In this article we present the major challenges of future machine-to-machine (M2M) cellular networks such as spectrum scarcity, and support for a large number of low-power, lowcost devices. As an integral part of the future Internet-of-Things (IoT), the true vision of M2M communications cannot be reached with conventional solutions that are typically cost inefficient. The cognitive radio concept has emerged to address spectrum under-utilization and scarcity. The heterogeneous network model is another alternative to relax the number of covered users. To this extent, we present a complete fundamental understanding and the engineering details of cognitive radios, the heterogeneous network model, and power and cost challenges in the context of future M2M cellular networks.pre-prin
Similar to all mobile communication networks, synchronization in the time-frequency domain is a fundamental step that allows a fifth-generation (5G) new radio (NR) user equipment (UE) to properly receive and transmit its data. Due to the wide range of frequencies that are defined for the 5G NR systems, the corresponding synchronization procedure becomes critical and presents many challenges, especially for the applications that would need accurate oscillators to reduce the large values of the frequency offset. In this paper, we present and detail the 5G NR physical layer. Then, we describe the required synchronization procedure for 5G NR. And finally, we present the main challenges and issues within the 5G NR synchronization.INDEX TERMS 5G NR systems, beam management, physical layer, frequency offset, time offset, synchronization procedure.
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