mmWave stands for millimeter wave, referring to radio waves that are about a millimeter long, or in the range of 30–300GHz. (Higher frequency radio waves have shorter wavelength, so you can identify a radio signal’s frequency if you know its wavelength and vice-versa.) 5G enables the efficient use of radio waves in this range to increase speeds.
Here’s some additional detail. “5G” is ushered in by a new standard that defines a new format for the radio signals between a cell phone and a tower. That new standard is called, creatively, “New Radio” or “NR” and it will in the long run replace LTE (which stands for Long Term Evolution). NR has several advantages over LTE.
NR is more efficient than LTE so right out of the gate you get a 10% or 15% boost in speed. It supports larger numbers of devices connected to a tower and therefore helps enable the Internet of Things (IoT). Some of the delay (latency) you experience on a cellphone is your phone waiting for its turn to transmit and NR helps reduce those delays. It also supports some sophisticated radio transmission technologies that help extend range and battery life.
If it was just that, though, would that be worth another “G”? I mean, those are great, but what we really want is more speed and I think most people want at least 2x the speed, if not 10x the speed for another “G”. NR enables that by being usable in the mmWave range of frequencies.
Unfortunately, getting that 10x boost in speed will require more than just the efficiency bump that NR will give us. We’ll need more spectrum - more frequencies, if you will. For the last couple of decades the FCC in the US and its equivalents in other countries have been handing out and auctioning off frequencies for use by cell phone companies in blocks of 10MHz or 20MHz or so. To get that 10x bump, though, we need blocks of 100Mhz or 200MHz. Most carriers, though, don’t have that kind of spectrum in the frequency range that has traditionally been used for cell phone service, which is in the range of 0.7GHz to 6GHz and often referred to as “sub 6.”
There are some big blocks of frequencies available in the mmWave range, though. So, NR is designed to operate at mmWave frequencies as well as sub 6 frequencies. Regulatory bodies have begun auctioning off mmWave blocks of frequencies.
Here’s the bad part about mmWave, though. Due to physics, radio frequencies in that range don’t pass through building materials very well, so the signals don’t penetrate houses or buildings very well. Even tree leaves tend to absorb them and there are a lot of trees around. To get good coverage, therefore, carriers utilizing mmWave spectrum will have to build towers more closely together. It’s not clear if, when or where carriers will invest in doing that. Some carriers might only build out mmWave facilities in densely-populated areas. Some carriers might even simply put up NR in some existing 10 or 20MHz bands and brag that they have 5G.
Getting the full benefits of 5G will not be a slam dunk. Some carriers, such as a combined Sprint/T-mobile in the US, might have enough sub 6 spectrum to provide a pretty good 5G service. Others will have some tough decisions to make.