Jean Pierre De Vries

LTE in Unlicensed Bands Is Neither Friend nor Foe to Wi-Fi

Proponents of deploying LTE in the 5 GHz band for providing additional cellular network capacity have claimed that LTE would be a better neighbour to Wi-Fi in the unlicensed band, than Wi-Fi is to itself. On the other side of the debate, the Wi-Fi community has objected that LTE would be highly detrimental to Wi-Fi network performance. However, there is a lack of transparent and systematic engineering evidence supporting the contradicting claims of the two camps, which is essential for ascertaining whether regulatory intervention is in fact required to protect the Wi-Fi incumbent from the new LTE entrant. To this end, we present a comprehensive coexistence study of Wi-Fi and LTE-in-unlicensed, surveying a large parameter space of coexistence mechanisms and a range of representative network densities and deployment scenarios. Our results show that, typically, harmonious coexistence between Wi-Fi and LTE is ensured by the large number of 5 GHz channels. For the worst-case scenario of forced co-channel operation, LTE is sometimes a better neighbour to Wi-Fi-when effective node density is low-but sometimes worse-when density is high. We find that distributed interference coordination is only necessary to prevent a “tragedy of the commons” in regimes where interference is very likely. We also show that in practice it does not make a difference to the incumbent what kind of coexistence mechanism is added to LTE-in-unlicensed, as long as one is in place. We therefore conclude that LTE is neither friend nor foe to Wi-Fi in the unlicensed bands in general. We submit that the systematic engineering analysis exemplified by our case study is a best-practice approach for supporting evidence-based rulemaking by the regulator.

A Risk-Informed Interference Assessment of MetSat/LTE Coexistence

Quantitative risk assessment has recently been proposed to assess the impact of a new radio service allocation on incumbents. This paper demonstrates its viability by performing a risk-informed interference assessment in a recent U.S. case: the protection of meteorological satellite earth stations from interference by cellular mobile transmitters. We find that the hazard selected by policy makers (co-channel interference with the receiving antenna at 5° elevation) was not the most severe, and that their worst case approach overlooked more significant risks, notably adjacent band interference. We begin with an inventory of the performance hazards. We survey consequence metrics that quantify the severity of interference, and select the interference protection criteria defined in Recommendation ITU-R SA.1026-4. We then use Monte Carlo modeling to calculate probability distributions of resulting interference due to co-channel and adjacent band transmissions. We identify a co-channel exclusion distance that keeps interference risk below the SA.1026-4 criteria. We show that the binding constraint is not the ITU-R “long-term” interference mode (5° antenna elevation), but rather the “short-term” interference when the elevation is 13°. We give an extensive sensitivity analysis showing that the propagation modeling, and particularly the choice of clutter model, can have a significant effect on the results. We conclude that quantitative risk assessment yields useful insights for analyzing coexistence. Protection criteria that combine an interfering power level with statistical exceedance limits were essential to our analysis, and we recommend that policy makers adopt statistical service rules more widely to support future risk analysis. Our analysis was limited by the unavailability of baseline values for service metrics, and the lack of transparency in previous studies, notably ITU-R recommendations. We recommend that regulators encourage parties to provide baseline values and the methods underlying interference criteria and coexistence assessments.

Risk-Informed Interference Assessment for Shared Spectrum Bands: A Wi-Fi/LTE Coexistence Case Study

Interference evaluation is crucial when deciding whether and how wireless technologies should operate. In this paper, we demonstrate the benefit of risk-informed interference assessment to aid spectrum regulators in making decisions, and to readily convey engineering insight. We apply, for the first time, risk assessment to an open question of inter-technology spectrum sharing, i.e., a Wi-Fi/LTE coexistence study in the unlicensed band, and we demonstrate that this method comprehensively quantifies the interference impact. We perform simulations with our newly publicly available tool and we consider throughput degradation and fairness as example metrics to assess the risk for different network densities, numbers of channels, and deployments. The risk assessment study shows that no regulatory intervention is needed to ensure harmonious technical Wi-Fi/LTE coexistence: for the typically large number of channels available in the 5 GHz band, the risk for Wi-Fi from LTE is negligible. As an engineering insight, Wi-Fi coexists better with itself in dense deployments, but better with LTE in sparse deployments. Also, both main LTE-in-unlicensed variants coexist well with Wi-Fi in general. For LTE intra-technology inter-operator coexistence, both variants typically coexist well in the 5 GHz band, but for dense deployments, implementing listen-before-talk causes less interference.

Unlocking Spectrum Value Through Improved Allocation, Assignment and Adjudication of Spectrum Rights

Technological developments have continued to increase the importance of radio spectrum, with citizens, companies and government users increasing their use of wireless-enabled services of all kinds, from smartphone apps to aerial surveillance. Since technology places limits on the coexistence of multiple radio systems, usage rights must be allocated among various competing uses. Currently, the management of the wireless spectrum in the United States (and elsewhere) is heavily constrained by government regulation. That makes it difficult for spectrum players — whether wireless service providers, citizens using unlicensed devices, or government users — to reach mutually agreeable, efficiency-enhancing agreements through direct negotiation with one another. This Hamilton Project discussion paper describes the importance of moving towards a more economically efficient system for managing the use of wireless spectrum and proposes concrete policy steps to move us closer to such a model. In particular, it sets forth three pillars of a reformed policy regime: (1) reduce ambiguity about the responsibilities of receivers to tolerate interference by defining harm claim thresholds that state the signal levels that must be exceeded before one operator can claim harmful interference from another; (2) reduce the drawbacks of excessive band fragmentation by introducing band agents that could represent large groups of licensees in negotiating changes in operating rights with neighbors; and (3) move adjudication from the current ad hoc and politically charged process to a more fact-based procedure that can resolve spectrum-related disputes in a timely fashion using judges with expertise in spectrum policy, either in the FCC and/or a newly created Court of Spectrum Claims. All three proposals reform the legacy spectrum policy framework by empowering individual spectrum licensees to develop win-win solutions without having to invoke time-consuming regulatory processes. Taken together, these reforms promise to move more spectrum management from one model more closely controlled by regulators to one authorizing end users to make more flexible, win-win uses of spectrum. Based on our rough estimates, we conclude that these reforms could bring a total of a

Risk-Informed Regulation: Lessons for FCC Spectrum Management from Nuclear Industry Policy Making

10 billion per year in additional consumer surplus.