Improving spatial reuse and MAC efficiency for future WLANs

One of the ways to provide greater coverage and capacity for future wireless networks is through network densification. This is also one of the drivers for future IEEE 802.11 deployments, aiming not only to improve throughput per link, but the overall network performance in dense deployments. That said, the IEEE 802.11ax amendment is currently focusing on addressing the challenges and improving the spectrum efficiency in dense deployments with hundreds of Access Points (APs) and Stations (STAs). This work strives to shed some light in the area of spectrum efficiency by trying to understand (i) the operation and the impact of the newly introduced Spatial Reuse feature of the IEEE 802.11ax amendment and (ii) if it is possible to realise multicast/broadcast transmissions over Wi-Fi while preserving reliability. Although the IEEE 802.11ax Spatial Reuse feature, namely BSS Color, offers several advantages and good potential for improving spectrum efficiency, it also imposes several challenges. Towards filling the aforementioned gaps and address challenges, particular contributions were made in this thesis. First, this work presents a performance evaluation of the BSS Color scheme in various scenarios, where its shortcomings are identified. Second, this work proposes a generic framework to obtain throughput for dense cellular-like (small-cell) deployments, based on a mathematical model. Third, this work introduces COST, a novel Spatial Reuse technique for improving BSS Color performance by exploiting the information provided by this scheme and providing throughput gain of up to 57% while preserving fairness between BSSs. Fourth, this thesis proposes the design of a rate control algorithm that leverages the BSS Color and COST, providing up to 113% throughput gain in dense deployments when compared to the traditional off-the-shelf MinstrelHT. Finally, this thesis elaborates a network coding approach to enable multicast/broadcast transmissions over Wi-Fi, that could enhance throughput performance by 20% when compared with the legacy MAC feedback mechanism. The main goal for this contribution is to provide a means for realising reliable multicast/broadcast communications by reducing the use of the Wi-Fi feedback mechanism. The above contributions were evaluated through system-level simulations, emulating real-world deployments. This work showed that advanced techniques, that exploit all available information by monitoring the inter-BSS and intra-BSS frames, are required to support the IEEE 802.11ax Spatial Reuse feature operation and provide throughput gain while preserve fairness among users. Furthermore, it was shown that the network coding should carefully be designed and enabled only when it is required, otherwise throughput loss could be observed due to the transmitted overhead. The scenario and application’s requirements should also be taken into account (e.g. latency).