Optimal Spectrum Partitioning and Licensing in Tiered Access Under Stochastic Market Models

We consider the problem of partitioning a spectrum band into $M$ channels of equal bandwidth, and then further assigning these $M$ channels into $P$ licensed channels and $M-P$ unlicensed channels. Licensed channels can be accessed both for licensed and opportunistic use following a tiered structure that has a higher priority for licensed use. Unlicensed channels can be accessed only for opportunistic use. We address the following question in this paper. Given a market setup, what values of $M$ and $P$ maximize the net spectrum utilization of the spectrum band? While this problem is fundamental, it is highly relevant practically, e.g., in the context of partitioning the recently proposed Citizens Broadband Radio Service band. If $M$ is too high or too low, it may decrease spectrum utilization due to limited channel capacity or due to wastage of channel capacity, respectively. If $P$ is too high (low), it will not incentivize the wireless operators who are primarily interested in unlicensed channels (licensed channels) to join the market. These tradeoffs are captured in our optimization problem which manifests itself as a two-stage Stackelberg game. We design an algorithm to solve the Stackelberg game and hence find the optimal $M$ and $P$ . The algorithm design also involves an efficient Monte Carlo integrator to evaluate the expected value of the involved random variables like spectrum utilization and operators’ revenue. We also benchmark our algorithms using numerical simulations.

I. Introduction

To support the ever-growing wireless data traffic, the Federal Communication Commission (FCC) released the underutilized Citizens Broadband Radio Service (CBRS) band for shared use in 2015 [2]. CBRS band is a federal spectrum band from to . The band is divided into 15 channels of each. The shared use of the CBRS band follows an order of priority. Federal users have the highest priority access to the channels. Out of the 15 channels, 7 are Priority Access Licenses (PALs). PAL licenses are sold through auctions and the lease duration of a PAL license may range between 1 – 10 years [2]–[4]. A PAL license holder can use their channel only if federal users are not using it. The remaining 8 out of the 15 channels are reserved only for opportunistic use by General Authorized Access (GAA) users. Opportunistic channel allocation to GAA users can happen at a time scale of minutes to weeks. GAA users can use these 8 channels if federal users are not using the channels. GAA users can also use the 7 PAL channels provided that neither federal users nor PAL license holders are using it.