Regular Bit Research Articles

Two-Bit Bit Flipping Algorithms for LDPC Codes and Collective Error Correction

A new class of bit flipping algorithms for low-density parity-check codes over the binary symmetric channel is proposed. Compared to the regular (parallel or serial) bit flipping algorithms, the proposed algorithms employ one additional bit at a variable node to represent its "strength." The introduction of this additional bit allows an increase in the guaranteed error correction capability. An additional bit is also employed at a check node to capture information which is beneficial to decoding. A framework for failure analysis and selection of two-bit bit flipping algorithms is provided. The main component of this framework is the (re)definition of trapping sets, which are the most "compact" Tanner graphs that cause decoding failures of an algorithm. A recursive procedure to enumerate trapping sets is described. This procedure is the basis for selecting a collection of algorithms that work well together. It is demonstrated that decoders which employ a properly selected group of the proposed algorithms operating in parallel can offer high speed and low error floor decoding.

Robust end-to-end loss differentiation scheme for transport control protocol over wired/wireless networks

The authors propose a robust end-to-end loss differentiation scheme to identify the packet losses because of congestion for transport control protocol (TCP) connections over wired/wireless networks. The authors use the measured round trip time (RTT) values to determine whether the cause of packet loss is because of the congestion over wired path or regular bit errors over wireless paths. The classification should be as accurate as possible to achieve high throughput and maximum fairness for the TCP connections sharing the wired/wireless paths. The accuracies of previous schemes in the literature depends on varying network parameters such as RTT, buffer size, amount of cross traffic, wireless loss rate and congestion loss rate. The proposed scheme is robust in that the accuracy remains rather stable under varying network parameters. The basic idea behind the scheme is to set the threshold for the classification to be a function of the minimum RTT and the current sample RTT, so that it may automatically adapt itself to the current congestion level. When the congestion level of the path is estimated to be low, the threshold for a packet loss to be classified as a congestion loss is increased. This avoids unnecessary halving of the congestion window on packet loss because of the regular bit errors over the wireless path and hence improves the TCP throughput. When the congestion level of the path is estimated to be high, the threshold for a packet loss to be classified as the congestion loss not to miss any congestion loss is decreased and hence improves the TCP fairness. In ns 2 simulations, the proposed scheme correctly classifies the congestion losses under varying network parameters whereas the previous schemes show some dependency on subsets of parameters.

High-fidelity multichannel audio coding with karhunen-loeve transform

A new quality-scalable high-fidelity multichannel audio compression algorithm based on MPEG-2 advanced audio coding (AAC) is presented. The Karhunen-Loeve transform (KLT) is applied to multichannel audio signals in the preprocessing stage to remove interchannel redundancy. Then, signals in decorrelated channels are compressed by a modified AAC main profile encoder. Finally, a channel transmission control mechanism is used to re-organize the bitstream so that the multichannel audio bitstream has a quality scalable property when it is transmitted over a heterogeneous network. Experimental results show that, compared with AAC, the proposed algorithm achieves a better performance while maintaining a similar computational complexity at the regular bit rate of 64 kbit/sec/ch. When the bitstream is transmitted to narrowband end users at a lower bit rate, packets in some channels can be dropped, and slightly degraded, yet full-channel, audio can still be reconstructed in a reasonable fashion without any additional computational cost.

Self-Stabilization of Wait-Free Shared Memory Objects

This paper proposes a general definition of self-stabilizing wait-free shared memory objects. The definition ensures that, even in the face of processor failures, every execution after a transient memory failure is linearizable except for an a priori bounded number of actions. Shared registers have been used extensively as communication medium in self-stabilizing protocols. As an application of our theory, we therefore focus on self-stabilizing implementation of such registers, thus providing a large body of previous research with a more solid foundation. In particular, we prove that one cannot construct a self-stabilizing single-reader single-writer regular bit from self-stabilizing single-reader single-writer safe bits, using only a single bit for the writer. This leads us to postulate a self-stabilizing dual-reader single-writer safe bit as the minimal hardware needed to achieve self-stabilizing wait-free interprocess communication and synchronization. Based on this hardware, adaptations of well-known wait-free implementations of regular and atomic shared registers are proven to be self-stabilizing.

Modelling of boundary regularity and thermo-magnetic writing process of magneto-optic recording

The regularity of the controlled area, the area in which the direction of the medium's magnetization is controlled by the direction of total field, is used to describe the regularity of the recorded bit marks. Research towards analytical modelling of the relationship between the regularity of the controlled area and recording conditions is presented and a general relationship is obtained. Some design requirements to achieve more regular bit mark boundary have been derived, including the medium's thermo-magnetic features, the relative importance of the head field in the writing process, the temperature gradient and so on. Relationship and conclusions obtained are also applicable to the discussion of the likelihood of sub-domain formation within the recorded bit marks.

Domain formation and bit shapes in polycrystalline garnet films for magneto-optical recording

Observation of domain nucleation and growth in a stationary medium is useful to characterize the micromagnetics and the magneto-optical recording properties of polycrystalline garnet films. The written bit shapes are strongly related to the domain growth pattern in the single- and double-layer garnet films. Both films show the same grain size of grain about 50 nm to 100 nm, but double-layer films give more regular bit shapes than single-layer films.

WEAK KEYS AND WEAK DATA FOILING THE TWO NEMESES

Cryptographic keys and plain text that possess predictable regularities are weak because they produce crypto text that can be analyzed to disclose either the plain text or the key. Regular bit sequ...

Recording experiments in magneto-optical disks using ultrathin Co/Pt and Co/Pd media

Magneto-optical media using ultrathin Co/Pt and Co/Pd films were prepared on 2P (photopolymer) glass substrates with a double-layer disk structure. Thermomagnetic writing was successfully made in the magneto-optical disks by the relatively low laser power above 3 mW. The values of the C/N ratio were 50 dB for the Co/Pt disk and 45 dB for the Co/Pd disk at a bit length of 5 μm. Clear and regular bit domains were observed even in the shorter recorded bit length.

Floating point acceleration in massively parallel architectures

Two techniques for floating point acceleration in bit-serial SIMD massively parallel computers are presented. The first technique does not require any additional hardware with respect to regular bit serial processor implementation; a reduction in the complexity is achieved by a shifting algorithm which minimizes the number of idle processors at each step. The second technique is based on the addition of a hardware stack to each processor. The paper illustrates both the techniques and discusses their complexity.

Improvement in optical and magnetic properties of Bi-substituted garnet sputtered films for magneto-optical recording

We have investigated the effect on the optical and magnetic properties of adding W or Co to Bi-substituted garnet films sputtered on glass substrates. Adding a small amount (<1.2 at. %) of W makes the film optically homogeneous. It also increases coercivity more than three times, probably due to wall pinning by W atoms. Adding Co reduces coercivity. On the thin film with added W, we have successfully performed a dynamic thermomagnetic writing with a regular bit shape. This promotes development of magneto-optical memory using garnet sputtered film.

Study on the Jet Behavior of the Rock Bit

In order to clarify the jet stream behavior of rock bit, pressures at a bottom plane are measured using the 33/4-in. soft formation type jet bit and regular bit. Water is used as the circulation fluid. About the jet bit, the velocity of impingement at bottom plane and the velocity of crossflow along the bottom surface are the function of impact force, ie. product of flow rate and jet velocity. They are proportional to the square root of the impact force. If nozzle velocity is same at different size nozzle, the jet impingement velocity and the crossflow velocity are greater at larger size nozzle, and if flow rate is same, the velocities are greater at smaller size nozzle. About the regular bit, pressure distribution under a cutter differs at each cutter. The smaller size nozzle makes greater crossflow velocity. The greater size nozzle has greater ability of washing cutters. The bottom cleaning ability of jet bit is proportional to the product of the impact force and is inversely proportional to the square of the hit diameter. The larger size bit requires greater impact force than the smaller one in order to obtain a perfect cleaning action.