With all the activity going on around 3G UMTS and LTE femtocells recently, it’s easy to overlook the progress that’s been made quietly on the 3G CDMA side of the fence. Here’s a quick update on the current status. Apologies for the acronyms and technical detail.
Recap of CDMA femtocells
CDMA is a different mobile radio technology to the popular GSM and UMTS, currently serving around 10% of mobile subscribers worldwide. Verizon, Sprint and Metro-PCS in the US and KDDI Japan are several well known CDMA adherents.
Sprint launched the first commercial femtocell service called Airave back in 2007, based on a Samsung product called Ubicell. This provided a 2G service – ie. Voice and text only, not high speed data – and was designed using entirely proprietary technology.
The CDMA standards body, 3GPP2, has been standardizing the architecture and protocols for 3G CDMA femtocells as a parallel activity to the mainstream 3G UMTS femtocell standards. They’ve chosen quite a different system architecture, introducing an IMS core network to handle the registration of the femtocells themselves. Some aspects of their standard are deliberately identical to those used in 3G UMTS, such as the security aspects and remote management.
As with other technologies, 3G CDMA femtocells are designed to operate with existing standard 3G handsets.
3G CDMA Femtocell Specifications Published
The 3GPP2 femtocell specifications were officially published in March 2010 and provide a complete description of the system architecture and protocols for each standard interface. These can be found on the 3GPP2 website and freely downloaded. The most relevant ones might be X.S0059 which provides an overview, together with X.S0059-100 covering high speed data and X.S0059-200 covering voice.
There is one more document still under development (X.S0059-400 targeted for Q4 2010). This covers the full provision of existing voice supplementary services in a femtocell implementation. (That’s not to say that current vendors can’t provide those services today – just that the standards documents don’t cover all of them yet/haven’t caught up).
There are several topics under discussion for inclusion in the next release (in 2011), mainly around Enterprise femtocell features and/or clusters of femtocells (e.g. in public areas)
- Optimised Routing. Currently, all voice calls are routed through the external media gateway and transcoded twice. This isn’t needed for femto-to-femto voice calls.
- Femto-to-Femto handoff. This avoids the load on the Femto Convergence Server which today co-ordinates the signaling for all handoffs.
- Some enterprise feature support.
- PBX integration for enterprise femtocells. Calls can be routed directly through your office switchboard without needing to go to the mobile phone network.
What’s Not Next (yet)?
There’s not yet mention of a native IMS client on devices – it’s on the menu but there’s said to be little support for it at this stage. This may be more interesting when IMS capable handsets are available and in use – so probably at least 1 standards revision cycle away.
Is there a need for Femtocell Aware Handsets for 3G CDMA?
The system is primarily designed for today’s existing CDMA handsets. The standard revision recently published is Revision E, which includes some femtocell handset features to improve power level awareness and system selection – similar to the Closed Subscriber Group feature of UMTS. It’s probably something like a year away before we’ll see handsets in production with this feature, which can be developed as a software enhancement.
How close is the 3G CDMA standard to being available for commercial use?
This femtocell standard is slightly behind the development activity that has gone on in parallel. Airvana and Tatara Systems already have femtocells and a femtocell convergence server which complies with the standard ready for primetime use. Where there are a few minor differences with what has been incorporated into the standard compared to the current pre-standard implementation which will be revised in future software releases.
Where can I find out more information?
You can find the official femtocell specifications on the 3GPP2 website
(My thanks to Phil Brown of Tatara Systems for his help is preparing this article.)