Constant envelope combination for components on different carrier frequencies with unequal power allocation

Abstract

With the growing requirement for various positioning, navigation, and timing services, all of the existing and emerging global navigation satellite systems (GNSS) will transmit more than two signal components in each transmission band, with complex modulation structures and enhanced performance. As the number of signal components increase, there is strong demand for developing advanced multiplexing techniques which can combine multiple binary spreading signals into an integrated signal with a constant envelope to achieve efficient operation of the satellite transmitter. Besides the constant envelope multiplexing of components with the same central frequency, in some application requirements, dual-frequency joint multiplexing has its unique advantage. For receivers, signals located at two adjacent frequencies can be received and processed separately, and the constant envelope combined signal also offers the possibility of wideband joint processing. In this paper, dual-frequency constant envelope combination techniques are discussed. A new dual-frequency constant envelope combination technique which can combine no more than four independent spreading codes with arbitrary power allocation is presented. This paper is structured as follows: Firstly, the mathematical model and the design process of the proposed dual-frequency constant envelope technique are given. Then we analyze and describe the constructing method and properties of the subcarrier waveform of this technique in detail, including the distribution of the phase points in the constellation, the shape of time domain waveforms, and the merging rules of the state points and waveforms in some specific power allocation cases. Finally, the correlation loss as well as the multiplexing efficiency are analyzed.