In satellite navigation system, performance estimation of the on-board atomic clocks will affect the accuracy of satellite clock offset modeling and prediction, and then impact user positioning and timing accuracy. On-board clock performance evaluation is of great significance for the control segment. In the application such as satellite clock offset modeling, simulation and prediction, not only characteristics determined by the medium- and long-term stability need to be known, short-term stability parameters of satellite clock also need to be obtained.
GPS satellite clock stability estimation is usually implemented using IGS precise clock data at present. The sampling interval of 30 s typically, even the sampling interval of 5 s provided by the Analysis Center for Orbit Determination
in Europe (rearview mirror GPS navigation ), can not meet the need of shorter sampling intervals (e.g. 1 s) frequency stability estimation. On the other hand, IGS products are only available for GPS and GLONASS system currently. COMPASS and Galileo system are in their early stage of construction, and there are no globally distributed stations for COMPASS to obtain continuous satellite tracking. In addition, only a few agencies have the measurement data of regional network due to access permission. For COMPASS and Galileo system, there are certain difficulties for common users to obtain precise satellite clock parameters presently.
Like when buying a motor vehicle these days, a consumer serves himself best by being well-informed. Thus, becoming a would-be consumer who does upfront research on the different models and features and prices of a possible standalone DVR purchase is completely apropos and strongly recommended. For most people these days, the Internet is likely the most efficient service to turn to first glean valuable information about things like consumer electronics items, including DVRs. A chat or two with a neighbor, friend, or relative who has purchased and used a Rearview Mirror DVR, or multiple DVRs, is also advisable prior to making a DVR selection.
Many manufacturers offer Rearview Mirror GPS as an option on their higher line vehicles. These systems use satellites to direct drivers to their desired destinations. Many navigational systems are integrated in the vehicle radio. Regardless of the display method, most navigational systems use a GPS antenna, to determine the vehicle’s location by latitude and longitude coordinates, and a gyroscope to determine vehicle turns. Usually map data, provided on a DVD, and navigation information are displayed on a thin film transistor, liquid crystal display (TFT, LCD) color screen. Voice prompts can be sent through the audio system speakers. A dual-element microphone module (DEMM) is located in either the dash, center console, or rearview mirror. The DEMM consists of microphone elements and electrical circuitry that includes a preamplifier network. In summary, the future of DVRs is strong. The future of DVRs is also fraught with questions. This is because of new forms of hardware and software that are doing differently what the core pioneer DVRs of the late 1990s once did, yet the newer versions are doing the same basic DVR functionality more cheaply or more elegantly, or with more quality and enhancement, for less money. Thus, just like the road to improvement of just about any popular device, in the home, in the car, or in the office, this too, will be the future of DVRs.