June 14, 2016
The saturation of 4G networks and emergence of 5G is changing the architecture of wireless networks, which are becoming denser to support the surge in demand for mobile data and integration of the Internet of Things (IoT). Engineering teams responsible for installing and maintaining the network are working on a wide range of technologies, including wireless, optical and transport, to achieve the high-speed and high bandwidth necessary for emerging applications. In this post, we will outline the technologies as well as test solutions that can be used to ensure the successful operation of each network element.
CPRI
With the significant growth in mobile data traffic, operators are moving baseband units (BBU) from macro cell sites to a central location allowing greater flexibility and cost savings. The connection from the BBU to the Remote Radio Head (RRH) is most commonly via CPRI operating between 614.4 kbps to 10,137.6 Mbps.
Test Solutions: Field technicians need optical test solutions, such as the one shown in figure 1, to test the fiber cables used in CPRI. Additionally, instruments like the BTS Master™ base station analyzer have CPRI options that allow RF tests on the RRHs to be conducted via the CPRI links, saving time and money.
Figure 1
DWDM Rings
Core DWDM fiber rings interconnect major metropolitan areas and populations. These networks consist of multiple 100 Gbps and 10 Gbps links over a single fiber, each on its own wavelength across the C- and L-bands.
Metro DWDM rings are similar in that they use 10 Gbps and 100 Gbps links over their own wavelength across the C- and L-bands. The metro version, however, consists of multiple rings per metropolitan area, so network bandwidth can be locally isolated.
Test Solutions: Optical transport testers that can test various technologies, including Ethernet, OTN, SDH/SONET, and PDH, are needed to verify these rings. Field instruments that integrate OTDRs, light sources, power meters and other tools are particularly helpful.
Macro Cell
Providing network coverage via a high-power base station, the macro cell may be mounted on a tall building or dedicated tower. Typically, the base transceiver station (BTS) radios are located in an equipment room at the tower base or on the rooftop. High-power radios provide coverage up to 20 km, with a microwave link or optical fiber serving as the connection back to the core network.
Test Solutions: The field technician’s toolbox will need to feature optical transport testers to measure the fiber elements. For the RF segments, cable and antenna analyzers, spectrum analyzers, and PIM analyzers are all necessary.
Small Cell
Small cells are low-power radios used in the cellular network to provide densification in urban environments over a limited range of typically 0.5 km to 4 km. Usually, the integrated radio is mounted on existing street infrastructure, such as lampposts, or on the side of a building.
Test Solutions: Figure 2 shows the BTS Master base station analyzer, which combines 30 instruments into one solution, making it a wise choice when testing small cells. Optical transport testers are necessary to test the optical elements, as well.
Figure 2
Remote Radio Head (RRH) Sitting atop a cell tower, the compact RRH is connected to the BBU via fiber 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.
Test Solutions: RRH is another network element that will require a comprehensive tool box. Technicians will need optical transport testers, OTDRs, as well as a cable and antenna analyzer and PIM analyzer.
BBU Hotel
A single location that houses the BBUs of many distributed RRHs, a BBU hotel can be many kilometers from the radio heads, typically using fibers running CPRI protocols between the two. By locating multiple BBUs at one location, radio resources can be allocated dynamically as demand changes. The radios can be mounted closer to the antenna to reduce RF cable losses and may improve PIM performance.
Test Solutions: A complete test instrument that has cable and antenna analysis, spectrum analysis, a vector signal generator, interference analyzer, power meter, and CPRI RF measurements, such as the BTS Master, is invaluable in this scenario. Optical transport testers and OTDRs are also necessary.
Microwave Radio
An alternative to optical fiber, microwave radio is a point-to-point link often used to connect remote cell sites back to the core network.
Test Solutions: Typically, field technicians can get by with a spectrum analyzer.
DAS
The most common method selected by operators and building owners to achieve in-building coverage and capacity is DAS. The reason is because DAS can accept inputs from a variety of sources, so they are equipment manufacturer and technology neutral.
Test Solutions: If it is an active DAS, fiber test tools such as optical transport testers, OTDRs, and light meters are required, as are base station analyzers, cable and antenna analyzers, and PIM analyzers for the RF elements. Passive DAS will need only the wireless test solutions. A cloud-based trace management tool, such as the award-winning SkyBridge Tools™ from Anritsu, is also extremely valuable here, as well as in most of the aforementioned elements of a C-RAN network.
To learn more about transport, optical, and RF testing elements of the C-RAN network download a free solutions brochure.
