Linearly-Constrained Adaptive Antenna Array for Ground-Based Radio Receivers of Global Navigation Satellite System

Abstract

Antenna arrays are widely used as the antennas of modern radio systems today. The ability to control the Radiation Pattern (RP) of such antennas underlies the operating principle of the Adaptive Antenna Arrays (AAA). These arrays suppress the signals from the interference sources whose frequency bands overlap with the frequency band of the desired (informational) signal. One of the most relevant applications of the AAAs is their usage in the ground-based equipment of the Global Navigation Satellite Systems (GNSS). Such equipment primarily utilizes the AAAs known as the interference cancelers. Like any AAA, they suppress interferences but do not guarantee the receiving of a predetermined number of satellite signals which are necessary for solving the navigation task. This paper proposes to use a version of the linearly-constrained AAA. The constrain ensures a fixed value of the AAA RP towards zenith. The received signals from the satellites, which are located in this direction, provide the maximal signal-to-noise ratio due to the shortest distance from satellites to Earth. The value of the RP specified by the constraint is independent of the values of the AAA weights calculated during the adaptation. To calculate these weights, a recursive least-squares algorithm based on the matrix inversion lemma and optimized for the number of arithmetic operations has been used. The computational complexity of this algorithm is lower than that of its non-optimized version. This complexity reduction is achieved by the taking into account the Hermitian structure of the correlation matrix of the AAA input signals. A further reduction in the computational complexity is achieved if the AAA is symmetric. Almost all operations in such the AAA can be executed using real valued arithmetic. Their number is a half that of the equivalent number of real valued operations in the similar AAA in complex valued arithmetic. Furthermore, compared to the complex valued arithmetic AAA, the transient response of the AAA under the consideration is two times shorter and the interference suppression is on average 3 dB bigger in the steady-state mode. The proposed AAA can be used not only in GNSS equipment but also in other radio systems.