We present an extrinsic information transfer (EXIT) chart-based design technique for irregular repeat-accumulate (IRA) codes used in 2-D magnetic recording (TDMR) turbo-equalization systems. The channel model includes Voronoi magnetic grains, 2-D intersymbol interference (2D-ISI) and additive white Gaussian noise (AWGN). The receiver uses a 2D-ISI BCJR equalizer and an IRA decoder. For one outer equalizer-decoder iteration, we propose theory and simulation-based methods for computing EXIT curves. The simulation method calculates experimental EXIT curves for the check node decoder (CND) and the combination of the variable node decoder (VND) and an equalizer. The theoretical approach recursively calculates CND and VND Gaussian mixture model parameters in order to calculate EXIT curves. We then fit the VND and CND EXIT curves to find optimized variable node degree distributions. Simulation results show that the TDMR-optimized IRA codes achieve up to a 6.2% density increase in user bits/grain (U/G) compared with IRA codes designed for AWGN channels. The theory-based code designs achieve the same or better U/G as the simulation-based designs, but require 98% less design computation time. We also derive optimized IRA codes for iterative turbo-equalization; these codes can achieve simultaneous U/G gains and SNR savings compared with AWGN-optimized codes.

This paper considers turbo equalization for 2-D magnetic recording. Magnetic grains are modeled as Voronoi regions of randomly distributed nuclei. Bits read from the magnetic grain model flow into a 2-D intersymbol interference (2D-ISI) model including additive white Gaussian noise. At high bit densities, some bits are not written on any grain, and hence are effectively “overwritten” by surrounding bits. The proposed system iteratively exchanges log-likelihood ratios (LLRs) between a 2D-ISI equalizer based on the forward-backward algorithm and an irregular repeat-accumulate (IRA) decoder. To combat bit overwrites, the system employs a non-linear function to map 2D-ISI extrinsic output LLRs to IRA decoder input LLRs. To pass back LLRs from the IRA decoder to the 2D-ISI equalizer, we design a simple likelihood-ratio-based LLR estimator. Simulations of the proposed system that employ the perturbed-bit-centers grain model proposed in a 2010 IEEE Transactions on Magnetics paper show a 6.5% increase in user bits per grain (U/G) and a 16.4 dB signal-to-noise ratio (SNR) gain compared with the previous paper, without iterative turbo equalization. Utilizing the LLR estimator to do iterative detection results in SNR gains of up to 1.7 dB compared with non-iterative detection. The random Voronoi model employed in this paper appears to be more difficult to equalize than the grain model in the 2010 paper. The proposed system with random Voronoi model achieves 0.4422 U/G at SNR =11.6 dB, i.e., about 8.8 Tb/in2at (typically assumed future grain density) 20 Tgr/in2; this is almost ten times the density of current systems at 10 Tgr/in2.

This paper studies the performance of a serial turbo code on two simplified rectangular-grain models of recording media for two dimensional magnetic recording at a density of more than 0.5 bits/grain. We derive one-dimensional (1D) and two-dimensional (2D) rectangular-grain media models and from these present finite-state-machine (FSM) representations. From the FSM for the 1D model we computed achievable information rates assuming independent and uniformly distributed (i.u.d.) binary inputs. From the (approximate) FSM for the 2D model, we present a detector. We then present a serial turbo code architecture with constituent convolutional codes that is capable of achieving 80\% of i.u.d. capacity for the 1D model and 65\% of the average of published upper and lower bounds on capacity for the 2D model.

The spin rate and spin axis orientation of the Laser Geodynamics Satellite 2 (LAGEOS-2) satellite were determined by analysis of photometric observation data. A photometer system developed at the Space Geodesy Facility at Herstmonceux, U.K., was used to time solar glints from the rotating satellite. It was found that the spin rate of LAGEOS-2 slowed by 38% per year between March 2000 and November 2002 and that the spin axis undergoes a slow, complex precession with respect to the Earth's rotation axis. Moreover, the analysis revealed that the direction of the spin was the reverse of that of the Earth's rotation and that the optical alignment of a reflector surface on LAGEOS-2 can deviate from its position vector by up to 15 arcmin.

This paper describes a small trial of an advanced cable TV network with evolutionary potential for the wideband local network of the future. Major features of the trial are optical fiber transmission throughout, switched program provision, and a star type of network. Initial experience is related giving both successes and difficulties encountered on design and installation phases. The conclusions point out the technology gap that exists for the wideband local network application and emphasize the potential of the network type used for enhanced services to the customer.