Adaptive antennas at the mobile and base stations in an OFDM/TDMA system

In recent years, several smart antenna systems have been proposed and demonstrated at the base station (BS) of wire-less communications systems, and these have shown that significant system performance improvement is possible. In this paper, we consider the use of adaptive antennas at the BS and mobile stations (MS), operating jointly, in combination with orthogonal frequency-division multiplexing. The advantages of the proposed system includes reductions in average error probability and increases in capacity compared to conventional systems. Multiuser access, in space, time, and through subcarriers, is also possible and expressions for the exact joint optimal antenna weights at the BS and MS under cochannel interference conditions for fading channels are derived. To demonstrate the potential of our proposed system, analytical along with Monte Carlo simulation results are provided

Spread spectrum techniques for indoor wireless IR communications

Multipath dispersion and fluorescent light interference are two major problems in indoor wireless infrared communications systems. Multipath dispersion introduces intersymhol interference at data rates above 10 Mb/s, while fluorescent light induces severe narrowband interference to baseband modulation schemes commonly used such as OOK and PPM. This article reviews the research into the application of direct sequence spread spectrum techniques to ameliorate these key channel impairments without having to resort to complex signal processing techniques. The inherent properties of a spreading sequence are exploited in order to combat the ISI and narrowband interference. In addition, to reduce the impact of these impairments, the DSSS modulation schemes have strived to be bandwidth-efficient and simple to implement. Three main DSSS waveform techniques have been developed and investigated. These are sequence inverse keying, complementary sequence inverse keying, and M-ary biorthogonal keying (MBOK). The operations of the three systems are explained; their performances were evaluated through simulations and experiments for a number of system parameters, including spreading sequence type and length. By comparison with OOK, our results show that SIK, CSIK, and MBOK are effective against multipath dispersion and fluorescent light interference becausc the penalties incurred on the DSSS schemes are between 0-7 dB, while the penalty on OOK in the same environment is more than 17 dB. The DSSS solution for IR wireless transmission demonstrates that a transmission waveform can he designed to remove the key channel impairments in a wireless IR system

Optimizing time and space MIMO antenna system for frequency selective fading channels

Smart or adaptive antennas promise to provide significant increases in system capacity and performance in wireless communication systems. In this paper, we investigate the use of adaptive antennas at the base and mobile stations, operating jointly, to maximize the average signal-to-interference and noise ratio (SINR) of each packet in the system for frequency selective channels with prior knowledge of the channel at the transmitter. Our approach is based on deriving an analytic formula for the average packet SINR and using the Lagrange multiplier method to determine an optimum. We derive necessary conditions for an optimum solution and propose an analytical expression for the optimum. Our analytical expression is not guaranteed to be the global optimum but it does satisfy the derived necessary conditions and, in addition for frequency flat channels, our results reduce to expressions for optimal weights previously published. To demonstrate the potential of the proposed system, we provide Monte Carlo simulation results of the system bit-error rates and make comparisons with other adaptive antenna systems. These show that significant improvements in performance are possible in a wireless communications context

Performance enhancement of multiuser MIMO wireless communication systems

This paper describes a new approach to the problem of enhancing the performance of a multiuser multiple-input-multiple-output (MIMO) system for communication from one base station to many mobile stations in both frequency-flat and frequency-selective fading channels. This problem arises in space-division multiplexing systems with multiple users where many independent signal streams can be transmitted in the same frequency and time slot through the exploitation of multiple antennas at both the base and mobile stations, Our new approach is based on maximizing a lower bound for the product of signal-to-interference plus noise ratio (SINR) of a multiuser MIMO system. This provides a closed-form (noniterative) solution for the antenna weights for all the users, under the constraint of fixed transmit power. Our solution is shown by simulation to have better performance than previously proposed iterative or noniterative solutions. In addition, our solution requires significantly reduced complexity over a gradient search-based method that directly optimizes the product SINgs while still maintaining similar performance. Our solution assumes channel state information is present at the base station or transmitter

‘Can I trust you?’A study of the psychological factors influencing school children’s decision to trust and peer’s perception of their trustworthiness

How children’s trust beliefs in others and how peers determine children’s levels of trustworthiness is the bedrock of all relationships. Yet very little prior research exists on understanding the nature of this relationship and even fewer studies compare across cultures to understand the specificity of potential interventions. Thisstudy addressed these gaps by conductinga set of serial mediation modelsto test the hypothesized causal flow from social mistrustand its subscales (home, school, general mistrust)to anxiety to aggression and to peer-rated untrustworthiness in 2,464 school children aged 8-14 years from the UK (N= 994; M= 11.38 years, female = 45.6%) and Hong Kong (N= 1,470, M = 11.46 years,female = 47.1%). Increased levels of self-reported social mistrust (and its associated subscales) were found to be independently associated with increased untrustworthiness in both countries. Children with high levels of social mistrust, particularly school mistrust, were more likely to have high levels ofanxiety and aggressive behaviors concurrently, which in turn was associated with higher levels of peer-rated untrustworthiness. This explanatory model suggests that future longitudinal intervention studies that aim to reduce aggressive responses from suspicious children may improve peer’s perception of untrustworthiness and childhood relationships with others

UCL-Penn Global Covid Study Webinar Report

The UCL-Penn Global COVID Study examines the short- and longer-term effects of COVID-19 on people's mental health, physical health, and social trust in others. This study consisted of three online surveys of 20-30 minutes long administered at Time 1 (April to July 2020), Time 2 (October - January 2021), and Time 3 (April to July 2021) to participants 18+ years and resident of any country. The survey was available in 7 languages. For more information about study specifics, please visit our OSF page. This summer webinar series sponsored by the UCL Global Engagement Fund featured five themed papers presented by study collaborators and critiqued by leaders and experts in policy, public health, economics, sustainability, aging, and psychology. The latter group of experts were not part of the study and helped inform and provide a more balanced debate on the application of our study findings and completmentary insights on the impacts of COVID-19. All webinar papers will now be peer-reviewed and collated alongside discussant commentaries in an open access COVID special issue as part of the UCL Open: Environment Journal. Webinar recordings can be found on our study website (https://globalcovidstudy.com/events/). This document summarises the webinar series including key take home messages and recommendations as helpfully collated by my research assistants, Kyleigh Melville, Kimberly Loke, and Sammi Lee from the UCL Institute of Education. We hope this document will spark new ideas, conversations, and action. Should you have comments/suggests, please feel free to reach out to us at [email protected]

First look at average-case complexity for planar maximum-likelihood detection

In this paper, an efficient exact maximum-likelihood (ML) detection scheme is presented for a multiple-input singleoutput (MI SO) system with real signal constellations. The proposed technique has a geometrical interpretation of exploring the points jointly "close" in all coordinate axes around the decoding hyperplane and is therefore dubbed planar detection. The fact that the lattice points which are close in all coordinate axes are much less, leads to dramatic reduction in detection complexity. Making a few approximations, this paper derives the average-case complexity exponent, ec, for planar detection analytically in a closed form. Numerical results show that for an (n, 1) 1 system, although the expected complexity is still exponential, complexity reduction of 2 exponents, i.e., from ec to ec - 2, is realized and such advantage is promised irrespective of the size of the signal constellations and the received signal-to-noise ratio (SNR). © 2005 IEEE.published_or_final_versio

A unified game-theoretic framework for discrete power minimization in wireless networks

This paper proposes a unified noncooperative game for discrete power minimization in wireless networks. We prove that the proposed game, with a carefully chosen payoff function, falls into the framework of potential games where pure strategy Nash equilibrium (NE) exists. The feasibility of the pure strategy NE is guaranteed with properly designed penalty functions and penalty factors. It is revealed that the optimal solution to the sum discrete power minimization problem constitutes a pure strategy NE of the proposed game under mild conditions. Also, we prove that the pure strategy NE of the proposed game is also the optimal solution to the sum discrete power minimization problem under some particular conditions. An iterative algorithm is then devised to obtain the pure strategy NE. Two examples which can be solved efficiently by using our framework are also provided

Pixel super-resolution in serial time-encoded amplified microscopy (STEAM)

Paper no. CTu3J.4We propose pixel super-resolution serial time-encoded amplified microscopy (STEAM) for achieves high speed and high-resolution imaging - relaxing the stringent requirement on the digitizer bandwidth while preserving the ultrahigh frame-rate (>MHz). © 2012 OSA.published_or_final_versio

Peer Problems and Low Self-esteem Mediate the Suspicious and Non-suspicious Schizotypy-Reactive Aggression Relationship in Children and Adolescents

The relationship between schizophrenia and violence has been well-established. Yet very little prior research exists on the factors that might explain the nature of this relationship and even fewer studies seek to clarify the etiology of aggressive behavior in adolescents with specific features of schizotypal personality that might help improve the specificity of intervention. The current study tested whether one dimension of schizotypy alone (i.e., the ‘suspicious’ feature) or the other 8 dimensions (i.e., the ‘non-suspicious’ features) were particularly associated with aggressive behaviors (reactive and proactive aggression), and if peer problems and low self-esteem mediated these relationships. A serial multiple mediation model testing the hypothesized flow from suspicious and non-suspicious schizotypy to peer problems to low self-esteem and to increased aggression was tested in Hong Kong schoolchildren aged 8- to 14-years (N = 1412; Mage = 11.47, SD = 1.67 years, female = 47.6%). Increased suspicious and non-suspicious schizotypal features were found to be independently associated with increased reactive aggression, but not proactive aggression. Children with high levels of suspicious schizotypy and non-suspicious schizotypy were more likely to have poor peer problems and low self-esteem concurrently, which in turn was associated with reactive aggression only. This explanatory model suggests that future longitudinal intervention studies that enhance self-esteem in schizotypal adolescents may potentially reduce co-morbid reactive aggressive behaviors too