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We have been attending the LTE World Summit, which takes place every late spring in Europe, for three years running. At each subsequent event the number of operators has increased and the hot topics have evolved from the theoretical - we think LTE works, but we aren't sure - to the actual - here is how my commercial LTE network is performing. The 2011 event, which took place in Amsterdam, was no exception.

Based on our active participation at the event and the meetings that we attended, we have come up with a list of this year's hot topics, appropriately filtered to reflect the stuff that interests us the most. Spectrum fragmentation tops the list with operators deploying LTE in at least 12 frequency bands with more frequency bands likely in the next couple of years. Unfortunately, while the industry was able to consolidate on a single technology it just isn't possible to consolidate on a single frequency band or even a minimum number of frequency bands. That being said, 1800MHz is growing in popularity for those operators that have it. In addition to supporting both coverage and capacity requirements, it is well suited for indoor deployments, not to mention the potential ability to reuse existing cell site infrastructure.

Voice over LTE, or the lack thereof, is still on everyone's minds, despite the dearth of LTE smartphones outside of MetroPCS and Verizon Wireless. Interim solutions, such as CSFB, were supposed to provide a smooth transition to full-blown VoLTE, but as it turns out CSFB won't be commercially viable from at least some vendors until early 2012. Two second multi-RAT handover times may also be acceptable for a data call that can leverage data buffering, but it won't suffice for real-time voice services.

HSPA+, including DC-HSDPA, was on several operators' minds - with one notable, albeit predictable, exception. Operators are looking to use both technologies, in particular DC-HSDPA, as a more suitable fallback technology where LTE coverage does not exist. DC-HSDPA is also no longer the technology for LTE "wannabes." In fact, two of the first LTE operators - TeliaSonera and CSL - also offer DC-HSDPA services.

Spectrum fragmentation and the growing interest in HSPA+/DC-HSDPA should put chipset and device suppliers on notice. At the extreme, tri-band or dual-band LTE devices which also support DC-HSDPA are starting to crop onto operators' requirement lists. There may be a market for single-mode LTE/TD-LTE devices/chipsets, but it will not represent the mainstream.

Finally, unlike last year, but consistent with the event from two years ago, there was a lot of talk about WiMAX. Unfortunately, this time around it was all about how WiMAX operators can transition to TD-

LTE. C'est la vie.