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In Global Navigation Satellite Systems,Dual-Frequency Constant Envelop Modulation Scheme includes ACE-BOC,TD-AltBOC and AltBOC.The three modulation schemes each have pros and cons on single item evaluation index such as ranging precision,navigation message demodulation performance,et al.,which cause difficulties for the comparison and final chosen.In this article,a method to evaluate the overall performance of navigation signals is proposed.This method takes the minimal signal power that satisfies some positioning precision as the evaluation index,which requires enough precise ranging as well as enough good navigation message demodulation at the same time,thus can reflect the overall performance of the signal in actual using.The overall performance of the three modulation schemes was compared by bed testing under conditions that the signal used the mainstream bit rate and channel encoding method.The bed testing results show that,for 3-dimension positioning precision better than 10 meters,the ACE-BOC need the minimal signal power,0.5~2.5dB lower than that for TD-AltBOC and AltBOC,thus the ACE-BOC has the best overall performance of the three schemes.