Industry analysts, players and authorities — including GSMA and Ericsson — have been heralding the mobile broadband (MBB) data traffic growth that will likely happen over the next 10-15 years. Meanwhile, 4G Long-Term Evolution (LTE) is positioned to remain the dominant mobile access technology while commercial scale 5G deployments continue to roll out. 

LTE has improved spectral efficiency since its introduction in the 3rd Generation Partnership Project (3GPP) Release (Rel) 8. Waveforms, modulation advancements, coding schemes (e.g., 64-QAM/256-QAM) and multiple-input and multiple-output (MIMO) antennas have pushed the download data speed limits over the gigabit mark. Then, they were pushed into the multiple gigabit range with 3GPP Rel 15, the first phase of 5G deployments. 

Not all the news about LTE or 5G and MBB is rosy. Devices in noisy environments dampen the efficiency of technological improvements by reducing data rate and capacity. Achieving a higher MIMO order is still a challenge for device manufacturers hosting multiple antennas in a limited space. Densifying the networks and intensifying the distribution of small cells can help. However, this deployment process presents effort and money challenges for mobile network operators (MNOs). 

Carrier Aggregation Drives Up MBB Demand

So far, carrier aggregation (CA) has been a successful option for overcoming MBB deployment obstacles. The more combined carriers, the more expansive the usable spectrum and the higher the data speed. 

Therefore, MNOs can better support the increasing demand for traffic growth while limiting superfluous infrastructure investments. However, they still need to acquire additional spectrum.

What Is the C-Band Spectrum?

Allocating new spectrum has become a mandatory requirement for the mobile industry to improve capacity and enhance mobile broadband (eMBB). 5G technology accommodated the use of millimeter wave (mmWave) spectrum between 24 GHz and 29.5 GHz. 

However, due to its wavelength, propagation at these high frequencies is complex and often requires line-of-sight (LOS) conditions between the base station and device. These conditions require highly directional beams and massive MIMO antennas that track users in real time. 

The sub-6 GHz domain contributes a critical portion of the spectrum on the lower bands. It offers a compromise between the broad coverage of lower frequencies and the higher capacity of mmWave. Part of this spectrum is known as C-band. C-band sits between 3.4 GHz and 4.2 GHz and has emerged as a prime resource for the capacity crunch. There was much controversy at the start of its use with the debate on whether C-band 5G cell towers might interfere with commercial airline operations. The FAA and MNOs have agreed on “exclusion zones” where specific C-band frequencies are not deployed near airports. 

What Are the Benefits of C-Band Spectrum? 

The benefit of C-band, compared to mmWave, can be assessed from two different viewpoints: 

• Economic: Overlay the C-band on existing macrocellular or small-cell grids without needing new cell sites, unlike mmWave. 
• Technical: Access to a spectrum range with fewer challenging propagation conditions than mmWave. This approach reinforces transmission in a non-line-of-sight (NLOS) environment and facilitates indoor penetration on a scale like lower-frequency bands. 

C-band spectrum also provides a few advantages over lower frequencies based on frequency-division-duplex (FDD-LTE) technology. C-band is a time-division-duplex technology (TDD-LTE). Even though TDD throughput per megahertz of spectrum is lower than FDD, the carrier bandwidth in TDD can be up to 100 MHz in sub-6 GHz 5G operations (versus 20 MHz in LTE). It also allows transmission and reception on the same channel, compared to FDD-LTE requirements for a paired spectrum with different frequencies and a guard band. For a TDD-LTE device, this capability eliminates using a dedicated diplexer to isolate transmission and receptions, which reduces the bill of materials (BOM) cost.  

Since they are part of the same 3GPP standards, FDD-LTE and TDD-LTE offer comparable performances and similar high-spectral efficiency. There is increasing industry interest in applying this technology to MBB. 

Although the most used TDD spectrum is Band 40, Bands 42 and 43 are gaining attention, especially across Europe and Asia-Pacific. These two C-bands are licensed globally for commercial terrestrial cellular deployment. Moreover, it allocates a potential spectrum of as much as 400 MHz between 3.4 GHz and 3.8 GHz. This spectrum generates frequency to support applications that require high data throughput (e.g., smartphones and industrial and home gateways). 

In the U.S. market, the Federal Communications Commission (FCC) allocated a similar spectrum in Band 48. This band has a range of 150 MHz from 3.55 GHz to 3.7 GHz to create the Citizens Broadband Radio System (CBRS). Three primary user tiers share access: incumbent, priority access license (PAL) and general authorized access (GAA). These levels create demand for operators looking to:  

• Enter the mobile wireless market  
• Facilitate a private LTE network for large enterprises  
• Expand capacity cost-effectively 

C-Band: A Steppingstone for 5G

As an active MBB ecosystem player, Telit continues collaborating technology, products and solutions in response to the increasing demand for more 5G mid-band support. We also deliver higher cost and production efficiencies for MBB devices. C-band range centered around 3.5 GHz can aid 5G by providing the NLOS spectrum industry players need. As the most cost-effective expansion spectrum for 5G, it is only natural that it would quickly become its most popular band globally. About 75% of MNOs set one of the three C-bands (i.e., n77, n78 and n79) as their primary 5G band.  

Are you ready to find out what C-band can do for your next MBB device? See how easy it is to get started with Telit’s 5G sample kit.  

Editor’s Note: This post was first published on 16 January 2019 and has since been updated.