  In this paper, we propose a securely precoded OFDM (SP-OFDM) system for
efficient and reliable transmission under disguised jamming, where the jammer
intentionally misleads the receiver by mimicking the characteristics of the
authorized signal, and causes complete communication failure. More
specifically, we bring off a dynamic constellation by introducing secure shared
randomness between the legitimate transmitter and receiver, and hence break the
symmetricity between the authorized signal and the disguised jamming. We
analyze the channel capacities of both the traditional OFDM and SP-OFDM under
hostile jamming using the arbitrarily varying channel (AVC) model. It is shown
that the deterministic coding capacity of the traditional OFDM is zero under
the worst disguised jamming. On the other hand, due to the secure randomness
shared between the authorized transmitter and receiver, SP-OFDM can achieve a
positive capacity under disguised jamming since the AVC channel corresponding
to SP-OFDM is not symmetrizable. A remarkable feature of the proposed SP-OFDM
scheme is that while achieving strong jamming resistance, it has roughly the
same high spectral efficiency as the traditional OFDM system. The robustness of
the proposed SP-OFDM scheme under disguised jamming is demonstrated through
both theoretic and numerical analyses.
