What is C-band and how will it accelerate 5G deployments

Recently, I participated in a Light Reading webinar about C-band frequency and the role that C-band spectrum will play in 5G. I discussed this (and more) through the lens of real-world 5G use cases. Since the topic of C-band garnered so much interest, I thought I’d share some of the participant questions that were asked during our lively Q&A session. So, below is part one and two of my two-part Q&A on C-band spectrum.

This article has been updated with part 2 of the Q+A. If you’ve already read part 1, click here to skip directly to part 2.

Part one

Q1: As opposed to unlicensed bandwidth (e.g., 2.45 GHz) is C-band spectrum licensed?

A1: Yes, C-band spectrum is licensed. Therefore, to deliver services over C-band frequencies, operators need to bid for and acquire available spectrum at auction.

Q2: Are best practices for 5G installation and activation the same when deploying lower frequency bands as they are when deploying C-band frequency bands?

A2: Whenever we're talking about lower frequency 5G bands, installations are similar to 4G LTE. However, unlike its predecessor, 5G installations don’t have coax cabling as they are full-fiber infrastructure builds. So best practices are different yet somewhat similar since end-to-end validation is still required. The 5G low band 600 Mhz is an exception, where testing is similar to 4G/LTE installations—including PIM testing and sweep testing. In summary, there are a few testing processes that were available for 4G LTE that are still required for low-band frequencies in 5G networks. As soon as we hit that 3-3.5 GHz mark (and higher), testing becomes a little different and technologies such as beamforming and millimeter wave (mmWave) come into play.

Q3: When interference is present on 5G non-standalone (NSA) sites, why is it primarily associated with 4G uplinks and not 5G downlinks, and where does C-band come into play?

A3: In 5G NSA, the reason why interference is seen more frequently on the uplink than on the downlink is because most initial 5G NSA installations use the 4G core on the uplink and 5G on the downlink, although this is beginning to change with C-band frequencies. When we talk about downlink signals from the antenna to the user equipment, those signals are usually powerful signals. So even if there is a small amount of interference present, the link is not affected due to the high level of power being transmitted over the air. The 4G uplink signal generally has more issues because it’s a low power level RF signal being transmitted by the user equipment (i.e., mobile phones) and is prone to being affected by interference.

Q4: Will the use of 5G standalone (5G SA), remove all RF interference?

A4: 5G SA networks will still be subject to interference, but interference will be greatly reduced compared to 4G networks. Let’s take a look at why.

First, let’s look at interference within a 4G LTE environment. The reason we encounter a lot of interference with 4G LTE connectivity is because there are many commonly used devices that operate over the same frequencies as mobile phones. In contrast, 5G standalone makes use of frequency bands that are not occupied by commonly used devices. Therefore, RF interference issues exist in 5G SA but to a lesser extent.

One of the new technologies developed to enable 5G is beamforming—a technology which also helps users avoid some types of interference. Beamforming is a signal processing technique that uses the multiple antennas available with massive MIMO to create a focused signal (or beam) between an antenna and specific user equipment. Signals can be controlled by modifying magnitude and phase, giving the ability for the antenna to focus on specific users. This concept can be compared to a music concert where a spotlight is focused on specific performers onstage. When beamforming is active, it’s able to counter certain types of interference (e.g., narrow band difference). This is done through the redirection of spectrum to different places which, in many cases, avoids certain types of interference. So, to reiterate, interference will still be present in 5G SA, but it will be less disruptive to users than it would be in a 4G LTE system. (For more information on beamforming and other RF technologies, check out our blog post ‘RF and 5G new radio: top 5 questions answered’.)

For more on C-band spectrum and C-band applications, watch our webinar ‘C-band Spectrum: What It Means for Accelerating 5G Deployments’. Stay tuned for part 2 of our Q+A on What is C-band and how will it accelerate 5G deployments.

Part two

In part one of my two-part Q+A on C-band spectrum I discussed interference in 5G NSA networks along with other issues. In part two I conclude the conversation about C-band frequencies with questions related to 5G radio units, automation in C-band deployments and more.

Q1: How do higher propagation and penetration loss affect the use of C-band and will this impose a strict line of sight between the base station and user equipment?

A1: Sitting in the 3.3 - 4.2 MHz range, C-band strikes the perfect balance between low and high bands — therefore, a strict line of sight isn’t required between the base station and user equipment. Additionally, C-band uses technologies such as massive MIMO and beamforming to obtain superior signal coverage.

Q2: With new 5G radio units (RU) that have antennas integrated and fed with a fiber, are power cables also required?

A2: Yes, power cables are required to the cell site, this is managed by the fiber/power distribution box with over voltage protection (OVP). There is an easy way to validate if the 5G RU is receiving power correctly by doing an eCPRI link validation at the base of the tower. This confirms that the transceiver is installed correctly, fiber is properly installed and that the radio is receiving power. Power issues don’t happen very often, the most common issues we see are transceivers not seated properly or the wrong transceiver installed. So, methods of procedure (MOP) that include fiber testing, inspection, transceiver verification and eCPRI link validation will dramatically reduce the time for 5G sites to go live.

Q3: How do you see the use of 5G NR base stations as a business case for fixed-wireless access in rural environments? Will wireless be a real alternative to fiber or cable deployments?

A3: It is very expensive to deploy fiber-to-the-home (FTTH) in rural areas. Due to this cost constraint, and the unaffordable fees that consumers would be charged for high-speed services delivered via fiber, that plan is off the table for most internet service providers and mobile network operators (MNOs). That said, the current challenge is how to upgrade these areas to higher speed service. The answer lies in 5G mid bands, including C-band spectrum, due to their reach and speed capacity. One cell site, deployed within a radius of a few kilometers from homes, can help residents obtain faster connection speeds.

Q4: Given that a 5G Synchronization Signal Block (SSB) can be located anywhere in the channel, how long can it take for an SSB scanner to locate a 5G SSB and synchronize to it?

A4: A synchronization signal block can be located anywhere in the channel bandwidth, so the answer to this question depends on how large the channel bandwidth is that’s being scanned. The SSB scanner will scan starting from the center frequency going outwards—basically trying to find the SSB as quickly as possible. The time required to locate the signal varies but is usually under one minute. For more on SSB and SSB scanners, watch the webinar ‘C-band Spectrum: What It Means for Accelerating 5G Deployments’

Q5: What are some examples of the need and role of automation in C-band deployment and validation?

A5: Automation has a role to play in terms of analyzing C-band frequency performance through the access of cell site data in real time. Currently, once cell sites are installed and running, it’s a challenge to know how they are performing. Analyzing the performance of cell sites in real time will mean that, whenever there is an issue, it can be tracked and troubleshooting can be performed immediately and specifically for the issue that is impacting the quality of service.

If you’d like to learn even more about C-band spectrum or C-band applications, watch our recent webinar presented by Light Reading: 'C-band Spectrum: What It Means for Accelerating 5G Deployments’. Interested to learn how EXFO’s helping operators validate 5G RAN installations faster than ever? Then discover the 5GPro Spectrum Analyzer, the industry’s only modular RF testing solution for analyzing both FR1 (including C-band) and FR2 (mmWave) bands.