Reduction of radio wave density in OCDMA satellite communication system

摘要

A spread spectrum CDMA communication system in which base stations communicate with a plurality of subscriber terminals located in different beams of a multi-beam satellite relay system. A base station transmits a signal for each beam which is comprised of a set of orthogonally spaced subcarriers, each of which is modulated by a set of orthogonal functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal. Each orthogonal function carries data for a single user in the beam. Selected carrier signals are modulated with information signals onto the subcarriers to form a beam signal. The available frequency spectrum is divided into non-overlapping segments which are assigned to different beams in a 1:Nru frequency reuse pattern. Each subscriber terminal has a receiver which coherently demodulate the base station signal. A PN spreading code, P2, with chipping rate Nru chi Rc is applied to all of the beam signals simultaneously to spread the signal energy over a wider bandwidth to reduce the power spectral density in each beam. The receiver correlates the received signal with a synchronized replica of P2 to remove P2 from the incoming signal without affecting beam-to-beam frequency isolation. The subcarriers of the beam signal are orthogonally spaced across the available frequency spectrum with spacing Nru chi Rc and Nru distinct sets of subcarriers frequencies are formed to be assigned in the 1:Nru beam frequency reuse pattern.