Lately there has been a lot of exciting news about LTE in unlicensed spectrum gaining traction with LTE-U, the first phase of this technology suitable for specific regions such as the U.S. and Korea. And while LTE-U moves toward commercialization this year, the next phase—Licensed Assisted Access (LAA) —is getting published as part of 3GPP Release 13 for global deployments in 2017.
A great deal of attention has been focused on the coexistence of LTE-U and Wi-Fi. In the past, we have shared extensive results from different trials and demonstrations performed by us as well as 3rd parties—for example: “Wi-Fi / LTE-U Coexistence and the User Experience” and “Can LTE-U fairly coexist with Wi-Fi?” We are excited to confirm that another 3rd party has verified LTE-U coexistence with Wi-Fi—the renowned Korean research institute ETRI (Electronics and Telecommunications Research Institute). The verification was based on a demonstration that was carried out last October in ETRI’s lab in Korea in a collaboration between ETRI and Qualcomm Technologies.
In this over-the-air demonstration, LTE-U co-existence was put to the test in scenarios with a large number of Wi-Fi access points (APs) from Cisco and Wi-Fi stations (STAs) from Samsung, all sharing the same 20 MHz channel in 5 GHz. The demonstration consisted of both functional tests and performance measurements to verify fair co-existence.
One of the functional tests was to verify that the Carrier Sensing Adaptive Transmission (CSAT) in LTE-U uses a fair share of the resources. For example, we confirmed that the CSAT limited the LTE-U utilization of the channel to 1/8th of the time when sharing it with seven Wi-Fi APs, which is the fair share.
In the performance testing we first looked at confirming that Wi-Fi is not negatively impacted if a Wi-Fi neighbor is replaced with LTE-U. The baseline consisted of 15 Wi-Fi APs, all on the same channel, where each AP was connected to one user (STA). Each STA was at a relatively close distance to its corresponding AP, which means that the signal quality was sufficiently guaranteed (the signal-to-interference ratio was larger than 18dB), both for the Wi-Fi AP-STA pairs and, when later introduced in the test, also the LTE-U eNB-UE pairs. In terms of interference between different pairs, the AP/eNBs were above the so-called energy detect threshold, i.e., they could hear each other without problem. Once we established the baseline performance of Wi-Fi with only Wi-Fi neighbors, we replaced one Wi-Fi user (AP–STA pair) with LTE-U (eNB-UE pair). We then continued to replace a Wi‑Fi users with LTE-U, one at a time, until we had 12 Wi-Fi users and 3 LTE-U users. As we can see in the figure below, the Wi-Fi users were not negatively impacted when one or several of their Wi-Fi neighbor was replaced with LTE-U, which verifies that LTE-U is as good of a neighbor as Wi-Fi itself.
Then we looked at the effects on the total network throughput in the downlink to all the 15 users. As we can see in the figure below, the total network throughput increased as more LTE-U nodes replaced Wi-Fi nodes. This is thanks to LTE’s better spectral efficiency but also its ability to operate with a reuse of 1, i.e., simultaneous transmission of the LTE-U eNB small-cells and efficient interference management at the LTE-U UE.
As in the previous trials, these joint over-the-air tests by Qualcomm Technologies, Inc. and ETRI clearly demonstrated that LTE-U co-exists fairly with Wi-Fi in the unlicensed 5 GHz bands. For more details on LTE-U, see our webpage LTE in unlicensed spectrum.