A CDMA overlay using frequency-diversity spread spectrum

The frequency bands currently used by existing narrowband users might be shared with a CDMA spread spectrum overlay system. Thus, the spectrum efficiency is improved providing more capacity for future personal communications networks. Since both narrow- and wide-band signals interfere with each other, a spread spectrum modulation scheme with a good resistance to narrowband interference results in an increased number of acceptable overlay users. We study a frequency-diversity spread spectrum modulation scheme for which optimal detection in the presence of narrowband interference is easy to implement. The acceptable number of overlay users is evaluated and compared to that of conventional direct-sequence spread spectrum modulation schemes with and without interference rejection filters