Beamformed Self-Interference Measurements at 28 GHz: Spatial Insights and Angular Spread

Abstract

We present measurements and analysis of self-interference in multi-panel millimeter wave (mmWave) full-duplex communication systems at 28 GHz. In an anechoic chamber, we measure the self-interference power between the input of a transmitting phased array and the output of a colocated receiving phased array, each of which is electronically steered across a number of directions in azimuth and elevation. These self-interference power measurements shed light on the potential for a full-duplex communication system to successfully receive a desired signal while transmitting in-band. Our nearly 6.5 million measurements illustrate that more self-interference tends to be coupled when the transmitting and receiving phased arrays steer their beams toward one another but that slight shifts in steering direction (on the order of one degree) can lead to significant fluctuations in self-interference power. We analyze these measurements to characterize the spatial variability of self-interference to better quantify and statistically model this sensitivity. Our analyses and statistical results can be useful references when developing and evaluating mmWave full-duplex systems and motivate a variety of future topics including beam selection, beamforming codebook design, and self-interference channel modeling. I. INTRODUCTIONResearch on full-duplex millimeter wave (mmWave) systems has been motivated by the potential for dense antenna arrays to strategically steer transmit and receive beams in a way

LoneSTAR: Analog Beamforming Codebooks for Full-Duplex Millimeter Wave Systems

“…In contrast, codebooks created for conventional mmWave systems can deliver high beamforming gain but are not necessarily robust to self-interference if used in full-duplex systems [10]. In fact, this was confirmed in our recent measurement campaign [9] and in our recent work [23], both of which showed that conventional beams typically couple prohibitively high amounts of self-interference if used in a practical full-duplex mmWave system.…”

“…Since transmission and reception happen simultaneously and in-band, a self-interference channel H ∈ C Nr×Nt manifests between the transmit and receive arrays of the full-duplex BS. Currently, there is not a reliable, measurement-backed model for the self-interference channel H [9], [10]. As such, the design herein is not based on any assumption of H, and we evaluate our design using multiple channel models in Section VII.…”

“…10a, we examine the impacts of imperfect self-interference channel knowledge, 2 > −∞ dB. To do so, we model H as in (35), meaning the true channel H is Gaussian distributed about H according to (9). We chose to model it in this fashion, rather than use H as the spherical-wave model in (35), for two reasons.…”

“…In[9], we observed that 28 GHz self-interference in an anechoic chamber was nearly static on the order of minutes, at least.…”

“…These transmit and receive beams couple over the MIMO channel that manifests between the arrays, plaguing a desired receive signal with self-interference. In a recent measurement campaign [9], we observed that the degree of this self-interference is typically prohibitively high for full-duplex operation in practical mmWave systems. This, along with the fact that modern mmWave systems rely on codebook-based beam alignment, motivates the need for beamforming codebooks designed specifically for full-duplex mmWave systems-as opposed to using conventional codebooks made for half-duplex systems [10].…”