Precoding for Multiple-Speed Data Transmission

In certain applications, because of noise, compatibility, or other considerations, it is desirable that a data transmission system have the flexibility to operate at multiple speeds. In this paper, a precoding scheme for multiple-speed digital or analog data transmission is presented. The scheme has a flexibility which allows the data rate and overall channel characteristics to be changed simultaneously by simply changing the data format and some resistive elements. There is no change in the filters, the equalization, the transmitter signaling interval, or the receiver sampling time. By using partial response channels, a number of commonly used data rates are easily obtained, using a physically realizable precoder and correlator. With correct timing and the use of orthonormal siginals, the signal-to-noise ratio is maximized at each data rate for bandlimited white noise under the constraints of fixed line signal power and no intersymbol interference. Timing error is considered in a two-speed transmission scheme, and the selection of a precoding matrix using eye opening as the criterion is studied. This study clearly demonstrates the advantage of changing the overall channel characteristics when changing the data rate. Eye openings obtained are equal to or larger than those of two conventional schemes transmitting at the same data rates.