Importance of Sub-6 5G Bands | How They Help in 4G-5G Interworking

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Importance of Sub-6 5G Bands | How They Help in 4G-5G Interworking

3GPP 5G New Radio (5G NR) Frequency Range 1 (FR1) includes sub-6 GHz frequency bands, and Frequency Range 2 (FR2), the mmWave bands, includes frequencies between 24 GHz and 52 GHz. 

In this blog, we will focus on the 5G sub-6 GHz spectrum. 

The 5G sub-6 GHz spectrum provides an ideal middle ground between the existing 4G LTE networks and 5G mmWave, which will still take a few years and a massive infrastructure overhaul, to gain momentum and take center stage.

5G Sub-6 GHz – An Overview 

5G sub-6 GHz refers to 5G deployments using spectrum below 6 GHz and falls under FR1. Some of the bands in this frequency range are already being used by the previous ‘Gs,’ and have been extended to cover the enhanced new spectrum offerings from 5G. Sub-6 provides a faster path into 5G from 4G while consistently improving user experiences by implementing standards-compliant RAN and Core technologies.

The sub-6 GHz 5G band is further categorized into two parts – low-band and mid-band. The low-band frequency ranges from 600 MHz to 2.4 GHz and is very similar to 4G’s operational range. Now, the mid-band of sub-6 is where things get really interesting. It operates between 3 GHz and 6 GHz and is currently the band-of-choice, deployed by many countries, to take 5G to the masses. India also expects to auction spectrums between 3.3 – 3.6 GHz and 5.2-5.9 GHz by the latter half of 2021. 

Since sub-6 GHz bands work on a similar frequency spectrum as 4G LTE, the telcos can roll out 5G while simultaneously running the existing LTE networks, making the transition to 5G much easier and smoother in the coming years. 

Having said that, though the frequency spectrum is similar to 4G’s operational range, sub-6 GHz gives better speed due to Massive MIMO, an upgrade on MIMO (Multiple Input Multiple Output) already being used in LTE, and other 5G improvements.

Also, despite the similar spectrum, the low band 5G is said to have an improved connection density than 4G. According to a 5G spec, 5G mobile broadband supports far more devices in a given area, enabling a connection density of 1 million users per square kilometer radius. Whereas 4G only supports around one hundred thousand users in a similar setup, making it a tenfold improvement.

Listed below are some salient features of 5G sub-6 GHz

Stand-Out Features of 5G Sub-6 Spectrum 

  • Provides a faster path into 5G from 4G while ensuring a consistent improvement in user experiences
  • Works on top of 4G architecture, so the carriers do not have to replace the existing infrastructure
  • Improves speed and connectivity by implementing RAN and Core technologies
  • 5G has enhanced MIMO, the dominant technology in 4G systems, to introduce Massive MIMO, further increasing network capacities and improving performance rates. Sub-6 GHz leverages the existing LTE technology but improves upon it by using more antennas at the base stations, allowing for more simultaneous connections, better consistency in dense areas, and a stronger base for 5G to grow on
  • Can support multiple connections to a single device and offers ten times better connection density than 4G in a similar band 
  • Allows the towers to multitask more efficiently, especially with a lot of users connected 

How Sub-6 GHz Helps in 4G-5G Interworking 

It isn’t possible to replace 4G with 5G overnight, and 5G sub-6 GHz spectrum is an ideal middle ground between the existing network backbones in the 4G space and on-the-horizon transformational 5G mmWave frequency bands. 

5G sub-6 leverages Dual Connectivity (EN-DC), a technology that enables the introduction of 5G services and data rates in predominant 4G networks. It allows cellular providers to roll out 5G services without the huge expense of a full-scale 5G core network. So, UEs (User Equipment) supporting EN-DC can simultaneously connect to LTE Master Node and 5G NR secondary Node gNB, allowing interworking between 4G and 5G networks. 

Also, let’s not forget that 5G bands can also work with 4G bands using DSS (Dynamic Spectrum Sharing). DSS is a RAN technique that can quickly expand 5G coverage to all 4G base stations and has been developed to allow 5G users to share access with existing 4G LTE base stations. DSS allows interworking between 4G and 5G signals that broadcast at the same frequency. It works only with 5G sub-6 frequencies because the only frequencies that work for both 4G and 5G are below 3 GHz. 

 5G sub-6 can achieve more with fewer cell sites and use the existing 4G infrastructure and equipment to improve the speed and consistency of mobile broadband. It can integrate 4G-5G to work in tandem, complementing each other, till 5G comes into its own. In short, tweaking current smartphone versions to introduce a 5G sub-6 GHz antenna and radio front-end redesign is relatively simple and more cost-effective vis-a-vis implementing new mmWave antennas. 


An ideal 5G setup deploys high-frequency bands mmWave 5G in densely populated urban settings with sub-6 GHz spectrum providing optimal coverage in suburban and rural areas. However, the sub-6 frequency range is better for the immediate future, as even though it won’t bring monumental speed improvements as seen in 5G mmWave, it is still a significant step up over 4G. 5G sub-6 is the gateway to the higher speeds and efficiencies that will come with mmWave and a fast-evolving 5G ecosystem.   


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