Xiaomei Tang

A Design Method of Code Correlation Reference Waveform in GNSS Based on Least-Squares Fitting

The multipath effect is one of the main error sources in the Global Satellite Navigation Systems (GNSSs). The code correlation reference waveform (CCRW) technique is an effective multipath mitigation algorithm for the binary phase shift keying (BPSK) signal. However, it encounters the false lock problem in code tracking, when applied to the binary offset carrier (BOC) signals. A least-squares approximation method of the CCRW design scheme is proposed, utilizing the truncated singular value decomposition method. This algorithm was performed for the BPSK signal, BOC(1,1) signal, BOC(2,1) signal, BOC(6,1) and BOC(7,1) signal. The approximation results of CCRWs were presented. Furthermore, the performances of the approximation results are analyzed in terms of the multipath error envelope and the tracking jitter. The results show that the proposed method can realize coherent and non-coherent CCRW discriminators without false lock points. Generally, there is performance degradation in the tracking jitter, if compared to the CCRW discriminator. However, the performance promotions in the multipath error envelope for the BOC(1,1) and BPSK signals makes the discriminator attractive, and it can be applied to high-order BOC signals.

GCE-BOC Modulation: A Generalized Multiplexing Technology for Modern GNSS Dual-Frequency Signals

For the purpose of structural enhancement and backwards compatibility, more than two binary signals on one carrier frequency are required to emit. In order to maximize the power efficiency, constant-envelope modulation is adopted. Alt-BOC and ACE-BOC modulations, the constant-envelope modulation that multiplexes four binary spreading codes as two QPSK signals at two different carrier frequencies, are proposed by Galileo and BeiDou respectively. A constraint of these new modulations is that the number of signals to be multiplexed must be no larger than four signal channels. In this paper, a generalized dual-frequency constant-envelope multiplexing technology, named generalized constant envelope BOC (GCE-BOC) modulation, is presented. The modulation can be regarded as the extended form of Alt-BOC and ACE-BOC modulations and provides a solution to dual-frequency constant envelope multiplexing problem for worldwide GNSS.

Analysis for Cross Correlation in Multiplexing

Several multiplexing techniques may be used in next generation GNSS, including QPSK, Interplex, AltBOC, TD-AltBOC, Dual QPSK, POCET. Multiple signals on the same carrier could be multiplexed into a constant-envelope signal with these techniques. Increasing of signals would deteriorate the crossing correlation and its impact on receiving is analyzed. It is shown that cross correlation between signals in-phase has considerable influence; in contrast, the effect could be neglected to signals quadrature. Simulation and real data test is given in the end to support the conclusion, which could guide the selection of multiplex technique and spreading code of Compass.

Analysis of Ranging and Positioning Performance Influenced by Signal Coherence Parameters

Multi-band, multi-service and multi-modulation are new trends of GNSS development. Since novel modulation types like BOC/MBOC and multiplex techniques of navigation signals have been utilized, the composite navigation performance is indeed improved. With increased modulated signals broadcasting on single frequency in satellite, Signal coherence parameter has become one of the most important monitoring parameter. For satellite navigation system, the coherence of phases between pseudo-random codes and between carriers are the prerequisite for realization to pseudo-random code ranging and carrier phase ranging, and they are also two of the main factors affecting on the satellite signal system. This paper discusses how the coherence of phases between pseudo-random codes, between carriers and between carrier and code affect pseudo-random range measurement, carrier phase range measurement and carrier phase smoothing pseudo range process. Furthermore, the relationship between code minus carrier and code phase carrier phase coherence is discussed. Then, the positioning error and code minus carrier measurement is given by the simulation of carrier phase smoothing pseudo range process. In the end, we test code minus carrier parameter and code phase carrier phase coherence parameter using the system built by ourselves.

A novel IRA-like codes construction method based on cyclic matrix permutation

Due to the structure limitation of navigation message, the channel coding used by the satellite navigation system should have as high a coding gain as possible under short code lengths. At the same time, in order to reduce the cost of the receiver, the channel coding suitable for the navigation system should have the lowest complexity for coding and decoding. A well-designed structured LDPC code can reduce the complexity of the codec significantly without the loss of performance. In this paper, a method based on cyclic matrix permutation is proposed to improve IRA-like codes, which is combined Irregular Repeat Accumulation Codes (IRA) with Quasi-Cyclic LDPC codes. Simulation results show our method has good iterative decoding performance in decreasing bit error rate and greatly reducing the number of iterations required for decoding as well as error platform.

Analysis of The GEO multipath impact on Ionosphere-Free Combination Positioning in BDS system

The satellites constellation of BeiDou regional navigation satellite system (BDS) is different from GPS, which consists of Geostationary Orbit (GEO), Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO). Due to the different constellation of navigation system, there should be some special characteristics of BDS to be analyzed thoroughly. For example, when used Ionosphere-Free Combination Positioning algorithm (IF) in BDS, the positioning accuracy performs worse than Single frequency positioning. This paper studies the genuine causes of this phenomenon initially. From the analysis, GEO multipath error should be the main reason which caused this phenomenon. GEO multipath error changes slowly, even calls “standing multipath error”. This paper analyzes this phenomenon and characteristics of GEO multipath error, then proposes an amended algorithm to estimate GEO multipath error. Finally used computed multipath error to correct Ionosphere-Free Combination Positioning. The simulation results show a significant promotion in positioning accuracy.

An Offline Signal Quality Monitoring Software of BeiDou Navigation Satellite System (BDS) with New Signal Plan Based on Software Defined Radio (SDR) Receiver

Multi-band, multi-service and multi-modulation are new trends of GNSS development. Since novel modulation types like BOC/MBOC and multiplex techniques like (POCET, Interplex) of navigation signals have been utilized [1], the composite navigation performance is indeed improved. However, new challenges have arisen in the navigation signal quality monitoring area. Generally, common standard instruments, monitoring receiver and offline data analysis are three basic methods in signal quality monitoring [2-9], while the former two are considered to be less comprehensive and inflexible when dealing with new signal plans. An offline signal quality monitoring software of BDS with new signal plan based on (SDR) receiver is developed for flexible signal quality monitoring task in BDS construction. The paper, analyzes the software monitoring parameters like carrier phase and navigation data based on the conclusion of traditional signal quality monitoring parameters. Among them, the parameters like correlation loss, correlation peak, and carrier-code coherence are emphasized. Accordingly, the method of offline data analysis is given. Lastly, a signal quality test of modernized BDS is taken by employing the offline data analysis, and the results prove the effectiveness and practicability of this software.