Some results of a radon survey in 207 Serbian schools

In this paper the results of radon concentration measurements performed in 207 schools in 7 communities of Southern Serbia are presented. The annual radon concentration varied from 17 Bqm-3 to 428 Bq m-3 with a median value of 96 Bq m-3. The arithmetic mean (AM) of the 207 annual averages was 118 Bq m-3 with a standard deviation (SD) of 78 Bq m-3. The best distribution fitting of radon concentration by log-normal function was obtained. The log-normal parameters are the following: geometric mean (GM) = Bq m-3, geometric standard deviation (GSD) = 1.9. In addition, a spatial distribution of the indoor radon concentration over the investigated areas is observed.JRC.E.8-Nuclear securit

Co-Creating Knowledge Work Automation Content

A number of trends undoubtedly show that what is today known as knowledge work will significantly change in the future. Stable employment will be increasingly a thing of the past. Employees will work in freelance mode, on a small piece of a bigger project, on their own time and with tools of their own choice. Yet they will have to smoothly cooperate and build and use organizational knowledge together. Knowledge will have “legs” and employees will have to make sure they are re-employable after every gig. Organizations will have to be increasingly agile and at the same time provide meaningful employee experiences in order to attract customers and talent. Automation will have a major effect on improving productivity and releasing time for more creative work. At the same it will also come with threat of loosing control to robots. The objective of this thesis was 1) to explore possibilities behind the automation of knowledge work, 2) make a contribution towards reducing negative effects associated with it and 3) turn it to a knowledge worker’s own advantage. By using a rich set of Service Design techniques a service business model has been proposed to meet the needs of the future agile organization, atomization of knowledge work, knowledge sharing between people and robots, bridging the gap between employees and their tools and putting the knowledge worker in control. The business model has been made around co-creation of reusable, atomic automation content. A hypothesis has been made that a digital knowledge worker, a.k.a. software robot, when smoothly embedded within the proposed business model, can significantly empower a human knowledge worker instead of simply being a threat. The above hypothesis was first validated by means of business simulations. It was shown that by carefully balancing investments between new business opportunities, manual- as well as digital workforce the ecosystem behind the proposed service can thrive and create value for all stake-holders. Furthermore, the business model has been validated by conducting interviews with the key stakeholders. It was confirmed that reusable, atomic automation content would bring value. It was concluded that automation has to be two-directional (human-robot-human) in order to ultimately bring value, enable learning and not harm innovation. It was also identified that creating such content is not easy, and requires special skill. This only confirms the need for the proposed service. Based on the results of validation, the proposed service model has been adjusted to better serve the real customer needs. Possible future research directions are laid out as well

Iterative receivers for interference cancellation and suppression in wireless communications

Abstract The performance of conventional receivers for wireless communications may severely deteriorate in the presence of unaccounted interference. The effectiveness of methods for mitigating these effects greatly depends on the knowledge that is available about the interference and signal-of-interest (SOI), therefore making the design of robust receivers a great challenge. This thesis focuses on receiver structures for channel coded systems that exploit different levels of knowledge about the SOI and interference in an iterative fashion. This achieves both robustness and overall performance improvement compared to non-iterative receivers. Code division multiple access (CDMA) and spatial division multiple access (SDMA) systems are considered. The overlay of a turbo coded direct-sequence spread-spectrum (DS-SS) system and strong digitally modulated tone interference is studied. An iterative receiver, which is capable of blind cancellation of both wideband and narrowband interference is proposed based on the adaptive self-reconfigurable -filter scheme. Asymptotic performance analysis of the iterative receiver shows that significant iteration gains are possible if the signal-to-interference-plus-noise-ratio (SINR) is relatively large and the processing gain (PG) of the SOI is relatively small. Robust diversity detection in turbo-coded DS-SS system with statistically modeled interference is studied. A non-parametric type-based iterative receiver that estimates the probability density function (PDF) of interference-plus-noise is proposed. Its performance is shown to be rather robust to the number of interferers and their distances from the victim receiver and very similar to the performance of a clairvoyant receiver. Amazingly, this is achievable with no prior knowledge about the interference parameters. Furthermore, iteration gain is shown to significantly reduce the length of the pilot sequence needed for the PDF estimation. A family of iterative minimum-mean-squared-error (MMSE) and maximum-likelihood (ML) receivers for convolutionally and space-time coded SDMA systems is proposed. Joint iterative multiuser-detection (MUD), equalization and interference suppression are proposed to jointly combat co-channel interference (CCI), inter-symbol-interference (ISI) and unknown CCI (UCCI) in broadband single-carrier systems. It is shown that both in convolutional and space-time coded systems the ISI and CCI interference can be completely eliminated if UCCI is absent. This is achievable with a number of receive antennas equal to the number of users of interest and not to the total number of transmit antennas. In case UCCI is present, the effectiveness of CCI and ISI cancellation and UCCI suppression depends on the effective degrees of freedom of the receiver. Receiver robustness can be significantly preserved by using hybrid MMSE/ML detection for the signals of interest, or by using estimation of the PDF of the UCCI-plus-noise. A low complexity hybrid MMSE/ML iterative receiver for SDMA is proposed. It is shown that its performance is not significantly degraded compared to the optimal ML receiver. Its sensitivity to spatial correlation and a timing offset is assessed by using field measurement data. It was shown that the hybrid MMSE/ML receiver is robust against spatial correlation. The sensitivity to the timing offset is significantly reduced if the receiver performs UCCI suppression

Space-time coded turbo equalization and multiuser detection-asymptotic performance analysis in the presence of unknown interference

Turbo MIMO equalization in multiuser space-time-trellis-coded (STTrC) system is considered in this paper. The low complexity MMSE receiver with soft cancellation (SC) is proposed for joint inter-symbol-interference (ISI), known co-channel interference (CCI) and unknown co-channel interference (UCCI) suppression. It is shown that in the multiuser scenario without UCCI the proposed iterative receiver achieves maximum-likelihood (ML) bound on performance of the single user. The number of receive antennas is thereby equal to the number of users and not to the number of transmit antennas. Furthermore, the upper bound on pairwise error probability (PEP) is derived in the presence of UCCI in the asymptotic case of ideal SC. The result shows that the effect of the interference on the diversity and coding gain is very similar to that of the channel correlation at the receiver side. Namely the diversity and coding gain depend on the rank of the inverse of the matrix R of the UCCI

Novel Techniques to Reduce Performance Sensitivity to Spatial Correlation and Timing Offset in Space-Time Coded MIMO Turbo Equalization

Spatial correlation among antenna elements both at transmitter and receiver sides in MIMO communications is known to have a crucial impact on system performances. Another factor that can severely degrade receiver performances is the timing offset relative to the channel delay profile. In this paper we derive a novel receiver for turbo MIMO equalization in space-time-trellis-coded (STTrC) system to jointly address the problems described above. The equalizer is based on low complexity MMSE filtering. A joint detection technique of the several transmit antennas is used to reduce the receiver's sensitivity to the spatial correlation at the transmitter and receiver sides. Furthermore, only the significant portion of the channel impulse response (CIR) is taken into account while detecting signals. The remaining portion of CIR is regarded as the unknown interference which is effectively suppressed by estimating its covariance matrix. By doing this the receiver's complexity can be reduced since only a portion of the CIR has to be estimated and used for signal detection. Furthermore, by suppressing the interference from the other paths outside the equalizers coverage the receiver's sensitivity to the timing offset can be reduced. The proposed receiver's performance is evaluated using field measurement data obtained through multidimensional channel sounding. It is verified through computer simulations that the performance sensitivity of the joint detection-based receiver to the spatial correlation is significantly lower than with the receiver that detects only one antenna at a time. Furthermore, the performance sensitivity to the timing offset of the proposed receiver is shown to be significantly lower than that of the receiver that ignores the existence of the remaining multipath CIR components

Iterative MIMO Turbo Multiuser Detection and Equalization for STTrC-Coded Systems with Unknown Interference

<p>Iterative multiuser detection in a single-carrier broadband multiple-input multiple-output (MIMO) system is studied in this paper. A minimum mean squared error (MMSE) low-complexity multiuser receiver is derived for space-division multiple-access (SDMA) space-time trellis-coded (STTrC) systems in frequency-selective fading channels. The receiver uses MMSE filtering to jointly detect several transmit antennas of the user of interest, while the interference from the undetected transmit antennas, cochannel interference (CCI), and intersymbol interference (ISI) are all cancelled by the soft cancellation. The performances of two extreme receiver cases are evaluated. In the first case, only one transmit antenna of the user of interest is detected at a time and the remaining ones are cancelled by soft cancellation. In the second case, all the transmit antennas are detected jointly. The comparison of the two cases shows improvement with the latter one, both in single-user and multiuser communications and in the presence of unknown cochannel interference (UCCI). It is further shown that in the multiuser case, the proposed receivers approach the corresponding single-user bounds. The number of receive antenna elements required to achieve single-user bound is thereby equal to the number of users and not to the total number of transmit antennas.</p

Iterative MIMO Turbo Multiuser Detection and Equalization for STTrC-Coded Systems with Unknown Interference

Iterative multiuser detection in a single-carrier broadband multiple-input multiple-output (MIMO) system is studied in this paper. A minimum mean squared error (MMSE) low-complexity multiuser receiver is derived for space-division multiple-access (SDMA) space-time trellis-coded (STTrC) systems in frequency-selective fading channels. The receiver uses MMSE filtering to jointly detect several transmit antennas of the user of interest, while the interference from the undetected transmit antennas, cochannel interference (CCI), and intersymbol interference (ISI) are all cancelled by the soft cancellation. The performances of two extreme receiver cases are evaluated. In the first case, only one transmit antenna of the user of interest is detected at a time and the remaining ones are cancelled by soft cancellation. In the second case, all the transmit antennas are detected jointly. The comparison of the two cases shows improvement with the latter one, both in single-user and multiuser communications and in the presence of unknown cochannel interference (UCCI). It is further shown that in the multiuser case, the proposed receivers approach the corresponding single-user bounds. The number of receive antenna elements required to achieve single-user bound is thereby equal to the number of users and not to the total number of transmit antennas.</p

A PDF Estimation-Based Iterative MIMO Signal Detection With Unknown Interference

The equivalent diversity order of iterative minimum mean squared error (MMSE) multiuser detectors for multiple input multiple output (MIMO) channels is decreased if they aim at suppressing unknown cochannel interference (UCCI) while detecting multiple users' signals. In this letter, we propose a new MIMO signal detection scheme with the aim to preserve the detector's diversity order by estimating the probability density function of the UCCI plus background noise. It is shown that the proposed detector significantly outperforms the conventional detector based on UCCI's covariance matrix estimation

Iterative PDF Estimation-Based Multiuser Diversity Detection and Channel Estimation with Unknown Interference

The equivalent diversity order of multiuser detector employing multiple receive antennas and minimum mean squared error (MMSE) processing for frequency-selective channels is decreased if it aims at suppressing unknown cochannel interference (UCCI) while detecting multiple users' signals. This is an unavoidable consequence of linear processing at the receiver. In this paper, we propose a new multiuser signal detection scheme with the aim to preserve the detector's diversity order by taking into account the structure of the UCCI. We use the fact that the structure of the UCCI appears in the probability density function (PDF) of the UCCI plus noise, which can be characterized as multimodal Gaussian. A kernel smoothing PDF estimation based receiver is derived. The PDF estimation can be based on training symbols only (noniterative PDF estimation) or on training symbols as well as feedback from the decoder (iterative PDF estimation). It is verified through simulations that the proposed receiver significantly outperforms the conventional covariance estimation in channels with low frequency selectivity. The iterative PDF estimation significantly outperforms the noniterative PDF estimation-based receiver with minor training overhead