Spectrum sharing for delay-sensitive applications with continuing QoS guarantees

We study a wireless network in which multiple users stream delay-sensitive applications such as video conferencing and video streaming. Existing spectrum sharing policies, which determine when users access the spectrum and at what power levels, are either constant (i.e. users transmit simultaneously, at constant power levels) or weighted round-robin time-division multiple access (TDMA) (i.e. users access the spectrum in turn, one at a time). Due to multi-user interference, constant policies have low spectrum efficiency. We show that round-robin policies are inefficient for delay-sensitive applications because the various "positions" (i.e. transmission opportunities) in a cycle are not created equal: earlier transmission opportunities are more desirable since they enable users to transmit with lower delays. Specifically, we show that (weighted) round-robin TDMA policies cannot simultaneously achieve high network performance and low transmission delays. This problem is exacerbated when the number of users is large. We propose a novel framework for designing optimal TDMA spectrum sharing policies for delay-sensitive applications, which can guarantee their continuing QoS (CQoS), i.e. the desired throughput (and the resulting transmission delay) starting from every moment in time is guaranteed for each user. We prove that the fulfillment of CQoS guarantees provides strict upper bounds on the transmission delays incurred by the users. We construct the optimal TDMA policy that maximizes the desired network performance (e.g. max-min fairness or social welfare) subject to the users\´ CQoS guarantees. The key feature of the proposed policy is that it is not cyclic as in (weighted) round-robin policies. Instead, it adaptively determines which user should transmit next, based on the users\´ remaining amounts of transmission opportunities needed to achieve the desired performance. We also propose a low-complexity algorithm, which is run by each user in a distributed manner, to - onstruct the optimal policy. Simulation results demonstrate that our proposed policy significantly outperforms the optimal constant policy and round-robin policies by up to 6 dB and 4 dB in peak signal-to-noise ratio (PSNR) for video streaming.