An Efficient Directional Modulation Transmitter With Novel Crest Factor Reduction Technique

Directional modulation (DM) is a physical layer security technology based on the multiantenna structure. Similar to traditional transmitters, the DM transmitter is also faced with the problem of high peak-to-average power ratio (PAPR) and nonlinear distortion. The existing peak clipping methods for crest factor reduction (CFR) are not suitable for the DM transmitter. This letter proposes a two-step peak clipping (TPC) scheme to specifically decrease the DM signals' PAPRs and presents a highly efficient DM transmitter with digital predistortion (DPD). Using a 16-QAM 20-MHz bandwidth signal, the PAPR of signals is reduced from 8.5 to 5.0 dB and the drain efficiency (DE) is improved from 26.6% to 45.9%. The corresponding error vector magnitude (EVM) and adjacent channel power ratio (ACPR) are -50.3 dBc and 1.86% after the DPD linearization.