Fronthaul

Even with additional spectrum and the introduction of long-term evolution (LTE) networks, there are geographical areas in mobile networks where demand is projected to exceed the capacity provided by the macro layer.

To expand their networks to other hard-to-reach locations, wireless providers are turning to the deployment of alternative infrastructures, like remote radio heads (RRH), distributed antenna systems (DAS) and other small-cell alternatives, most of which are fiber-based.

There's more to it than just wireless

Since physical and transport layers remain the foundation of a network, they require proper testing to:

• Qualify the system and document it for future reference
• Ensure that the network meets transmission-system requirements (standards)
• Avoid delays and costly repairs when the system is turned up

Remote radio head (RRH) and FTTA

To bring bandwidth connection to cell towers, operators must now rely on fibers to connect the base station to the backhaul, and the RRH to the base station.

Typically, in a new cell-tower deployment, fibers run from the base station to the RRH–at the top of the antenna. Due to the number of existing cell sites, operators can also choose to upgrade the cell site by replacing old coax cables with fibers from the base station to the RRH. In most cases, they will use contractors specializing in installation and maintenance to complete these jobs.

Key considerations and challenges:

• Dispatching a “tower climber” technician for repairs can be very expensive, making repeat jobs unfeasible.
• Technicians with expertise in copper or RF, may have limited fiber-testing knowledge. Lack of training can lead to basic errors, incorrect results interpretation and other mistakes.
• Neutral host concept: Towers are frequently operated by companies that rent wireless spectrum to telcos. Towers that are offline are very costly (SLAs must be delivered).

Distributed antenna system (DAS) and fiber-fed small cell

A distributed antenna system, or DAS, is a network of spatially separated antenna nodes connected to a common source via a transport medium (fiber) that provides wireless service within a geographic area or structure. DAS elevations are generally at or below the clutter level, and node installations are compact.

Similar network design is also seen in other fiber-fed, small-cell infrastructures.

Key considerations and challenges:

• Very short deadlines: Telcos and operators are in a race to get this extra coverage as fast as possible. Contractors need to hire inexperienced technicians with very little time to invest in training.
• An agreement with the landlords and building owners is required, and installation must be flawless (e.g., esthetic considerations, efficiency, minimum disruption and reduced access to the building).
• A high level of standardization in terms of deployment and processes is required as a DAS can support multiple carriers and multiservice platforms (e.g., GSM, CDMA and HSDPA).

Key testing considerations and solutions

Connector endface cleanliness

What you should do: perform visual inspection to detect dirty/damaged connectors; clean them if required

The tools you need:

• Fiber inspection probes
• Automatic analysis software

Fiber-link characterization

What you should do: look for anything potentially impacting total budget loss (dB), such as macrobends, splices, 
bad connectors, fiber breaks, etc.

The tools you need:

• OTDRs
• iOLM
• Post-processing software

Transport validation

What you should do: FTTA validation for CPRI from 1.2 Gbit/s to 9.8 Gbit/s via BER testing

The tools you need:

• NetBlazer V2 Series – Multiservice tester
• FTB-700 V2 Series – Optical/Ethernet/multiservice tester

Fault isolation

What you should do: continuously check in-service fiber pairs for changes that can be localized and potentially impact services quality

The tools you need:

• OTDR-based fiber monitoring
• iOLM-based in-service remote testing