ORLA/OLAA: Orthogonal Coexistence of LAA and WiFi in Unlicensed Spectrum

• Published in: IEEE/ACM transactions on networking Vol. 26; no. 6; pp. 2665 - 2678
• Main Authors: Garcia-Saavedra, Andres, Patras, Paul, Valls, Victor, Costa-Perez, Xavier, Leith, Douglas J.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3GPP; Anchors; Coexistence; Collision avoidance; Downlink; IEEE 802.11 Standard; LAA; listen-before-talk; Long Term Evolution; LTE-U; Mobile communication systems; spectrum sharing; Throughput; Transmitters; unlicensed LTE; WiFi; Wireless communications; Wireless fidelity; Wireless networks
• ISSN: 1063-6692; 1558-2566
• DOI: 10.1109/TNET.2018.2876590

Future mobile networks will exploit unlicensed spectrum to boost capacity and meet growing user demands cost-effectively. The 3 rd Generation Partnership Project (3GPP) has recently defined a License Assisted Access (LAA) scheme to enable global Unlicensed LTE (U-LTE) deployment, aiming at 1) ensuring fair coexistence with incumbent WiFi networks, i.e., impacting on their performance no more than another WiFi device; and 2) achieving superior airtime efficiency as compared with WiFi. We show the standardized LAA fails to simultaneously fulfill these objectives, and design an alternative orthogonal (collision-free) listen-before-talk coexistence paradigm that provides a substantial improvement in performance, yet imposes no penalty on existing WiFi networks. We derive two optimal transmission policies, ORLA and OLAA, that maximize LAA throughput in both asynchronous and synchronous (i.e., with alignment to licensed anchor frame boundaries) modes of operation, respectively. We present a comprehensive evaluation through which we demonstrate that, when aggregating packets, IEEE 802.11ac WiFi can be more efficient than LAA, whereas our proposals attains 100% higher throughput, without harming WiFi. We further show that long U-LTE frames incur up to 92% throughput losses on WiFi when using 3GPP LAA, whilst ORLA/OLAA sustain >200% gains at no cost, even in the presence of non-saturated WiFi and/or in multi-rate scenarios.