Qualcomm Insists LTE-U Will Not Unfairly Use Wi-Fi Resources at 5 GHz

As appealing as spectrum sharing is, access fairness is an issue where it comes to allowing Long Term Evolution devices to use Wi-Fi spectrum as well.

In the fall of 2013, Qualcomm began working on technologies to bring the benefits of 4G LTE to unlicensed spectrum, for example.

Any technology that meets a minimal set of technical rules is allowed in unlicensed spectrum, and no one using this spectrum has any priority over anyone else, says Dean Brenner, Qualcomm

SVP, Government Affairs.

The obvious corollary is that any direct use of Wi-Fi by LTE networks (as opposed to passive use of Smartphone Wi-Fi radios) must ensure fairness in terms of how LTE-U devices contend for Wi-Fi spectrum.

There are three forms of LTE Unlicensed, known as LTE-U, LAA, and MuLTEfire. From the outset, Qualcomm says it has worked to ensure that LTE Unlicensed will have no adverse impact on Wi-Fi.

Huawei, for example, has tested LAA and says it coexists peacefully with other Wi-Fi users.

The company has done a great deal of technical design and development work to ensure that LTE Unlicensed will coexist very well with Wi-Fi, sharing the unlicensed spectrum fairly.

Qualcomm tests show that adding a neighboring LTE Unlicensed node does not impact an existing Wi-Fi node any more than would adding another Wi-Fi node.

In fact, in many cases, replacing a Wi-Fi node with an LTE-U node improves the throughput for nearby Wi-Fi users, Brenner says.

For example, one of the tests measured average Wi-Fi throughput in an extremely dense deployment. The base scenario used eight commercial off-the-shelf, carrier-grade Wi-Fi access points all operating in the same 5 GHz channel and each sending data to a different client device.

When two of the Wi-Fi access points are replaced with LTE-U small cells operating in the same conditions, the average throughput of the remaining Wi-Fi nodes increased by 16 percent. When four of the eight Wi-Fi nodes are replaced with four LTE-U nodes, the gain increases 38 percent over the baseline.

Some say LTE-U will interfere with Wi-Fi unless LTE-U operates with an energy detection level that is 100 times (20 dB) more sensitive than the level that Wi-Fi itself uses to detect non-Wi-Fi technologies and decide whether a channel is available for use, additional tests were performed.

Additional Qualcomm tests confirmed that LTE-U successfully shares spectrum with Wi-Fi when realistic assumptions are used.

These tests likewise confirmed that LTE-U actually improves Wi-Fi performance when LTE-U is operating either above or below Wi-Fi’s Energy Detect (ED) level. In other words, LTE-U protects Wi-Fi to a greater degree than Wi-Fi protects itself.

Further tests confirm that LTE-U has a negligible impact on Wi-Fi beacon delivery or latency sensitive Wi-Fi applications, such as VoIP.

No everyone will agree with those assertions. But “how” one tests makes a difference.

Qualcomm argues it is totally improper to compare the coexistence test results of LTE-U/LAA and Wi-Fi to single-link, interference-free Wi-Fi throughput.

Test results show that when two neighboring Wi-Fi Access Points share a single channel, the Wi-Fi throughput drops below 50 percent of the single-link Wi-Fi throughput.

The point, Qualcomm argues, is that commercial Wi-Fi access points often display unequal sharing behavior with each other, both in terms of throughput and medium utilization time.

The point, one might argue, is that LTE-U does no worse, and can improve throughput when sharing a channel with other types of Wi-Fi devices.

LTE-U does not use all of the available 5 GHz band, reserving more than 200 MHz exclusively for other Wi-Fi devices.

An LTE-U small cell scans portions of 5 GHz looking for a vacant channel, and if there is no vacant channel, it finds the least occupied channel.

It then takes turns using that channel with Wi-Fi users, ensuring that it never uses the channel more than its proportionate share of the time, and it vacates the channel when no longer needs it.

Unlike Wi-Fi, which does not currently have a coexistence specification, the companies involved in developing LTE-U have adopted and will follow the very extensive coexistence specifications and testing requirements that have been published at www.lteuforum.org.

Also in contrast to Wi-Fi, LTE-U’s protocol scales very well with node density since each LTE-U node deterministically clears the channel after using a fair share of the channel resources.

All versions of LTE Unlicensed will fully comply with FCC’s rules and any other regulations in those regions where it will be deployed.

In other words, LTE Unlicensed has no adverse impact on Wi-Fi, Qualcomm argues.