## 6 Conclusions  
In order to combine several FH-BOC signal components into a constant-envelope signal, we propose ACE-FHBOC modulation that is not only a generalized ACE-BOC but also a multicarrier constant-envelope multiplexing modulation. The ACE-FHBOC  
Figure 16: NELP multipath errors for the example signals. Figure 15: Tracking errors for the example signals. provides higher design flexibility in the number of subcarrier frequencies than ACE-BOC while maintaining the same flexibility of signal design as ACE-BOC in the number of signal components and power ratio among components. The subcarrier frequencies of ACE-FHBOC can be flexibly specified by changing the frequency-hopping pattern, and the number and power of its signal components can be allocated by adjusting the power ratio vector. The number of the signal components of ACE-FHBOC ranges from 1 to 4. There are two expression forms of ACE-FHBOC, namely the time domain form and the phase domain form, which can be converted to each other. The time domain form is intuitive and easy to understand, while the phase domain form can be implemented flexibly and conveniently in hardware. According to these two expression forms, we give two signal generation schemes, which are direct generation and phase rotation generation. As a generalized modulation of ACE-BOC, the generation schemes of ACE-FHBOC can be implemented based on those of ACE-BOC with minor modifications. Due to the frequency-hopping subcarrier, the generation of the ACE-FHBOC generally requires more resources than ACE-BOC. In addition, the performance analysis of ACE-FHBOC by comparing different example signals of ACE-FHBOC and ACE-BOC is conducted. The frequency-hopping pattern and power ratio vector determine the shapes of ACF and PSD of an ACE-FHBOC signal, which affect the measurement performance and spectrum compatibility of the signal. Therefore, we can shape the ACF and PSD according to the signal performance index by adjusting the frequency-hopping pattern and power ratio vector. The numerical simulation results show that ACE-FHBOC and ACE-BOC have the same multiplexing efficiency. The probabilities of false locking on ACF side peaks of ACE-FHBOC is lower than that of ACE-BOC under the same condition because ACE-FHBOC has a lower ACF side peak ambiguity. Furthermore, the tracking error of ACE-BOC is smaller than that of ACE-FHBOC under the same condition. But the anti-narrowband interference and multipath performance of ACE-FHBOC is better than that of ACE-BOC under the same condition. ACE-FHBOC is essentially a hybrid DS/FH spread spectrum modulation, which inherits the advantages of the direct-sequence spread spectrum and the frequency-hopping spread spectrum. Unlike the traditional DS/FH signal, the ACE-FHBOC signal is multilevel and can be realized digitally. Furthermore, the performance for carrier phase measurements and Doppler measurements is not affected because the frequency hopping for ACE-FHBOC is implemented in subcarriers. Since ACE-FHBOC has a two-dimensional multiple access space, it enables more multiple accesses than ACE-BOC. ACE-FHBOC improves the flexibility of GNSS signal design and has advantages in low ACF ambiguity and anti-interference, which can be used in new generation GNSS signal design, especially military signal design. With high design flexibility, it can also be used in signal design for GNSS-like systems. [PERSON] and [PERSON] conceived the conceptualization. [PERSON] completed the implementation of the multiplexing modulation and the writing of the paper and supported the writing--review and editing. [PERSON], L.D. and [PERSON] provided theoretical guidance and suggestions for revision of the paper. All authors have read and agreed to the published version of the manuscript. Funding was supported by National Key Research and Development Program of China (Grant Nos.2017 YFC1500904, 2016 YFB0501301), the National 973 Program of China (GrantNos.613237201506), and the Advance Research Project of Common Technology (No.41418050201).