This paper concerns power allocation in relay-assisted wireless channels for two-hop transmission. First, the transmitter sends the information to both the relay and receiver parts. Next, in the second hop, the transmitter cooperates with the relay to increase the received signal to noise ratio (SNR), assuming the relay makes use of the Amplify and Forward (AF) strategy. Moreover, it is assumed a linear combiner is employed at the receiver to effectively combine the received signals of two hops. In this regard, under total transmit power constraint, an iterative power allocation strategy together with a proper combining method is proposed, showing the proposed approach achieves a comparable SNR as compared to the best known methods addressed in the literature, while having much lower complexity.