Reem Karaki

Licensed-Assisted Access LTE: coexistence with IEEE 802.11 and the evolution toward 5G

LAA is a new operation mode of LTE in the unlicensed spectrum, which will be featured in LTE Release 13. Under LAA, licensed carriers will be aggregated with unlicensed carriers in order to opportunistically enhance downlink user throughput while still offering seamless mobility support. In order to coexist with WiFi, some of the new functionalities required of LAA LTE include a mechanism for channel sensing based on listen-before-talk, discontinuous transmission on a carrier with limited maximum transmission duration, and multicarrier transmission across multiple unlicensed channels. This article presents a detailed overview of the design agreements for LAA, the impact of unlicensed spectrum operation on the LTE physical layer architecture, and the scope of additional enhancements beyond LTE Release 13. A range of simulations for indoor and multicarrier scenarios show that fair coexistence between LAA and WiFi can be achieved, and that deployment of LAA can provide a boost in WiFi performance.

Design and Evaluation of Licensed Assisted Access LTE in Unlicensed Spectrum

Licensed assisted access (LAA) is a new feature for 3GPP LTE systems to operate in the unlicensed spectrum. Under LAA, licensed carriers will be aggregated with unlicensed carriers in order to opportunistically enhance user throughput, while still offering seamless mobility and outdoor coverage. In order to coexist with other technologies in the unlicensed bands, several new functionalities for LAA LTE have been introduced, including longterm channel selection, short-term channel sensing based on listen-before-talk (LBT), and discontinuous transmission on a carrier with limited maximum transmission duration. In this article, we present research findings behind the designs for LAA systems. We discuss the impact of several parameters of the LAA LBT framework on the channel access opportunities of LAA, and its coexistence performance toward co-channel networks based on extensive system-level simulation results. The investigation covers both single-channel as well as multi-channel operation and coexistence scenarios. In addition to the finalized designs for downlink LAA operations in Release 13, our findings in this article further shed light on the uplink LAA operations to be introduced in Release 14.

Globally Stable Wireless Data Flow Control

Packet data flow control from internet nodes to wireless transmission nodes will become increasingly important in 5G wireless systems. One reason is the new requirement to maintain and guarantee a maximum round-trip loop delay for high-bandwidth feedback control applications. Another driver is the emerging multipoint mobile broadband internet access, where data starvation needs to be avoided in the transmit queue buffers of the wireless transmission nodes. Moreover, robust global stability is a requirement, since an only locally stable data flow controller would have a nonzero likelihood to malfunction algorithmically. The resulting networked control problem is further complicated by an uncertain internet backhaul loop delay, in combination with a one-directional data flow that introduces saturation in the feedback loop. The paper therefore contributes with a proof of global robust stability for a nonlinear networked window-based packet flow control algorithm. The performance and stability of the controller are assessed with simulation, which shows that the algorithm performs as required.

Practical energy-aware cell association for small cell deployment

In this work, we consider a heterogeneous network consisting of macro and pico base stations. Our goal is to associate users to one of the base stations,while minimizing the energy consumption of the network. Moreover, the algorithm should consider constraints of a real system and thus, only include the necessary complexity that helps reducing the energy consumption. Therefore, we first formulate the energy minimization problem in three different manners, each one including a different level of modeling details. The solution of each problem is analyzed to identify the important factors to consider when designing an energy-optimized cell association algorithm. Based on this analysis, we then develop a practical energy-aware cell association heuristic. Finally, the developed algorithm is evaluated using complex system simulations. Results show that significant energy savings are achievable by the developed algorithm compared with the conventional cell association in cellular networks. Copyright

Uplink Performance of Enhanced Licensed Assisted Access (eLAA) in Unlicensed Spectrum

Licensed-Assisted Access (LAA) is a new feature for 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE) system to operate in the unlicensed spectrum. LAA utilizes the carrier aggregation technology to aggregate both licensed and unlicensed carriers in order to opportunistically boost user throughput, while maintaining seamless mobility, quality of service and good indoor and outdoor coverage. In order to coexist with other technologies in the unlicensed bands, several new coexistence functionalities for LAA LTE have been introduced, including long term channel selection, short-term channel sensing based on listen-before-talk (LBT), and discontinuous transmission on a carrier with limited maximum transmission duration. LAA will be supported for both Downlink (DL) and Uplink (UL) transmissions. This paper presents a detailed overview of the design challenges for UL LAA access on unlicensed bands due to the scheduling aspects of LTE. We present solutions to address grant and scheduling request (SR) overhead and delays. We also discuss possible UL LBT options to increase the performance and the flexibility of scheduled LTE when operating on unlicensed bands. A range of simulations show fair coexistence between LAA and Wi-Fi. Furthermore, this paper sheds lights on possible future enhancement for UL LAA using unscheduled UL transmission.