The direct and reflected signals can be concurrently received by both antennas of a conventional global navigation satellite system reflectometer (cGNSS-R) in ground-based settings. It is unfavorable for cGNSS-R carrier phase altimetry, but it also provides cGNSS-R the possibility of retrieving reflector height in the way of interferometric reflectometry. An initial ground-based water surface experiment was carried out to investigate the feasibility of cGNSS-R interferometric altimetry. GPS L1 C/A signals were received by an up-looking right hand circularly polarized (RHCP) antenna and a down-looking left hand circularly polarized (LHCP) antenna and then collected by a dual-channel sampler. The raw signals were postprocessed to generate their correlation power sequences. These sequences were then subjected to the GNSS interferometric reflectometry altimetry technique in order to estimate the LHCP antenna heights. Experimental results show that the correlation coefficients between the retrieved values and the true values are 0.77 and 0.95 for the RHCP antenna and the LHCP antenna, respectively. The mean absolute errors of the results are 0.15 m and 0.04 m, and the root mean square errors are 0.17 m and 0.04 m. It indicates that both the RHCP antenna and the LHCP antenna of a conventional GNSS reflectometer can be used for ground-based interferometric altimetry, and the LHCP antenna performs better in this openness-limited scenario.

Enhancing the signal waveform's power efficiency and information transmission efficiency is one of the issues in tracking, telemetry, and command (TT&C) system waveform design. It is found that the basic characteristics such as biorthogonal, optimal time-frequency energy aggregate, and spectral controllable of prolate spheroidal wave functions (PSWFs) make it be a reliable candidate for TT&C signal waveform design. In this paper, PSWF are introduced into TT&C signal waveform design, and a four-dimensional unified spread spectrum TT&C signal waveform design method based on PSWF waveform shaping is proposed. This new idea, by using high-energy aggregation PSWF as waveform shaping functions, can obtain higher power efficiency and information transmission rate, better anti-interference and anti-interception capabilities. It provides a better waveform scheme for the design of TT&C signal waveforms. For instance, the suggested approach can boost the spread spectrum gain by 3.44 dB and the information transmission rate by one when compared to conventional TT&C signals based on rectangular pulse functions under the same system error performance.

Using GNSS-R technology for remote sensing of surface parameters has become a new trend in the field of remote sensing. With the rapid development of GNSS-R technology, GNSS-R simulation has become one of the new hot spots. Now the researches of the GNSS-R simulation are all the simulations that consider a single star or a single frequency point, and in actual applications, the signal captured by the receiver is often the reflected signals of multiple stars. In view of this situation, from the perspective of multi-satellite simulation, this paper gives the model of GNSS-R multi-satellite ocean simulation on the basis of analyzing the remote sensing principle, reflection signal model and simulation principle of GNSS-R technology. Based on the GNSS-R multi-satellite ocean simulation model and the fast parallel computing capability of GPU, the GNSS-R multi-satellite ocean simulator was designed. Finally, the direct and reflected signals generated by the GNSS-R multi-satellite simulator were tested and verified. The results show that the positioning result of the direct signal meets the positioning accuracy requirements; The delay-related power results obtained from the simulated two-satellite reflected signals processing are in good agreement with the theoretical model, and the correlation coefficients are all above 0.99; The generated signals are used for GNSS-R height measurement technology, the height measurement error is about 1.4~1.8 m, which is in line with the accuracy of the C/A code ranging receiver; And the parallel operation of the GPU for multi-satellite simulation calculation is 800—900 times higher than the traditional CPU calculation. It proves that the proposed model and the designed simulator are feasible and accurate.