| 摘要 |
<p>Wideband, direct-to-RF multi channel QAM modulation is described whereby IFFT 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 multi-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 one half the master clock frequency. Multi-rate techniques can be employed to yield high-speed digital processing from digital logic incapable of operating directly at the master clock frequency.</p> |
