Fair Wi-Fi and cellular wireless coexistence benefits everyone

How much do you rely on Wi-Fi?  What if the Wi-Fi in your home or at your neighborhood Starbucks stopped working? Who would you call? What would you do?

We all rely on Wi-Fi, as well as cellular wireless technologies, for much of our daily communication, news and information, and entertainment. Cellular and Wi-Fi both use wireless spectrum and, as we are increasingly reliant on both, it’s important that they can work together fairly and responsibly. That’s why Wi-Fi Alliance (WFA) has been developing a Coexistence Test Plan for new, non-standards-based LTE technologies that wish to fairly share unlicensed spectrum with Wi-Fi.

This week, we joined with Hewlett Packard Enterprise and Broadcom in a letter to WFA expressing our support for this work, and appreciation of the progress to date.

While the pace of progress is of concern to some WFA member companies that are developing LTE-based products, as one of WFA’s founding members, Microsoft observes that this program will be rolled out almost twice as fast as any other program in the history of WFA.

While we support the plan, we do have concerns that we shared in our joint letter to WFA.

First, LTE-U Forum members continue to oppose the inclusion of Wi-Fi links that operate at low-signal levels into the testing scenarios.

Wi-Fi’s ability to operate at low-signal levels is one of the key reasons why an incredible number of simultaneous users can take advantage of the technology. We believe it is both fair and reasonable to insist on testing real-world scenarios that make use of this core aspect of Wi-Fi, and are concerned that continued pressure to exclude low-signal level testing is an indication that LTE-U Forum members are having difficulty fulfilling their promise of fairness in a number of real-world scenarios using the methods they have chosen.

However, the currently proposed compromise threshold is significantly higher than that received by Wi-Fi access points from many battery-powered Wi-Fi clients. Under the current test plan, millions of Wi-Fi devices operating today will be ignored by LTE-U equipment while it is calculating how to share fairly, with the result that some of these devices will be interfered with, and, in the worst-case scenario, will be denied access to the channel completely when some LTE-U devices transmit a signal that will cause Wi-Fi devices to turn off when they assert that it is their turn to transmit.

In addition, we continue to be concerned that there is still no clear understanding about how various unlicensed LTE devices will determine their duty cycle. Microsoft has been involved in cognitive radio research for over a decade, and we are skeptical of the notion that unlicensed LTE equipment can garner enough information to operate fairly based on the amount of energy it receives. To the best of our knowledge, the use of received energy to decide the impact of a radio’s transmissions on an unknown number of neighbors is still an open question in research.

Even with these concerns, however, Microsoft recognizes that the nearly completed test plan represents a pragmatic and significant compromise between competing viewpoints, and we endorse it. WFA has a 17-year history of delivering effective certification programs for continuously evolving wireless technologies and, as we noted in our joint letter, we believe that the WFA Coexistence Test Plan process has been fact-based, conducted professionally, and that WFA is the right organization to do this work.

We are hopeful that a successful conclusion to this process will result in fair and responsible coexistence that improves the wireless experience for all.

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