###### Abstract
Therefore, 5G RedCap could be considered as LPWAN-MHS (medium-high speed), i.e., an LPWAN with medium to high-speed applications support based on the specification for improved distance and low power. Moreover, other challenges exist, such as coexistence, interference, spectrum insufficiency, and scalability issues, due to this heterogeneity densification. These problems can affect the quality of service (QoS) requirements of IoT applications, including performance degradation of LPWAN devices. Several methods have been advocated to address these problems. For instance, in addressing the problems of interference and spectrum insufficiency, the authors in [8] suggested that spectrum allocation can be moved from the 2.4 GHz band to a license-free spectrum in the sub-1 GHz free band. However, as the use cases increase in the sub-1 GHz band due to IoT network densification, this band will face comparable interference issues to the 2.4 GHz band. Further, the use of multi-radio access technology (multihoming) integration has been suggested in [9] in dealing with the problems of coexistence and scalability issues. Consequently, to circumvent the identified problems, this paper proposes a lightweight heterogenous network model for enabling LPWANs' coexistence and diverse IoT applications in a heterogenous dense smart city's IoT network. Hence, to actualize this, the following objectives are enumerated:  
* To integrate a manageable license-free LPWAN that will coexist with 5G private and public cellular networks. * To develop an LHM-N model for enabling the coexistence of different LPWANs. * To provide a very cost-effective solution model in a heterogeneous dense smart city environment. * To develop a secured, lightweight, energy-efficient packet-size forwarding engine (PSFE) algorithm. To this end, the original contributions of this paper include:  
* Proposing a model with a low error rate that improves the data throughput by a magnitude of over five times more than the conventional quadrature amplitude modulation (QAM) protocol scheme with reduced energy cost for medium- to high-bandwidth industrial IoT (IIoT) applications. * Optimizing the Physical (PHY) layer protocol of 5G reduced capability (RedCap) IoT devices to operate comparatively with LPWAN in terms of signal-to-noise ratio (SNR) symbol energy while maintaining medium to high data throughput. * Designing and implementing a lightweight heterogenous multihomed network (LHM-N) model for diverse smart city applications. * Advocating and incorporating a manageable license-free LPWAN coexistence with 5G private and public cellular networks to provide a very cost-effective solution model in a heterogeneous dense smart city environment. * Proposing a packet-size forwarding engine (PSFE) algorithm for secured lightweight energy-efficient and minimized errors in packet forwarding. * Integrating a 5G reduced capability (RedCap) IoT device in the multihomed LPWAN solution model, thereby supporting high-bandwidth smart cities applications, such as industrial wireless sensors (smart manufacturing/smart factory), video surveillance, etc. The rest of this paper is organized as follows: In Section 2, related works are discussed. Section 3 presents the architecture and design methodology of the lightweight heterogenous multihomed network (LHM-N) model. The implementation of the LHM-N model is carried out in Section 4. Results and analysis are presented in Section 5. Finally, Section 6 provides the concluding remarks of the paper.