CDMA systems knowledge

1 CDMA system concept
CDMA system is based on code division technology (Spread Spectrum) and multiple access technology, communication systems, the system for each user allocated address their specific code. Address code between each other quasi-orthogonal, in order to time, space and frequency can overlap; will be required to send the signal has a bandwidth of the data, with a bandwidth of the signal bandwidth is much larger than the pseudo-random code modulation, so that The original data signal bandwidth has been expanded to carry out the receiving end to the anti-process for expanding access, and enhanced anti-jamming capabilities.
CDMA systems belonging to the sub-interference system.
2 CDMA system:
0:00 systems: the definition at 0:00 on the January 6, 1980 for the whole system start-up time. Bias zero yards long and short code at the same time, at this time of the initial state
GPS base stations will be all the time even seconds of each start-up time (80ms or after the entire Department several times) as a PN code offset 0 (for the period 80 / 3 ms) at the beginning of the state, that is, before that happens to the output A "1" in a row and 15 "0" such a chip PN
All base stations will be required at 0:00 on the January 6, 1980 (GPS start-up time) as a long sequence of m-code at the beginning of (this happens before the output of a "1" chip in a row and 41 of the "0" Chip )
The use of GPS timing of benefits: fast switching, and simple synchronization.
3 CDMA system shortcomings:
From non-synchronous CDMA network in a different sequence spread spectrum users are not completely orthogonal, which led to the MAI;
Due to use the same carrier frequency, many users share the same channel, the signal of a weak signal inhibited, resulting in "far - close to the" effect of the impact of user calls.
CDMA system using power control technology "--- far into the" effect