Original Bit Research Articles

On Generating Set Index Functions for Randomized Caches

Caches hide the growing latency of accesses to the main memory from the processor by storing the most recently used data on-chip. To limit the search time through the caches, they are organized in a direct mapped or set-associative way. Such an organization introduces many conflict misses that hamper performance. This paper studies randomizing set index functions, a technique to place the data in the cache in such a way that conflict misses are avoided. The performance of such a randomized cache strongly depends on the randomization function. This paper discusses a methodology to generate randomization functions that perform well over a broad range of benchmarks. The methodology uses profiling information to predict the conflict miss rate of randomization functions. Then, using this information, a search algorithm finds the best randomization function. Due to implementation issues, it is preferable to use a randomization function that is extremely simple and can be evaluated in little time. For these reasons, we use randomization functions where each randomized address bit is computed as the XOR of a subset of the original address bits. These functions are chosen such that they operate on as few address bits as possible and have few inputs to each XOR. This paper shows that to index a 2 m -set cache, it suffices to randomize m + 2o rm + 3 address bits and to limit the number of inputs to each XOR to 2 bits to obtain the full potential of randomization. Furthermore, it is shown that the randomization function that we generate for one set of benchmarks also works well for an entirely different set of benchmarks. Using the described methodology, it is possible to reduce the implementation cost of randomization functions with only an insignificant loss in conflict reduction.

Analysis of Multipath Routing—Part I: The Effect on the Packet Delivery Ratio

In this paper, we develop an analytical framework for evaluating multipath routing in mobile ad hoc networks. The instability of the topology (e.g., failure of links) in this type of network due to nodal mobility and changes in wireless propagation conditions makes transmission of time-sensitive information a challenging problem. To combat the inherent unreliability of these networks, we propose a routing scheme that uses multiple paths simultaneously by splitting the information between a multitude of paths, so as to increase the probability that the essential portion of the information is received at the destination without incurring excessive delay. Our scheme works by adding an overhead to each packet, which is calculated as a linear function of the original packet bits. The resulting packet (information and overhead) is fragmented into smaller blocks and distributed over the available paths. The probability of reconstructing the original information at the destination is derived in an analytical form and its behavior is studied for some special cases. It is shown that, under certain constraints, the packet dropping probability decreases as the number of used paths is increased.

AFBV

No abstract available.

Multipath routing in the presence of frequent topological changes

In this article we propose a framework for multipath routing in mobile ad hoc networks and provide its analytical evaluation. The instability of the topology (e.g., failure of links) in these types of networks, due to nodal mobility and changes in wireless propagation conditions, makes transmission of time-sensitive information a challenging problem. To combat this inherent unreliability of these networks, we propose a routing scheme that uses multiple paths simultaneously by splitting the information among the multitude of paths, to increase the probability that the essential portion of the information is received at the destination without incurring excessive delay. Our scheme works by adding some overhead to each packet, which is calculated as a linear function of the original packet bits. The resulting packet (information and overhead) is fragmented into smaller blocks and distributed over the available paths. Our goal is, given the failure probabilities of the paths, to find the optimal way to fragment and then distribute the blocks to the paths so that the probability of reconstructing the original information at the destination is maximized. Our algorithm has low time complexity, which is crucial since the path failure characteristics vary with time and the optimal block distribution has to be recalculated in real time.

Cryptographical properties of Ising spin systems.

The relation between Ising spin systems and public-key cryptography is investigated using methods of statistical physics. The insight gained from the analysis is used for devising a matrix-based cryptosystem whereby the ciphertext comprises products of the original message bits; these are selected by employing two predetermined randomly constructed sparse matrices. The ciphertext is decrypted using methods of belief propagation. The analyzed properties of the suggested cryptosystem show robustness against various attacks and competitive performance to modern cryptographical methods.

Typical performance of gallager-type error-correcting codes

The performance of Gallager's error-correcting code is investigated via methods of statistical physics. In this approach, the transmitted codeword comprises products of the original message bits selected by two randomly constructed sparse matrices; the number of nonzero row/column elements in these matrices constitutes a family of codes. We show that Shannon's channel capacity is saturated for many of the codes while slightly lower performance is obtained for others which may be of higher practical relevance. Decoding aspects are considered by employing the Thouless-Anderson-Palmer approach which is identical to the commonly used belief-propagation-based decoding.

Highly scalable wavelet-based video codec for very low bit-rate environment

We introduce a highly scalable video compression system for very low bit-rate videoconferencing and telephony applications around 10-30 kbits/s. The video codec first performs a motion-compensated three-dimensional (3-D) wavelet (packet) decomposition of a group of video frames, and then encodes the important wavelet coefficients using a new data structure called tri-zerotrees (TRI-ZTR). Together, the proposed video coding framework forms an extension of the original zero tree idea of Shapiro (1992) for still image compression. In addition, we also incorporate a high degree of video scalability into the codec by combining the layered/progressive coding strategy with the concept of embedded resolution block coding. With scalable algorithms, only one original compressed video bit stream is generated. Different subsets of the bit stream can then be selected at the decoder to support a multitude of display specifications such as bit rate, quality level, spatial resolution, frame rate, decoding hardware complexity, and end-to-end coding delay. The proposed video codec also allows precise bit rate control at both the encoder and decoder, and this can be achieved independently of the other video scaling parameters. Such a scheme is very useful for both constant and variable bit rate transmission over mobile communication channels, as well as video distribution over heterogeneous multicast networks. Finally, our simulations demonstrated comparable objective and subjective performance when compared to the ITU-T H.263 video coding standard, while providing both multirate and multiresolution video scalability.

Hardware implementation of a differential QAM modem

A QAM modem based on certain modifications of the CCITT Recommendation V.29, is presented. A predominantly digital implementation without the use of DSP devices is given. Although the implementation is for telephone bandwidth the idea can be expanded to achieve higher rates. In this design approach the modulation is based on ROM-stored symbols while the demodulation is based on a symbol-by-symbol determination for the recovery of the original information bits. Specifically, the paper refers to a D16QAM design. Most of the stages are digital, a feature that simplifies the VLSI implementation. The synchronisation (timing recovery) is based on a modified phase locked loop.

Selection of aBorrelia burgdorferiantigenic variant by cultivation in the presence of increasing amounts of homologous immune serum

This investigation was undertaken to select antigenic variants of a Borrelia burgdorferi strain in vitro. The original strain BITS was cultivated in BSK medium supplemented with increasing concentrations of homologous hyperimmune serum raised in rabbits. After a few serial passages starting from a subinhibitory serum dilution of 1:800 in BSK up to 1:200, a variant named BITSv was obtained; it grew abundantly like the control culture in the presence of hyperimmune serum. Analysis of the antigenic pattern of the original and derived variants by Western blotting revealed that BITSv, compared to the original strain BITS, had lost the reactivity with the immune serum at the level of the oligosaccharide moiety. These experiments, designed to mimic the possible action of antibodies that arise during a Borrelia infection, suggest that lipopolysaccharides are surface located and that they play a role in the integrity of the outer membrane during the multiplication of Borrelia burgdorferi.

Selection of a Borrelia burgdorferi antigenic variant by cultivation in the presence of increasing amounts of homologous immune serum

This investigation was undertaken to select antigenic variants of a Borrelia burgdorferi strain in vitro. The original strain BITS was cultivated in BSK medium supplemented with increasing concentrations of homologous hyperimmune serum raised in rabbits. After a few serial passages starting from a subinhibitory serum dilution of 1:800 in BSK up to 1:200, a variant named BITSv was obtained; it grew abundantly like the control culture in the presence of hyperimmune serum. Analysis of the antigenic pattern of the original and derived variants by Western blotting revealed that BITSv, compared to the original strain BITS, had lost the reactivity with the immune serum at the level of the oligosaccharide moiety. These experiments, designed to mimic the possible action of antibodies that arise during a Borrelia infection, suggest that lipopolysaccharides are surface located and that they play a role in the integrity of the outer membrane during the multiplication of Borrelia burgdorferi.

A new modulation scheme for multitransmitter simulcast digital mobile radio communication

Many mobile radio communication systems require digital signaling simultaneously from multiple transmitters from the viewpoints of efficient frequency utilization and simplified receiver construction. A new modulation scheme intended to realize simulcast digital transmission is described. In this method, a modulation signal is made by superimposing a specific wave on an ordinary rectangular digital wave. The two conditions necessary for obtaining a diversity effect equivalent to the maximal-ratio combining are mathematically derived. The specific waves for the various transmitters may be sinusoidal waves having a frequency equal to the original bit rate, and phases which differ from one transmitter to another. In order to clarify the feasibility of this technique, experimental simulation tests have been performed in the 900-MHz band in a two-transmitter configuration. It is proved that this modulation scheme, in comparison with the carrier-frequency offset strategy, not only gives the same amount of improvement in digital signaling in an overlapped area, but also makes the allowable carrier frequency drift more than ten times larger.

Some Features of the HC-278 Modem

The recently developed HC-278 digital data modem provides full-duplex data transmission at rates up to 1200 bit/s over voice bandwidth channels in fixed or transportable ground electronic systems. Using phase continuous frequency shift modulation, the modem meets the operational requirements of JCS Publ. 10 (TADIL-B) and the interface requirements of MIL-STD188B. Suitable transmission channels include wire lines and tropospheric scatter radio equipment. Maximum usage of digital techniques and integrated circuits provides economy, reliability, simplicity, and compactness. The modulator accepts synchronous serial digital data at standard rates of 75, 150, 300, 600, or 1200 bit/s and converts the bits into tones representing MARK frequency (logical 1) and SPACE frequency (logical 0). At the receiving terminal, the composite line signal containing the above tones is decoded into the original serial bit stream. System timing is derived from a crystal oscillator with a frequency of 1.0752 MHz and stability of 1 \times 10^{-7} per month.