Compared with traditional GPS signals, modern GNSS signals are much more complex and have various new modulations. This introduces a difficulty in combining multiple signal components into a constant-envelope signal that maximises the power efficiency of High Power Amplifiers (HPA) on satellites. This paper first describes the fundamental Phase-Optimised Constant-Envelope Transmission (POCET) technique that searches the optimum combining solution for multiple binary navigation signals. Then the Compass B1/B3 signals are modelled by POCET. For the B1 band, a binary complex sub-carrier is adopted to implement the centre frequency difference between regional and global Compass navigation systems. Regional B1 Open Service (OS) signals and global TMBOC signals are combined with optimum loss of 1·0 dB. For the B3 band, Interplex modulation is proved to be the optimum method to combine QPSK (10) and BOC (15, 2·5) signals. Signal quality in the presence of finite word-length effects of Digital-Analog (DA) converters is analysed. Simulations for signal model validation are conducted. The result indicates that relative amplitude error less than 0·01 and angle error less than 0·1 degree can be achieved with 10 bit DA converters. The POCET method is demonstrated as an efficient solution for Compass signals.

In recent months the US and the EU have agreed to change the modulation scheme for the new civil GPS and Galileo signals in the L1 band from Binary Offset Carrier (1,1) (BOC(1,1)) to a scheme having the so-called Multiplexed Binary Offset Carrier (MBOC) spectrum, although each system will implement this differently. This paper compares the performance of the new system in a number of areas against the original baseline. It is shown that the MBOC signal offers significant advantages in multipath and tracking performance, while retaining compatibility with BOC(1,1) receivers at the cost of a small correlation loss.