Integrated Sensing and Communication for 6G : Resolving Range and Velocity Ambiguity in ISAC OFDM Systems

Sammanfattning

Integrated Sensing and Communication (ISAC) is an emerging technology for6G networks that enables radar sensing and wireless communication to sharethe same hardware, spectrum, and waveform. Orthogonal Frequency-DivisionMultiplexing (OFDM) is a promising waveform candidate for ISAC due toits flexibility, spectral efficiency, and compatibility with existing communication infrastructure. In ISAC OFDM systems, sensing is enabled by insertingknown pilot symbols into the time-frequency grid. However, when these pilotsare spaced sparsely to preserve communication resources, the maximum unambiguous range and velocity of the system are reduced, leading to ambiguoustarget parameter estimation.The uniform allocation is shown to produce accurate estimates within its unambiguous limits but offers no means of resolving ambiguity with sparse pilotconfigurations. The coprime resource allocation method successfully extendsthe unambiguous range and velocity at the cost of elevated sidelobes, which aresubstantially mitigated by applying the MUltiple Signal Classification(MUSIC)algorithm.The proposed multislot method assigns a different uniform pilot spacing toeach successive OFDM slot, with spacings chosen to be pairwise coprime. Bycombining measurements across slots using the Chinese Remainder Theorem,the true range and velocity of multiple targets are estimated unambiguously.Simulation results demonstrate that the multislot method achieves competitiveperformance while using fewer sensing resources than the uniform method andinherently resolves range and velocity ambiguities.The results suggest that both coprime and multislot resource allocation areviable approaches to ambiguity resolution in ISAC OFDM, with the preferredchoice depending on the operational scenario and system constraints.