remote access and monitoring of fiber-based fronthaul

app note

Remote access and monitoring of fiber-based fronthaul networks

appnote

© 2018 EXFO Inc. All rights reserved. 2

SkyRAN Fronthaul remote access and monitoring solution

Radio frequency (RF) spectrum is one of the most valuable resources for a mobile network operator (MNO). Maximizing network throughput (bit/Hertz) is critical to success and the fronthaul infrastructure is constantly evolving to accommodate this. The resulting pressure on several field groups within the organization to maintain fronthaul network performance is enormous.

The move to 5GChanges in the radio access network (RAN) have introduced new challenges: RF over fiber optic cable using technologies such as CPRI and OBSAI; placement of remote radio heads (RRHs) at the top of hard-to-reach towers and buildings.

More and more RRHs are being deployed due to the evolution of technology (i.e., small cells, the introduction of 5G with massive MIMO, higher frequencies, smaller coverage areas) which will further impact this growth. Consequently the number of RF signals and fiber optic connections being monitored, and the trouble tickets being generated, is skyrocketing.

Already, today’s field personnel are forced to triage trouble tickets to address the most pressing needs. With workloads set to more than triple, and OPEX unlikely to rise to meet this demand, organizations need more efficient methods of maintaining their mobile networks to remain competitive.

Figure 1. Small cell growth 2013 to 2022.

application note


Remote access and monitoring of fiber-based fronthaul networksSkyRAN is EXFO’s solution to meeting the demands of these fronthaul network challenges, both now and in the future. SkyRAN provides fast, easy access to the status of fiber optic infrastructure and RF spectrum, at any time, and from anywhere. Its industry-leading resolution and accuracy allow users to troubleshoot and pinpoint problems without having to perform on-site tests beforehand. This allows the timely assignment of the correct resources to fix a network issue.

Automated monitoringWith the exponential rise in RRH deployment, SkyRAN addresses the increased workload by constantly examining every RF waveform and fiber optic link to ensure reliable and efficient operation. SkyRAN detects passive interference modulation (PIM) as well as narrowband and wideband interference. When interference exceeds user-defined limits, SkyRAN generates alarm conditions (such as email alerts) and automatically updates the status of SkyRAN’s element management system (EMS) so the user can see network issues at a glance.

SkyRAN’s ultra-sensitive RF-monitoring capabilities outperform traditional management systems, detecting and addressing interference issues before they impact key performance indicators (KPIs) and affect customers, potentially saving days of customer dissatisfaction.

Similarly, SkyRAN monitors fiber optic cables for losses and records the precise location and nature of the fault should these exceed user-defined limits.

SkyRAN’s EMS offers a complete picture of the entire network being monitored and can drill down to deliver more detailed information as required. For RF interference, real-time traces of the RF waveform are available for replay; for fiber optic issues, OTDR traces of the problem can be displayed. The current alarm log shows which issues are still present and the alarm history identifies any recurring issues. Users can also consult a specific RRH to see its current RF spectrum and optical network status.

SkyRAN shortens mean time to repair (MTTR) on interference issues, improving KPIs and overall network performance.

Instant visibilitySkyRAN’s EMS complements and interfaces with existing management system infrastructure, providing consistent measurement of RF and fiber optic performance in a multi-vendor environment.

It correlates the data from each SkyRAN system and provides intelligent diagnostics to the higher-level management infrastructure. Similarly, the management infrastructure sends SkyRAN information to help diagnose fronthaul issues.

The SkyRAN EMS graphical user interface (GUI) provides real-time status of the entire fronthaul network and details any issue.

application note


Remote accessSkyRAN provides detailed RF and fiber optic information remotely, eliminating most “diagnostic” truck rolls and delivering huge time savings. Remote insight means the right resources can be dispatched to the right site. Too often, teams arrive onsite only to find they need further help (external contractors, other internal teams) or that the real issue lies at another location. With SkyRAN, obstacles associated with access (e.g., airport security, health and safety regulations during major events, or location-specific safety concerns during unsociable hours) are a thing of the past.

This frees up time and resources for other issues while tower crews, interference hunting teams and third-party resources complete work identified by the remote diagnosis.

Figure 2. Multiple SkyRAN installations with EMS.

High-resolution RF spectrumSkyRAN sees exactly the same RF spectrum, at the same resolution that the RRH sends to the base station, eliminating the uncertainties that arise when over-the-air RF spectrum measurements are made at ground level. In fact, SkyRAN offers the industry’s highest spectrum resolution, together with precise value and location of fiber-optic cable-plant losses and distance to fault of fiber cuts.

SkyRAN’s unparalleled resolution and ability to track values over time lets users detect problems before they affect KPIs, providing more time to address issues before they become a problem. Reactive troubleshooting makes way for preventative maintenance, and remedial work is carried out in designated maintenance windows, avoiding impact on network performance during peak hours.

application note


ApplicationsMacrocellsThe flexible, modular SkyRAN solution is easy to deploy in remote macrocells requiring long travel times or troublesome macrocells in need of frequent visits. SkyRAN’s remote access capability saves time and money by eliminating unnecessary truck rolls—less windshield time, faster problem resolution!

Instrumenting macrocells also helps interference hunters as triangulation can be used to locate interference sources.

Figure 3. Macrocell site configuration.

Large venuesSkyRAN is also suitable for locations with numerous RRHs, such as stadiums, shopping malls, airports or hospitals. A single SkyRAN system can monitor each and every RRH, providing a big picture view. SkyRAN simplifies interference hunting by monitoring and providing visibility of the receive spectrum on every antenna. Limited access to monitoring locations during ‘special events’ or ‘secure area’s’ are overcome using SkyRAN’s remote access capability.

SkyRAN features automated monitoring for effortless reliability and performance, warning users ahead of time of potential issues.

Figure 4. Large venue configuration.

application note


C-RAN hubsC-RAN hubs are the most obvious application for SkyRAN. When placed in the hub, SkyRAN monitors each of the remote radio heads it is connected to. It constantly monitors the long fiber optic spans and various RF waveforms, providing accurate and timely information on fronthaul infrastructure performance.

SkyRAN correlates the information received from the various cell sites monitored, providing a more insightful view of what is happening.

Fiber optic network monitoringIn traditional macrocell installations where fiber optic cable typically runs from the bottom of the tower to the RRH at the top, fiber optic cable issues are easy to isolate and repair. However, in the case of C-RAN installations where the base station and the radio head are several hundred meters apart, troubleshooting can be much more complicated.

Take the example of an RRH located at a site six miles away from a BBU, inside the C-RAN hub. The BBU is connected through patch cables and connectors to a fiber optic cable owned by a third-party. The third-party provides an optical connection between the C-RAN hub and the various cell sites. At the cell site, ground-based patch cables are connected inside an over-voltage protection panel to the riser cable going up the cell tower. An additional junction box connects this riser cable to the RRH through another patch cable.

Traditional management systems typically indicate the power levels at the RRH and BBU. These alert the user to a problem (e.g., low receive power at the BBU when transmit power at the RRH is normal) but are of little use in troubleshooting as they do not provide information on the location of the fault.

Based on the information available from the management system, the problem could be at the C-RAN hub or on the ground at the cell tower. Alternatively, it could be in the 3rd party cable running between the C-RAN hub and the cell site or it could be located on or at the top of the cell tower. In each case, different resources would be called upon to fix the fault. Without SkyRAN, determining the precise nature and location of the fault would require taking the RRH out of service and likely investigating via an OTDR at the C-RAN hub. Only then could the correct resources be dispatched and corrective action taken, which would probably require additional truck rolls. The longer it takes to diagnose a problem the costlier it becomes.

NOC Radio engineering

Field crew Total

Time 4 hours 1 day + 3.5 hours 6 hours 1.5 days

Effort (man hours) 2 5.5 8.5 16

Cost (US$ or €) 200 600 1500 2300

Figure 5. The high cost of problem escalation and troubleshooting.

application note


Figure 6. Remote site connected to C-RAN hub.

SkyRAN performs constant OTDR traces of the fiber optic link. EXFO’s patented iOLM technology presents data in a user-friendly format, displaying each loss due to connectors, bends or breaks, along with the distance to fault and suggested remedy. That makes it easy to dispatch the right resources to the right location and ensure they have the skills and equipment to fix the fault.

EXFO’s solution goes beyond traditional troubleshooting methods to provide a quicker diagnosis and speedier repair, freeing up resources for other issues and ultimately saving time and money.

Figure 7. Fiber optic trace view using iOLM.

Interference huntingOften the first sign of an interference problem is that a management system reports poor KPIs. Through further investigation, it may detect a high RSSI value at one or more cell site sectors. The next step is to determine the location and source of the interference. A traditional management system provides low-resolution data, and often a visit to the cell site is the first recourse. RF spectrum measurements taken at ground level can be problematic as they do not have the same line of sight as the cell site antenna. Like fiber optic issues, interference may be located at the bottom of the tower due to faulty equipment, at the top of the tower due to issues such as PIM, or away from the site due to third-party interference. Each type of interference may require the services of other teams to fix it, requiring additional truck rolls and prolonging resolution time.

application note


As SkyRAN is constantly monitoring the RF spectrum of all RRHs connected to the system, interference is often detected before it impacts KPIs. Interference is captured automatically and can be replayed by the user at full resolution and in real time. This allows it to be characterized without a visit to the cell site, using the same data seen by the BBU.

Consider a waveform representing a leaking oscillator: since the same waveform will appear in sectors of other cells in the area, the location can be approximated through triangulation. The interference hunting team will then know the shape and frequency range of the waveform and its rough location. This reduces the time needed to track down and mitigate the interference source and return the site to normal operation. Knowing the shape of the interfering signal makes it easy to capture the signal in the field and provides clues to its possible source.

Figure 8. High-resolution, real-time RF spectrum analyzer.

An interference hunting team can be sent directly to the location of the interference, eliminating one whole truck roll to investigate the problem and the need to visit the cell site first. This frees up the engineer to process another trouble ticket.

SkyRAN features other tools for determining interference sources, such as PIM monitoring. Each waveform is evaluated and an alarm is raised if PIM exceeds user-defined limits. The RF waveform is also saved for evaluation. Since users can view the receive spectrum on every antenna, they can determine whether PIM is only present on a single port, which would indicate the likelihood of an internal PIM issue. The ability to stimulate the transmit channel remotely via tools such as an orthogonal channel noise simulator (OCNS) and a remote electrical tilt (RET) control to change the tilt angle of the antenna allows for further diagnosis.

Figure 9. PIM detection.

application note


SkyRAN provides the tools necessary to accurately determine internal vs. external sources of interference and narrow down the location of the latter. Accurate RF waveforms provide the shape and frequency of external interference that technicians need to trace and eliminate the source. If they suspect a PIM issue, they can check that they have the necessary resources to access the coaxial cable and antenna system prior to visiting a site. The result is efficient use of resources and improved mean-time-to-repair (MTTR) statistics.

Preventative maintenanceIssues in the fronthaul network are not usually the result of an instantaneous event such as a cable cut or the appearance of a new external interferer. The majority of problems occur as a result of a steady deterioration in performance over time.

SkyRAN’s EMS monitors and provides trending reports of key parameters over time and alerts users when these parameters exceed pre-defined limits. If the limits are set appropriately, then failure to meet KPIs can be reduced or avoided altogether by taking remedial action.

Using both warning and critical alarm limits affords more time to plan and assign resources for preventative maintenance on cell sites and avoid performance issues down the road.

Ideally such preventative maintenance should be performed within a planned maintenance window to avoid shutting down the site at peak times.

Figure 10. SkyRAN EMS trend analysis.

Trend analysis sometimes involves monitoring each point of loss in the fiber optic infrastructure. Dirt or moisture in fiber optic connections increases optical power loss through the connector. SkyRAN can compare the current loss against a benchmark taken when the system was commissioned and compare the current loss with previously measured results. As more pollution enters the connector, the losses will increase until eventually there may be insufficient power at the BBU or RRH to maintain the CPRI link. SkyRAN will warn users when the losses are abnormal and again when they become critical. Maintenance crews can be assigned to clean and seal the connector before losses become unacceptable.

Similarly, if moisture enters the connectors, it can cause PIM in the coaxial cable system. This will increase the PIM value in the RF spectrum being monitored, and SkyRAN’s EMS will raise an alarm.

It is well known that temperature significantly impacts the life of a small form-factor pluggable (SFP) device and that monitoring internal SFP variables gives a good indication of impending failure. SkyRAN can track SFP trends, prompt a replacement and flag the need for additional temperature control at the cell site.

application note

EXFO serves over 2000 customers in more than 100 countries. To find your local office contact details, please go to www.EXFO.com/contact.


Variations in the RF spectrum at a cell site can also be caused by changes in the external environment such as new buildings or structures, seasonal variations and other gradual shifts over time. These changes can be monitored to determine if they impact performance and what remedial action can be taken.

By using SkyRAN to prevent failures, fronthaul teams can avoid having to be totally reactive to trouble tickets as they are raised and move towards more planned activities. This results in fewer trouble tickets and better overall network performance.

Benefits of SkyRANProven return on investmentSkyRAN provides fast, easy access to the status of the fiber optic infrastructure and RF spectrum, at any time, from anywhere. It affords significant tangible and intangible benefits:

− Reduced truck rolls − Less wasted time (diagnosing faults, traveling to sites) − Preventative maintenance − The right people, equipment and parts sent to the right places − Better working conditions

Eliminating a single truck roll can cover the investment in a SkyRAN monitoring port, making SkyRAN affordable for DAS, stadium, C-RAN hub or even macrocell implementation.

Typical return on investment for a SkyRAN system ranges from 6 to 18 months.

Scalable InfrastructureSkyRAN features a modular design so that the number of spectrum analysis ports and the ratio of analysis ports to physical ports can be chosen to match the scale of the site being monitored. Architectures can be scaled from a single macrocell with 12 or fewer ports up to a complete C-RAN hub with over 700 ports.

As the capacity of a site increases, SkyRAN modules can be added to the existing setup, as required, to monitor the new fronthaul infrastructure.

SkyRAN comes with the most efficient form factor available, with 48 port switches requiring only 0.5U of rack space and the SkyRAN rack taking up only 1U of space.

Switching times between ports are instantaneous, ensuring that SkyRAN is monitoring CPRI links 24/7.

Future-proof technologyTechnology such as SkyRAN needs to be able to cope with the rapidly changing RAN environment. SkyRAN switches are designed to support link rates in excess of 100G and its spectrum analysis ports can support all CPRI and OBSAI rates found in the field (rates 2 through 7). The spectrum analysis hardware can support all foreseeable changes in CPRI (rates 7A through 9) with a simple firmware upgrade. Future technologies such as even higher CPRI rates and Ethernet-based RAN are also covered through a combination of firmware and interface card upgrades, protecting user investments in the SkyRAN infrastructure for years to come.

APPNOTE357.2EN 18/05

remote access and monitoring of fiber-based fronthaul

Documents