Qualcomm pushes LTE-A beyond 5GHz
Qualcomm has created a technology that enables LTE Advanced (LTE-A) over the 5GHz band to address an expected 1,000x increase in mobile data traffic. The company may just have drawn first blood in a battle between cellular and WiFi over the unlicensed spectrum.
The Qualcomm technology is so far just a prototype with no announced plans for products supporting it. Nevertheless, it raises the question of how best to use the 5GHz band to handle a rising tide of mobile data, most of it carried today on cellular services operating in sub-3GHz licensed bands.
Vendors including Qualcomm's Atheros division are selling multiple WiFi products operating at 5GHz. Some vendors may use 5GHz and even 60GHz links on an emerging class of small-cell cellular base stations. And researchers working on next-gen cellular technologies are exploring cellular services on everything from 5-60GHz.
"The foundation [for more data] is more small cells everywhere, new deployment models and more low-cost ways of deploying," stated Rasmus Hellberg, senior director of technical marketing for Qualcomm. "Unlicensed [spectrum] is ideal for automatic mobility... [and LTE-A] works better with more nodes because it can bring coordinated scheduling and synchronization between nodes to help provide performance when it becomes crowded."
Hellberg stated that LTE-A over unlicensed spectrum is superior to carrier WiFi due to its longer range, "controlled and robust reliability," and seamless end-user experience. In addition, he added, mobile operators could benefit from a unified cellular service.
LTE over unlicensed spectrum "works just as carrier aggregation does today. The main thing is to get support for the frequency band where a license is: there is 500MHz of spectrum available in 5GHz."
A diagram of a unified licensed and unlicensed spectrum, using LTE A. (Source: Qualcomm)
Although Qualcomm made no commitment on product availability, the LTE-A capability will be integrated into future SoCs, Hellberg noted. The announcement may be too early as such integration is three to five years off, said analyst Jack Gold.
"I think what you're going to see happen is that next-generation wireless protocols are going to start converging," indicated Gold, president and principal analyst of J. Gold and Associates. "Qualcomm tends to talk about things well in advance of when they're practical. The biggest problem is legacy equipment in place that may not be compatible with what they're trying to achieve."
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 US, 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 5GHz 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," said 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," stated Gold.
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 continued. "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
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