Wireless technology provides an array of applications viz wireless phones,wireless Internet access &WLAN.These systems are prone to performance degradation due to multipath fading, pol. mismatch So Service,Quality,Security and Capacity are of primary importance.To solve these space time processing is used,that is signal processing performed on a system in both the spatial and temporal dimensions of the radio cannel.These can be applied at the Tx or Rx or both.At the Receiver MIMO techniques are used.Rx Diversity schemes are MRC,EGC &SC.Of these MRC is considered as it provides the maximum SNR at the output.In MRC the output signal is the weighted sum of the input signals present at the input of the array.In a practical combiner the channel can never be estimated perfectly because of multipath fading. This results in errors in channel estimation which effect the weighing factors of the combiner.The performance of the MRC degrades w.r.t.output SNR and BER. Here the effects of imperfect channel estimation resulting in gaussian errors in the weights of MRC are studied.Performance of MRC in different fading channels with imperfect channel estimates & digital mod.tech. is analyzed.