The paradigm of integrated sensing and communication (ISAC) is envisioned as a key enabler for the evolution of 6G, leveraging inherent similarities of dual functions in hardware architectures and signal processing to sense the environment and send messages via a shared waveform. In this paper, we establish a theoretical framework to evaluate the sensing and communication (S&C) performance of bistatic ISAC systems under Gaussian fading channels at finite blocklength, where a primary focus lies in uncovering the fundamental tradeoff between dual functions due to limited resources. In particular, we first formulate the joint S&C problem in bistatic single-input and single-output (SISO) ISAC systems, and define the rate-error tradeoff to quantify the performance balance between S&C. Then we derive the achievability and converse bounds for the rate-error tradeoff, providing a deep comprehension of the interplay between S&C functions. Finally, we discuss the extensions of our framework involving infinite blocklength regime, general parameter estimation and multiple-input and multiple-output (MIMO) channel.

Existing integrated sensing and communication technology designed for monostatic settings segregates sensing and communication (S&C) at distinct terminals, impeding their adaptability to network paradigms. In this paper, we propose a general framework for joint target-localization and data-detection (JTD) in bistatic settings by using a combination of the deterministic known (DK) and random unknown (RU) symbols, e.g., pilot and data symbols. We first derive the performance limits for target localization-related parameters with combined symbols. We demonstrate that the Fisher information matrix (FIM) for target localization using the DK part can be expressed in a closed form through orthogonal projection, while that using the RU part aligns with the modified FIM in monostatic settings at an exponential rate with respect to the signal-to-noise ratio. Then, we propose a JTD scheme to exploit the reciprocal advantages for S&C, i.e., the detected data symbols are harnessed to enhance target localization in an alternating way. Finally, simulation results validate our theoretical analysis and the effectiveness of the proposed JTD scheme.

Integrated sensing and communication (ISAC) has been proposed as a promising paradigm in the future wireless networks, where the spectral and hardware resources are shared to provide a considerable performance gain. It is essential to understand how sensing and communication (S&C) influences each other to guide the practical algorithm and system design in ISAC. In this paper, we investigate the performance tradeoff between S&C in a single-input single-output (SISO) ISAC system with finite blocklength. In particular, we present the system model and the ISAC scheme, after which the rateerror tradeoff is introduced as the performance metric. Then we derive the achievability and converse bounds for the rateerror tradeoff, determining the boundary of the joint S&C performance. Furthermore, we develop the asymptotic analysis at large blocklength regime, where the performance tradeoff between S&C is proved to vanish as the blocklength tends to infinity. Finally, our theoretical analysis is consolidated by simulation results.