170 research outputs found
Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks
Modern cellular networks in traditional frequency bands are notoriously
interference-limited especially in urban areas, where base stations are
deployed in close proximity to one another. The latest releases of Long Term
Evolution (LTE) incorporate features for coordinating downlink transmissions as
an efficient means of managing interference. Recent field trial results and
theoretical studies of the performance of joint transmission (JT) coordinated
multi-point (CoMP) schemes revealed, however, that their gains are not as high
as initially expected, despite the large coordination overhead. These schemes
are known to be very sensitive to defects in synchronization or information
exchange between coordinating bases stations as well as uncoordinated
interference. In this article, we review recent advanced coordinated
beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP
while achieving good performance in realistic conditions. By stipulating that,
in certain LTE scenarios of increasing interest, uncoordinated interference
constitutes a major factor in the performance of CoMP techniques at large, we
hereby assess the resilience of the state-of-the-art CB to uncoordinated
interference. We also describe how these techniques can leverage the latest
specifications of current cellular networks, and how they may perform when we
consider standardized feedback and coordination. This allows us to identify
some key roadblocks and research directions to address as LTE evolves towards
the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin
MIMO Transmission for Single-fed ESPAR with Quantized Loads
Compact parasitic arrays in the form of electronically steerable parasitic antenna radiators (ESPARs) have emerged as a new antenna structure that achieves multipleinput- multiple-output (MIMO) transmission with a single RF chain. In this paper, we study the application of precoding on practical ESPARs, where the antennas are equipped with load impedances of quantized values. We analytically study the impact of the quantization on the system performance, where it is shown that while ideal ESPARs with ideal loads can achieve a similar performance to conventional MIMO, the performance of ESPARs will be degraded when only loads with quantized values are available. We further extend the performance analysis to imperfect channel state information (CSI). In order to alleviate the performance loss, we propose to approximate the ideal current vector by optimization, where a closed-form solution is further obtained. This enables the use of ESPARs in practice with quantized loads. Simulation results validate our analysis and show that a significant performance gain can be achieved with the proposed scheme over ESPARs with quantized loads. Finally, the tradeoff between performance and power consumption is shown to be favorable for the proposed ESPAR approaches compared to conventional MIMO, as evidenced by our energy efficiency results
Tunable Load MIMO with Quantized Loads
In this paper, we study the application of precoding schemes on practical electronically steerable parasitic array radiators (ESPARs), where quantized load impedances are considered for each antenna element. The presence of quantization in the loads results in a performance loss for practical ESPARs. To alleviate the performance loss, we propose to approximate the ideal current vector with convex optimization, where it is further shown that the optimality is achieved by optimizing the feeding voltages only. Specifically, we obtain the closed-form expression when single-fed ESPARs are assumed. Numerical results show that the proposed quantization-robust scheme can achieve a significant performance gain over ESPARs with quantized loads
Introduction to the Issue on Hybrid Analog-Digital Signal Processing for Hardware-Efficient Large-Scale Antenna Arrays (Part I)
The papers in this special section focus on hybrid analog-digital signal processing for hardware efficient large scale antenna arrays. Hybrid analog-digital (HAD) processing provides a key technology for the coming generations of wireless networks, as a means of obtaining hardware-efficient transceivers. The principle behind HAD is that the transceiver processing is divided into the analog and digital domain, where networks of analog components implement large-dimensional processing at the transceiver front end, allowing for a low-dimensional digital processing which necessitates only a few RF chains. This technology has recently been brought at the forefront of research motivated by the proliferation of millimeter-wave (mmWave) communications, as a solution to circumvent the use of large numbers of expensive mmWave RF components. Its scope however is not limited solely tommWave, as hardwareefficient transmission is key for small cell deployments in the microwave frequencies and also in emerging applications such as the internet of things (IoT) involving massive connectivity. All these applications still rely on transceivers capable of beamforming, using cheap, low-power, and physically small devices. Accordingly, the aim of this Special Issue (SI) has been to gather the relevant contributions focusing on the practical challenges of hybrid analog-digital transmission
Efficient algorithms for solving aggregate keyword routing problems
National Research Foundation (NRF) Singapore under International Research Centres in Singapore Funding Initiativ
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