November 11, 2021
The C-band spectrum auction held by the Federal Communications Commission (FCC) was surrounded with so much fanfare it seemed impossible it would meet the hype. Well, more than $80 billion later, it’s safe to say that all the “noise” seems warranted. The question now becomes, how do mobile operators get the best possible return on investment (ROI)?
Verizon (estimated 3,500 total licenses) led the way, followed by AT&T (1,621 licenses), with T-Mobile (142 licenses) rounding out the top three. Considering the investment in the midband spectrum, which is well positioned to optimize certain 5G use cases, mobile operators must have a tactical approach with deployment. A key part of that strategy must emphasize network quality to maintain customer satisfaction, meet key performance indicators (KPIs), and limit customer churn. A sound test approach from antenna installation to operation helps achieve this goal.
Understanding C-band and its Impact
Before outlining test procedures, it’s important to consider how C-band (figure 1) fits into the 5G infrastructure. C-band has such appeal because it addresses coverage and bandwidth issues. It is part of Frequency Range 1 (FR1), which operates from 450 MHz to 6 GHz. 3GPP Release 15 stipulates the n77, n78, and n79 bands for 5G operation in the C-band. The potential service bandwidth is up to 100 MHz, making it ideal for 5G enhanced mobile broadband (eMBB) use cases.
C-band utilizes Time Division Duplexing (TDD), which has spectral efficiency benefits. TDD requires only unpaired spectrum, making the technology advantageous in environments with limited frequency resources.
On the other hand, timing and synchronization challenges are common with TDD. Because downlink (DL) and uplink (UL) share the same spectrum in a TDD system, strict timing restrictions are enforced to limit interference. If synchronization is in error, TDD framing will drift outside the guard period and into adjacent time slots. The result is network performance lags due to interference.
Spectrum Clearing A Necessity
A key consideration is that much of C-band needs to be cleared before mobile operators can use the spectrum. That’s because the frequencies were (and is some cases still are) used for government, public and private broadcast and satellite services. For this reason, extra attention with respect to deploying, installing, and maintaining C-band base stations must be given.
Contractors retained by mobile operators must conduct spectrum clearing as an initial step. Typically, a handheld spectrum analyzer with an omni-directional antenna (figure 2) may be used to determine if the spectrum is clear and ready for 5G usage.
In a similar vein, on-going interference monitoring should be conducted. The same spectrum analyzer with a directional antenna configuration can be used when a performance issue is identified to conduct an interference hunt once the network is live.
Conversely, mobile operators will be required to ensure their 5G base stations do not impact satellite transmissions that have migrated to the upper portion of the C-band. This is particularly important, as massive MIMO and beam steering used in 5G can interfere with low noise block (LNB) downconverters of satellite antenna systems. Such an unattractive scenario is possible if the antenna is too close to the satellite earth station.
eCPRI is a key element of a C-band base station. It enables efficient and flexible radio data transmission over a packet-based fronthaul transport network. Using Ethernet for transport has a few advantages. For one, it is backward compatible with commodity equipment, enabling greater convergence of access networks. It also makes statistical multiplexing possible, which will help lower the aggregate bit-rate requirement.
There are hurdles with eCPRI, though. Unlike CPRI, eCPRI is not a synchronous technology. GPS, precision time protocol (PTP), and synchronous Ethernet are technologies used to address synchronization. Therefore, technicians need to conduct eCPRI tests to measure throughput, delay, and packet jitter when deploying and maintaining C-band.
Another key aspect of C-band verification is to ensure that Over-the-Air (OTA) network performance and coverage meet the network design specifications published by the operators. Coverage mapping tools can help satisfy this requirement.
Anritsu spectrum analyzers can accurately measure RF power measurements over a wide frequency range, which, when attached with an antenna, become Received Signal Strength (RSSI). With coverage mapping, RSSI and Adjacent Channel Power Ratio (ACPR) measurements are combined with on-screen map displays to create a versatile solution for mapping coverage.
With a touch of a button, coverage mapping can be started, so technicians at any experience level can conduct measurements. The user has full control over the threshold values and measurement settings. Each measurement point is assigned a color correlating to the threshold values, and this fully customizable function allows for quick results.
For contractors, payment for services requires submission and subsequent approval of close-out reports. Smart Aligner App (figure 3), a unified reporting solution for antenna alignment and line sweep measurements helps expediate payment. With the app, close out reports can be prepared, saved as pdf files, and sent to operators from the site location, saving time and money while providing operators with confidence that new base stations have been installed according to specification.
Reports can be submitted directly as an email attachment sent over the cellular network. Confirmation of acceptance can be given before the crew departs from the site, eliminating the additional costs and time associated with return visits. Anritsu’s handheld field base station test solutions, including Site Master™ cable and antenna analyzers support the close out app.
To learn more about Anritsu’s interference measurement tools, visit a dedicated technologies page.