Graceful Performance Degradation and Improved Error Tolerance via Mixed-Mode Distributed Coherent Radar

Distributed coherent radar (DCR) is a distributed multiple-input–multiple-output (MIMO) radar concept, which holds the potential to significantly improve signal-to-noise ratio (SNR) over single aperture and statistical MIMO systems. DCR achieves coherence in one of two modes: Cohere on transmit (COT), which yields an ${N}^{{3}}$ improvement in SNR ( ${N}$ is the number of radars) but requires ideal coherence parameter (CP) information before transmission, and cohere on receive (COR), which yields an ${N}^{{2}}$ improvement in SNR but can generally estimate CPs adaptively on reception. System concepts generally make a binary choice between COR and COT operation based on the error level. This has led to multiple studies of CP error and its impact on performance of each mode. In this work, a CP error analysis has been extended to include all three principle CPs (delay, phase, and frequency), as well as simultaneous consideration for the number of radars in the constituent system. This novel analysis reveals significant relationships between the number of elements in a system and the resulting error tolerance. A novel DCR operating mode, mixed-mode DCR (MM-DCR), is introduced, which exploits this relationship and achieves ${N}^{{2} + \log _{N}({M})}$ SNR gain, where ${M}$ is the number of elements used for each subaperture. MM-DCR is shown to yield better performance than COR and COT under a broad set of error conditions, yielding overall system error tolerance improvements. Moreover, as error varies during system operation, MM-DCR facilitates graceful performance degradation by varying the size of the subapertures.