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
Risk Assessment for Wi-Fi/LTE Coexistence:(1) inventory of harmful interference
• 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
Risk Assessment for Wi-Fi/LTE Coexistence:(1) inventory of harmful interference
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
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• throughput model of incumbent AP for downlink
,
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• throughput model of incumbent AP for downlink
,CSMA/CA protocol efficiency(Bianchi’s model)
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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)
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
AP transmit power
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
AP transmit power
propagation loss
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
AP transmit power
propagation loss
co-channel interference
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
AP transmit power
propagation loss
co-channel interference
adjacent channel interference
Risk Assessment for Wi-Fi/LTE Coexistence:(2) define consequence metric
• 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
AP transmit power
propagation loss
co-channel interference
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!