March 29, 2017
The latest CPRI specification remains on schedule to be releaed in August of this year, according to a news release published by the CPRI Industry Initiave. The new specification, known as eCPRI, will place emphasis on 5G fronthaul support and is expected to include increased efficiency to meet the anticipated high-speed, high-bandwidth needs of 5G networks. The goal of the eCPRI specification is to offer numerous benefits to engineers designing base stations. Among the expected advantages are:
- A new physical layer split point to enable a ten-fold reduction of the required bandwidth
- Required bandwidth that can scale flexibly based on the user’s plane traffic
- Use of mainstream transport technologies such as Ethernet to possibly carry eCPRI and other traffic simultaneously in the same switched network
- Use of sophisticated coordination algorithms for optimal radio performance
- Easy-to-upgrade foundation so future introductions can be done via software updates in the radio network.
In addition to the new eCPRI specification, work continues to further develop the existing CPRI specifications to keep it as a competitive option for all deployments with dedicated fiber connections in fronthaul, not only 5G.
This comes as no surprise to anyone involved in the design and deployment of base stations. After all, the integration of CPRI into the traditional RF space of an eNodeB was done to address the faster speeds and higher bandwidths associated with LTE networks. Plus, many of the existing CPRI specifications have 5G elements within them.
For engineers and field technicians, though, while one eye may be on 2020 when 5G is expected to launch, the other is clearly focused on current base stations, which continue to evolve in their own right. To verify performance of today’s base stations, test solutions must have new features that not only meet the technology challenges but also the demands for more time- and cost-effective testing procedures.
Base Station Performance Updates
CPRI Line Rate 8, which operates at 10.1376 Gbps, is becoming more common in base stations. While its faster transmission speeds are better suited for streaming and similar applications, it also means test instrumentation must keep pace. Fortunately, handheld analyzers are now available that support CPRI Line Rate 8.
Another example is that newer Base Band Units (BBUs) are supporting and implementing 20 MHz compression technology. Handheld test solutions that are durable enough to withstand the terrain associated with bases stations will now also have to provide 20 MHz compression support. Figure 1 shows an example of the Anritsu BTS Master, which now has a compression capability that allows for resampling of 20 MHz bandwidth IQ data signals from 30.72 Msps to 23.04 Msps to meet this market condition.
One of the biggest issues facing operators right now is interference on the uplink, which can drastically affect KPIs. To address this concern, handheld test tools have the capability to tap into the CPRI fiber link and monitor the uplink spectrum. Coupled with an ultra-fast sweep speed when conducting CPRI RF measurements, these solutions make it much easier for field technicians to capture and analyze transient and bursty signals typical of many interference types. Another recent feature is the ability to tune to anywhere within the spectrum and zoom in for more detailed analysis, to better and more efficiently locate issues that may hinder network performance.
Multi AxC Traces
Making base station testing more efficient is another key goal for most operators. Again, test solutions are advancing to make verifying and troubleshooting networks faster and easier. For example, there is now the ability to view from one to four AxC Group traces in a single spectrum view (figure 2). A Dual Display capability that allows two different AxC traces, such as spectrum and Spectrogram, to be viewed simultaneously is also now available.
The combination of Multi Trace AxC and Dual Display gives users plenty of flexibility in looking for interferers by being able to look at the different MIMO signals simultaneously. It also allows RF engineers to look at RF loading and balance, also known as diversity testing, between MIMO radios on a live signal.
Staying up-to-date with base station technologies is no easy task. That’s one reason why Anritsu published a dedicated Base Station Technologies page that offers insight on all aspects of base stations and ensuring their deployment, installation, and operation. You can also download a white paper entitled Improving Wireless Network Flexibility Using CPRI Technology.