## 3 Architecture and Design Methodology of the LHM-N Model  
### Lightweight Heterogenous Multihomed Network (LHM-N) Architecture  
The LHM-N architecture ensures the connection of sensing end devices (EDs), gateway/radio modules, and end-to-end connectivity to the various servers and entities. This helps the transmission of status, sensed data, and control messages throughout the entire IoT ecosystem. The adopted architecture in LHM-N employs a special mixed topology approach:  
1. The usual cellular network topology, in which EDs communicate directly with gateway/base station (BS), then from BS to network server/entity, and then to the IoT cloud.
2. The communication of EDs with the gateway, then from the gateway directly to the cloud, and then to the server.  
The network employs a 5G private network as the main backhaul over an unlicensed spectrum band. In cases where there is no available 5G private network, a licensed 5G public network is utilized as an alternative backhaul from the commercial cellular network operator. Figure 1 demonstrates the end-to-end connectivity and highlights the network architecture in LHM-N, which comprises the following:  
IoT end devices (EDs): This consists of single EDs and multihomed EDs. The single EDs are Sigfox ED, LoRaWAN, and NB2-IoT. The multihomed ED is the LHM-N access ED module, which contains the following interfaces: Sigfox, LoRaWAN, and RedCap interface. The IoT EDs communicate directly with the LHM-N gateway.  
Multihomed LHM-N Gateway: This contains multi-radio interfaces that are built on top of a lightweight Raspberry Pi Zero. The multi-radio interfaces include Sigfox, LoRaWAN, RedCap, and NB2-IoT. The block diagram of the multihomed LHM-N gateway is shown in Figure 2. It communicates with EDs through its various interfaces, then transmits collected information via the main backhaul 5G private network over the license-free band to various designated servers. If the 5G private network is not available, the information destined for the 5G core network server is routed via a licensed 5G public network as an alternative backhaul for data delivery.  
gNB base station: This is a 5G base station that communicates directly with mobile devices. It also communicates with the LHM-N gateway and serves as an alternative backhaul in transmitting data to the 5G server via the 5G public network.  
5G core network: Leverages a service-based architecture comprising many interconnected 5G Network Functions (NFs). The collected information is provisioned in the IoT cloud/software as a service (SaaS). LoRaWAN network server: Processes the data collected from a LHM-N gateway, which is then provisioned to various application servers.  
Application servers: These servers house respective processed information collected from the LoRaWAN network server, which can further be provisioned to the IoT cloud/SaaS. Sigfox cloud: This is the cloud hub that directly stores received data from the multihomed gateway via the Sigfox radio interface. The stored data can be integrated into the IoT platform/SaaS via an IoT-integrated plugin from the application backend for better management and usability. The Sigfox data are also accessible by vertical industry IoT solutions. Vertical industry servers: Vertical industry, such as the IoT solutions industry's servers, collects Sigfox data for monitoring and proper management of EDs, including data visualization and analytics. This will enable efficient data usage.