Insight: Microwave and Millimeter Wave Spectrum for 5G

Posted by Mae Kowalke on Thursday, April 16, 2015 with No comments

Among stakeholders working to define 5G and develop appropriate standards, there is growing consensus that the next generation of mobile communications will require use of both microwave and millimeter wave spectrum, in addition to sub-3GHz radio frequency (RF) already in use, to address bandwidth demands. 

But, leaving aside the regulatory aspects of RF management, there are some significant technological and economical challenges with using this short wavelength, high frequency spectrum for mobile networks. Primarily, the issue has to do with transmission range, although the amount of power needed to send signal is also a problem.

RF microwaves between 3 GHz and 30 GHz (super high frequency or SHF) require line of sight between transmitter and receiver, and are limited in terrestrial applications to about 40 miles. Microwaves also typically do not penetrate building walls well enough for useful reception.

Extremely high frequency (EHF) RF electromagnetic waves between 30 GHz and 300 GHz (the “millimeter wave” section of spectrum) travel even shorter useful distances: transmission is traditionally understood to be limited to about one kilometer (about 6/10th of a mile). Of course, these waves are more focused and concentrated, but that capacity comes at the cost of distance.

The good news for millimeter frequency, at least, is that at the higher end of the band, signal loss may not be as much of an issue as it first appears. Modern recent research seems to indicate that attenuation problems fall away when you go up to 28, 38, or 70GHz. These radio channels appear to behave similarly to today's cellular and Wi-Fi frequencies. 

Nonetheless, using microwave and millimeter wave spectrum would mean investment in additional transmitters and receivers (requiring more power) to concentrate signal and extend its range. More hops from Point A to Point B also inevitable introduces delay, which could conflict with mandates to have 5G deliver sub-1ms latency. Is the investment worth it for network operators? Time will tell. 
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