**6. Conclusions**

In this paper, we proposed and demonstrated delta-sigma digitization and coherent transmission of DOCSIS 3.1 signals for the first time. A low-pass CRFB delta-sigma ADC was designed to digitize 20 × 192-MHz DOCSIS 3.1 channels

**85**

*Delta-Sigma Digitization and Optical Coherent Transmission of DOCSIS 3.1 Signals in Hybrid…*

with 16384QAM and transmit the digitized RF spectrum over 80 km of fiber via a single-λ 128-Gb/s DP-QPSK or 256-Gb/s DP-16QAM coherent fiber link. Both one-bit and two-bit digitization were realized and supported by QPSK and 16QAM coherent links, respectively. To facilitate its application in HFC networks, a low-cost coherent fiber system was built based on narrowband optical modulator and RF amplifiers. Frequency pre-equalization was exploited to compensate the bandwidth limitation. MER larger than 50 dB was achieved for all 20 DOCSIS 3.1 channels, and high order modulation up to 16384QAM was supported. To date, this is the highest order of modulation transmitted over fiber in HFC networks. BER tolerance of delta-sigma digitization was also evaluated and negligible degradation of MER performance was observed for

and 1.7 × 10<sup>−</sup><sup>4</sup>

, for one-bit and two-bit digitization,

*DOI: http://dx.doi.org/10.5772/intechopen.82522*

BER values up to 1.5 × 10<sup>−</sup><sup>6</sup>

BBU baseband unit

BER bit error ratio BS base station

CM cable modem

CD chromatic dispersion CFO carrier frequency offset

CNR carrier-to-noise ratio CPR carrier phase recovery

DP dual-polarization DSL digital subscriber line DSP digital signal processing

HFC hybrid fiber coax HPF high-pass filter I in-phase

EVM error vector magnitude FTTH fiber-to-the-home

BDF/BDR baseband digital forward/return

CCAP converged cable access platform

CMA constant modulus algorithm

CPRI common public radio interface C-RAN cloud-radio access networks CRFB cascade resonator feedback

EPON Ethernet passive optical network

GPON gigabit passive optical network

MBH/MFH mobile backhaul/fronthaul MER modulation error ratio ML maximum likelihood MME mobile management entity MZM Mach-Zehnder modulator

NTF noise transfer function

E-UTRA evolved universal terrestrial radio access

IM/DD intensity modulation/direct detection

NG-PON2 next-generation passive optical network stage 2

OFDM orthogonal frequency division multiplexing

CMMA constant multiple modulus algorithm

DOCSIS data over cable system interface specification

respectively.

**Acronyms**

*Delta-Sigma Digitization and Optical Coherent Transmission of DOCSIS 3.1 Signals in Hybrid… DOI: http://dx.doi.org/10.5772/intechopen.82522*

with 16384QAM and transmit the digitized RF spectrum over 80 km of fiber via a single-λ 128-Gb/s DP-QPSK or 256-Gb/s DP-16QAM coherent fiber link. Both one-bit and two-bit digitization were realized and supported by QPSK and 16QAM coherent links, respectively. To facilitate its application in HFC networks, a low-cost coherent fiber system was built based on narrowband optical modulator and RF amplifiers. Frequency pre-equalization was exploited to compensate the bandwidth limitation. MER larger than 50 dB was achieved for all 20 DOCSIS 3.1 channels, and high order modulation up to 16384QAM was supported. To date, this is the highest order of modulation transmitted over fiber in HFC networks. BER tolerance of delta-sigma digitization was also evaluated and negligible degradation of MER performance was observed for BER values up to 1.5 × 10<sup>−</sup><sup>6</sup> and 1.7 × 10<sup>−</sup><sup>4</sup> , for one-bit and two-bit digitization, respectively.
