Transform Domain Communications: Interference-Avoidance and Acquisition Capabilities

This research characterizes the initial acquisition performance of a TDCS via modeling and simulation. As previously demonstrated, a TDCS provides an effective interference suppression capability and differs from traditional spread spectrum systems in two primary ways: 1) spectrally crowded regions are avoided via adaptive spectral notching, and 2) no carrier modulation is employed; rather; "noise-like" basis functions are data modulated. Relevant TDCS research has unrealistically assumed perfect synchronization conditions, a vitally important and complete element of most digital communication systems. This research investigated initial TDCS acquisition performance for various synchronization codewords and several acquisition methods, e.g., direct time correlation (DTC) and German's technique, using both peak and threshold detection techniques. Theoretical development and MATLAB(R) simulation results indicate a TDCS can achieve a high probability of detection (P-D > 0.9) for relatively low input Signal-to-Noise Ratios (SNRs), as low as -23 dB for peak detection and -21 dB far threshold detection. For peak detection, DTC provides the best acquisition performance, i.e., the highest P-D for a given input SNR and fixed probability of false alarm, P-FA. For threshold detection with fixed P-FA of 0.01, DTC provides the best acquisition performance for SNRs below -12 dB, and German's technique provides the best acquisition performance above -12 dB. DTC results are shown to approximate matched filter performance while providing reasonable improvement over radiometric processing. Extensive computer simulations and subsequent analysis indicate that a TDCS cart adequately acquire and accurately align a locally generated reference waveform with a received noise-like TDCS signal.