This paper presents a performance closed-form error analysis of cooperative relaying communications with fixed gain and CSI-assisted relays. We derive analytical expressions for the performance of cooperative transmission between a source terminal and a destination terminal using a relaying model. More specifically, we first evaluate the statistical behavior of two multipath fading channels: Rayleigh fading and Rician fading and study the probability density functions of the fading amplitude and the instantaneous signal-to-noise ratio (SNR) per symbol of the channel. Next, we present both simulation and theoretical bit error rate performance of two relaying methods: Amplify-and-Forward (AF) and Decode-and-Forward (DF).