Performance evaluation and transmitter optimization for AN-aided FH communication against time misalignment

To guarantee secure communication against eavesdropping and malicious attack, an artificial noise (AN)-aided frequency-hopping (FH) architecture is adopted in this article. But the inevitable time misalignment between the received signal and locally reconstructed AN will deteriorate the AN cancellation performance, yielding significant secrecy degradation at the FH receiver. In view of this, first, the AN cancellation performance under time misalignment is evaluated via signal to AN-plus-noise ratio, and the system secrecy is analyzed via secrecy rate. Then, to mitigate the performance degradation raised by time misalignment, the transmitting power allocation scheme for AN and confidential signal (CS) is optimized, and the optimal hopping period is designed. Notably, the obtained conclusions in both the performance evaluation and transmitter optimization sections hold no matter whether the eavesdropper can realize FH synchronization or not. Simulations verify that time misalignment will raise non-negligible performance degradation. Besides, the power ratio of AN to CS should decrease as time misalignment increases, and for perfect time synchronization, the transmitting power of AN and CS should be equivalent. In addition, a longer hopping period is preferred for secrecy enhancement when time misalignment gets exacerbated.