Cooperative relaying is an important feature for the fourth generation wireless system to upgrade system performance. Mobile relays can offer better results than fixed relays without any additional infrastructure cost. However, efficient cooperation decision as well as resource allocation are critical to satisfy model constraints as required quality of service (QoS). In this work, simple mobile users with advantageous channels can act as potential relays for cell edge users for an uplink transmission. They multiplex, in the frequency domain, their own data to that of the relayed sources, with the objective for both relay and sources to reach a target data rate. An optimal joint resource blocks (RB) allocation and power allocation scheme under a required data rate constraint per user is proposed. The optimization problem is formulated to minimize the total system power. Dual decomposition and subgradient method are used to solve the optimization problem after dividing it into independent subproblems with less complexity to find the optimal solution. The cooperation decision and the sources-relays association is either performed as a first step of resource allocation, or jointly optimized with RB and power allocation. Simulation results show that these proposed algorithms both reduce system's power consumption while ensuring the required QoS. Joint optimization of relay selection, RB and power allocation provides a higher power consumption decrease, but requires higher complexity and overhead.