Showing papers by "Jack K. Wolf published in 1996"

Method and apparatus for providing variable rate data in a communications system using statistical multiplexing

Abstract: The present invention discloses a variable rate transmission system wherein a packet of variable rate data generated by a variable rate data source (20) is modulated on traffic channel by traffic channel modulator (30) if the capacity of said traffic channel is greater than or equal to said data rate of said packet. The packet of variable rate data is modulated onto traffic channel by traffic channel modulator (30) and at least one overflow channel by traffic channel modulator (32) if the capacity of said traffic channel is less than said data rate. The present invention further discloses a receiving system for receiving variable rate data wherein a received packet of variable rate data is received on traffic channel if the capacity of said traffic channel is greater than or equal to a data rate of said packet and wherein a packet of variable rate data is received on traffic channel and at least one overflow channel if the capacity of said traffic channel is less than said data rate.

Applications of a new simulation model for media noise limited magnetic recording channels

Abstract: A new model for the signal dependent transition noise and partial erasure which occur in the readback signal from thin film recording media is reviewed. This model, which is referred to as the microtrack model, has its basis in physics and can be entirely specified by three parameters of the media. It is used both as a simulation tool and for analytical calculation. Through simulation, the effect of various amounts of media noise on a PR4 channel is shown. Analytically, the amount of jitter and widening effects of the noise produced by the model are examined. Also, the autocorrelation of this noise and the effect of partial erasure on it is examined.

On the weight distribution of linear block codes formed from convolutional codes

Abstract: We explain how to obtain the weight enumerator and the performance of linear block codes formed in several distinct ways from a convolutional code.

Method and apparatus for encoding/decoding QAM trellis coded data

Abstract: A method and apparatus for encoding and decoding QAM trellis modulated data. In the transmitter, a subset of bits of an input bit set are convolutionally encoded based upon a punctured convolutional code of a lower data rate to provide a set of coded symbols. The coded symbols and the uncoded bits of the input bit set are provided to a QAM modulator to provide a QAM modulation signal indicative of the values of coded symbols and the uncoded bits. In the receiver a QAM demodulator converts the received QAM signal to QAM signal space coordinates. A decoder employing the Viterbi algorithm is used to reconstruct a corrected estimate of the values of the coded data bits from the received signal coordinates. The corrected estimate of the values of the coded data bits are then used in conjunction with the received signal coordinates to provide corrected estimates of the values of the uncoded input bits.

Trellis codes for (1,k) E/sup 2/PR4ML with squared distance 18

Abstract: Finite truncation depth codes are obtained using periodically pruned module N trelises. One approach uses a runlength limited (d,k)=(1,7) code with rate R=2/3 as the underlying code. Another approach which results in a lower complexity detector trellis uses a rate R=3/5 sliding-block code that prohibits NRZI "10001" and adheres to a (d,k)=(1,8) constraint. The design of the module N trellis is described, and sufficient conditions for finite truncation depth are developed and applied to obtain several codes.

Experimental analysis of the effects of tape thickness on magnetic recording

Abstract: Advances in magnetic tape recording have produced media with magnetic layers as thin as 0.1 μm. In this article, a metal particulate tape with a magnetic layer thickness of ∼0.37 μm is compared to a standard thick media tape with a magnetic layer thickness of ∼4 μm. Measurements of the isolated pulse are made and shown to compare well with micromagnetic simulations. The replay voltage versus current is measured with a 4 μm track width, shielded magnetoresistive head at various densities. The thin tape shows better high density response at high currents than the thick tape. The simulations show that the transitions are sharper on the thin tape due to both the reduction in thickness, and an improvement in the particle orientation. The better oriented particles yield narrower pulses, thereby improving the high frequency response of the tape. Frequency response measurements are also taken with the magnetoresistive head, which yield a signal to noise ratio of ≳20 dB at 200 kfci. Last, overwrite performance versus current is compared for the two tapes plus a metal‐evaporated (ME) tape with a 0.2 μm thick layer. A significant improvement in overwrite is seen on the ME tape.

A sliding threshold detector for the ternary 1-D channel

Abstract: In this work we design a sliding threshold implementation of a Viterbi detector for a ternary 1-D recording channel. We show that the final detection scheme is both simple and easy to implement in analog fashion, much like the binary equivalent.