차세대 GNSS를 위한 GIG 부호 기반 시간다중 이진부호심볼 변조기법

Abstract

In this paper, we propose a time multiplexed binary coded symbol (TMBCS) modulation scheme based on Gray and inverse Gray (GIG) codes for the next generation global navigation satellite system (GNSS). A representative binary coded symbol (BCS) is a binary offset carrier (BOC). Compared to the existing binary phase shift keying (BPSK) modulation, which is a representative GNSS modulation scheme, BOC modulation has a high degree of freedom in terms of frequency band shape design and is less affected by multipaths because the correlation function is sharper at the correct code phase. However, since several sub-peaks occur in the correlation function of the BOC-modulated pseudo-noise signal, false locks can easily occur during code tracking. This disadvantage is called the ambiguity of the BOC modulated signal. Time multiplexed binary Walsh spreading (TMBWS) modulation, which is a TMBCS scheme that uses a Walsh code, is one method for reducing ambiguity and is a perfectly orthogonal code with a very good correlation among BCSs. However, Walsh codes can only be generated with a power of two length. In this paper, we propose a novel TMBCS modulation scheme using quasi-orthogonal GIG codes that can be generated with lengths that are multiples of 2. The proposed scheme maintains the same bandwidth and spectral separation coefficient compared to TMBWS when a symbol of length 8 is used. In addition, the proposed scheme has a higher degree of freedom in terms of band shape design compared to TMBWS modulation, because the length can be designed in multiples of 2 (such as 6, 10, or 12) and has high multipath immunity with unambiguity.