You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Survey of RF Communications and Sensing Convergence Research 
Chapter Title:  VI. BOUNDS ON JOINTLY OPTIMIZED SYSTEMS 
1. Abstract of Cited Paper (BIB001):  This paper presents a high-level overview of the Fundamental Limits studies for the DARPA SSPARC program. It focuses on the key techniques and insights that have resulted from this effort and presents possible future research directions that have been suggested by these studies1.

Literature Review:
While state of the art systems have mild elements of codesign, future systems must be co-designed to jointly sense VOLUME 5, 2017 and communicate, maximizing spectral efficiency. Traditionally, communications performance related to spectral efficiency is measured by the channel capacity. This is the achievable, but maximum operating rate of arbitrary data communications for a given channel probability distribution  . For example, for a Gaussian, band-limited, powerlimited system, the maximum communications data rate is defined as BIB001 : where B is the receiver bandwidth, P com,rx is the received communications power, and N 0 is the noise power spectral density. Often, prior to recent work on information theoretic bounds, radar estimation performance limits are dictated by the CRLB. For radar range estimation, this is given by  : where T p is the radar pulse duration, B rms is the radar waveform RMS bandwidth, and P rad,rx is the radar receive power. While these metrics work in isolation for each user, they do not adequately measure joint performance. To address this, researchers have derived fundamental limits on joint radar and communications operation, and were successful in producing several alternative interpretations of joint radar-communications performance and bounds on those resulting joint metrics BIB002 . Next, we highlight several research threads that investigate bounds on joint radarcommunications performance for future systems.