An Approximation of the Outage Probability for Multi-hop AF Fixed Gain   Relay
  In this letter, we present a closed-form approximation of the outage probability for the multi-hop amplify-and-forward (AF) relaying systems with fixed gain in Rayleigh fading channel. The approximation is derived from the outage event for each hop. The simulation results show the tightness of the proposed approximation in low and high signal-to-noise ratio (SNR) region. 
Jun Kyoung Lee, Janghoon Yang, Dong Ku Kim