There seems to be an undercurrent of skepticism about some of the usage scenarios for femtos - in particular, the notion of why anyone should bother with femto offload, if an increasing set of devices all have WiFi anyway.
The Femto Forum has released a study on femto/WiFi coexistence which highlights some reasons it sees for combined deployment, but I think a couple of additional ideas are also useful.
One important factor is the difference between laptop PCs and smartphones:
- In a 3G-enabled laptop, WiFi is almost always switched on, but 3G is usually only on part of the time (not least because most users will only plug in the dongle when needed)
- In a 3G-enabled smartphone, 3G is almost always switched on, but WiFi is usually only on part of the time
And for both, 3G (or at least data access on the phone) is likely to be switched off when roaming internationally.
This will mean that laptop 3G data offload is probably best done via WiFi, but smartphones may be more femto-centric - especially as smartphones are more likely to have operator-branded services that make it advantageous to keep the traffic on-net. Laptop data is 99.999% straight to and from the web, with almost zero operator value-add, so it makes sense to dump it to the cheapest connection as often as possible.
I've been using an iPhone 3GS the last few weeks, and the battery life is atrocious. So I've done the usual power-management tricks of turning down screen brightness, turning off GPS, and manually switching off WiFi when I leave my house, only switching it back on when I know I have access to free WiFi elsewhere such as a hotel or certain cafes.
So although it's not hitting the cellular network all the time, and my home WiFi certainly takes quite a lot of the strain, it's certainly not able to offload everywhere where the operator might like, or might have WiFi offload deals with hotspot providers.
My two local branches of Starbucks gives me a real sense of the paradox:
- I know I can get access to the BT Openzone WiFi for free with my Vodafone iPhone contract.... but I've got the WiFi switched off by default, it requires me to do some sort of registration process with my account number (which is at home) and 3G coverage works fine in both cafes, so I don't bother.
- For my 3UK dongle for my laptop, one cafe has good HSPA signal and the other is lousy. In the one which is lousy, I use the WiFi, which I can again get for free with a Starbucks loyalty card (there's no offload deal in place with 3). In the other, I always use the dongle as the WiFi access controller seems to have a 20-second setup time before hitting the splash page, and another 20 seconds before I get authenticated. And if I'm using the 3G, I'll switch off WiFi to save battery.
Now re-imagine these scenarios with a femtocell viewpoint. At home, I'd probably still use WiFi rather than a femto, as I'd expect it to be faster - and some pretty innocuous websites I visit fall foul of Vodafone's over-zealous content filter and get blocked. VoIP provider Fring's website is censored, for example. I can't be bothered to phone up for "adult access" permission, and anyway I'm sure there are other things in the T's and C's about fair usage that I can obviously ignore when I'm on my own WiFi. I obviously never use the 3UK dongle when I'm at home within range of WiFi, as my laptop just connects and authenticates immediately and without extra intervention.
The cafes are different - if there was a Vodafone femto and the iPhone switched onto it, I'd probably notice an improved performance and likely lower power consumption. Same thing with the 3UK dongle in the branch where I currently don't have coverage - I'd probably switch back from the WiFi with its more-cumbersome login process with passwords and splash screens.
But you've probably already spotted the problem - does Starbucks want 4 or 5 femtos in every branch, from different operators? Who would pay for them? The cafes already have "sufficient" connectivity for everyone with WiFi - it's unlikely to want to bear the cost of just making it marginally more convenient for a select group of its customers.
The point here is that the neat idea of a monoculture of WiFi offload everywhere, or 3G offload to femtocells do not fit with the annoying peculiarities of consumer behaviour. People very quickly find the most convenient / cheapest / fastest / best battery-saving strategies for their personal circumstances. It's very difficult for operators wanting to conduct offload to work their way around those optimisations - unless they use either very smart connection-management software, or very brute-force ways of ignoring the subtleties.
One other thing occurs to me: I wonder if it's possible to get the presence of a WiFi SSID to trigger a device to switch on 3G and look for a femto in that location. Or for the presence of a specific femto (on any carrier's network) to trigger a client to power up smartphone WiFi if it's switched off, and use that instead.