With the completion of the experimental and regional phases, China's BeiDou Navigation Satellite System (BDS) is being speedily expanded to a global and multifunctional satellite navigation system, BDS III. Confronted with challenges such as limited frequency resources and diversified user requirements, new signals with novel modulation techniques are adopted in BDS III. In addition to the legacy B1I and B3I signals, new open service signals, B1C and B2a/B2b, as well as some new authorized service signals, will be broadcast by BDS III satellites. Among them, B1C and B2a are compatible and interoperable with GPS and Galileo. The modulation techniques and the detailed signal structures of B1C and B2a are introduced in this paper, along with analysis of the initial in‐orbit test results of the new signals.

The sine-BOC (binary offset carrier) modulation is used in several signals of the new European Global Navigation Satellite System, Galileo, and modernized GPS. It provides these signals with enhanced robustness against multipath and increases the precision of the range measurement. However, this modulation presents some drawbacks. The most severe is the ambiguity problem in acquisition and tracking, which introduces a large bias in the pseudo-range measurement. In order to solve this problem, an unambiguous tracking technique for sine-BOC signals is proposed. This technique is based on a pseudo correlation function (PCF) which does not have any side peak and thus completely removes all of the false lock points on the discriminator output. Impacts of thermal noise and multipath on the proposed technique are investigated. Theoretical and numerical results obtained with BOC(n,n) and BOC(2n,n) signals show that this technique has a good noise mitigation performance and an average multipath performance.

In the signal design of new generation global navigation satellite systems, there is a strong demand for multiplexing multiple binary spreading signals on two adjacent frequencies into an integrated signal with a constant envelope. In this paper, a dual-frequency constant envelope multiplexing (DCEM) technique with high-design flexibility based on subcarrier waveform reconstruction, named asymmetric constant envelope binary offset carrier (ACE-BOC), is presented. This multiplexing technique can be seen as a generalized alternate BOC. It can combine four or fewer independent, bipolar, direct sequence spread spectrum signals onto two sidebands of a spectrum-split integrated signal, where each sideband consists of two or fewer signals with arbitrary power ratio modulated onto the quadrature components. The design principle, diversified generation methods of ACE-BOC signals, as well as the characteristics in both time and frequency domains are investigated. Multiplexing efficiency and receiving performance of this signal are also analyzed. Analysis with typical examples shows that, for both transmitters and receivers, ACE-BOC signals have multiple processing forms. Compared with existing DCEM methods, ACE-BOC has much higher design flexibility in the number of signal components, power ratio among components, hardware complexity of both transmitters and receivers, and spectrum compatibility. Such high-level design flexibility provides system designers great room in signal scheme optimization for varied navigation applications in the future.

This paper presents a Lidar / ultra-wideband (UWB) fusion algorithm for simultaneous localization and mapping (SLAM) with anti-degeneration capability. In the proposed algorithm, the sensor states are estimated by minimizing the sum of the Mahalanobis norm of all measurement residuals associated with the Lidar sensor and the UWB sensors. Additionally, considering that a poor geometric distribution of the sensor measurements will introduce large estimation uncertainties in the fusion algorithm, a trade-off parameter with its self-adjustment strategy is introduced in the fusion algorithm to adjust the ratio of the contributions provided by the Lidar measurement residuals and the UWB measurement residuals in the state estimation according to their degeneration degrees. A method that can detect and determine the degeneration degree of the sensor measurements is also presented in the paper. In order to evaluate the performance of the proposed fusion algorithm, two experiments were carried out. Results of the experiments show that the proposed Lidar/UWB fusion algorithm can automatically adjust the trade-off parameter according to the degeneration degrees of the sensor measurements and mitigate the effects of the degeneration.

In this letter, a side-peak cancellation unambiguous acquisition technique is proposed for sine-phased binary offset carrier (BOC) modulated signals. The test criterion used in this technique is based on a synthesized correlation function which has no major positive side peak. This synthesized correlation function is obtained by subtracting the cross-correlation between the received sin-BOC signal and an auxiliary signal from the autocorrelation of sin-BOC signal. For different types of BOC signal, the proposed technique employs corresponding modulated symbols of the auxiliary signal. The common solution of the symbol shape vector is derived, and the theoretical false alarm and detection performance formulas are given. Theoretical and simulation results show that at the expense of some performance degradation this technique completely removes the ambiguity threat in acquisition process.

Cooperation of multiple robots in simultaneous localization and mapping (SLAM) systems has more advantages compared to single robot configurations such as a faster exploration speed of the environment and the ability to perform tasks with high complexity. In this paper, we present an online multi-robot SLAM system which merges range measurements provided by UWB sensors and Lidar data provided by different mobile robots to build a globally-consistent map that contains individual point cloud maps and the trajectory estimations of all the robots. The proposed system does not require overlaps between robot trajectories. However, when the maps of different robots overlap, the system can further refine the relative robot transformations. The performance of the proposed system is evaluated through two experiments. The results of the experiments show that the proposed system can achieve accurate environment mapping and self-positioning by the cooperation of multiple robots in real-time.