3,715 research outputs found
Port Decoupling for Small Arrays by Means of an Eigenmode Feed Network
An alternative approach to port decoupling and matching of arrays with tightly coupled elements is proposed. The method is based on the inherent decoupling effect obtained by feeding the orthogonal eigenmodes of the array. For this purpose, a modal feed network is connected to the array. The decoupled external ports of the feed network may then be matched independently by using conventional matching circuits. Such a system may be used in digital beam forming applications with good signal-to-noise performance. The theory is applicable to arrays with an arbitrary number of elements, but implementation is only practical for smaller arrays. The principle is illustrated by means of two examples
Spatial channel characterization for smart antenna solutions in FDD wireless networks
This paper introduces a novel metric for determining the spatial decorrelation between the up- and down-link wireless bearers in frequency division duplex (FDD) networks. This metric has direct relevance to smart or adaptive antenna array base-station deployments in cellular networks, which are known to offer capacity enhancement when compared to fixed coverage solutions. In particular, the results presented were obtained from field trial measurement campaigns for both urban and rural scenarios, with the observations having a direct impact on the choice of down-link beamforming architecture in FDD applications. Further, it is shown that significant spatial decorrelation can occur in urban deployments for bearer separations as small as 5 MHz. Results are presented in terms of both instantaneous characteristics as well as time averaged estimates, thus facilitating the appraisal of smart antenna solutions in both packet and circuit switched network
Enhancing wireless communication system performance through modified indoor environments
This thesis reports the methods, the deployment strategies and the resulting system
performance improvement of in-building environmental modification. With the
increasing use of mobile computing devices such as PDAs, laptops, and the expansion
of wireless local area networks (WLANs), there is growing interest in increasing
productivity and efficiency through enhancing received signal power. This thesis
proposes the deployment of waveguides consisting of frequency selective surfaces
(FSSs) in indoor wireless environments and investigates their effect on radio wave
propagation. The received power of the obstructed (OBS) path is attenuated
significantly as compared with that of the line of sight (LOS) path, thereby requiring
an additional link budget margin as well as increased battery power drain. In this
thesis, the use of an innovative model is also presented to selectively enhance radio
propagation in indoor areas under OBS conditions by reflecting the channel radio
signals into areas of interest in order to avoid significant propagation loss.
An FSS is a surface which exhibits reflection and/or transmission properties as a
function of frequency. An FSS with a pass band frequency response was applied to an
ordinary or modified wall as a wallpaper to transform the wall into a frequency
selective (FS) wall (FS-WALL) or frequency selective modified wall (FS-MWALL).
Measurements have shown that the innovative model prototype can enhance 2.4GHz (IEEE 802.11b/g/n) transmissions in addition to the unmodified wall, whereas
other radio services, such as cellular telephony at 1.8GHz, have other routes to
penetrate or escape.
The FSS performance has been examined intensely by both equivalent circuit
modelling, simulation, and practical measurements. Factors that influence FSS
performance such as the FSS element dimensions, element conductivities, dielectric
substrates adjacent to the FSS, and signal incident angles, were investigated. By
keeping the elements small and densely packed, a largely angle-insensitive FSS was
developed as a promising prototype for FSS wallpaper. Accordingly, the resultant can
be modelled by cascading the effects of the FSS wallpaper and the ordinary wall (FSWALL) or modified wall (FS-MWALL). Good agreement between the modelled,
simulated, and the measured results was observed.
Finally, a small-scale indoor environment has been constructed and measured in a
half-wave chamber and free space measurements in order to practically verify this
approach and through the usage of the deterministic ray tracing technique. An initial
investigation showing that the use of an innovative model can increase capacity in
MIMO systems. This can be explained by the presence of strong multipath
components which give rise to a low correlated Rayleigh Channel. This research work
has linked the fields of antenna design, communication systems, and building
architecture
Novel ring resonator-based integrated photonic beamformer for broadband phased array receive antennas - part I: design and performance analysis
A novel optical beamformer concept is introduced that can be used for seamless control of the reception angle in broadband wireless receivers employing a large phased array antenna (PAA). The core of this beamformer is an optical beamforming network (OBFN), using ring resonator-based broadband delays, and coherent optical combining. The electro-optical conversion is performed by means of single-sideband suppressed carrier modulation, employing a common laser, Mach-Zehnder modulators, and a common optical sideband filter after the OBFN. The unmodulated laser signal is then re-injected in order to perform balanced coherent optical detection, for the opto-electrical conversion. This scheme minimizes the requirements on the complexity of the OBFN, and has potential for compact realization by means of full integration on chip. The impact of the optical beamformer concept on the performance of the full receiver system is analyzed, by modeling the combination of the PAA and the beamformer as an equivalent two-port RF system. The results are illustrated by a numerical example of a PAA receiver for satellite TV reception, showing that—when properly designed—the beamformer hardly affects the sensitivity of the receiver
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