DOCSIS Modulation Analysis 89600 VSA Software Option 89601BHMC

• See through the complexity of DOCSIS 3.1 and 4.0 with a comprehensive set of tools for demodulation and vector signal analysis

• Analyze downstream and upstream signals and derive signal quality parameters: MER, BER, constellations, and IQ error plots

• Automatically detect, demodulate, and decode the PLC to extract configuration parameters from OCD and DPD messages with downstream signals

• Detect basic parameters, excluded/unused/guard bands, and minislot configuration for MER and BER with upstream signals

• Report the IQ demodulation traces like MER vs. subcarriers, MER vs. symbols and MER per minislot for further troubleshooting

DOCSIS 3.1 and 4.0 Modulation Analysis

The 89600 VSA software’s option 89601BHMC provides comprehensive analysis capabilities in frequency, time, and modulation domains of DOCSIS (Data-Over-Cable Service Interface Specifications) 3.1 and 4.0 downstream and upstream fully-coded signals with powerful automatic signal detection and decoding capabilities. Capture signals by connecting to hardware like the Keysight N9040B UXA signal analyzer or N9030B PXA signal analyzer and setting the center frequency, analysis span, and optimized amplitude range. By acquiring the fully-coded physical link channels (PLC) or manually-configured signal parameters of downstream, the software can detect, demodulate, and decode PLC automatically to run the modulation error ratio (MER) and bit error rate (BER) measurements quickly and easily to characterize the DOCSIS 3.1 downstream signal under test. You can also measure upstream signal MER and BER when switching measurement. MER and BER results can be accumulated with multiple frame data to gain more confidence of the performance and signal quality with your device under development. The software provides frequency, time, and modulation domain analysis results in a single measurement. By configuring result traces of spectrum; acquisition time; and DOCSIS 3.1 and 4.0 modulation quality traces and tables, system engineers can identify overall signal characteristics and troubleshoot intermittent error peaks or repeated synchronization failures. For the automated testing, remote interfaces of .NET API and SCPI are available to accelerate the system design and move to the design verification and manufacturing phase.

Only need un-coded DOCSIS 3.1 and 4.0 signals or upstream MER?

For DOCSIS 3.1 and 4.0 MER with un-coded signals, option BHF Custom OFDM modulation analysis of 89600 VSA software can be used for MER and other modulation quality measurements. DOCSIS 3.1 and 4.0 configuration wizard helps to create the OFDM setup file based on DOCSIS 3.1 and 4.0 downstream and upstream specifications for MER measurements. Refer Custom OFDM technical overview (5992-4238EN) for more details.

Key Features DOCSIS 3.1 and 4.0 Downstream Signal Auto-Detections

Take advantage of effortless automatic signal detection, demodulation, and decoding to simplify cable modem termination system (CMTS) and cable modem (CM) transmitter testing. When a downstream signal containing coded physical link channels (PLC) is acquired with the appropriate center frequency, span, and amplitude settings, the software automatically detects the key signal parameters. The parameters include FFT length, cyclic prefix, and PLC start index to quickly demodulate and decode PLC to extract key parameters from the OFDM channel descriptor (OCD) and downstream profile descriptor (DPD) messages. This information is used to demodulate the signal and provide measurement results such as MER and BER, as well as modulation quality parameters in various traces and result tables. You can manually set up PLC parameters to run the measurement even if the signal does not contain the fully-coded PLC for automatic detection.

Facing test challenges with DOCSIS 3.1 and 4.0?

If you're familiar with DOCSIS 3.0 single-carrier QAM (SC-QAM) but unfamiliar with OFDM (orthogonal frequency division multiplex) and OFDMA (orthogonal frequency division multiple access) used in DOCSIS 3.1, refer an application note, DOCSIS 3.1 PHY Layer Measurement (5992-1826EN).

DOCSIS 3.1 and 4.0 Downstream MER and BER

Though MER is the most common metric used to characterize signal quality in DOCSIS CMTS and CM testing, BER is also an important metric for evaluation of signal integrity in devices and network systems. To fulfill these test requirements, the software makes MER measurements with captured IQ data, and provides the BER metric with accumulated data up to a specific number of bits. As previously mentioned, the software will automatically determine fundamental signal settings like FFT size and PLC location with the acquired signal data. Those extracted parameters are provided in the table of PLC decoding information with OCD including roll-off factor, OFDM spectrum location, time interleaving depth, locations of excluded bands, locations of continuous pilots, profile assignments for next codeword pointer (NCP), and user profiles in DPD. Along with NCP demodulation and decoding to determine the location of codewords and zero-bit-loaded subcarriers, you can obtain the report of BER before low-density parity-check code (LDPC) decoding, codewords error, and error ratio before and after BCH codes. You are able to create longer frame data accumulation for BER with as many (non-contiguous) frames as desired simply by turning on averaging or playing the recorded continuous IQ data signals.

In-depth analysis and troubleshooting

Color-coded traces and tables provide more insight than using MER metric alone. Easily track errors on subcarriers and symbols across multiple views with coupled markers. Configure result tables, like frame summary, IQ constellation and error traces of MER versus spectrum (in subcarriers), and MER versus time (in symbols). In figure 4, pilot (colored in sky blue) is easily found in the frame summary with MER and power, IQ constellation trace as BPSK, and MER traces in spectrum (subcarrier) and time (symbol) domains. If MER gets worse in a specific subcarrier and symbol location, you can zoom in to determine the error position and pinpoint any system design issues and/or add coupled markers for troubleshooting. Troubleshooting with raw bits and LDPC pass/fail status, open the demodulation result summary of ZBL, PLC, NCP and codeword in the demod property menu. To detect errors, the table can be exported to easily create the test report and in-depth analysis.