Heterogeneous networks (HetNets) are likely to provide ubiquitous access to mobile broadband services as they involve various small cells, each targeting a different environment in the network. In this paper, we are interested in improving the system performance at the cell edge. Hence, we consider a HetNet composed of an eNodeB (eNB) coexisting with different relay nodes (RNs) situated at the cell border. We propose a cooperative physical resource blocks (PRBs) sharing scheme in a dual-hop LTE-Advanced in which every node can transmit on some of the PRBs assigned to a coexisting node without causing it harmful interference. To do so, we use a powerful mathematical tool, i.e., game theory. First, we consider two nodes in the macrocell and define a new repeated game in which a selfish node is encouraged to cooperate under the threat of punishment. Then, we enlarge the number of RNs in the network and find the optimal pairs of nodes that will cooperate, due to a new coalition formation game. Simulation results show that the proposed cooperative PRB sharing scheme significantly improves the utilization of the spectrum and the achieved total throughput in the system. We also demonstrate that both games rapidly attain Pareto efficiency.