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Power consumption is one of the significant challenges in millimeter wave (mmWave) systems due to the need to support wide bandwidths and large numbers of antennas. This paper explores energy efficient implementations of the baseband trans-receiver components for a multi-carrier 3GPP New Radio (NR) system. The analysis considers key components including channel selection filters, digital beamforming and FFT engines for the OFDM processing. A methodology is presented for optimizing bit widths in various components, which is critical in low power designs. Fully digital and analog beamforming architectures are also compared. Preliminary power estimates are provided using a TSMC 28 nm process for a 400 MHz system at 28 GHz similar to 5G systems today and a hypothetical 1.6 GHz system at 140 GHz for potential 6G deployment. 

Spatial linear transforms that process multiple parallel analog signals to simplify downstream signal processing find widespread use in multi-antenna communication systems, machine learning inference, data compression, audio and ultrasound applications, among many others. In the past, a wide range of mixed-signal as well as digital spatial transform circuits have been proposed-it is, however, a longstanding question whether analog or digital transforms are superior in terms of throughput, power, and area. In this paper, we focus on Hadamard transforms and perform a systematic comparison of state-of-the-art analog and digital circuits implementing spatial transforms in the same 65 nm CMOS technology. We analyze the trade-offs between throughput, power, and area, and we identify regimes in which mixed-signal or digital Hadamard transforms are preferable. Our comparison reveals that (i) there is no clear winner and (ii) analog-to-digital conversion is often dominating area and energy efficiency-and not the spatial transform.