Identifying and Locating Interference with CellAdvisor™

Identifying and Locating Interference with CellAdvisor™
and Locating
Interference with
Interference lowers signal-to-noise ratios (SNR) and reduces both coverage areas and
throughput rates. Effectively analyzing the spectrum and identifying interfering signals
ensures service coverage—but troubleshooting interference can be both challenging and
The Challenge
For several months, a tier 1 service provider experienced low,
intermittent throughput issues at one their eNodeB sectors. Unable
to identify the root cause, the provider replaced the RRH as well as
fiber—to no avail. The performance issues continued.
Identifying radio link issues quickly and easily challenges the entire
RF industry. External issues elevating RX noise floors are most often
interference. But when RX noise issues are improperly diagnosed, time
to repair increases, expenses are incurred unnecessarily, and customers
suffer. And the penalty for poor QoE is severe: it increases churn.
Operators and providers need tools that isolate interference issues to
quickly restore the best QoE for their end users.
Case Study
The Solution
To find an answer, the operator’s performance and operations team
contacted Viavi. Together, they isolated the performance issue at the
cell site by:
yy Verifying sync between the digital unit and the RRH
yy Inspecting and cleaning fiber
yy Installing a fiber optic tap via the SFP and panel and performing
RFoCPRI™ analysis
Spectrogram result showing a PIM issue on antenna 2
CellAdvisor RFoCPRI test architecture
Technicians on the ground connected the Viavi Solutions™ CellAdvisor.
It decoded RF information sent on the CPRI link from the RRH to the
BBU and displayed those results in a traditional spectrum analyzer
view. This clearly indicated that the uplink noise floor for that sector
was higher than normal.
The cause of high uplink noise floors on remote radio heads (RRHs)
can be either internal or external. Internal issues are often due
to passive intermodulation (PIM) and, because most RRHs are
inaccessible from the ground, repairing them is costly. In a typical PIM
case, reviewing the spectrogram for abnormal noise levels will show a
visible difference between two antenna measurements. In the case of
external interference, both antenna links will show a noise rise.
Comparative spectrogram results showing consistent interference on both
antennas; note rolling rises in the noise floor across the whole band
2 Identifying and Locating Interference with CellAdvisor
Several kinds of licensed and unlicensed transmitters can generate
interference signals that decrease service quality. Identifying, isolating,
and eliminating this interference—quickly—is an absolute must for
wireless service providers. In this case, remediation required just one
test set that performed the following measurements:
yy Fiber inspection
yy RFoCPRI uplink measurements
CellAdvisor RFoCPRI result displaying RRH uplink noise
CellAdvisor™ is a powerful tool for detecting interference, significantly
reducing the time it takes to identify issues. In this case, it identified
external interference as the most likely culprit. Thereafter, just 3
hours of driving and walk-testing a nearby building identified the
interference source: a misconfigured bi-directional amplifier located
approximately 1,000 meters from the base station and unknown to
the wireless service provider.
Source of interference
3 Identifying and Locating Interference with CellAdvisor
yy Interference hunting
CellAdvisor and its RFoCPRI capabilities give providers clear visibility
of uplink spectrum, from the ground, to identify and mitigate
interference sources. This decreases time-to-resolution and reduces
expenses associated with unnecessary tower crew work.
Contact Us
+1 844 GO VIAVI
(+1 844 468 4284)
To reach the Viavi office nearest you,
© 2015 Viavi Solutions Inc.
Product specifications and descriptions in this
document are subject to change without notice.
30179586 000 1115
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