Uplink integrated sensing and communication (ISAC) systems have recently emerged as a promising research direction, enabling simultaneous uplink signal detection and target sensing. In this paper, we propose flexible projection (FP)-type receivers that unify the projection-type receivers and the successive interference cancellation (SIC)-type receivers by using a flexible tradeoff factor to adapt to dynamically changing uplink ISAC scenarios. The FP-type receivers address the joint signal detection and target response estimation problem through two coordinated phases: 1) Communication signal detection using a reconstructed signal whose composition is controlled by the tradeoff factor, followed by 2) Target response estimation performed through subtraction of the detected communication signal from the received signal. With adjustable tradeoff factors, the FP-type receivers can balance the enhancement of the signal-to-interference-plus-noise ratio (SINR) with the reduction of correlation in the reconstructed signal for communication signal detection. The pairwise error probabilities (PEPs) are analyzed for both maximum likelihood (ML) and zero-forcing (ZF) detectors, revealing that the optimal tradeoff factor should be determined based on the adopted detection algorithm and the relative power of the sensing and communication (S&C) signal. A homotopy optimization framework is first applied for the FP-type receivers with a fixed trade-off factor. This framework is then extended to develop dynamic FP (DFP)-type receivers, which iteratively adjust the trade-off factor for improved algorithm performance and environmental adaptability. Subsequently, two extensions are explored to further enhance the receivers' performance: parallel DFP (PDFP)-type receivers and a block-structured receiver design. Finally, the effectiveness of the proposed receiver designs is verified via simulations.

翻译：上行链路集成感知与通信（ISAC）系统作为新兴研究方向，能够同时实现上行信号检测与目标感知。本文提出一种灵活投影（FP）型接收机，通过引入灵活折衷因子来统一投影型接收机与连续干扰消除（SIC）型接收机，从而适应动态变化的上行ISAC场景。该接收机通过两个协调阶段解决联合信号检测与目标响应估计问题：1）利用受折衷因子控制重构的信号进行通信信号检测；2）从接收信号中减去已检测的通信信号以完成目标响应估计。通过调节折衷因子，FP型接收机能够在提升信号检测的信干噪比（SINR）与降低重构信号相关性之间取得平衡。本文分析了最大似然（ML）与迫零（ZF）检测器的成对错误概率（PEP），揭示最优折衷因子应根据所采用的检测算法以及感知与通信（S&C）信号的相对功率来确定。首先将同伦优化框架应用于固定折衷因子的FP型接收机，进而扩展该框架以开发动态FP（DFP）型接收机，通过迭代调整折衷因子提升算法性能与环境适应性。随后探讨两种扩展方案以进一步增强接收机性能：并行DFP（PDFP）型接收机与块结构接收机设计。最后通过仿真验证了所提接收机设计的有效性。