Θds/G). The value of ALN(k × G × fSC) shall be coded as:
ALN(k × G × fSC) = −35 − (n(k)/2) dBm/Hz.
This data format supports a ALN(f) granularity of 0.5 dB with a range of values for ALN(f) from −35.5 to
−160 dBm/Hz , corresponding to the set of valid values of n = 1 to 250.
A special value n = 0 indicates a value of ALN = –35 dBm/Hz or higher.

A special value n = 251 indicates a value of ALN = –160.5 dBm/Hz or lower. A special value n = 254 indicates
that no measurement could be done for this subcarrier group because none of its subcarriers is in the
transmitter MEDLEY set with gi > 0.

A special value n = 255 indicates that the parameter is undetermined.
All other values are reserved by ITU-T.

11.4.1.2.5 Actual transmit PSD reference per subcarrier (ACTPSDREF-ps)
In the downstream direction, the actual transmit PSD reference ACTPSDREF for a particular subcarrier shall
report the V2PSD (in dBm/Hz). The V2PSD values shall not deviate from the actual PSD during O-P-
VECTOR2, as calculated into the termination impedance (see clause 7.3 of [ITU-T G.9700]) at the U-O
interface, by more than 1 dB.

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