Microsoft supports the Wi-Fi Alliance (WFA) with the Coexistence Test Plan (CTP); which would allow new LTE technologies to share the same unlicensed spectrum as Wi-Fi. Microsoft joined two other WFA member companies, HP Enterprise and Broadcom, in a letter to WFA to support the CTP and the amount of progress made with CTP so far.
WFA member companies that are currently producing LTE-based products see the CTP progress as slower than expected. However, Microsoft, one of WFA's founding members, notes that the CTP will be deployed almost twice as fast as any other program in WFA history. While Microsoft supports CTP, Microsoft does have some concerns about the plan specifics.
In a letter to the WFA, Microsoft noted a few problems with the CTP.
"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."
While WFA has been successful in delivering effective certification programs for wireless technology for over 17 years, Microsoft still has some reservations about the Coexistence Test Plan (CTP). At the moment, Microsoft supports the WFA. However, Microsoft hopes once the CTP is complete, there will be a fair balance between Wi-Fi and LTE, giving everyone the best wireless service possible.