I've had two briefings (with Nextivity and Andrew) in the last 24 hours that have made me remember about cellular repeaters. Essentially these act a bit like the boosters you might use for improving TV signals indoors, but for mobile. They're different from femto base stations - they're not a separate cell.
There's a wide variety of non-femto/pico ways of improving coverage in buildings such as distributed antennas and assorted active/passive systems. They're commonly used in office buildings, hotels and the like, as well as in tricky places like railway tunnels or other coverage blackspots.
There are two main sorts:
- carefully located ones installed by the network operators, taking into account positioning, impact on noise and interference etc. These can improve the situation significantly, but need expensive work with RF measurements and location to get right.
- self-installed ones (especially illegal ones in peoples homes & offices) which can do horrible things to a carefully planned network, raising the noise floor and generally causing difficult-to-cure havoc. Historically, most radio folk at operators have hated these with a vengeance.
But given the push to femtos, the need for 3G indoor coverage, and the demands of dongles & iPhones, some radio network departments are having to hold their noses, and re-evaluate whether there's a role for small repeaters after all, especially as it looks as though some may now be "smart" enough to minimise disruption to the macro network.
The femtocell-advocate response is that repeaters don't add capacity to the macro network, which is true. However, they help the network get much closer to its theoretical rated capacity by avoiding the need to waste lots of power blasting at indoor users, so they can improve effective capacity. They also lose out on all the nice integrated triple/quadplay propositions, femtozone services and the like.
But on the other hand, femtos aren't much use where the customer doesn't have broadband at all, or it's poor quality, or its from an "unfriendly" operator that won't prioritise femto-gateway destined traffic. And although some of the models I've heard were suggesting subsidised repeaters, it's at least technically feasible for them to boost multiple operators' signals rather than just one.
Like most things in technology, there won't be a "one size fits all" answer. But based on these discussions, I think it's going to be important to keep an eye on the femto/repeater balance over the next year or two.