Low-complexity QoS-aware frequency provisioning in downlink multi-user multicarrier systems

This paper studies quality-of-service (QoS)-aware frequency provisioning schemes for a downlink multi-user multi-carrier system in a frequency-selective fading environment with diverse user-QoS requirements in terms of target delay and effective capacity (EC). Since a jointly optimal power and sub-carrier allocation requires an exponential-time exhaustive search, we explore an alternative simpler approach with two steps: (i) frequency provisioning to allocate the available subcarriers to the demanding users, followed by (ii) power allocation for the set of subcarriers assigned to each user. The single-user EC-based power allocation can be directly applied to step (ii). Furthermore, its results can also be used to develop a low-complexity knowledge-based frequency provisioning algorithm for step (i). The proposed iterative frequency provisioning algorithm starts with an initial rate-based guess and analyzes the incremental cost of power with respect to each user´s QoS requirement to modify the allocated numbers of subcarriers that can further reduce the power consumption, if possible, in each subsequent iteration. Illustrative results show that the initial rate-based guess can be very effective in many situations, whereas, when the demanding users have similar required ECs but widespread delay requirements, the initial rate-based guess can be far from the optimum solution and therefore, more iterations are needed.