Backward Channel Research Articles

Can the RHIC J/ψ puzzle(s) be settled at LHC?

One observes strong suppression effects for hard probes, e.g. the production of J/ψ or high-pT particles, in nucleus–nucleus (AA) collisions at RHIC. Surprisingly, the magnitude of the suppression is quite similar to that at SPS. In order to establish whether these features arise due to the presence of a thermalized system of quarks and gluons formed in the course of the collision, one should investigate the impact of suppression mechanisms which do not explicitly involve such a state. We calculate shadowing for gluons in the Glauber–Gribov theory and propose a model invoking a rapidity-dependent absorptive mechanism motivated by energy-momentum conservation effects. Furthermore, final-state suppression due to interaction with comoving matter (hadronic or pre-hadronic) has been shown to describe the data at SPS. We extend this model by including the backward reaction channel, i.e. recombination of open charm, which is estimated directly from pp data at RHIC. Strong suppression of charmonium both in pA and AA collisions at LHC is predicted. This is in stark contrast with the predictions of models assuming QGP formation and thermalization of heavy quarks.

Selective imaging in second-harmonic-generation microscopy with anisotropic radiation

As a novel modality of optical microscopy, second-harmonic generation (SHG) provides attractive features including intrinsic optical sectioning, noninvasiveness, high specificity, and high penetrability. For a biomedical application, the epicollection of backward propagating SHG is necessary. But due to phase-matching constraint, SHG from thick tissues is preferentially forward propagation. Myosin and collagen are two of the most abundant fibrous proteins in vertebrates, and both exhibit a strong second-harmonic response. We find that the radiation patterns of myosin-based muscle fibers and collagen fibrils are distinct due to coherence effects. Based on these asymmetric radiation patterns, we demonstrate selective imaging between intertwining muscle fibers and type I collagen fibrils with forward and backward SHG modalities, respectively. Thick muscle fibers dominate the forward signal, while collagen fibril distribution is preferentially resolved in the backward channel without strong interference from muscle. Moreover, we find that well-formed collagen fibrils are highlighted by forward SHG, while loosely arranged collagen matrix is outlined by backward signal.

Linear beamformer schemes with simple relay selection in MIMO relay networks

This article considers a wireless multi-hop/mesh network where single multi-antenna source-destination pair communicates through a selected relay subset using simple relay selection under the constraint of fixed relay's number. Compared with random selection, the simple relay selection can yield certain capacity advantages while linear zero-forcing (ZF) receiver and linear beamformer are considered at the relay. For match-filter (MF) beamformer and amplified-and-forward (AF) beamformer with a fixed number of relays, the capacities are given. Furthermore, we extend the simple selection methods to the relaying scheme with orthogonal-triangular (QR) beamformer and investigate these linear beamformer schemes over spatially correlated multi-input multi-output (MIMO) links for both the backward and forward channel over the two-hop MIMO relay networks.

On the design of globally optimal communication strategies for real-time noisy communication systems with noisy feedback

A real-time communication system with noisy feedback is considered. The system consists of a Markov source, forward and backward discrete memoryless channels, and a receiver with limited memory. The receiver can send messages to the encoder over the backward noisy channel. The encoding at the encoder and the decoding, the feedback, and the memory update at the receiver must be done in real-time. A distortion metric that does not tolerate delays is given. The objective is to design an optimal real-time communication strategy, i.e., design optimal real-time encoding, decoding, feedback, and memory update strategies to minimize a total expected distortion over a finite horizon. This problem is formulated as a decentralized stochastic optimization problem and a methodology for its sequential decomposition is presented. This results in a set of nested optimality equations that can be used to sequentially determine optimal communication strategies. The methodology exponentially simplifies the search for determining an optimal real-time communication strategy.

Backward channel aware Wyner–Ziv video coding: A study of complexity, rate, and distortion tradeoff

Wyner–Ziv video coding is a coding method that exploits source statistics at the decoder. Many Wyner–Ziv video coding schemes encode a video sequence into two types of frames, key frames and Wyner–Ziv frames, and rely on the frequent use of INTRA frames as key frames such that the decoder can derive sufficiently accurate side information. While the use of INTRA frame as key frames keeps the encoding complexity low, it also leads to much lower coding efficiency compared to state-of-the-art predictive video coding. In this paper we present a Wyner–Ziv video coding scheme that uses backward channel aware motion estimation to encode the key frames, where motion estimation is performed at the decoder and motion information is sent back to the encoder. Two motion vector selection methods are proposed and we present a model to study the complexity–rate–distortion tradeoff in such coding schemes.

Backward Channel Protection Based on Randomized Tree-Walking Algorithm and Its Analysis for Securing RFID Tag Information and Privacy

Eavesdropping on backward channels in RFID environments may cause severe privacy problems because it means the exposure of personal information related to tags that each person has. However, most existing RFID tag security schemes are focused on the forward channel protections. In this paper, we propose a simple but effective method to solve the backward channel eavesdropping problem based on Randomized-tree walking algorithm for securing tag ID information and privacy in RFID-based applications. In order to show the efficiency of the proposed scheme, we derive two performance models for the cases when CRC is used and not used. It is shown that the proposed method can lower the probability of eavesdropping on backward channels near to ‘0.’

Relay Techniques for MIMO Wireless Networks with Multiple Source and Destination Pairs

A multiple-input multiple-output (MIMO) relay network comprises source, relay, and destination nodes, each of which is equipped with multiple antennas. In a previous work, we proposed a MIMO relay scheme for a relay network with a single source and destination pair in which each of the multiple relay nodes performs QR decompositions of the backward and forward channel matrices in conjunction with phase control (QR-P-QR). In this paper, we extend this scheme to a MIMO relay network employing multiple source and destination pairs. Towards this goal, we use a group nulling approach to decompose a multiple S-D MIMO relay channel into parallel independent S-D MIMO relay channels, and then apply the QR-P-QR scheme to each of the decomposed MIMO relay links. We analytically show the logarithmic capacity scaling of the proposed relay scheme. Numerical examples confirm that the proposed relay scheme offers higher capacity than existing relay schemes.

Optical limiting in defective quadratic nonlinear photonic crystals

By using a nonlinear transfer matrix method and an iteration method, we investigated an optical limiting in a defective quadratic nonlinear photonic crystal under strong pump-depletion conditions. Due to a giant enhancement of the second harmonic (SH) generation induced by the strong localization of light near the defective band, the progress of the energy exchange from the forward fundamental frequency (FF) channel to the SH channels (both forward and backward) and the backward FF channel is speeded up. The structure can therefore be used as a high-efficient compact optical power limiter. We have also studied the effects of two important parameters of the defective nonlinear periodic structure, the number of the periods and the nonlinear efficiency of the composite material, on the optical limiting.

Design and stability analysis of networked control systems with random communication time delay using the modified MPC

This paper describes a novel control technique to deal with networked control systems with random communication time delay, which is known to highly degrade the control performance of the controlled system. This problem can be solved using a modified model predictive control, which uses the future control sequence to compensate for the forward communication time delay. Also, using a model predictor, the time delay in the backward channel can be compensated as well. Another key part of this paper is to analyse the stability of the networked control systems. The analytical criteria are obtained for both fixed and random communication time delays. The simulation results and practical experiments illustrate that the proposed controller design is realistic.

Adaptive vector quantization in SVD MIMO system backward link with limited number of active sub channels

This paper presents combination of Channel Optimized Vector Quantization based on LBG algorithm and sub channel power allocation for MIMO systems with Singular Value Decomposition and limited number of active sub channels. Proposed algorithm is designed to enable maximal throughput with bit error rate bellow some tar- get level in case of backward channel capacity limitation. Presence of errors effect in backward channel is also considered.

Rotating Stall in Centrifugal Compressor Vaneless Diffuser: Experimental Analysis of Geometrical Parameters Influence on Phenomenon Evolution

The rotating stall is a key problem for achieving a good working range of a centrifugal compressor and a detailed understanding of the phenomenon is very important to anticipate and avoid it. Many experimental tests have been planned by the authors to investigate the influence on stall behavior of different geometrical configurations. A stage with a backward channel upstream, a 2‐D impeller with a vaneless diffuser and a constant cross‐section volute downstream, constitute the basic configuration. Several diffuser types with different widths, pinch shapes, and diffusion ratios were tested. The stage was instrumented with many fast response dynamic pressure sensors so as to characterize inception and evolution of the rotating stall. This kind of analysis was carried out both in time and in frequency domains. The methodology used and the results on phenomenon evolution will be presented and discussed in this article.

Rotating Stall in Centrifugal Compressor Vaneless Diffuser: Experimental Analysis of Geometrical Parameters Influence on Phenomenon Evolution

The rotating stall is a key problem for achieving a good working range of a centrifugal compressor and a detailed understanding of the phenomenon is very important to anticipate and avoid it. Many experimental tests have been planned by the authors to investigate the influence on stall behavior of different geometrical configurations. A stage with a backward channel upstream, a 2-D impeller with a vaneless diffuser and a constant cross-section volute downstream, constitute the basic configuration. Several diffuser types with different widths, pinch shapes, and diffusion ratios were tested. The stage was instrumented with many fast response dynamic pressure sensors so as to characterize inception and evolution of the rotating stall. This kind of analysis was carried out both in time and in frequency domains. The methodology used and the results on phenomenon evolution will be presented and discussed in this article.

A real time transport scheme for wireless multimedia communications

In wireless communications systems, a mobile station is typically equipped with limited processing capability and buffer space for transmitting and receiving. The radio link is usually found to be noisy and its propagation delay is sometimes non-negligible as compared with the packet transmission delay. And because of the necessity of flow control and packet retransmission upon error, the delay and throughput performance cannot satisfy the need of a particular traffic type, i.e., real-time multimedia. This paper presents a scheme suitable for the above condition, called the Burst-oriented Transfer with Time-bounded Retransmission (BTTR). The present scheme uses a large transmission window for sending/receiving a burst of time-sensitive data and, within this window, another smaller observation window is repeatedly used for error status feedback via the backward channel. There is time limitation on each retransmission such that the burst of data can be received in a timely manner, however, with some degradation on the packet loss rate. An analysis is given in terms of the expectations of delay, throughput, and packet drop rate. A comparison with an error-free link protocol will also be given. The result shows that the proposed scheme can meet the delay and throughput requirement under reasonable packet drop rate.

Error resilient video coding controlled by backward channel signaling

We have proposed an error resilient video coding system, which dynamically replaces reference pictures in inter-frame coding according to the backward channel signaling. This system can prevent the temporal error propagation, because the encoder would not use the erred picture as the reference picture. This system has two modes, one is ACK mode and the other is NACK mode. ACK mode is effective in more erroneous condition, and NACK mode is effective in less erroneous condition. In this paper, we explain both modes and focus on the mode switching mechanism according to the error condition on the network so that the optimal performance can be achieved in any error conditions by the proposed system. We show the performance of our proposed system compared with the previous version of ITU-T H.263, which did not have a reference picture selection mode, by a computer simulation as well.

モバイル映像メディアと画像符号化 受信確認を利用した誤り耐性動画像符号化方式における適応的モード切替方式

This paper proposes an adaptive mode switching for error resilient video coding. The error resilient video coding system dynamically replaces reference pictures in inter-frame coding according to backward channel signaling. This system prevents temporal error propagation by preventing the encoder from using the erroneous picture as the reference picture. This system has two modes; the ACK mode is effective in more erroneous condition, and the NACK mode is effective in less erroneous condition. The mode switching mechanism and the error condition on the network is explained, and the performance of the system compared with the conventional H.263 system is shown by computer simulation.

Performance analysis of ARQ error controls under Markovian block error pattern

The authors investigate the effect of forward/backward channel memory (statistical dependence in the occurrence of transmission errors) on ARQ error controls. To take into account the effect of backward channel errors in the performance analysis, they suppose some modified ARQ schemes that have an effective retransmission strategy to prevent the deadlock incurred by the errors on acknowledgments. They consider two modified go-back-N schemes with timer control and with buffer control, one modified selective-repeat scheme and one modified stop-and-wait scheme. By analytical and simulation results, they show how much the performance in throughput and delay of the modified ARQ schemes is affected by the degree of error burstiness when the forward and backward channels are governed by a first-order Markovian block error pattern. They also show that there exists a large difference between the performances with the burst and independent error cases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Universal decoding for memoryless Gaussian channels with a deterministic interference

In [1] universal decoding schemes for finite-alphabet, finite-state channels were proposed end shown to be optimal in the sense of attaining the highest possible random coding error exponent, when the channel input vectors are chosen randomly under a uniform probability distribution. In other words, the average error probability over the ensemble of randomly selected codewords, decays at the fastest exponential rate. In the special case of DMC'S, the proposed universal decoder selects a codeword that minimizes the empirical conditional entropy of the channel input given the channel output. We derive an analogous result for memoryless Gaussian channels with an unknown deterministic interference from a fairly wide class. The empirical conditional entropy of the input given the output is induced by an auxiliary backward channel whose parameters are estimated from the given output vector and each one of the codewords. We also allow a more general class of input distributions by slightly modifying the decoding rule. Similarly to [1], it is shown that the proposed universal decoder attains the same error exponent as that of the ML decoder which is fully informed of the channel and the interfering signal. The proposed decoder is different from an heuristic approach [2], where the channel and message are jointly estimated by the ML method. While the former decoder is based on the backward channel as mentioned earlier, the latter corresponds to the forward channel. For the simple special case where there is no interference and the only uncertainty is in the channel fading parameter, it is demonstrated that the error exponent of the proposed rule might be strictly better than that of the joint ML channel-and-message estimation approach.

Novel satellite digital video TDMA system for business video communications

The authors propose a satellite video signal transmission system that uses a time division multiple access (TDMA) scheme for digital video signal transmission and a code division multiple access (CDMA) scheme for voice signal transmission from a video signal reception-only earth station (backward voice signal transmission). The adoption of a TDMA scheme makes it possible to transmit video signals from various places and to communicate in multipoint-to-(multi)point mode. For backward voice channel transmission from video signal reception-only earth stations, a superposed CDMA voice signal transmission over TDMA video signals by using the same transponder is proposed. The employment of high coding gain forward error correction and development of a cochannel interference cancellation technique have made it possible for the proposed system to transmit a practical number of voice channels. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously. >

Ultrastructure of intestinal and gall-bladder epithelium in the teleost Gasterosteus aculeatus L., as related to their osmoregulatory function

Intestinal and gall-bladder epithelial cells in sticklebacks have been examined in ultrathin sections and freeze-etch replicas. Enterocytes throughout the intestine appear to have a well-developed basal labyrinth similar to that of renal tubular cells, consisting of baso-lateral infoldings closely associated with numerous mitochondria. The lumen inside these intracellular membranes is continuous with the intercellular space via pores. Such a membrane system is also present in the epithelial cells lining the gall bladder, distinguishing them from gall-bladder cells of higher vertebrates. Morphometric analysis indicates that the basal labyrinth of enterocytes in the posterior part of the intestine increases markedly in both sexually mature males and androgen-treated females. This does not occur in the anterior part or gall bladder. In sticklebacks, androgens cause reduced urine excretion and enhanced fluid release via the anus. We conclude that the cells lining the intestine and gall bladder possess an extensive basal labyrinth that may function as a backward channel system, enabling fluid to be produced in the intestine of fish. The androgen-induced increase in the extent of the basal labyrinth in the posterior part of the intestine may be related to the enhanced rate of intestinal fluid excretion observed in sexually mature male sticklebacks.

Public Policy Implications of Reverse Channel Mapping for Lesotho

Reverse Channel Mapping (RCM) is a research method for evaluating the effectiveness of macromarketing systems. RCM uniquely incorporates into backward channel mapping an objective function to allow evaluation of the effectiveness (social goal achievement) of the marketing system. An application of this approach to mapping a food life-support system (LSS) for Lesotho is described to demonstrate strengths of the method and build an argument for its general application.