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Analysing Wi-Fi/LTE Coexistence to Demonstratethe Value of Risk-Informed Interference Assessment

Andra M. Voicu, Ljiljana SimićRWTH Aachen University, Germany

J. Pierre de VriesSilicon Flatirons Centre, University of Colorado, USA

Marina Petrova, Petri MähönenRWTH Aachen University, Germany

• risk-informed interference assessment• e.g. risk assessment for Wi-Fi/LTE coexistence

• results:– risk assessment – comprehensive, intuitive, quantitative– e.g. Wi-Fi/LTE coexistence

• no regulatory intervention needed for technical coexistence• better coexistence for Wi-Fi: sometimes with itself; sometimes with LTE• in practice typically negligible interference risk

Overview

Introduction• inter-technology spectrum sharing ↔ mutual

interference

• interference assessment for

• complementary method to worst-case: risk assessment

spectrum regulators (operational bounds)

engineers(performance optimization)

Aim & Scope

• apply risk assessment to a real-life problem of inter-technology spectrum sharing− e.g. Wi-Fi/LTE coexistence in 5 GHz band

• show benefit of risk-informed interference assessment− policy perspective− engineering perspective

LTE-in-unlicensed

• main variants

• LTE-in-unlicensed and Wi-Fi operate in the 5 GHz band

• implicit policy question: is regulatory intervention required to ensure harmonious technical coexistence?

LTE-U• MAC: adaptive duty cycle

Licensed Assisted Access (LAA)• MAC: listen-before-talk (LBT)

Risk-Informed Interference Assessment

• risk assessment uses likelihood-consequence for hazard scenarios

• risk assessment in spectrum management*(1) inventory of harmful interference hazard modes(2) define consequence metric(3) assess likelihood and consequence(4) aggregate findings for decision making

*J. P. de Vries, “Risk-informed interference assessment: A quantitative basis for spectrum allocation decisions”, Telecommunications Policy, 2017

Risk Assessment for Wi-Fi/LTE Coexistence:(1) inventory of harmful interference

• simulation model

Wi-Fi incumbent APs coexisting with:− LAA entrants− LTE-U entrants− Wi-Fi entrants


• simulation model: Monte Carlo simulations

indoor/indoor scenario outdoor/outdoor scenario(also w/o walls)

incumbent APs: 10entrant APs: 1–30 AP density: 600–12000 APs/km2

incumbent APs: 10entrant APs: 1–10 AP density: 7–150 APs/km2

• simulation model


NO. OF CHANNELS

PARAMETERS1 4

(non-DFS)

maximum(19 indoor,11 outdoor)

Channel selectionscheme

incumbents - random random

entrants -random or sense

randomorsense

Interference type co-channelco- & adjacent channel

co- & adjacent channel

• two throughput metrics for the incumbents– throughput degradation ↔ technical public policy question

– throughput unfairness among incumbents ↔ engineering optimization insight

• Jain’s fairness index:

• unfairness:

Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric

= , , Wi-Fi incumbent throughput for:• standalone Wi-Fi incumbent• Wi-Fi incumbent & Wi-Fi entrant

∑∑1


• throughput model of incumbent AP for downlink

,



,CSMA/CA protocol efficiency(Bianchi’s model)




degradation due toduty cycle frames(i.e. for coexistence with LTE-U)





fraction of time when AP xtransmits






mapping user SINRto bit rate



,

,

CSMA/CA protocol efficiency(Bianchi’s model)






,

,





AP transmit power



,

,





AP transmit power

propagation loss



,

,





AP transmit power

propagation loss

co-channel interference



,

,





AP transmit power

propagation loss


adjacent channel interference



,

,





AP transmit power

propagation loss


adjacent channel interference

noise

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence

• how do we read risk assessment charts?

in general for our WiFi/LTE example(throughput degradation)

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence & (4) aggregate findings

• throughput degradation: indoor/indoor, 1 channel, 1-30 entrants, standalone Wi-Fi

• throughput degradation increases with the AP density• for regulator: LTE (LAA/LTE-U) is sometimes friend, sometimes foe to Wi-Fi• for engineer: Wi-Fi (high risk, low degradation) vs. LTE (high risk, high degradation)

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence & (4) aggregate findings• throughput degradation: indoor/indoor, 1 channel, 1-30 entrants, Wi-Fi & Wi-Fi

• for regulator: similar likelihood of LTE being friend or foe to Wi-Fi

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence & (4) aggregate findings• unfairness among incumbents: indoor/indoor, 1 channel, 1-30 entrants

• for engineer: unfairness for incumbents higher with LTE than with Wi-Fi entrants

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence & (4) aggregate findings• throughput degradation: indoor/indoor, different no. of channels, 10 entrants

• throughput degradation decreases when no. channels increases• for regulator & engineer: typical case: 19 channels and sense→ degrada on 0• for engineer: sense better than random for 4 channels

Risk Assessment for Wi-Fi/LTE Coexistence:(3) assess likelihood and consequence & (4) aggregate findings• throughput degradation: different scenarios, 1 channel, 10 entrants

• for regulator: LTE is consistently sometimes friend, sometimes foe to Wi-Fi

Conclusions

• risk-informed interference assessment: comprehensive, intuitive, and quantitative

• for regulator: LTE sometimes friend sometimes foe to Wi-Fi → no interven on needed for technical coexistence

• for engineer: – dense deployments: lower risk when Wi-Fi coexists with Wi-Fi– sparse deployments: lower risk when Wi-Fi coexists with LTE

• in practice typically low risk for Wi-Fi coexisting with LTE-in-unlicensed → no interven on from regulator or engineer

Thank you!