An Improved Navigation Pseudolite Signal Structure Based on the Kasami Sequences and the Pulsing Scheme

Abstract

Pseudolites (PLs) are ground‐based satellites, providing users with navigation solutions. However, implementation of the PL system leads to the near‐far problem. In this paper, we proposed an improved navigation PL signal structure of combing Kasami sequences and the pulsing scheme to mitigate the near‐far effect. The pulse modulation method is adopted to ensure that the PLs transmit signals at different timeslots and reduce the PL signals’ mutual interference. Additionally, we employ the small set of Kasami sequences with good cross‐correlation properties to improve the anti‐interference ability. A simulation test based on software is carried out to evaluate the performance of the proposed signal. The simulation proves that the improved PL signal has an impulsive power spectral density, makes it a feasible solution to mitigate the near‐far effect, and performs better in the capture.

Response Analysis of a Piezoelectric Ceramic Transducer Pair Excited by Phase-Modulated Signals for Improved Echo Measurement

“…Kasami sequences are very often used in code division multiple access systems [23]. These codes stand out by having a very low cross-correlation within the generated set of codes [22], [23], [24], [25], [26], [27], [28]. These binary code sequences were thus sequentially generated and fed to the piezoelectric ceramic transmitter and the respective responses from the piezoelectric ceramic receiver were digitized and further analyzed.…”

Generation of Slot Index Tables for Time-Hopping Pseudolites with the Constructed Congruence Codes

“…The TH pulsed PL signal is often realized by gating the continuous local-generated GNSS-like signal with a chain of TH pulses, and the positions of these pulses are controlled by a basic TH pattern or slot index table (SIT) which consists of multiple permutation sequences of time-hopping slot indices (THSIs) [2,3,7]. To get better performance, the design of a SIT requires [4,8,9]: 1) the THSIs in a SIT should be pseudo-random so that the spectral shape of the original GNSS-like signal can be maintained as much as possible after gating; 2) the spreading factor of the PL signal in one SIT period should be same as or larger than that of the original GNSS-like signal in one data period; 3) each PL should be assigned with a different SIT so that the receiver can further use the SIT to distinguish different PLs besides the pseudo-random noise (PRN) codes of the underlying GNSSlike signal.…”

“…Meanwhile, it may cause the tracking problem due to the yield of some unbalanced long TH pulse intervals [2]. For the latter, THSIs of a SIT are generated by number theory and stored in memory prior to use [3], [8]. Compared with the former, the number of THSIs generated with the block-based method in one permutation period can be theoretically any predetermined value, and this will bring convenience to design different TH pulsed PL signal for different satellite navigation system.…”