Using optical signal processing to reduce electronic hardware costs for wideband beamforming with RF antenna arrays

We consider optical processing of wideband RF signals for beamforming with antenna arrays. We focus on the applications with the number of antenna elements L much greater than the number of users K, e.g. multibeam satellites. For wideband signals, beamforming requires frequency selective processing that is expensive if electronic filters are used. We investigate the use of optical signal processing to reduce the number of electronic filters from L in the base case with one filter per antenna element. We first show that wideband nulling of K -1 interfering users can be done by performing conventional beamforming in optics followed by K electronic filters. We then focus on digital transmission with K users and show that, instead of K independent symbol detections after interference nulling, joint detection allows us to perform conventional beamforming in optics followed by K electronic matched filters. The key observation is that the number of electronic filters depends on the number of users K and not on the number of antenna elements L.

I. Introduction

The use of antenna arrays instead of a single antenna provides benefits in several applications including diversity against fading in cellular phone systems, interference rejection in radar systems, and frequency reuse in multibeam satellites. Recently, there is strong interest in wideband applications such as ultra-wideband (UWB), spread sprectrum, and high data rate satellite communication systems. Most existing array processing techniques rely on the narrowband assumption. While it is possible to split wideband signals into several narrowband components and use narrowband signal processing. the cost for doing so is expensive.