Frequency-Selective Near-Field Focusing with True-Time-Delay Beamforming, BWAC Core Project
As wireless networks evolve to operate at higher frequencies and with larger antenna arrays, communication in wideband near-field scenarios is becoming more prevalent. True-time-delay (TTD) precoding is an effective approach for analog beamforming in wideband settings. This project investigates the use of a joint TTD and phase-shifter-based architecture for multi-user communication in the near-field. We will design a method for optimizing delays and phases to maximize the multi-user sum spectral efficiency and enable near-field spatial multiplexing. Our proposed method will be compared against existing TTD and phase-shifter-based approaches and our analysis will reveal how relative user position affects TTD beamforming performance.
Sponsor
Broadband Wireless Access and Applications Center (BWAC) - Research Site at NCSU
The grant—running from July 1, 2022 to June 30, 2023—is for a total of $30,000.
Principle Investigators
Robert Wendell Heath Jr
More Details
Large antenna array sizes and higher operating frequencies are pushing modern wireless networks towards communicating under wideband near-field (WNF) conditions. The near-field region is typically associated with distances physically close to the antennas. In reality, the near-field boundary expands with both the array dimensions and the carrier frequency, and this distance can be comparable to the cell size for millimeter-wave (mmWave) and sub-THz communication. For example, the near-field transition of a mmWave array of size 10 – 100 cm can extend to approximately 100 m from the array. Bandwidths as systems go beyond 5G are also expected to grow to the order of GHz to provide high data rates to multiple users. These developments signal that a significant portion of wireless communication could fall under WNF scenarios in the near future.
True-time-delay (TTD) precoding is an approach for analog beamforming in wideband settings. Massive arrays generally use analog or hybrid architectures to maintain reasonable power consumption levels by reducing the number of required radio-frequency chains and data converters. The frequency-flat nature of conventional phase-shifter-based architectures complicates precoder design over large bandwidths. In contrast, TTD units apply a time delay to the signal. The resulting frequency-domain phase-shift is dependent on both the delay and the subcarrier frequency, which enables frequency-selective beamforming. In wireless, TTD has been used to mitigate beam squint and to generate frequency-selective beams over varying spatial directions. While TTD is not a new technology, recent improvements in the power consumption, footprint, and delay resolution of TTD units have paved the way for its use in modern wireless devices.
In this project, we propose the use of a joint TTD and phase-shifter architecture for multi-user communication in the near-field. TTD has been shown to be effective at allocating different frequencies to different spatial directions. Near-field beamforming, however, must focus energy into a small spatial region rather than just a direction. We will first investigate how the near-field beamforming pattern varies across a large bandwidth when using a joint TTD and phase-shifter architecture. We will then design a method for optimizing the delays and phases to maximize the multi-user sum spectral efficiency and enable near-field spatial multiplexing. Our proposed method will be compared against existing phase-shifter- and TTD-based approaches. We further expect that our analysis will reveal how the relative position between users affects the performance of near-field TTD multi-user beamforming.