Data Transfer Rates in HFC Networks

摘要

Current access networks need to transmit data with increasingly higher rates. HFC (Hybrid Fiber Coaxial) networks offer growth capacity. To obtain maximal transfer rates, we propose releasing the 500 MHz spectrum -currently assigned to the transmission of analog and even digital television-, to convert HFC networks into entirely data networks, by using the first 200 MHz of the total spectrum for upstream, and from 258 MHz and up to 1.8 GHz for downstream. As the architecture of HFC networks must decrease the number of active amplifiers, we use an N + 0 design, which allows serving smaller service areas while decreasing the noise and distortion indexes. The DOCSIS 3.1 standard uses the OFDM (Orthogonal Frequency Division Multiplexing) system for transmission in downstream and OFDMA (Orthogonal Frequency Division Multiple Access) for upstream, employing multiple sub-carrier schemes, each of which is modulated with up to 16K QAM in downstream and up to 4K QAM in upstream. Multiple modulation profiles (MMP) are associated to the quality of the channel. FEC-LDPC (Forward Error CorrectionLow Density Parity Check) is used for error correction. The maximal transfer rate calculated in downstream is 16.9 Gbps, and 1.86 Gbps in upstream. To achieve these values, it is necessary to maintain a SNR higher than 40 dB in the HFC network. In this way, HFC networks represent a valid alternative to meet demand for transfer rates in the short and medium term.