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RTK technology is now expanding from the traditional geo-spatial communities (such as, surveying applications, construction machine and precision farming) to automotive markets, and is becoming the key and essential component for autonomous driving. Traditionally, RTK corrections, normally in RTCM standard format, are generated from a centralized server using a complicated GNSS algorithm (for example, VRS (Virtual Reference Station) or MAC (Master Auxiliary Correction)) and the raw GNSS measurements from a set of GNSS reference stations (normally in the order of tens to hundreds). Due to the computational and network connection limitations, such systems (for example, Trimble’s VRSNet, Leica’s SpiderNET and Topcon’s TopNET) to provide RTK services, can only handle hundreds’ GNSS reference stations and thousands of user connections for RTK corrections. Also due to the complexity of algorithms to generate the corrections and operating a GNSS network, nowadays, RTK correction services are only locked by government institutions and large private companies. Or you need to setup a base station by yourself, which requires a lot of professional experience, thus it doesn't scale, and not applicable sometimes. The rapid development of autonomous driving market requires a large scale (national-wide or global) RTK network correction service, for example, Qianxun SI is spending huge efforts to build a nationalwide RTK correction service in China, especially design for autonomous driving market in China. This paper describe a new network model---PAS(Precision as Service). PAS employs a blockchain secured by a Proof-of-Stake and Proof-of-Accuracy (POA) hybrid as the consensus model. Proof-of-Stake(POS) is a consensus protocol widely used in recent blockchain projects. In our setup, service provider miners (validator, v-node) need to stake tokens to participate in system consensus. Each node will have its chance to produce blocks based on the BLS algorithm weighted by the staked token. We use the BLS algorithm for fast and reliable BFT-like (Byzantine Fault Tolerant) consensus. Multiple parties use threshold signature to reach an agreement on a blockchain proposal. The staking will also improve economic security by punishing any misbehaving validators. Anyone who owns a PAS token can bond (or delegate) their coins and become a validator, making the validator set open and permissionless. Similar to POW, POA requires external resource consumption to add entropy to the system. This external resource is in the form of physical geospatial coordinates. It is unique, computationally inexpensive, yet fully decentralized available to a large group of people. With very affordable RTK hardware, each base station miner can provide accurate RTK location streaming data with their unique geospatial coordinates. Service provider miners collect those streaming data, verifying the data's accuracy relative to their physical position, creating proof of accurate geographic span in a cryptographically secure way. POS and POA's combination is to create a fast, scalable, and secure blockchain for various applications on top of it. BLS signature By using a curve pair, BLS signature can be used to verify that the point pairs on the two (or the same) curves conform to the multiplicative commutative law: e(P, Q) ? n e(x×P, Q) = e(P, x×Q). The threshold signature (threshold sig) is essentially the signature method of m-of-n. Under the condition that m signatures are known, a unique and valid signature can be synthesized. The combination of any m signature fragments is the same verifiable signature. If fewer than m fragments are shared on the network, no individual will know the full signature. So even with many parties, the BLS signature size could be as small as the size of one signature. That will improve the efficiency of data storage of blockchain-based systems. Also, the BLS signature could be viewed as a robust random seed, as any party can not guess the combined signature, yet it can be verified quickly by everyone. Token economics Token will play an essential role inside the PAS platform. The native token in the PAS platform is called PCS. PCS's primary functions are in staking, payment method for all applications or services in the PAS platform. PCS tokens will also be used to pay transaction fees and the reward for miners and validators. Reward Types Reward Users of PCS stake tokens to subsidize operating and capital expenditures. A reward can happen in two ways. A. Stakers can stake tokens to active Service Provider Miner. Each staked token will be rewarded proportionally according to the set inflation ratio. B. Base Station Miner can uniquely bind to a Service Provider Miner. Once bound, Base Station Miner will stream accuracy RTK data to Service Provider Miner. Service Provider Miner will validate the data and use the combined geospatial RTK coverage map inside the block proposal for additional token reward, besides the staked token reward. In return, Service Provider Miner will distribute mining rewards back to Base Station Miners. Additionally, Service Provider can provide accurate location service to end customer such as surveyor, autonomous vehicle, drone, etc. Service Providers can market their service to an intended user group and create a service payment plan. Service Provider's revenue can be split among Base Station Miner in a preset distribution contract, in the form of a smart contract in PAS Network, or even an off-chain contract. Limits on Number of Validators At the PAS Network's initial stage, the number of validators will be limited to a certain number (e.g., 64). The number of validators will increase gradually as the PAS Network coverage increases. The selection of validators will be based on the balanced consideration of staked token and RTK map coverage area associated with that validator. Staked token RTK data stream Services Provider Staking reward Data reward Base station miner Staker Reward System A Service Provider Miner commits to provide services for at least time t and intends to earn service income r based on staked token T. The minimal number of Base Station Miners is about 10,000. To ensure robust service with enough system redundancy, the ideal number of base station miners could be 3x. Base Station Miners' density may vary from area to area, as the demand for RTK service may change dramatically. |
