## 4 Distributed Hotspot Network Architecture
### Distributed and Decentralized Hotspot Network Layer
#### 4.2.6 Proof of Coverage  
The PoC is used to verify that the hotspots are actually in the locations that they claim to be [99]. The PoC aims to verify that hotspots are in their original locations and perform IoT device-related wireless network coverage from their specified locations. Any network that can be created using our architecture should be a physical wireless network. The success of such a physical wireless network depends on the reliability and availability of the network coverage for the IoT devices in the environment. The PoC algorithm uses the key properties of some radio frequencies (RF) as evidence that the hotspots are operating as smoothly as they claim to be. The properties of the radio frequencies are as follows:  
* The radio frequency has a limited range for propagation.
* The radio frequency signal that is received at a terminal can be used to measure the signal strength by applying the proportional squared distance law.
* Radio frequencies have a minimum latency because they propagate at the speed of light.  
The associated blockchain periodically polls all the connected hotspots using the PoC algorithm to verify that they provide a stable and reliable coverage for the IoT devices. In this way, the PoC confirms that the hotspots are constantly transmitting IoT data and storing it as blocks in the blockchain. Such a policy can be seen as proof that the hotspots are working, while their coverage is being used for the IoT devices.  
The PoC essentially poses a challenge to all the hotspots as a discrete unit of work of the algorithm. Several million such challenges can be issued to the hotspots and processed simultaneously by the associated blockchain [99]. With each new challenge, the PoC confirms that the hotspot network is functioning as desired. The main goal of the PoC is to minimize the PoC interval to a certain limited number of \(\alpha\)-blocks or less. At any point in time, a hotspot has one of the following three main roles:  
* Interrogator: Usually, such nodes are full hotspot nodes or other designated validators that create the PoC challenge and issue it to the condemned node. It challenges the PoC for a convicted target node.
* Convicted: it is a hotspot node that is the target of the PoC challenge, and it is expected to transmit the challenge packets so that the nearby hotspots can observe its activity.
* Witness: Such hotspots are located in the immediate (geographic) vicinity of the convicted node and also report to the querying system, the status of the challenge packets that is sent by the convicted node (High Performance Remote Procedure CallgRPC). Such a witness is directly connected to all the light-weight hotspot nodes. Such lightweight nodes, that are PoC challenge witnesses, can use validators to which they are connected so that the entire query validator search process can be managed using the hash of the PoC packet. This routing information is later used by the light-weight hotspot to deliver the witness report directly to the query sender. Once the query sender receives both the convicted receipts and witness reports after a certain time, it transmits them to the blockchain and the PoC challenge is complete.