Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

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COMPUTER OPERATIONS AND HARDWARE
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20000063494 Nanogen, Inc., San Diego, CA USA
Photo-Electronic Optical Memory - Write/Read System Final Report, Jun. 1997 - Jun. 1999
Heller, Michael; Apr. 2000; 31p; In English
Contract(s)/Grant(s): F30602-97-C-0229; AF Proj. 4594
Report No.(s): AD-A376242; AFRL-IF-RS-TR-2000-36; No Copyright; Avail: CASI; A01, Microfiche; A03, Hardcopy
Chromophoric DNA polymers are being developed for high density optical data storage applications. This project involves
the design and synthesis of chromophoric DNA polymers which absorb light energy at a single wavelength and re-emit at predetermined
multiple wavelengths. by emitting spectra rather than binary on/off bits, the data word size can be increased significantly
and parallel access is enabled. The diffraction limit normally experienced with classical optical interrogation of a binary data site
can now be overcome, because the number of data bits per unit area is increased in relation to the number of wavelengths produced
at that site. In relation to this DNA optical memory project, a potentially more powerful write process is now being proposed for
incorporating higher bit/byte densities in these DNA optical materials. This process, called a ”photo-electronic write”, involves
using spatial light addressing to a photoactive substrate material which creates microscopic electric fields. These electric fields
affect the rapid transport and attachment of charged chromophoric (color) DNA’s to the selected write locations. The ”photoelectronic
write process” has advantages over this earlier UV write process for the optical storage systems, with potential capacities
approaching petabytes on a 5 1/4” disc.
DTIC
Optical Memory (Data Storage); Data Structures; Data Storage; Read-Only Memory Devices
20000065638 New Mexico State Univ., Klipsch School of Electrical and Computer Engineering, Las Cruces, NM USA
Concatenated Coding and Equalization of Data Transmission and Storage
Ghrayeb, Ali, New Mexico State Univ., USA; Ryan, William, New Mexico State Univ., USA; Jun. 05, 2000; 138p; In English
Contract(s)/Grant(s): NAG5-7520
Report No.(s): NMSU-ECE-00-008; Copyright; Avail: Issuing Activity
The steady growth of data rates in magnetic recording systems is translated into an increase in recording densities. This results
in an increase in the nonlinear intersymbol interference (ISI), which degrades the reliability of the retrieved data. The resulting
ISI comprises both precursor and postcursor terms. In this dissertation, we introduce new equalization and coding techniques that
are superior to previously knovm techniques. In the equalization area, we propose two new nonlinear equalizers for mitigating
the effects of nonlinear ISI in magnetic recording systems. These equalizers, which we call RAM-Search algorithms, have been
devised to cancel both precursor and postcursor (nonlinear) ISI. They were tested against two nonlinear models: a simple partialerasure
model for the nonlinear write process, and a third-order polynomial model for the nonlinear read process. A performance
improvement of about 2.5 dB at a bit error rate of P (sub b) = 10 (exp -5) has been shown possible via simulations. The efficacy
of these equalizers has also been demonstrated on captured spinstand signals which siiffer from a significant amount of nonlinear
ISI. In the coding area, we study the serial concatenation of a single convolutional code (CC) and a precoded partial response (PR)
channel separated by an interleaver, and is decoded using two iterative decoders that implement the a posteriori probability (APP)
algorithm. One of the weaknesses of this scheme is that its error rate curves tend to hit an error rate floor near P (sub b) = 10 (exp
-6). The level of the floors have been found to depend on the interleaver and precoder (for a given outer CC and a PR channel).
In this regard, we discuss analytical techniques that lead to the joint optimization of interleaver and precoder for a fixed outer CC
and a given PR channel, where optimality is in the sense of achieving the lowest floor. Such techniques result in lowering the error
rate floor significantly at no additional decoder complexity. Additionally, the soft-output Viterbi algorithm (SOVA), which is a
suboptimal version of the APP algorithm, is derived for PR channels. We also introduce a slight modification of the SOVA so that
it works for arbitrarily high code rates.
Author
Concatenated Codes; Data Transmission; Equalizers (Circuits); Data Storage; Mathematical Models