Low Probability of Detection Communication using Inverse Beamforming in GNU Radio using Code Division Multiple Access

Travis B. Rennich


The primary goal of this thesis is to design a communications system that is more covert than existing systems while maintaining a constant Bit Error Rate (BER). Inverse Beamforming is the use of multiple spreading codes by a transmitter, each with a fraction of the power that would have been used by a single spreading code, to transmit the same message over multiple different antennas. At the receiver, there is a single antenna that splits the signal multiple ways. Each channel locks to a different spreading code, and is used to reconstruct the original message. In Chip-Oset Inverse Beamforming, successive users have an increasing number of chip offsets added in between each replication of the spreading code for each bit of the data message. This is done to decrease autocorrelation spikes to lower detection performance. With the inclusion of chip offsets, both the BER and the intercept receiver detection performance decreased in some situations.