PARTIAL-RESPONSE SIGNAL SAMPLING FOR HALF-SPEED DATA TRANSMISSION

• US 3,573,622 A
• Filed: 04/23/1968
• Issued: 04/06/1971
• Est. Priority Date: 04/23/1968
• Status: Expired due to Term

• Current Assignee: John R. Sheehan, Louis N. Holzman
• Original Assignee: John R. Sheehan, Louis N. Holzman
• Inventors: Holzman, Louis N., Sheehan, John R.
• Application Number:
  US04/723,456
• Time in Patent Office: 1,078 Days
• US Class Current: 375/290
• CPC Class Codes: H04L 25/497 by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems transversal equalizers at the transmitter end H04L25/03343

Abstract

Theoretically maximum equivalent binary data transmission rates are obtainable in partial-response channels; i.e., bandlimited channels with filter shaping which disperses the impulse response to individual data inputs over more than one signaling interval. However, the resultant multilevel line signals occasionally give rise to system start-up problems. These problems are eliminated by initial sampling of alternate data input pairs for one particular partial-response format to produce a two-level line signal which preserves transitions occurring at the basic signaling interval. The same technique provides means for signaling at half the design rate without changing channel filters or the basic clock rate.

Claims

1. The combination with a data transmission channel having a fixed bandwidth and spectral shaping such as to generate an impulse response which includes more than one nonzero component for each input data sample at multiples of the reciprocal of twice its bandwidth and normally converting data samples taken at twice its bandwidth into a multilevel channel signal and means generating a two-level channel signal for fractional speed transmission comprising:

a binary data source;

means sampling the output of said source at an average rate equal to said bandwidth; and

gating means admitting data samples from said sampling means to said channel at only one of the sampling intervals at which nonzero response components for each input to said channel occur.

2. The combination defined in claim 1 and a receiver at the far end of said transmission channel reconstructing the transmitted binary data train.

3. The combination defined in Claim 1 W which:

the bandwidth of said transmission channel is W cycles per second and the spectral shaping is such as to produce an impulse response with two equal nonzero components of opposite polarity at a spacing of 1/W second and zero-level components at all other multiples of 1/2W second;

said sampling means generates sampling pulses at the rate 2W per second; and

said gating means admits alternate pairs of data samples from said sampling means to said transmission channel.

4. A data transmitter for generating a two-level line signal with zero-crossing transitions occurring at intervals of the reciprocal of twice the bandwidth of a bandlimited transmission channel having a spectral shaping such that the normal impulse response extends over more than one signaling interval and results in a three-level line signal comprising:

a binary data source;

a symbol clock source generating a clock signal wave at a rate equal to twice the bandwidth of said transmission channel;

means controlled by said clock source generating a sampling wave at a rate equal to the bandwidth of said channel and a gating wave at a rate equal to half the bandwidth of said channel and initially opposite in phase to said sampling wave;

modulator means controlled by said gating wave and having a signal input and a signal output, said signal output being clamped to a ground reference value during alternate half-cycles of said gating wave;

shift-register means transferring samples from said data source to the signal input of said modulator under the control of said sampling wave;

means standardizing the amplitude of data samples applied to said modulator from said register means; and

partial-response filter means driven by the signal output of said modulator means during unclamped half-cycles of said gating wave shaping the response of said transmission channel to generate for each data sample applied thereto two nonzero components of equal amplitude but opposite polarity spaced by the reciprocal of the bandwidth of said channel.

5. The data transmitter and transmission channel as defined in claim 4 in combination with a data receiver comprising:

a further symbol clock source generating a clock signal wave at a rate equal to twice the bandwidth of said transmission channel;

means controlled by said further clock source deriving a sampling wave at a rate equal to the bandwidth of said channel, a gating wave at a rate equal to half the bandwidth of said channel and a clamping wave at a rate equal to one-fourth the bandwidth of said channel;

a three-stage shift register;

means slicing the signal wave incoming over said channel;

means applying said sliced signal wave to the first stage of said shift register;

means applying said sampling wave to the terminal stage of said shift register to control the advance thereof;

means combining said gating wave and said clock signal wave to provide advance signals to the first and second stages of said shift register;

counter means timed by said clock signal shifted in phase by 180* and having toggle and reset inputs;

means combining said sliced signal wave and said clamping wave to provide a signal to the toggle input of said counter means during alternate groups of four clock signal intervals and to disable said counter means otherwise;

means inverting said clamping wave to reset said counter means at the termination of said alternate groups of four clock signals; and

means combining the outputs of said counter means and said clamping wave to shift the phase of said gating and clamping waves whenever said counter means has a count standing therein at the termination of said alternate groups of four clock signals.