JNTU B.Tech IV GLOBAL POSITIONING SYSTEM Previous Question Paper (July/August - 2022 - R16)

The primary purpose of the GPS navigation data is to provide the user receiver with the necessary information to calculate the precise position of the satellite in space at any given time. This broadcast ephemeris data allows the receiver to determine the satellite's orbital parameters, clock corrections, and health status, which are essential for performing trilateration.

The navigation message is transmitted at a rate of 50 bps and is structured into frames, subframes, and words:

• Frame: Each frame consists of 1500 bits and lasts 30 seconds.
• Subframes: Each frame is divided into five subframes, each 300 bits long (6 seconds). Subframes 1, 2, and 3 are repeated every 30 seconds, while subframes 4 and 5 are sub-commutated over 25 frames.
• Subframe 1: Contains satellite clock correction parameters and health information.
• Subframes 2 and 3: Contain the precise ephemeris data (orbital parameters) for the transmitting satellite.
• Subframes 4 and 5: Contain almanac data, ionospheric models, and UTC parameters for all satellites in the constellation.

To calculate the free space path loss (FSPL) in decibels, we use the formula:

Given:

• Frequency (f) = 1575.42 MHz = 1.57542 × 10⁹ Hz
• Distance (d) = 1.5 × 10⁷ m
• Speed of light (c) ≈ 3 × 10⁸ m/s

Substituting the values:

The free space loss for the L1 signal at the given distance is approximately 179.92 dB.