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Receivers
Selected AbstractsDevelopment of an Accurate Positioning System Using Low-Cost L1 GPS ReceiversCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2006Masayuki 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] Load-Adaptive MUI/ISI-Resilient Generalized Multi-Carrier CDMA with Linear and DF ReceiversEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2000Georgios B. Giannakis A plethora of single-carrier and multi-carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all-digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner-code/outer-code principle, which guarantees MUI/ISI-elimination regardless of the frequency-selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels. [source] Borehole-guided AVO analysis of P-P and P-S reflections: Quantifying uncertainty on density estimatesGEOPHYSICAL PROSPECTING, Issue 5 2006Hugues A. Djikpesse ABSTRACT Seismic properties of isotropic elastic formations are characterized by the three parameters: acoustic impedance, Poisson's ratio and density. Whilst the first two are usually well estimated by analysing the amplitude variation with angle (AVA) of reflected P-P waves, density is known to be poorly resolved. However, density estimates would be useful in many situations encountered in oil and gas exploration, in particular, for minimizing risks in looking ahead while drilling. We design a borehole seismic experiment to investigate the reliability of AVA extracted density. Receivers are located downhole near the targeted reflectors and record reflected P-P and converted P-S waves. A non-linear, wide-angle-based Bayesian inversion is then used to access the a posteriori probability distributions associated with the estimation of the three isotropic elastic parameters. The analysis of these distributions suggests that the angular variation of reflected P-S amplitudes provides additional substantial information for estimating density, thus reducing the estimate uncertainty variance by more than one order of magnitude, compared to using only reflected P-waves. [source] Riverine, estuarine and marine migratory behaviour and physiology of wild and hatchery-reared coho salmon Oncorhynchus kisutch (Walbaum) smolts descending the Campbell River, BC, CanadaJOURNAL OF FISH BIOLOGY, Issue 3 2008C. M. Chittenden Eighty coho salmon Oncorhynchus kisutch smolts (40 wild and 40 hatchery-reared) were surgically implanted with acoustic transmitters and released into the Quinsam River over 2 days. Differences in physiology, travel time and migratory behaviour were examined between wild and hatchery-reared fish. In addition, tagged and control fish of both wild and hatchery-reared stock were raised for 3 months following surgery to compare survival and tag retention. Detection ranges of the acoustic receivers were tested in the river, estuary and ocean in a variety of flow conditions and tide levels. Receivers were placed in the river, estuary and up to 50 km north and south from the river mouth in the marine environment. Wild smolts were significantly smaller by mass, fork length and condition factor than hatchery-reared smolts and exhibited significantly higher levels of sodium, potassium and chloride in their blood plasma than hatchery-reared smolts. The gill Na+K+ -ATPase activity was also significantly higher in the wild coho smolts at the time of release. Ninety-eight per cent of wild and 80% of hatchery-reared fish survived to the estuary, 8 km downstream of the release site. No difference was found in migration speed, timing or survival between smolts released during daylight and those released after dark. Wild smolts, however, spent less time in the river and estuary, and as a result entered the ocean earlier than hatchery-reared smolts. Average marine swimming speeds for wild smolts were double those of their hatchery-reared counterparts. While hatchery smolts dispersed in both a northward and southward direction upon entering the marine environment, the majority of wild smolts travelled north from the Campbell River estuary. The wild coho salmon smolts were more physiologically fit and ready to enter sea water than the hatchery-reared smolts, and as a result had higher early survival rates and swimming speeds. [source] Computational Models for the Combination of Advice and Individual LearningCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 2 2009Guido Biele Abstract Decision making often takes place in social environments where other actors influence individuals' decisions. The present article examines how advice affects individual learning. Five social learning models combining advice and individual learning-four based on reinforcement learning and one on Bayesian learning-and one individual learning model are tested against each other. In two experiments, some participants received good or bad advice prior to a repeated multioption choice task. Receivers of advice adhered to the advice, so that good advice improved performance. The social learning models described the observed learning processes better than the individual learning model. Of the models tested, the best social learning model assumes that outcomes from recommended options are more positively evaluated than outcomes from nonrecommended options. This model correctly predicted that receivers first adhere to advice, then explore other options, and finally return to the recommended option. The model also predicted accurately that good advice has a stronger impact on learning than bad advice. One-time advice can have a long-lasting influence on learning by changing the subjective evaluation of outcomes of recommended options. [source] Priority-Driven Acoustic Modeling for Virtual EnvironmentsCOMPUTER GRAPHICS FORUM, Issue 3 2000Patrick 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 ReceiversCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2006Masayuki 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] Divergence in Female Duetting Signals in the Enchenopa binotata Species Complex of Treehoppers (Hemiptera: Membracidae)ETHOLOGY, Issue 12 2006Rafael L. Rodríguez Sexual communication often involves signal exchanges between the sexes, or duetting, in which mate choice is expressed through response signals. With both sexes acting as signalers and receivers, variation in the signals of males and females may be important for mate choice, reproductive isolation, and divergence. In the Enchenopa binotata species complex , a case study of sympatric speciation in which vibrational duetting may have an important role , male signals are species-specific, females choose among males on the basis of signal traits that reflect species and individual differences, and female preferences have exerted divergent selection on male signals. Here, we describe variation in female signals in the E. binotata species complex. We report substantial species differences in the spectral and temporal features of female signals, and in their timing relative to male signals. These differences were similar in range to differences in male signals in the E. binotata complex. We consider processes that might contribute to divergence in female signals, and suggest that signal evolution in the E. binotata complex may be influenced by mate choice in both sexes. [source] Intra- and Intersexual Selection for Multiple Traits in the Peacock (Pavo cristatus)ETHOLOGY, Issue 9 2005Adeline Loyau Animal communication involves a multitude of signals ranging from morphological to behavioural traits. In spite of the diversity of traits used in animal signalling, most studies of sexual selection have focused on single male traits. Moreover, the two forces of sexual selection (male,male competition and female preference) may target different traits and favour the diversification of male signalling. Still, little is known on the combined effects of intra- and intersexual selection on the evolution of multiple signals. The peacock is often cited as one of the best examples of the strength of sexual selection in producing exaggerated traits. Here, we investigated traits under intra- and intersexual selection in a population of free-ranging common peafowl. Peacocks with longer trains and tarsi were more likely to establish a display territory in a central position within the lek and had a higher number of intrusions and agonistic interactions. These traits appeared therefore to be under intrasexual selection. Female selection was assessed as the number of copulations. Mating success was positively correlated with behavioural traits (display activity) and with train ornamentation (number and density of ocelli) suggesting that females use multiple cues during mate selection. Therefore, intra- and intersexual selection seem to operate on different sets of traits. Overall, our results stress the role of multiple receivers on the evolution of multiple signals. [source] Chemical Alarm Signals Enhance Survival of Brook Charr (Salvelinus fontinalis) During Encounters with Predatory Chain Pickerel (Esox niger)ETHOLOGY, Issue 11 2001Reehan S. Mirza A diversity of aquatic organisms release chemical alarm signals when attacked or captured by a predator. These alarm signals are thought to warn other conspecifics of danger and, consequently, may benefit receivers by increasing their survival. Here we experimentally investigated the differences in behaviour and survival of hatchery-reared juvenile brook charr Salvelinus fontinalis that had been exposed to either brook charr skin extract (experimental treatment) or a control of swordtail skin extract (control treatment). Charr exposed to conspecific skin extract exhibited a significant reduction in movement and/or altered their foraging behaviour in the laboratory when compared with charr exposed to swordtail skin extract. We also exposed charr to either water conditioned by a single brook charr disturbed by a predatory bird model or water conditioned by a single undisturbed brook charr. Charr exposed to disturbance signals reduced activity significantly more than charr exposed to chemical stimuli from undisturbed charr. These results demonstrate the existence of both damage-released alarm signals and disturbance signals in brook charr. Wild brook charr also responded to damage-released alarm cues under natural conditions. Charr avoided areas of a stream with minnow traps labelled with conspecific alarm cues vs. control cues. During staged encounters with chain pickerel Esox niger in the laboratory, predator-naive charr fry were better able to evade the predator if they were previously warned by an alarm signal, thus suggesting a survival benefit to receivers. Collectively, these results demonstrate that the presence of alarm signals in brook charr has important implications for understanding predator,prey interactions. [source] A Method for Simulating Signal Evolution Using Real AnimalsETHOLOGY, Issue 10 2000Björn Forkman We studied response biases to visual stimulation using a new experimental technique. The subjects (hens, Gallus gallus domesticus) were confronted with several rewarding and non-rewarding patterns on a computer screen. In contrast with standard discrimination tasks the rewarding patterns were not identical and varied in a dimension differentiating them from the non-rewarding patterns. The rewarding patterns changed in response to hens' biases in selection of patterns. The aim of the study was to examine the possibility of receivers being a driving force in signal evolution. In one of the experiments a clear-cut result was obtained. During the course of the experiment the rewarding patterns became gradually more different from the non-rewarding one, a result expected from theoretical studies of the effect of response bias in signal evolution. A second similar experiment was less conclusive, with ceiling and floor effects influencing the results. [source] Parallel interference cancellation in DS-CDMA optical networks using bias compensationEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2009A. 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] Performance analysis of optically preamplified DC-coupled burst mode receiversEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2009T. 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] High-resolution estimation for time-variant MIMO channel sounding,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2008Sofia Martinez Lopez A wideband vector channel sounder with 16 parallel RF chains is proposed for parameter estimation in an indoor channel. Low-cost and high-resolution are obtained by using a chirp probe signal, five-port receivers and the MUSIC algorithm. The system covers up to 500,MHz centred at 2.45,GHz. Experimental results show errors inferior to 1,ns in the time domain and of few degrees in the angular domain. Accurate results are found in static as well as in time-variant scenarios. Copyright © 2008 John Wiley & Sons, Ltd. [source] Frequency domain equalisation in CDMA detectionEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2008Ihan Martoyo The present paper introduces frequency domain equalisation (FDE) as an efficient means for single-user detection (SUD) in universal mobile telecommunication systems (UMTS) handhelds. Such an SUD is, at least partially, able to remove multiple access interference (MAI) like a multi-user detector (MUD), however with several important advantages the operation principle of an FDE-SUD is simple and easy to understand, the FDE-SUD shows low numerical complexity and therefore, it is not power hungry like an MUD. The problem of applying FDE without zero-padding or cyclic-prefix insertion is solved by using the overlap-cut method. In this paper we also prove that the performance of the FDE-SUD is practically identical to that of linear MUD for a fully loaded UMTS cell. Furthermore, armed with the idea of FDE for code division multiple access (CDMA), we can construct a common receiver structure for CDMA, time division multiple access (TDMA), orthogonal frequency division multiplexing (OFDM) and multi-carrier CDMA (MC-CDMA) systems. This is an extremely useful idea in enabling a software-defined radio (SDR) which can operate seamlessly in several environments such as UMTS, the IEEE 802.11a and WiMaX. FDE based receivers could be one important building-block for the next generation mobile communications. Copyright © 2008 John Wiley & Sons, Ltd. [source] The soft-output principle,reminiscences and new developments,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 8 2007Peter A. Hoeher A major breakthrough in digital communications was the provisioning of ,soft' outputs at each processing stage, with appropriate capabilities to use this as soft inputs in the next processing stage. This allowed for much more performant receivers especially in difficult mobile radio channel conditions, and set the stage for iterative processing. This article will outline the development of soft output algorithms over the last two decades along with associated state-of-the-art applications and conclude with an outlook towards novel applications of the soft principle. Copyright © 2007 John Wiley & Sons, Ltd. [source] Intermediate frequency zero-crossing detection of filtered MSK based on irregular samplingEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2007Tobias Scholand Short range communication systems such as Bluetooth and DECT (Digital Enhanced Cordless Telecommunications) deploy Gaussian frequency shift keying (GFSK), which is a continuous phase modulation (CPM) scheme derived from minimum shift keying (MSK). Since these short range communication systems require low-cost transceiver structures, the development of appropriate receiver techniques has been a major research topic. Particularly, analogue limiter--discriminator--integrator (LDI) dump filtering techniques have received considerable attention. With the availability of digital signal processing (DSP), the digital implementation of LDI techniques has become increasingly attractive. In order to make LDI receivers more accessible, zero-crossing detection was proposed. First, the authors shall focus on the establishment of an appropriate mathematical discrete-time system model, taking bandlimiting receiver filters into account explicitly. This system model serves as the basis for the development of a multitude of digital zero-crossing detection techniques. Starting from this mathematical discrete-time system model, the authors shall focus on a novel, yet promising, approach to digital zero-crossing detection in the intermediate frequency domain, using irregular sampling instead of the commonly employed regular sampling. The novel detectors shall be termed zero-crossing decorrelation detectors (ZXDDs), because a decorrelating approach will be used. The authors shall present three different variants of the ZXDD. The performance of these ZXDD schemes has been analysed in simulations by the authors and obtained results shall be presented and compared to the performance of known LDI and zero-crossing detection based techniques. Copyright © 2007 John Wiley & Sons, Ltd. [source] Gaussian inputs: performance limits over non-coherent SISO and MIMO channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2007Rasika 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] On extrinsic information of good binary codes operating over Gaussian channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007M. Peleg We show that the extrinsic information about the coded bits of any good (capacity achieving) binary code operating over a Gaussian channel is zero when the channel capacity is lower than the code rate and unity when capacity exceeds the code rate, that is, the extrinsic information transfer (EXIT) chart is a step function of the signal to noise ratio and independent of the code. It follows that, for a common class of iterative receivers where the error correcting decoder must operate at first iteration at rate above capacity (such as in turbo equalization, iterative channel estimation, parallel and serial concatenated coding and the like), classical good codes which achieve capacity over the Additive White Gaussian Noise Channel are not effective and should be replaced by different new ones. Copyright © 2006 AEIT. [source] Multiuser detection techniques with decision statistics combining for layered space-time coded CDMA systemsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2006Slavica Marinkovic This paper considers a low-complexity iterative multiuser detection/decoding algorithm in single user layered space-time coded (LST) systems and LST coded code division multiple access (CDMA) systems. We concentrate on the iterative multiuser receiver based on parallel interference cancellation (PIC) and compare it to the iterative PIC with the minimum means square error (MMSE) detection, as these two approaches seem to be most efficient in meeting the performance-complexity trade-off required by practical systems. In iterative PIC structures, a decision statistics bias severely limits the system performance for a large number of multiple access (MA) or multiple-input multiple-output (MIMO) interferers. A decision statistics combining (DSC) method, originally proposed for iterative PIC receivers in CDMA systems, is used to minimize the bias effect in space-time coded systems for iterative PIC receivers. Significant performance improvements have been confirmed with the iterative PIC receiver with DSC (PIC-DSC) relative to the standard iterative PIC receivers in LST systems for both flat and frequency selective fading channels. This advantage is retained in layered coded CDMA systems as well. The proposed iterative PIC-DSC detector approaches the performance of the much more complex iterative PIC-MMSE receiver. Copyright © 2006 AEIT. [source] Joint compensation of IQ imbalance, frequency offset and phase noise in OFDM receivers,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2004Jan Tubbax Zero-IF receivers are getting a lot of attention because of their potential to enable low-cost OFDM terminals. However, zero-IF receivers also introduce IQ imbalance which can have a huge impact on the performance. Rather than increasing component cost to decrease the IQ imbalance, an alternative is to tolerate the IQ imbalance and compensate for it digitally. Current solutions either require additional analog hardware or are based on digital algorithms that converge too slowly for bursty communication. Moreover, the impact of a frequency offset and phase noise on the IQ imbalance estimation/compensation problem is not considered. In this paper, we analyze the joint IQ imbalance/frequency offset/phase noise estimation and propose a low-cost, highly effective, all-digital mitigation scheme. For large IQ imbalance large frequency offsets and in the presence of phase noise our solution still results in an average implementation loss below 0.5,dB. It, therefore, enables the design of low-cost, lowcomplexity OFDM receivers. Copyright © 2004 AEI [source] Adaptive group detection for DS/CDMA systems over frequency-selective fading channels,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2003Stefano Buzzi In this paper we consider the problem of group detection for asynchronous Direct-Sequence Code Division Multiple Access (DS/CDMA) systems operating over frequency-selective fading channels. A two-stage near-far resistant detection structure is proposed. The first stage is a linear filter, aimed at suppressing the effect of the unwanted user signals, while the second stage is a non-linear block, implementing a maximum likelihood detection rule on the set of desired user signals. As to the linear stage, we consider both the Zero-Forcing (ZF) and the Minimum Mean Square Error (MMSE) approaches; in particular, based on the amount of prior knowledge on the interference parameters which is available to the receiver and on the affordable computational complexity, we come up with several receiving structures, which trade system performance for complexity and needed channel state information. We also present adaptive implementations of these receivers, wherein only the parameters from the users to be decoded are assumed to be known. The case that the channel fading coefficients of the users to be decoded are not known a priori is also considered. In particular, based on the transmission of pilot signals, we adopt a least-squares criterion in order to obtain estimates of these coefficients. The result is thus a fully adaptive structure, which can be implemented with no prior information on the interfering signals and on the channel state. As to the performance assessment, the new receivers are shown to be near-far resistant, and simulation results confirm their superiority with respect to previously derived detection structures. Copyright © 2003 AEI. [source] Exploiting the short,term and long,term channel properties in space and time: Eigenbeamforming concepts for the BS in WCDMAEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2001Christopher Brunner The deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space,time (ST) processing, processing may take place in reduced dimension, i. e., pre,filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long,term and short,term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short,term and long,term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well,known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte,Carlo simulations. Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed,loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short,term channel properties. Even though the short,term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/,beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantageous feedback signalling. [source] GSn: A new service type for integrated services on the internet,EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2001Enrico Gregori Network services with deterministic guarantees are based on a worst,case description of user,generated traffic. When designing a policing and scheduling algorithm for guaranteed services on the Internet, accuracy of description of the traffic profile has to be traded with simplicity of implementation. The result of this trade off is often expressed as the number of token buckets required by the service along with the choice of their parameters. The GS type of service proposed by the IETF uses two token buckets both for characterizing the traffic and for policing it. The choice of using only two token buckets is primarily driven by policing costs. In this paper we propose a method that allows the number of token buckets used for characterizing the traffic to be greater than what is actually needed to police it. This means we can obtain an accurate profile of the traffic while keeping policing simple. The method consists of computing a profile of the traffic which involves a number of token buckets of the order of ten, and then doing the policing using only the first token bucket, plus another one which is chosen depending on the delay requirements of the receivers. This paper shows that with this simple enhancement we obtain a guaranteed service whose performance closely approaches the theoretical limits of services with deterministic guarantees. [source] Load-Adaptive MUI/ISI-Resilient Generalized Multi-Carrier CDMA with Linear and DF ReceiversEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2000Georgios B. Giannakis A plethora of single-carrier and multi-carrier (MC) CDMA systems have been proposed recently to mitigate intersymbol interference (ISI) and eliminate multiuser interference (MUI). We present a unifying all-digital Generalized Multicanier CDMA framework which enables us to describe existing CDMA schemes and to highlight thorny problems associated with them. To improve the bit error rate (BER) performance of existing schemes, we design block FIR transmitters and decision feedback (DF) receivers based on an inner-code/outer-code principle, which guarantees MUI/ISI-elimination regardless of the frequency-selective physical channel. The flexibility of our framework allows further BER enhancements by taking into account the load in the system (number of active users), while blind channel estimation results in bandwidth savings. Simulations illustrate the superiority of our framework over competing MC CDMA alternatives especially in the presence of uplink multipath channels. [source] Iridescent hindwing patches in the Pipevine Swallowtail: differences in dorsal and ventral surfaces relate to signal function and contextFUNCTIONAL ECOLOGY, Issue 4 2010Ronald L. Rutowski Summary 1.,Iridescent colour signals are directional but, like diffusely reflected colours, vary within and among species in ways that may be adaptations to specific types of receivers in specific light environments. 2.,The hindwings of pipevine swallowtail butterflies exhibit brilliant blue and iridescent colour patches on the ventral surface in both sexes and on the dorsal wing surface in males. Evidence suggests that the ventral iridescent blue is a component of the warning coloration of this distasteful species, while the dorsal blue iridescent wing area is a sexual signal. Given differences in the function and ecological context of signal production, we analysed reflectance spectra from the iridescent blue areas of both field-caught and laboratory-reared animals to test several predictions about the iridescent colour patches on these wing surfaces. 3.,The ventral blue patches in the warning coloration of males and females should be most visible early and late in the day, due to wing orientation relative to sun angle. We therefore predicted that these iridescent colour patches would be brighter and of longer wavelengths than the male dorsal blue patch displayed during midday courtships. The prediction about reflectance intensity was supported but the prediction about hue was not. 4.,We predicted that the sexually selected dorsal hindwing iridescence of males would be more variable among individuals and condition dependent than the naturally selected ventral iridescent colour patches. To assess variation and condition dependence, laboratory-reared and field-captured individuals were compared. The prediction about variation was not supported, but only the dorsal wing surfaces showed evidence of being condition dependent. 5.,We investigated whether development of dorsal and ventral blue iridescence was coupled by determining correlations in colour properties between the wing surfaces. Our finding of positive correlations indicated a potential developmental constraint in the evolution of colour differences between the two wing surfaces. 6.,Results of this study suggest that some properties of iridescent coloration on the hindwing of the pipevine swallowtail (especially intensity) may have been fine-tuned by evolution in response to prevailing ambient light conditions and viewing perspectives that differ among types of signal receivers. [source] Array-conditioned deconvolution of multiple-component teleseismic recordingsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010C.-W. Chen SUMMARY We investigate the applicability of an array-conditioned deconvolution technique, developed for analysing borehole seismic exploration data, to teleseismic receiver functions and data pre-processing steps for scattered wavefield imaging. This multichannel deconvolution technique constructs an approximate inverse filter to the estimated source signature by solving an overdetermined set of deconvolution equations, using an array of receivers detecting a common source. We find that this technique improves the efficiency and automation of receiver function calculation and data pre-processing workflow. We apply this technique to synthetic experiments and to teleseismic data recorded in a dense array in northern Canada. Our results show that this optimal deconvolution automatically determines and subsequently attenuates the noise from data, enhancing P -to- S converted phases in seismograms with various noise levels. In this context, the array-conditioned deconvolution presents a new, effective and automatic means for processing large amounts of array data, as it does not require any ad-hoc regularization; the regularization is achieved naturally by using the noise present in the array itself. [source] Sedimentary and crustal structure from the Ellesmere Island and Greenland continental shelves onto the Lomonosov Ridge, Arctic OceanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010H. Ruth Jackson SUMMARY On the northern passive margin of Ellesmere Island and Greenland, two long wide-angle seismic reflection/refraction (WAR) profiles and a short vertical incident reflection profile were acquired. The WAR seismic source was explosives and the receivers were vertical geophones placed on the sea ice. A 440 km long North-South profile that crossed the shelf, a bathymetric trough and onto the Lomonosov Ridge was completed. In addition, a 110 km long profile along the trough was completed. P -wave velocity models were created by forward and inverse modelling. On the shelf modelling indicates a 12 km deep sedimentary basin consisting of three layers with velocities of 2.1,2.2, 3.1,3.2 and 4.3,5.2 km s,1. Between the 3.1,3.2 km s,1 and 4.3,5.2 km s,1 layers there is a velocity discontinuity that dips seaward, consistent with a regional unconformity. The 4.3,5.2 km s,1 layer is interpreted to be Palaeozoic to Mesozoic age strata, based on local and regional geological constraints. Beneath these layers, velocities of 5.4,5.9 km s,1 are correlated with metasedimentary rocks that outcrop along the coast. These four layers continue from the shelf onto the Lomonosov Ridge. On the Ridge, the bathymetric contours define a plateau 220 km across. The plateau is a basement high, confirmed by short reflection profiles and the velocities of 5.9,6.5 km s,1. Radial magnetic anomalies emanate from the plateau indicating the volcanic nature of this feature. A lower crustal velocity of 6.2,6.7 km s,1, within the range identified on the Lomonosov Ridge near the Pole and typical of rifted continental crust, is interpreted along the entire line. The Moho, based on the WAR data, has significant relief from 17 to 27 km that is confirmed by gravity modelling and consistent with the regional tectonics. In the trough, Moho shallows eastward from a maximum depth of 19,16 km. No indication of oceanic crust was found in the bathymetric trough. [source] Required source distribution for interferometry of waves and diffusive fieldsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009Yuanzhong Fan SUMMARY The Green's function that describes wave propagation between two receivers can be reconstructed by cross-correlation provided that the receivers are surrounded by sources on a closed surface. This technique is referred to as ,interferometry' in exploration seismology. The same technique for Green's function extraction can be applied to the solution of the diffusion equation if there are sources throughout in the volume. In practice, we have only a finite number of active sources. The issues of the required source distribution is investigated, as is the feasibility of reconstructing the Green's function of the diffusion equation using a limited number of sources within a finite volume. We study these questions for homogeneous and heterogeneous media for wave propagation and homogeneous media for diffusion using numerical simulations. These simulations show that for the used model, the angular distribution of sources is critical in wave problems in homogeneous media. In heterogeneous media, the position and size of the heterogeneous area with respect to the sources determine the required source distribution. For diffusion, the sensitivity to the sources decays from the midpoint between the two receivers. The required width of the source distribution decreases with frequency, with the result that the required source distribution for early- and late-time reconstruction is different. The derived source distribution criterion for diffusion suggests that the cross-correlation-based interferometry is difficult to apply in field condition. [source] Imaging fractures and sedimentary fabrics using shear wave splitting measurements made on passive seismic dataGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009J. P. Verdon SUMMARY The ability to detect aligned fractures using seismic anisotropy provides a valuable tool for exploiting hydrocarbon reservoirs better. Perhaps the most direct way of identifying anisotropy is by observing shear wave splitting. However, the interaction of shear waves with subsurface structure is often complicated. Although fractures in hydrocarbon reservoirs are usually subvertical, shear waves recorded on downhole receivers from microseismic events in or near the reservoir are not likely to have travelled vertically. As such, interpreting splitting measurements made on such waves is a non-trivial problem. Here we develop an approach to model the effects of subsurface structure on non-vertically propagating shear waves. Rock physics theory is used to model the effects of sedimentary fabrics as well as fractures, allowing us to use shear wave splitting measurements to invert for aligned fractures. We use synthetic examples to demonstrate how it is possible to assess in advance how well splitting measurements will image structures, and how this is highly dependent on the available range of ray coverage. Finally, we demonstrate the inversion technique on a passive seismic data set collected during hydraulic fracture stimulation. Despite an unfavourable source,receiver geometry, the strike of an aligned fracture set is accurately identified. [source] | ||||||||||||||||||||||||||||