![]() The first module, the PC, simulates the selected GNSS constellations and executes all necessary computations to generate the high-rate zero IF GNSS baseband signal. The simulator is cross-platform and can run on Windows, Linux, or OS X operating systems. ![]() To allow for different configurations and hardware connectivity, the data link can be either PCIe x4, PCIe x1, 10-gigabyte Ethernet, or 1-gigabyte Ethernet. The two modules are connected via a high rate data link. Two modules comprise the SDR simulator under consideration (in turnkey configuration): 1) a PC or laptop and 2) a USRP. Consequently, SDRs are constantly evolving, improving the RF signal quality and increasing the signal bandwidth. Moreover, the programming of such devices is based on general programming tools and does not require special skills, greatly facilitating the evolution and portability of the simulator.Īs for USRPs, these universal SDR platforms are sold in large quantities and economies of scale keep the price low. Meanwhile, as with integrated circuits, the processing power of GPUs follows Moore’s Law and doubles every 18 months. GPUs are sold as mass-market products with relatively low prices. High-rate modulation is carried out on the GPU instead of the dedicated FPGA modules. In contrast, a SDR GNSS simulator uses off-the-shelf products such as a PC equipped with GPU and USRPs. Also, in order to add additional signals or constellations, some or even all of the hardware has to be replaced, which may be very expensive and impractical. Adding new features or functionalities can be difficult and costly, as the programming of FPGAs requires special programming tools and skills. ![]() For more than three decades, the conventional simulators evolved into a very precise and robust GNSS test equipment allowing for millimeter-level precision on simulated code- and carrier-based range measurements.ĭedicated hardware simulation approaches, however, have some disadvantages, perhaps the most important of which are a high cost per unit and reduced flexibility due to a slow product-development evolution as these types of simulators are typically deployed in low numbers. At that time, no other alternative but FPGA-based technology existed for high-rate digital signal processing to enable real-time simulation. The simulators brought repeatability and control to simulated satellite constellation and impairments. Depending on the FPGA’s specific functionality, a number of dedicated channels per module cannot be changed for a given hardware design.Ĭonventional hardware simulators were used for GPS/GNSS receivers testing and validation from the beginning of GPS. The high-rate modulation is usually done in field-programmable gate array (FPGA) modules. The pseudorange, Doppler, and power per satellite are computed and serve as stimuli for processing in the hardware circuits. Low-rate processes usually deal with simulation of satellites orbit, receiver trajectory, atmospheric delays, antenna pattern, impairments, and so forth. Generally speaking, the conventional simulators use a dedicated hardware for high-rate signal modulation and a personal computer (PC) for low-rate computations.įigure 1 schematically illustrates the most common architecture of conventional GNSS simulators. The SDR approach has some advantages when compared with conventional simulators. The results section presents the measurements that we obtained, along with their analysis. The methodology section describes the test setup and the approach employed for analyzing the test data. The first section will introduce the SDR GNSS simulator design. This article presents the test methodology, results, and conclusions drawn from these tests. The purpose of the tests was to evaluate the real performances of the SDR simulation approach when used in conjunction with high-grade GNSS receivers. The team of LASSENA (Laboratory of Space Technologies, Embedded System, Navigation and Avionic) of the École de technologie supérieure in collaboration with Skydel Solutions conducted a series of tests with a new SDR GNSS simulator. Nevertheless, this is an important aspect to consider for all potential users who consider the SDR approach as an alternative solution to conventional hardware-based simulation equipment. Moreover, opinions are divided as to the quality of USRP performance and their usability for high-grade GNSS receiver testing. ![]() However, to the best of our knowledge, all the most recent studies seem to share a lack of results in portraying the detailed performance of such simulators in presence of high-grade GNSS receivers. ![]()
0 Comments
Leave a Reply. |