Orthogonal frequency division multiplexing (OFDM), which has been the dominating waveform for contemporary wireless communications, is also regarded as a competitive candidate for future integrated sensing and communication (ISAC) systems. Existing works on OFDM-ISAC usually assume that the maximum sensing range should be limited by the cyclic prefix (CP) length since inter-symbol interference (ISI) and inter-carrier interference (ICI) should be avoided. However, in this paper, we provide rigorous analysis to reveal that the random data embedded in OFDM-ISAC signal can actually act as a free ``mask" for ISI, which makes ISI/ICI random and hence greatly attenuated after radar signal processing. The derived signal-to-interference-plus-noise ratio (SINR) in the range profile demonstrates that the maximum sensing range of OFDM-ISAC can greatly exceed the ISI-free distance that is limited by the CP length, which is validated by simulation results. To further mitigate power degradation for long-range targets, a novel sliding window sensing method is proposed, which iteratively detects and cancels short-range targets before shifting the detection window. The shifted detection window can effectively compensate the power degradation due to insufficient CP length for long-range targets. Such results provide valuable guidance for the CP length design in OFDM-ISAC systems.
Joint Detection and Velocity Estimation in OFDM-ISAC Cell-Free Massive MIMO Networks
Consorzio Nazionale Interuniversitario per le Telecomunicazioni（意大利国立电信联盟）；DIEI, Universita degli Studi di Cassino e del Lazio Meridionale（卡西诺及南拉齐奥大学 DIEI）
Phase noise (PN) can become a major bottleneck for integrated sensing and communications (ISAC) systems towards 6G wireless networks. In this paper, we consider an OFDM ISAC system with oscillator imperfections and investigate the impact of PN on monostatic sensing performance by performing a misspecified Cramér-Rao bound (MCRB) analysis. Simulations are carried out under a wide variety of operating conditions with regard to SNR, oscillator type (free-running oscillators (FROs) and phase-locked loops (PLLs)), 3-dB bandwidth of the oscillator spectrum, PLL loop bandwidth and target range. The r…
Secure OFDM Waveform Design for ISAC: Artificial Phase-Doppler Shifts Against Passive Sensing
Karlsruhe Institute of Technology（卡尔斯鲁厄理工学院）；Nokia Bell Labs Stuttgart（诺基亚贝尔实验室斯图加特）；Hensoldt Sensors GmbH（亨索尔特传感器有限公司）；Technical University of Munich（慕尼黑工业大学）
CRLB and Parameter Estimation for OFDM-ISAC with Non-Uniform Sparse Resource Allocation
National Mobile Communications Research Laboratory, Southeast University（东南大学）；School of Information Science and Engineering, Hohai University（河海大学）；Purple Mountain Laboratories（紫金山实验室）
Tensor Decomposition-Based Wireless Sensing for MIMO-OFDM ISAC via Flexible Spatial-Temporal-Spectral Optimization
Nanjing University of Science and Technology（南京理工大学）；Key Laboratory of Near-Range RF Sensing ICs and Microsystems (NJUST), Ministry of Education, School of Electronic and Optical Engineering, Nanjing University of Science and Technology（南京理工大学电子与光学工程学院、近场射频集成电路与微系统教育部重点实验室）；Qian Xuesen College, Nanjing University of Science and Technology（南京理工大学钱学森学院）；College of Communications Engineering, Army Engineering University of PLA（中国人民解放军陆军工程大学通信工程学院）；The Sixty-Third Research Institute, National University of Defense Technology（国防科技大学第六十三研究所）；National University of Singapore（新加坡国立大学）；Department of Electrical and Computer Engineering, National University of Singapore（新加坡国立大学电气与计算机工程系）
This letter analyzes the fundamental performance of integrated sensing and communications (ISAC) systems. For downlink and uplink ISAC, the diversity orders are analyzed to evaluate the communication rate (CR) and the high signal-to-noise ratio (SNR) slopes are unveiled for the CR as well as the sensing rate (SR). Furthermore, the achievable downlink and uplink CR-SR regions are characterized. It is shown that ISAC can provide more degrees of freedom for both the CR and the SR than conventional frequency-division sensing and communications systems where isolated frequency bands are used for se…
