To analyze the performance of cooperative communication wireless network, the bit error rate (BER) and probability of outage of the system are considered for a given transmitted signal to noise ratio (SNR).

Average Signal-to-Noise Ratio (y): It is measured at the output of the receiver and is thus related directly to the data detection process itself. It is easiest to evaluate among all the existing system performance measures. It serves as an excellent indicator of the overall fidelity of the system. The term noise in signal to noise ratio refers to the thermal noise which is present at the input of the receiver in the context of a communication subject to fading impairment. The more appropriate performance measure is average SNR (y) where the word average refers to statistical averaging over the probability distribution of the fading.

n CO

Average SNR, ^ JQ yPy (y) dy

P Y (у) denotes the probability density function (PDF) of y.

Outage Probability (P„ut): It is defined as the Probability that the instantaneous error probability exceeds a specified value or equivalently, the Probability that the output SNR, Y, falls a certain specified threshold Yth. Threshold value of total SNR is the value at which system is not in outage. Outage is a condition of a system at which user becomes unable to get the proper service from the system.

Pout = JorthPY (Y )dY

Pout is equal to the CDF (cumulative distribution function of Y, namely, PY (Y), evaluated at Y = Yth.

Average Bit Error Probability (BEP): It is the most difficult of the three to compute. On the other hand, it is the one that is most revealing about the system behaviour. The difficulty arises in its evaluation because of the fact that the conditional BEP is in general a non-linear function of the instantaneous SNR, the nature of the nonlinearity being a function of the Modulation/detection scheme employed by the system. Thus we sum up that cooperative communication is an emerging paradigm where multiple mobiles share their bandwidth and power (resources) to achieve better overall performance. Performances can be investigated by different measures as discussed above. We are going to investigate and analyse the performance of different cooperative communication schemes under different fading environments.

Continuous research is done to analyse and improve the performance of decode and forward,,,,, amplify and forward,,, and coded cooperation,,,,.

*CONCLUSIONS*

This paper presents an extensive insight into cooperative wireless communication, which creates a virtual MIMO and helps single antenna users to achieve spatial diversity. Three types of cooperative signaling techniques are explained with their advantages in this paper. System performance evaluation is also done. Research till now indicates that the cooperative communication is going to be the characteristic feature of wireless communication.