Steven J. Crowley, P.E.
In the first of a series of webinars, Qualcomm today began reporting on the results of its “1000x Data Challenge,” an initiative to meet what it sees as the need, someday, to increase mobile capacity 1000-times. The webinar, conducted by Rasmus Hellberg, Qualcomm’s Senior Director of Technical Marketing, was an overview. He discussed spectrum, small cells, and other techniques to increase capacity. More-detailed webinars on each of these are forthcoming: spectrum initiatives on September 18, small cells and heterogeneous networks on October 18, and more efficient networks, applications, and devices on November 14. Today’s webinar should be posted tomorrow, and a white paper should appear in about a week.
A recurring theme is that the whole is greater than the parts, and there are significant gains to be had by looking at the above matters holistically. Another theme is that this is doable, that the mobile industry can increase capacity 1000x and do so cost-efficiently. While many companies are looking at ways to increase mobile capacity significantly, Qualcomm’s campaign does the most go beyond standards bodies and bring this issue to the attention of the public, including, and perhaps especially, regulators.
Without specifying an amount, Qualcomm would like to see more spectrum used for mobile broadband. It’s not picky about the method used to accomplish this: 1) customary auctions of cleared spectrum, 2) shared spectrum similar to that proposed by PCAST, and 3) unlicensed spectrum (especially 5 GHz). Qualcomm sees 3.5 GHz as promising for small cells, as well as unlicensed 60 GHz which is being standardized in IEEE 802.11. These frequencies are quite high, but that’s not so important for small cells because their lossy propagation paths are so short.
Qualcomm wants to be able to aggregate bands to further increase performance. Not only would it aggregate, say, different 4G bands, it would also aggregate licensed, unlicensed, and shared. In addition, unpaired spectrum could be combined with paired to improve downlink performance.
Same-frequency small cells can be placed within a macrocell, without objectionable interference, to increase capacity. LTE Advanced contains interference mitigation techniques that will make this more practical. With 4 small cells, Qualcomm estimates capacity in the area covered by the macrocell would be increased 5.7x. This improves to 21x with 16 small cells and 37x with 32 small cells. Note that capacity improvement roughly scales with the number of small cells.
I’ve previously discussed how the outside-in approach of macrocells is turning inside-out, bring the user closer to the indoor “base station” with Wi-Fi and femtocells. Qualcomm takes this notion and ramps it up with an ambitious vision of small base stations “basically everywhere!” These small cells would use new spectrum, perhaps in the 3.5 GHz bands, and use about 10 times the spectrum bandwidth the macrocell uses on the 4G frequencies. In Qualcomm’s model, if 9% of households get these small cells, capacity in the macrocell goes up 500x. If 20% of the households get them, capacity increases to 1000x. These indoor base stations also reach outside of homes somewhat, and would be available to outside users. Selling points to the operator include use of existing household broadband for backhaul, low cost, “high quality” licensed spectrum, and operator control.
I was struck by the presentation’s support for Wi-Fi, the strongest I’ve yet seen from Qualcomm. Hellberg says Wi-Fi is “becoming the norm.” Qualcomm is driving an end-to-end IEEE 802.11ac ecosystem with smartphones among the devices. In this scheme, the user device has the ability to choose the best means of access (3G, 4G, Wi-Fi, etc.) depending on licensed or unlicensed signal quality, operator preference, and the traffic characteristics of the application. Since we’re inside most of the time, one can see mobile broadband macrocells using 4G spectrum become more of a backup for those few times a user is not near Wi-Fi (or a licensed small cell), or for when the user is moving rapidly.
Small cells need backhaul and Qualcomm addresses this. In addition to more conventional backhaul techniques such as fiber or microwave link, 4G spectrum itself can be used to relay small-cell backhaul. There’s also the use of existing wireline broadband as discussed above. Qualcomm has some other techniques its working on that it said it couldn’t discuss now. The message is that backhaul is under control and will be practical.
Other ways to increase capacity
Another interesting a part of the presentation was the notion of significant gains that are possible for certain classes of traffic:
- Small data bursts consume inordinate network resources due to to signalling requirements; HSPA+ Advanced included techniques that can increase capacity 10x for these bursts.
- Rather than send the same content to multiple users on unique channels, the same content can be broadcast on one. (Sounds familiar.) If six users in a cell are getting the same content, capacity can increase 10x if it is broadcast instead.
- Under certain assumptions, device-to-device transmission such as using LTE Direct can increase capacity 10x.
So, for certain content, when it occurs, one can get 10x capacity gains. It adds up.
In sum, Qualcomm sees multiple ways to reach 1000x. Operators are unique, and their solutions will be also. No matter what the solution, Qualcomm is positioning itself as the expert. That’s the last major theme from today.