1. Introduction
Ambient assisted living (AAL) is a research field that aims to bring smartness to our everyday environments by acquiring data from various sensors, understanding people’s activities, behavior, and living problems, and deciding on proactive interventions to support the management of identified issues (see
Figure 1) [
1]. With the advance in sensing technologies and the prevalence of miniaturized, affordable Internet of Things (IoT) sensor applications have been developed to improve the beneficiary’s quality of life and support personalized care [
2]. A wider range of proof of concept applications for various use scenarios along with associated technologies can be found in the literature, such as fall detection systems [
3], cognitive decline management [
4], personalized care [
5], remote follow-up [
6], nutrition management [
7], medication review [
8] and well-being management [
9].
Having more IoT devices and sensors associated with living environments leads to collecting patient data that must be shared among multiple parties on different sides [
10]: validators, processors, healthcare stakeholders, etc. Nowadays, the ambient assisted living systems move the data collected in cloud systems (see
Figure 1), where the potentially unlimited computation resources help in dealing with analytics and decision making [
11]. Using decentralized distributed ledger solutions will allow multiple nodes to host the same set of encrypted data in multiple care systems that are hosted in different places and kept up to date with the actual state and data of the system [
12]. Additionally, most of the collected data are rather sensitive and personal data of vulnerable people; thus, security and privacy have always been issues to deal with [
13]. They constitute a barrier between vulnerable people and assistive technologies and prevent the adoption and good use of existing software solutions in the field [
14]. People may become digitally vulnerable as data theft, fraud, and the unauthorized use of personal, medical, and financial information are often not even known by the victims [
15].
The privacy and security problems are critical for data-driven assisted living applications and IoT networks such as the Internet of Medical Things [
14]. Data ownership and elimination of potential breaches are objectives for keeping the data, and the system secured [
16]. However, because of the lack of precise specifications, even ordinary procedures might result in security breaches [
17]. There is a strong need to make such applications transparent, immutable, and distributed [
18]. In general, in the discussions concerning privacy and security, how consumers understand privacy is key [
19]. People are more inclined to value decentralized solutions for their capacity to safeguard their privacy goals [
20]. On top of technical privacy issues, lately, personal details (i.e., used to identify a person) have become one of the most valuable commodities [
21]. This information might be as basic as a name or identification number, or it can be more sensitive, such as medical or behavioral data [
22]. As the world becomes more digitized, internet activity is increasingly recorded, often without the user’s knowledge or agreement, constituting a barrier to ambient technologies adoption.
Blockchain technology is seen as a good solution for tackling IoT monitoring, data management, interventions, and privacy concerns [
23] in ambient assisted living applications [
24]. Stakeholders from the ambient assisted and care fields are interested in integrating blockchain technologies into their systems to benefit from improved security, privacy, and data ownership (see
Figure 2) [
24]. Conventional ambient assisted living solutions use centralized cloud-based models focused on structuring data rather than privacy, ownership, and decentralization. The adoption of blockchain technology can change this landscape [
25]. In a blockchain-driven assistive living application, the users will join a blockchain network, and asymmetric encryption solutions will enforce the security of data sharing [
26]. The IoT devices deployed in the user environment can be joined with smart contracts to automatically generate and sign transactions and forward them to the blockchain to be stored immutably [
27]. The generated transactions are aggregated in blocks disseminated in the network and will be mined in the future blocks. To change a value in a block, the entire history of previously linked blocks needs to be rehashed, requiring a lot of computational power not being feasible these days [
28]. To prove the ownership of the data, the IoT device provides a signature of the transaction, which is also useful for authentication and validation [
29]. The updates are stored in chained blocks, taking advantage of the technology’s properties such as reliability, availability, immutability, and consensus [
30]. The blockchain enforces the provenance of data by a linked list of nodes; thus, data can be traced back by iteration of the chain [
31]. In addition, securely storing the sensor’s data and respecting the personal data regulations is difficult considering the perspective of the domain [
32]. So, using a decentralized, user-centric approach regarding data privacy can address security and data ownership problems in developing ambient assisted living applications.
Even though the research field is still at the beginning, relevant studies in the literature can be found. The motivation of this paper is to systematically review and organize them according to the research problems they address. To the best of our knowledge, there are no reviews conducted on solutions for integrating blockchain technology with ambient assisted living systems. To conduct this review, we have defined a search methodology with clear criteria for including or excluding papers, set up a reference interval, and focused on current important databases. We have included in the survey 87 papers on blockchain and ambient assisted living systems that were reviewed and organized. Thus, a reader would effortlessly gain insights into the current state-of-the-art research in the field. Nevertheless, there are still many gaps and open issues that would require increased attention from the research community in the coming years, such as data sharing and integration of care paths with blockchain, storage, and transactional costs, personalization of data disclosure paths, interoperability with legacy systems, legal issues, digital rights management, etc.
The remainder of the article is organized following the Introduction, Methods, Results, and Discussion (IMRAD) structure:
Section 2 presents the methodology and methods used in conducting the literature review;
Section 3 illustrates the results by describing and organizing the most relevant research works;
Section 4 presents a discussion on the survey findings, and
Section 5 draws the conclusions.
2. Materials and Methods
In carrying out our study, we have used the PRISMA methodology that defines the guidelines for conducting systematic reviews, which is widely accepted by most Web of Science (WoS) journals for organizing review-type articles [
33]. More specifically, we have selected the “PRISMA 2020 flow diagram for new systematic reviews which included searches of databases and registers only” variant that features four main phases: articles identification, screening, eligibility, and inclusion. The goal of our systematic study is to create an overview of the domain of blockchain and IoT applications for ambient assisted living and to construct a snapshot of the state-of-the-art works for general or specific topics in this domain. This approach will also allow identifying current hot trends, future research directions, and research gaps.
The first step in our research study was to clearly define search strategy in terms of research questions, keywords, or key phrases to cover the study targeted topic of blockchain, IoT, and AAL applications. The following research questions have been selected for our study:
Identify use-cases for blockchain and IoT applications in AAL;
Identify applications, techniques, and tools developed for this domain;
Highlight the challenges and limitations of blockchain and IoT in AAL;
Find what are the main open research directions to be tackled
This led to the definition of the following main search keywords to be used in the next stage of the study:
Blockchain IoT healthcare;
Blockchain and Ambient Assisted Living;
Blockchain and Active Assisted Living;
Blockchain and Ambient Intelligence
Blockchain and remote care;
Blockchain data ownership in health care;
Blockchain data sharing and analytics in health care;
Blockchain and IoT security and privacy in health care
Using the above, the second step of applying the PRISMA methodology was to select the scientific databases for the search process. In this context, we have selected Web of Science as the main database for our study since it is the most comprehensive scientific database widely recognized for including high-quality conference and journal articles from the most important publishers (MDPI, IEEE, Elsevier, ACM, Springer, Wiley, etc.). Using the WoS database allowed us to focus our search on a single platform while receiving results from articles from multiple publishers. To conduct the search, we have used the Clarivate WoS web platform [
34]. As a search method in this platform, we have selected the Topic type because it covers the key information from the WoS indexed research articles: title, abstract, author, keywords, and Keywords Plus. The search keywords have been transformed into search strings in the platform, e.g., “blockchain” AND “ambient intelligence”.
Figure 3 illustrates the PRISMA 2020 flow diagram used to identify the articles that were included in the review. In the PRISMA identification phase, after aggregating the search results, we have identified 491 articles matching our search criteria. We have refined this set of articles and removed duplicate records (19 items), resulting in 472 records to be included in the Screening phase. In this phase, we have defined specific inclusion criteria for our study to further filter the results, thus, removing 312 records. Similarly, to further narrow the set of records in the Eligibility phase, we defined several exclusion criteria that helped us drop another 73 records. Both criteria are presented in
Table 1.
Finally, in the inclusion phase, we obtained 48 records to be considered in the study for an in-depth analysis of the presented work, concepts, approaches, and solutions for blockchain in AAL.
Figure 4 presents the included papers distribution per publishing year. It can be noticed that most of the research around the studied topics has been accelerated from 2020 onwards.
Figure 5 shows the distribution of the selected articles using the journal/conference publisher as criteria. As it can be seen in the figure, all major highly rated publishers (Elsevier, IEEE, MDPI, and Springer) have shown interest in the blockchain and AAL research direction, 80% of the selected papers being published under one of the four.
As per the types of papers included in the study, in
Figure 6, we illustrate the main categories of the analyzed papers, with an emphasis on article types.
Figure 7 shows the distribution of the included papers per journal and conference proceeding highlighting that more research related to the study domain has been published in IEEE Access and Sensors MDPI journals.
Table 2 summarizes the query results as the number of records together with the number of items included in the study per each category.
4. Discussion
As the population of the world is aging, societal challenges will need to be faced, especially about the delivery of care, which needs to be improved, and new care system paths need to be designed. At the same time, the development of IoT sensors and technology such as blockchain can ease this process by the implementation of ambient assisted living services which aim at moving the care from hospitals and care centers to home. The integration of sensors in older adults or patients’ homes to enable remote follow-up and care is seen as key in delaying.
The ambient assisted living systems address many of the concerns of patients in this transition towards remote care and personalized interventions, such as (1) time-consuming process for healthcare professionals caused by the lack of accurate monitoring and follow-up support, (2) patient data-sharing gaps across the care continuum, (3) not having a proper care support network in place to reduce patient anxiety or worries; (4) patients and family caregivers lacking sufficient knowledge and skills to optimize self-care; (5) patient difficulties in adherence to postdischarge instructions, e.g., medication usage or behavioral changes.
Despite advantages brought to the care process, the ambient assisted living solutions have a rather limited adoption mostly because of the problems related to IoT sensors integration, data sharing, trust, ethical considerations, data confidentiality, privacy, etc. (see
Table 6). As shown by the qualitative review conducted, blockchain technology can play a significant role in addressing some of the concerns related to the ambient assisted living services adoption, but at the same time, several technological barriers require further investigation.
Blockchain scalability is important for integrating the technology into ambient assisted living systems. The monitoring data related to the patient’s state and well-being, captured using IoT sensors, must be disseminated through the blockchain network. However, nowadays, the scalability of blockchain networks is low for handling an increasing number of transactions as more people will utilize the platform. The quantity of data to be saved on the blockchain will increase in tandem with the number of transactions on the network. It may cause problems related to the network speed and high costs. It is difficult to assess blockchain performance concerning the integration of IoT monitoring devices in living environments and the storage and dissemination of patient data for remote follow-up. Because the technology is decentralized, there is no benchmark against which to compare performance. However, there are a few methods for assessing performance. One method is to look at how many transactions a blockchain network processes in a particular amount of time. Another technique to assess performance is to look at a blockchain network’s average transaction time.
As scalability is a significant issue of the blockchain, managing a high number of transactions is important to gain broad acceptance in ambient assisted living systems. However, there are several solutions for improving scalability. Sharding is one potential solution in which the blockchain is split into several shards, each of which may execute transactions concurrently and can be correlated with the organization and data-sharing procedures in healthcare. It would enable the network to handle a considerably higher volume of transactions without compromising speed or efficiency. Another option is off-chain scaling, which entails shifting part of the data off-chain, and this can be a relevant option even to relieve some of the privacy concerns as the patient monitoring data will be stored at the edge.
In the blockchain, there is a lot of room for privacy. This is relevant for ambient assisted living systems where private data and informed consent must be carefully handled. With blockchain, we may construct a safe and private transactional environment to share patient health records and data. Blockchain, if properly used, has the potential to eliminate fraud and improve transparency. However, ensuring privacy needs further research and development. One of the difficulties is that all parties must have a common concept of the data confidentiality, and new care and data-sharing paths need to be created in the healthcare systems. The creation of a digital identity is another way that blockchain may aid in the enforcement of privacy. This would allow us to choose which personal information is shared and with whom. In an ambient assisted living system, we may, for example, select to share the data partially with our family and not at all with our insurance company. A digital identity would offer us complete control over our personal information, allowing us to guarantee that it is shared only with the people we choose.
Another issue of ambient assisted living systems is the possibility of data leaks and modification. Unauthorized parties may have access to monitoring data if they is not protected adequately. Therefore, data may be encrypted using blockchain. This makes it extremely difficult for anyone who is not allowed to read it and modify it. A decentralized network is what defines a blockchain. It implies that our data are not stored in a single area, making it extremely difficult to be modified. Smart contracts can be created using blockchain technology. Integrated into ambient assisted living systems, they may automatize the IoT devices integration as well as the data processing jobs. As a result, we may designate how and by whom our data can be utilized. If someone tries to use our data in a way we have not approved, the smart contract will prohibit them immediately. The data stay private and safe by utilizing blockchain to encrypt data, build a decentralized network, and construct smart contracts.
Finally, the ability of various systems to communicate and interoperate is important for care and support systems that need to integrate stakeholders across the whole continuum of care. The capacity to exchange currency and data between various blockchain networks is one of the advantages of blockchain interoperability. It may contribute to developing a more integrated and efficient care ecosystem. Another advantage of blockchain interoperability is that it might reduce fragmentation risks. It can assist in guaranteeing that there is a single source of truth and that information is not segregated by allowing multiple blockchain networks to collaborate. Interoperability on the blockchain can let consumers have a more efficient experience. Users may hopefully avoid dealing with numerous distinct care applications by allowing blockchains to interact and integrate. Interoperability across blockchains can also assist in enforcing security. It is possible to uncover potential risks and weaknesses by allowing multiple blockchain networks to share data and information. Interoperability on the blockchain can also assist in cutting expenses. It is possible to prevent duplication of effort and resources.
5. Conclusions
In this paper, we have used the PRISMA methodology to identify, study, and report the relevant state-of-the-art literature around blockchain and its applicability in ambient active living. We have defined inclusion and exclusion criteria, have set several international databases for pooling articles, and finally selected 87 research papers in the qualitative study. As many of the desirable features of ambient assisted living systems may be assured by integrating and using the blockchain technology, we have organized the review to reflect the solutions in relation to the IoT monitoring and integration of environmental sensors, managing and sharing of data, and security and privacy aspects.
The outcome of the study shows that the integration of blockchain with ambient assisted living systems is a hot topic in many of the papers published after 2020. The adoption of remote assistive care was accelerated by the COVID-19 pandemic, and as shown by the qualitative review conducted, blockchain technology can play a significant role in addressing some of the concerns related to ambient assisted living services adoption. Although blockchain technology has the potential to revolutionize the care and ambient assisted living industry, more research is needed to fully understand its implications and applications. Future research includes expanding and replicating existing frameworks, performance, scalability, privacy, and interoperability of blockchain systems in IoT healthcare applications. More studies are needed on the adoption of blockchain in the health and care ecosystem, concentrating on topics such as scalability, costs, creation of new care and data-sharing paths for care transition from hospital to home, governance, and interoperability.