One of the most read posts on this blog is Six differences between Massive MIMO for sub-6 GHz and mmWave, where we briefly outlined the key differences between how the Massive MIMO technology would be implemented and utilized in different frequency bands. Motivated by the great feedback and interest in this topic, we joined forces with Liesbet Van der Perre and Stefano Buzzi to write a full-length magazine article. It has recently been submitted to IEEE Wireless Communications and a pre-print can be found on ArXiv.org:
Massive MIMO in Sub-6 GHz and mmWave: Physical, Practical, and Use-Case Differences
Several intriguing questions remain unanswered:
Will mmWave mMIMO be implemented with full digital beamforming? Which mMIMO features will be actually used in 5G networks? Will the multiplexing capabilities ever be pushed as high as illustrated in the Central Park example? How will traffic patterns and applications evolve?
So can we pick this as a PhD research…?
Yes, these are important questions for future work, but you might need to fine smaller subtasks to consider in PhD research.