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.

Real-time Industrial applications in the scope of Industry 4.0. present significant challenges from the communication perspective: low latency, ultra-reliability, and determinism. Given that wireless networks provide a significant cost reduction, lower deployment time, and free movement of the wireless nodes, wireless solutions have attracted the industry attention. However, industrial networks are mostly built by wired means because state-of-the-art wireless networks cannot cope with the industrial applications requirements. In this article, we present the hardware implementation of wireless SHARP (w-SHARP), a promising wireless technology for real-time industrial applications. w-SHARP follows the principles of time-sensitive networking and provides time synchronization, time-aware scheduling with bounded latency and high reliability. The implementation has been carried out on a field-programmable gate array-based software-defined radio platform. We demonstrate, through a hardware testbed, that w-SHARP is able to provide ultra-low control cycles, low latency, and high reliability. This implementation may open new perspectives in the implementation of high-performance industrial wireless networks, as both PHY and MAC layers are now subject to be optimized for specific industrial applications.

Wireless communications have attracted great interest from the industry due to its lower cost and the possibility of enabling new use cases. The new use cases are commonly related to mobile robotics, such as Unmanned Aerial Vehicles. The design of wireless systems for these use cases requires deep knowledge of the channel behavior. However, the weight and size of full channel sounders exceed the payload of most mobile robots. In addition, full channel sounders usually require wired time synchronization. Hence, channel measurements in these scenarios are constrained to use limited channel sounders, which can only measure some specific parameters (frame error rate, channel attenuation, etc.). In this paper, we present the design and implementation of a portable 802.11-based channel sounder combined with a sub-nanosecond wireless time synchronization algorithm. Thanks to the wireless time synchronization, the channel sounder can be used to periodically take complex baseband Channel Impulse Response samples synchronized to absolute time. From these samples, relevant channel parameters can be extracted, including the Power Delay Profile, Doppler spectrum, and channel delay. The verification of the channel sounder through a wireless channel emulator confirms its feasibility for mobile robotics applications.

The time-sensitive network paradigm envisions the integration of operation technology and information technology in the same network. One of the requirements for building time-sensitive networks is sharing a global time along the network. This requirement is especially critical in wireless systems, where there are few robust methods to perform accurate time transfer. In this article, the problem of time transfer over realistic wireless channels is studied, and a time distribution scheme is proposed. The time distribution scheme has three components: Precision time protocol, a novel timestamping method (enhanced timestamps) and an algorithm to implement the enhanced timestamps. The performance of the proposed scheme has been evaluated in MATLAB using the IEEE 802.11n Standard under several standard wireless local area network channel models. The results show that the system can reach subnanosecond time transfer accuracy under non-line-of-sight and time-variant conditions, but its performance greatly depends on the signal-to-noise ratio and on the channel variation rate.

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.