Operators are starting to implement carrier aggregation to increase capacity and make better use of disparate frequencies. However, they are also looking for additional spectrum, usually in bands where LTE will need to share with other technologies.
Two particularly contentious options are 5-GHz, where Qualcomm is pushing an LTE-Unlicensed option in WiFi’s traditional band; and 3.5-GHz, which in the US would involve sharing with federal agencies, and could provide a blueprint for dynamic spectrum access (DSA) in other bands.
Qualcomm spearheaded the LTE-U proposal, which effectively uses 5-GHz licence-exempt spectrum for supplemental downlink (SDL), adding capacity to a primary cell in a licensed band. Similar SDL techniques have been pioneered in other bands – for instance, Qualcomm tested SDL with AT&T, using 700-MHz unpaired frequencies, and Orange has trialled the approach using mobile satellite spectrum in 2-GHz to add downlink capacity to LTE.
However, the 5-GHz approach has greater complexities, and greater political sensitivity, because the band is unlicensed and the main area where WiFi has been expanding in capacity and capability. The current gigabit standard, 802.11ac, is mainly focused on 5-GHz, as is the future 802.11ax for ultra-dense deployments. All this has made 5-GHz the flagship band for those who campaign for more unlicensed spectrum and, more importantly, open technologies to harness it. Shortages in wireless broadband capacity can then be addressed by a wide range of service providers with flexible models and affordable prices, not a small group of carriers with closed networks.
Qualcomm, the great flagwaver for the cellular status quo, hits directly at this argument by proposing LTE-U, which give mobile operators more spectrum capacity, for free, while maintaining their control in a way that WiFi offload does not. LTE-U might be running in unlicensed frequencies, but because it acts as a secondary system under the control of the primary network controller, it is still fully within the carrier’s walls.