RF Interference - PCTELrfsolutions.pctel.com/artifacts/InterferenceMitigationApplication... · RF Interference Is your wireless ... interference can be caused by traditional modulated

APPLICATIONNOTE rfsolutions.pctel.com|[email protected]|301.515.0036

Sept2016RevA|Page1of11

RF Interference

Is your wireless network suffering from inconsistent Quality of Service? Are network upgrades and new deployments falling short of expected improvements? In either case, there is a good chance that RF interference is the cause. Any radio frequency signal that negatively affects a wireless network is a source of RF interference. This Application Note will teach you how to mitigate interference and deliver a better Quality of Experience (QoE) for your customers.

Effects of RF Interference

While RF interference can appear at any time on any network, it most often affects LTE networks on newly allocated or re-farmed spectrum. Effects of interference on 4G and 5G networks may include:

Customer Carrier· Low data throughput

· Video pixilation

· Poor voice quality

· Dropped calls

· Latency

· Inconsistent Quality of Service

· Poor user experience

· Customer churn

· Lost revenue

Types of interference

There are many types of interference. Internal interference comes from within the network. Examples include inter-cell interference (ICI) and co-channel interference. External interference can be caused by traditional modulated RF sources like unterminated cables, passive intermodulation (PIM), and malfunctioning bi-directional amplifiers from other networks. Unmodulated sources such as florescent lights, baby monitors, and electric motors may also interfere with wireless networks.

Spectrum

Interference can occur in any network band. However, networks operating at lower frequencies are more vulnerable to both internal and external interference. Lower frequencies are more difficult to control because lower frequencies propagate farther. This leads to coverage bleeding into neighboring cells, causing internal interference. The greater range of lower-frequency signals also means that outside sources of interference are more likely to negatively affect the network. Wireless networks broadcasting between 300 MHz and 900 MHz have the highest rate of customer complaints that have been attributed to interference.

HOW TO MITIGATE EXTERNAL RF INTERFERENCE

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The vast majority of external interference that can hurt customer QoE occurs on the uplink (UL). This is due to the low transmitting power of customer devices. External Downlink (DL) interference rarely affects a customer’s QoE, due to the high power levels of the signal sent from the base station. However, these same high power levels mean that internal DL interference is a significant threat to QoE, particularly at lower frequency ranges.

Interference Mitigation

A successful interference management program minimizes the effects of network interference through multiple preventive, reactive, and proactive measures. One of the most crucial—and most difficult—components of an interference management program is external interference mitigation. External interference mitigation is the process of finding and eliminating individual sources of external interference.

Successful interference mitigation requires access to supporting network data, the right network testing tools, and user skill and knowledge. There are four primary steps to mitigating external interference:

1. Identify the type of interference.2. Detect the interfering frequency.3. Locate the interference source.4. Eliminate the interference source.

This application note will walk you through the external interference mitigation process from start to finish. In Steps 2 and 3, we will focus in detail on an example of external UL interference, using real-world data from the SeeWave® interference locating system. By the end of this application note, you will understand the methods, tools, and strategies necessary for successfully mitigating interference and improving network QoE.

Step 1: Identify

Interference mitigation begins by identifying the existence of an interference problem as well as its general location and approximate frequency range. Indicators of both UL and DL interference are found in network statistics, customer service records, and data from routine drive testing. Common red flags that indicate interference problems in a particular portion of the network include:

Uplink:• Clusters of customer complaints in specific sectors• High Receiver Total Wideband Power (RTWP)• Poor Key Performance Indicators (KPIs)

Downlink:• Clusters of customer complaints in specific sectors• Pilot pollution• Poor KPIs• Low Carrier to Interference Noise Ratio (CINR)• Low Received Signal Received Quality (RSRQ)

Sometimes, networks have internal problems:• Radio Network Controller (RNC) configuration problems• Outdated equipment• Firmware issues• Bad jumper cable• Poor installation• Voltage Standing Wave Radio (VSWR) errors

AtaGlance: Step1-Identify

Identify the type of interference by investigat-ing network issues. If it is internal, take appropri-ate actions to correct the problem. If there is strong evidence that an external interferer is disrupting an otherwise strong network, testing tools are needed to detect and locate the source.




These potential sources of internal interference should be eliminated before pursuing external interference mitigation. Check internal equipment and settings to ensure everything is correct. If all is clear, but there are still active indicators of interference, the problem is likely caused by external interference.

Step 1 should leave you with both a target geographical area and an approximate frequency range for the interference. For this example, we have identified interference at approximately 780 MHz. Proceed to the affected portion of the network to detect and locate the external interferer.

Step 2: Detect

Once external interference has been identified as the source of a problem in the network, the next step is to detect the interferer in the field. For this step, an engineer should be equipped with equipment designed to detect the interfering signal.

While simple spectrum analyzers may suffice for the most experienced engineers, more advanced tools can make the process more efficient. PCTEL’s SeeWave® builds on the SeeGull® scanner’s spectrum analysis capability with specialized capabilities for both detecting and locating interference.

Figure 1 – SeeWave with IBflex®




In our example, Step 1 indicated that an external interference issue is suspected in uplink of E-UTRA band 13, ranging from 777 to 787 MHz. To search for an interfering signal in this range using SeeWave, set the Center, Start, Stop frequencies in the Setup tab as shown in Figure 2.

Figure 2 – Scan Parameters

SeeWave will automatically select the optimal Resolution Bandwidth (RBW) for the frequency range.

Once setup is complete, SeeWave will display a visual representation of RF activity within the chosen range in the Charts tab.




An interfering signal will register as an unusual blip or spike in the data. In Figure 3, we can see a possible source of interference at approximately 783.00 MHz.

Figure 3 – Initial Scan

To focus on a smaller portion of the frequency range, pinch the SeeWave display. This will show a clearer view of the interfering signal.




Figure 4 – Zoom in on Suspected Interferer

After zooming in the source of interference will be clearer. The blip at 783.00 MHz is not a normal cellular signal.

If you are unable to find a clear source of interference, slowly rotate SeeWave’s directional antenna 360 degrees. An interferer’s power level will spike when the antenna is pointed toward the source.

AtaGlance: Step2-Detect

Use SeeWave’s spectrum charts to detect the interfering frequency.




Step 3: Locate

Once the interference has been detected and its frequency determined, you are ready to locate the interferer. Triangulation eliminates a great deal of guesswork at this stage and speeds up the process.

To prep for triangulation, make sure that SeeWave’s compass and GPS have been calibrated. Next, point SeeWave in the direction in the interferer’s power spikes the highest. Finally, using SeeWave’s proprietary algorithms, move the primary marker to the frequency where power spikes the highest -93.38 dBm at 783.00 MHz as shown in Figure 5.

Figure 5 – Primary Marker Set for Triangulation




To triangulate, select the Maps tab. Taking environment factors (roads, buildings, topography, accessibility, etc.) into account, take bearings in a circular pattern around the suspected interference location. The walking path can be adjusted on the go if the suspected location of the signal changes based on early bearing results.

Figure 6 – Suspected Area of Interference

Taking and selecting accurate bearings is crucial for successful triangulation. A mix of expertise and trial and error may be necessary to overcome challenges such as multipath and noisy spectrum. See our Tips for Overcoming Multipath for more details.

Fortunately, SeeWave’s specialized features make taking and selecting bearings a bit easier. First, SeeWave offers two triangulation modes: Automatic mode for constant signals, and manual mode for varying signals. Automatic mode makes it much easier to take bearings—simply walk all the way around the source as SeeWave takes bearings. Second, SeeWave allows users to compare bearings in real time. Users should select the strongest bearings for use in triangulation.




Figure 7 – Triangulation of Interference Location Area

Once bearings have been taken and selected, SeeWave creates a polygon zone indicating the area in which the signal is located, along with a dot on the most likely location, as shown in Figure 7. Depending on the accuracy of the bearings and size of the polygon, a second round of triangulation may be useful.

Once the signal has been successfully triangulated, proceed to the area indicated by the polygon and dot. SeeWave’s power reading and audio cue options can be used to help visually identify the source.

AtaGlance: Step3-Locate

Use SeeWave’s triangulation and audio cues to find the exact location of the interference. Identify the source visually.




Step 4: Eliminate

Once you have located the source of interference, take note of both what it is and where it is located. You may want to take a photograph of the interferer. You can now take appropriate steps to eliminate the interferer, which may include contacting the property owner or the appropriate authorities.

Figure 8 – Visually Identify the Interference Source

Tips for Overcoming Multipath:

1. Take a set of four power readings at an intersection—one from each direction. Move toward the strongest reading.

2. When possible, take bearings from higher ground, above obstructions that could be reflecting signals.

SeeWave Tips:

1. Confirm compass is calibrated and accurate by pointing down a street or at a landmark and checking the indicated direction against a map.

2. Set the primary marker to the interfering frequency on the spectrum chart before moving to the map to triangulate.

3. Complete a full sweep back and forth to take a bearing in automatic mode.

4. Take multiple bearings at each location and only include the strongest to triangulate.

5. Turn on the amplifier for low power interference.

6. Turn on the attenuator when close to a high power interferer.




Conclusion

External RF interference mitigation is a crucial part of an overall interference mitigation program. There are four primary steps to interference mitigation:

1. Identify the type of interference.2. Detect the interfering frequency.3. Locate the interference source.4. Eliminate the interference source.

SeeWave interference locating system simplifies interference mitigation resulting in mitigation efficiency and the delivery of better customer experience.

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Figure 9 – Interference Located



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RF Interference - PCTELrfsolutions.pctel.com/artifacts/InterferenceMitigationApplication... · RF Interference Is your wireless ... interference can be caused by traditional modulated