Originally proposed in 1983, [34], Distributed Coherent Radar (DCR), composes a single radar system from multiple (N), highly spatially diverse, independent radars such that they act as a single array. This approach offers the advantage of an N2 or N3 improvement in signal-to-noise ratio (SNR) depending on whether the radars are operated in a Cohere-on- Receive (COR) mode (signals are aligned at reception) or Cohere-on-Transmit (COT) mode (signals are aligned before transmission and again at reception). The improvement in SNR when operating in a DCR mode can facilitate the composition of smaller, cheaper, radars that yield similar performance to a more costly larger (potentially prohibitively large) single radar system. At the time of its original description, underlying technologies were largely insufficient for the realization of such systems. With the advent of modern highly software programmable radio frequency (RF) technologies such as Software Defned Radios, improved communication capabilities, and increased computing power, DCR has seen a resurgence of interest in the literature [13, 16, 19, 26, 27, 28, 39, 46, 53, 65, 68, 73, 74, 75, 77]. Some works focus on the development of conceptual systems, while others investigate theoretical performance bounds or address specific concepts and particulars of operating modes.
Unfortunately due to the highly complex nature of the technology, no single work includes a complete analytical framework for the sources of coherence loss and DCR specific phenomonology challenges at a system level. The authors contend that isolated analytical discussions often fail to capture the full complexity and challenges associated with DCR systems. For example, no other single work combines analysis of all coherence parameters with variation in the number of elements in a DCR system.
This work leverages a set of fundamental coherence parameter variables (phase, delay, and frequency) from which all other coherence related losses can be derived. Complete general case analytical system descriptions of the two principle DCR operating modes, COR and COT, are developed including critical aspects of DCR system realization, as well as clear derivations for the ideal case SNR improvements from a system perspective. Analytical models are augmented with discussion of the sources of non-ideal performance for each mode such as waveform leakage, target kinematics, clock jitter, etc. The analysis also includes a novel generalized SNR formulation that should facilitate easier future analysis under a common framework, in contrast with other currently published simplifed variants of the same.
Leveraging our complete foundational analysis, we develop a novel operating mode called "Mixed Mode DCR" (MM-DCR). MM-DCR is then analyzed for performance bounds, fol- lowed by performance under error conditions. The results show that MM-DCR provides a path for graceful performance degradation and improved error tolerance over COR and COT modes [41].
This work then extends the analytical system descriptions with a complete empirical modeling and simulation (M&S) capability, including a proposed architectural description for such capabilities. The authors contend that empirical analysis from a well defined modeling and simulation capability is the only viable approach for DCR system analysis beyond the trivial cases. M&S is used to verify the fundamental behaviors described in the analytical descriptions and extend with additional complexity such as waveform variation and stochastic errors to provide a well rounded complete analysis of the Fundamentals of Distributed Coherent Radar.