摘要 |
Wideband, direct-to-RF multi channel QAM modulation is described whereby IFF T processing is employed to modulate a plurality of encoded symbol streams (202A, 202B, ~ 202n) in parallel onto a like plurality of uniformly spaced carriers. A high-frequency master clock and high-performance, high-frequency D/A converters (210) are employed. The IFFT modulation process yields a mult i- channel multiplex at an intermediate "baseband" frequency. The multi-channel multiplex is then synchronously converted to analog form and synchronously frequency shifted upward by one-half the master clock frequency using a quadrature doubly-balanced mixing scheme (222A, 222B, ~ 222n). The resultant multi-channel encoded multiplex occupies a frequency band centered around on e half the master clock frequency. Multi-rate techniques can be employed to yield high-speed digital processing from digital logic incapable of operatin g directly at the master clock frequency.
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