Survey of RF Communications and Sensing Convergence Research <s> A. RADAR ESTIMATION RATE AND JOINT BOUNDS <s> We investigate cooperative radar and communications signaling. While each system typically considers the other system a source of interference, by considering the radar and communications operations to be a single joint system, the performance of both systems can, under certain conditions, be improved by the existence of the other. As an initial demonstration, we focus on the radar as relay scenario and present an approach denoted multiuser detection radar (MUDR). A novel joint estimation and information theoretic bound formulation is constructed for a receiver that observes communications and radar return in the same frequency allocation. The joint performance bound is presented in terms of the communication rate and the estimation rate of the system. <s> BIB001 </s> Survey of RF Communications and Sensing Convergence Research <s> A. RADAR ESTIMATION RATE AND JOINT BOUNDS <s> The constant information radar, or CIR, is a tracking radar that modulates target revisit time by maintaining a fixed mutual information measure. For highly dynamic targets that deviate significantly from the path predicted by the tracking motion model, the CIR adjusts by illuminating the target more frequently than it would for well-modeled targets. If SNR is low, the radar delays revisit to the target until the state entropy overcomes noise uncertainty. As a result, we show that the information measure is highly dependent on target entropy and target measurement covariance. A constant information measure maintains a fixed spectral efficiency to support the RF convergence of radar and communications. The result is a radar implementing a novel target scheduling algorithm based on information instead of heuristic or ad hoc methods. The CIR mathematically ensures that spectral use is justified. <s> BIB002 </s> Survey of RF Communications and Sensing Convergence Research <s> A. RADAR ESTIMATION RATE AND JOINT BOUNDS <s> We model the effects of phase noise on clutter cancellation and study the overall impact it has on the radar estimation rate. Cooperative bounds involving radar cancellation for additional communications access are impacted by complicating the overall model. We assume the clutter is static with small intrinsic clutter motion (ICM). Treating the clutter cancellation residual due to intrinsic clutter motion and phase noise as an additional noise source, the radar estimation rate is negatively impacted. This clutter cancellation residual further degrades the communications channel, affecting the communications data rate as well. We also study the relationship between the clutter cancellation residual and the range of the scatterer. <s> BIB003
To measure spectral efficiency, we look at recent research quantifying radar information as a function of time: radar estimation rate BIB001 , BIB002 - BIB003  where I (x; y) is the mutual information between random vectors x and y, and T is the time period between spectral accesses. This can be a pulse repetition interval (PRI) or a target revisit period. This allows construction of joint radarcommunications bounds, and allows future system designers to score and optimize systems relative to a joint information metric. For a simple range estimation problem with a Gaussian tracking prior, this takes the form [13]  where σ 2 proc is the range-state process noise variance, and σ 2 CRLB is the CRLB for range estimation given by Equation  . One immediately notes the similarity to Equation  , where the ratio of the source uncertainty variance to the range estimation noise variance forms a pseudo-SNR term in the Gaussian mutual information. An example of the joint multiple access channel (MAC) is shown in Figure 19 by plotting the communications data rate on one axis and the radar estimation rate on the other axis. Modern systems will attempt to get as close to the upper right hand corner of the outer manifold as possible. Here, inner bounds from prior work are shown to see how they compare to the joint theoretical limiting bounding box.