Why the Mobile Industry is asking for Big, Contiguous Spectrum Blocks 

While the mobile industry has always requested more spectrum from the FCC, the recent ask has been for big, clean, contiguous blocks, sometimes as large as 200 or even 400 MHz.  But given that 4G LTE was usually deployed with 10 MHz or 20 MHz channels, why the need for bigger chunks of spectrum? 

The answer, as you may imagine, is somewhat technical. Wireless network technology has advanced significantly since LTE was designed and deployed. The use cases for 5G, 5G advanced and soon 6G are very different from what was supported by 3G or imagined for 4G LTE. Loading email, sending a few photos and loading a text-based web page all take far less bandwidth than streaming HD video, uploading images and video or accessing web pages with embedded video and images. Today’s consumer expects access to all types of multimedia, instantly, on a variety of devices no matter where they are located. Many mobile apps and services are also more latency sensitive, requiring faster network responses. 

The simple fact is that to get more bandwidth, you need more spectrum. A 20 MHz channel delivered more bandwidth to the user than a 10 MHz channel. Similarly, a 100 MHz channel supports far more bandwidth than a 20 MHz channel. 

However, gluing five separate 20 MHz channels together will result in less bandwidth than one big, clean block of a 100 MHz channel. The bigger the channel size available, the greater the overall benefit.  In effect, you get more ‘free’ bandwidth from bigger channels than several smaller channels added up. 

But why does this happen?   

The answer is simple: overhead. Just like a business carries financial overhead (the cost of space, lighting, insurance, etc.) so a wireless network has overhead. In the wireless case, overhead includes the control signals, reference signals, synchronization and guard bands (to minimize interference) – all of this overhead is needed to control and manage the user traffic in the channel.   

Think of the user traffic as the vehicles rolling down the highway and the overhead as all of the associated signage, lines, lighting, barriers and medians – a highway may be 100 feet wide but you can only use 80 feet for the actual traffic. A six lane highway has two medians – but a two lane highway also has two medians that take the same space.  Therefore a six lane highway is more efficient. 

The mobile industry has used carrier aggregation (CA) for some time to effectively add separate channels together to create a bigger bandwidth pipe. But using carrier aggregation adds more overhead – not only does each channel have to be managed, but the overall aggregation must be coordinated hence adding overhead. CA also consumes more power on the device, reducing battery life. 

There is also an impact in the RAN (radio access network) hardware itself. Each channel must have its own filtering, power amplification and baseband processing. Five separate channels will require five times the hardware of one large channel.  The bigger the channel, the more efficient the radios and antennas will be, resulting in potentially lower hardware and operating costs. 

Finally, there is the impact on MIMO (multiple-input multiple-output) and especially massive MIMO – this is a large antenna array that can form narrow beams to focus the signal in a particular location. This allows spectrum to be reused very efficiently. But massive MIMO works best when it has a wide, continuous slice of spectrum to operate in – fragmented channels force radios to juggle multiple carriers, reducing beamforming efficiency and increasing processing complexity. With one big block of spectrum, the radio can focus energy more precisely, improve cell-edge performance, and deliver higher average speeds. 

The newer wireless modulation schemes – which encode information onto carrier signals for communication – are being designed to take advantage of large channel blocks. This is the equivalent to having a wider traffic lane on a highway – manufacturers will build bigger vehicles to fill the available space.  The result is that the new vehicles will not work well on old, narrow highways.  The same applies to wireless technologies – the newer modulation schemes will not work well on smaller channel sizes. 

All of this is to say that the wireless industry’s request for larger blocks of contiguous spectrum is not just nice-to-have – the request is based on the technical capabilities of the networks and the need to provide more and more bandwidth to media-hungry consumers and businesses. Big, contiguous blocks of spectrum are therefore what make the next generation of wireless possible.