A radio receiver (16) for direct sequence spread spectrum signals incorporates a quadrature zero-IF architecture, means for comb filtering (36,37) the two quadrature related channels (I and Q) and a means of non-coherent demodulation of each channel; the non-coherent demodulating means comprising delays (40,41) and mixers (42,43). This process obviates the need for locally generated versions of the spreading code used to produce the signals and considerably shortens the time-consuming process of correlating the received and the locally generated codes at receiver switch-on.
A homodyne radio system for receiving direct sequence spread spectrum communications enables a received signal to be down-converted directly to a baseband signal. An input RF amplifier receives and amplifies a carrier signal modulated by a digital code sequence. A local oscillator provides a signal having a frequency substantially equal to the frequency of the carrier signal. A phase splitter coupled to the input RF amplifier receives the modulated carrier signal, and splits the signal into corresponding quadrature component signals. The mixer combines a first one of the quadrature component signals with the local oscillator signal to generate a first quadrature baseband output signal. A second one of the quadrature component signals is combined with the local oscillator signal shifted in phase by 90.degree. to generate a second quadrature baseband output signal. A transmitted signal can be generated by mixing quadrature baseband input signals with the same local oscillator and phase shifted local oscillator signals.
A data demodulator of a receiving apparatus for spread spectrum communication for removing the phase difference remaining after detection for improving reception quality. In-phase and quadrature axis received signals are multiplied by pseudonoise codes PNI(t) and PNQ(t) and the results are averaged by averaging sections for calculating the correlation. By performing correlation processing, .rho.kO cos .theta., -.rho.O sin .theta., .rho.kO sin .theta., and .rho.kO cos .theta. are output when the amplitude of receive path signal is assumed to be .rho., the phase difference to be .theta., and a proportional constant to be kO. These signals are multiplied by in-phase and quadrature axis received signals and the results are added by adders, thereby removing the effect of the phase difference .theta.. The signal is used for data demodulation and data recovery circuit.
A data demodulator circuit for spread spectrum communication, presenting improved demodulation characteristics by allowing the elimination of the influence of a carrier offset remaining after down converting, and the removal of the interference caused by pilot signals with different timing. In-phase axis receive signal and operate with their respective reception timing of pilots signal. Phase difference information is extracted from the input signals and the signals are delayed to insure that the extracted phase difference information is equivalent to the average phase revolution. The influence of the carrier offset is eliminated by use of the extracted phase difference information. A data demodulator with canceler removes an interference I.sub.DF of pilot signals with different timing originating from the outputs of an interference amount calculator.
When a multiplier receives data transmitted from a transmitting equipment in a spread spectrum communications system, it multiplies the received data by the periodic wave output from a crystal oscillator. The output data from the multiplier is filtered by a low-pass filter, and then binarized by a limiter. The multiplier and a delay circuit differential-decodes the binarized data. A correlation circuit obtains correlation between the decoded data and the PN code generated by the PN code generation circuit, and outputs the data as transfer data when the correlation is obtained. In another aspect, an input signal is divided, and then one is multiplied by an I-phase wave. Similarly, another is multiplied by a Q-phase wave. Each signal is individually processed and input to a correlation value/data value determination circuit. The correlation value/data value determination circuit compares an I-phase correlation value with a Q-phase correlation value, and obtains and outputs a data value of one of the phases whichever indicates a larger value.
A spread spectrum noise shaper uses a modulation technique to achieve a greater signal-to-noise or signal-to-interference ratio (SNR or SIR). The technique doubles the system SIR, in principle. This doubling yields a doubling in system capacity. SNR is increased by receiving the spread spectrum signal in the presence of less noise near the edge of the spread spectrum bandwidth. The technique requires only small additions to a conventional spread spectrum system, in the form of an extra modulator at the transmitter, and an extra demodulator and filter at the receiver.
