Page 654 - 5G Basics - Core Network Aspects

2 Transport aspects

The LPM (see clause 7.2.1) specifies the absolute maximum limit of the TxPSDM. The subcarrier mask (SM),
PSD shaping mask (PSM), notching mask (NM) and low-frequency edge stop-band mask (LESM) provide
reduction and shaping of the TxPSDM using four mechanisms:
− subcarrier masking;

− notching of specific frequency bands;
− PSD shaping; and
− low-frequency edge stop-band masking.

Support of these four mechanisms is mandatory in both the FTU-O and the FTU-R.
The TxPSDM shall comply with applicable national and regional regulatory requirements.

NOTE 1 – When determining the correct PSD to use in a particular jurisdiction, operators should use tools provided to
ensure compliance with national and regional electromagnetic compatibility (EMC) regulations giving special
consideration to protecting receivers for the safety of life services which may not be immediately adjacent to the drop
wires carrying ITU-T G.9701 signals. Examples include various VHF aeronautical radio navigation channels in the band
108-117.975 MHz, and aeronautical emergency communications channels (e.g., 121.5 MHz) and maritime emergency
communications channels in the HF and VHF bands.
NOTE 2 – In addition to the masks defined in this Recommendation that provide absolute limits to the TxPSDM (both
in-band and out-of-band), [ITU-T G.9701] defines two mechanisms: a mechanism of discontinuous operation that
allows the FTU to dynamically switch off the transmit power in each particular connection when no data is present for
transmission and a mechanism of low power mode (L2). Both mechanisms allow the system to further reduce the
transmit power to a value that is sufficient to achieve the given bit rate and quality of service (QoS) targets.
NOTE 3 – TXPSDM is defined in various averaging bandwidths according to frequency as defined in Table 8-1, except in
sub-bands at the low frequency band edge and in the region of MIB defined notches, where TXPSDM_W (1 MHz
wideband) and TXPSDM_N (10 kHz narrowband) masks apply as described in clauses 6.5 and 6.6.

6.2 Limit PSD mask (LPM)

The limit PSD mask (LPM) defines the absolute maximum PSD limit of the TxPSDM that shall never be
exceeded. All the other mask definitions and mechanisms used to construct the TxPSDM can only result in a
reduction of the mask from the limits established by the LPM.

6.3 Subcarrier masking

Subcarrier masking shall be used to eliminate transmission on one or more subcarriers. The subcarrier mask
(SM) is configured in the distribution point management information base (DP-MIB) by use of the ITU-T
G.997.1 parameter CARMASK. The transmit power of subcarriers specified in the SM shall be set to zero
(linear scale). The SM shall override all other instructions related to the transmit power of the subcarrier.
The SM is defined as a number of masked frequency bands. Each band is specified by a start subcarrier
index (xL) and a stop subcarrier index (xH), as {xL, xH}. An SM including S bands can be represented in the
following format:
SM(S) = [{xL1, xH1}, {xL2, xH2}, … {xLS, xHS}]
All subcarriers within the band, i.e., with indices higher than or equal to xL and lower than or equal to xH,
shall be switched off (transmitted with zero power).
NOTE – The SM is intended to incorporate both masked subcarriers that are defined by an annex defining regional
requirements so as to comply with local regulations and masked subcarriers that are defined by the user or service
provider to facilitate local deployment practices. Protection of radio services is not intended to be addressed by
subcarrier masking; it is addressed by notching (see clause 6.5).

6.4 Power spectral density shaping
Power spectral density (PSD) shaping allows reduction of the TxPSDM in some parts of the spectrum,
mainly for spectrum compatibility and coexistence with other access and home network technologies. The
PSD shaping mask (PSM) is configured in the DP-MIB by use of the ITU-T G.997.1 parameter PSDMASK.

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