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9 - Coordinated multi-point transmission in 5G
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- By Roberto Fantini, Telecom Italia, Wolfgang Zirwas, Nokia, Lars Thiele, Ericsson, Danish Aziz, Alcatel-Lucent (now Nokia), Paolo Baracca, Alcatel-Lucent (now Nokia)
- Edited by Afif Osseiran, Jose F. Monserrat, Patrick Marsch
- Foreword by Mischa Dohler, King's College London, Takehiro Nakamura
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- Book:
- 5G Mobile and Wireless Communications Technology
- Published online:
- 05 June 2016
- Print publication:
- 02 June 2016, pp 248-276
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- Chapter
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Summary
Introduction
The performance of a wireless network strongly depends on the user positions in a cell. More precisely, the UEs (User Equipments) at the cell border typically experience much lower throughput than those nearer to the transmitting Base Station (BS). This is mainly due to the presence of inter-cell interference, generated by concurrent transmissions in other cells. Inter-cell interference is particularly relevant for modern wireless communication systems like Universal Mobile Telecommunications System (UMTS) or Long-Term Evolution (LTE), and also 5G, where the frequency reuse factor is one or very close to one. In such scenario the system is primarily interference limited, and the performance cannot be improved by simply increasing the transmitted power. Hence, techniques are necessary in order to (1) target inter-cell interference and (2) reduce the gap between the cell edge and average throughput. Consequently, these alternative techniques allow a more even user experience throughout the whole network.
In principle, the following techniques can be pursued to tackle inter-cell interference:
• Interference can simply be treated as white noise. This is clearly suboptimal, as it ignores properties of the interfering signals that could be exploited in order to improve signal reception quality.
• Interference can be avoided through statically leaving some transmit resources in some cells muted (e.g. fractional frequency reuse), or otherwise constraining the usage of resources, or through coordinated scheduling among cells, as investigated in Chapter 11.
• The impact of interference can be alleviated at the receiver side through e.g. Interference Rejection Combining (IRC), where multiple receive antennas and subsequent receive filters are used to attenuate the interference to a certain extent.
• Interference may be decoded and cancelled, a technique that is for instance studied in 3GPP in the context of Network-Assisted Interference Cancelation (NAIC).
• At the transmitter side, interference can also be partially avoided by performing interference-aware precoding, i.e. applying precoding such that the interference caused toward adjacent cells is reduced.
• Ultimately, signals from other cells can in fact be treated as a useful signal energy instead of interference, if (in the downlink) multiple nodes jointly transmit signals that coherently overlap at the intended receiver, and destructively overlap at interfered receivers. In the uplink (UL), multiple nodes can jointly receive and decode the signals from multiple UEs, and in this form also exploit interference rather than seeing it as a burden.
Microstructure and Luminescence Properties of ZnS:Cu Powders and Electroluminescent Lamps
- Luigi Sangaletti, Laura E. Depero, Brigida Allieri, Livio Antonini, Roberto Fantini, Marco Bettinelli
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- Journal:
- MRS Online Proceedings Library Archive / Volume 471 / 1997
- Published online by Cambridge University Press:
- 10 February 2011, 257
- Print publication:
- 1997
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- Article
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We report on a microscopy and diffraction study of commercially available Cu-doped ZnS powders, along with an optical spectroscopy study of electroluminescent lamps fabricated with these powders. The results allowed us to identify a correlation between the microstructure and the optical properties (i.e. photoluminescence) of the ZnS powders. It is found that the best powders for EL lamps are those displaying a prevalent cubic, i.e. zincblend, structure, while the poor performances of the mixed phase (cubic + hexagonal) are tentatively ascribed to the quenching of luminescence due to defects (stacking faults) introduced into the cubic structure and resulting in a considerable amount of hexagonal phase, as detected by XRD. The mostly cubic powders have been selected to realize EL lamps. The optical properties of these lamps have been investigated by photoluminescence and electroluminescence spectroscopies with the aim to identify the degradation mechanisms leading to a decrease of brightness. The quenching of electroluminescence is primarily ascribed to a deterioration of the electrical contacts. However, the reduced brightness in photoluminescence spectra seems to indicate that additional quenching of luminescence is induced by transformations at the emitting layer of the lamps. This degradation is tentatively ascribed to the presence of voids in the emitting layer, which might induce, acting as traps for moisture, transformations in the optical and electrical properties of the transparent electrode (ITO).
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