Waveform design for radar-embedded communications exploiting spread spectrum technology

Radar-embedded communication (REC) provides a reliable and low probability of intercept (LPI) communication link to the intended receivers while masking its presence from intercept receivers. This study summarises all the waveform design schemes as well as receiver processing strategies for intra-pulse REC, which forms the communication symbol waveform during one pulse interval and utilises de-correlation processing on the receiver side. Based on the set of eigenvectors after eigen-decomposition of sampled radar waveform, three design approaches are considered: eigenvectors-as-waveforms, weighted-combining and dominant-projection (DP). Specifically, DP performs better than the other two approaches even in multipath environment by using one projection matrix masked random vector to represent a communication symbol. Aimed by the drawbacks of DP, the authors propose a novel waveform generation approach called modified DP (MDP) in this study. MDP uses a common digitally-modulated communication symbol spread by a pseudorandom sequence, so that it can enlarge the Euclidean distances between different data symbols and generate soft information for soft decision decoding, thus improving symbol error ratio and bit error ratio. Simulation results show that MDP significantly improves the reliability performance especially when channel coding is used, while also maintaining a relatively equal anti-intercept performance.