Flow-level modeling and analysis of dynamic TDD in LTE

We present a queueing analysis of elastic traffic performance in LTE systems using the dynamic TDD scheme. Both fair resource sharing and performance optimization using different approaches are considered. We first analyze the system without any restrictions in the resource allocation between the uplink and downlink and demonstrate that a simple dynamic scheduling scheme (called here dynamic-PS), where the allocation for a single flow is always inversely proportional to the total number of active flows, shows good performance and fairness properties compared with any optimized static allocation scheme. We also consider the achievable gains with more detailed traffic statistics, including the application of the Gittins index policy and SRPT. However, the actual LTE TDD system only supports a discrete set of possible allocations in the capacity region. We then investigate how these allocation constraints impact the performance of the discretized variant of the dynamic-PS policy by using different approaches. To optimize the performance we apply MDP for exponential service times and, for example, derive a structural result that the optimal policy always selects among two corner points of the capacity region. Also, an SRPT-like heuristic scheduling algorithm is given. The analytical and simulated results suggest that the discrete dynamic-PS policy is robust against impact of different service time distributions, fair and performs reasonably well.