Nowadays with the introduction of smart phones along with the development of audio and video applications increases people's demands for the ubiquitous high-data rate coverage. One of the cost-effective solutions adopted in the Long-Term Evolution (LTE) standard that extends coverage and enhances throughput is the placement of heterogeneous nodes: low-power Relay Nodes (RNs) are deployed to assist transmissions between an evolved Node B (eNB) and multiple User Equipments (UEs). In this framework resource allocation becomes an important and crucial problem that directly influences the potential capacity and coverage improvements. In this paper an overview of the basic relaying concept is provided. Furthermore, resource allocation in a relay-enhanced LTE network is discussed. Lastly, an efficient analytical model for a relay-enhanced LTE downlink channel is presented in detail. Various resource allocation schemes are analyzed, among which the proportional one achieves the best performance.