/ˈoʊ ɛf diː ɛm/
noun — "splitting data across many orthogonal subcarriers for robust, high-speed transmission."
OFDM (Orthogonal Frequency-Division Multiplexing) is a digital modulation technique that transmits data by dividing a high-rate data stream into many lower-rate streams sent simultaneously over closely spaced, mutually orthogonal subcarriers. This structure makes OFDM highly resilient to multipath interference, frequency-selective fading, and channel distortion, which are common in wireless and wired broadband environments. As a result, OFDM underpins modern communication systems including Wi-Fi, LTE, and 5G NR.
Technically, OFDM maps incoming bits onto symbols using a modulation scheme such as QAM, then distributes those symbols across many subcarriers whose frequencies are mathematically orthogonal. Orthogonality ensures that, despite overlapping spectra, subcarriers do not interfere at the sampling instants. Implementation relies on fast digital signal processing using the FFT (Fast Fourier Transform) and its inverse, allowing efficient modulation and demodulation. A cyclic prefix is typically added to each symbol to absorb delay spread caused by reflections, preventing inter-symbol interference.
Key characteristics of OFDM include:
- Orthogonal subcarriers: overlapping frequencies without mutual interference.
- Multipath robustness: resilience to echoes and reflections in complex channels.
- Spectral efficiency: tight subcarrier spacing maximizes bandwidth usage.
- Flexible adaptation: supports adaptive modulation and coding per subcarrier.
- Digital implementation: efficient realization using FFT-based processing.
In practical workflows, OFDM is used whenever high data rates must be delivered reliably over imperfect channels. For example, a Wi-Fi transmitter encodes user data, maps it to QAM symbols, spreads those symbols across hundreds or thousands of OFDM subcarriers, and transmits them in parallel. At the receiver, the FFT separates the subcarriers, equalization compensates for channel effects, and the original data is reconstructed. Cellular base stations use similar workflows to serve many users simultaneously under varying signal conditions.
Conceptually, OFDM is like dividing a heavy load among many smaller carts rolling side by side: each cart moves slowly and steadily, but together they deliver the cargo quickly and reliably, even over rough terrain.
Intuition anchor: OFDM trades single fast signals for many coordinated slow ones, turning hostile channels into manageable pathways for high-speed digital communication.