PAJ GPS POWER Finder- Magnet Mount GPS Tracker- Tracking Device for Cars, Machinery, Boats- 40 Days’ Battery while active and up to 90 Days in Stand by- Real-time Tracker with Antitheft Protection

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In addition to the PRN ranging codes, a receiver needs to know the time and position of each active satellite. GPS encodes this information into the navigation message and modulates it onto both the C/A and P(Y) ranging codes at 50bit/s. The navigation message format described in this section is called LNAV data (for legacy navigation). Whereas the C/A PRNs are unique for each satellite, each satellite transmits a different segment of a master P-code sequence approximately 2.35x10 14 chips long (235,000,000,000,000 chips). Each satellite repeatedly transmits its assigned segment of the master code, restarting every Sunday at 00:00:00 GPS time. (The GPS epoch was Sunday January 6, 1980 at 00:00:00 UTC, but GPS does not follow UTC leap seconds. So GPS time is ahead of UTC by an integer number of seconds.) An interesting side effect of having each satellite transmit four separate signals is that the MNAV can potentially transmit four different data channels, offering increased data bandwidth. The second advancement is to use forward error correction (FEC) coding on the NAV message itself. Due to the relatively slow transmission rate of NAV data (usually 50 bits per second), small interruptions can have potentially large impacts. Therefore, FEC on the NAV message is a significant improvement in overall signal robustness. General features [ edit ] A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 45°N, changes with time.

An ephemeris is valid for only four hours; an almanac is valid with little dilution of precision for up to two weeks. [7] The receiver uses the almanac to acquire a set of satellites based on stored time and location. As each satellite is acquired, its ephemeris is decoded so the satellite can be used for navigation. The delay for PRN numbers 34 and 37 is the same; therefore their C/A codes are identical and are not transmitted at the same time [5] (it may make one or both of those signals unusable due to mutual interference depending on the relative power levels received on each GPS receiver).

The L1C pilot and data ranging codes are based on a Legendre sequence with length 10 223 used to build an intermediate code (called a Weil code) which is expanded with a fixed 7-bit sequence to the required 10,230 bits. This 10,230-bit sequence is the ranging code and varies between PRN numbers and between the pilot and data components. The ranging codes are described by: [37] L1C i ( t ) = L1C ′ ( t mod 10 230 ) L1C i ′ ( t ′ ) = { W i ( t ′ ) if t ′ < p i ′ S ( t ′ − p i ′ ) if p i ′ ≤ t ′ < p i ′ + 7 W i ( t ′ − 7 ) if t ′ ≥ p i ′ + 7 S = ( 0 , 1 , 1 , 0 , 1 , 0 , 0 ) W i ( n ) = L ( n ) ⊕ L ( ( n + w i ) mod 10 223 ) L ( n ) = { 1 if n ≠ 0 and there is an integer m such that n ≡ m 2 ( mod 10 223 ) 0 otherwise {\displaystyle {\begin{aligned}{\text{L1C}}_{i}(t)&={\text{L1C}}'(t{\bmod {10\,230}})\\{\text{L1C}}'_{i}(t')&={\begin{cases}W_{i}(t')&{\text{ if }}t'

The P-code is a PRN sequence much longer than the C/A code: 6.187104x10 12 chips. Even though the P-code chip rate (10.23 Mchip/s) is ten times that of the C/A code, it repeats only once per week, eliminating range ambiguity. It was assumed that receivers could not directly acquire such a long and fast code so they would first "bootstrap" themselves with the C/A code to acquire the spacecraft ephemerides, produce an approximate time and position fix, and then acquire the P-code to refine the fix. In each subframe, each hand-over word (HOW) contains the most significant 17 bits of the TOW count corresponding to the start of the next following subframe. [14] Note that the 2 least significant bits can be safely omitted because one HOW occurs in the navigation message every 6 seconds, which is equal to the resolution of the truncated TOW count thereof. Equivalently, the truncated TOW count is the time duration since the last GPS week start/end to the beginning of the next frame in units of 6 seconds.

A dataless acquisition aid is an additional signal, called a pilot carrier in some cases, broadcast alongside the data signal. This dataless signal is designed to be easier to acquire than the data encoded and, upon successful acquisition, can be used to acquire the data signal. This technique improves acquisition of the GPS signal and boosts power levels at the correlator. Pre-operational signal with message set "unhealthy" until sufficient monitoring capability established