Chapter 5: OFDM Revisited Through the DD Lens

Learning Objectives

• Express an OFDM signal in the delay-Doppler domain via the Zak transform
• Prove that an OFDM symbol spreads uniformly across all Doppler bins
• Quantify OFDM's inter-carrier interference (ICI) under Doppler spread
• Identify what OFDM signaling "wastes" — the untapped DD sparsity
• Motivate the OTFS design as the natural remedy for OFDM's DD-domain inefficiency