The Global Positioning Satellite (GPS) Receiver reuses a system of 24 earth orbiting satellites to triangulate a point on the earth with extreme accuracy. Design Considerations The Global Positioning System (GPS) works on the principle that if you know your distance from several locations, then you can calculate your location. The known locations are the 24 satellites located in six orbital planes at an altitude of 20,200Km. These satellites circle the Earth every 12 hours and broadcast a data stream at the primary frequency L1 of 1.575GHz which carries the coarse-acquisition (C/A) encoded signal to the ground. The GPS receiver measures the time of arrival of the C/A code to a fraction of a millisecond, and thus determines the distance to the satellite. The Core Subsystems include: Front End - the GPS L1 signals (Maximum = 24 signals) at 1.575GHz are received at the antenna and amplified by the Low-Noise-Amplifier (LNA). The RF front-end further filters, mixes, and amplifies (AGC) the signal down to the IF frequency where it is digitally sampled by a ADC. ' Baseband Processor/CPU - the ADC samples of GPS C/A code signals are correlated by the DSP and then formulated to make range measurements to the GPS satellites. The DSP is interfaced with a general-purpose CPU, which handles tracking channels and controls user interfaces. TI OMAP integrates both DSP and ARM processor on the same chip.' Memory - the processor runs applications stored in memory. The OS is stored in non-volatile memory such as EE/FLASH/ROM. Applications may be loaded in FLASH or DRAM. ' User Interface - allows user to input/output data from the receiver using input commands via microphone, touch screen, and output MP3 to the earplug.' Connectivity - allows the receiver to connect to the USB port.' Power Conversion - converts input power (battery or wall plug) to run various functional blocks.
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