**3. Interoperability strategies**

There are currently many radio technologies (RAT) available when thinking about the interconnection of sensor networks. Depending on the coverage radius, BR, QoS, or consumption of these devices one or the other can be selected. To obtain greater flexibility in the design of networks that adapt to different scenarios, it may be interesting to combine several of them. The options to achieve interoperability between the different technologies can be very varied, both in a software way or in a hardware way. The IoT network designer is often faced with this dilemma when it comes to choosing one technique or another. Many manufacturers already develop, for example, configurable chipsets that can integrate different radio access technologies (RAT's) [21–23], usually using different transceivers interconnected with a microcontroller unit (MCU) through SPI or UART interfaces. Through these combinations, it is not only intended to expand the coverage of the sensor network, but also to be able to reach areas where a single specific technology cannot do due to environmental conditions (obstacles, indoor/outdoor scenarios, density of nodes, etc.).

Another interesting alternative is the one proposed by [24] in which interoperability between different technologies is achieved through software defined networking (SDN). The objective is the coexistence between different radio access technologies in terms of protocols, coding, or signaling in a transparent way to the final application in the IP network. The architecture is organized into six levels, and the interoperability is classified into: device level, syntactic level, semantic level, network level, and platform level. Each technology has its own modulation, coding scheme, protocols, routing methods, or end-to-end applications communications. The proposed architecture is based on the implementation of software defined radio (SDR), network function virtualization (NFV), and SDN to solve the interoperability problem.

This chapter presents cases of hardware interoperability between two LPWAN technologies or between LPWAN and PAN technologies. A classification could be made into two types of interoperability from the Hardware point of view:


**Figure 3** shows the two interoperability models mentioned.

#### **3.1 Inter-network interoperability**

This philosophy is applicable, mainly if the conditions of the environment set the radio access technology to be used in different areas of the total network, or to separate the traffic of one network from another implementing a topology contemplating subnets. It is possible, for example, that in cases of long extensions of land or marine or river environments, there are areas, where 4G or 5G coverage is available, such as

*Hybrid Architectures to Improve Coverage in Remote Areas and Incorporate Long-Range LPWAN… DOI: http://dx.doi.org/10.5772/intechopen.113328*

#### **Figure 3.**

*Two kinds of interoperability possibilities including multi-hop: a) inter-network, b) distributed.*

urban or suburban environments and others without this type of network deployed. In the case of long-range technologies, we would choose options such as NB-IoT or LoRa, for example. Another possibility is to interconnect a cellular network already deployed with a network of sensors located at long distances and indoors, as would be the case of greenhouses or fish farms. In these cases, the philosophy used would be to create gateway nodes between the different RAT's. Its function is to adapt protocols, contents of the payloads, and control of access to the medium. In addition, this separation enables the possibility of existence of pre-processing before communication between networks, reducing the traffic load between subnetworks and in the entire network (Edge Computing) [25]. The latency in cases of Sensor/Actuator interaction can also be reduced with this arrangement since the data does not have to be sent to the rest of the network in the event that they are on the same subnet. Examples of this philosophy are presented below.

#### *3.1.1 LoRa-ZigBee interoperability*

As seen in previous sections, one of the biggest challenges of this type of network is the reduction of power consumption. ZigBee technology, based on the 802.15.4 [26] standard, is widespread in sensor communications networks. It allows flexible network configuration, moderate ranges (10–100 meters), low-power consumption, and data transmission rates from 40 to 250 Kbps depending on the band of use (915 MHz or 2.4 GHz). It is more susceptible to be used indoors and in the absence of obstacles.

In the comparison between LoRa and ZigBee, the latter is characterized by its lower cost, as well as its lower power consumption and a higher BR, to consist of a shorter range. The combination, therefore, of both technologies can mean energy and economic savings in some cases. In the case of smart buildings, for example, there are performance comparisons of both [27] that ratify the above in addition to the fact that LoRa technology provides greater penetrability through walls or cement walls. In these cases, it would be possible to implement a network that follows the philosophy of **Figure 3a**, where the ZigBee nodes would be forming a subnet within the same enclosure without wall obstacles and are interconnected by LoRa links, longer range and more robust to obstacles. Within the same smart buildings ecosystem, there are other proposals such as [28], where the inverse strategy is presented, that is, the interconnection with the end nodes is formed by LoRa links, while the ZigBee links implement the connection with the central data collector and the IP network. In this way, the BR of the ZigBee technology is used in the final stretch of the network, as well as its greater security thanks to the AES 128 [29] encryption algorithm.

Another environment, where interoperability is applicable, is that of remote natural parks or crops, where greenhouses appear scattered over a large area. In these cases, it is essential to sensorize them. ZigBee is a very suitable technology for this, case, but, if it is necessary to cover large areas, LPWAN technologies result more suitable to implement the backbone of the complete system. This is the philosophy that this research group has followed in [30], adding VLC communications systems [31]. The overall architecture of the system is shown in **Figure 4**, where interoperability between the different technologies (LoRaWAN, ZigBee, and VLC) is implemented in each of the access points of the ZigBee subnets.

In case that there is communication between nodes of the same ZigBee subnet, it is forwarded directly by each access point, avoiding the increase in latency in a possible sensor-actuator communication or in the case of alarm action. When making the gateway between the two RAT's it is necessary to take into account the size of the payloads of both. In this case, the Waspmote [23] hardware platform of Libelium has been used, which contains an ATmega1281 microcontroller with a series of connected sensors and allows two simultaneous communication modules connected *via* SPI bus. The microcontroller is responsible for storing the messages from each node of the network and retransmission by the necessary technology. In the case of ZigBee-LoRaWAN, a fragmentation of the data packets is necessary as shown in **Figure 5**.

In addition, the use of VLC is proposed for the transmission to a mobile device [32] of contents stored in the memory of the access point or transmitted through LoRaWAN from the central gateway of the network. The goal was to create a cellular network, where ZigBee and VLC coverage were given to each cell.

#### *3.1.2 Lora-NB-IoT*

Another contribution within the strategies reflected in **Figure 4**. a is based on LoRa and NG-IoT technologies [33] where a network of LoRa-NB-IoT gateways is implemented between areas where there is 4G or 5G coverage, and those where there is not. NB-IoT operates in the licensed bands associated with mobile operators and allows communications with low consumption and with BR from 120 to 160 Kbps. In addition, it has a low latency of the order of 1 to 10 sec. This can be an inconvenience, but for sensor networks, it is not a critical aspect. In this case of hybrid network, the

*Hybrid Architectures to Improve Coverage in Remote Areas and Incorporate Long-Range LPWAN… DOI: http://dx.doi.org/10.5772/intechopen.113328*
