4.3 Green Networking and Resource Constrained Clients for Smart Cities

The Internet of Things (IoT) will enable a variety of new use cases by linking billions of IoT devices. Introducing new use cases each day, IoT devices will be found everywhere in the future. With a new generation of resource-constrained clients, communication networks have to face new challenges such as high communication ranges, small data transmission efficiency, and large scalability. With the Narrowband Internet of Things (NB-IoT) and enhanced Machine Type Communication (eMTC), cellular communication solutions have been adapted to these new challenges. Including mechanisms for larger communication ranges as well as lower power consumption, NB-IoT and eMTC aim to fulfil the requirements defined by new massive Machine Type Communication (mMTC) use cases. While performance is often only optimized on the lower layers, upper layers including transmission and application protocols need to be addressed by reducing overhead and enabling efficient small data transmissions in order to deliver good performance for resource-constrained clients. This section describes the achievements in evaluating the performance of Low-Power Wide-Area Network (LPWAN) solutions for resource-constrained clients in terms of energy efficiency, spectral efficiency, and latency. Therefore, new cellular IoT features for power saving and coverage extension are explained in detail, while taking the costs for the scalability of the networks into account.With this knowledge, a performance analysis of resource-constrained LPWAN clients with different coverage conditions is provided. Although both NB-IoT and eMTC use the same power-saving techniques as well as repetitions to extend the communication range, the analysis reveals a different performance in the context of data size, rate, and coupling loss. While eMTC comes with a 4% better battery lifetime than NB-IoT when considering 144 dB coupling loss, the NB-IoT battery lifetime has 18% better performance in 164 dB coupling loss scenarios. The overall analysis shows that in coverage areas with a coupling loss of 155 dB or less, eMTC performs better, but requires much more bandwidth. Taking the spectral efficiency into account, NB-IoT is in all evaluated scenarios the better choice and more suitable for future networks where the number of devices connected is expected to be close to or go beyond the network capacity. While communication is possible with coupling losses up to 164 dB, the results show that the overall performance is very limited with decreasing signal quality. Although being designed for extended coverage, the mobile network operators should continuously improve the signal quality for both uplink and downlink directions. When increasing the number of base stations is not feasible, alternative signal quality improvement solutions should be addressed. In this context, the coverage and link quality improvement of cellular IoT networks with multi-operator and multi-link strategies was evaluated as a case study, using the smart city Dortmund, Germany. The results show that the link quality can be improved by up to 13.6 dB, which enables shorter time-on-air for resource-constrained devices and thus drastically improves the energy and spectral efficiency.