Using the Time and Frequency Division Multiplexing (TaFDM) method, the OFDMA and SCQAM channels, which are allowed to overlap in DOCSIS 3.1, are also allowed to use the upstream at different times. With the implementation of TaFDM, both OFDMA and SC-QAM can simultaneously operate on separate frequencies. They can also operate on the same frequencies, but in different times.
TaFDM enables the OFDMA capability across the entire spectrum, while retaining the backward compatibility with legacy DOCSIS SC-QAM channels.
TaFDM is typically configured at the controller level. However, it is implemented at the Mac Domain level. Overlapping channels cannot be bound to different Mac Domains.
Overlapping SC-QAM and OFDMA channels using TaFDM may be bonded. However, we recommend this bonding only if the modems are provisioned with UGS flows and another non-overlapping SC-QAM is not available.
For a better performance of UGS flows on overlapped SC-QAM channel, configure OFDMA channel with 50kHz subcarrier spacing, lower symbols per frame, and lower cyclic prefix.
To achieve a higher OFDMA channel traffic throughput, configure OFDMA channel with 25kHz subcarrier spacing, and higher pilot pattern.