Hybrid Blockchain Platforms for the Internet of Things (IoT): A Systematic Literature Review – PMC

Table of Contents

1. Introduction

For the last few years, the global demand for using Internet of Things (IoT) devices is highly increasing due to the increasing global market demand for faster and more efficient ways of manufacturing, required improvements of the military capabilities, and transforming things into smart ones such as smart homes, smart factories, and smart cities. Although IoT devices have numerous benefits, they also have several weaknesses, such as generating a huge amount of data, requiring a lot of energy to work, and considerations regarding the trust issues as they are centralized, controlled by an administrator who can manipulate the underlying system or even stop it entirely. The IoT system enables the devices to collect data about themselves and the environment around them, and later share these collected data with a device, and finally send these data to a central server. Blockchain technologies allow the IoT devices to exchange collected data with each other or send them to a cloud server securely and reliably [1]. As a result, blockchain technology has been introduced to minimize these potential weaknesses and risks.

Nakamoto [2], who is the pseudonym of the creator of Bitcoin, introduced the first cryptocurrency that uses distributed ledger technology (DLT) (a.k.a., blockchain). Since then, blockchain technology has penetrated the Internet of Things (IoT) market, allowing smart devices that can connect to the Internet to use a secure, immutable, and verifiable network. Blockchain is a decentralized ledger that secures, verifies, and records all peer-to-peer transactions quickly, safely, and transparently. The primary benefit of using blockchain technology over traditional technologies is that it enables two parties to perform secure transactions online without the need for a trusted authority. As a result of the lack of this authority, transaction rates are cheaper than the other conventional approaches [3].

As the world is becoming more and more dependent on smart devices, the number of connected IoT devices by the year 2025 is estimated to be 16.44 billion devices, and 25.44 billion by the year 2030 [4]. As such, we expect a dramatic change in the IoT market, and the contribution of this new blockchain technology is expected to be disruptive. Many vendors are currently developing new platforms, tools, and techniques. While blockchain platforms are very useful in terms of security and transparency, all the generated data cannot be stored in these platforms. In most cases, a separate data warehouse is needed to store the huge amount of data that cannot be stored directly in the blockchain platform. This can be a cloud data warehouse or a traditional central database management system; however, cloud data warehouses are mostly preferred due to their elasticity and other advanced features. Many blockchain applications and platforms have been developed recently using the cloud as storage units.

Since blockchain platforms cannot store all the generated data, they are mostly supported with cloud data warehouses, which can be called a hybrid blockchain platform. Another perspective for hybrid blockchain definitions is the use of both public and private blockchains in the same project. Ref. [5] described the hybrid blockchain as a street with many stores, where everyone can access and view the stores, similar to public blockchains, however, one cannot access the back offices of the stores without permission, which is similar to the private blockchain. From this point of view, a hybrid blockchain can be considered as a combination of a private and a public blockchain where the private blockchain can be hosted on the public blockchain. A hybrid blockchain can be entirely customized, where hybrid blockchain users can decide which transactions are made public or who can take part within the blockchain.

While several systems have been developed based on the idea of hybrid blockchains, a systematic overview of the current state of the art on the use of hybrid blockchain platforms is lacking. Knowing how this integration has been performed would help facilitate future research on hybrid blockchains. Although there are several relevant papers on this topic, this has not been evaluated in detail yet. The objective of this study is to present the main challenges and possible solutions and, also, different aspects related to this hybrid blockchain research. As such, we performed a systematic literature review study to collect and synthesize the required data on the state-of-the-art in this field.

In this paper, we particularly focus on the integration of blockchain and IoT, its motivations, challenges, and the domains by performing a systematic literature review (SLR) on research articles collected from different digital databases.

The following research questions are defined in this SLR study:

The contributions of this study are as follows:

This first SLR study using 38 research articles on hybrid blockchains shows that efficiency, data integrity, and security are the major motivations for adopting integration of IoT and blockchains. Researchers mostly focused on health, energy, agriculture, and manufacturing domains and applied fog computing, edge computing, telecommunications, and cloud computing technologies. The most preferred blockchain platform is Ethereum, and several challenges are discussed in this study. The following sections are organized as follows: Section 2 provides the background and related work. Section 3 describes the adopted research methodology. Section 4 presents the results of this SLR, and Section 5 presents the discussion. Finally, Section 6 discusses the conclusions and future work.

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