Implementation of Constant Envelope Multiplexing Based on Extended Interplex and Inter-Modulation Construction Method

X.M. Zhang, X. Zhang, Z. Yao, M. Lu

Abstract: One of the future GNSS systems development trend is multiplexing several signal on the same carrier. This is because that with the growing demand for multiple positioning and location services, all GNSS would provide more than two signals in each transmission band. Considering the character of the High Power Amplifier (HPA) in satellites, a constant-envelope signal is desirable to achieve efficient operation of the satellite transmitter. When the number of signals on the same carrier increase, good signal multiplex techniques is of great importance. The goal of combining several binary spreading codes with a constant envelope is more efficient and less interference. So far, there are several multiplex methods proposed under the constraint condition of constant-envelope. The first one is Interplex/CASM[1], where CASM is short for Coherent Adaptive Subcarrier Modulation which is mathematically equivalent to the Interplex modulation. A second well-known multiplex technique is called Majority Vote (MV) [2]. Inter-Vote [3] is another method through a hybrid use of the Majority-Vote and Interplex. The latest technique is Phase Optimized Constant Envelope Transmission (POCET) [4]. POCET modulation method is described that optimizes the multiplexing of several signal components, while maintaining specified power levels and phase relations, as perceived in the user´s correlation receiver. The key implementation of POCET approach is an optimized, fixed table of transmitted phase values, one for each combination of bits of the spreading codes. However this looking-up table implementation cannot tell any details of the combining. It also cannot be written into an expression of the useful signal components and intermodulation (IM) signals like Interplex. To analyzing the combining details of the POCET method, a set of basis signal including useful signals and inter-modulation signals are established. Two new constant envelope multiplexing method are proposed base on basis signal. The first one is called Extended Interplex (EI) method which is applied in phase expression field. The second one named Inter-Modulation Construction (IMC) method, mainly in amplitude field. In fact, these two methods are closely linked. Then, three different general implement structures are compared, which are structure based on looking up tables, structure based on extended Interplex method and structure based on inter-modulation construction method. Finally, two examples simulations are carried out.
Published in: Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012)
September 17 - 21, 2012
Nashville Convention Center, Nashville, Tennessee
Nashville, TN
Pages: 893 - 900
Cite this article: Zhang, X.M., Zhang, X., Yao, Z., Lu, M., "Implementation of Constant Envelope Multiplexing Based on Extended Interplex and Inter-Modulation Construction Method," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 893-900.
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