Theory , Principles and Calculations of Globel Position System.?

Question

How is the calculation done to detect the position of the globle.

Answer 1

The GPS system is driven by sattelites that transmit unique signals. These signals provide a signature of the sattelite that provides position information to a GPS receiver. In order to compute position the receiver either must see at least two sattelites. For accurate elevation information, three sattelites are required.

The theory behind the system is that each sattelite is in a known orbit a given distance from the surface of the earth. The signal transmitted to the GPS receiver tells the reciever "I am here in three dimensional space". This is done digitally. Since the signature varies with time, the more bits that the reciver is able to decode, the more accurate the measurement.
From that information the relative azimuth is calculated between the reciever and the sattelite by the receiver. Since the receiver can see two sattelites, it takes the position information for one instant and computes the intersection of the two lines. This is then provided as longitude and lattitude information. With three sattelites, elevation is also provided.

One of the fundamental principles of the sattelite signature is the concept of a maximally long psuedo-random shift register. This device generates a unique digital "word" that is as long as the number of flops in the register, and generates N-1 combinations. When words from two complimentary registers are added together, the distribution appears Gaussian, and virtually impossible to decode, unless you know the length and sequence of the registers. This is a comon technique in encription technology.

Not to worry, all of this is in the public domain.

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