76 research outputs found
Pulse width modulation (PWM) method for power components estimation under harmonic distortion conditions:A. G. Bakaoukas; K. Triantafyllos
No full textIn this paper a Pulse Width Modulation (PWM) based method for the measurements of both Active Power (AP) and Reactive Power (RP) under harmonic distortion conditions in power systems is proposed. The method takes advantage of the fact that frequencies present in a power line are of a specific fundamental frequency range (a range centred on the 50Hz or 60Hz) and that in case of the presence of harmonics the frequencies of those dominating in the power line spectrum can be specified on the basis of the fundamental. In contrast to a number of existing methods a time delay or shifting of the input signal is not required by the method presented and the time delay by π/2 of the Current signal with respect to the Voltage signal required by many of the existing measurement techniques, does not apply in the case of the PWM method as well. Another advantage of the presented method is that the fundamental frequency of the power line is considered as an unknown parameter simultaneously estimated with the signal's spectrum, so the method becomes insensitive to fundamental power line frequency changes. Complex computations that include multiplication of the Voltage and Current sample values by trigonometric functions are also avoided
Adaptive Interference Tolerant Receivers for Asynchronous Cooperative MIMO Communications
Full text linkAdaptive single user receivers are demonstrated in this paper for a Cooperative Virtual MIMO network applying Spread Spectrum Sequences. In asynchronous decentralized cooperative systems, it is expected that, for typical wireless environments, user transmissions from adjacent relaying nodes (and other cells) will create interference. Large scale MIMO antenna arrays can mitigate interference with sufficient degrees of freedom but they can be underdetermined in decentralized non orthogonal multiple access (NOMA). In this paper we use Spread Spectrum CDMA sequences when user cooperation and relaying is necessitated and correspondingly apply decentralized single user algorithms utilizing an adaptive multiuser detection approach. The approach does not require Channel State Information (CSI) and operates in a decentralized manner without requiring knowledge of the transmissions from other users (i.e. power, channel gain and phase, and multiuser chips). This yields a low interference cooperative MIMO communication network that is useful for communication in areas with poor coverage or to temporarily increase spectral efficiency to enable a high throughput uplink or downlink channel. The adaptive algorithm utilized in this paper is investigated for both chip-level and symbol-level optimization where it noted that when applying chip-level optimization, a more interference robust receiver can be built when utilizing processing gain (rather than receiver dimensionality) as a metric to combat interference when the number of transmitter antennas used are fixed
Interference resistance of adaptive multiuser detection in asynchronous detect and forward relaying CDMA networks
No full textThe uplink of an asynchronous Detect and Forward CDMA wireless network interference tolerance is investigated in this paper where relays and base station use Adaptive Multiuser Detection to detect incoming signals. Relays exchange data and channel information with the base station to achieve diversity gains. Due to non orthogonality of random spreading waveforms, Multiple Access Interference occurs, at both the relays and base station. In order to mitigate Multiple Access Interference, Adaptive Multiuser detection is been used by fractionally spaced linear transversal bank of filters. It is shown that Adaptive Multiuser Detection enables asynchronous cooperative communications while it is extremely effective with mitigating channel interference. It is also shown that the BER and Capacity performance of the scheme proposed in this paper is arbitrarily close to non linear MLSE theoretical upper bound results in a channel interference free operation. However, in the presence of channel interference our scheme outperforms the theoretical upper bound approach by nearly 9 dB at a BER of 10−3 and by 17 bits/s/Hz in Capacity at a SNR of 30dB
Adaptive combining of signals with unequal noise variances
No full textThis paper demonstrates the signal combining by use of adaptive algorithms for wireless communication networks. The adaptive combiner operates under different noise variances on each branch of the multi-antenna receiver. We utilise adaptive signal combining technique with least mean squares (LMS) algorithm based on Newton's Recursion Method. It is shown that the adaptive combining filter with LMS converges with respect to signal to noise ratio (SNR) and not to the transmit power Simulation results show that the Adaptive Combining technique proposed in this paper provides significant mean square error (MSE) improvement which reflects to BER performance improvement. This improvement is more obvious when two independent signals arrive at the receiver communication terminal (at different antennas) with 10dB of SNR difference, which is a very common situation in wireless communication systems
Radio propagation modeling for capacity optimization in wireless relay MIMO systems with partial CSI
No full textThe enormous growth of wireless communication systems makes it important to evaluate the capacity of such channels. Multiple Input Multiple Output (MIMO) wireless communication systems are shown to yield significant performance improvement to data rates when compared to the traditional Single Input Single Output (SISO) wireless systems. The benefits of multiple antenna elements at the transmitter and receiver have become necessary to the research and the development of the next generation of mobile communication systems. In this paper we propose the use of Relaying MIMO wireless communication systems for use over long throughput. We investigate how Relays can be used in a "demodulate-and-forward" operation when the transmitter is equipped with spatially correlated multiple antenna elements and the receiver has only partial knowledge of the statistics of the channel. We show that Relays between the source and destination nodes of a wireless communication system in MIMO configuration improve the throughput of the system when compared to the typical MIMO systems, or achieve the desired channel capacity with significantly lower power resources needed
Relaying MIMO channel capacity with imperfect channel knowledge at the receiver
No full textIn this paper, we study a scenario of multiple input multiple output system using relays in an angle showing how the topology of the system can play its role in the situation. We assume perfect channel knowledge at the transmitter and the relay(s) which is represented by a matrix of zero mean circularly symmetric complex Gaussian (ZMCSCG) random variables with known covariances, but imperfect channel state information (CSI) at the receiver. The imperfect CSI at the receiver causes errors to the received signal and as a consequence the channel capacity saturates. We derive the channel capacity formulas for two different transmission algorithms; uniform and waterfilling. Finally we simulate and compare the result
Adaptive Receiver for Cooperative MIMO Communication Systems
No full textAn Adaptive single user receiver algorithm is demonstrated in this paper for a Cooperative Virtual MIMO network. The algorithm does not require Channel State Information and operates in a decentralized manner - that being the statistics at the receiver front end are enough to drive near-optimum single channel detection/estimation in multi-channel wireless environments. This yields an advantage in terms of computational resources and enables an autonomous Virtual Antenna Array Network be implemented for transmitting messages in areas with poor coverage or to increase spectral efficiency of the communication channel for high throughput uplink or downlink traffic. The same algorithm that drives interference rejection at the receiver is utilized in forming a metric for initializing the Cooperative Virtual Antenna MIMO Communication Channel. In this paper we show that our approach achieves an information spectral efficiency close to the maximum information rate upper bound while yielding polynomial complexity irrespective of the number of communication terminals initialized. It is shown that our approach is capable of a theoretical information spectral efficiency up to 48 bits/s/Hz at an SNR of 30dB and a BER performance of 10 -4 at a SNR of about 30 dB for 64-QAM. The optimum MLSE receiver (Upper Bound) yields 5dB SNR gain over our approach with the caveat of being an NP-Hard problem. Conversely when our algorithm is compared with the MMSE detector, we observe a gain of 5dB SNR
Relaying MIMO for cooperative mobile networks
No full textRelay networks achieve high performance by utilizing cooperation between nodes that can be classified as multi-hop networks and cooperative MIMO relaying networks. Cooperative diversity is a transmission technique to overcome fading, multipath and inter-channel interference. As an important part of “spatial diversity” systems, cooperative diversity involving multi hop data relays is a solution to improve propagation performance, expanding coverage and enhancing system capacity in such wireless environments. In a cooperative diversity system, the “third party” mobile devices acting as relays to help the main transmission link for improving the performance such as bit error rate (BER), data rate, coverage. This paper is a study of analyzing the system performance for MIMO-Relaying MIMO in different wireless channel and results show the better performance of cooperative communication
Adaptive Signal Combining with Unequal Channel Noise Variances
No full textThis paper demonstrates the signal combining by use of adaptive algorithms for wireless communication networks. The proposed adaptive combiner operates under different communication channel noise variances on each branch of the multi-antenna receiver. The used algorithm for adaptive signal combining is least mean square (LMS) algorithm based on Newton’s Recursion Method. The proposed algorithm uses inverse of noise variances estimate in step size of adaptive algorithm. It is shown that the adaptive combining filter with LMS converges with respect to signal to noise ratio (SNR) and not to the received power. Simulation results in Gaussian channels with different channel noise variances shows that proposed scheme provide performance very close to wiener’s solution of signal combining. It provide 10−4 bit error rate (BER) at 10.dB SNR. The performance of system in Flat Fading Raleigh channels is about 10−5 at 20 dB SNR. Where as the classical maximum ratio combining, adaptive combining with classical LMS and recursive least square algorithm provide 10−3 bit error rate at 20 dB SNR. The improvement in MSE and BER performance with purposed algoritm is more obvious when two independent signals arrive at the receiver of communication terminal (on multiple antennas) with 10dB of SNR difference, which is very common situation in wireless communication systems
MIMO relay channels with partial channel knowledge/estimation error and spatial correlation
No full textIn this paper we show the effect of partial channel
knowledge at the receiver which causes estimation error of the channel at the receiver and the spatial correlation on MIMO Relay wireless communication systems. We assume that the transmitter has perfect knowledge of statistical parameters of the channel such as covariance or mean. We show how the topology of the equipment can upgrade or degrade the channel and we generalize a relaying MIMO scenario. We mathematically approach the gain of a system that uses relaying antennas. We assume a Zero Mean Circular Symmetric Complex Gaussian(ZMCSCG) channel elements and ZMCSCG noise elements. As we examine spatial correlation at the transmitter only, we assume that the elements of the rows of the channel matrix of the first hop are correlated. Partial CSI at the receiver causes errors at the estimation of the channel at the receiver which results the
channel capacity to degrade and to saturate at certain levels of SNR. Numerical simulations are conducted in order to support the theoretical results used in this pape
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