By Vishal Donthireddy, VP Engineering and Sangram Tidke, Director of Software Engineering
The joy of being a trailblazer is being the first to anticipate, ascertain, and experience problems and challenges. We at Inseego chose to be the trailblazers for new wireless technologies. As such, we bring the fruits of our hard work to our customers so that they experience the joy and benefits without the hardships of using an untested technology. 5G has proven itself to be a treasure trove of challenges, and along with that comes a fabulous set of rewards once those challenges are solved. The more we dig in, the more we realize how extraordinary those rewards are. And we are only at the beginning of this venture.
First, the millimeter wave spectrum is the band of spectrum between 30 GHz and 300 GHz. The challenges of 5G mmWave can be divided into two parts. The first one stems from it being a new air link technology. The second one is related to tackling a new spectrum band that hasn’t been a popular option for cellular communications so far. Although the former challenge is formidable, it is standard to face obstacles whenever a new technology is introduced. We would call this a “known challenge” and usually there is a methodical way of addressing it, including understanding the specification, deciding what features to support in what phases, developing hardware and software for those features, working with infrastructure vendors for full interoperability, and so on. The latter, however, is a tough nut to crack. There are reasons, why mmWave has not previously been used for cellular technology. But thanks to modern technology such as massive MIMO, beamforming and beam tracking, as well as an increasing market for large bandwidths, network densification, and others, we’re finding ways around those limitations.
The major issue with mmWave is short coverage distance. One way to overcome that is by employing many more antennas. The antennas are very tiny, so you create an array with eight or more such antennas. You might need several of these arrays in a device to support beamforming in all 360 degrees. Then the challenge changes. It becomes a question of how many antennas can be placed in the portable device form factor. And of course, more antennas mean higher cost. So, you must hit the right balance. You could put MIMO on top of the antennas to increase performance. Because of the number of antennas involved (up to 64 at the base station), this is often referred to as Massive MIMO.
The mmWave also has limited penetration through hard and opaque objects. Many might think that means no indoor coverage. It’s beyond that. The phones themselves are made up of hard, opaque material such as plastic and metal, both of which are detrimental to mmWaves. So, even before hitting the building wall or any other obstruction, the signal has to penetrate though the body of the device. In such a case, the antenna design and placement and the type of material as well as the device enclosure thickness must be considered very carefully.
One option to improve coverage characteristics is to increase the device’s transmitter power. But there are stringent FCC regulations on how high you can go with this. Going higher on power might also create other challenges. One is SAR, or Specific Absorption Ratio. This is the measure of how much of the RF energy is being absorbed by the human body. The FCC has extremely stringent mandatory limits for all the commercial devices, which vary based on criteria such as type of device and use case. So, the device transmit power can only be as high as the SAR limits allow.
The second challenge is heat. We are still in the process of characterizing the heat generated by mmWaves and associated circuitry, but early tests show it is higher than today’s traditional bands. This means that the device form factor, its size, surface area, and its whole industrial design is critical for managing the heat dissipation. We are working on developing the right industrial design and sophisticated algorithms to mitigate and manage heat dissipation.
From the network perspective, mmWave has other issues as well. The cell site range with mmWave is short, with limited indoor penetration. Due to initial deployments of 5G being only in urban cores, 5G mmWave devices have to rely of either sub-6GHz bands, or more likely, on 4G/LTE for seamless ubiquitous coverage. That means 5G devices have to support seamless handoff with 4G from day one. The only positive thing about this situation is that since most of the initial 5G mmWave deployments will be in Non-Stand Alone (NSA) mode, they rely on 4G for the core network and call management.
Well, that is a long list of challenges! If indeed the challenges of 5G mmWave are so tough, why are we even trying to solve them? Well, the rewards of solving the mmWave challenges are extraordinary. The mmWave bands potentially have 10s of GHz of available spectrum, compared to 100 to 200 MHz of lower bands. With that kind of availability, mmWaves are the future to satisfy the insatiable demand for data.
For some time now, Inseego has been working on our own as well as with our able partners to solve all of these issues. The good news is that we are making great progress and are very confident in the direction we are headed. Stay tuned to hear more about our solutions and how Inseego is leading the industry in not only paving the path but clearing the road for 5G commercialization.