We present single-layer, direct digitally modulated, reconfigurable intelligent surface (RIS) unit-cell (UC) designs at 12GHz. These UCs find application in low-power, gigabits per second (Gbps) ON-OFF Keying (OOK) modulators where each UC of the surface can be individually programmed using Gbps general purpose input-output (GPIO) lines. The key challenge is to realize a large shift in response from a small voltage change (the direct digital drive). We propose that transmission efficiency $\eta_{T}$ should be maximized and modulation depth $m$ should be greater than 20 dB.

This article presents a 39-GHz 800-Mb/s antenna-coupled ON–OFF-key (OOK) receiver with a baseband output capable of driving a 50- $\Omega $ load. The antenna-coupled receiver demonstrates a bit error rate (BER) of $10^{-3}$ over a range of 18 cm while dissipating only 0.71 mW for a record energy efficiency per distance metric of 0.049 pJ/bit/cm. A wireline version of the receiver achieves a record sensitivity level of −36 dBm without preamplification while dissipating only 1.15 mW, resulting in an energy efficiency of 1.44 pJ/bit at a BER of $10^{-3}$ . Including 11.5 dB of RF gain prior to the wireline receiver, 800-Mb/s communication is demonstrated at 3.67 m for a BER of $10^{-5}$ . The low power consumption and long range make this receiver suitable for scaling to hundreds or thousands of elements in massive multi-in–multi-output (MIMO) arrays for next-generation millimeter-wave wireless communications systems.

We provide a mutual information lower bound that can be used to analyze the effect of training in models with unknown parameters. For large-scale systems, we show that this bound can be calculated using the difference between two derivatives of a conditional entropy function. We provide a step-by-step process for computing the bound, and apply the steps to a quantized large-scale multiple-antenna wireless communication system with an unknown channel. Numerical results demonstrate the interplay between quantization and training.

Low-resolution transceivers are being considered for millimeter-wave and higher frequency communications because of their simplicity and low power consumption. However, the non-linearities introduced by low-resolution digital-to-analog converters at the transmitters can cause significant out-of-band emissions since traditional bandwidth-limited pulse-shaping is not generally available. We model the performance of a low-resolution transmitter in terms of its spectral efficiency under out-of-band emission constraints. We show that the spectral efficiency can increase linearly with the symbol rate while satisfying out-of-band constraint. This implies that in order to achieve a given spectral efficiency under the bandwidth constraint, the symbol rate of the transmitter should be larger than a threshold. We derive an upper bound on this threshold.