Understanding Impulse Noise
One of the most common issue related to impulse noise is bad IPTV performance, such as slower frame rate or frame loss, which can cause image to freeze or introduce pixelization.
Impulse noise is a type of electromagnetic interference (EMI) that typically emanates from power transmission, radio and TV, electronics, and even cell phones.
The latest high-speed DSL technologies (such as VDSL2) typically operate at critical SNR margins using a very broad part of the frequency spectrum, and are more susceptible to impulse noises than legacy voice or ADSL.
Impulse noise, as for other types of noise, reduces the SNR margin—which is critical to DSL performance (and services such as IPTV and VoIP)—and must be characterized and the source identified to mitigate it.
However, noise emitters—particular those from non-continuous sources—are very difficult to detect and isolate due to the fact that they are intermittent, very fast, and are different from typical telecom signals.
Therefore, specialized tools designed to detect and characterize impulse noise should be used earlier in the troubleshooting process to understand impulse noise and make a plan to mitigate it.
Every telecom technicians who installs and maintains FTTN/B networks knows this: one of the most difficult steps while troubleshooting is to pinpoint the source, type and impact of the noise affecting the performance and capacity of the xDSL line.
Seeing the Problem
- Impulse noise is intermittent by nature, and much harder to detect and analyze than traditional interference.
- Its fast burst nature defies traditional troubleshooting methods.
- Nowadays, high-end bench-type oscilloscopes can help see, capture and analyze impulse noises during field tests.
- Bursty, high-frequency impulses cause packet and pixel loss (video and audio) and degrade or freeze services like IPTV or over-the-top video (e.g., Netflix).
- Repetitive electrical impulse noise (REIN), prolonged electrical impulse noise (PEIN), short impulse noise event (SHINE) and electromagnetic interference (EMI) all affect DSL services in their own way. The sources of these various types of noise are also different. Understanding impulse duration, repetition and frequency helps to identify the source.
- Time of day: knowing when each type of impulse noise occurs is key to targeting the source.
The Test Approach
Signs of impulse noise degradation
- Bad voice quality
- Pixelization on IPTV
- DSL not synchronizing
The outcome: low QoE
- Validate the full range triple-play services
- Analyze low QoS on the DSL line
- Use of a powerful hybrid field-testing tool is required
Identify the type of noise
- Narrow-band noise
- Wideband noise
- Disruptive impulse noise
Capture and visualize the noise
- Simultaneous time and frequency domain analysis
- Recognize the signature and the source of the noise
- Also works in the case of complex EMI, REIN or SHINE issues.
Impulse Noise Scope
Analyze the noise duration and disruption
- See the variations of the noise over time
- See the distribution of fast and slow impulses over time
Impulse Noise Duration Disruption (IDD)