  This work presents a novel technique for joint secured and robust
transmission of orthogonal frequency division multiplexing (OFDM) based
communication systems. The proposed system is implemented by developing a new
OFDM symbol structure based on symmetric key cryptography. At the receiver
side, data detection becomes infeasible without the knowledge of the secret
key. For an intruder who tries to detect the data without the knowledge of the
key, the signal will be a noise-like signal. In addition to the system
security, theoretical and simulation results demonstrated that the proposed
system provides time and frequency diversity, which makes the system highly
robust against severe frequency-selective fading as well as other impairments
such as impulsive noise and multiple access interference. For particular
frequency-selective fading channels, the bit error rate (BER) improvements was
about 15 dB at BER of 10E-4.
