How to design a scalable OFDMA engine for WiMAX

Scalable orthogonal frequency-division multiple access (OFDMA) is a key technology behind mobile WiMAX—as it is with other wireless technologies. OFDMA is also expected to play a key role 3GPP and 3GPP2 long term evolution standards.

More information on OFDMA is available at All about OFDMA.

To achieve competitive systems, however, designers and OEMs must choose a silicon platform that offers flexibility, scalability and a risk-free cost-reduction path. This is particularly true of an OFDMA engine because of its high performance requirements.

The scalable OFDMA engine should possess the following features:

• Support for 128, 512, 1K, and 2K FFT sizes to address variable bandwidths from 1.25 to 20 MHz
• Support for both downlink partial usage of subchannels (PUSC) and full usage of subchannels (FUSC) and uplink PUSC mandatory schemes
• Support for both fixed and variable pilots and runtime configurable cyclic prefix insertion
• Highly parameterizable design
• Optimized for efficient use of FPGA device resources

Click here for Figure 1
Figure 1: Scalable OFDMA Reference Design Blocks (Note: IFFT = Inverse fast Fourier transform.

WiMAX PHY layer system design
WiMAX is gaining popularity as a broadband wireless access technology with significant market potential. To achieve competitive systems it is necessary to choose a silicon platform that offers flexibility, scalability and a risk-free cost-reduction path.

A comprehensive wireless ecosystem portfolio offers a broad family of FPGA devices, intellectual property (IP), reference designs, development boards and WiMAX-compliant, off-the-shelf channel and RF card solutions through partners. By leveraging these offerings and partners, WiMAX OEMs can accelerate their own internal make solution or buy a complete off-the-shelf solution and get to market faster utilizing FPGA-based WiMAX designs.

Figure 2 shows the blocks used in this reference design to implement a scalable OFDMA physical layer in WiMAX basestations. The Scalable OFDMA Reference design represents a module of the WiMAX Phyisical layer that is well defined by the specification and so this design may be used as a black box in order to reduce development time.

In this way, it is possible to concentrate design effort and resources in the implementation of more differentiating components. This article describes the functionality and implementation of the Scalable OFDMA Engine.

Click here for Figure 2
Figure 2: WiMAX Physical Layer Implementation.