Distribution by Scientific Domains

Kinds of Receiver

  • rake receiver

  • Terms modified by Receiver

  • receiver coil
  • receiver design
  • receiver domain
  • receiver function
  • receiver location
  • receiver locations
  • receiver operating characteristic
  • receiver operating characteristic analysis
  • receiver operating characteristic curve
  • receiver operating characteristic curve analysis
  • receiver operating curve
  • receiver operator characteristic
  • receiver operator characteristic curve
  • receiver operator curve

  • Selected Abstracts

    2-Dimensional code design for an optical CDMA system with a parallel interference cancellation receiver

    MikaŽl Morelle
    The objective of this paper is to design a two-Dimensional Optical Code Division Multiple Access system (2D-OCDMA) for application in access networks, with coding and decoding functions performed by electronic devices. We present a new construction method of Multi-Wavelength Optical Orthogonal Codes (MWOOC), which permits a high flexibility in the code parameters choice. This work evaluates in the noiseless case, the MWOOC potentialities for two receiver structures: a Conventional Correlation Receiver (CCR) and a Parallel Interference Cancellation receiver (PIC). We show that with a PIC receiver, it is possible to design two-Dimensional codes that respect the access specifications. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Des-,-carboxyprothrombin, ,-fetoprotein and AFP-L3 in patients with chronic hepatitis, cirrhosis and hepatocellular carcinoma

    Francisco A Durazo
    Abstract Background and Aim:, Hepatocellular carcinoma (HCC) is a common complication in patients with chronic viral hepatitis. Detection of HCC at an early stage is critical for a favorable clinical outcome. The study aim was to: (i) compare the levels of des-,-carboxyprothrombin (DCP), ,-fetoprotein (AFP) and AFP-L3 in HCC patients and in chronic viral hepatitis patients without HCC; (ii) define the level of each tumor marker with the best sensitivity and specificity for HCC diagnosis; and (iii) to correlate the levels of these markers with respect to size and tumor burden. Methods:, Two hundred and forty patients with either hepatitis B virus (HBV) or hepatitis C virus (HCV) infection were studied. These included 144 with HCC, 47 with chronic hepatitis (fibrosis stage I,III on liver biopsy) and 49 with cirrhosis. Results:, Levels of DCP, AFP and AFP L-3 were significantly higher in patients with HCC than in those without HCC (P , 0.0001). Receiver,operating curves (ROC) indicated that the cut-off value with the best sensitivity and specificity for each test was ,84 mAU/mL for DCP, ,25 ng/mL for AFP and ,10% for AFP-L3. The sensitivity, specificity and positive predictive value (PPV) for DCP was 87%, 85% and 86.8%, for AFP 69%, 87% and 69.8%, and for AFP-L3 56%, 90% and 56.1%, respectively. DCP levels were below the ROC cut-off in all patients without HCC. In patients with single lesions, there was a direct correlation of DCP to tumor size. High levels of AFP correlated with diffuse type of HCC. All three markers were significantly elevated in the presence of metastatic HCC. No advantage was observed by combining two or three markers for HCC diagnosis. Conclusion:, DCP had the highest sensitivity and PPV for HCC diagnosis, had a direct correlation with tumor size, and was not elevated in any patients without HCC. DCP should be used as the main serum test for HCC detection. [source]

    Fluid therapy in acute myocardial infarction: evaluation of predictors of volume responsiveness

    J. SNYGG
    Background: Static vascular filling pressures suffer from poor predictive power in identifying the volume-responsive heart. The use of dynamic arterial pressure variables, including pulse pressure variation (PPV) has instead been suggested to guide volume therapy. The aim of the present study was to evaluate the performance of several clinically applicable haemodynamic parameters to predict volume responsiveness in a pig closed chest model of acute left ventricular myocardial infarction. Methods: Fifteen anaesthetized, mechanically ventilated pigs were studied following acute left myocardial infarction by temporary coronary occlusion. Animals were instrumented to monitor central venous (CVP) and pulmonary artery occlusion (PAOP) pressures and arterial systolic variations (SPV) and PPV. Cardiac output (CO) was measured using the pulmonary artery catheter and by using the PiCCOģ monitor also giving stroke volume variation (SVV). Variations in the velocity time integral by pulsed-wave Doppler echocardiography were determined in the left (,VTILV) and right (,VTIRV) ventricular outflow tracts. Consecutive boluses of 4 ml/kg hydroxyethyl starch were administered and volume responsiveness was defined as a 10% increase in CO. Results: Receiver,operator characteristics (ROC) demonstrated the largest area under the curve for ,VTIRV [0.81 (0.70,0.93)] followed by PPV [0.76 (0.64,0.88)] [mean (and 95% CI)]. SPV, ,VTILV and SVV did not change significantly during volume loading. CVP and PAOP increased but did not demonstrate significant ROC. Conclusion: PPV may be used to predict the response to volume administration in the setting of acute left ventricular myocardial infarction. [source]

    The Patient Health Questionnaire 12 Somatic Symptom scale as a predictor of symptom severity and consulting behaviour in patients with irritable bowel syndrome and symptomatic diverticular disease

    R. C. Spiller
    Summary Background, Anxiety, depression and nongastrointestinal symptoms are often prominent in irritable bowel syndrome (IBS), but their relative value in patient management has not been quantitatively assessed. We modified the Patient Health Questionnaire 15 (PHQ-15) by excluding three gastrointestinal items to create the PHQ-12 Somatic Symptom (PHQ-12 SS) scale. Aims, To compare the value of the PHQ-12 SS scale with the Hospital Anxiety and Depression (HAD) scale in predicting symptoms and patient behaviour in IBS and diverticular disease. Methods, We compared 151 healthy volunteers (HV), 319 IBS patients and 296 patients with diverticular disease (DD), 113 asymptomatic [ASYMPDD] and 173 symptomatic DD (SYMPDD). Results, Patient Health Questionnaire 12 SS scores for IBS and SYMPDD were significantly higher than HV. Receiver,operator curves showed a PHQ-12 SS >6, gave a sensitivity for IBS of 66.4% with a specificity of 94.7% and a positive likelihood ratio (PLR) = 13.2, significantly better than that associated with an HAD anxiety score >7, PLR = 3.0 and depression score >7 PLR = 6.5. PHQ-12 SS correlated strongly with IBS severity scale and GP visits in both IBS and DD. Conclusion, The PHQ-12 SS scale is a useful clinical tool which correlates with patient behaviour in both IBS and symptomatic DD. [source]

    The new DR-70 immunoassay detects cancer of the gastrointestinal tract: a validation study

    A. Kerber
    Summary Background :,Malignant cells characteristically possess high levels of plasminogen activator, which induce local fibrinolysis. The DR-70 immunoassay is a newly developed test, which quantifies fibrin degradation products in serum by a proprietary antibody. Aim :,To evaluate the DR-70 immunoassay as a detection assay for the presence of gastrointestinal cancers. Methods :,We prospectively collected blood sera of 85 patients with histologically proven tumour and 100 healthy blood donors. Ten microlitres of the sera was used for the DR-70 immunoassay. Nineteen patients had a hepatocellular and 10 cholangiocellular carcinoma, 13 cancer of the pancreas, 30 colorectal cancer, 10 stomach cancer and three cancer of the oesophagus. Results :,Receiver,operator curve analysis revealed <0.7 ,g/mL as the best cut-off value to distinguish between patients with cancer and healthy controls. Using this cut-off value, the DR-70 immunoassay showed a good clinical performance with a sensitivity of 91% and a specificity of 93%. Patients with advanced tumour spread showed significantly higher DR-70 values than those with early-stage tumours (P < 0.0003). Conclusion :,The DR-70 immunoassay reliably differs between cancer patients and healthy controls. Therefore, it promises to become a useful test for the detection of cancer in clinical practice. [source]

    Clinical Implications of QRS Duration and QT Peak Prolongation in Patients with Suspected Coronary Disease Referred for Elective Cardiac Catheterization

    M. Nadeem Attar M.D., M.R.C.P.
    Background: The electrocardiogram (ECG) remains a simple, universally available, and prognostically powerful investigation in heart failure, and acute coronary syndromes. We sought to assess the prognostic utility of clinical, angiographic, and simple ECG parameters in a large cohort of patients undergoing elective cardiac catheterization (CC) for known or suspected coronary artery disease. Methods: Consecutive consenting patients undergoing CC for coronary disease were enrolled at a single tertiary center. Patient data, drug therapy, catheter reports, and ECG recordings were prospectively recorded in a validated electronic archive. The primary outcome measure was death or nonfatal myocardial infarction (MI) over 1 year or until percutaneous or cardiac surgical intervention. Independent prognostic markers were identified using the Cox proportional hazard model. Results: A total of 682 individuals were recruited of whom 17(2.5%) died or suffered a nonfatal MI in 1 year. In multivariate analysis QRS duration (ms) (HR 1.03 95% CI 1.01,1.05, P = 0.003), extent of coronary disease (HR 2.01 95% CI 1.24,3.58, P = 0.006), and prolonged corrected QT peak interval in lead I (HR 1.02 95% CI 1.00,1.03, P = 0.044) were independently associated with death or nonfatal MI. Receiver-operator characteristic (ROC) analysis for the multivariate model against the primary end point yielded an area under the curve of 0.759 (95% CI 0.660,0.858), P < 0.001. Conclusions: QRS duration and QT peak are independently associated with increased risk of death or nonfatal MI in stable patients attending for coronary angiography. [source]

    Glasgow Aneurysm Score as a predictor of immediate outcome after surgery for ruptured abdominal aortic aneurysm

    S. J. Korhonen
    Background: The aim of the study was to assess the value of the Glasgow Aneurysm Score in predicting postoperative death after repair of a ruptured abdominal aortic aneurysm (AAA). Methods: Between 1991 and 1999, 836 patients underwent surgery for ruptured AAA. Their operative risk at presentation was evaluated retrospectively using the Glasgow Aneurysm Score, based on data from the nationwide Finnvasc registry. Results: The operative mortality rate was 47∑2 per cent (395 of 836); 164 patients (19∑6 per cent) had cardiac complications and 164 (19∑6 per cent) required intensive care treatment for more than 5 days. Predictors of postoperative death in univariate analysis were: coronary artery disease (P = 0∑005), preoperative shock (P < 0∑001), age (P < 0∑001), and the Glasgow Aneurysm Score (P < 0∑001). In multivariate analysis the predictors were: preoperative shock (odds ratio (OR) 2∑13 (95 per cent confidence interval (c.i.) 1∑45 to 3∑11); P < 0∑001) and the Glasgow Aneurysm Score (for an increase of ten units: OR 1∑81 (95 per cent c.i. 1∑54 to 2∑12); P < 0∑001). Receiver,operator characteristic (ROC) curves showed that the best cut-off value of the Glasgow Aneurysm Score in predicting postoperative death was 84 (area under the curve 0∑75 (95 per cent c.i. 0∑72 to 0∑78), standard error 0∑17; P < 0∑001). The operative mortality rate was 28∑2 per cent (114 of 404) in patients with a Glasgow Aneurysm Score of 84 or less, compared with 65∑0 per cent (281 of 432) in those with a score greater than 84 (P < 0∑001). Conclusion: The Glasgow Aneurysm Score predicted postoperative death after repair of ruptured AAA in this series. Copyright © 2004 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd. [source]

    Anal vector volume analysis complements endoanal ultrasonographic assessment of postpartum anal sphincter injury

    M. M. Fynes
    Background The aim of this study was to determine the role of anal vector manometry in the assessment of postpartum anal sphincter injury and to establish the most suitable method of anal vector volume analysis for identifying significant external anal sphincter (EAS) injury in an at-risk parous population. Methods A total of 101 consecutive women with a history of instrumental or traumatic vaginal delivery was recruited. Anal ultrasonography and anal vector manometry were performed. Receiver,operator characteristic curves were used to determine the usefulness of anal manometry and anal vector volume analysis in the identification of significant EAS disruption (full thickness, more than one quadrant involved) detected by ultrasonography. Results Seventeen women had significant EAS disruption identified by anal ultrasonography. Anal vector manometry provided complementary functional information. Anal vector symmetry index (VSI), determined by analysis of mean maximum squeeze pressure, yielded 100 per cent sensitivity for significant EAS disruption, with a positive predictive value of 61 per cent. Conclusion Anal vector manometry complements endoanal ultrasonography. VSI, determined by means of the squeeze pressure profile, correlates best with significant EAS disruption identified at anal ultrasonography. © 2000 British Journal of Surgery Society Ltd [source]

    Evaluation of faecal calprotectin as a valuable non-invasive marker in distinguishing gut pathogens in young children with acute gastroenteritis

    ACTA PAEDIATRICA, Issue 9 2010
    Josef Sżkora
    Abstract Aim:, The aim of the study is to evaluate faecal calprotectin (f-CP) in children ,3 years of age with acute gastroenteritis (AG) as an early predictor of bacterial inflammation. Methods:, We prospectively analysed f-CP levels and diagnostic workup in 107 consecutive children (66 AG, 41 controls). Results:, Children with bacterial AG (BAG) was found to have higher diarrheal frequency (p < 0.01), fever (p < 0.01), erythrocyte sedimentation rate (p < 0.001), white blood count (p < 0.01) and C-reactive protein (CRP) (p < 0.001) compared with viral AG (VAG). Vomiting was frequent in VAG (p < 0.001). f-CP negatively correlated with age in controls (r = ,0.5998). BAG demonstrated significantly higher f-CP levels [median, 219 ,g/g, interquartile range (IQR): 119,350.2] compared with VAG (49.3 ,g/g, IQR: 8.8,131.1) as well as controls (26.5 ,g/g, IQR: 14.9,55.1) (p < 0.001). VAG and control f-CP levels were similar. f-CP was the best-rated marker of BAG with a diagnostic accuracy of 92%. Receiver,operator characteristic analysis revealed an area under curve of 0.95 for identifying BAG; sensitivity and specificity of f-CP were 93% and 88%, respectively, at an adjusted cut-off point of 103.9 ,g/g faeces. Combined f-CP and CRP yield improved diagnostic accuracy of 94% for BAG. Conclusion:, f-CP facilitates early discrimination between bacterial and viral causes of AG in young children. Combining f-CP with CRP increases the diagnostic power of diagnosing BAG. [source]

    Priority-Driven Acoustic Modeling for Virtual Environments

    Patrick Min
    Geometric acoustic modeling systems spatialize sounds according to reverberation paths from a sound source to a receiver to give an auditory impression of a virtual 3D environment. These systems are useful for concert hall design, teleconferencing, training and simulation, and interactive virtual environments. In many cases, such as in an interactive walkthrough program, the reverberation paths must be updated within strict timing constraints - e.g., as the sound receiver moves under interactive control by a user. In this paper, we describe a geometric acoustic modeling algorithm that uses a priority queue to trace polyhedral beams representing reverberation paths in best-first order up to some termination criteria (e.g., expired time-slice). The advantage of this algorithm is that it is more likely to find the highest priority reverberation paths within a fixed time-slice, avoiding many geometric computations for lower-priority beams. Yet, there is overhead in computing priorities and managing the priority queue. The focus of this paper is to study the trade-offs of the priority-driven beam tracing algorithm with different priority functions. During experiments computing reverberation paths between a source and a receiver in a 3D building environment, we find that priority functions incorporating more accurate estimates of source-to-receiver path length are more likely to find early reverberation paths useful for spatialization, especially in situations where the source and receiver cannot reach each other through trivial reverberation paths. However, when receivers are added to the environment such that it becomes more densely and evenly populated, this advantage diminishes. [source]

    Development of an Accurate Positioning System Using Low-Cost L1 GPS Receivers

    Masayuki Saeki
    This system employs an inexpensive L1 GPS receiver and a small patch antenna. As these devices are very inexpensive and small, they can be attached to an array of sensor nodes of a wireless network sensing system. In the present study, we first develop a program that can be used to estimate the relative positions of receivers and evaluate its performance. Next, a number of experiments were conducted to assess the performance of the inexpensive L1 GPS receiver with a patch antenna. Compared to the results obtained using a sophisticated antenna, the present measurement system, which uses a patch antenna, is less accurate. However, the present system achieves an accuracy of 1,2 cm. This system can be used as a localization system for the sensor nodes or, because of its accuracy, as a displacement monitoring system. [source]

    Dynamic range expansion of receiver by using optimized gain adjustment for high-field MRI

    C.H. Oh
    Abstract In high-field magnetic resonance imaging (MRI) system, the signal-to-noise ratio of MR signal is so high that the receiver frequently cannot cover the full dynamic range of the MR signal. Although this problem can be overcome by using a compander (compressor and expander) composed of logarithmic amplifiers and a ROM table to retrieve the nonlinearity of the logarithmic amplifiers or by simply increasing the number of bits of analog-to-digital converter, the methods can be costly and complex or even impossible for most commercial systems. In addition, the spectrometer has to be specifically designed to operate in those modes. In this article, we developed a simple dynamic range improvement method using a receiver with optimized variable gain control in which function can be implemented without any hardware modification to the spectrometer, if the spectrometer can do gain control during a scan. Simulations as well as experiments for the brain and resolution phantom have been performed, and the results demonstrate the utility of the proposed method. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 243,254, 2010. [source]

    In vivo proton spectroscopy without solvent suppression

    David B. Clayton
    Abstract In 1H MR spectroscopy of the human brain, it is common practice to suppress the solvent signal prior to acquisition. This reduces the large dynamic range which is otherwise required of the MR receiver and digitizer in order to detect the dilute metabolite resonances in the presence of the much larger water signal. However, complete solvent suppression is not always obtainable, particularly over large volumes and in superficial regions containing large susceptibility gradients. In this work, it demonstrated that modern commercial MR scanners possess the dynamic range necessary to adequately resolve the 1H metabolites in unsuppressed spectra. Moreover, a postacquisition method is presented which can completely remove the intact water signal and accurately quantitate the metabolite peaks. Preserving the water signal in in vivo spectroscopy has several useful benefits, such as providing a high signal-to-noise ratio internal concentration, frequency, and line shape reference. Comparison is made between suppressed and unsuppressed spectra from both a phantom and the human brain acquired at 4 T. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 260,275, 2001 [source]

    DS/CDMA throughput of a multi-hop sensor network in a Rayleigh fading underwater acoustic channel

    Choong Hock Mar
    Abstract Asynchronous half-duplex Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a suitable candidate for the MAC protocol design of underwater acoustic (UWA) sensor networks owing to its many attractive features. Our ad-hoc multi-hop network is infrastructureless in that it is without centralized base stations or power control. Hence, we develop an asynchronous distributed half-duplex control protocol to regulate between the transmitting and receiving phases of transmissions. Furthermore, multi-hop communications are very sensitive to the time variability of the received signal strength in the fading channel and the ambient noise dominated by snapping shrimp in harsh underwater environments, because a broken link in the multi-hop path is enough to disrupt communications and initiate new route searches. In our configuration, we use the Ad hoc On-demand Distance Vector (AODV) routing protocol optimized for UWA networks. Empirical studies show that we can model the channel as a slow-varying frequency non-selective Rayleigh fading channel. We theoretically analyze the throughput of our configuration by considering three salient features: the ability of the receiver to demodulate the data, the effect of our control protocol and the effect of disconnections on the generation of routing packets. The throughput under various operating conditions is then examined. It is observed that at optimal node separation, the throughput is improved by a factor of 10. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Targeted screening for undiagnosed diabetes reduces the number of diagnostic tests.

    DIABETIC MEDICINE, Issue 8 2004
    Abstract Aims To determine the cost and performance of a Danish risk score, fasting plasma glucose (FPG), and HbA1c as single screening tests and in combination with targeted screening. Subjects and methods In the Inter99 study, 12 934 inhabitants of Copenhagen County were invited to participate. All participants underwent anthropometric measurements, blood samples, and a 75-g standardized oral glucose tolerance test [N = 6784 (52.5%)]. Results Of the 6117 individuals included in the analysis, 252 (4.1%) had previously undiagnosed diabetes. As a stand-alone test, the FPG had the highest performance expressed by a significantly higher area under the receiver,operating curve [0.89; 95% confidence interval (CI) 0.86, 0.99] compared with the Danish risk score (0.78; 95% CI 0.76, 0.81) and HbA1c (0.76; 95% CI 0.72, 0.80). Targeted screening where the initial test was a risk score reduced the FPG measurements by 72% (100% vs. 27.8%). Using FPG in population-based screening, the cost per newly diagnosed diabetic individual was 583 euro compared with 270 euro if screened by questionnaire followed by FPG. The sensitivity and specificity were 78.6% and 87.7% for FPG, and 61.5% and 89.2% for the combination of the questionnaire and FPG, respectively. Conclusions The performance of FPG was superior to a questionnaire and HbA1c used as single tests. However taking into account workload, the burden on the population and the cost per identified person with undiagnosed diabetes, targeted screening using a questionnaire followed by FPG appears to be the strategy of choice. Diabet. Med. (2004) [source]

    Disclosures and Asset Returns

    ECONOMETRICA, Issue 1 2003
    Hyun Song Shin
    Public information in financial markets often arrives through the disclosures of interested parties who have a material interest in the reactions of the market to the new information. When the strategic interaction between the sender and the receiver is formalized as a disclosure game with verifiable reports, equilibrium prices can be given a simple characterization in terms of the concatenation of binomial pricing trees. There are a number of empirical implications. The theory predicts that the return variance following a poor disclosed outcome is higher than it would have been if the disclosed outcome were good. Also, when investors are risk averse, this leads to negative serial correlation of asset returns. Other points of contact with the empirical literature are discussed. [source]

    Multiple Referrals and Multidimensional Cheap Talk

    ECONOMETRICA, Issue 4 2002
    Marco Battaglini
    In previous work on cheap talk, uncertainty has almost always been modeled using a single,dimensional state variable. In this paper we prove that the dimensionality of the uncertain variable has an important qualitative impact on results and yields interesting insights into the "mechanics" of information transmission. Contrary to the unidimensional case, if there is more than one sender, full revelation of information in all states of nature is generically possible, even when the conflict of interest is arbitrarily large. What really matters in transmission of information is the local behavior of senders' indifference curves at the ideal point of the receiver, not the proximity of players' ideal point. [source]

    State Policy, Economic Crisis, Gender, and Family Ties: Determinants of Family Remittances to Cuba

    ECONOMIC GEOGRAPHY, Issue 1 2004
    Sarah A. Blue
    Abstract: This article advances the argument that changing economic conditions in the home country act as an important determinant for sending remittances. Research on the determinants of remittances has tended to focus on the characteristics of the sending population. In the case of Cuba, disproportionate attention is paid to political disincentives to send remittances and not enough to changing state policy and the growing economic demand for remittances in that country. Using empirical data gathered from households in Havana, this article tests the importance of economic conditions in the home country, political ideology, the relationship of the sender to the receiver, the length of time away from home, and gender as determinants for remittances. Migration during an economic crisis, having immediate relatives in the home country, and female gender positively influenced remittance behavior for Cuban emigrants. Visits to the home country, especially for migrants who had left decades earlier, were found to be critical for reestablishing family connections and increasing remittances. No support was found for political disincentives as a major determinant of remittance sending to Cuba. [source]

    The effect of linguistic abstraction on interpersonal distance

    Margreet Reitsma-van Rooijen
    It is well known that people describe positive behaviors of others close to them (e.g., in-group member, friend) in abstract terms, but with concrete terms in the case of people who they are not close to (e.g., out-group member, enemy). In contrast, negative behaviors of people who we are close to are described in concrete terms, but in abstract terms for people who are distant. However, the communicative impact of such subtle differences in language use on a receiver who is also the actor of the behavior being described has never been addressed. We hypothesized and found that a positive abstract message compared to a positive concrete message leads to perceived proximity to the sender, while a negative abstract message compared to a negative concrete message leads to perceived distance. The implications of this study, which is the first to show the communicative impact of biased language use, are discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Parallel interference cancellation in DS-CDMA optical networks using bias compensation

    A. Okassa-M'foubat
    A receiver based on the parallel cancellation of multiple access interference by bias compensation is considered here for a direct sequence unipolar optical code division multiple access (DS-OCDMA) system. It relies on the estimation of interferences from undesired users, the regeneration of interfering signals at the output of first canceller stage and their substraction from the received signal after amplification by a bias compensation factor in the second stage. The performance of such a technique is analysed in a synchronous network using orthogonal optical codes and the results are compared with those for different types of conventional receivers. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Optimised spreading code redistribution PAPR reduction technique for MC-CDMA systems

    Lin Yang
    Multicarrier code division multiple access (MC-CDMA) is one of the most promising techniques considered for future broadband mobile services. However, the high peak to average power ratio (PAPR) problem associated with MC-CDMA systems can significantly degrade the power efficiency at the transmitter. This paper proposes an efficient PAPR reduction technique for the downlink of MC-CDMA systems. It regards the order of the CDMA spreading codes as an extra degree of freedom and exploits it to effectively reduce the PAPR of the signal. The proposed technique requires only slight modification to the MC-CDMA base station and negligible complexity to the mobile terminals. Both lightly loaded and fully loaded systems are examined when using the orthogonal sets of Walsh,Hadamard (WH) and Golay complementary sequences (CSs). It will be demonstrated that the proposed technique achieves significant PAPR reduction with low system complexity at both transmitter and receiver. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    New joint frame synchronisation and carrier frequency offset estimation method for OFDM systems,

    Zhongshan Zhang
    We propose a new joint frame synchronisation and carrier frequency offset estimation scheme for burst transmission mode OFDM systems. This scheme uses a central-symmetric and comb-like (CSCL) training sequence, which eases the power detection at the receiver without increasing the total training sequence power. Fine frame synchronisation as well as carrier frequency offset acquisition with a maximum acquisition range of times the sub-carrier spacing can also be performed based on the proposed CSCL training sequence, where N is the discrete Fourier transform (DFT) length and SF is an integer-valued spreading factor used to generate CSCL. The post-acquisition residual carrier frequency offset can be further estimated and corrected via a fine adjustment algorithm. In order to reduce performance loss due to the high peak-to-average power ratio (PAPR) of the CSCL training sequence, a time-domain constant-envelope (CE) training sequence is also proposed. The superior estimation accuracy of the proposed algorithm over that of the Moose algorithm and the SS (Shi and Serpedin) algorithm is proved by computer simulation. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Performance analysis of optically preamplified DC-coupled burst mode receivers

    T. J. Zuo
    Bit error rate and threshold acquisition penalty evaluation is performed for an optically preamplified DC-coupled burst mode receiver using a moment generating function (MGF) description of the signal plus noise. The threshold itself is a random variable and is also described using an appropriate MGF. Chernoff bound (CB), modified Chernoff bound (MCB) and the saddle-point approximation (SPA) techniques make use of the MGF to provide the performance analyses. This represents the first time that these widely used approaches to receiver performance evaluation have been applied to an optically preamplified burst mode receiver and it is shown that they give threshold acquisition penalty results in good agreement with a prior existing approach, whilst having the facility to incorporate arbitrary receiver filtering, receiver thermal noise and non-ideal extinction ratio. A traditional Gaussian approximation (GA) is also calculated and comparison shows that it is clearly less accurate (it exceeds the upper bounds provided by CB and MCB) in the realistic cases examined. It is deduced, in common with the equivalent continuous mode analysis, that the MCB is the most sensible approach. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Enhanced system design for download and streaming services using Raptor codes,,

    Tiago Gasiba
    Raptor codes have been recently standardised by 3rd Generation Partnership Project (3GPP) to be used in the application layer (AL) for multimedia broadcast and multicast services (MBMS) including download delivery and streaming delivery. Furthermore, digital video broadcast (DVB) has also recommended the inclusion of these Raptor codes for IP-datacast services. In this paper, enhancements on the system and receiver design using Raptor codes are studied, namely the permeable layer receiver (PLR) and the individual post-repair mechanism. With the PLR, the partial information ignored in the conventional receiver is passed from lower layer to higher layer. We show how a practical and efficient implementation of the Raptor decoder as a PLR can be done, which can not only achieve huge performance gains, but the gains can be achieved at an affordable low decoding complexity. Whereas the PLR is employed for enhancing both download and streaming services, the post-repair aims at guaranteeing reliable download delivery when a feedback channel is available. We propose here two efficient post-repair algorithms which fully exploit the properties of the Raptor codes. One allows to find a minimum set of source symbols to be requested in the post-delivery, and another allows to find a sufficient number of consecutive repair symbols. Selected simulations verify the good performance of proposed techniques. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    CGU-frame-based representations and their connection with Reed,Solomon and DCT/DST coding schemes

    Fatma Abdelkefi
    We investigate the use of overcomplete frame representations to correct errors occurring over burst-based transmission channels or channels leading to isolated errors. We show that when the overcomplete signal representation is based on a class of frames, called cyclic geometrically uniform (CGU) finite frames, the family of frames containing finite harmonic frames (both in and ), this representation becomes equivalent to a Reed--Solomon (RS) coding scheme. Hence, introducing an RS decoding procedure at the receiver, leads to remove the errors introduced by the transmission channel and consequently results in a quasi-perfect reconstructed signal. The advantage of this approach is to exploit the RS coding scheme without using it explicitly at the transmitter, which would lead to a robust and low complexity transmission. Furthermore, we prove that the discrete cosine transform (DCT) coding is a special case of CGU-frame-based representations and this property holds also true for the discrete sine transform (DST) coding scheme. Simulation results are presented to confirm our claims. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Two-stage detection of partitioned random CDMA

    Lukasz Krzymien
    Random Code Division Multiple Access (CDMA) with low complexity two-stage joint detection/decoding is considered. A sequence partitioning approach is used for modulation, where every spreading sequence is divided into M sections (partitions) which are interleaved prior to transmission. This setup, called partitioned CDMA, can be understood as a generalisation of (chip) interleave division multiple access (IDMA). An analysis of a low-complexity iterative cancellation receiver is presented for arbitrary received power distributions. It is shown that for equal rate and equal power users the asymptotic performance of partitioned CDMA is equal to the performance of CDMA with optimal a posteriori probability (APP) detection for system loads K/N,<,1.49. Effects of asynchronous signal transmission are quantified for standard pulse shaping filters and it is shown that the signal-to-noise ratios achievable in an asynchronous system are improved with respect to fully synchronous transmission. The effect of unequal received powers is examined and considerable gains in performance are obtained by judicious choices of power distributions. For certain power distribution, partitioned CDMA with iterative detection can achieve arbitrary system loads, that is detection is no longer fundamentally interference limited. The practical near-far resistance of the proposed system is illustrated using an example of a receiver with a circular receive footprint and uniformly distributed transmitters (single cell system). Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Performance analysis of a generic system model for uncoded IDMA using serial and parallel interference cancellation,

    Oliver Nagy
    This paper shows how to accurately describe a fully synchronised interleave division multiple access (IDMA) scheme without channel coding by a matrix model. This model allows the derivation of the optimal detector and provides additional insights into the IDMA principle, and we show that the matrices are structured and sparse. We use BER and EXIT charts to study the performance of parallel and serial interference cancellation schemes and demonstrate that the latter converges faster and is independent of the scrambling code. Any bit interleaved DS-CDMA system can be viewed as a special case of IDMA, and an IDMA receiver can therefore be used to detect DS-CDMA signals. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    2-Dimensional code design for an optical CDMA system with a parallel interference cancellation receiver

    MikaŽl Morelle
    The objective of this paper is to design a two-Dimensional Optical Code Division Multiple Access system (2D-OCDMA) for application in access networks, with coding and decoding functions performed by electronic devices. We present a new construction method of Multi-Wavelength Optical Orthogonal Codes (MWOOC), which permits a high flexibility in the code parameters choice. This work evaluates in the noiseless case, the MWOOC potentialities for two receiver structures: a Conventional Correlation Receiver (CCR) and a Parallel Interference Cancellation receiver (PIC). We show that with a PIC receiver, it is possible to design two-Dimensional codes that respect the access specifications. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Gaussian inputs: performance limits over non-coherent SISO and MIMO channels

    Rasika R. Perera
    Performance limits of information transfer over a discrete time memoryless Rayleigh fading channel with neither the receiver nor the transmitter knowing the fading coefficients except its statistics is an important problem in information theory. We derive closed form expressions for the mutual information of single input single output (SISO) and multiple input multiple output (MIMO) Rayleigh fading channels for any antenna number at any signal to noise ratio (SNR). Using these expressions, we show that the maximum mutual information of non-coherent Rayleigh fading MIMO channels is achieved with a single transmitter and multiple receivers when the input distribution is Gaussian. We show that the addition of transmit antennas for a fixed number of receivers result in a reduction of mutual information. Furthermore, we argue that the mutual information is bounded by the SNR in both SISO and MIMO systems showing the sub-optimality of Gaussian signalling in non-coherent Rayleigh fading channels. Copyright © 2006 AEIT [source]

    Suppression of sidelobes in OFDM systems by multiple-choice sequences,

    Ivan Cosovic
    In this paper, we consider the problem of out-of-band radiation in orthogonal frequency-division multiplexing (OFDM) systems caused by high sidelobes of the OFDM transmission signal. Suppression of high sidelobes in OFDM systems enables higher spectral efficiency and/or co-existence with legacy systems in the case of OFDM spectrum sharing systems. To reduce sidelobes, we propose a method termed multiple-choice sequences (MCS). It is based on the idea that transforming the original transmit sequence into a set of sequences and choosing that sequence out of the set with the lowest power in the sidelobes allows to reduce the out-of-band radiation. We describe the general principle of MCS and out of it we derive and compare several practical MCS algorithms. In addition, we shortly consider the combination of MCS sidelobe suppression method with existing sidelobe suppression methods. Numerical results show that with MCS approach OFDM sidelobes can be reduced significantly while requiring only a small amount of signalling information to be sent from transmitter to receiver. For example, in an OFDM overlay scenario sidelobes power is reduced by around 10,dB with a signalling overhead of only 14%. Copyright © 2006 AEIT. [source]