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What is massive MIMO? Let’s start with MIMO, Multiple in Multiple out.
What is MIMO?
Well, in wireless technology MIMO means that you have several antennas and radios all on one BTS. So, you have one BTS with a
sector that has multiple antennas for transmit and receive. So, the alpha sector could have four transmit and four receive all in one panel. With only a few transmit and receive, the radio head could be behind the antenna. MIMO is already deployed across the US by almost all the carriers helping LTE reach the speeds it has today. That along with carrier aggregation, improved processing, optimization techniques, and a myriad of additional features making that smartphone look faster than your laptop when running an app.
What is massive MIMO?
This is where we have more active elements in the antenna; this could be 64T64R or 128T128R or even higher. The 64T is 64 transmit elements, and 64R is 64 receive elements. Just imagine the feature we get from MIMO, listed above, are suddenly on steroids 
and making the current features even better! WOW!
This changes many things on the tower. Since running 64 coax jumpers is not practical, the OEMs are inclined to create an active antenna. That would be an antenna with the radio head inside of the antenna so that they could have a connection between each radio head to each element. It just makes sense. No more coax and fiber direct to the antenna. No more radio head and power to the antenna.
What changes will happen in the eNodeB? The BBU will need to handle more processing than ever! They will also need to improve the BBU, the baseband unit.
Why do we need massive MIMO?
Several reasons come to mind, listed below, feel free to add more.
- High bandwidth needed for throughput
- Spectral efficiency for improved spectrum usage
- Lower latency
- Improved device density connectivity
- It is a step towards 5G
What does the BBU need to do to support massive MIMO?
It needs to process so much more data. Now, instead of controlling one or 8 radio heads, it will need to process and distribute the power 
across 64 or more individual radio elements. It needs to pass more data.
The BBU needs to be significantly improved. What will it do?
- Process more data
- More bandwidth
- Control more radio heads
- Talk to more UE devices
- Handle carrier aggregation
- Process more services simultaneously
- Perform self-optimizing network, SON, services
- Capture data
- Handle neighbor list to avoid interference
What about the backhaul?
It needs to be upgraded to handle more data since we are now going to increase the broadband throughput. 1Gbps backhaul may not cut it because it may need to be much more. What does this mean?
- Better routers at the sites
- More strands of fiber for each site
- Aggregation of the fiber carriers so that it looks like a massive pipe of over 10Gbps
- Improved network slicing functions for the router to perform more functions than before
What about the fronthaul?
The fronthaul is the fiber, (or wireless), the line between the BBU and the radio heads which now should be in the active antenna.
This may require more strands per sector so that the data can be sent to each sector. Look at it this way, instead of dealing with one antenna with 4 to 8 elements; now you are dealing with one active antenna that could be simultaneously sending data to more than 64 elements in one concentrated antenna system. That is a lot of data! In theory, it could be more than 1Gbps per sector! WOW!
Fronthaul will need to be:
- Improved for more bandwidth and data
- Lower latency than before
- Perhaps more strands of fiber
Can CRAN or C-RAN be a massive MIMO system?
The jury is out because of the massive bandwidth and low latency. This is going to be worked out, but it is essential that we know that a Centralized RAN and a Cloud RAN are essential parts of the 5G system. As you all know, massive MIMO is a huge stepping stone for 5G.
What about CRAN and C-RAN?
This is going to be a challenge to get to no BBU at the site, but it can be done. The need for MEC, Mobile Edge Computing is still there because we want low latency. That is right; the routing needs to be as short as possible. Also, the RF equipment is doing an excellent job of lowering latency. The 5G standards are asking for lower and lower latency, looking for 1ms or less, wow! That is going to be a real challenge if you rely on the cloud to do the BBU processing or if you have the BBU hotel somewhere else. Why? Even though it is light running through the fiber, it takes time to travel across town, the state, or anywhere. Hence, that is how MEC may be able to save the day! Direct routing would be a key factor instead of running everything back to the core.
How does it affect the UE device?
The UE probably won’t have more than four antennas in it, if that. They may have 2 to 4 receive antennas, and two transmit. The thing is though, with massive MIMO and the way it should work, an element or 2 can focus on one US device freeing up the other to talk individually to other devices. This will improve throughput and lowers latency.
The bottom line is that it will help the UE in 2 ways. The UE will get more bandwidth, especially as they add more antennas internally, they already have two receive in most devices which allow for better downloads. The massive MIMO will be able to talk directly to an individual device and lower latency. This will help the response time of the device, making the device seem more responsive and once again, quicker! Now it is up to the device makers to speed up the internal processing speed and improve the memory in each device so that we can enjoy the new low latency services.
What changes at the site?
This is going to require new equipment at the site, no matter how you look at it. The equipment that is there now will need to be upgraded or replaced. Most likely, some of it will need to be replaced. It would make sense to have 64 or more radio heads so that you would replace the existing antennas and radio heads with an active antenna. You would remove all coax and run fiber to the antenna. You would need a BBU that can kick ass with processing power and bandwidth. You need to improve your backhaul, which means a better router CRAN quality equipment at the site. You need to improve your fronthaul between the BBU and the active antenna.
What does it mean for business?
Here’s the deal, the equipment we have today will not cut it. Replacing the existing BBU and radio heads and antennas with the new system. It must happen. So, this means a lot more work for the deployment crews. As always, it will all happen at once, causing a strain on the tower workforce.
- Tower crews – busy replacing equipment on tower and the ground
- Engineering teams – new RF engineering and optimization along with drive tests to complete the rollout of the new system. Let’s not forget the potential for self-interference that’s going to happen. There is a learning curve.
- Backhaul:
- The fiber needs to be upgraded, new fiber or additional fiber.
- Wireless backhaul will need to be replaced, added, or upgraded.
- The router needs to be upgraded or replaced.
- Backhaul will need to be upgraded, so the service provider had a real opportunity to make some additional money on installation and possibly monthly reoccurring for fiber delivery services.
- The OEMs will have a significant push for getting the new gear out to carriers, mostly in urban areas, so it will not be the entire system that gets upgraded, but the specific markets where loading is needed or where 5G is a priority.
- The carriers need to invest in this, apparently, the stepping stone to real 5G bandwidth and performance. Enough said.
- The tower companies may not get any more money. The way most leases are written leaves room for these upgrades. Of
course, the tower companies will find ways to make incremental dollars like site access, new structural for less weight, and so on. What they will not get is the additional rent money that is their bread and butter. However, we will Those larger tower owners are savvy. - What about small cells? I bring this up because, in theory, the way that the massive MIMO improves densification it may reduce the need for a small cell that usually would fall within the coverage area of the tower for loading purposes. This hurts me to say, but small cells will be a fill site outdoors. Indoors we will still need small cells for coverage and offloading. The outside in coverage does not cover as well with new environmentally friendly windows. We need the indoor small cells more than ever.
- Looking at the additional parts associated with the deployments we need to see that coax is going to be reduced dramatically. What’s the need when you run fiber everywhere. Let’s look at the list and make this easy.
- Coax, hardline, jumpers, and associated connectors and ground kits will no longer be needed for this type of deployment. Get ready to see a lot more of the old stuff on the scrap metal places.
- Fiber will increase. I am curious if the carriers will continue buying the hybrid cables for fronthaul or if they will just buy armored fiber lines to run to the radio heads up the tower or in the rooftops. They still need power to the antenna, which they initially needed for the radio heads. Remember that the connectors may change, so we will have to think about the distribution of jumper.
- Tower mounts may change. All the weight from the radio heads will be shifted to the actual antenna mount. Whether it is a simple mast of the whole mount. The radio head weight will be gone from behind the antenna, and now it is going to be in the antenna. Weight distribution has changed from being evenly distributed to being concentrated on the antenna. Site engineering should be fun.
- Possibly power upgrades will be needed which means potentially new rectifiers and battery upgrades and then utility upgrades. Remember that we were trying to get more power efficiency at the sites, this may be a set back for that effort. If you need a new rectifier, then maybe new or additional batteries and associated cables and hardware. Then the power from the utility to power said rectifiers.
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