23-05-2012, 03:43 PM
CDMA methods
CDMA methods.ppt (Size: 374 KB / Downloads: 33)
History of CDMA
A method for multiple access
(single channel , multiple users)
The conventional methods were FDMA
Then after developing synchronization TDMA was developed in early 1980s it was introduced
Its first use was done in military
in early 1990s its first use was done in cellular communication system
Different CDMA methods
CDMA is infact a
SPREAD SPECTRUM(SS) method
Special features of SS are resistance to
Signal Exploitation
Spoofing
Hence military or intelligence application
PN(pseudo noise) codes
PN –CODE is a sequence of high data rate bits(“chips”) ranging from –1 to + 1 (polar)
or 0 to 1 (non polar).
By “chips” we mean the no. of small data bits in the PN-CODE per single bit of the original signal
They are either linear codes generated by EX-OR gates used in shift register feedback path or otherwise non linear codes. Hence, greater “chips” used results in a wider bandwidth
Power Management
Breathing :varies attenuation in the forward link
Wilting :gradual decrease in the transmitted power of the base station to bring down a sector
Blossoming: gradual increase of power in the new sector