Proof of Coverage
Proof of Coverage
The Helium blockchain uses a novel work algorithm called "Proof of Coverage" ("PoC") to verify that Hotspots accurately represent their location, configuration, and the wireless Network coverage they create.
Why Proof of Coverage
The Helium Network is a physical wireless Network that succeeds based on the reliable coverage it can create for users deploying connected devices. As such, it required a working algorithm built for this use case. Proof of Coverage takes advantage of radio frequency's (RF) unique, undeniable properties to produce meaningful proofs to the Helium Network and its participants. Specifically, PoC relies on the following characteristics:
- RF has limited physical propagation and, therefore, distance.
- The strength of a received RF signal is inversely proportional to the square of the distance from the transmitter.
- RF travels at the speed of Light with (effectively) no latency.
The Helium blockchain uses the data generated by ongoing proofs to verify the wireless coverage provided by Hotspots on the Network.
Oracled Proof of Coverage
- Oracled Proof of Coverage ChainVar was set in block 1,731,335.
- The first Oracled Proof of Coverage Receipts were in block 1,731,339.
- Bitter Concrete Parakeet is the animal name of the Injector Oracle for Oracled PoC.
Oracled PoC moves the responsibility of validating all PoC events to dedicated Oracles, powerful machines that ingest completed challenges, verify challenges, and witness validity, then inject the results back into the Helium L1 blockchain for rewards to be issued.
Oracles interact with data and systems outside of a native blockchain environment where the processing can be completed much more efficiently and at scale, providing a solution to a fundamental limitation of smart contracts.
Oracled Proof of Coverage allows Hotspots running miner version
2022.12.13.0 or later to
"self-beacon," transmitting Beacons on their own to participate in Proof of Coverage, ensuring more
reliable Beacon events.
At the start, Hotspots are intended to self-beacon every 6 hours, though this time window may change as Oracled PoC is improved. In addition, the Beacon rate includes a "jitter" component to offset the Beacon timing across Hotspots on the Network to avoid overloading the Oracles with large data spikes.
Oracled PoC is essential in implementing HIP-70 and the Helium Network's migration to the Solana blockchain and is a significant step forward in increasing the usability and scalability of the Network.
Proof of Coverage Roles
The "challenge" is the discrete unit of work for Proof of Coverage. To date, 10s of millions of challenges have been issued and processed by the Helium blockchain.
PoC Challenges involve three distinct roles:
Hotspots "Self Beacon" transmitting (or "beaconing") challenge packets to be witnessed by geographically proximate Hotspots.
Hotspots that are geographically proximate to the Beaconer and report the existence of the transmitted challenge packet. Any Hotspot hearing the transmitted packet will serve as a Witness and submit their Witness report to the Oracle.
Oracles are powerful machines that ingest completed challenges, verify the challenge and witness validity, and then inject the results back into the Helium L1 blockchain for rewards to be issued. In addition, Oracles interact with data and systems outside of a native blockchain environment, providing a solution to a fundamental limitation of smart contracts.
PoC Reward Scaling
In every epoch, rewards split amongst Hotspots that had a role in that reward pool.
For example, a Hotspot might earn a "reward unit" for witnessing a beacon. If five additional Hotspots successfully witnessed a Beacon during the epoch, each earning a "reward unit." In that case, each Hotspot gets 1/6th of the 20% of rewards in that epoch.
With the activation of HIP-15 and HIP-17, we introduced the idea of scaling these "reward units," so the units earned when being witnessed or witnessing a packet scale depending on two things:
- The number of Witnesses, as detailed in HIP-15
- The number of Hotspots in the hex tile of the transmitter, detailed in HIP-17
The HIPs themselves provide a rich explanation of these mechanisms, so you're encouraged to read those, but they can be summarized as follows:
For the Transmitters, the more witnesses, the more the transmitter earns.
For the Witness, each additional Witness past a total of four reduces what is earned by each Witness in that challenge.
The Witness earns less if the number of Hotspots in the area of the transmitter exceeds the "target density." Target density varies by hex resolution, as detailed in the HIP and defined in several chain variables.