The first part Fr of Equation (1) only depends on the range R, and the second part Fd is the Doppler frequency introduced by the radial velocity .The IMPALA radar is panoramic. It is a monostatic radar, i.e., a common antenna is used for both transmitting and receiving. The rotating antenna achieves a complete 360�� scan around the vehicle in one second, and a signal acquisition is realized at each degree. The maximum range of the radar is 100 m. The radar includes microwave components, electronic devices for emission and reception, data acquisition and signal processing unit.Data acquisition and signal processing units are based on an embedded Pentium Dual Core 1.6 GHzPC/104 processor. Computed data is transmitted using an Ethernet link for visualization and further processing.
Main characteristics of the radar are described in Table 1.Table 1.Characteristics of the IMPALA radar.In order to solve the distance-velocity ambiguity, a triangular modulation function is applied. In Figure 1(a), the full line represents the transmitted signal while the dashed line is the echo signal on a stationary target at a distance R of the sensor. The beat frequency fb is defined as the difference between the transmitted and the received wave:fb=freception?femissionTime shift ��t is directly linked to the distance of the detected target.Figure 1.Triangular modulation with (a) static target; (b) mobile target.An example o
For more than one decade China has been working on its own BeiDou navigation satellite system (abbreviated to BDS) .
On 27 December 2012, the regional system was officially announced to provide operational Anacetrapib positioning services over the Asia-Pacific region. Due to its similar signal structure and analogous frequencies with respect to that of the American GPS, BDS-capable multi-GNSS receivers had been developed before its Interface Control Document (ICD)  was publically disclosed. These receivers are utilized in a number of studies on BDS precise orbit determination and clock estimation [3�C8], Precise Point Positioning (PPP)  and relative positioning [3,7,10]. All the studies confirm that BDS is able to provide positioning and navigation services of similar accuracy to GPS.Besides precise positioning, GNSS is also employed to retrieve tropospheric information, such as zenith tropospheric delays (ZTD) or slant tropospheric delays, for meteorological study and weather forecasts . The GPS derived ZTD was validated of an accuracy of about 6 to 10 mm by various technologies or instruments, such as radiosonde, water vapor radiometer, and Very Long Baseline Interferometry (VLBI) [12�C14].