Abstract
The low earth orbit (LEO) satellite network is undergoing rapid development
with the maturing of satellite communications and rocket launch technologies,
and the demand for a global coverage network. However, current satellite
communication networks are constrained by limited transmitting signal power,
resulting in the use of large-size and energy-consuming ground terminals to
provide additional gain. This paper proposes a novel technology called
distributed beamforming to address such challenges and support direct
communications from LEO satellites to smartphones. The proposed distributed
beamforming technique is based on the superposition of electromagnetic (EM)
waves and aims to enhance the received signal strength. Furthermore, we utilize
EM wave superposition to increase the link budget and provide the coverage
pattern formed by the distributed antenna array, which will be affected by the
array structure and the transmitter parameters. In addition, the impact of
Doppler frequency shift and time misalignment on the performance of distributed
beamforming is investigated. Numerical results show that the enhancement of the
received power depends on the angle formed by those radiated beams and can be
up to the square of the number of beams; namely, a maximum enhancement of 6 dB
could be obtained by using two satellites and a maximum of 12 dB increase
through four satellites, which provide a clear guideline for the design of
distributed beamforming for future satellite communications.