Keywords

1 Introduction

Transportation of goods, despite the crisis caused by COVID-19, continues to grow. Forecasts indicate a further increase in merchandise trade volume, and thus also in global and intercontinental shipping, as well as in last-mile transport. A big challenge in such transportation is constant supervision and detailed monitoring of individual batches of goods in the context of the increasingly frequent transport of general cargo. Monitoring more comprehensive and automated logistics centers is also a significant challenge, especially with rising energy prices. Also, ensuring the safety and optimization of employees’ work, especially in the Western European market, where an employee’s supply significantly shrinks, becomes a significant problem.

These and many other challenges make you check how you can monitor warehouse spaces and freight so that it is as precise and reliable as possible, not energy-consuming, and simultaneously qualitatively competitive with the currently used methods. These considerations lead to a comparison of several leading monitoring methods, both in the global frame of reference and confined spaces such as warehouses, production halls, the interior of container ships, etc. The analysis of technologies and methods that can be used to determine the location of people and objects in warehouse centers should begin with determining the factors based on which the optimal strategy will be selected.

At this stage, it should be noted that the set of 8 factors responsible for the technology division has a large impact on the target choice and should be made dependent on a specific application. Their detailed description in the context of the paper’s topic is presented. The study considered six technologies (including vision and radio) that were analyzed in the context of their use in warehouses and distribution centers. A detailed description of the methods and their potential with the adopted coefficients is presented. Based on the analysis, it was decided to conduct a study of the UWB technology, which showed the most significant potential applicability in the context of low-energy monitoring of warehouse spaces.

1.1 Methods of Assessing the Quality of Positioning Systems

The proposed system for monitoring storage space can be characterized in the following areas:

  • System application place (indoor/outdoor/mixed)

  • Energy demand (AC/battery/computing power)

  • Accuracy and precision

  • Operating range (local, global, scalability)

  • Price

  • Required infrastructure

  • Communication and other sensing possibilities

  • Working conditions & ease of use

The selection of parameters is based on an analysis of the literature and a review of the most frequently raised weaknesses of the systems [1,2,3]. It was also decided to place a detailed description of the parameters near the tables they refer to in the next chapter.

1.2 Systems Included in the Analysis and Their Discussion

Based on the study of the systems currently used on the market and of potentially good solutions enabling the achievement of the set goals, six methods were selected, which were then analyzed based on the criteria presented above. The systems finally considered were:

  • Vision recognition [4,5,6,7]

  • Barcodes [8,9,10]

  • GPS (Global Positioning System) [11,12,13,14]

  • UWB (Ultra-Wideband) [3, 15,16,17,18]

  • LoRaWAN (LoRa Wide Area Network) [19,20,21]

  • RFID (Radio-frequency identification) [22,23,24]

To prepare the characteristics in the best possible way, the features of the systems are listed in eight tables, each table for one of the features. To simplify the description of each technology, an identifier is assigned in the first table, represented in the following.

The first area to be dealt with is the system application place. This parameter defines the capabilities of the system application. A modern system should enable tracking in the door-to-door system with the simultaneous possibility of interoperability within the warehouse space, sea freight process, road transport, etc. Assigning subsequent identifiers in this process, with the simultaneous change of monitoring systems, leads to errors resulting from the human factor. At the same time, monitoring both shipments and a fleet of specialized vehicles (forklifts, self-propelled warehouse vehicles, indoor cargo vehicles) is an essential aspect of security. For example, the ability to detect potential collisions among staff, monitor unforeseen events among employees and respond faster in case of a need for cooperation. A detailed comparison of systems in the context of this parameter is presented in Table 1.

Table 1. System application place.
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Another proposed parameter is energy demand – a factor gaining importance in the continuous increase in electricity prices. It makes it possible to determine whether the planned system can take the form of mobile devices in the form of wearable IoT or it will be an energy-consuming system, forcing a constant power supply from the mains. At the same time, attention should be paid to the frequency of charging devices and the risk of semi-portable infrastructure, i.e., one that formally works on battery power, but in the operation process, the battery life does not coincide with the employee’s working time unit, so it is necessary to replace the cells or their recharging during work A comparison of the systems in this respect is shown in Table 2.

Table 2. Energy demand.
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Accuracy and precision are other parameters taken into account. These are two independent position measurement attributes that depend on the system used. The first one – accuracy – tells us about the overall quality of determining the position. The system with this feature can indicate the distance range from the tag to search for the located object. The second factor – precision, illustrates the certainty of finding a given object with the search area, e.g., on a heatmap. If both factors provide high quality, we can accurately indicate the desired object regarding its place and distance. Their comparison in the context of systems is presented in Table 3.

Table 3. Accuracy and precision.
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Operating range – this parameter is similar to the application place, but it expresses the possible location area in a broader context. We can distinguish direct systems requiring contact at a distance of a few cm, systems with a wider range of operations within one locating point, or global systems that allow us to determine the location regardless of the infrastructure we manage. The operating range of the analyzed systems is shown in Table 4.

Table 4. Operating range.
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Another factor taken into account is price. It considers two components: the cost of implementation (including initial investments in infrastructure and hardware) and operating costs (related to consumables, licenses, software, and maintenance). The estimated list of prices, based on the analysis of available solutions, is presented in Table 5.

Table 5. Price (based on commercial systems)
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A factor that cannot be overlooked when implementing significant complex investments is the required infrastructure. Depending on the form of infrastructure (centralized or distributed), it may be necessary to purchase local modules (endpoints of the location system) that can be connected to cloud services. It may also be required to buy a central infrastructure in the form of computing and aggregating systems, decision-making systems, etc. Some systems require a similar or very similar infrastructure, which is included in Table 6.

Table 6. Required infrastructure.
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Communication and other sensing possibilities verify whether there is computing capacity on the part of the located object and the possibility of feedback (in the form of a message, warning) or sensing the parameters of the positioned object (e.g., temperature measurement of transported goods, verification if the object is in motion, etc.). The description of the implementation (and its availability) of communication is presented in Table 7.

Table 7. Communication and other sensing possibilities.
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The last factor taken into account is working conditions & ease of use. It is information on what environmental conditions a given system can operate and the level of complexity of the service. For example, some solutions require direct contact, being in sight, under the open sky, etc. At the same time, the level of complexity of service is essential in determining the cost of implementing a new employee or functional expansion of the proposed system. A summary of the capabilities of the proposed systems in relation to this parameter is presented in Table 8.

Table 8. Working conditions & ease of use.
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2 Analysis of the Prepared Statement

From the analysis performed, it can be seen that there is a huge discrepancy between the positioning systems used in trade and logistics, and in particular, among the systems that can be used to track a shipment from the manufacturer of the goods through logistics hubs and centers up to “last mile” delivery. It is impossible to select an undisputed leader regarding the entire process. Still, it can be pointed out that its elements – are due to the constant development of wireless technologies and their advantage over solutions, e.g., video. The steps involved in covering long distances in the open air are indeed unrivaled regarding satellite navigation technologies (whether GPS or other commonly available technologies). However, in the context of logistics centers, warehouses, and their immediate vicinity, the matter is more complex due to the lack of GPS signal.

For retail customers, cheap solutions will most often be the leading one because monitoring parcels worth several or several dozen USD is challenging to implement with systems exceeding their value (even assuming that these systems will be returnable). However, if we consider small and medium-sized enterprises, the situation is no longer so obvious.

Both reducing errors in logistics, ensuring constant monitoring of transport conditions and quality, as well as precise step-by-step tracking of deliveries allow us to believe that the systems enabling two-way communication – such as UWB – will be the future of forwarding in this area. In addition, the UWB technology is the only one of the discussed technologies that allow for two-way communication while meeting the RTLS requirements, which also allows for implementation in the warehouse as an internal system of communication and warning about danger.

Based on these dependencies, it is proposed that the system under which logistics is carried out should be based on a layered model. In this case, on par with the currently used solution, it also uses the approach based on UWB technology. It can be used as a support or transition period, as presented in Fig. 1.

Fig. 1.
figure 1

Proposition of coexistence of a UWB-based system at various stages of storage and shipping.

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The advantage of the proposed solution is interoperability (e.g., within a ship whose position is determined using GPS, there is also the possibility of visualizing the position of containers and determining, e.g., the humidity prevailing in them). It can also increase safety (the forklift operator no longer has to be warned about a dangerous event) by the security guarding the video surveillance. Still, it can be done by a system that will automatically inform about a potential collision or even turn off the drive. Finally, there is also a guarantee of delivery, where the courier, even if by mistake scans the wrong label, will be informed when leaving the parcel that the wrong one is the package was removed from the delivery truck.

The current expansion of UWB technology remains a question. It indicates two main trends – the development of mobile applications, the implementation of the latest flagship smartphones of brands such as Apple [26] or Google [27], and the trend focused on automotive technology. Of course, the interoperability of these two approaches is also possible. So, for example, Apple is considering cooperation with BMW [28], where cars are to be opened using virtual keys stored on the brand’s phones and communicating with vehicles using UWB technology. None of these approaches fit in with market solutions aimed directly at industry and transport, but more and more companies are offering such solutions commercially on a smaller scale [29]. Moreover, the intensified development of this technology in the above-mentioned areas allowed for its gradual miniaturization and cost reduction.

3 Summary and Conclusions

The article presents several requirements and how the latest technologies used in warehouses and distribution centers deal with them. As has also been shown, no one-size-fits-all method can meet the requirements of large-scale shipment monitoring and security, and positioning within warehouses. Nevertheless, it has been shown that many warehouse requirements can be met with radio technologies, which allow for constant location monitoring, with simultaneous, two-way communication and low energy consumption. The technology that attracted particular attention is UWB, which both meets the requirements presented above and is currently strongly developed in the context of industry and consumer solutions. In addition, there are more and more commercial solutions on the market that introduce this technology for use within the discussed topic.