The Capacity of Analog Optics in DOCSIS 3.1 HFC Networks

摘要

The DOCSIS 3.1 (D3.1) HFC network, supporting OFDM, requires potentially higher system performance (CNR or MER) for both downstream (DS) and upstream (US) signals compared with the previous DOCSIS 3.0 (D3.0) counterpart. This pushes the limitations of current analog optics technology. How much optical link budget can current technology support? It mainly depends on the per channel optical modulation index of the laser, and optical detection limitations which are dominated by receiver (Rx) equivalent input noise (EIN). This paper will mainly focus on evaluating the noise limitation of the downstream and upstream analog optical links. We explore whether D3.1 PHY layer defined OFDM/OFDMA QAM signals and the extended channel loading bandwidth can be satisfied using an analog optical link. The results show that DS 4K-QAM OFDM signals with full loading (5×192 MHz) can be supported when the optical Rx input power is no less than -2 dBm. Similarly, US 1K-QAM OFDMA signals with full loading (2×96 MHz) can be supported when the US optical Rx input power is -13 dBm. In other words, analog optical links can still support the D3.1 PHY layer defined 4K-QAM/1K-QAM for DS/US, but there are limitations of fiber link loss. Digitizing the optical link of HFC using EDR or Remote PHY can help break the power budget limitations of the analog optical link.