OFDMsignal

OFDM signal refers to the time-domain waveform used in orthogonal frequency-division multiplexing (OFDM) communication systems. It represents data as a large number of parallel subcarrier signals, each modulated with a low-rate data stream, and then combined to form a single composite signal. The subcarriers are spaced so that they remain orthogonal over the symbol duration, allowing efficient packing of spectrum.

Generation and processing: In typical implementations, data streams are mapped to modulation constellations (for example QPSK, 16-QAM, or 64-QAM) for each subcarrier. An inverse discrete Fourier transform (IFFT) converts the frequency-domain symbols into a time-domain OFDM signal. A cyclic prefix is added to each symbol to mitigate inter-symbol and inter-carrier interference caused by multipath channels. The signal may be windowed or filtered to reduce out-of-band emissions.

Key properties: OFDM achieves high spectral efficiency and provides simple equalization in frequency—frequency-selective channels can be addressed by per-subcarrier processing. The orthogonality condition leads to a narrow subcarrier spacing Δf = 1/Tu, where Tu is the useful symbol duration. OFDM can accommodate adaptive modulation and coding across subcarriers. However, it exhibits a high peak-to-average power ratio (PAPR) and is sensitive to synchronization errors and Doppler shifts.

Applications: OFDM is a core technology in many modern communication standards, including Wi‑Fi (IEEE 802.11a/g/n/ac/ax), digital television (DVB-T/T2), power-line communication, and mobile networks such as LTE and 5G NR.