Spectrum sharing policies for heterogeneous delay-sensitive users: A novel design framework

We develop a novel design framework for spectrum sharing among distributed users with heterogeneous delay-sensitivity (e.g. users with video streaming that requires low delay, and users with video conferencing that requires very low delay). Most existing spectrum sharing policies are stationary, i.e. users transmit at constant power levels simultaneously. Under stationary policies, the users have low throughput due to the strong interference from each other. Nonstationary spectrum sharing policies, which allow users to transmit at time-varying power levels, can significantly improve the spectrum efficiency. The most well-known and simple nonstationary policy is the round-robin TDMA (time-division multiple access) policy, in which the users access the spectrum in turn. Although the round-robin TDMA policy increases the spectrum efficiency by eliminating multi-user interference, it is suboptimal in terms of quality of experience for delay-sensitive users, especially when they have heterogeneous delay-sensitivity. This is because the round-robin TDMA policy allocates the users' transmission opportunities in a predetermined order such that they have (roughly) the same amount of transmission opportunities in any duration of time. However, some users may have earlier deadlines and need more transmission opportunities early on, while some can wait until later. This heterogeneity in delay-sensitivity is not considered in the round-robin TDMA policy. In this paper, we propose nonstationary policies that allocate the transmission opportunities based on the users' delay-sensitivity and their past deadline-abiding transmissions. As we will see, the optimal policy is not cyclic at all as is the round-robin TDMA policy. We also propose a low-complexity algorithm, which can be run by each user in a distributed manner, to construct the optimal nonstationary policy. Simulation results validate our analytical results and quantify the performance gains enabled by the proposed policies.