December 5, 2016
As the wireless industry moves towards Remote Radio Head (RRH) hardware to address the significant increase in mobile data traffic, the need to emulate the Baseband Unit (BBU) becomes a key tool for managing and reducing time-driven costs during site build, commissioning, and troubleshooting. Utilizing the proper emulation tools can help maximize network profits while also saving valuable time by reducing repeat site visits by crews to commission new sites.
In a Common Public Radio Interface (CPRI) site design, the BBU is connected to the tower-mounted or pole-mounted RRH via a fiber optic line. In a typical build project, the RRH is mounted and the BBU is installed later. If problems arise with the RRH, they’re not discovered until after the BBU is installed and commissioned. Resolution involves creating and tracking a trouble ticket, then scheduling and performing subsequent site visits – all of which incurs unanticipated operational expenses (OpEx) and reduces profit margin.
RRH installations can be plagued by various hardware complications. There may be issues with the RRH itself, problems with the Small Form Factor Pluggable (SFP) optical transceivers, RF glitches with coax cables or antennas, and complications with the fiber optic lines or connectors. Additionally, there can be problems with the on-site RF environment, including Passive Intermodulation (PIM) from nearby metal-junction issues or poor RF connectors, and interference from nearby RF sources. RRH antennas need to be adjusted for tilt and azimuth to manage PIM, reduce environmental RF noise, and to optimize downlink performance.
Troubleshooting or managing these potential issues requires the RRH to be connected to a working BBU. In most new build scenarios, however, the BBU may be installed but has not been commissioned and is not available to verify the operation of the RRH. It is in these scenarios where the value of a BBU emulator will be realized.
Initial testing of an RRH (either in-place, or in a depot prior to going on-site) may be done by attaching a BBU emulator via a section of fiber optic line. This confirms that the RRH is configured correctly, responding properly to CPRI signals, and that the RRH will be able to attach successfully to the actual BBU. Testing of the SFPs may also be necessary, and is easily accomplished with a BBU emulator. Testing from the base of the tower provides confirmation that the fiber optic line is intact, the SFP is installed in the correct port and that the fiber is clean and seated properly.
Determining if PIM is an issue is done by analyzing the uplink receiver and looking for characteristic patterns in the noise floor, while the RRH is transmitting a LTE signal. Environmental RF noise will also appear during this test. It may be possible to reduce or eliminate PIM and any environmental noise by adjusting the RRH antennas for tilt or azimuth. Likewise, adjusting RRH antennas for optimized downlink performance is best done with the RRH activated by a BBU emulator, and measuring signal performance at the anticipated user locations using an LTE analyzer.
A key value of the BBU emulator is the time and cost savings realized from testing and resolving these problems before the BBU is commissioned, thus reducing truck rolls. This approach helps ensure that projects will be completed on-time and within budget constraints. Anritsu’s BBU Emulation, available on the BTS Master™ MT8220T handheld base station analyzer, replicates the functions of a standard BBU. Field engineers and technicians can use a solution such as this to fully test and exercise the RRH with both feet on the ground to validate and sign off on the installation before the BBU is installed (figure 1).
Anritsu has developed an informative webinar on the topic to help streamline RRH installations. You can access the presentation entitled Validating the Performance of Cellular Networks with CPRI Fiber Interfaces Between Ground Level Baseband Units and Tower Mounted Radios here.