A DS-CDMA system using despreading sequences weighted by adjustable chip waveforms

This paper evaluates the performance of a direct-sequence code-division multiple-access system using coherent receivers in which the despreading sequences are weighted by adjustable chip waveforms. The chip weighting waveforms under consideration are designed for multiple-access interference (MAI) rejection. Assuming that the received chip waveforms are rectangular, new expressions for the signal-to-interference-plus-noise ratio (SINR) of the decision variable are derived when different weighted despreading sequences (WDS's) are used in the receiver. The novelty of the derived expressions is that each of the expressions, when the system parameters are given, is determined only by one parameter of the adjustable chip waveforms employed. As a result, we can simply tune the parameter to its optimal value in real-time for MAI rejection without knowing the other users' spreading codes, timing, and phase. The criterion for tuning the parameter is to maximize the SINR of the decision variable based on the relative strength between the additive Gaussian white noise and the MAI. Numerical results show that when the multiple-access interference is significant, the receivers using WDS's outperform significantly the conventional receiver using a rectangular despreading sequence. Brief analysis for band-limited spreading signals is also provided to reveal the practical implications of the proposed technique. © 1999 IEEE.published_or_final_versio

A CDMA Receiver Using Exponentially Weighted Despreading Waveforms

This paper presents a DS-CDMA receiver using exponentially weighted despreading waveforms (WDW). The chip weighting waveforms are designed for the purpose of multiple access interference (MAI) rejection by emphasizing the transitions of the received signal of interest. The WDW is determined only by one parameter, which leads to easy tuning of the WDW in practice to achieve the best performance. As a result, we show that the proposed receiver can reject MAI without knowing co-user's spreading codes, timing, and phase, and hence increase system capacity. Analysis and numerical results show that the proposed receiver outperforms the conventional receiver especially when MAI is significant. Finally, a discussion on the effect of bandlimited spreading signals is also given on the practical implications of the proposed technique.published_or_final_versio

Capacity enhancement of band-limited DS-CDMA system using weighted despreading function

This paper addresses capacity enhancement of a band-limited direct-sequence code-division multiple-access system by using a weighted despreading function (WDF) in the receiver. An ideal Gaussian channel with perfect power control is assumed. The system performance is measured by the signal-to-interference-plus-noise ratio of the decision variable derived in the frequency domain, the bandwidth efficiency factor, the capacity enhancement factor, and the bit-error rate. It is shown that tuning a parameter of the WDF employed helps to partially flatten the in-band cross-spectrum of a pair of spreading and despreading functions. Numerical results show that the capacity of the proposed system improves over the conventional system using rectangular despreading function. To assess practical implications of the WDF receiver, the sensitivity to timing error is also analyzed.published_or_final_versio

Effects of of weighted despreading sequence on CDMA performance

This paper received the best paper award in the conferenceWaves of the Year 2000This paper addresses the effects of a weighted despreading sequence on the performance of a coherent receiver in a DS-CDMA system. The chip weighting waveforms used in the receiver are designed for the purpose of multiple access interference rejection by emphasizing the transitions of the received signal of interest. Since the resulting weighted despreading sequence is determined only by one parameter, this leads to easy tuning of the weighted despreading sequence in practice to achieve the best performance. The criterion of tuning the parameter is to maximize the derived signal to interference plus noise ratio of the decision variable based on the relative strength between white noise and multiple access interference. As a result, according to the proposed approach, we can reject the multiple access interference without knowing the co-user's spreading codes, timing, and phase since maximizing the signal to interference plus noise ratio in Gaussian noise minimizes the probability of error of the receiver.published_or_final_versio

DS-CDMA with power control error using weighted despreading sequences over a multipath rayleigh fading channel

In this paper, closed-form solutions for the average bit error rate (BER) performance of a direct-sequence codedivision multiple-access system with imperfect power control are derived for both coherent and noncoherent receptions operating over a multipath Rayleigh fading channel. The RAKE structure receivers under consideration employ despreading sequences weighted by adjustable exponential chip waveforms optimized for multiple-access interference rejection. The chip-weighting waveforms employed are determined only by one parameter γ which leads to easy tuning of the waveforms in practice to achieve the best performance. The results indicate that the number of active users supported at a given BER for the case of γ tuned to maximize the average signal to interference plus noise ratio H is much larger than the case of γ = 0 (fixed or rectangular despreading sequence). It is shown that imperfect power control affects the irreducible BER for the case of γ = 0. On the other hand, the effect of imperfect power control on BER performance for the case of γ tuned to maximize Ĥ is equivalent to a reduction in the average signal-to-noise ratio, and, hence, system performance can be compensated by increasing the transmitter power. It is further shown that the effect due to imperfect power control on BER performance is significant while that on the maximum value of Ĥ obtained by tuning γ is rather insignificant. Index Terms-Code-division multiple access, RAKE receivers, spread-spectrum communication. © 1999 IEEE Publisher Item Identifier S 0018-9545(99)05722-9.published_or_final_versio

Coherent DS-SS receiver using exponentially weighted despreading function with imperfect power control in multipath Rayleigh fading environment

In this paper, a closed-form solution for the average bit error rate (BER) performance of a coherent DS-CDMA system with imperfect power control is derived for a multipath Rayleigh fading channel. The RAKE receiver under consideration employs exponentially weighted despreading function with an adjustable parameter γ optimized for multiple access interference rejection in multipath environment. The results indicate that the number of active users supported at a given BER for the case of γ tuned to maximize the average signal to interference plus noise ratio SINR̄ is much larger than commonly used rectangular despreading function (γ = 0). It is shown that imperfect power control affects the irreducible BER for the case of γ = 0. On the other hand, the effect of imperfect power control on BER performance for γ tuned to maximize SINR̄ is equivalent to a reduction in the average signal to white noise ratio γ̄b and hence system performance can be compensated by increasing the transmitter power.published_or_final_versio

A crucial sequence for transglutaminase type 2 extracellular trafficking in renal tubular epithelial cells lies in its N-terminal {beta}-sandwich domain

Transglutaminase type 2 (TG2) catalyzes the formation of an -( -glutamyl)-lysine isopeptide bond between adjacent peptides or proteins including those of the extracellular matrix (ECM). Elevated extracellular TG2 leads to accelerated ECM deposition and reduced clearance that underlie tissue scarring and fibrosis. The extracellular trafficking of TG2 is crucial to its role in ECM homeostasis; however, the mechanism by which TG2 escapes the cell is unknown as it has no signal leader peptide and therefore cannot be transported classically. Understanding TG2 transport may highlight novel mechanisms to interfere with the extracellular function of TG2 as isoform-specific TG2 inhibitors remain elusive. Mammalian expression vectors were constructed containing domain deletions of TG2. These were transfected into three kidney tubular epithelial cell lines, and TG2 export was assessed to identify critical domains. Point mutation was then used to highlight specific sequences within the domain required for TG2 export. The removal of -sandwich domain prevented all TG2 export. Mutations of Asp94 and Asp97 within the N-terminal -sandwich domain were identified as crucial for TG2 externalization. These form part of a previously identified fibronectin binding domain (88WTATVVDQQDCTLSLQLTT106). However, siRNA knockdown of fibronectin failed to affect TG2 export. The sequence 88WTATVVDQQDCTLSLQLTT106 within the -sandwich domain of TG2 is critical to its export in tubular epithelial cell lines. The extracellular trafficking of TG2 is independent of fibronectin

Examining the relationship between processing fluency and memory for source information

Familiarity-based processes such as processing fluency can influence memory judgements in tests of item recognition. Many conventional accounts of source memory assume minimal influence of familiarity on source memory, but recent work has suggested that source memory judgements are affected when test stimuli are processed with greater fluency as a result of priming. The present experiments investigated the relationship between fluency and the accuracy of source memory decisions. Participants studied words presented with different source attributes. During test, they identified words that gradually clarified on screen through progressive demasking, made old/new and source memory judgements, and reported confidence ratings for those words. Response times (RTs) recorded from the item identification task formed the basis of a fluency measure, and identification RTs were compared across categories of item recognition, source accuracy and confidence. Identification RTs were faster in trials with correct retrieval of source information compared with trials for which source could not be accurately retrieved. These findings are consistent with the assumption that familiarity-based processes are related to source memory judgements

Syndecan-4 knockout leads to reduced extracellular transglutaminase-2 and protects against tubulointerstitial fibrosis

Transglutaminase type 2 (TG2) is an extracellular matrix crosslinking enzyme with a pivotal role in kidney fibrosis. The interaction of TG2 with the heparan sulfate proteoglycan syndecan-4 (Sdc4) regulates the cell surface trafficking, localization, and activity of TG2 in vitro but remains unstudied in vivo. We tested the hypothesis that Sdc4 is required for cell surface targeting of TG2 and the development of kidney fibrosis in CKD. Wild-type and Sdc4-null mice were subjected to unilateral ureteric obstruction and aristolochic acid nephropathy (AAN) as experimental models of kidney fibrosis. Analysis of renal scarring by Masson trichrome staining, kidney hydroxyproline levels, and collagen immunofluorescence demonstrated progressive fibrosis associated with increases in extracellular TG2 and TG activity in the tubulointerstitium in both models. Knockout of Sdc-4 reduced these effects and prevented AAN-induced increases in total and active TGF-b1. In wild-type mice subjected to AAN, extracellular TG2 colocalized with Sdc4 in the tubular interstitium and basement membrane, where TG2 also colocalized with heparan sulfate chains. Heparitinase I, which selectively cleaves heparan sulfate, completely abolished extracellular TG2 in normal and diseased kidney sections. In conclusion, the lack of Sdc4 heparan sulfate chains in the kidneys of Sdc4-null mice abrogates injury-induced externalization of TG2, thereby preventing profibrotic crosslinking of extracellular matrix and recruitment of large latent TGF-b1. This finding suggests that targeting the TG2- Sdc4 interaction may provide a specific interventional strategy for the treatment of CKD

Study of thermal bubble motion in microchannel

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The micro capillary pumped loop system (MCPL) is a highly efficient device for heat transfer because the main driving force is a result of thermo-bubbles in micro-channel. In this study, the scaling effect with respect to the dimensional geometry of MCPL was studied for improving the heat transfer performance. The results showed that when a larger heating power was provided by microheater, the growing rate of thermal bubble was faster. Generally speaking, injecting a larger amount of working fluids resulted in faster thermo bubble motion. When the size of channel was scaled down, the nucleation of thermal bubble occurred easily and a positive performance of heat transfer was expected. These findings will be useful to the further optimal design of MCPL.This study is funded by the National Science Council of the Republic of China, Taiwan, under Contract No. NSC- 98-2221-E-197 –018