Achieving Quality of Service for LTE in Unlicensed Bands

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Wireless networks aim to integrate different radio access networks, such as the WiFi and Long Term Evolution (LTE) heterogeneous systems, to provide seamless access and continuous service. The coexistence of different access techniques poses a challenge for admission control and resource allocation. Meanwhile, due to the limited licensed bandwidth, Licensed-Assisted-Access (LAA) is used to extend LTE links into the unlicensed band, and the coexistence of LTE and WiFi in the unlicensed bands has attracted considerable research interests. In this thesis, we investigate how to achieve Quality-of-Service (QoS) for the LTE system in unlicensed bands for LTE and WiFi heterogeneous wireless networks. Firstly, we propose a resource denotation method in the WiFi and LTE heterogeneous networks based on a concept of spectral bandwidth mapping. This method simplifies the denotation of system resources and makes it possible to calculate residual system capacity. The network selection algorithm based on an economic model is designed in both under-loaded and over-loaded traffic scenarios in heterogeneous networks. The simulation results demonstrate that this algorithm achieves better performance than the existing scheme in terms of increasing system capacity, achieving load balancing, and reducing the new call blocking probability in heterogeneous networks. Secondly, we extend our work to LTE unlicensed bands (LTE-U) to guarantee the QoS for LTE devices coexisting with WiFi. We quantitatively analyze the MAC delay for the tagged LTE evolved Node Base Station (eNB) under the saturated WiFi traffic condition. We propose a delay-guaranteed admission control scheme that considers the freezing time of busy slots caused by collision or successful transmission. We introduce the exponential backoff mechanism for the delay analysis. Validated by simulation results, our method provides essential insights into the system admission performance and fairness of access. Thirdly, we propose Deterministic Channel Aggregation (DCA) for LTE-U under the condition of unsaturated WiFi traffic, where the LTE eNB aggregates a predetermined number of channels in the unlicensed spectrum to achieve high data-rate communications. We introduce the MAC layer design and analyze the collision probability and channel occupation ratio for DCA. Simulation results validate the effectiveness of DCA and our analytical results when the eNB coexists with multiple WiFi systems under a wide range of traffic load conditions. DCA is particularly useful for applications requiring high bandwidth and enables efficient access control of mobile broadband applications in the LTE Unlicensed bands.
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