Code division multiplexing CDM or code division multiple access CDMA is a method of sharing channels. Each user can communicate using the same frequency band at the same time. An important feature of the CDMA system is that this
system allocates to each station Not only must the chip sequences be distinct, they must also be orthogonal to each other.
- The orthogonal result is 1, indicating that 1 was sent
- The orthogonal result is 0, which means no data is sent.
- The orthogonal result is -1, indicating that 0 was sent
example:
1. A total of 4 stations perform code division multiple access CDMA communication. The chip sequences of the 4 stations are:
A.(-1 -1 -1 +1 +1 -1 +1 +1)
B(-1 -1 +1 -1 +1 +1 +1 -1)
C.(-1 +1 -1 +1 +1 +1 -1 -1)
D.(-1 +1 -1 -1 -1 -1 +1 -1)
The chip sequence is received first: (-1 +1 -3 +1 -1 -3 +1 +1) Which station sent the data? Is the data sent 1 or 0?
untie:
S is orthogonal to A = (+1-1+3+1-1+3+1+1)/8 = 1 A sent 1
S is orthogonal to B = (+1-1-3-1-1-3+1-1)/8 = -1 B sent 0
S and C are orthogonal = (+1+1+3+1-1-3-1-1)/8 = 0 C does not send data
S and D are orthogonal = (+1+1+3-1+1+3+3-1)/8 = 1 D sent 1