Symbol error probability for double selection/equal gain combining of branches in a Rayleigh fading environment without channel statistical information

We present a new, exact, expression for the symbol error probability of a diversity system which selects the 2 largest branches out of N available and combines them using equal gain combining. The system operates in a Rayleigh fading environment but does not make any assumptions about the channel statistics. Furthermore, an approximation for the high SNR, static fading case is derived which provides insight into the effect of the noise power distribution among the branches to the error performance of the system