4,837 research outputs found
Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays
Massive MIMO (multiple-input multiple-output) is no longer a "wild" or
"promising" concept for future cellular networks - in 2018 it became a reality.
Base stations (BSs) with 64 fully digital transceiver chains were commercially
deployed in several countries, the key ingredients of Massive MIMO have made it
into the 5G standard, the signal processing methods required to achieve
unprecedented spectral efficiency have been developed, and the limitation due
to pilot contamination has been resolved. Even the development of fully digital
Massive MIMO arrays for mmWave frequencies - once viewed prohibitively
complicated and costly - is well underway. In a few years, Massive MIMO with
fully digital transceivers will be a mainstream feature at both sub-6 GHz and
mmWave frequencies. In this paper, we explain how the first chapter of the
Massive MIMO research saga has come to an end, while the story has just begun.
The coming wide-scale deployment of BSs with massive antenna arrays opens the
door to a brand new world where spatial processing capabilities are
omnipresent. In addition to mobile broadband services, the antennas can be used
for other communication applications, such as low-power machine-type or
ultra-reliable communications, as well as non-communication applications such
as radar, sensing and positioning. We outline five new Massive MIMO related
research directions: Extremely large aperture arrays, Holographic Massive MIMO,
Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive
MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin
Channel Fading Statistics For Real-Time Data Transmission In Emergency Call Systems And Unmanned Aerial Systems
The Third Generation Partnership Project (3GPP) selected an in-band modem to transmit emergency data over cellular voice channel for the European Union emergency call (eCall) system. However, the road test results presented by the Harmonized eCall European Pilot project showed that the success rate of data delivery was only 71%, indicating that there is significant potential to improve its performance.
In this dissertation, a testbed is designed for the eCall system that satisfies the 3GPP TS 26.267/268/269 standards. A method is proposed to measure the power of the received signal that passes through the in-band channel. Experiments are performed with the in-vehicle system testbed in a laboratory or a car travelling in city, suburb, country- side, or freeway. Fading statistics of the received signal after power control are found and discussed, together with cumulative distribution function (CDF), level crossing rate (LCR), and average fade duration (AFD). It is found that with probability less than or equal to 0.1%, fading and attenuation can vary from -19 dB for the continuous wave (CW) signal at 500 Hz to -9.5 dB for the CW signal at 2000 Hz. This dissertation recommends moving the CW signals at 500 Hz and 800 Hz for detection and synchronization in the 3GPP standard to 1500 Hz and 2000 Hz, respectively. This will give 9.5 dB improvement in detection and synchronization.
The fading results are used to calculate the bit error rate (BER) performance for the eCall in-band modem. Synchronization detection probability are obtained by transmitting the synchronization preamble through various adaptive multi-rate vocoders and an additive white Gaussian noise channel.
The testbed and proposed method are also used to measure the power of signals received by an unmanned aerial systems (UAS) and by the receiver in the operation center, respectively. Field experiments are carried out by flying the UAS above different locations. Statistics, including CDF, LCR, and AFD, are calculated for the six test-sites. The results of the fading statistics, synchronization detection probability, and BER can be directly applied to design real-time communication systems, including detection, delay estimation, modulation and coding
Motor learning in children with hemiplegic cerebral palsy : feedback effects on skill acquisition
Purpose. Augmented feedback is an important variable influencing motor learning. Previous studies show reduced feedback frequency benefits motor learning in young adults more than a comparison group of children, who benefit from frequent feedback during practice. It is unclear how motor and central nervous system differences in children with cerebral palsy may impact their use of feedback in motor skill acquisition. This study investigated the effect of augmented visual feedback (FB) on performance and learning of an upper extremity motor skill in children with spastic hemiplegic cerebral palsy (SHCP) as they practiced with their less affected arm, compared to typically developing children (TDC). Methods. Participants were 8-17 years with academic performance within two grade levels. Both TDC (n = 20) and participants with SHCP (n = 19) were screened for visual perception (MVPT-3) and manual dexterity (Box and Block). Children were divided into groups receiving frequent FB (100%) or faded FB (62%). Group differences for acquisition, retention, and reacquisition were compared in relation to FB level. Results. Both groups of children used visual FB to improve motor performance during skill practice. All children receiving 62% FB performed with greater error than children receiving 100% FB during the acquisition phase (p =.012), delayed retention no-feedback test (p =.017), and reacquisition phase (p =.042). Children with SHCP in both FB groups performed with significantly greater error than TDC during the entire acquisition phase (p \u3c .001), delayed retention no-feedback test (p = .031) and reacquisition phase (p = .001). While no significant within group feedback effect was found for children with SHCP, there was a trend for greater accuracy in the 100% group as compared to the 62% group during acquisition (p =.092) and this trend was seen again during reacquisition when FB was reintroduced (p =.092). Conclusions. Results suggest that for children with SHCP skill acquisition is furthered by visual FB regarding their movement accuracy. Children with SHCP use visual FB in a manner similar to TDC, although differences in learning were evident during the acquisition, delayed retention, and reacquisition phases. Further investigation is needed to determine clinical implications
Tax morale, eastern Europe and European enlargement
This study tries to remedy the current lack of tax compliance research analyzing tax morale in 10 Eastern European countries that joined the European Union in 2004 or 2007. By exploring tax morale differences between 1999 and 2008, it shows that tax morale has decreased in 7 out of 10 Eastern European countries. This lack of sustainability may support the incentive based conditionality hypothesis that the European Union only has a limited ability to influence tax morale over time. The author observes that events and processes at the country level are crucial to understanding tax morale. Factors such as perceived government quality and trust in the justice system and the government are positively correlated with tax morale in 2008.Taxation&Subsidies,Debt Markets,Subnational Economic Development,Emerging Markets,National Governance
External Economic Costs of Intelligent Urban Transportation Systems: A Method to Evaluate the Externalities of Comparative Technology Adoption Pathways in the Urban Mobility Service sector
By 2050, urban mobility demands will increase to 2.6 times the current level, even faster than the urban population growth. Current urban transportation plans fail to address these rapidly increasing urban mobility demands. Inefficient urban transportation generates great economic losses in traffic congestion, air pollution and climate change. The current urban transportation pressure and emerging technology-driven trends have revolutionized how industry players respond to changing consumer behavior, develop partnerships, and drive transformational changes. A transition (P2S) from current product-based competition to a marketplace focused on mobility services is expected. Electric vehicles, automated driving systems and mobility-sharing platforms are introduced to provide mobility services by market-agents in the P2S transition. The adoption of these technologies has proven to be beneficial in simulations. In reality, externalities occur when introducing disruptive technologies into a marketplace with the absence of instrumental institutions (non-market agents). However, all agents fail to evaluate the economic impacts of different technology adoption pathways at the mass-adoption scale. The method proposed in this research contains: (1) a resource-demand view framework to capture multiple technology adoption pathways in the P2S transition (2) scenario designs that integrate electric vehicle technology, automated driving systems, and mobility sharing platforms in one or several combinations (3) a set of economic externality models to evaluate the costs of traffic congestion, human health impact, and climate change resulting from each variation. This dissertation is an informative comparative study that demonstrates the externalities (social economic impacts) of different sets of technology adoptions in urban mobility. Regulators can utilize the method while funding research and designing regulations for disruptive automotive technologies. The method also provides a platform for market-agents to quantify the economic impact of new product designs in the mobility marketplace
The State and Future of Autonomous Vehicle Regulation in the United States
Autonomous vehicle technology is poised to revolutionize transit around the world. There are currently tens of private companies either testing or building autonomous vehicles, including industry juggernauts like Ford and Google. This new mode of transportation falls into a regulatory grey area. Once cars reach full autonomy, governments will have to decide what entities will regulate them, where they will be allowed to drive, who will be responsible for them and a host of other issues. In some municipalities like San Francisco and Phoenix, autonomous vehicles (AVs) are being tested on public streets in real life conditions. Meanwhile, in 2017, 33 US states have released frameworks on how they believe AVs should operate in real world environments. There is broad consensus that AVs should be programmed to prioritize safety, but the details in each plan vary to accommodate the specific circumstances of different localities.
If AVs are indeed inevitable as urban planners and futurists believe they are, then we must completely rethink the way vehicles use the road. The introduction of autonomous vehicles could bring massive reductions in greenhouse emissions, more efficient land use due to the elimination of parking structures, less traffic, safer roads, and other benefits.
Without proper forethought and planning however, business as usual automotive policy could create impenetrable walls of autonomous vehicles on cities in highways for elite drivers and limit transit options for everyone else.
Examining existing US federal and state law has shown that the burden of regulating future autonomous vehicles is on the states. Some states already have regulations concerning the testing of autonomous vehicles on the books. The US federal government plays an advisory role only. Guided by best practice principles ratified at the Kaohsiung conference, states should develop frameworks to encourage and regulate autonomous vehicle testing to make sure that it is safe and accountable
Legal Origin, Juridical Form and Industrialisation in Historical Perspective: The Case of the Employment Contract and the Joint-Stock Company
The timing and nature of industrialization in Britain and continental Europe had significant consequences for the growth and development of labour market institutions, effects which are still felt today and which are visible in the conceptual structure of labour law and company law in different countries. However, contrary to the claims of the legal origin hypothesis, a liberal model of contract was more influential in the civilian systems of the continent than in the English common law, where the consequences of early industrialization included the lingering influence of master-servant legislation and the weak institutionalization of the juridical form of the contract of employment. Claims for a strong-form legal origin effect, which is time invariant and resistant to pressures for legal convergence, are not borne out by a growing body of historical evidence and time-series data. The idea that legal cultures can influence the long-run path of economic development is worthy of closer empirical investigation but it is premature to use legal origin theory as a basis for policy initiatives.varieties of capitalism; legal origin; labour law; company law; corporate governance
Legal Origin, Juridical Form and Industrialisation in Historical Perspective: The Case of the Employment Contract and the Joint-Stock Company
The timing and nature of industrialization in Britain and continental Europe had significant consequences for the growth and development of labour market institutions, effects which are still felt today and which are visible in the conceptual structure of labour law and company law in different countries. However, contrary to the claims of the legal origin hypothesis, a liberal model of contract was more influential in the civilian systems of the continent than in the English common law, where the consequences of early industrialization included the lingering influence of master-servant legislation and the weak institutionalization of the juridical form of the contract of employment. Claims for a strong-form legal origin effect, which is time invariant and resistant to pressures for legal convergence, are not borne out by a growing body of historical evidence and time-series data. The idea that legal cultures can influence the long-run path of economic development is worthy of closer empirical investigation but it is premature to use legal origin theory as a basis for policy initiatives.capitalism, varieties of; financial markets; industrial relations; institutional complementarity; labour law; labour market institutions; corporate governance
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