This paper proposes a study on the performance of multi-hop relays networks. We demonstrate the importance of the relays for coverage and capacity enhancement and study how the number of relays and their position inside the cell impact the performance, and how an efficient relay location scheme can guarantee better performance with less relays per cell. Further we give an estimation of the amount of power per square meter on the ground when relays are used, with respect to traditional network, showing the fundamental role of relays for green networking. We consider the downlink of an LTE-Advanced network, in which all the User Equipments (UE) are supposed to be attached to the eNode-B (eNB) or Relay Node (RN) from which they receive more power. Numerical results are obtained through Monte-Carlo simulations and the performance measures are represented by the average effective Signal to Interference and Noise Ratio (SINR) and the average spectral efficiency.