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Uplink Performance of Large Optimum-Combining Antenna Arrays in Poisson-Cell Networks  [PDF]
Siddhartan Govindasamy
Computer Science , 2013,
Abstract: The uplink of a wireless network with base stations distributed according to a Poisson Point Process (PPP) is analyzed. The base stations are assumed to have a large number of antennas and use linear minimum-mean-square-error (MMSE) spatial processing for multiple access. The number of active mobiles per cell is limited to permit channel estimation using pilot sequences that are orthogonal in each cell. The cumulative distribution function (CDF) of a randomly located link in a typical cell of such a system is derived when accurate channel estimation is available. A simple bound is provided for the spectral efficiency when channel estimates suffer from pilot contamination. The results provide insight into the performance of so-called massive Multiple-Input-Multiple-Output (MIMO) systems in spatially distributed cellular networks.
Optimum Combining for Rapidly Fading Channels in Ad Hoc Networks
Sonia Furman,David E. Hammers,Mario Gerla
Journal of Systemics, Cybernetics and Informatics , 2003,
Abstract: Research and technology in wireless communication systems such as radar and cellular networks have successfully implemented alternative design approaches that utilize antenna array techniques such as optimum combining, to mitigate the degradation effects of multipath in rapid fading channels. In ad hoc networks, these methods have not yet been exploited primarily due to the complexity inherent in the network's architecture. With the high demand for improved signal link quality, devices configured with omnidirectional antennas can no longer meet the growing need for link quality and spectrum efficiency. This study takes an empirical approach to determine an optimum combining antenna array based on 3 variants of interelement spacing. For rapid fading channels, the simulation results show that the performance in the network of devices retrofitted with our antenna arrays consistently exceeded those with an omnidirectional antenna. Further, with the optimum combiner, the performance increased by over 60% compared to that of an omnidirectional antenna in a rapid fading channel.
Studies of Power-Combining of Open Slot Antenna Arrays
Chien-Jen Wang;Yang Dai
PIER , 2011, DOI: 10.2528/PIER11081503
Abstract: In this paper, we propose several array topologies to achieve good power-combining characteristics for the open slot antenna. By utilizing an appropriate feeding structure and injecting in-phase or out-of-phase signals, power-combining radiation patterns can be derived. Simulated surface current distributions of several antenna structures are presented to explain radiation mechanism. From the results of radiation performance, the advantages of gain enhancement and pattern reconfiguration are shown. By varying the phase difference of two injected signals of the open slot antenna array, two-dimensional beam-scanning radiation patterns are successfully demonstrated.
Optimum High Impedance Surface Configuration for Mutual Coupling Reduction in Small Antenna Arrays
Nicolas Capet;Cedric Martel;Jerome Sokoloff;Olivier Pascal
PIER B , 2011, DOI: 10.2528/PIERB11050506
Abstract: In this paper, the electromagnetic properties of two different High Impedance Surfaces (HIS) with or without Electromagnetic Band Gap (EBG) in different configurations are investigated for mutual coupling reduction in small antenna arrays. The resonant mechanisms of these structures are studied using transmission calculations in a parallel plate waveguide. An optimum configuration is then proposed. It is shown that a good isolation performance can be achieved without the need of metallic vias when the structure is embedded in a metallic cavity, which limits significantly the number of HIS cells needed to perform a good isolation and the cost of manufacture.
Spectral Efficiency Analysis for the Uplink Generalized Distributed Antenna System with Different Signal Combining Algorithms  [PDF]
Dongming Wang,Zhanjun Jiang,Xinsheng Zhao,Ming Chen
Information Technology Journal , 2008,
Abstract: In this study, the closed-form expressions of the means and cumulative distribution functions of the spectral efficiency for centralized antenna system and distributed antenna system with different signal combining algorithms are derived. These theoretical results demonstrate how overall performance is affected by system parameters such as shadowing intensity and number of antennas. Through numerical experiments it is shown that these results can consistently produce highly accurate results.
Capacity Analysis Based on Using Adaptive Antenna Arrays Jointly Optimized for Trunking and Spatial Efficiency  [cached]
Howitt Ivan,Awad Fahed H
EURASIP Journal on Advances in Signal Processing , 2002,
Abstract: Cellular systems using adaptive antennas for spatial processing have been shown to provide an increase in capacity. When employing adaptive antennas, the standard approach to achieve capacity gain has been to maximize the link quality between the mobile and base station via optimum combining. This paper presents an alternative optimization approach based on jointly optimizing the adaptive antenna array to maximize the spatial and trunking efficiencies. An upper bound on the joint optimization was formulated to evaluate the capacity. Based on this upper bound, the effect of using adaptive antenna arrays to maximize the trunking efficiency was subsequently an outstanding issue. Monte Carlo simulations, substantiated with theoretical analysis, were used to evaluate this issue. Based on the analysis, utilizing the adaptive antennas to optimize trunking efficiency could increase the capacity by 2 to 4 times.
Power-Controlled CDMA Cell Sectorization with Multiuser Detection: A Comprehensive Analysis on Uplink and Downlink  [cached]
Changyoon Oh,Aylin Yener
EURASIP Journal on Wireless Communications and Networking , 2007, DOI: 10.1155/2007/62379
Abstract: We consider the joint optimization problem of cell sectorization, transmit power control and multiuser detection for a CDMA cell. Given the number of sectors and user locations, the cell is appropriately sectorized such that the total transmit power, as well as the receiver filters, is optimized. We formulate the corresponding joint optimization problems for both the uplink and the downlink and observe that in general, the resulting optimum transmit and receive beamwidth values for the directional antennas at the base station are different. We present the optimum solution under a general setting with arbitrary signature sets, multipath channels, realistic directional antenna responses and identify its complexity. We propose a low-complexity sectorization algorithm that performs near optimum and compare its performance with that of optimum solution. The results suggest that by intelligently combining adaptive cell sectorization, power control, and linear multiuser detection, we are able to increase the user capacity of the cell. Numerical results also indicate robustness of optimum sectorization against Gaussian channel estimation error.
Power-Controlled CDMA Cell Sectorization with Multiuser Detection: A Comprehensive Analysis on Uplink and Downlink  [cached]
Oh Changyoon,Yener Aylin
EURASIP Journal on Wireless Communications and Networking , 2007,
Abstract: We consider the joint optimization problem of cell sectorization, transmit power control and multiuser detection for a CDMA cell. Given the number of sectors and user locations, the cell is appropriately sectorized such that the total transmit power, as well as the receiver filters, is optimized. We formulate the corresponding joint optimization problems for both the uplink and the downlink and observe that in general, the resulting optimum transmit and receive beamwidth values for the directional antennas at the base station are different. We present the optimum solution under a general setting with arbitrary signature sets, multipath channels, realistic directional antenna responses and identify its complexity. We propose a low-complexity sectorization algorithm that performs near optimum and compare its performance with that of optimum solution. The results suggest that by intelligently combining adaptive cell sectorization, power control, and linear multiuser detection, we are able to increase the user capacity of the cell. Numerical results also indicate robustness of optimum sectorization against Gaussian channel estimation error.
Near-Optimum Detection with Low Complexity for Uplink Virtual MIMO Systems  [cached]
Sanhae Kim,Oh-Soon Shin,Yoan Shin
EURASIP Journal on Wireless Communications and Networking , 2009, DOI: 10.1155/2009/307407
Abstract: In mobile worldwide interoperability for microwave access (WiMAX) or 3rd Generation partnership project long-term evolution (3GPP-LTE), uplink virtual multiple input multiple output (MIMO) technology is adopted to perform spatial multiple access with two portable subscriber stations (PSSs), where each PSS has an antenna. As two PSSs transmit simultaneously on the same orthogonal frequency division multiple access (OFDMA) resource blocks, the overall uplink capacity will be doubled. To employ this interesting technique with high performance, most system venders demand the optimal maximum-likelihood detection (MLD) scheme in the radio access station (RAS). However, the optimal MLD is difficult to implement due to its explosive computational complexity. In this paper, we propose two efficient MIMO decoding schemes that achieve near-optimum performance with low complexity for uplink virtual MIMO systems that have an iterative channel decoder using bit log-likelihood ratio (LLR) information. The simulation results show that the proposed schemes have almost the same block error rate (BLER) performance as that of the optimal MLD with only about 15.75% and 28% computational complexity in terms of real multiplication, when both PSSs transmit 16 quadrature amplitude modulation (QAM) signals, and only about 3.77% and 7.22% for 64 QAM signals.
Near-Optimum Detection with Low Complexity for Uplink Virtual MIMO Systems  [cached]
Kim Sanhae,Shin Oh-Soon,Shin Yoan
EURASIP Journal on Wireless Communications and Networking , 2009,
Abstract: In mobile worldwide interoperability for microwave access (WiMAX) or 3rd Generation partnership project long-term evolution (3GPP-LTE), uplink virtual multiple input multiple output (MIMO) technology is adopted to perform spatial multiple access with two portable subscriber stations (PSSs), where each PSS has an antenna. As two PSSs transmit simultaneously on the same orthogonal frequency division multiple access (OFDMA) resource blocks, the overall uplink capacity will be doubled. To employ this interesting technique with high performance, most system venders demand the optimal maximum-likelihood detection (MLD) scheme in the radio access station (RAS). However, the optimal MLD is difficult to implement due to its explosive computational complexity. In this paper, we propose two efficient MIMO decoding schemes that achieve near-optimum performance with low complexity for uplink virtual MIMO systems that have an iterative channel decoder using bit log-likelihood ratio (LLR) information. The simulation results show that the proposed schemes have almost the same block error rate (BLER) performance as that of the optimal MLD with only about 15.75% and 28% computational complexity in terms of real multiplication, when both PSSs transmit 16 quadrature amplitude modulation (QAM) signals, and only about 3.77% and 7.22% for 64 QAM signals.
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