This paper studies a communication-centric integrated sensing and communication (ISAC) system, where a multi-antenna base station (BS) simultaneously performs downlink communication and target detection. A novel target detection and information transmission protocol is proposed, where the BS executes the channel estimation and beamforming successively and meanwhile jointly exploits the pilot sequences in the channel estimation stage and user information in the transmission stage to assist target detection. We investigate the joint design of pilot matrix, training duration, and transmit beamforming to maximize the probability of target detection, subject to the minimum achievable rate required by the user. However, designing the optimal pilot matrix is rather challenging since there is no closed-form expression of the detection probability with respect to the pilot matrix. To tackle this difficulty, we resort to designing the pilot matrix based on the information-theoretic criterion to maximize the mutual information (MI) between the received observations and BS-target channel coefficients for target detection. We first derive the optimal pilot matrix for both channel estimation and target detection, and then propose an unified pilot matrix structure to balance minimizing the channel estimation error (MSE) and maximizing MI. Based on the proposed structure, a low-complexity successive refinement algorithm is proposed. Simulation results demonstrate that the proposed pilot matrix structure can well balance the MSE-MI and the Rate-MI tradeoffs, and show the significant region improvement of our proposed design as compared to other benchmark schemes. Furthermore, it is unveiled that as the communication channel is more correlated, the Rate-MI region can be further enlarged.

翻译：本文研究了一种以通信为中心的集成感知与通信（ISAC）系统，其中多天线基站（BS）同时执行下行通信与目标检测。提出了一种新颖的目标检测与信息传输协议，该协议中BS依次执行信道估计与波束赋形，并在信道估计阶段联合利用导频序列、在传输阶段联合利用用户信息辅助目标检测。我们研究导频矩阵、训练时长与发射波束赋形的联合设计，以在满足用户最小可达速率约束的条件下最大化目标检测概率。然而，由于检测概率关于导频矩阵不存在闭式表达式，设计最优导频矩阵极具挑战性。为克服此困难，我们基于信息理论准则设计导频矩阵，以最大化用于目标检测的接收观测值与BS-目标信道系数之间的互信息（MI）。首先推导用于信道估计与目标检测的最优导频矩阵，进而提出一种统一导频矩阵结构以平衡最小化信道估计误差（MSE）与最大化MI。基于所提结构，提出了一种低复杂度的逐次优化算法。仿真结果表明，所提导频矩阵结构能够良好平衡MSE-MI与Rate-MI折衷，且相较于其他基准方案，所提设计实现了显著的区域性能提升。此外，研究揭示当通信信道相关性增强时，Rate-MI区域可进一步扩大。