Patent ID: 6038249
Filing Date: 2000-03-14
Classification: H04B,H04L

Abstract:
A spectrum spread system transmission apparatus using a binary phase shift keying (BPSK) system or a quadrature phase shift keying (QPSK) system and a spectrum spread system by direct spread modulation, wherein two or more channels are provided by using a spread code having the number of repetition bits (chip length) smaller than a longest channel code permitted by a predetermined transmission band and a predetermined transmission rate, and carrier frequencies of the channels are set to different values from each other, said transmission apparatus comprising:(a) a receiver including:a receiving antenna,a BPSK or QPSK demodulator for each channel, connected to said receiving antenna, anda spectrum inverse-spread circuit for each channel, receiving a base band signal from said BPSK or QPSK demodulator;(b) a transmitter including:a spectrum spread circuit for each channel, receiving an information code,a BPSK or QPSK modulator for each channel, receiving said spread code signal of the base band from said spectrum spread circuit, anda transmitting antenna connected to said BPSK or QPSK modulator; and(c) a frequency characteristic control circuit inserted at a point between said spectrum spread circuit for each channel of said transmitter and said transmitting antenna and a point between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver, for limiting bands of frequency characteristics of corresponding channels to ranges narrower than a main robe band determined by chip rates of the spread code of the corresponding channels,wherein said frequency characteristic control circuit inserted between said spectrum spread circuit for each channel and said transmitting antenna of said transmitter is a root roll-off filter, and said frequency characteristic control circuit inserted between said receiving antenna and said spectrum inverse-spread circuit for each channel of said receiver comprises a first filter having two taps for summing the demodulated base band signal and a signal delayed from the base band signal by one half period of a pulse period of the spread signal, and a second filter for eliminating frequency components having frequencies higher than the frequency of the spread signal in the base band signal.