High-Precision Doppler Frequency Estimation Based Positioning Using OTFS Modulations by Red and Blue Frequency Shift Discriminator

Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.

Communication-based positioning systems:past,present and prospects

This paper reviews positioning systems in the context of communication systems. First, the basic positioning technique is described for location based ser- vice （LBS） in mobile communication systems. Then the high integrity global posi- tioning system （iGPS） is introduced in terms of aspects of what it is and how the low Earth orbit （LEO） Iridium telecommunication satellites enhance the global posi- tioning system （GPS）. Emphasis is on the Chinese Area Positioning System （CAPS） which is mainly based on commercial geostationary （GEO） communication satellites, including decommissioned GEO and inclined geosynchronous communication satel- lites. Characterized by its low cost, high flexibility, wide-area coverage and ample frequency resources, a distinctive feature of CAPS is that its navigation messages are generated on the ground, then uploaded to and forwarded by the communication satellites. Fundamental principles and key technologies applied in the construction of CAPS are presented in detail from the CAPS validation phase to its experimental system setup. A prospective view of CAPS has concluded it to be a seamless, high ac- curacy, large capacity navigation and communication system which can be achieved by expanding it world wide and enhancing it with LEO satellites and mobile base stations. Hence, this system is a potential candidate for the next generation of radio navigation after GPS.

Design and performance evaluation of a novel ranging signal based on an LEO satellite communication constellation

Driven by improvements in satellite internet and Low Earth Orbit(LEO)navigation augmenta-tion,the integration of communication and navigation has become increasingly common,and further improving navigation capabilities based on communication constellations has become a significant challenge.In the context of the existing Orthogonal Frequency Division Multiplexing(OFDM)communication systems,this paper proposes a new ranging signal design method based on an LEO satellite communication constellation.The LEO Satellite Communication Constellation Block-type Pilot(LSCC-BPR)signal is superimposed on the com-munication signal in a block-type form and occupies some of the subcarriers of the OFDM signal for transmission,thus ensuring the continuity of the ranging pilot signal in the time and frequency domains.Joint estimation in the time and frequency domains is performed to obtain the relevant distance value,and the ranging accuracy and communication resource utilization rate are determined.To characterize the ranging performance,the Root Mean Square Error(RMSE)is selected as an evaluation criterion.Simulations show that when the number of pilots is 2048 and the Signal-to-Noise Ratio(SNR)is 0 dB,the ranging accuracy can reach 0.8 m,and the pilot occupies only 50%of the communication subcarriers,thus improving the utilization of communication resources and meeting the public demand for communication and location services.

Time synchronization in communication networks based on the Beidou foundation enhancement system

Communication networks rely on time synchronization information generated by base station equipment(either the Global Navigation Satellite System receiver or rubidium atomic clock) to enable wireless networking and communications. Meanwhile, the time synchronization among base stations depends on the Network Time Protocol. With the development of mobile communication systems, the corresponding time synchronization accuracy has increased as well. In this case, the use of sparsely distributed-high-precision synchronization points to synchronize time for an entire network with high precision is a key problem and is the foundation of the enhanced network communication. The current receiver equipment for China's digital synchronous network typically includes dedicated multi-channel GPS receivers for communication; however, with the development of GPS by the USA, network security has been destabilized and reliability is low. Nonetheless, network time synchronization based on Beidou satellite navigation system timing devices is an inevitable development trend for China's digital communications network with the establishment of the independently developed BDS, especially the implementation and improvement of the Beidou foundation enhancement system.