Abstract: At a transmit site of a spread spectrum communication system, a header is produced containing integers M and N (where M>1 and N.gtoreq.0) and a frame is assembled with symbol bits. The header is converted to I and Q signals having a predetermined number of signal points in a signal constellation, which are spread with a predetermined pseudorandom sequence, and quadrature-modulated and transmitted. Using integers M and N, (M+N) data bits in a symbol are separated into M- and N-bit portions. The M-bit portion of each symbol is converted to I and Q signals having 2.sup.M signal points in the signal constellation, which are spread with one of 2.sup.N pseudorandom sequences according to the N-bit portion of each symbol, quadrature-modulated and transmitted. At a receive site, the transmitted header is converted to I and Q signals which are despread with the predetermined PN sequence to detect the integers M and N. The transmitted frame is converted to I and Q signals, which are sequentially despread with 2.sup.

Abstract: The present invention is an art of spread spectrum modulation systems, wherein a binary serial data is divided into a first bit data and a second bit data, the first bit data is primarily modulated, a spread code corresponding to the second bit data is selected, and the modulated data is spread by multiplying the primarily modulated first bit data by the selected spread code. In reception side, the spread code used for spreading in transmitter is detected in correlator, the second bit data is specified and the first bit data is demodulated.