In a post on the problem with WiFi-based offload, Dean Bubley makes an interesting point:
“If I walk 5 minutes from home to my local tube station, I need to switch off WiFi temporarily, if I actually want to use mobile data – otherwise I have a constant stream of pop-ups from the connection manager on-screen, and no reliable connection.
It probably wouldn’t help with a high density of femtocells either, until there’s a reliable way of doing femto-to-femto handoff as you walk down the street.”
I’m delighted to say that help is at hand – femto-to-femto hand-off does work reliably. But as Dean suggests, it’s not a simple scenario. There are some specific challenges in the street environment he describes, notably interference, battery life, handover and signalling implications. This introduces the need for additional sophistication if the solution is to be kept simple and practical. Fortunately UMTS is better suited to addressing these than WiFi.
We at Ubiquisys implemented a femtocell solution a couple of years back that covered the majority these requirements for Enterprise deployments, e.g. femto-femto handover, interference mitigation/self-optimisation, battery life preservation, signalling optimisation. Two additional challenges in the street scenario compared to Enterprise is that there is no single LAN for femto-femto communication, nor can the femtos necessarily “see” each other (in the radio sense) to know who their neighbours are. The good news is there is an innovative solution to these too but I’m going to keep you all guessing.
Obviously, the femtocells in the street scenario would have to run in open mode to benefit all customers. This brings challenges of its own over standard “closed mode” femtocells in terms of performance, sustained load handling and dynamic load balancing. The only commercial deployment of open mode femtocells is SoftBank in Japan – which ooh I forgot to mention is Ubiquisys.