Orthogonality-Based Generalized Multicarrier Constant Envelope Multiplexing for DSSS Signals

The new generation global navigation satellite systems will broadcast multiple direct sequence spread spectrum signals on multiple different central frequencies, with complex spreading chip waveforms. There is a strong demand for efficient and flexible multiplexing techniques to combine these signals into a constant envelope composite signal. In this paper, a high efficiency generalized multicarrier joint constant envelope multiplexing (CEM) technique for multilevel DSSS signals is proposed. The basic idea of this technique is adding an auxiliary component into the direct superposition of signals to keep the envelope of the integrated signal constant. Design principle, constraints, and optimization method of the auxiliary component are investigated. An analysis with typical case studies demonstrates the high efficiency and high flexibility of the proposed technique. Compared with existing CEM techniques, the proposed technique has much higher design flexibility in the number of subbands, the number of signal components, power ratio and phase relationship among components, and the spreading chip waveforms. It can be applied to any number of bipolar or multilevel DSSS signals with arbitrary power distribution at one or more subcarrier frequencies. Such high-level design flexibility provides system designers great room in signal scheme optimization for varied navigation applications in the future.