Cooperative diversity is a transmission technique, where multiple terminals pool their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we examine the basic building block of cooperative diversity systems, a simple fading relay channel where the source, destination, and relay terminals are each equipped with single antenna transceivers. We consider three different time-division multiple-access-based cooperative protocols that vary the degree of broadcasting and receive collision. The relay terminal operates in either the amplify-and-forward (AF) or decode-and-forward (DF) modes. For each protocol, we study the ergodic and outage capacity behavior (assuming Gaussian code books) under the AF and DF modes of relaying. We analyze the spatial diversity performance of the various protocols and find that full spatial diversity (second-order in this case) is achieved by certain protocols provided that appropriate power control is employed. Our analysis unifies previous results reported in the literature and establishes the superiority (both from a capacity, as well as a diversity point-of-view) of a new protocol proposed in this paper. The second part of the paper is devoted to (distributed) space-time code design for fading relay channels operating in the AF mode. We show that the corresponding code design criteria consist of the traditional rank and determinant criteria for the case of colocated antennas, as well as appropriate power control rules. Consequently space-time codes designed for the case of colocated multiantenna channels can be used to realize cooperative diversity provided that appropriate power control is employed.
On the other hand, several MIMO configurations have been considered to compare performances in terms of channel capacity including electromagnetic parameters of the antenna, such as radiation patterns and mutual coupling. The Spatial Channel Model from 3 GPP has been used for the simulations. Higher capacity has been obtained in the configuration where the two antennas has been placed in parallel with a spacing of 0.4 wavelengths within a PDA, mainly due to the lower mutual coupling and thus to uncorrelation between MIMO subchannels. Moreover, the radiation pattern for both antennas has been measured and MIMO channel measurement have been carried our in an indoor environment, obtaining in average higher capacity in the case of the designed PIFAs. ACKNOWLEDGMENTThe authors wish to thank S.R.F. Moyano, from Dragados Industrial, especially to Mr. Alberto Martínez Ollero, for the support of this research work conducted as part of the PIDEA SMART project and partially funded by PROFIT FIT-330210 -2005-107
Multiple-input multiple-output (MIMO) antenna systems employ spatial multiplexing to increase spectral efficiency or transmit diversity to improve link reliability. The performance of these signaling strategies is highly dependent on MIMO channel characteristics, which, in turn, depend on antenna height and spacing and richness of scattering. In practice, large antenna spacings are often required to achieve significant multiplexing or diversity gain. The use of dual-polarized antennas (polarization diversity) is a promising cost-and space-effective alternative, where two spatially separated uni-polarized antennas are replaced by a single antenna structure employing orthogonal polarizations. This paper investigates the performance of spatial multiplexing and transmit diversity (Alamouti scheme) in MIMO wireless systems employing dual-polarized antennas. In particular, we derive estimates for the uncoded average symbol error rate of spatial multiplexing and transmit diversity and identify channel conditions where the use of polarization diversity yields performance improvements. We show that while improvements in terms of symbol error rate of up to an order of magnitude are possible in the case of spatial multiplexing, the presence of polarization diversity generally incurs a performance loss for transmit diversity techniques. Finally, we provide simulation results to demonstrate that our estimates closely match the actual symbol error rates.
Recent work has shown that the use of multiple antennas in a fading environment results in a linear increase in capacity. This paper examines the capacity of a Multiple Antenna Element Array (MEA) in a quasi-static flat fading environment with a rank deficient channel. We assume that the channel is known at the receiver and the existence of a feedback path to the transmitter. For a particular channel realization, we show that the judicious use of fewer transmit antennas when the channel matrix is ill-conditioned can increase system capacity. We develop a criterion for selecting an optimum set of transmit antennas. This selection is optimal in the sense that the capacity of the resulting MEA system is greater than that for any other configuration with the same nuniber of transmit antennas chosen from t,he original set. The resulting channel is full rank.
The goal of this paper is to assess the impact of real-world propagation conditions on the maximum achievable diversity performance of communication over Ricean multipleinput multiple-output (MIMO) channels. To this end, we examine a MIMO channel employing orthogonal space-time block codes (OSTBCs) and study the diversity behavior of the resulting effective single-input single-output (SISO) channel. The performance criteria employed are symbol error rate, outage capacity, and wideband spectral efficiency. For general propagation conditions, we establish key quantities that determine performance irrespective of the performance criterion used. Furthermore, we discuss the relation between the notion of diversity order related to the slope of the average error probability versus signal-to-noise ratio (SNR) curve and diversity order related to the slope of the outage probability versus SNR curve. For Ricean fading MIMO channels, we demonstrate the existence of an SNR-dependent critical rate R crit , below which signaling with zero outage is possible and, hence, the fading channel behaves like an additive white Gaussian noise (AWGN) channel. For SISO channels, R crit is always zero. In the MIMO case, R crit is a simple function of the angle between the vectorized Ricean component of the channel and the subspace spanned by the vectorized Rayleigh fading component.
In this paper, we study the channel typical for cellular broadband fixed wireless applications. A measurement system for a two-element-transmit by two-element-receive antenna configuration was built. Measurements were conducted in a suburban environment with dual antenna polarization and transmit separation.We present results on K-factor, Cross-PolarizationDiscrimination (XF' D) and Doppler spectrum. Our results address the influence of distance and antenna height for Kfactor and XPD. We also comment on the properties of a fixed wireless channel and describe its Doppler spectrum.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.