LTE Femtocell Framework

Femto and pico-BTS are small basestations (i.e., the size of a WLAN access point, that are designed for small areas and coverage of a low number of subscribers). Pico-BTS (picocells) are typically operator-installed equipment, while femto-BTS (femtocells) are likely to be consumer-purchased and installed equipment. For the following information, the term femtocells includes both femto and picocells.

Femtocell Development Challenges and Altera Solutions

Development of femtocell technology has many challenges and risks. Technically, a Femtocell’s complexity is comparable to a full macro basestation, but it needs the integration level of a WLAN box to meet cost, power, and footprint requirements. Femtocell technology is a still an immature technology and the business model is not yet well understood.

With these challenges in mind, Altera^® FPGAs and HardCopy^® ASICs, together with a fully customizable LTE system-on-a-chip (SoC) framework, is an ideal vehicle to allow OEMs to fully develop their solutions, conduct field trials, and resolve interoperability issues before committing to volume production. This flexibility enables the OEM to channel and maximize R&D investment by focusing on differentiating products rather than initially investing in costly ASIC development.

System Architecture

A typical femtocell SoC solution consists of a combination of control plane processor, data plane processing elements (PEs) that execute the various air-interface digital signal processing (DSP) functions, and the necessary interfaces for communication (see Figure 1).

Figure 1. Generic Femtocell SoC Diagram

Note:

1. ADC = analog-to-digital converter; DAC = digital-to-analog converter

The Altera SoC framework enables the construction of the desired solution by taking you much closer to the desired goal by providing the following:

• A common off-chip framework
  • An in-place, fully tested peripheral infrastructure 
  • Easy instantiation, configuration, and application program interface (API)
• A common core framework
  • On-chip interconnect topology
  • Combination of Avalon^®-MM and Avalon-ST system interconnect fabric, SOPC, and SignalTap^® logic analyzer debug
• Flexible processing element implementation options
  • The best methodology to address different intellectual property (IP) requirements:
    • Fast Fourier transform (FFT)/inverse FFT (IFFT)/discrete Fourier transform (DFT): custom built blocks using Altera IP or user customized IP
    • Automatic gain control circuitry (AGC)/automatic frequency control (AFC)/channel estimation: use soft DSP engines
    • Control plane written in C code running on a soft processor
• A user-friendly build, debug, iterate environment
  • Best-in-class FPGA tools
  • In-field and In-system design changes and upgrades
• A working template that showcases all features on hardware development platform
  • End-to-end system demonstration capability
• Push-button conversion of FPGA design to HardCopy ASIC.

The design methodology described allows an efficient and flexible solution, with design entry that is familiar to and suitable for hardware and software engineers.  Available processing power on Altera’s FPGAs allows the required system to be instantiated on a single FPGA. Moreover, the design methodology allows a transition to HardCopy ASICs, therefore significantly reducing risk, cost, power, and IP protection, while retaining software programmability. Additional benefits include:

• Customizable system-on-a-chip that significantly lowers R&D cost , risk, and power, and provides time-to-market efficiency
• FPGA and HardCopy ASIC path that allows you to create one design using one methodology, one tool, and one company and then ramp production when it makes sense
• Highly scalable and flexible to enable the design to scale up or down for various targets (for example, from SME/SOHO pico to femto, from 32 users to 6 users, etc.)
• Software capability with re-programmability retained in FPGA and ASIC fabric

To learn more about how Altera can help with your custom SoC, please contact your local Altera sales representative.