Qualcomm tells FCC that single-band 700MHz LTE is infeasible, proposes its own seven-band chip instead

Qualcomm tells FCC that single-band 700MHz LTE is infeasible, proposes its own seven-band chip instead
This week, Qualcomm submitted a filing to the FCC that suggested that the FCC does not need to take any action to introduce interoperability for LTE networks on the Lower 700MHz spectrum (which AT&T and many regional carriers use).

Qualcomm’s reason is that it is already working to solve the solution technologically, and has provided interim solutions to the smaller carriers who wish to enable roaming with AT&T. Qualcomm warned the communications agency that “the performance of devices using this solution would be degraded” and so they declined to use it.

Qualcomm explains that the issue with resolving the LTEinteroperability problem with Lower 700MHz lies with Channel 51 (the TV channel) and the unpaired D and E blocks of US Digital Dividend spectrum.

As a result of its efforts to develop its MediaFLO technology with the D and E block, Qualcomm conducted extensive field testing and research into the problem. It discovered that actively-used E block stations would cause such destructive interference that B and C block (AT&T’s spectrum) receivers would never be able to get the signals from the towers. According to Qualcomm, AT&T’s band configuration (band class 17) reduces this issue by an appreciable degree by using A block spectrum as de facto guard bands. The regional carriers’ band configuration (band class 12) enables A block spectrum for active use, and does not provide any sort of protection against E block interference.

Channel 51 causes another set of problems too. In areas where Channel 51 is currently active, band class 12 A block deployment is expressly forbidden by the FCC. This is because Channel 51 is literally adjacent to A block spectrum, so catastrophic levels of destructive interference would occur. The interference can even bleed over to B and C block receivers if the receivers are configured for band class 12 (but apparently not band class 17). However, this issue is likely to fade away over time, as the FCC has frozen Channel 51 and will eventually be forced to shut down existing Channel 51 users.

In any case, Qualcomm has noted that it has finished developing a new RF transceiver that supports three sub-1GHz frequency bands, three super-1GHz frequency bands, and one “very high” frequency band (like Clearwire’s 2.5GHz TDD band). This transceiver, the WTR1605L, is compatible with Qualcomm’s Snapdragon S4 MSM8960, and units supporting band classes 12, 17, 13 (Verizon’s), and 25 (Sprint’s) will be sent to device makers next month. Qualcomm expects devices that include the transceiver to become available by the end of the year. It believes that because it has developed the solution to the problem, the FCC does not need to step in to fix it.

Whether Qualcomm’s solution would correct the problem or not remains to be seen. It largely depends on whether carriers will choose to integrate Qualcomm’s new technology. Not to mention that new power amplifiers need to be developed to work more effectively with the new transceiver. It is also quite likely that many smaller carriers will be unable to afford to offer devices that use Qualcomm’s Snapdragon S4 (since most smaller carriers only get devices that are at least a year out of date), which makes this solution totally worthless for at least another year or so. Will a feasible solution emerge? We all sure hope so, because the future of useful LTE interoperability hinges on decisions like these.

Read more at the FCC