Performance Analysis for Bit Error Rate of DS- CDMA SensorNe(3)

TELKOMNIKA

ISSN: 1693-6930 167

The output of the correlation receiver for user 1, at t = Tb is= + + , where is the desired received signal for user number 1, is the interference from other users and is the AWGN term with variance of /2. In other words, the three terms are:

= ( )

= ∑ /2.{ .Γ , +Γ ( )}

= ( )

The Γ , and Γ ( ) are the continuous – time partial cross correlation function defined as followes:

Γ , = ( )

Γ = ( )

Pd1= 1/T( 0(b ) dt = 2b if ( ) {0,1} (5)

Where 1is the percentage of high bits for m1(t) during the transmission duration of T second. The MAI and AWGN powers can be shown to be

2 Pn1= N0 Tb / 4 + ∑ (6) =2( 1 Pk / 2 ) σ

So, the SNR in the energy-efficient DS-CDMA system can be found as

2 SNR = P1 /(( 1N0Tb/2) + ∑ Pk σ ) (7)

For analyzing influence error probability of a CDMA receiver several schemes have been presented in the literature over the past couple of years. The approach that first appeared in [7] is followed in this study. And, the MAI is assumed sufficiently well represented by an equivalent Gaussian random process with assuming that the power control for all the transmitters signals arrive at the receiver of transmitter high bit for each transmitter are same, i.e., 1 = 2 = …= .. For such condition Eq. (7) can be further simplified as

To evaluate the system performance the signal to noise ratio (SNR) is analyzed. The SNR is a perfect index to evaluate the quality of the received signal. So, to find the (SNR), the signal power of the ( ) is computed as ( )2 2( )

SNRME=( 1{

where is energy per bit and is the node density.

The bit error usually occurs in moving from high bit signal into a lower bit signal or vice

versa. The average error probability of reciver1 for transmitting one bit as:

= . ≥ | =0 + . < | =1 (9)

where is the probability of transmitting "zeros" signals and is the probability of transmitting "ones" signals for the first transmitter and δ is the threshold for bit detection. If =0; the output of the integrator can be explained to

1 -1+ (8) 3 2

Performance Analysis for Bit-Error-Rate of DS-CDMA Sensor Network …. (Ali M. Fadhil)