# Compressive Sensing-Based IoT Applications: A Review
## 4 CS-Based IoT Applications
### Sensing Layer  
The proper integration of sensors, actuators, RFIDs and communication technologies will deliver a strong foundation for the sensing layer of any IoT platforms. An adequate sensing layer that meets the high demands of energy-efficient IoT application should be empowered by exploring efficient hardware/software solutions. The latter consist of incorporating state-of-the-art compression techniques and data routing protocols. The hardware part of the IoT sensing layer is enabled using two main technologies, RFIDs and WSNs. While RFIDs are mainly used to enable low-cost identification and tracking applications, WSNs can provide the IoT with broad sensing and actuation capabilities. In addition, intensive research and efforts have already been dedicated to expanding the WSNs to cover unlimited set of IoT applications. RFIDs generally consist of two major elements, an RFID tag embedded on a chip with a unique identification sequence (ID) and a radio scanner device, called RFID reader. RFIDs have gained a lot of attention in IoT applications, they serve to store data, to track objects and to communicate with other devices [59]. Moreover, RFIDs present appealing solutions due to their ability to operate in battery-free mode and their lowest cost and small dimension [23]. For IoT applications, RFIDs have been used in different variations, the tags could be implemented on the human body [60], deployed on the skin [59] or attached to the walls or other objects. Although the reading distance of RFIDs (the distance between the tags and the reader) is not large (5-6 m), they can be deployed efficiently for indoor tracking applications [61]. Several IoT applications have witnessed the integration of RFIDs, for instance, [PERSON] et al. [62] presented the design and the implementation of a GPS-RFID tag that can be effectively deployed for different IoT tracking applications. The designed tag operates in a semi-passive mode (battery assisted) with a reading range up to 5.6 m. In addition, it can be reconfigured to serve as a continuous data transmitting platform in the online mode or as data logging platform in the offline mode. [PERSON] et al. [63] presented new chipless RFID tag using microelectromechanical (MMES) systems technology for IoT applications, the proposed prototype is expected to reduce the cost of the RFID tag as the chip fabrication is eliminated, hence, the cost of the RFID tag will be as low as barcode labels. On the other hand, WSN-based IoT applications can be divided into two categories: outdoor and indoor. Outdoor monitoring collects environmental data that can be used in the context of smart cities (light, humidity, traffic, GPS tracking, and air monitoring), whereas indoor monitoring is more concerned with smart-home applications that can provide remote healthcare services, in which the  
Figure 2: CS-based IOT platform. sensors can be either distributed over the house to measure humidity, temperature and detect motion or they can be deployed over the human body to acquire vital signs such as electrocardiogram (ECG), electroencephalography (EEG), blood pressure, glucose level in the blood, etc. It should be noted that most of the progress made in the WSN-based monitoring applications can be adapted easily for IoT. However, there is a crucial difference between most IoT applications and their WSN counterparts in terms of device heterogeneity, i.e., WSNs usually deploy a set of similar sensors that collect a single type of data, whereas, in IoT applications, a large scale of sensors acquire different types of data. Moreover, inadequate deployment of WSN nodes can result in a severe degradation in the reliability of the system and increase the complexity and the cost for the overall platform. Thus, numerous researches that aim to bridge the gap between exciting WSNs and future IoT platforms have been widely discussed in the literature [64, 65, 66, 67]. The major problem to tackle in the sensing layer is the high power consumption.