|
|
От
|
NetReader
|
|
|
К
|
MG151
|
|
|
Дата
|
27.01.2002 17:00:33
|
|
|
Рубрики
|
Армия; ВВС; Космос;
|
|
Re: GPS
>Сейчас амеры начали делать приемники GPS как систему наведения в высокоточном оружии, а как они решают проблему помех? Ведь GPS это ненаправленный приемник, а сигнал от спутника весьма слабый и имхо забить его помехами весьма просто.
В GPS используются широкоугольные, но направленные (в верхнюю полусферу) антенны и шумоподобный кодированный сигнал, и забить его помехами "не весьма" просто. Помеха должна высоко висеть и уметь излучать ТАК ЖЕ, как настоящие спутники GPS. Простым свистом тут не обойдешься :)
http://www.colorado.Edu/geography/gcraft/notes/gps/gps_f.html
"GPS Satellite Signals
The SVs transmit two microwave carrier signals. The L1 frequency (1575.42 MHz) carries the navigation message and the SPS code signals. The L2 frequency (1227.60 MHz) is used to measure the ionospheric delay by PPS equipped receivers.
Three binary codes shift the L1 and/or L2 carrier phase.
The C/A Code (Coarse Acquisition) modulates the L1 carrier phase. The C/A code is a repeating 1 MHz Pseudo Random Noise (PRN) Code. This noise-like code modulates the L1 carrier signal, "spreading" the spectrum over a 1 MHz bandwidth. The C/A code repeats every 1023 bits (one millisecond). There is a different C/A code PRN for each SV. GPS satellites are often identified by their PRN number, the unique identifier for each pseudo-random-noise code. The C/A code that modulates the L1 carrier is the basis for the civil SPS.
The P-Code (Precise) modulates both the L1 and L2 carrier phases. The P-Code is a very long (seven days) 10 MHz PRN code. In the Anti-Spoofing (AS) mode of operation, the P-Code is encrypted into the Y-Code. The encrypted Y-Code requires a classified AS Module for each receiver channel and is for use only by authorized users with cryptographic keys. The P (Y)-Code is the basis for the PPS.
The Navigation Message also modulates the L1-C/A code signal. The Navigation Message is a 50 Hz signal consisting of data bits that describe the GPS satellite orbits, clock corrections, and other system parameters."