Comments on “a study on the interconnection of slotted random access networks”

Abstract

The results obtained in many experimental data show that the effect of turbulent diffusion on the performance of an electrostatic precipitator (ESP) is significant. The ways of handling the turbulent diffusion effect in different efficiency models are different. The effects of turbulent diffusion modeling on ESP performance models are investigated by comparing various models which include plug, Deutsch, Cooperman, Leonard‐Mitchner‐Self (L‐M‐S), and 2nd‐order closure models. The results obtained show that the largest difference of the estimation values of collection efficiency between various models in the range 0–10000 cm²/s of diffusivity is about 28%. When the diffusivity is less than 300 cm²/s, the x‐direction diffusion effect makes no obvious contribution to collecting process but the y‐direction diffusion effect makes a marked contribution. When the diffusivity is larger than 300 cm²/s, the uncollected particles are mixed well in the y‐direction and the influence of x‐direction diffusion effect on collection efficiency becomes sensitive with the increase in diffusivity. Moreover, it is shown that the collection efficiency decreases when the entrance concentration increases. When the flow velocity is small, the migration velocity increases with increasing flow velocity. This anomalous phenomenon can be explained by the ionic wind effect, and the case studies show that there exists a maximum collection efficiency when the flow velocity is about a half of the ionic wind velocity.     

Mechanochemical synthesis and characterization of poly(2,5‐dimethoxy aniline) salts

The interfacial interaction and orientation of molecules during the polymerization process plays a vital role in the enhancement of the surface properties of conducting polymers. In this perspective, a solid‐phase mechanochemical route is employed to prepare poly(2,5‐dimethoxy aniline) (PDMA) and its salts with superior properties. Various studies performed on the as‐prepared polymer highlights the formation of polymeric particles with excellent physicochemical properties. Elemental analysis showed the presence of dopants anion in the polymeric backbone. Spectroscopic profile of PDMAs revealed the formation of emeraldine form of PDMAs. Moreover, these studies indicate the formation of PDMA‐HCl in a highly doped state. The surface morphological pictures of PDMAs revealed the formation of aggregated microstructured to nanostructured particulates. X‐ray diffraction, cyclic voltammetry were used to evaluate the physicochemical properties of PDMAs. PDMA salts exhibited crystalline behavior and good electrochemical activity. TG/DTA analysis showed that all the PDMAs were thermally stable up to 240°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Communications with two data rates in the presence of a hostile jammer

Abstract

The performance of a communication system in a hostile environment can often be evaluated by game theory. If one chooses the payoff appropriately, then the results of finite two‐person zero‐sum games are directly applicable. In this paper, we study the performance of a communication link with two data rates in the presence of a hostile jammer. Ensemble mean of the time average throughput is defined as the payoff to the communicator and the system is modeled as a two‐person zero‐sum game. The saddlepoints as well as the value of the game are determined for both symmetric and asymmetric communication strategy cases. Some results for similar systems have been obtained and discussed in Ref. [5]. However, in this paper, we allow the jammer to locate himself in some region at his will, and hence include the model discussed in Ref. [5] as a special case. It is found that the payoff to the communicator is larger if an asymmetric communication strategy is adopted. Like the conclusion stated in Ref. [5], the system results obtain from optimal asymmetric communication strategy may become non‐ergodic. The results obtained analytically are applied to a practical and interesting example.     

Design of a low power video decompression chip set for portable applications

This paper describes the design process of a chip set which performs real-time video decompression for wireless portable applications and concentrates on four critical aspects of the design: compression algorithm development, control complexity, programmability, and throughput. For each of these design areas, this paper evaluates the design trade-offs between low power, compression efficiency, and throughput, which are the three main requirements for wireless portable video. The chip set consists of a subband reconstruction chip and a pyramid vector quantization (PVQ) decoder chip and requires no external memory support or frame buffer. For portable applications with a resolution of 176 pixels wide, 240 lines, and 30 frames per second color video, the chip set, operating at a 1.35 V supply, dissipates less than 9 mW.This research was supported by JSEP contract number DAAH04-94-G-0058.     

Analysis of some channel selection methods for networks with multiple channels

Abstract

Communications networks with multiple parallel channels become more feasible more than before because of the decreasing cost of equipments. Advantages of using multiple parallel channels to connect terminals include better reliability and fault‐tolerance capability, higher throughput and lower delay, easier implementing priority schemes, and more adaptable to provide various kinds of network services. We analyze in this paper the performances of four different channel selection methods in a network with multiple parallel channels. The basic idea is that the performance can be significantly improved by transmitting multiple copies of the same packet simultaneously. We also evaluate the performance deterioration caused by channel failures. The deterioration is observed to be significant if users do not know which channels are out of order. However, an efficient fault‐diagnosis technique is very helpful to alleviate the deterioration. Some easily implementable priority schemes, which are called priority by diversity, priority by privilege, and priority by diversity and privilege, are discussed and evaluated. By appropriately adjustig the values of the control parameters, one can get a suitable priority scheme to achieve the desired performance.     

Optimal memoryless strategies of a two‐rate communication link

Abstract

Game theory has been applied to study the performance of a communication system in a hostile environment. By appropriately choosing the payoff, a communication system in the presence of a hostile jammer can be modeled as a finite two‐person zero‐sum game. In this paper, we model a two‐rate communication link interfered by an on‐off jammer as a two‐person zero‐sum game and derive the optimal memoryless communication and jamming strategies. The ensemble mean of the time average throughput is considered as the payoff to the communicator. It is found that, under average jamming power constraints, the optimal memoryless jamming strategy is, in general, to allocate as much jamming power as possible to one direction. We study both symmetric and asymmetric communication strategy cases. The performance of the communication system is better if an asymmetric communication strategy is adopted. However, the system resulting from an optimal asymmetric communication strategy may become non‐ergodic.     

Throughput performance of a set of continuous ARQ strategies for Markov channels

Abstract

The throughput efficiency of a set of continuous ARQ strategies for Markov channels is analyzed in this paper based on regenerative theorems. The operation of the investigated ARQ strategies can be described as follows. For each data block, a chunk of n or less copies are transmitted contiguously to the receiver. Whenever a repeat request is received, the transmitter goes back to that data block and retransmits the same data block continuously until an ACK is received. Results show that the throughput efficiency depends heavily on the value of n. Therefore, an optimal value of n can be selected to maximize the throughput efficiency. We also compare the throughput performance of the investigated ARQ strategies for Markov systems and systems under the independent error model. It is found that using the independent error model to describe Markov channels may result in significant deviation.     

A low power video-rate pyramid VQ decoder

This paper describes a pyramid vector quantization (VQ) decoder chip used for real-time video decompression. The chip is designed for portable applications with very low power requirements, operating at a 1.35 V supply and consuming 6.7 mW with a 6.4 MHz clock, sufficient to decode 1.27 Mpixels/s for a color display of 176 pixels wide, 240 lines, at 30 frames per second. The chip performs decompression by converting pyramid vector quantization codewords into data values and integrates all functionality on a single die, requiring no external hardware support or memory     

Performance analysis of a new hybrid token‐CSMA/CD protocol

Abstract

A new hybrid token‐CSMA/CD protocol is proposed and analyzed in this paper. The new hybrid protocol is suitable for bus‐structured local area networks. Basically, the new hybrid protocol is a modification of the one proposed by Gopal and Wong [3]. In our new hybrid protocol, the first time slot after the channel changes state from busy to idle, is reserved for the exclusive use of the priority user who possesses the token. Results show that, by this simple modification, our new hybrid protocol has a better performance than the one proposed in [3], especially when the time wasted in detecting a collision is large. The reason is that most of the packet collisions will be avoided by reserving one time slot for the exclusive use of the priority user.     

Error-resilient pyramid vector quantization for image compression

Pyramid vector quantization (PVQ) uses the lattice points of a pyramidal shape in multidimensional space as the quantizer codebook. It is a fixed-rate quantization technique that can be used for the compression of Laplacian-like sources arising from transform and subband image coding, where its performance approaches the optimal entropy-coded scalar quantizer without the necessity of variable length codes. In this paper, we investigate the use of PVQ for compressed image transmission over noisy channels, where the fixed-rate quantization reduces the susceptibility to bit-error corruption. We propose a new method of deriving the indices of the lattice points of the multidimensional pyramid and describe how these techniques can also improve the channel noise immunity of general symmetric lattice quantizers. Our new indexing scheme improves channel robustness by up to 3 dB over previous indexing methods, and can be performed with similar computational cost. The final fixed-rate coding algorithm surpasses the performance of typical Joint Photographic Experts Group (JPEG) implementations and exhibits much greater error resilience.