As a promising approach to assist the fifth-generation (5G) communication system, geostationary (GEO) satellite communication technology is expected to be utilized to provide an efficient and reliable coverage for the terrestrial cellular network. Most multi-beam GEO satellites work on the low-inclination GEO orbit. Due to various unexpected factors, e.g., the imperfect satellite orbit, attitude, and antenna deformation, the practical satellite beam pointing on the earth surface will deviate unfortunately from its designed theoretical location. Although the center boresight-to-ground point of the satellite multi-beam antenna can be maintained via the control of attitude bias and track retention, the practical beam pointing center would still experience inevitable deviations, causing unwanted ground coverage drifting in engineering applications. To combat this, in this paper, we first provide a comprehensive calculation approach for the actual beam pointing on the ground of a satellite multi-beam, which is also validated via the theoretical analysis on the measurement from a ground-based calibration station. On this basis, a simple yet effective data-driven model is established to characterize the dynamical deviating trends induced by various unexpected influences. Finally, a novel beam pointing calibration scheme is designed, based on the Kalman filter. By tracking the coupling coefficients between elevation angle and azimuth angle in our simple model, a pre-deformation is added to the designed beam. Our proposed approach for the beam pointing calibration is validated by the numerical simulations. An improvement of 78.26% is achieved in maximum ground-surface pointing deviation distance.INDEX TERMS Geostationary-orbit satellite, multi-beam antenna, beam pointing, equivalent dynamic modeling, Kalman filtering. I. INTRODUCTIONThe emerging fifth generation (5G) communication network is expected to provide an ubiquitous connection with extremely high capacity, reliability and security for the user [1]. Such an urgent requirement will bring enormous pressure for the existing terrestrial wireless communication system. To cope with the above issue, satellite communication is regarded as a key technology in future 5G communication network to ensure large-scale coverage and ultra-high data rate, and thereby establish a seamless satelliteto-terrestrial integrated system to better satisfy future wireless communication demands [2]- [5].The associate editor coordinating the review of this manuscript and approving it for publication was Qilian Liang.
Pilot spoofing attack (PSA) is a kind of active eavesdropping, which launches the identical training sequence to manipulate the channel estimation outcome during the pilot training phase. The newly proposed intelligent reflecting surface (IRS) system is vulnerable to the PSA because it relies on the pilotassisted channel estimation methods to obtain channel statement information (CSI). To combat PSA in IRS-assisted systems, we consider two significant challenges: 1) channel distribution information (CDI) is uncertain, which will make the PSA detection methods based on the statistic feature (SF) invalid; 2) the noise is uncertain when detecting PSA in practical scenarios, which would impair the popular energybased detectors. In this paper, we design a three-step training (TST) scheme. The effective detector could achieve reliable detection performance by examining the transmitter's received signal power levels when PSA occurs. The proposed method does not require the prior knowledge of noise variance and could obtain the CSI of both legitimate and illegitimate dyadic backscatter channels. Theoretical analysis and numerical simulations are presented further to demonstrate the efficiency of our proposed TST scheme.
The pilot spoofing attack (PSA) is one kind of active eavesdropping that happens in the channel training phase, in which an intelligent eavesdropper transmits identical pilot sequences synchronously with the legitimate user to spoof the transmitter. This attack leads to the estimated channel being a mix of a legitimate channel (the channel from the transmitter to the legitimate user) and an eavesdropper channel (the channel from the transmitter to the eavesdropper). And as a result, confidential information is leaked to the eavesdropper during the data transmission phase. Especially when the eavesdropper utilizes sufficiently large power, the channel rate at the legitimate user end decreases observably and increases dramatically at the eavesdropper. To against the active PSA, we propose a new effective scheme called the spatial spectrum method (SSM) which can be applied in situations in which the eavesdropper attacks not only the transmitter but also the legitimate user in multiple-input multiple-output (MIMO) communication systems. Specifically, this method utilizes the spatial spectrums that are attained by the uplink training phase to detect the eavesdropper. Besides it also can locate the legitimate user and the eavesdropper by identifying the direction-of-arrival (DOA) of the legitimate user and the eavesdropper based on the symmetry of the uplink and downlink channels in a time-division-duplex (TDD) system and estimating the geographical distance between the legitimate user and the eavesdropper. Consequently, the secure transmission of secret information can be guaranteed by utilizing spatial information, such as by adopting beamforming technology. Numerical results show that our method can effectively detect and locate the eavesdropper.INDEX TERMS Physical layer security, spatial spectrum method, pilot spoofing attack, multiple-input and multiple-output.
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