Code Division Multiple Access (CDMA) phần 5 ppt

P1: IML/FFX P2: IML

MOBK023-02 MOBK023-Buehrer.cls September 28, 2006 15:54

68 CODE DIVISION MULTIPLE ACCESS (CDMA)

10 15 20 25 30 35

10-6

10-5

10-4

10-3

10-2

10-1

Eb

/No

(dB)

Probability of bit error

No diversity

Diversity order 2

Diversity order 4

Diversity order 8

FIGURE 2.32: Performance of FH/SS with non-coherent BFSK modulation with various levels of

diversity.

distributed and are assumed random and memoryless, and (e) perfect power control is achieved

at the receiver.

The probability of error for FH-CDMA can be written as [35]

Pe = Po (1 − Ph ) + P1Ph (2.89)

where Po is the probability of error when there are no collisions (or hits) between users (i.e.,

when two users avoid hopping to the same frequency at the same time), Ph is the probability

of at least one hit, and P1 is the probability of error when at least one hit has occurred. With

BFSK and non-coherent reception, the probability of error in the absence of collisions is [22]

Po = 1

2 exp

−1

2

Eb

N0

(2.90)

Now, with independent random hopping codes, the probability of at least one hit can be written

as

Ph = 1 − (1 − P2)

K−1 (2.91)