13 Jun 2007

Femto cell Architecture

The business case for indoor femto cells has gained increasing traction in the last few weeks, and lots of news comments about various femto cell development companies. For example, check here, here and here.

Although the femto cell concept is quickly gaining grounds towards complete and operational products, there is still some misunderstanding on how the overall network architecture will look like. I'll try to address this issue in this post.

A femto cell router is a small device, the size of any Wi-Fi router, which is in effect a miniature base station. The radio is a standard based radio such as UMTS/HSPA which the operator will likely require a license to operate on. The router connects to a DSL line. The idea is to enable the subscriber to make and receive mobile calls indoors, with low signal levels which has a number of benefits to the operator:
- Hopefully accelerate fixed line substitution.
- Reduce the cost of building a full macro layer network.
- Lock subscriber in to the operator and reduce the likelihood of churn.
- Provide a viable medium for content distribution (the ugly walled garden paradigm)

It is not my intention here to argue for or against these benefits. I will dedicate a full post on the business case for the femto cell and the potential cons sometime soon. So let us stay on the technology side and try to investigate how a UMTS based femto cell routers will be integrated with the operator's core network.

Basically, there are a number of ways, the first of which is the conventional hierarchy using an RNC . Just like any node-b is connected back to an RNC which is then in turn is connected to the core network, the femtocell routers can be treated like individual node-bs and connect to RNCs. This may appeal to big manufacturers who already have substantial deployments and many RNC on the ground. The downside to this approach is the limited chances of inter-operable devices if the operators chooses to diversify their suppliers. Although the Iub interface (base station to RNC) is standardised, the reality is most implementations are proprietary. Typically operators don't like to put all their eggs in one basket and would prefer to get solutions from various suppliers. The other downside of this approach is that most available RNC solutions are geared towards Macro/Micro type of deployments. In other words they are built in order to support relatively small number of cells with a huge number of subscribers in each cell. They don't scale very well to support Femto cell deployments with almost as many cells as there are subscribers, and a handful of subscribers per cell.

An alternative approach is to use UMA (or now called GAN). UMA was originally conceived to support dual mode cellular/WiFi-over-Internet type of connectivity. When the mobile is detected indoors within the range of pre-determined WiFi coverage, a UMA concentrator does the core network negotiation on behalf of the mobile, e.g. registering, and updating location ... etc. It is thought that a similar procedure can be used for femto cells. When the mobile is detected within the coverage of a femto cell, UMA kind of hand shaking takes place to ensure that: 1. the mobile is allowed to access the network at this particular femto cell, 2. the traffic between the mobile and the core network is forwarded accordingly. Using this method a UMA concentrator is required, so in a way, the solution is still hierarchical and it is certainly one of the criticisms of this method is that it is not a fully flat architecture. Kineto is one of the companies promoting this approach.

Yet another alternative approach is enabling femto cell connectivity through an IMS service. In this approach, the femto cell router talks SIP over the internet back to an IMS service which acts as a bridge between the femto layer and the rest of the network. Although this is considered the "flattest" approach, it is yet to understand how it will work in practice, the delay in working fully featured IMS platforms is one of the concerns of femto cell development companies.

Incidentally, my current clients are hedging their bets by supporting more than one approach and have developed partnerships with various companies in their respective fields to make the Femto architecture as flexible as possible.

15 comments:

Asa Kalavade said...

Good summary of the different approaches to Femtocell integration.
In reference to your comment on the third SIP based approach - it is useful to note that the SIP based approach can be offered in a pre-IMS network as well. The SIP traffic basically flows from the Femto to a 'server' in the network, which can interwork the SIP and CS worlds. The SIP world can be a vanilla VOIP network, migrating to an IMS network as networks evolve.

iohan said...

One question... can anyone deploy a femtocell in one of the spectrums used by mobile phone... or only the licenses holder of the spectrum can deploy them.

Andy said...

Only an operator with licensed spectrum can deploy femtocells. The femtocell layer becomes part of the operator's radio access network.

Housam Housami said...

Thank you Asa for your insightful comment.

siva said...

hi asa,

normally how much will be BOM( Cost), For femtocell...& can u tell the BOM( wat r the main components like procesor ,rfic chip ,antennas etc..) For The FEMTOCELL.

Daniel S. said...

Thank you for the clarificatoin on Femtocell technologies. As for the busines model and licensing enviroment requirements the asumption is that:
- An operator aquires an IMT spectrum that will be used primarily in closed spaces confined so that high reuse is possible an no interference with mobile operators. (In urban enviroment the problem of GSM pico repeaters planning and regulations is avoided).
- Interconnection /roaming agreement between Femto operator and a Mobile operator.
- Where no IMS or NGN platform exists, backhauling and integration of Femtocells is not feasible right.
- In countries where additional 3G spectrum femto cell is not availble for assignment but in new bands like 2.6Ghz, femto cells are unlikely to make any impact until handsets with support of multiband multimode including those of the newly assigned 2.5-.269GHz are availble ? right!

Daniel

eclip said...

femtocell.com.pl

Microcell Femtocell said...

MLL Telecom

Walter M. said...

DSL interface is the main weakness for this solution. It should contain ethernet port with VPN client, it's much more flexible.

Wijitha said...

When using the Femto cell do you need to have your broadband RSP and your mobile RSP same or can you have different RSPs serving.

Business Communications Los Angeles said...

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