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

TL;DR

This paper introduces orthogonal coexistence schemes, ORLA and OLAA, that enable unlicensed LTE to outperform WiFi in throughput without harming WiFi performance, addressing limitations of the current LAA standard.

Contribution

The paper proposes two novel orthogonal coexistence policies, ORLA and OLAA, that improve unlicensed LTE throughput while ensuring fair coexistence with WiFi networks.

Findings

ORLA/OLAA achieve over 200% throughput gains compared to LAA.

WiFi can be more efficient than LAA when aggregating packets.

LAA causes up to 92% throughput loss on WiFi, mitigated by ORLA/OLAA.

Abstract

Future mobile networks will exploit unlicensed spectrum to boost capacity and meet growing user demands cost-effectively. The 3GPP has recently defined a Licensed-Assisted Access (LAA) scheme to enable global Unlicensed LTE (U-LTE) deployment, aiming at ($i$) ensuring fair coexistence with incumbent WiFi networks, i.e., impacting on their performance no more than another WiFi device, and ($ii$) achieving superior airtime efficiency as compared to WiFi. In this paper 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 LAA 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 performance evaluation through which we demonstrate that, when aggregating packets, IEEE 802.11ac WiFi can be more efficient than 3GPP LAA, whereas our proposals can attain 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.