As part of Qualcomm's "3G & 4G and Chipset Evolution" workshop at 4G World in Chicago, Qualcomm's director of technical management, Rasmus Hellberg, spoke on the future of wireless evolution. Specifically, he discussed the progression of HSPA+ into HSPA+ Advanced and LTE into LTE Advanced.
"HSPA+ is the new baseline for 4G," said Hellberg, who pointed to statistics showing that the HSPA family is the fastest growing form of connectivity. Over the course of the first five years of its existence, HSPA was the fastest adopted by subscribers compared to the likes of LTE and WCDMA. "It's a very successful technology that's going to be around for a long time," he said. In order to do that, he said, Qualcomm needs to achieve the best possible performance in 5 MHz carriers.
Of course, a large part of that is heterogeneous networks, or HetNets. HetNets, as Hellberg explained, are made up of multiple bands, radio access technologies, and base stations of varying transmission power, which helps expand network capacity and coverage. Hellberg touched on the evolution of multi-carrier service, saying, "Instead of aggregating from two different frequencies, say F1 and F2, HSPA+ Advanced can aggregate on the same frequency from two different cells in what's called multipoint."
Another leap in performance, he said, comes from the use of small cells like picocells, femtocells (allowing service providers to extend service coverage indoors) and remote radio heads (which also help extend coverage, usually in rural areas or tunnels).
HetNet optimization is also important, said Hellberg, and one example of this is multipoint range expansion: more overlapping coverage with these small cell deployments, which allows for more use of multipoint, resulting in higher capacity and faster rates. "So it's not just about adding more cells," said the Qualcomm exec. "If you do something smarter on top of that, you can get even more out of these small cells." With that optimization, the peak rates of HSPA+ Advanced can reach as high as 336 Mbps, either by way of more 4x4 MIMO (multiple input, multiple output) antennas or through more 5 MHz carriers.
"But it's not just about sexy peak rates; it's about coverage and cell edge performance as well," said Hellberg, who explained how uplink beamforming improves coverage and user data rates. "If you get a better uplink, you get better performance in the downlink."
But the proliferation of internet-capable devices poses an issue for the future of 4G. "How do we connect these billions of devices?" asked Hellberg. "How do we handle ?the internet of everything'? How do we handle the smartphone explosion? We need to continue to work on cell fetch." Besides having enhanced cell fetch Hellberg added that HSPA+ can look into using the aforementioned multicarrier for this stage, as well as axis controls as a means to prevent overloads.
"So HSPA+ Advanced is all about getting the best possible performance with 5 MHz carriers," summarized Hellberg. "Not only does it provide more capacity, it provides denser capacity, improves coverage, enhances the user experience, and will help connect billions of internet-ready devices."
At this point, Hellberg turned his attention towards the future of LTE: LTE Advanced.
LTE Advanced, which has the potential to reach 1 Gbps peak rates with 8x8 MIMO, will use both the FDD and TDD spectrum. Hellberg maintained that Qualcomm "is committed to continuing the evolution of LTE, similar to HSPA." He pointed out that Qualcomm has built a HetNet test bed in San Diego to show real-world applications of LTE Advanced and their results.
"LTE Advanced brings different dimensions of improvements," said Hellberg. "It helps bring the most gain from HetNets by leveraging their topology. It's not just about adding small cells; LTE advanced makes the leap bigger by applying advanced interference management to HetNets." As an example, he said that drawing four picocells to a 1x macrocell brings the median downlink data rate up to a mere 1.2x, but then if you add interference management, you get a 2.2x median data rate thanks to range expansion, which improves the utilization of small cells.
Qualcomm will use adaptive interferences management with LTE Advanced; as the name implies, it adapts to network changes and the actual network load and balances the load accordingly. It also adapts to added nodes like the previously mentioned picocells, benefitting all HetNets.
Interference cancellation is not new, though, as it is actually a very important factor for 3G connectivity. Still, by cancelling overhead channels, it enables users' phones to discover small cells from much further away. This, in turn, enables higher data rates and full range expansion.
So that's where Qualcomm's recipe for LTE Advanced success comes in. Their "secret sauce," as Hellberg called it, is to make sure they enable that range expansion that allows more users to benefit from small cells, while also ensuring adaptive resource partitioning, advanced receiver devices, and full backward compatibility.
"These small cells provide the next performance leap, but LTE Advanced makes the leap bigger with a higher capacity and enhanced user experience," said Hellberg. "And it's is closer to commercialization [than HSPA+ Advanced]. It could be commercial as soon as 2013."
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