C-RAN

The Rise of C-RAN

C-RAN networks bring baseband units together into BBU Hotels, and implement network functions in software on standard IT platforms to enable the virtualization of the network. This network function virtualization (NFV) will enable significant benefits in lower energy costs, greater network resilience and dynamic allocation of network resources with time.

For those responsible for installing and maintaining the network, the engineering teams will be working on a wider range of technologies including wireless, optical and transport. Test solutions need to be matched to the technologies in the network and flexible enough to troubleshoot a wide range of issues.

Anritsu has a long history of testing all aspects of the C-RAN. Our instruments evolve to meet the new challenges of testing the C-RAN networks being rolled out today.

Key Network Elements

C-RAN Network

With the large increase in mobile data traffic, network operators are moving the BBU (BaseBand Units) from macro cell sites to a common central location allowing greater flexibility and cost savings. The connection from the BBU to the RRH (Remote Radio Head) is most commonly via CPRI at rates between 614.4 kbps to 10,137.6 Mbps.

Core DWDM (Dense Wavelength Division Multiplexing) Ring

Today’s networks are interconnected by core DWDM fiber rings, interconnecting major metropolitan areas and populations. These networks consist of multiple 100 Gbps and 10 Gbps links over a single fiber, each on their own wavelengths across the C (1530–1565 nm) and L (1565–1625 nm) bands.

Metro DWDM Ring

Consisting of multiple rings per metropolitan area allowing the network bandwidth to be locally isolated. With rapidly growing demand for data, cloud resources are now being localized to within the metro ring, removing the requirement of the traffic transiting the core network. Multiple 10 Gbps, and some 100 Gbps, links each on their own wavelength across the C and L bands.

Macro Cell

A cell in a mobile phone network that provides network coverage using a high power cellular radio base station. The macro cell may be mounted on a tall building or a dedicated radio tower. Typically, the base transceiver station (BTS) radios are located in an equipment room at the base of the tower or on the rooftop. High power radios provide coverage up to 20 km. Connection back to the core network is typically by microwave link or optical fiber.

Small Cell

Low power radios used in the cellular network to provide densification in urban environments. Range may be limited to 0.5 km to 4 km. Typically the integrated radio is mounted on existing street infrastructure such as lamp posts or on the side of a building.

Remote Radio Head (RRH)

Part of a distributed base station that locates the BBUs at the base of a cell tower, or even remotely at a BBU hotel, and the radios at the top of the tower close to the antennas. The compact RRH is connected to the BBU via a fiber optic cable, typically using CPRI protocols. Use of RRH reduces power loss in long RF cable runs and potentially improves network flexibility, especially to distribute load at peak times.

BBU Hotel

This is the name given to a single location which houses the baseband units of many distributed RRH. A BBU hotel can be many kilometers from the radio heads, typically using fibers running CPRI protocols between the two. By locating multiple BBU at a common location, radio resources can be allocated dynamically as demand changes. The radios can be mounted closer to the antenna which reduces RF cable losses and may improve PIM performance. OPEX may also be reduced as smaller equipment rooms and less cooling is required at each site.

Common Public Radio Interface (CPRI)

CPRI is an open specification for an interface between Radio Equipment Controllers (REC) often referred to as BBU, and Radio Equipment (RE), often referred to as RRH. The use of a CPRI interface run over a single mode or multi-mode fiber enables the radio equipment to be mounted at the top of a tower very close to the antennas. The BBU and RRH can be up to 2 km apart using single mode fiber or up to 25 km in a C-RAN network, facilitating the use of BBU hotels. The latest specification version 7.0 supports up to 24 Gbps line rates.

Microwave Radio

A point to point radio link that is often used to connect remote cell sites back to the core network, in place of optical fiber.

DAS (Distributed Antenna Systems)

DAS are the most common method selected by operators and building owners to achieve in-building coverage and capacity. DAS are able to accept inputs from a variety of sources making them equipment manufacturer and technology neutral (2G, 3G, 4G).

Passive DAS

Signals from one or more RF sources are distributed throughout a venue using only passive components: coaxial cable, splitters and antennas. Sectorization is achieved by dedicated RF cable feeds to each antenna branch. Typically used for small DAS installations such as SME offices, conference

centers and hotels.

Active DAS

Downlink signals from one or more RF sources are conditioned, combined and converted to light for distribution over fiber cable to radio units located around the venue. Radio units convert the signal back to RF, amplify and re-broadcast them. This allows for greater range within the DAS and is

typically used at large sports stadiums, airports and very tall buildings.

Network Interference

The best planned networks are subject to performance degradation from illegal or accidental radio interferers such as unlicensed radio microphones, radios on visiting commercial shipping, leaking cable TV cables or illegal FM transmitters.

Transport Layer

A general term for the layer of the OSI Reference Model that provides connection services for high layer applications. Optical Transport Networks (OTN) run up to 400 Gbps, other transport technologies include: Ethernet, CPRI/OBSAI, SDH/SONET, PDH/DSn.

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