Design, Implementation, and Performance Analysis of ACE-BOC Modulation

Z. Yao, M. Lu

Abstract:	In the construction of new generation global navigation satellite systems (GNSS), in order to provide more diversified positioning, navigation, and timing services for users, and to ensure enough robustness for each service, all of the existing and emerging systems will transmit more than one signal in each transmission band, with complex spreading modulation and data-plus-pilot channel structures. The significant increase of signal components has promoted the development of constant envelope multiplexing techniques. In the domain of constant envelope multiplexing, multi-frequency joint multiplexing, especially dual-frequency multiplexing, is one of the hottest issues in recent years, since from both the transmitter saving side and the link characteristics correlation side, as well as the system smooth transition side, there are strong demand for finding an efficient multiplexing technique to combine several signal components, which are modulated at two different center frequencies with different modulation methods and different chip rates, into a composite signal on the same carrier with a constant envelope. The most famous existing dual-frequency multiplexing technique is represented by AltBOC, which combines two QPSK signals located in two different central frequencies into an 8-PSK integrated signal, in which those 4 signal components have equal power. More recently, a new dual-frequency multiplexing technique named Asymmetric Constant Envelope BOC (ACE-BOC) multiplexing, has been presented, which breaks the limitations of both 4-component and equipower. In ACE-BOC multiplexing, no more than 4 in components number, they can be combined into a constant envelope integrated signal with arbitrary power allocation. In the previous results [1], the waveform, modulation constellation, as well as the multiplexing efficiency in component separate receiving mode under several typical power allocation schemes is analyzed. However, objectively, those results are still some way from practical engineering applications. Firstly, the direct type of ACE-BOC signal generation is somewhat complex for digital logical circuit in payload. A more easily implemented structure is needed. Secondly, under the fundamental representation of ACE-BOC signal time domain waveform, the analytical power spectrum density and the multiplexing efficiency are hard to obtain. When system builders concern with the RF compatibility, the power budget, and the receiving performance of effective components, they have to use numerical simulation. To address the above insufficient of ACE-BOC multiplexing, in this paper, we present a series of general design and analysis methods for multi-frequency joint multiplexing, on the base of which the engineering practicality of ACE-BOC multiplexing is further enhanced, more suitable implementations for the generating of ACE-BOC signal in satellite payload are proposed, and the transmitting and receiving performance of this technique is analyzed detailedly. By employing a powerful analytical tool proposed in our previous study [2], named inter-modulation construction method, we construct a new expression of ACE-BOC signal with a more clear physical conception. On that basis, the analytical expression of ACE-BOC signal is derived and verified by numerical simulation. The inherent code tracking and multipath mitigation performance limit, as well as the accurate multiplexing efficiency are also obtained. As an application example, in the context of B2 band signal design in Compass Phase III, with a specific power allocation relationship, a proposed ACE-BOC scheme is compared with the other options. Results show that ACE-BOC multiplexing is not only practical but also has great design flexibility. The B2 signal option based on proposed technique can have a remarkable receiving performance and interoperability with other systems. [1] Z. Yao, & M. Lu, Constant envelope multiplexing technique for components on different carrier frequencies with unequal power allocation, ION ITM 2013. [2] X. Zhang, X. Zhang, Z. Yao, and M. Lu, Implementations of constant envelope multiplexing based on extended Interplex and inter-modulation construction method, ION GNSS 2012.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	361 - 368
Cite this article:	Yao, Z., Lu, M., "Design, Implementation, and Performance Analysis of ACE-BOC Modulation," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 361-368.
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