| 摘要 |
The modulation scheme has two versions that can transform two data streams into two mutually orthogonal modulated signals within the same carrier-frequency band. In one embodiment, the modulation scheme is a quadrature-phase shift-keying (QPSK) modulation scheme having an in-phase part and a quadri-phase part. In this embodiment, one version of the QPSK modulation scheme conforms to the IS-95 telecommunications standard. In this version, the in-phase part is applied to a first data stream to generate an in-phase signal that is multiplied by a cosine function of the carrier frequency. In a parallel path, the quadri-phase part is applied to the first data stream to generate a quadri-phase signal that is multiplied by a sine function of the carrier frequency. The resulting signals are combined to generate a conventional IS-95 signal. In this embodiment, the other version of the QPSK modulation scheme is designed to transform a second data stream into a second modulated signal that is orthogonal to the IS-95 signal, even though the second modulated signal is within the same carrier-frequency band and even if the second data stream is encoded using the same Walsh code sequence as the first data stream. In one implementation of the second version, the logical negation of the quadri-phase part of the QPSK modulation scheme is applied to the second data stream to generate an quadri-phase signal that is multiplied by the cosine function of the carrier frequency. In a parallel path, the in-phase part of the QPSK modulation scheme is applied to the second data stream to generate an in-phase signal that is multiplied by the sine function of the carrier frequency. The resulting signals are combined to generate a modulated signal that is orthogonal to the IS-95 signal and which therefore will not interfere with the IS-95 signal, even though the two modulated signals exist within the same carrier-frequency band and may in fact be based on two data streams that were encoded using the same Walsh code sequence. Those skilled in the art will understand that the modulation scheme of the present invention can be implemented in contexts other than the IS-95 standard.
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