## 3 Methodology
### Planning the Review
#### 3.1.5 RQ 5  
Which Modalities Are Used in MI Systems with IoT and AR? In 2014, [PERSON] [6] reported the remaining challenges in MI systems regarding architectures, usability, and security. Furthermore, although the article provides a useful introduction to the topic of MI systems, it does not qualify as a systematic literature review. Since 2014, technologies that are related to AR, IoT, and interaction modalities have improved, and we believe that it is time to identify new research challenges that have emerged. Thus, we seek to identify open research challenges that are related to MI systems that use IoT and AR. By answering this research question, we aim to identify the gaps between unsolved challenges and the results that were provided by existing studies. We selected a number of keywords to find suitable studies to obtain answers to the aforementioned research questions. The selected keywords were terms relevant to MI systems, IoT, and AR, such as \"multimodal interaction\", \"Internet of Things\", \"augmented reality\", \"mixed reality\", \"multimodality\", \"architecture\", and \"framework\". We combined two or more keywords with Boolean logic for our search and also used abbreviations and short forms of the selected keywords (e.g., \"IoT\", \"AR\", \"MR\", \"multimodal\", \"interaction\", \"augmented\") to extend the coverage. When searching with keywords, we included singular and plural forms (e.g., \"multimodalities\", \"interactions\") to include as many studies as possible. Table 1 presents the keyword combinations that we used in our search. We conducted a search with the aforementioned keywords in the following scientific libraries and journal databases that supported searches with Boolean operators:  
1. ACM Digital Library
2. Google Scholar
3. IEEE Xplore
4. ScienceDirect
5. Scopus
6. SpringerLink
7. Taylor & Francis OnlineWe selected two journal databases, because their studies were relevant to our research domain. Both of the journals supported an advanced search engine that could accept Boolean operators to search studies within their database. We were aware that there were other high quality journals; however, some journals were unable to search their databases with complex keyword combinations with Boolean operators; thus, we used digital libraries that covered these journals' databases, such as the International Journal of Human-Computer Interaction and the Human-Computer Interaction that wascovered by Taylor & Francis Online. Our strategy for searching and for selecting studies consisted of three steps: (1) initial literature search, (2) first pass, and (3) second pass. In the initial literature search, we collected studies that were written in English and published between 2014 and 2020. Because of the low relevance between search terms and results after reaching a certain number of findings from the literature databases, we only downloaded the first 50 studies that were sorted by relevance to the search terms for each keyword combination. In the first pass, the results of the initial literature search were assessed by their titles and abstracts in order to determine whether to use them in the second pass. We skimmed the body of the paper if the title or abstract did not provide enough information to identify whether the study was about an MI system with IoT and AR. Studies that presented a system consisting of IoT, multiple modalities, and AR/MR were included in the list of studies to be analyzed, whereas duplicate and irrelevant studies were excluded. We only selected research papers that were published in a scientific peer-reviewed journal, conference, or magazine. Therefore, we excluded patents, books, and reports. After the first pass, we thoroughly read the body of the remaining studies, including the discussion and conclusion, and then examined them based on the following criteria as part of the second pass: