  Frequency hopping (FH) has been widely used as a powerful technique for
antijamming in wireless communications. However, as the wireless spectrum is
becoming more and more crowded, it is very difficult to achieve efficient
antijamming results with FH-based schemes. Orbital angular momentum (OAM),
which provides the new angular/mode dimension for wireless communications,
offers an intriguing way for antijamming. In this paper, we propose to use the
orthogonality of OAM-modes for antijamming in wireless communications. In
particular, we propose the mode hopping (MH) scheme for antijamming within the
narrow frequency band. We derive the closed-form expression of bit error rate
(BER) for multiple users scenario with our developed MH scheme. Our developed
MH scheme can achieve the same antijamming results within the narrow frequency
band as compared with the conventional wideband FH scheme. Furthermore, we
propose mode-frequency hopping (MFH) scheme, which jointly uses our developed
MH scheme and the conventional FH scheme to further decrease the BER for
wireless communication. Numerical results are presented to show that the BER of
our developed MH scheme within the narrow frequency band is the same with that
of the conventional wideband FH scheme. Moreover, the BER of our developed MFH
schemes is much smaller than that of the conventional FH schemes for wireless
communications.
