Chapter 14: Orthogonal Frequency Division Multiplexing (OFDM)

Learning Objectives

• Explain the principle of OFDM as converting a frequency-selective channel into parallel flat-fading sub-channels and derive the orthogonality condition for subcarriers
• Describe the DFT/IDFT-based implementation of OFDM and explain how the cyclic prefix eliminates both ISI and ICI through circular convolution
• Compare pilot placement strategies (comb-type, block-type, scattered) and derive LS and MMSE channel estimators for OFDM subcarriers
• Define PAPR, derive its statistical distribution for OFDM signals, and evaluate reduction techniques including clipping, SLM, and tone reservation
• Analyse the effects of carrier frequency offset on OFDM reception, distinguish integer and fractional CFO, and describe synchronisation algorithms
• Design per-subcarrier adaptive modulation and coding strategies using CQI feedback and water-filling power allocation
• Compare OFDM generalisations including SC-FDMA (DFT-spread OFDM), FBMC, and OTFS in terms of PAPR, spectral containment, and Doppler resilience
• Calculate cyclic prefix overhead, spectral efficiency, and OFDM system parameters for practical wireless standards such as LTE and 5G NR