  The effectiveness of frequency hopping for anti-jamming protection of
wireless channels is analyzed from an information-theoretic perspective. The
sender can input its symbols into one of several frequency subbands at a time.
Each subband channel is modeled as an additive noise channel. No common
randomness between sender and receiver is assumed. It is shown that capacity is
positive, and then equals the common randomness assisted (CR) capacity, if and
only if the sender power strictly exceeds the jammer power. Thus compared to
transmission over any fixed frequency subband, frequency hopping is not more
resilient towards jamming, but it does increase the capacity. Upper and lower
bounds on the CR capacity are provided.
