Energy and Latency of Beamforming Architectures for Initial Access in mmWave Wireless Networks

Abstract

Future millimeter-wave systems, 5G cellular or WiFi, must rely on highly directional links to overcome severe pathloss in these frequency bands. Establishing such links requires the mutual discovery of the transmitter and the receiver, potentially leading to a large latency and high energy consumption. In this work, we show that both the discovery latency and energy consumption can be significantly reduced using fully digital front-ends. In fact, we establish that by reducing the resolution of the fully digital front-ends we can achieve lower energy consumption compared to both analog and high-resolution digital beamforming. Since beamforming through analog front-ends allows sampling in only one direction at a time, the mobile device is “on” for a longer time compared to a digital beamformer, which can get spatial samples from all directions in one shot. We show that the energy consumed by the analog front-end can be four to six times more than that of the digital front-ends, depending on the size of the employed antenna arrays. We recognize, however, that using fully digital beamforming post beam discovery, i.e., for data transmission, is not viable from a power consumption standpoint. To address this issue, we propose the use of digital beamformers with low-resolution analog to digital converters (4 bits). This reduction in resolution brings the power consumption to the same level as analog beamforming for data transmissions while benefiting from the spatial multiplexing capabilities of fully digital beamforming, thus reducing initial discovery latency and improving energy efficiency.

The Impact of Multi-Connectivity and Handover Constraints on Millimeter Wave and Terahertz Cellular Networks

“…In mmWave cellular networks we assume a UE coverage range of 100 m [32], whereas in the THz cellular network we assume a UE coverage range of 23 m and 56 m [42], due to the significantly higher path loss at THz frequencies. Furthermore, as a larger number of antenna elements at the UE and BS are required for efficient beamforming to overcome the path loss at the THz systems, the BS discovery time in the THz systems can be significantly higher as compared to mmWave systems [21], [22]. While the BS discovery time can be reduced using digital beamforming, it requires a large number of independent RF chains making it impractical for THz systems [49].…”

“…To overcome such high path loss, a highly directive antenna pattern must be used, which however results in frequent misalignment of beams due to small scale mobility (UEs) [20]. High directivity is achieved by narrow beam-vectors steered by large number of antenna elements, which requires a lengthy period to achieve beam alignment [21], [22]. As a result, the cell search time, or equivalently the Base Station (BS) discovery time, can be significantly higher for THz systems as compared to mmWave systems.…”

Deep Learning on Multimodal Sensor Data at the Wireless Edge for Vehicular Network

“…The SS transmitted in a certain beam configuration is referred as the SS block, with multiple SS blocks from different beam configurations grouped into one SS burst. The NR standard defines that the SS burst duration (T ssb ) is fixed to 5 ms, which is transmitted with a periodicity (T p ) of 20 ms [46]. In the mmWave band, a maximum of 32 SS blocks fit within a SS burst, which allows for 32 different beam pairs to be explored within one SS burst.…”

Leveraging Waveform Structure to Develop a Power Scalable AoA Estimation

“…An AoA estimation using an analog/hybrid architecture requires a sweep of measurements to cover the angular space [28]- [31]. In [42], the authors claimed that the beam sweep in an analog architecture increases power consumption compared to a digital architecture. Digital solutions have higher estimation performance and low latency.…”

“…Using the result in (42), the sub-Nyquist signal model in (36), and the decomposition of the D decimated pilot matrix derived in (20), this step yields…”