Page 801 - 5G Basics - Core Network Aspects

Transport aspects 2

• m=10 for TDD frame length MF=23

• m=10 for TDD frame length MF = 36
• m=16 for TDD frame length MF = 23
• m=33 for TDD frame length MF = 36.
In all cases, the following relations shall hold: LCP > β and LCS = β.

The same value of LCP shall be selected for both upstream and downstream.
NOTE – The setting of the LCP (for both upstream and downstream) are exchanged during the ITU-T G.994.1 phase of
initialization. The same LCP values are set in all lines of the vectored group.

Figure 10-25 – Cyclic extension, windowing and overlap of symbols

For a given setting of the CP length, the symbols will be transmitted at a rate equal to:
2 N  f
f DMT  SC

2 N  L CP
The symbol period Tsymb, accordingly, equals to 1/fDMT (see Figure 10-25).
If the CP length corresponds to m = 10, this results in a symbol rate of 48 000 symbols/s.

10.4.5 Synchronization
The FTU-R shall use loop timing mode, i.e., it shall extract its symbol clock from the received signal. In loop
timing mode, the FTU-R operates as a slave; the transmit clock of the FTU-R shall be locked to the transmit
clock of the FTU-O. Prior to starting a transmission, the FTU-R shall acquire (or re-acquire) the downstream
timing; no transmission is allowed if loop timing is not established.

To facilitate loop timing, the FTU-R may request FTU-O to assign pilot tones. The number of pilot tones and
their subcarrier indices are determined during initialization (see clause 12.3.4.2.8). The FTU-O shall transmit
assigned pilot tones during the showtime in all data symbols and pilot symbols. Pilot tones shall not be
transmitted during sync symbols, idle symbols or quiet symbols. The maximum number of pilot tones is 16.
To facilitate loop timing during L2.1 and L2.2 states, the FTU-R may request the FTU-O to transmit pilot
symbols (see clause 10.4.5.1).

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