Band-limited dual-frequency multiplexing technique for GNSS signals

Abstract

Global navigation satellite systems (GNSSs) usually adopt constant-envelope multiplexing (CEM) techniques to deal with the nonlinear characteristic of high-power amplifiers (HPAs) on satellites. However, almost all the existing navigation signal CEM techniques assume that the bandwidth of the transmitter is large enough when compared to that of navigation signals, which often contradicts reality, especially for the multiplexing of wideband navigation signals such as the signals in the Galileo E5 and BDS-3 B2 bands. Consequently, the constant-envelope characteristic deteriorates severely when the composite signal passes through the filter, which leads to nonlinear distortion and low amplification efficiency. Even if the nonlinear distortion can be mitigated by using amplifier linearization techniques, the actual transmitted signal power still suffers from a high peak-to-average power ratio (PAPR) of the composite signal. In order to address this problem, we present a new band-limited, dual-frequency multiplexing technique. The main premise of this method is to consider the impact of the filter on the navigation signals at first and then introduce the band-limited auxiliary signals to reduce the peak power of the composite signal as much as possible, thereby increasing the actual transmission power of the navigation signals. Simulation results demonstrate that the proposed method has lower PAPR and higher amplification efficiency than existing methods. In addition, implementation of the proposed multiplexing technique is still based on a look-up table, which has little change compared with previous CEM methods, and the complexity of signal generation is affordable.