Research of AltBOC modulation

When the modulation method of AltBOC was just promoted,the Galileo E5 signal's envelope will not be constant if it brings one pilot component in upper and lower band separately. That may influence the HPA's power efficiency. Galileo navigation system takes PRN codes to modulate new 4-level subcarriers instead of 2-level subcarriers then obtain a equivalent 8-PSK AltBOC broad band modulation. But it's arduous to understand the complicated modulation way which multiplexes 4 navigation signal components. And the mathematical formulations are not easy to comprehend. So,in the paper,the author has researched constant envelope modulation's characteristics and detailed 8-PSK AltBOC principles by describing phase jumping rule of the E5 signal's Fresnel plot. Then presents how the modulation method forms a envelope constant 4-code multiplexed signal.