ISO 21806-13-2021 pdf download.Road vehicles – Media Oriented Systems Transport (MOST)一 Part 13: 50-Mbit/s balanced media physical layer conformance test plan.
In order to get to a representative average value, it requires a long-term observation. Depending on the chosen SP2 and applied channel losses, intersymbol interference impact affects the signal to be measured. It may lead to locally distributed RMS minima and maxima when choosing only short snippets of the signal. The acquired waveform shall have a minimum length of 125 us (125 is equals six frames with a frame rate of 48 kHz).
DC offset in the measurements shall be minimized as it may indirectly compromise RMS signal voltage amplitude results, see ]ü.2 and 1th3.
8.3 PSD of SP2 output signal
PSD as specified in ISO 21806-12:2021,9.2 is used as a link quality criterion at SP2. The main purpose is to limit pulse shape variations and inherently limit the transmitted signal bandwidth.
Several measurement options are available to perform spectral signal analysis. A method using time- domain data acquisition followed by FFT post-processing is given for reference. Other measurement methods are permitted. In the case of discrepancies, the reference method shall be used.
PSD shall be measured with an RMS detector and using an effective RBW of 500 kHz. Besides directly measuring PSD with 500 kHz resolution bandwidth, this can be achieved by using lower RI3W setting and averaging spectral results in the amount n of overlapping groups of the lower RBW bands to produce the effect of 500 kHz RBW sliding window (linear scale). (i.e. measurement with RBW 10 kHz, averaged in overlapping groups of fifty bands, therefore n = 50). To achieve statistical representation, the spectral density results of multiple trace segments are averaged to form the final result, The number of trace segments contributing to the averaged spectrum equals the sweep time.
The following is an example procedure for measuring PSD.
— The IUT transmitter sends multiple MOSTSO bPKY PSD patterns.
— Differential signal at terminated SP2 is measured with a differential probe. Other methods to measure a single ended representation of the differential signal are acceptable (e.g. use BALU N or use test fixture with matched length 50 fi coaxial cables, measured with 2 channels and mathematical combination).
— An oscilloscope acquires the SP2 signal. To reduce noise in the measurement channel, it is recommended to use an averaging technique for time domain data acquisition. Selectingoscilloscope sampling rate and acquisition length leads to the inherent RBW for the acquisition, which is the reciprocal of the acquired duration time. The appropriate duration can be achieved by adjusting horizontal oscilloscope settings accordingly or by acquiring longer traces and slice the trace into appropriate trace segments for the further processing.
— For further post-processing, FFT algorithm can be applied on the oscilloscope or via processing per external script on a PC. In frequency domain, PSD is then formed as a moving average (linear scale) of n consecutive samples of the inherent RBW bands.
— To achieve statistical representation, the spectral density results of multiple trace segments are averaged to form the final result. The number of trace segments contributing to the averaged spectrum equals the sweep time.
— Described procedure provides spectral density for consecutive 500 kHz bands in the relevant frequency range and can be directly compared with the limit lines.ISO 21806-13 pdf download.