Improvement of multiple access capability in m‐ary‐FSK/direct‐sequence SSMA
Yukiji Yamauchi, Masashi Sato, Norihiko Morinaga, Toshihiko Namekawa · Electronics and Communications in Japan (Part I Communications) · 1986
Abstract In the conventional SSMA (Spread Spectrum Multiple Access) system, the number of co‐channel users is unexpectedly small and the increase in the number of co‐channel users is one of the subjects of SSMA. Introduction of error correcting codes, improvement on primary modulation, etc., have previously been proposed. Especially in direct‐sequence SSMA, primary modulation using modified M‐ary FSK has been reported to provide a remarkable improvement. A primary modulation scheme using modified M‐ary FSK, named “unpacked MFSK/DS,” is presented here for improving the multiple access capability on direct‐sequence SSMA by flattening the power spectrum of transmitted SS signals. It is shown that the number of co‐channel users in SSMA can be increased to twice as many as that of the conventional MFSK/DS systems only by modifying the frequency allocation of MFSK symbols and without modifying the conventional MFSK transmitter/receiver configuration.