Increasing spectrum resources in cellular networks are always needed to carry the exponential data traffic growth in wireless cellular networks. Limited spectrum resources in the licensed band have necessitated Long-Term Evolution (LTE) to explore available unlicensed spectrum where an incumbent WiFi system already exists. With the deployment of Licensed Assisted Access (LAA) that utilizes Listen Before Talk (LBT) for channel access in the unlicensed spectrum along with an incumbent WiFi, the coexistence of LAA and WiFi with acceptable fairness is a major challenge. In this work, we address the issues of licensed assisted access coexisting with incumbent WiFi in an unlicensed spectrum and provide solutions to dynamically tune system parameters of LAA stations to achieve maximum total throughput from the overall system taking into account fair allocation of throughput and airtime across different networks and stations. One major system parameter we study is the contention window size for back-off. Using the method of coupled Markov Chain, we show how an inherent trade-off between throughput and airtime fairness can be managed by adjusting the CW size of LAA. For single-channel, we show how coexistence with WiFi can be managed better with LAA-Cat3 than LAA-Cat4 when total throughput and fairness are to be taken into account. For multi-carrier sensing, we establish better coexistence by optimizing contention window sizes of each LAA station separately using an assignment technique based on a genetic algorithm. We extend our work into dual-carrier aggregation where some stations have the ability to combine two independent channels into a single aggregated channel to achieve higher performance. We show that in such a dual-carrier aggregation scenario, the distribution of stations (partition) over an individual and aggregated channel, and the system parameters (contention window size and load intensity) could be optimized to ensure fair allocation of resources without affecting the secondary channel too much
