I. Introduction
With the increasing demand for bandwidth-hungry applications, the mobile network operators (MNOs) are under pressure to meet efficiently demands for more capacity and better quality-of-service (QoS). The continuous increase of spectral efficiency is not enough — there is a clearly articulated demand for more spectrum, e.g. in 5G [1]. Rather than using only their licensed bands, operators can utilize also unlicensed bands, e.g., as in LTE-unlicensed [2], and develop new business models such as bundling in [3]. As unlicensed spectrum has become also congested, another option known as dynamic spectrum access (DSA) enables a secondary user (SU) network increase its capacity by using the spectrum holes in the licensed bands which correspond to the inactivity times of the licensed transmitters of the band, i.e., primary user (PU). However, the SU network has to ensure that it can detect a reappearing PU traffic timely and with high accuracy after which the SU network aborts its transmission in the PU channel. To satisfy this requirement, as previous research has experimentally [4] and theoretically [5] shown, the SU network has to deploy multiple spectrum sensors rather than single nodes sensing the spectrum. Instead of deploying the sensors itself, the SU network can offload the sensing task to nearby sensor nodes, called helpers, whose spectrum observations can reflect accurately the spectrum state at the SU’s neighborhood. Helpers can be any node ranging from low-end sensors or mobile phones to more advanced spectrum scanners, owned by individuals or by companies.
Spass system model: SU network is interested in accessing the primary user’s band opportunistically to serve its users. Helpers are the nodes offering sensing service. The agreement and transactions are processed through the smart contract defined in Ethereum blockchain.