**5.2 One-bit digitization**

**Figure 7** shows the experimental results of 32 GSa/s one-bit digitization (Case V). 20 DOCSIS 3.1 channels are digitized into four 32 Gb/s OOK signals, and then transmitted by a 32 Gbaud DP-QPSK link. The RF spectra before (blue) and after (red) delta-sigma digitization are shown in **Figure 7(a)**. Five 192-MHz DOCSIS 3.1 channels occupy a frequency range from 258 to 1218 MHz. It can be seen that after delta-sigma digitization, the signal spectrum is kept intact, and the quantization noise is pushed out of the signal band with in-band CNR larger than 40 dB. **Figure 7(b)** shows the MER performance of five channels, and each of them satisfies the requirements (dashed lines) of DOCSIS 3.1 specifications. Channel 2 has MER > 50 dB carrying 16384QAM; channel 4 has MER > 41 dB carrying 4096QAM; the remaining three have MER > 44 (44.5) dB carrying 8192QAM. This is the first time that modulation orders higher than 4096QAM have been demonstrated over fiber in HFC networks. Constellations of each modulation are shown in **Figure 7(c, d, e)**. For 8192QAM, the worst case, channel 3 with lowest MER of 44.5 dB, is shown.
