Multimode spread spectrum communication system tolerant to varying

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.N PN sequences determined by the detected integer N, and then stored in a memory. Correlations between the I and Q signals of the frame and the 2.sup.N PN sequences are detected and a maximum correlation is identified for each symbol. A modulo-2.sup.N count is incremented in response to each correlation to produce a series of modulo-2.sup.N counts, and one of which is selected that corresponds to the maximum correlation. N-bit data representing the selected count is produced to read I and Q signals from the memory. The read I and Q signals are converted to M-bit data using integer M, and the M- and N-bit data are converted to a serial form.