Introduction to Orthogonal Frequency Division Multiplexing

What we have learned so far can now be applied to build an orthogonal frequency division multiplexing (OFDM) modem.

Background

The OFDM is one of the most popular digital transmission schemes employed in many of the wireless technologies we use every day. Some examples of the wireless networks that use OFDM include:

• Wireless local area networks (LAN)
• WiFi (e.g., IEEE 802.11a, g, n, ac, ah)
• Digital radio systems (e.g., Digital Audio Broadcasting or DAB)
• Terrestrial digital TV systems (e.g., Digital Video Broadcasting or DVB)
• 4G long term evolution (LTE) cellular networks
• 5G New Radio (NR) cellular networks

Why is OFDM so popular? As we’ll see, when data rates are increased on a wireless channel, severe interference arises from within the multiple copies of the signal itself arriving through different paths. Combating this interference, a process known as equalization is computationally quite intensive if done through conventional communication techniques. OFDM provides a simple and fast equalization methodology that can cope with the demands of very high data rates. There are several other reasons to adopt OFDM in wireless standards beyond the scope of this course.

Block diagram

Let’s build a simple OFDM modem with the help of the block diagram below that shows the transmitter (Tx) side implementation. The functionality of each block will be explained in its own lesson.