Another challenge Qualcomm faces is “being a good neighbor to WiFi,” and ensuring both technologies can exist simultaneously without stealing service from each platform, said Gold. Regulations for using LTE vary across the world, though the United States, Korea, and China have relatively lax regulations.
Qualcomm plans to implement WiFi “coexistence features,” and, while Hellberg declined to comment on exact steps taken in advance of demonstrations planned for Mobile World Conference, he outlined several possible mitigation measures:
- Dynamic channel selection. Avoid using the same sub-channels on the 5 GHz band and adjust transmit power if someone is using an adjacent channel, to decrease interference.
- Supplemental downlink. If you use only unlicensed spectrum to boost downlink, use licensed spectrum for uplink. This would decrease uplink interference and improve performance.
- Listen before talk features. Built-in sensing and disconnection capabilities during particular time intervals.
“For coexistence features, most regulations are stringent, so you have to make changes to the waveform,” says Hellberg. “We are working on defining exactly how this can happen and how we make sure everyone is implementing this.”
Gold questioned whether WiFi proponents will implement similar measures to “be a good citizen.”
“802.11ac has frequency hopping capability, but what if it’s open this microsecond but not the next because the signal is taken up by LTE? There’s going to be a lot of stuff that gets stepped on. I don’t know how you manage that effectively,” Gold said.
Additionally, there has long been divisive conversation regarding use cases in the unlicensed spectrum. Although LTE-A in the unlicensed spectrum may improve user experience and increase chip production, adding additional management function within nodes makes the system more complicated and raises prices.
“Some people are opposed to it, some people love it -- this conversation is one hurdle that has to be passed through before [LTE-A on unlicensed] happens," Hellberg said.
Nevertheless, "there is operator interest,” he told us. “To solve this complex problem, we foresee almost impossible wireless changes where we can see LTE-A going to new areas and helping solve the 1000x challenge.”
— Jessica Lipsky, Associate Editor, EE Times