Massive MIMO (multiple input, multiple output) is a method of increasing capacity on a spectrum by using multiple antennas to transmit and receive multiple RF signals in parallel. In recent years, and especially so far in 2018, Massive MIMO has become a promising path towards 5G.
The Race to 5G
In the race to 5G, some of the biggest obstacles for designers have been traversing the crowded bandwidths of established networks while still being able to handle the high data rates required by the new 5G standard. Millimeter waves have been the wavelength of choice to provide the increased data rates, but they have their own set of challenges to deal with. Their short wavelength has limited range and requires line of sight, which makes the distribution of 5G signals extremely difficult in terms of both design and logistics.
The concept of ever-shrinking components, familiar perhaps especially because of the mobile devices Sprint aims to connect, also applies to the radio modules. In the image below, you can see an example of the Massive MIMO radio next to the 8T8R (8-branch transmit, 8-branch receive) radio module, first used by Sprint in 2013, that currently operates on the 2.5GHz spectrum:
Sprint's Massive MIMO and 8T8R modules side-by-side. Screenshot courtesy of Sprint.
If that doesn't look like much of a reduction in size, consider that the Massive MIMO unit includes both the radio and the antenna within that comparable space. This push for smaller form factors in radio modules represents an increase in costs. Additionally, these 5G antennas will need to be much closer together than 3G or 4G towers were.
There are a few different methods for 5G that have been successfully tested on a small scale by Verizon and Qualcomm but a commercially viable network still eludes them. Still, the first company that can successfully make a network that allows users to stream 8k video while their cars drive themselves stands to gain a huge market advantage, so the race is on!
Sprint's Massive MIMO Cell Sites
Verizon and Qualcomm have teamed up in the designing a 5G network that uses New Radio (NR) to focus on securing the 28GHz and 39GHz spectrum bands. Verizon's and Sprint's 5G designs are similar in that they focus on utilizing narrow bandwidths and are compatible with Qualcomm's Snapdragon X50 modem.
Sprint's 5G network will feature Massive MIMO cell sites working on the 2.5 GHz spectrum band. Sprint's MIMO cell sites have 64 transmitters and receivers, making a total of 128 antennas per station. In addition to being mounted on existing cell towers in Sprint's network, many new smaller MIMO cell sites will need to be distributed in cities to ensure coverage.
Six Cities by 2019
Sprint hopes to have a smooth transition to 5G without compromising their existing 4G and LTE networks, so they plan to roll out their first 5G networks in Atlanta, Chicago, Dallas, Houston, Los Angeles, and Washington DC, cities they think already have the necessary infrastructure (and lots of tall buildings) to support the thousands of cell sites necessary for a functional 5G network.
Sprint hopes to have 5G networks in the aforementioned cities by April 2019 by upgrading their existing cell sites to have tri-band service using 800 MHz, 1.9 GHz, and 2.5GHz, while adding new MIMO radios to cover the gaps in between. Sprint is already working with Ericsson, Nokia, and Samsung to make sure that new mobile devices are compatible with the network.
One of Sprint's Massive MIMO stations. Each of the small squares is one of the 128 antennas. Screenshot courtesy of YellowFan Studios.
If Sprint can successfully integrate their 5G Massive MIMO network into these cities, they will pull ahead of Verizon and their 5G New Radio network. The race to 5G will only have a winner in the short term since six 5G-capable cities hardly counts as nationwide coverage. Likely, Sprint and Verizon will conquer different areas of their "turf" gradually, making the 5G service providers of consumers dependent on the city they live in. Those designing 5G-capable mobile devices will likely need to be familiar with both to ensure cross-compatibility.
Learn More About the 5G Wireless Standard and Massive MIMO
There is far more to the 5G Wireless Standard and Massive MIMO than I can cover in this article, so I've compiled some more articles below if you'd like to learn more about it!
- Basics of the 5G Wireless Standard
- Massive MIMO and Beamforming: The Signal Processing Behind the 5G Buzzwords