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Proceedings/ IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), Sydney; 09/2012
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Conference Record - International Conference on Communications 06/2012;
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ABSTRACT: This paper analyzes the exact average symbol error rate (SER), outage probability and ergodic capacity performance of beamforming in spatially correlated multiple-input single output systems with channel estimation error and feedback delay. We derive the joint distribution function of two correlated quadratic forms and employ the result to obtain expressions for the cumulative distribution function, probability density function, moment generating function and moments of the signal-to-noise ratio. Using these expressions, we investigate the exact SER applicable for a large number of modulation schemes, outage probability and the ergodic capacity of the system. The results show that the average SER performance is sensitive to both feedback delay, channel estimation and spatial correlation at the transmitter. Furthermore, feedback delay causes an error floor and has the most degrading impact on performance. We also present Monte Carlo simulation results as verification of our analytical results.
IEEE Transactions on Wireless Communications 09/2011; · 2.59 Impact Factor
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ABSTRACT: Given n independent but not necessarily identical random processes, this paper investigates the general problem of determining how frequently, on average, any given process becomes at least the p-th (p = 1, 2, . . . , n - 1) largest among all processes. This problem requires determining the level crossing rate (LCR) of a carefully defined ordered process, which we solve by developing a general mathematical framework based on the theory of permanents. Our results are very general and may be applicable for a wide range of engineering applications which involve ordered random processes. To demonstrate the applicability to wireless communications, we present closed-form formulas for the LCR for the case where the processes correspond to time-varying Rayleigh fading channels, and use these to characterize the required switching rate for a particular branch of a generalized selection combining diversity receiver.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: Limited feedback precoding is part of the LTE standard. Despite standardization, important fundamental questions, especially relating to the performance due to the use of codebooks and receiver processing techniques, remain to be explored. In order to understand these questions, we consider a single user in a single cell employing single or multi-stream transmission using a variety of codebooks and a choice of different receiver types. We derive expressions for capacity loss relative to perfect feedback due to the limited size of codebook. When multistream transmission is deployed, we show that codebook feedback manifests itself as inter-stream interference resulting in a capacity loss for all receiver types. In the case of SVD receivers, this interference results in a capacity floor. We define a precoding matrix index (PMI) coherence time and bandwidth and show how these parameters are respectively related to channel coherence time and bandwidth. The PMI coherence parameters shed new light on how often feedback is required, both in time and frequency domains, and help us to determine the capacity penalty if feedback is delayed beyond the coherence parameters. Finally, we show the distribution of PMI and also show that this is environment dependent. This supports the need for codebooks that are adaptable to different environments and are not strictly tied to i.i.d. channels.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: This paper reports upon the design of electromagnetic vibration-driven energy generators using a variational formulation to derive the equation of motion of such generators, thereby gaining insight into the device physics. Using this approach, the characteristics of the generator are analytically studied, a newly developed optimization theory of the generator is derived, and a guide for the sizing process is described. A fabricated prototype of an electromagnetic vibration harvester is presented. For the fabrication of the prototype, printed circuit board materials and PMMA have been used to lower the cost and to achieve lightweight device. Analytical and experimental results are presented and compared. The fabricated harvester weighs 7 g, delivers 315 μW at optimum excitation parameters at room temperature, and has a mechanical damping ratio of 0.0186. Experimental and analytical results show good agreement with the newly developed optimization theory. An analytical expression of the optimum load resistance is also developed and validated with experimental results, which show the frequency dependence of the optimum load resistance. It is also demonstrated that the optimization process needs two iterations if the mechanical damping ratio is unknown at the start of development and that the coil parameters represent the degree of freedom of the designer.
Journal of Microelectromechanical Systems 05/2011; · 2.10 Impact Factor
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ABSTRACT: This paper reports on a low-cost high-performance generator, which is based on a hybrid approach that uses polymethyl methalcrylate and electrodeposited foil to convert mechanical vibration into electrical power based on Faraday's law of magnetic induction. The generator is equipped with four wire-wound micro-coils that can be used separately or connected together depending on the voltage and electrical power requirement of the application. The fabricated generator which has a harvester effectiveness of 55.5% was able to supply a 500-Ω load with 422 μW of electrical power. Investigations have revealed that the utilization factor of the mechanical resonator can be used as an indicator of the lifetime of the generator with respect to fatigue analysis. The reported generator weighs only 12.7 g and is a good candidate for applications where lightweight generators are important.
IEEE Sensors Journal 02/2011; · 1.52 Impact Factor
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ABSTRACT: This article reports on a number of experiments that have been performed, which show that the resistance of silver lines formed in channels is lower than silver lines that have been formed on unstructured surfaces. Channels were formed either by being cut into polyimide (Kapton) using a laser or by hot embossing a polycarbonate blend (Bayfol). An ink jet printer was used to dispense silver-containing ink over the embossed channels, the laser cut channels and over unstructured Kapton and Bayfol to allow comparison. Two types of silver-containing ink were used, one was a nanoparticle (NP) ink and the other was a metallo-organic decomposition (MOD) ink. For the NP ink, a decrease in resistance was seen for the lines formed in hot embossed channels. For the MOD ink, the resistance decrease was seen for lines formed in both the embossed and the laser cut channels. (C) 2011 Society for Imaging Science and Technology [DOI: 10.2352/J.ImagingSci.Technol.2011.55.4.040302]
Journal of Imaging Science and Technology 01/2011; 55(4). · 0.93 Impact Factor
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ABSTRACT: In this paper, we consider the interference caused by a secondary system to the primary system in a cognitive radio network. We consider a secondary system deployed in a field of primary receivers. Primary receivers are assumed to be distributed according to a Poisson point process with a density parameter λ<sub>p</sub>. We assume that the secondary system consists of source, relay, and destination terminals, and the source terminal can communicate with the destination terminal either directly (direct mode) or using the relay (relaying mode). We derive analytical expressions for the outage probability of both modes including pathloss, shadowing and multipath fading, and validate the analytical results by simulation. We also derive analytical expressions for the maximum interference caused by both modes to the primary receivers. The results show that to achieve the same median SNR level, the relaying mode may cause less interference to the primary receivers than the direct mode in high pathloss and low shadowing conditions. However, the relaying mode has much higher interference than the direct mode if both modes have the same capacity performance. The results also show that the capacity of the relaying mode has to be reduced by about one half to provide the same level of interference as the direct mode in a typical channel environment.
Wireless Advanced (WiAD), 2010 6th Conference on; 07/2010
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ABSTRACT: This paper investigates the distribution of the condition number of complex Wishart matrices. Two closely related measures are considered: the standard condition number (SCN) and the Demmel condition number (DCN), both of which have important applications in the context of multiple-input multiple-output (MIMO) communication systems, as well as in various branches of mathematics. We first present a novel generic framework for the SCN distribution which accounts for both central and non-central Wishart matrices of arbitrary dimension. This result is a simple unified expression which involves only a single scalar integral, and therefore allows for fast and efficient computation. For the case of dual Wishart matrices, we derive new exact polynomial expressions for both the SCN and DCN distributions. We also formulate a new closed-form expression for the tail SCN distribution which applies for correlated central Wishart matrices of arbitrary dimension and demonstrates an interesting connection to the maximum eigenvalue moments of Wishart matrices of smaller dimension. Based on our analytical results, we gain valuable insights into the statistical behavior of the channel conditioning for various MIMO fading scenarios, such as uncorrelated/semi-correlated Rayleigh fading and Ricean fading.
IEEE Transactions on Communications 07/2010; · 1.68 Impact Factor
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ABSTRACT: The standard condition number (SCN) is a fundamental metric in the context of multiple-input multiple-output communication systems, linear detection and classical linear algebra. Hence, in this paper we propose a novel generic framework for the SCN distribution of three different classes of Wishart matrices which leads to new results and insights. In particular, our analysis covers both central and non-central Wishart distributions of arbitrary dimension and therefore is applicable to uncorrelated/semi-correlated Rayleigh fading and Ricean fading scenarios. For the special case of dual semi-correlated central Wishart matrices, we derive exact and asymptotic polynomial expressions for the SCN distributions. All analytical results are validated via Monte-Carlo simulations with the attained accuracy being excellent in all cases. The impact of the model parameters on channel conditioning is also investigated in detail.
Communications (ICC), 2010 IEEE International Conference on; 06/2010
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ABSTRACT: Cognitive radio (CR) design aims to increase spectrum utilization by allowing the secondary users (SUs) to coexist with the primary users (PUs), as long as the interference caused by the SUs to each PU is properly regulated. At the SU, channel-state information (CSI) between its transmitter and the PU receiver is used to calculate the maximum allowable SU transmit power to limit the interference. We assume that this CSI is imperfect, which is an important scenario for CR systems. In addition to a peak received interference power constraint, an upper limit to the SU transmit power constraint is also considered. We derive a closed-form expression for the mean SU capacity under this scenario. Due to imperfect CSI, the SU cannot always satisfy the peak received interference power constraint at the PU and has to back off its transmit power. The resulting capacity loss for the SU is quantified using the cumulative-distribution function of the interference at the PU. Additionally, we investigate the impact of CSI quantization. To investigate the SU error performance, a closed-form average bit-error-rate (BER) expression was also derived. Our results are confirmed through comparison with simulations.
IEEE Transactions on Vehicular Technology 06/2010; · 1.92 Impact Factor
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ABSTRACT: In a receive diversity system the use of multiple antennas at one end of the link produces multiple channels. A useful, although ill-defined, metric for such a link is the number of independent channels provided. In this letter we discuss several candidate metrics and compare their utility. We show that most of the metrics available in the literature have limitations and can exhibit non-physical behaviour. In order to improve on their performance, we develop two novel measures for the number of independent channels based on the statistical construction of the channel and channel capacity.
Wireless Communications and Networking Conference (WCNC), 2010 IEEE; 05/2010
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ABSTRACT: The future deployment of cognitive radios (CRs) is critically dependent on the fact that the incumbent primary user (PU) system must remain as oblivious as possible to their presence. This in turn heavily relies on the fluctuations of the interfering CR signals. In this letter we compute the level crossing rates (LCRs) of the cumulative interference created by the CRs. We derive analytical formulae for the LCRs in Rayleigh and Rician fast fading conditions. We approximate Rayleigh and Rician LCRs using fluctuation rates of gamma and scaled noncentral x<sup>2</sup> processes respectively. The analytical results and the approximations used in their derivations are verified by Monte Carlo simulations and the analysis is applied to a particular CR allocation strategy.
IEEE Transactions on Wireless Communications 05/2010; · 2.59 Impact Factor
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ABSTRACT: The paper presents an ergodic capacity analysis of MIMO three product channels. We first derive the exact non-asymptotic and asymptotic probability density functions of the arbitrary eigenvalue of the system. From these, a non-asymptotic and asymptotic expression for the ergodic capacity of the system is derived. The non-asymptotic results involve several single numerical integrations and the number of numerical integrations increases with the number of antennas used in the system. However, the asymptotic result has only one numerical integration and a more compact form, hence providing a simpler alternative to the non-asymptotic ergodic capacity result. We also validate the results by using simulations. The results show that the non-asymptotic analytical results are in good agreement with the simulations and the asymptotic analytical results provide a good approximation to the exact results even when the system has very few antennas.
Communications Theory Workshop (AusCTW), 2010 Australian; 03/2010
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ABSTRACT: In this paper we consider the capacity of the cognitive radio (CR) channel in different fading environments under a "low interference regime". First we derive the probability that the "low interference regime" holds under shadow fading as well as Rayleigh and Rician fast fading conditions. We demonstrate that this is the dominant case, especially in certain practical CR deployment scenarios. The capacity of the CR channel depends critically on a power loss parameter, ¿, which governs how much transmit power the CR dedicates to relaying the primary message. We derive a simple, accurate approximation to ¿ in Rayleigh and Rician fading environments which gives considerable insight into system capacity. We also investigate the effects of system parameters and propagation environment on ¿ and the CR capacity. In all cases, the use of the approximation is shown to be extremely accurate.
IEEE Transactions on Wireless Communications 03/2010; · 2.59 Impact Factor
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ABSTRACT: Inkjet printing has been used to produce resonant radio frequency coils that are comparable to those produced by conventional printed circuit board (PCB) methods. The coils, which consist of a conductive loop and in-series capacitors, form part of a receiver circuit that is used for magnetic resonance imaging (MRI). The resonant circuit is selective at the predetermined frequency of 400 MHz. The required electrical components (resistor, capacitor, and inductor) were produced by inkjet printing, with scaling experiments for resistor and capacitor performed before the complete loops with integrated capacitors were printed. Numerical simulation was used to determine the required values for the components. The inkjet printed circuit was combined with a small tuning and matching board before being connected to a network analyzer and the MRI hardware. With a matching of -38 dB at 400 MHz the achieved results were comparable to those from standard PCB techniques. The performance of the inkjet printed component as a receiver device for nuclear magnetic resonance and MRI was verified by imaging reference phantoms and a whole kiwifruit; it compares favorably to standard MRI devices. Inkjet printing can, therefore, be considered a feasible technique for producing MRI receiver circuits on flexible substrates.
IEEE Transactions on Medical Imaging 03/2010; · 3.64 Impact Factor
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ABSTRACT: In a previous paper we outlined an operational concept for managing traffic in Super Dense Operations (SDO) airspace based on a knowledge elicitation effort involving traffic managers and pilots. In this paper we extend this effort, soliciting feedback from a new set of 10 experienced controllers, asking them to evaluate the assumptions and design recommendations making up this operational concept. In the previous paper at this conference, we presented an operational concept for the functioning of airspace operating under Super Density Operations (SDO) that assumes that, in the mid-term (2018) the controllers for SDO for Next Generation Air Transportation System (NextGen) airspace are still responsible for separation assurance and for the merging and spacing of arrivals, departures and overflights. The concept further proposes extensive use of procedural separation based on a predefined ¿plays¿ based on a set of alternative advanced Area Navigation (RNAV) arrival and departure routes and based on a set of alternatives for using airspace for arrivals and departures. Assuming datalink capabilities to communicate a new route to the flight deck, the concept further allows for dynamically generated advanced RNAV arrival and departure routes when the set of predefined ¿plays¿ is insufficient to deal with weather or traffic constraints. In general, the participants were strongly in favor of having predefined route and airspace structures in SDO airspace, with the ability to deal with weather and traffic constraints using predefined alternatives or ¿plays¿ whenever possible, but considering dynamically generated route and airspace structures when the predefined ¿plays¿ are inadequate. Additional details are provided below.
Digital Avionics Systems Conference, 2009. DASC '09. IEEE/AIAA 28th; 11/2009
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ABSTRACT: This paper presents an ergodic capacity analysis of an amplify-and-forward multiple-input, multiple-output two-hop system including the source to destination (direct) link. We first derive an expression for the probability density function of an unordered eigenvalue of the system. Then, using this result, a closed form expression for the ergodic capacity of the system is derived. The ergodic capacity expression has one integral that needs to be evaluated numerically. The results produced are valid for all SNR values and for arbitrary numbers of antennas at the source, relay and destination. We also present simulation results to validate our analysis. The results show that the analysis exactly matches the simulations and quantifies the improvements in capacity due to the diversity offered by the direct link.
Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
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ABSTRACT: In this paper we describe a model for calculating the aggregate interference encountered by primary receivers in the presence of randomly placed cognitive radios (CRs). We show that incorporating the impact of distance attenuation and lognormal fading on each constituent interferer in the aggregate, leads to a composite interference that cannot be satisfactorily modeled by a lognormal. Using the interference statistics we determine a number of key parameters needed for the deployment of CRs. Examples of these are the exclusion zone radius, needed to protect the primary receiver under different types of fading environments and acceptable interference levels, and the numbers of CRs that can be deployed. We further show that if the CRs have apriori knowledge of the radio environment map (REM), then a much larger number of CRs can be deployed especially in a high density environment. Given REM information, we also look at the CR numbers achieved by two different types of techniques to process the scheduling information.
Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
