Popular for wireless modulation, orthogonal frequency division multiplexing (OFDM) is used in broadcast applications and "last-mile" connectivity applications such as multichannel multipoint distribution systems (MMDS) and wireless local area networks.
Conventional single-carrier modulation schemes such as amplitude modulation (AM) or frequency modulation (FM) send one signal at a time, using one radio frequency. OFDM is a multi-carrier modulation scheme that sends multiple high-speed signals concurrently on different frequencies. This concurrent signaling uses bandwidth efficiently and clearly, in the presence of frequency-selective fading.
Altera® APEX™ devices combined with signal processing intellectual property functions are ideal for the high-throughput requirements of wireless OFDM applications. Key Altera advantages include:
- Comprehensive signal processing intellectual property solutions
- Parallel processing performance advantages
- Programmable logic flexibility
- High level of integration
Using Altera devices and signal processing intellectual property, designers can quickly adapt to new standards such as the Wireless 802.11a, Wireless Broadband Working Group 802.16, and HiperLAN/2.
In Figure 1, the dark blue blocks represent Altera IP solutions and the light blue blocks represent programmable logic solutions. Click on the blue blocks for more information.
Figure 1. OFDM Transmitter Block Diagram
Systems using OFDM modulation (i.e., DVB, DAB, and MMDS) utilize channel coding to combat multipath propagation. Data symbols are then mapped onto an appropriate constellation (i.e., QPSK or, QAM). The resulting I and Q values are stored in a buffer, and the inverse fast Fourier transform (IFFT) is applied. The IFFT performs the modulation onto orthogonal carriers. The data is prepared for transmission, first through serialization, and then by the addition of a cyclic prefix for multipath immunity. The resulting data is then sent to an antenna for transmission.
Complete System Solution
Altera's high-performance APEX devices and comprehensive signal processing intellectual property portfolio represent a complete system solution with all the flexibility and time-to-market advantages of using programmable logic.
