Learning disabilities: description, diagnosis or explanation?

This article explores the semantics of the term, learning disabilities. As currently used, the term often tends to reflect the professional and/or personal interest of the user rather than a concern for the respect and treatment of the child so labeled. The authors suggest that if the field were re-oriented toward learning how to teach these children, it could, perhaps, evolve as an instructional discipline with more tangible benefits for the children, their teachers and their parents

Topology-Aware Space-Time Network Coding in Cellular Networks

Space-time network coding (STNC) is a time-division multiple access (TDMA)-based scheme that combines network coding and space-time coding by allowing relay nodes to combine the information received from different source nodes during the transmission phase and to forward the combined signal to a destination node in the relaying phase. However, STNC schemes require all the relay nodes to overhear the signals transmitted from all the source nodes in the network. They also require a large number of timeslots to achieve full diversity in a multipoint-to-multipoint transmission. Both conditions are particularly challenging for large cellular networks where, assuming a downlink transmission, base stations (BSs) and users only overhear a subset of all the BSs. In this paper, we exploit basic knowledge of the network topology in order to reduce the number of time-slots by allowing simultaneous transmissions from those BSs that do not overhear each other. Our results show that these topology-aware schemes are able to increase the spectral efficiency per time-slot and bit error rate with unequal transmit power and channel conditions

Can the Use of Reconfigurable Antennas Overcome the CSI Bottleneck for FDD Massive MIMO?

Massive MIMO has been proposed as a means of achieving huge spectral efficiency in cellular networks. However, its implementation is usually based on linear precoding schemes using Channel State Information (CSI). For this reason, the use of the Time Division Duplex (TDD) mode is typically assumed since it removes the dependence on the number of antennas at the transmitter to acquire CSI. Unfortunately, most of the cellular network operate in the Frequency Division Duplex (FDD) mode in which the acquisition of CSI depends proportionally to the number of transmit antennas. For this reason, the implementation of Massive MIMO is handicapped to few transmit antennas for the current cellular networks. In this paper we study the use of reconfigurable antennas that can switch among a set of preset modes, i.e., radiation patterns, through Blind Interference Alignment schemes. We show that it is a solution to exploit a very large number of antennas at the transmit side, overcoming the bottleneck that today constitutes the acquisition of CSI in Massive MIMO systems operating in FDD mode

Topology-aware space-time network coding

Space-Time Network Coding (STNC) is a time division multiple access (TDMA)-based scheme that combines network coding and space-time coding by allowing relays to combine the information received from different sources during the transmission phase and to forward the combined signal to a destination in the relaying phase. However, STNC schemes require all the relays to overhear the signal transmitted from all the sources in the network and also a large number of time-slots to achieve full diversity in a multipoint-to-multipoint transmission, which is particularly challenging for large cellular networks. In this paper, we exploit a basic knowledge of the network topology, i.e. the knowledge of the base stations overheard by other base stations and users, to reduce drastically the number of time-slots. Our results show that our scheme is able to increase the spectral efficiency with a marginal decrease of the spatial diversity compared to traditional STNC