22.9 Conclusions

In chaotic modulation schemes, the transmitted signal is a wide-band signal. The objectives of using a wide-band signal as the carrier are twofold:

• to overcome the multipath propagation problem, and

• to reduce the transmitted power spectral density in order to avoid interfering with other radio communications.

Of the chaotic modulation schemes published to date, DCSK with orthonormal basis functions, also referred in the literature as to FM-DCSK ^[8], offers the best robustness against multipath and channel imperfections.

It is frequently asked whether chaotic modulation schemes can offer any advantages over conventional narrow-band systems.

If the propagation conditions are so good that the basis function(s) can be regenerated at the receiver, then digital modulation schemes using conventional orthonormal (typically periodic ^[3]) basis functions, and orthonormal chaotic basis functions can achieve similar levels of noise performance, as discussed in Sec.s 22.5 and 22.6. The main question from an implementation perspective is the ease with which the basis functions can be regenerated.

We believe that it is fundamentally easier to regenerate a periodic basis function than a chaotic one. We conjecture, therefore, that the noise performance of digital chaotic modulation with coherent correlation receivers will always lag behind that of equivalent modulation schemes using periodic basis functions.

If the propagation conditions are such that coherent detection is impossible, then chaotic switching with orthonormal DCSK basis functions and a differentially coherent receiver (DCSK, for short), offers the best possible performance for a chaotic digital modulation scheme. In the limit, the...