The concept of the femtocell has caused excitement in the 3G infrastructure and operator world as well as with new players. From the concept perspective it is quite radical for the following key reasons:

• Equipment volumes of millions provided directly to consumers.
• Short lifetime providing rolling market for manufacturers connected to a backhaul funded by users.
• Reduced customer churn beyond that provided by attractive handset bundles.

It is suited to solve 3G network problems of poor indoor coverage and capacity and to reduce network capital and operating costs, but how do vendors and operators make it stand up commercially?

Current 3G basestations (Node Bs) only sell in volumes of tens of thousands of units and are generally software and firmware configurable to future proof against a decade of evolving standards. Although very effective for traditional Node B requirements, this processing platform costing hundreds of dollars has a prohibitively high cost for the femtocell basestation.

Network operators and consumers alike are keen to have low cost femtocell product for more effective outdoor coverage and improved indoor coverage (to suit high bandwidths needed for bundled products).

In this scenario there will be a high volume need for basestation equipment; current predictions suggest the market could be 10s or even 100s of millions of units over several years.

The reduced lifetime typically seen for domestic ‘gadgets’ results in shorter equipment cycles and a stronger roadmap for products. This makes the femtocell product attractive to infrastructure manufacturers as well as new entrants experienced in high volume consumer products.

Whilst femtocells seem an attractive innovation there are a number of key questions to answer. The first is who pays for the equipment?

Mobile customers in many markets are unused to paying significant sums for their handsets and are unlikely to be willing to pay for the femtocell to improve their experience, instead assuming that is the responsibility of the operator. If, however, the sums involved are small, the customer may be prepared to contribute, particularly if additional services are bundled with the cost, such as providing a wireless broadband “dongle” and a discount on the service.

The second question is whether the user is prepared to share their broadband network with the operator, as again they may feel that is unfair. The package offered must therefore allow users to configure how the femtocells makes use of their broadband connection, particularly to prevent them being charged additional fees by their provider when bandwidth limits are exceeded.

If it is to become a successful mass market product, a femtocell base station must have a packed-up factory-gate cost of no more than $100 in volume production.

Partitioning the design shows that this leaves only about $40 for the complex processing platform compared with its macrocell counterpart which typically costs hundreds or thousands of pounds.

PA believes a single-chip processing platform, performing a 3G Access-Point Function, can achieve the required cost for the volume, domestic and small office femtocell product using various combinations of devices and by partitioning and multiplexing the processing elements carefully.

For example, we have shown that the functionality can be compressed initially into a single FPGA and then migrated to a structured Asic, full custom Asic or an ASSP (application-specific standard product) to achieve the cost target.

Another potential approach is the PicoArray from PicoChip, a design which is already used in several femtocell products. The advantage of this approach is that it gives a flexible development platform, with a straightforward route through to production.

David Stansell and Steve Watts work for the PA Consulting Group.