You have to realize that spectrum is mostly licensed for specific applications including radar, television broadcasts, and satellite communications. Other unlicensed millimeter-wave frequencies are available (for example 92-95 GHz in the United States). However, the international availability as well as the bandwidth magnitude available for 60 GHz carrier frequencies is quite unique when we consider all the “power players” together.

So to answer your question, if the same amount of bandwidth was available at 30 GHz internationally (compared to 60 GHz), it would almost certainly be receiving more attention since it would observe less path loss and atmospheric absorption.

It would be interesting to compare the proof employed here with that in the paper by Mohseni and Cioffi.

A few comments on the nuts and bolts of this writeup:
1) Throughout the writeup we see that the governing system equation has user $n$ receiving $y_n = H_nx_n+v_n$. It seems, though, that the transmitter would send $x$ to user $n$, not just $x_n$ (which is what user $n$ wants to decode).
2) There seems to be a mistake in the achieved rate for user 2 in the case where DPC encoding entails encoding user 2’s signal first. The determinant in the denominator should have $S_1$, not $S_2$ (since user 1’s signal would interfere with user 2’s signal).
3) The definition of the enhanced DAMIMO-BC is somewhat confusing. It would seem more straightforward to have the constraint $cov(\hat{v}_i)\leq cov(v_i^{*})$ for $i = 1,2$. Currently, $cov(\hat{v}_1)$ is compared with $cov(v_2^{*})$, but how is this an improvement over the DAMIMO-BC? I wonder if the accompanying sum constraint on the covariances is the key to understanding this.

I think a good system engineer should be able to write a good paper and file a good patent. Usually the leader of standard team in a company knows both very well. But as a grad student, to do both is really hard.. therefore it’s cool if there’s a patent lawyer in WNCG to help us filing our ideas as patents.