Waveform Optimization for Multiple Beam Communications under Radar Constant Modulus Constraints

Abstract

Satellite communications (SatComs) are anticipated to provide global Internet access. Low Earth orbit (LEO) satellites (SATs) have the advantage of providing higher downlink capacity owing to their smaller link budget compared with medium Earth orbit (MEO) and geostationary Earth orbit (GEO) SATs. In this paper, beam-broadening algorithms for uniform rectangular arrays (URAs) in LEO SatComs were studied. The proposed method is the first of its kind that jointly considers the path loss variation from SAT to user terminal (UT) due to the Earth's curvature to guarantee quality of service (QoS) inspired by the synthesis of isoflux radiation patterns in the literature, constant modulus constraint (CMC) favored for maximizing power amplifier (PA) efficiency, and out-ofbeam radiation suppression to avoid interference. A URA design problem is formulated and decomposed into two uniform linear array (ULA) design subproblems utilizing the idea of Kronecker product beamforming to reduce the computational complexity of designing URA. The non-convex ULA subproblems are solved by a convex iterative algorithm. Simulation results reveal the advantages of the proposed method for suppressing out-of-beam radiation and achieving design criteria. In addition, channel capacity evaluation is carried out and shows that the proposed "broadened-beam" beamformers can offer capacities that are at least four times greater than "narrow-beam" beamformers employing an array steering vector when beam transition time is taken into account. The proposed method holds potential for LEO broadcasting applications such as digital video broadcasting (DVB).Index Terms-Satellite communications (SatComs), low Earth orbit (LEO) satellite, beampattern synthesis, beam-broadening algorithm, isoflux radiation pattern, constant modulus constraint (CMC), Kronecker product beamforming, uniform rectangular array (URA), uniform linear array (ULA), Digital video broadcasting (DVB).