With the sustainable development of global navigation satellite system (GNSS), the navigation requirements are broadened continuously. In order to meet emerging navigation requirements, it is required to transmit more navigation signals in the navigation bands, which increases the complexity of satellite payload significantly. In order to reduce the complexity, it is desired to multiplex several signals to a constant-envelope signal and transmitted it by a single transmitter. Up to now, several constant-envelope multiplexing (CEM) methods has been proposed and applied in the construction or update of GNSS, including Majority Voting (MV), Interplex and POCET. However, each of these CEM methods has its own shortcomings. For instance, MV can only be applied for candidate signals with equal power and the number of candidate signals must be odd. By employing Interplex, one of the candidate signal must be allocated in the quadrature-phase channel and others is allocated in the in-phase channel. In addition, to obtain an optimal efficiency, the power of candidate signal allocated in the quadrature-phase is higher than others. Compared with MV and Interplex, POCET is more flexible and there are no limitations on the power and phase for the candidate signals. With numerical optimization, the efficiency of POCET is higher than MV and Interplex. However, POCET is still facing with the problem of bad convergence. In addition, the symmetry constraint of POCET will lead to a low efficiency in some special cases. To improve the efficiency, asymmetrical POCET is proposed. But without symmetry constraint, the direct-current (DC) component may exist in the multiplexed signal which will cause a significant degradation in the autocorrelation performance of the multiplexed signal. To solve these problems, a generalized transparent constant envelope multiplexing (GTCEM) method is presented in this paper. This paper firstly reviews an intermodulation-addition model which regards the multiplexing problem as construction of intermodulation component. Next, GTCEM is proposed with the introduction of transparency constraint and no-DC constraint. At last, the performance of our method is analyzed and compared with POCET by an example. Theoretical analysis and simulation results shows that there are three evident benefits for the proposed method. First, there is no DC component in the multiplexed signal and the multiplexing is transparent to candidate signals. Second, the proposed method has no limitation on the power ratio and initial phase of candidate signals. Third, we can obtain the optimal efficiency by appropriate numerical optimization.
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