Chapter Summary

Chapter Summary

Key Points

• 1.

  ISAC is a Pareto optimization. Given a resource budget $(W, T, P_t)$, the Pareto frontier in the $(R_{\text{comm}}, D_{\text{sens}}^{-1})$ plane sets the best achievable ISAC operating points. Any waveform sits somewhere on or inside this frontier; the goal is to position on the frontier.

• 2.

  OTFS is the natural ISAC waveform — two structural reasons. (1) Data and target scene live on the same DD grid: joint processing reduces to a unified optimization on one grid. (2) Thumbtack ambiguity gives OTFS Pareto-optimal sensing at information-theoretic limits, simultaneously with full data throughput. Competitor waveforms (OFDM, chirp) are strictly inside the frontier.

• 3.

  CommIT contributions define the framework. Gaudio-Kobayashi- Caire-Colavolpe (IEEE TWC 2020) established OTFS's thumbtack ambiguity and CRLB-matching. Yuan-Schober-Caire (IEEE ComMag 2024 Part III) synthesized the full ISAC framework, positioning OTFS as the leading 6G ISAC candidate. Together, these two papers are the foundation of the OTFS-ISAC literature.

• 4.

  Joint estimation-detection is a 2-3 iteration EM algorithm. Alternating between data detection (given estimated channel) and target refinement (given estimated data) converges to a local MAP estimate in 2-3 iterations at typical SNRs. Total complexity: $3\times$ single-task OTFS. The thumbtack ambiguity is essential for reliable convergence.

• 5.

  Super-resolution refines estimates to sub-grid accuracy. Newton iteration on the local ambiguity surface refines target parameters below the grid resolution. At 30 dB SNR, range to 1 cm, velocity to 5 mm/s. Enables fine tracking applications (health monitoring, gesture recognition, automotive pedestrian detection).

• 6.

  Three tradeoffs shape ISAC deployment. (1) Compute: OTFS-ISAC is $\sim 2\times$ data-only OTFS, within 5G NR budgets. (2) PAPR: OTFS has $\sim 4$ dB higher PAPR than OFDM. PA back-off required; real link budget cost. (3) Latency-Doppler: mmWave ($f_0 \geq 28$ GHz) keeps fine velocity resolution at URLLC latencies.

• 7.

  Applications span automotive, UAV, healthcare. Automotive: 77 GHz, 3 ms frame, 8 cm range accuracy, 3.6 cm/s velocity, $\sim 200$ Mbps data. UAV: 28 GHz, 5 ms frame, 400 Mbps data + terrain survey. Healthcare: 60 GHz, 5 ms frame, sub-mm motion detection. All with a single waveform, continuous operation, single receiver.