Application of optimization techniques to spectrally modulated, spectrally encoded waveform design

A design process is demonstrated for a coexistent scenario containing SMSE and Direct Sequence Spread Spectrum (DSSS) signals. Coexistent SMSE-DSSS designs are addressed under both perfect and imperfect DSSS code tracking conditions using a noncoherent delay-lock loop (DLL). Under both conditions, the number of SMSE subcarriers Nf and subcarrier spacing Deltaf are the optimization variables of interest. For perfect DLL code tracking conditions, the GA and RSM optimization processes are considered independently with the objective function being end-to-end DSSS bit error rate Pb. A hybrid GA-RSM optimization process is used under more realistic imperfect DLL code tracking conditions. In this case, optimization is accomplished through a correlation-degradation metric with the GA process being first applied to generate a "coarse" solution followed by RSM processing which provides the final optimized solution. For all perfect and imperfect DLL code tracking scenarios considered, the optimized DSSS P b minimization results yielded SMSE waveform designs and Pb performance that was consistent with scenarios having no coexistent SMSE signal present (best-case coexistent performance). For the optimized DSSS Pb maximization solutions, worst-case SMSE-DSSS coexistence was achieved for SMSE waveform designs that were spectrally "matched" to the DSSS signal, i.e., greatest Pb degradation was experienced when the resultant SMSE subcarrier spacing Deltaf was an integer multiple of the spectral line spacing DeltafChip of the DSSS spreading code.