Simplified and Enhanced Multiple Level Nested Arrays Exploiting High-Order Difference Co-Arrays

Based on the high-order difference co-array concept, an enhanced four-level nested array (E-FL-NA) is first proposed, which optimizes the consecutive lags at the fourth-order difference co-array stage. To simplify sensor location formulations for comprehensive illustration and also convenient structure construction, a simplified and enhanced four-level nested array (SE-FL-NA) is then proposed, whose performance is compromised but still better than the four-level nested array (FL-NA). This simplified structure is further extended to the higher order case with multiple sub-arrays, referred to as simplified and enhanced multiple level nested arrays (SE-ML-NAs), where significantly increased degrees of freedom can be provided and exploited for underdetermined direction of arrival estimation. Simulation results are provided to demonstrate the performance of the proposed E-FL-NA, whereas a higher number of detectable sources is achieved by the SE-ML-NA with a limited number of physical sensors.