Identifiability and Parameter Estimation of Linear Continuous-time Systems under Irregular and Random Sampling**The work was supported by National Key Basic Research Program of China (973 program) under grant No. 2014CB845301 and the NSF of China under Grants No. 61273193, 61120106011, 61134013, and 61403027, and in part by the Army Research Office under grant W911NF-12-1-0223.