Executive Summary
DOCSIS® 3.1 (D3.1) offers a new physical layer based on orthogonal frequency division multiplexing (OFDM) technology and more powerful forward error correction (FEC).
DOCSIS 3.1 also enables new analysis techniques using receive modulation error ratio (RxMER) per subcarrier and other proactive network maintenance (PNM) features. This Operational Practice provides insight into the capabilities and limitations of D3.1 cable modem (CM) RxMER measurements in comparison to traditional test equipment. The procedure for determining the sensitivity of cable modem RxMER measurements is described. Some results for accuracy are presented and expectations are discussed.
Scope
DOCSIS 3.1 PNM offers a diverse set of new test features to quickly and accurately characterize the effects of HFC impairments on the OFDM signals to optimize throughput and reliability of service. These features were previously only available in test equipment such as spectrum, vector, and network analyzers. Given the adaptive nature of DOCSIS 3.1 coupled with HFC network impairments, accurate measurements using these new 3.1 PNM tools are essential to creating modulation profile performance models. In particular, deep insight into the network health can be determined by using the DOCSIS 3.1 PNM feature downstream RxMER per subcarrier to determine the OFDM signal fidelity at the cable modem. This Operational Practice document summarizes the steps to confirm the accuracy of a CM’s reported RxMER values.
Benefits
The following procedure is intended to help provide a better understanding of the capabilities and limitations when using DOCSIS 3.1 PNM measurements in lieu of traditional test equipment. Obtaining good statistical analysis is predicated on the CM’s ability to measure RxMER accurately. It is up to the cable operator to repeat the procedures outlined in this document and test the CM’s RxMER accuracy with each code version and new product. The procedures in this operational practice are based upon research which demonstrated that first generation DOCSIS 3.1 CMs and cable modem termination systems (CMTSs) can do a precise RxMER measurement sometimes similar to a quality lab analyzer.[1]
It is necessary for operators to understand the limits of using such measurements. While there is a great potential to improve operational efficiency, it is also possible that incorrect measurements or interpretation could have the opposite effect on efficiency.
Intended Audience
The intended audience includes development engineers, test engineers, and technical operations personnel.
[1]Dr. R. Prodan, “Demystifying the DOCSIS 3.1 PHY”, 2014 SCTE·ISBE Cable-Tec Expo proceedings