# Design and Performance Analysis of Navigation Signal Based on OFDM
## 6 Conclusions  
In this paper, a new navigation modulation is proposed that is based on OFDM modulation. We proposed a mathematical model of an OFDM navigation signal with a guard interval according to the classical OFDM communication signal. The ACF and PSD expressions of OFDM navigation signal were derived, and the correctness of the analytical expressions is verified through simulation. We discussed the influence of the OFDM modulation parameters on the ACF and PSD, which helps navigation signal designers choose the appropriate OFDM parameters. Through the simulation analysis of the OFDM navigation signals and other typical navigation signals, the results show that OFDM navigation signals not only have a high tracking accuracy and strong anti-interference ability, but also form a very low bit error rate for communication signals in the pass-through integration, showing a good pass-through compatibility.  
Although the modulation system of the OFDM navigation signal was designed and its performance was comprehensively analyzed in this paper, the research on the design of the OFDM navigation signal receiver is not in-depth. The next step is to study the design of the receiver based on the OFDM navigation signal and to make full use of the characteristics of the cyclic prefix in the modulation process of the OFDM. The frequency synchronization plays an important role in the OFDM receiver, and we will study frequency synchronization in OFDM navigation modulation in a future work.  
The integration of an OFDM navigation signal and OFDM communication signal can greatly enhance the indoor positioning ability of a navigation signal, improve the ability of a GNSS service, and meet more user needs. The research results of this paper provide a feasible reference scheme for the design and optimization of a GNSS signal system. The fusion of an OFDM navigation signal and OFDM communication signal can make full use of existing wireless communication base stations to play the navigation signal with a low upgrade cost and wide navigation coverage; this provides a solution to the problem of high-precision indoor positioning.  
Figure 15: Bit error rate of the communication signal varies with the signal-to-noise ratio. (**a**) When the power ratio of communication and navigation signals is 20 dB; (**b**) When the power ratio of communication and navigation signals is 10 dB.  
**Author Contributions:** [PERSON] and [PERSON] conceived the conceptualization and algorithm. [PERSON] completed the implementation of the algorithm, the writing of the paper, and supported the writing--review and editing. [PERSON] completed some preliminary simulations and performed the preliminary research and summary. [PERSON] and [PERSON] reviewed the experimental results and gave formal analysis and suggestions. [PERSON] and [PERSON] provided suggestions in the revision of the paper. All authors have read and agreed to the published version of the manuscript. Funding was supported by the National Key Research and Development Program of China (Grant No. 2017 YFC1500904 and 2016 YFB0501301) and National 973 Program of China (Grant No. 613237201506). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.