## 3 Wireless Communication Networks
* _Transmission agreements._ Transmission power, modulation format, and frequency of operation are some examples of parameters agreed in this phase. * _Topology and routing._ The interconnection network defines the topology, i.e., the available communication links among nodes establishing the architecture, while routing defines the paths that follow the information to reach its destination. * _Management scheme._ There are schemes that ensure the operation, access to channel, and control of transmission parameters. Presently, dynamic and intermittent behavior of WE represent relevant challenges for networking, so the new requirements of WCN such as flexibility in architecture, mobility, and high traffic play a very important role for modern networks. Reconfigurable ability is considered a prominent network paradigm for future WCN [28]. Besides, high density of WE also represents additional challenges due to closeness of WE and the phenomena that it involves, e.g., multiuser channel access problem, multiuser, and multiple access interferences. Reconfigurable wireless networks (RWN) are dynamic networks suitable for the frequent changes in topology, connectivity, routing, WE status, and wireless channel conditions. These networks have the ability of modifying their configuration, with or without infrastructure, that establish the allocation decisions; self-organization networks imply an _intelligence_ process, which can have centralized or no centralized management, that make them attractive to networks as sensors and ad-hoc. The access to resources and multiple transmissions in WCN face important challenges such as:  
* _Coexistence._ It consists of the study of the presence of WE in a given area, the communication among WE, and their influence in the wireless communication channel. Coexistence schemes ensure the communication of multiple WE through the management and distribution of resources. * _Energy efficiency._ It refers to the efficient use of energy by WE. Strategies seeking to extend the lifespan of battery due to the limited source of energy. Thus, there are strategies based on efficient routing, schedule, low processing systems, and topology and traffic control which reduce the energy consumption from different aspects. * _Interference._ The received signals from wireless channel can be distorted due to the presence of interference which can be caused by natural or transmission factors. Hence, techniques for mitigation, avoidance, cancelation, and management interference play an important role. * _Reception algorithms._ It refers to strategies used to extract the information from the channel. The study of algorithms based on reception and detection strategies are proposed which can be classified according to the techniques and methodologies used [29]. * _Security._ Protocols and strategies that provide privacy and authentication of information to avoid vulnerabilities due to malicious eavesdropping. * _Complexity._ It refers to the difficulty of resolving computational problems through efficient algorithms. Communication systems used for RWN use orthogonal or semi-orthogonal multiple access channel techniques to avoid multiple users channel problems. They consider temporal, spectral, and spatial dimensions to separate users. However, their implementation requires to control the access to resources using elaborated schemes and protocols to ensure the communication. These devices have limited resources such as low power, computing capacity, narrow bandwidth transmission, so on, high sensibility to interference, and autonomous behavior. New trends incorporate a communication system that allows the formation of temporal wireless reconfigurable networks (WRN), i.e., sensors and ad hoc networks, that share information by establishing communication links through technologies and schemes that ensure their operation in free bands or unlicensed, e.g., BLE, ZigBee, and WiFi in the bands 2.4 and 5 GHz. The high density of WDs leads the multiuser channel problem, which occurs when multiple users share spectrum resources.