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Reducing CO 2 emissions is an important global environmental issue. Over the recent years, wireless and mobile communications have increasingly become popular with consumers. An increasingly popular type of wireless access is the so-called Wireless Mesh Networks (WMNs) that provide wireless connectivity through much cheaper and more flexible backhaul infrastructure compared with wired solutions. Wireless Mesh Network (WMN) is an emerging new technology which is being adopted as the wireless internetworking solution for the near future. Due to increased energy consumption in the information and communication technology (ICT) industries, and its consequent environmental effects, energy efficiency has become a key factor to evaluate the performance of a communication network. This paper mainly focuses on classification layer of the largest existing approaches dedicated to energy conservation. It is also discussing the most interesting works on energy saving in WMNs networks. KEYWORDSWireless mesh network (WMN), 802.11s, energy saving, routing protocols, MAC protocols. ENERGY CONSERVATION IN NETWORK LAYERThe network layer is responsible for network self-configuration and data routing. For configuring network topology, the network layer select an appropriate mode for a node and determines the most suitable neighbors with which to associate and form communication links.The routing protocols enable a network to make dynamic adjustments to its conditions; these decisions do not have to be predetermined and static. Even though the routing protocols functions are plausible, they still face challenges in energy efficiency.Routing protocols can be classified into three, namely: Table-driven, the Demand-driven and the Hybrid routing protocols. The table-driven routing protocols are also known as proactive routing protocol; each node maintains one or more tables which have routing information to all other nodes within the network. In this protocol, all nodes update each other on the same network and further update their tables to maintain a consistent and up-to-date view of the network. Demand-driven well known as reactive routing protocols creates routes only when desired by the source node [6]. When a node requires a route to its destination, it initiates a route discovery process within the network. The process is completed once a route is found or all possible route permutations had been examined. The hybrid routing protocols combines both the table-driven and the Demand-driven routing protocols to transport the packets from the source to the destination. It takes both the advantages of table-driven and on demand-driven routing protocols. One of the popular Hybrids routing protocol in the WMN is Hybrid Wireless Mesh Protocol (HWMP) [7]. This is a default routing protocol for IEEE 802.11s, which is consists of two features, namely: it is table-driven; and also an on-demand protocol. This protocol is based on the protocol called RM-OADV (Radio Metric-Ad Hoc on-Demand Vector) routing protocol, which is the extension of AODV. ...

Heterogeneous wireless networks is a term referring to networks combining different radio access technologies with the aim of establishing the best connection possible. In this case, users with multi-mode terminals can connect via different wireless technologies, such as 802.16, 802.11, UMTS, HSPA and LTE, all at the same time. The problem consists in the selection of the most suitable from all radio access technologies available. The decision process is called network selection, and depends on several parameters, such as quality of service, mobility, cost, energy, battery life, etc. Several methods and approaches have been proposed in this context, with their objective being to offer the best QoS to the users, and/or to maximize re-usability of the networks. This paper represents a survey of the network selection methods used. Multiple attribute-dependent decision-making methods are presented. Furthermore, the game theory concept is illustrated, the use of the fuzzy logic is presented, and the utility functions defining the network selection process are discussed.

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