This work presents a practical implementation that integrates three emerging wireless technologies: millimeter-wave (mmWave) communications, non-orthogonal multiple access (NOMA), and intelligent reflective surfaces (IRS). The goal is to provide multi-user mmWave indoor coverage in an indoor setting. Coverage in the mmWave band, often affected by blind spots, is extended by the ad-hoc design and deployment of a fully passive IRS that requires no power supply. Contrary to the use of a reconfigurable intelligent surface (RIS), this solution lacks the dynamic reconfigurability of the relay but offers a low-cost, easy-to-deploy alternative with zero power consumption. The integration with power-domain NOMA provides increased spectral efficiency by multiplexing two users in the same frequency, time and code slot. To the best of our knowledge, this is the first mmWave NOMA implementation and the first prototype that includes both NOMA and IRS. The radio frequency (RF) design ensures a bandwidth of 400 MHz centered at 24.45 GHz, with the IRS covering an angular synthesized margin of 10 degrees when illuminated by a half-power beamwidth of less than 3 degrees. The communication link is evaluated through over-the-air (OTA) measurements of channel power, error vector magnitude (EVM) and symbol error rate (SER), considering different user positions and superposition coding strategies. The system achieves a spectral efficiency of up to 4.62 bps/Hz while serving two users per frequency subchannel with a SER below 10-3.

This paper addresses the problem of designing asymptotically optimal improper constellations with a given circularity coefficient (correlation coefficient between the constellation and its complex conjugate). The designed constellations are optimal in the sense that, at high signal-to-noise-ratio (SNR) and for a large number of symbols, yield the lowest probability of error under an average power constraint for additive white Gaussian noise channels. As the number of symbols grows, the optimal constellation is the intersection of the hexagonal lattice with an ellipse whose eccentricity determines the circularity coefficient. Based on this asymptotic result, we propose an algorithm to design finite improper constellations. The proposed constellations provide significant SNR gains with respect to previous improper designs, which were generated through a widely linear transformation of a standard M-ary quadrature amplitude modulation constellation. As an application example, we study the use of these improper constellations by a secondary user in an underlay cognitive radio network.