## 2 Background
### Criteria for Evaluating HIoT Approaches  
The criteria used to evaluate the suggested HIoT techniques are described in this section.  
1. Security and Privacy: Smart healthcare systems must prioritise security and privacy in order to protect health data against attacks such as side-channel attacks, physical attacks, and malicious attacks, as well as to maintain privacy and prevent unauthorised ingress to health data.
2. Accuracy: Accuracy is essential for healthcare system carers. Depending on how the system is used, accuracy in healthcare IoT systems refers to how accurately the data collected reflect the patient's condition, how accurate the data used in the computation were, and how accurately the decision was made.
3. Performance: Healthcare providers must perform well in order to obtain precise data, process the data, and offer services quickly. This parameter is a combination of efficiency, load balancing, resource utilization, overhead, and computing time, as well as network quality of service (QoS) factors including throughput, latency, delivery rate, mean time between failures, and bandwidth usage.
4. Time: The time it takes for consumers to receive service after making a request is described by this parameter. The concept of time encompasses calculation time,  
Figure 1: Layered architecture of IoT in healthcare.  
average response time, execution time (run-time), and latency (as the time lag in healthcare systems).
5. Cost: This refers to the overall expense a patient who requests healthcare services may incur to receive the best care possible. The cost of computation, communication, data storage, and the upkeep of the desired service are all included.
6. Energy: Energy conservation is crucial for device and network survival, since HIoT devices lack resources and are powered with meagre energy resources. Additionally, when there are more HIoT devices linked to the network, the network's energy usage grows as well. On the other hand, more energy use results in higher operating expenses, more carbon dioxide produced, and a shorter network lifetime.
7. Interoperability: Interoperability refers to the capability of more than two HIoT systems to communicate and exchange information in a dependable, consistent, and efficient manner, use the information exchanged, and share resources. More than one medical informatics system, for example, may be necessary. The capacity to successfully grasp data across organizational or system boundaries is referred to as data interoperability. HIoT systems require the usage of standardized communication as well as a number of other interoperability-supporting technologies.
8. Scalability: This refers to the capability of the system to extend and build an IoT-based healthcare methodology as service needs and expectations grow. These capabilities can be leveraged to create smart devices, new operations that act as user service nodes, and network infrastructures, while not adjusting the quality or effectiveness of healthcare services. Extending the system requires either the addition of new hardware or services or improvement of the operation of current hardware or services.
9. Reliability: The capacity of a system to carry out its necessary functions under pre-determined circumstances and at a predetermined time. A healthcare system based on IoT is said to be reliable if it can provide requested services to patients in most conditions.  
Research question 1 has been addressed in this section through our discussion of the layered architecture of healthcare IoT and steps to evaluate different HIoT approaches.