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Energy efficiency (EE) is currently the key performance evaluation metric for wireless networks. This paper considers the maximization of EE of an uplink wireless network that uses single‐carrier frequency division multiple access. The EE metric considered is bits/Joule, and a joint power and subchannel allocation problem is formulated to maximize this EE metric under constraints on the minimum achieved data rate of each user, the maximum transmit power budget of each user, and the exclusive as well as the consecutive allocation of single‐carrier frequency division multiple access subchannels among the users. This problem is a nonlinear and combinatorial optimization problem, and its optimal solution is prohibitively difficult. To make the problem tractable and find its optimal solution, it is transformed into an equivalent binary integer programming problem, which is a standard set partitioning problem. This approach named as the optimal energy‐efficient (OPT‐EE) algorithm finds optimal solution with significantly reduced computational complexity compared to the solution of the original problem. In addition, a heuristic suboptimal energy‐efficient approach is also investigated, which has acceptable performance with much less computational complexity compared to the OPT‐EE algorithm. Simulation results demonstrate the performance of OPT‐EE and heuristic suboptimal energy‐efficient algorithms and their comparison with the available work in the literature.

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The Internet of Engineering Task (IETF) developed a lighter application protocol (Constrained Application Protocol (CoAP)) for the constrained IoT devices operating in lossy environments. Based on UDP, CoAP is a lightweight and efficient protocol compared to other IoT protocols such as HTTP, MQTT, etc. CoAP also provides reliable communication among nodes in wireless sensor networks in addition to features such as resource observation, resource discovery, congestion control, etc. These capabilities of CoAP have enabled the implementation of CoAP in various domains ranging from home automation to health management systems. The use of CoAP has highlighted its shortcomings over the time. To overcome shortcomings of CoAP, numerous enhancements have been made in basic CoAP architecture. This survey highlights the shortcomings of basic CoAP architecture and enhancements made in it throughout the time. Furthermore, existing challenges and issue in the current CoAP architecture are also discussed. Finally, some applications with CoAP implementation are mentioned in order to realize the viability of CoAP in real world use cases.