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SoCs drive down femtocell costs

Posted: 04 Dec 2008 ?? ?Print Version ?Bookmark and Share

Keywords:broadband? femtocell? SoC platform?

With the boom of mobile broadband data services, operators are looking to find new ways and cost models to facilitate the delivery of wireless service capacity to subscribers.

Femtocells have emerged as one possible solution for mobile in-home service delivery!targeting residential and small-business markets. A femtocell is a compact mobile base station, typically in the form factor of a residential gateway, targeting the in-building environment of subscribers.

A key obstacle of femtocell adoption is the cost of such deployments!not just the equipment, but also the installation and maintenance cost of such a large number of small, but relatively complex, mobile base station devices.

In order to solve the basic cost equation of femtocell deployment, operators are looking at a subsidized, self-installation-based business model. In this approach, residential subscribers purchase a femtocell bundled with a service subscription, take delivery at home or in a retail store, then install the device by themselves in their homes.

This model requires femtocells to be quite intelligent, capable of reaching an operational state in a self-sufficient manner once connected to the fixed broadband network connection at home.

However, in the end, femtocells are solving an operator problem!after all, high-quality service delivery into residential homes is a subscriber expectation, not a consumer value proposition. Hence, the cost of equipment and the additional service plan must be kept low. This is especially true if the expectation is a broad adoption of this new mobile service delivery method in order to provide the operator with the anticipated systematic relief for the outdoor RAN infrastructure.

The "magic line" is expected to be somewhere below $100 as a price to the operator. Otherwise, operator subsidies required to drive market adoption would quickly add up to break the business case.

Complete mobile wireless base station functionality is comprised of several subsystems, typically a DSP for radio signal processing (e.g. MIMO), a high-capacity network processor delivering broadband data services with the required QoS and a control plane processor that maintains connection with the operator's service layer.

Building such equipment based on available baseband silicon chips is problematic, since the add-on cost for network and control plane processing is too high to reach the target price. As this is how most femtocells are designed today, equipment pricing in the range of several hundred dollars is quite common.

The required low-level pricing can only be reached by designs utilizing highly integrated SoC silicon platforms. An approach integrating all processing components, as well as necessary network synchronization and interference management capabilities, is required.

Streamlined design
The following provides a list of cost considerations for a streamlined femtocell design:

  • Integrated control plane and networking functions: A femtocell provides control plane connectivity to the mobile operator's service control level, by means of secure connectivity through the fixed broadband backhaul connection. The femtocell SoC has to provide high-speed encryption capability for IPSec processing, as well as other networking and routing capabilities related to control and service connectivity for nomadic and mobile stations in the home environment.

  • Integrated network processing: The in-home deployment of femtocells leads to excellent wireless signal strength, shared by only a small number of closely located devices. Hence, peak and average performance of a femtocell can reach much higher levels than typically found in outdoor service delivery models. Thus, the femtocell SoC must offer integrated high-capacity network processing capability.

  • RFIC interface: In order to minimize the cost of the radio subsystem, femtocells typically utilize RFICs from the mobile station market. In many mobile baseband implementations, the RFIC offers a low-cost analog interface to the mobile baseband processor!hence, the most cost-effective way is to include the analog front-ends (ADC/DAC) in the femtocell SoC to provide glueless connectivity to low-cost RFICs.

  • Network synchronization: The industry has recognized the issue of interference between the outdoor RAN and indoor femtocells, and eventually amongst femtocells!requiring tight network synchronization and interference management, which is also needed for optimized hand-over performance. The femtocell SoC has to offer integrated network synchronization options (e.g. 1588), without the cost penalty of external ICs and components.

  • Embedded software licensing: The price of a femtocell product can vary greatly depending on the underlying licensing structure for the related software. The most synergistic option is to utilize integrated software capabilities provided by the femtocell SoC silicon vendor. This can eliminate several layers in the value chain, each layer adding unnecessary margin. To facilitate the lowest price of femtocells to the operator, while maintaining vendor margin, it is advantageous to look for femtocell SoC vendors offering a fully pre-integrated software package. Doing so allows the vendor to focus resources on differentiating features.

- Joachim Hallwachs
VP of Marketing, DesignArt Networks

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