We analyzed and dissected the spectral efficiency gain of an uplink Cognitive Radio (CR) Multi-Input-Multi-Output system in which the Primary User (PU) shares the spectrum with the Secondary User (SU), using a specific pre coding scheme to communicate with a common receiver. The main contemplation of our proposal is the selection of relay and to analyze spectrum sharing in cognitive radio networks and to perform the selection of relays models to reduce the interference of primary region and achieve the maximize rate in secondary region. We are implementing Multiple Relays to carry out the communication even more effectively, we are also using ARP(Alternating Relay Protocol) to increase the data rate in the primary side and to reduce the interference in the secondary side, appending to this we are using Monte Carlo Algorithm for continuous iteration of communication because communication always should be in a continuous form to increase its efficiency, so for this reason we use this algorithm because it not only allows the iteration of communication in a continuous form but also it reduces the power consumption which also make economically feasible and finally we are using Frequency Selective Fading to select the frequency range according to our rationale and we are not using TDMA and CDMA which basically involves lot of disadvantages like the selection of the desired time slot and apposite users which will suit for only certain type of communication as it will be found to have many disadvantages, so in our paper the implementations which we made is found to stand as a strong refuge in meeting the customer satisfaction and also it is found to be economically feasible. At the common receiver, we also adopt a Successive Interference Cancellation (SIC) technique to eliminate the effect of the detected continuous interference in the primary signal. We exemplify that a water-filling power allocation algorithm at the Primary User which can increase the secondary rate with a complete elimination of interference in the primary side and also the power consumption is found to be low as we are amending this water filling algorithm with the multiple relays and also it initiates the increase in the data rate to ensure the more effective communication.