Coexistence Requirements of 802.11 WLAN and LTE in Unlicensed Spectrum

Presentation from July 2014 discussing the impact of LTE in unlicensed spectrum on 802.11 WLAN networks. Highlights proposals for TGax functional requirements document. Examines LTE-U and its challenges for coexistence with other technologies like Wi-Fi. Details LTE quiet periods and lab test conditions comparing LTE and Wi-Fi in the 2.4 GHz band. Analyzes the interference power of LTE on Wi-Fi throughput in various scenarios.

• Coexistence
• LTE
• Unlicensed Spectrum
• Wi-Fi
• TGax

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1. July 2014 doc.: IEEE 802.11-14/0821r2 Coexistence Requirements of 802.11 WLAN and LTE in Unlicensed Spectrum Date: 2014-07 Authors: Name Affiliation Address Phone Email 858 Coal Creek Cir Louisville, CO 80027 USA Alireza Babaei CableLabs +1 303 661 3405 a.babaei@cablelabs.com Belal Hamzeh Jennifer Andreoli-Fang Joey Padden ? CableLabs CableLabs CableLabs Submission Slide 1 Alireza Babaei, CableLabs

2. July 2014 doc.: IEEE 802.11-14/0821r2 Abstract This presentation Provides results on the impact of LTE in unlicensed spectrum on the performance of 802.11 WLAN networks Proposes a requirement for TGax Functional Requirements document. Submission Slide 2 Alireza Babaei, CableLabs

3. July 2014 doc.: IEEE 802.11-14/0821r2 Background 3GPP is considering extending the use of LTE into the unlicensed spectrum as a seamless approach to enable traffic offload. This new approach is dubbed LTE Unlicensed (LTE-U). LTE-U, being a centralized scheduling system, will change the ecosystem in unlicensed spectrum. LTE-U introduces new coexistence challenges for other technologies operating in the same unlicensed bands, particularly for legacy Wi-Fi. Submission Slide 3 Alireza Babaei, CableLabs

4. July 2014 doc.: IEEE 802.11-14/0821r2 LTE Quiet Period quiet period LTE is an almost continuously transmitting protocol. A Wi-Fi device needs to wait for a quiet period, when LTE is not transmitting, before attempting to transmit. Even when LTE is not transmitting data, it periodically transmits a variety of Control and Reference Signals. 1 subframe 12 subcarriers LTE quiet period depends on the periodicity of these signals. For FDD LTE mode, the maximum quiet period is only 215 sec (depicted here). In the absence of data, or when subframes are intentionally muted, maximum LTE quiet period is 3 msec in TD-LTE mode. and it will be at the discretion of the eNodeB scheduler control channel control signaling reference symbols DL Control and Reference Signals (LTE FDD) It will be difficult for Wi-Fi to grab the channel from LTE, Submission Slide 4 Alireza Babaei, CableLabs

5. July 2014 doc.: IEEE 802.11-14/0821r2 Lab Test Conditions 2.4 GHz Band LTE Wi-Fi ISM Ch. 1 (2.412 GHz) Conducted testing 20 MHz LTE FDD downlink frequency converted into the 2.4 GHz Band LTE UE to setup the connection - no data passed LTE had equal power at AP and client 1 AP and 1 Client Wi-Fi Signal power -60 dBm (good average signal level) DL/UL Loss was symmetrical 1 spatial stream, long guard interval (max MCS 4) or 39 Mbps 100 Mbps UDP traffic offered load Reported throughput figures are average over 1 minute. Submission Slide 5 Alireza Babaei, CableLabs

6. July 2014 doc.: IEEE 802.11-14/0821r2 802.11n Wi-Fi vs. Rel. 8 Downlink LTE Co- Channel 20 MHz Scenario Modeled in Lab Setup LTE Interference Power vs. Wi-Fi Throughput* eNodeB Wi-Fi AP Wi-Fi Client 30 Wi-Fi to Wi-Fi Wi-Fi Throughput (Mbps) 25 Distance LTE to Wi-Fi Locations Fixed 20 15 Wi-Fi throughput diminishes as LTE transmission moves closer to Wi-Fi devices With LTE power at Wi-Fi client energy detect threshold, throughput approaches zero 10 5 0 -120 -110 -100 -90 -80 -70 -60 -50 -40 Interference Power (dBm) *Shape of curve dependent on device tested, trend is key take away Submission Slide 6 Alireza Babaei, CableLabs

7. July 2014 doc.: IEEE 802.11-14/0821r2 Coexistence with Duty Cycle LTE Duty Cycle Period LTE Off LTE On LTE On time Wi-Fi access gaps when LTE is off Duty Cycle: % of cycle LTE is active One popular concept for spectrum sharing is Duty Cycling Allow LTE to occupy the channel for fixed (or semi dynamic) percentage of time for each period Selection of the period (in milliseconds) is critical to the performance on Wi-Fi network Submission Slide 7 Alireza Babaei, CableLabs

8. July 2014 doc.: IEEE 802.11-14/0821r2 Duty Cycle Approach- Wi-Fi Throughput Wi-Fi throughput is consistent across LTE higher cycle periods Wi-Fi gets <1Mbps for 10ms / 70% case Same as TD-LTE w/ 3 ms quiet period configuration Wi-Fi Throughput vs. LTE Duty Cycle and Period Co-Channel 35 30 Wi-Fi Throughput (Mbps) 25 Baseline (0%) 20 30% 15 50% 10 70% 90% 5 0 10ms 50ms Duty Cycle Period 100ms 200ms 500ms Submission Slide 8 Alireza Babaei, CableLabs

9. July 2014 doc.: IEEE 802.11-14/0821r2 Duty Cycle Approach- Wi-Fi Delay Wi-Fi 95th %-tile Delay vs. LTE Duty Cycle and Period Co-Channel Light Load Light load Wi-Fi 95th percentile delay shows the real impact of duty cycle period Delay increases 20x, 40x, 60x or more Mean delay follows same trend 450 400 350 300 Delay (ms) 0% (Baseline) 250 30% 200 50% 150 70% 100 90% 50 0 10ms 50ms Duty Cycle Period 100ms 200ms 500ms Submission Slide 9 Alireza Babaei, CableLabs

10. July 2014 doc.: IEEE 802.11-14/0821r2 Coexistence Requirements We propose following requirements to be added to the 802.11ax FR document: The TGax amendment shall enable a mode of operation that efficiently utilizes the spectrum and ensures minimum performance levels for TGax devices when coexisting with non- listen-before-talk compliant devices in the same unlicensed band that act as constantly or partially on interferers The minimum performance levels is TBD after group discussion Submission Slide 10 Alireza Babaei, CableLabs

11. July 2014 doc.: IEEE 802.11-14/0821r2 Straw Poll 1. Do you support adding following requirment to the TGax Functional Requirements document? The TGax amendment shall enable a mode of operation that efficiently utilizes the spectrum and ensures minimum performance levels (TBD) for TGax devices when coexisting with non-listen-before-talk compliant devices in the same unlicensed band that act as constantly or partially on interferers i. ii. iii. Yes No Abstain Submission Slide 11 Alireza Babaei, CableLabs

12. July 2014 doc.: IEEE 802.11-14/0821r2 References A. Babaei, J. Andreoli-Fang and B. Hamzeh, On the Impact of LTE-U on Wi-Fi Performance, To appear in Proceedings of IEEE PIMRC 2014. Submission Slide 12 Alireza Babaei, CableLabs