Abstract
The concept of relaying was raised recently in networking world. This technology has a great impact on multi-hop wireless networks. There had been many research studies on the role of Relay Node placement in Multi-hop Wireless Networks. Therefore, in this paper a comprehensive review on the strategies and techniques of Relay Node placement in MWNs, categorized based on either ad hoc or infrastructure-based, is presented. Ad hoc category contains WSNs strategies and techniques which classified into quality of service, fault tolerance, Federating disjoint segments and connectivity restoration. While Infrastructure-based includes WiMAX, Wireless Mesh Networks and LTE-Advanced networks. This work proposes open research ideas in this filed. As a result, several findings and recommendations are emerged that greatly direct the researchers to new and important research areas.