Engaging Students in Homework Assignments and Self-Study: A Study Case

This paper discusses teaching and learning activities (TLAs) that foster students’ commitment to homework and self-study. The discussion is illustrated with an exercise class, part of the International Master Programme in Wireless Communications at Lund University. The TLAs favored do not only look after the cognitive state and learning style preferences of the students, but they also take into account the teaching abilities of professors. An incremental approach is advocated for, in which more advanced TLAs are gradually added to the teaching and learning situation as the teacher gains in skills and confidence

Massive MIMO Extensions to the COST 2100 Channel Model: Modeling and Validation

To enable realistic studies of massive multiple-input multiple-output systems, the COST 2100 channel model is extended based on measurements. First, the concept of a base station-side visibility region (BS-VR) is proposed to model the appearance and disappearance of clusters when using a physically-large array. We find that BS-VR lifetimes are exponentially distributed, and that the number of BS-VRs is Poisson distributed with intensity proportional to the sum of the array length and the mean lifetime. Simulations suggest that under certain conditions longer lifetimes can help decorrelating closely-located users. Second, the concept of a multipath component visibility region (MPC-VR) is proposed to model birth-death processes of individual MPCs at the mobile station side. We find that both MPC lifetimes and MPC-VR radii are lognormally distributed. Simulations suggest that unless MPC-VRs are applied the channel condition number is overestimated. Key statistical properties of the proposed extensions, e.g., autocorrelation functions, maximum likelihood estimators, and Cramer-Rao bounds, are derived and analyzed.Comment: Submitted to IEEE Transactions of Wireless Communication

Measurements of Large-Scale Parameters of a Distributed MIMO Antenna System in a Microcell Environment at 2.6 GHz

Multi-site multi-antenna measurements for semiurban microcell environment at 2.6 GHz are performed with four base stations (BSs) and one mobile station (MS). Three BSs are provided with four antenna elements in closely spaced copolarized configuration, and one BS is provided with a single antenna element. The MS is equipped with a cylindrical uniform array consisting of 64 dual-polarized antenna elements and moves along some predefined routes. The values of large-scale fading (LSF) from 19 measurement runs with a total of 1900 snapshots at different locations are extracted. The cross-correlation properties of the LSF between different BS links are analyzed. It was found that, in the selected propagation environment, the influence of the BS location on the LSF cross-correlation properties is negligible. However, the location of the MS has a significant influence on the LSF cross-correlation properties of the different BS links

Massive MIMO Performance - TDD Versus FDD: What Do Measurements Say?

Downlink beamforming in Massive MIMO either relies on uplink pilot measurements - exploiting reciprocity and TDD operation, or on the use of a predetermined grid of beams with user equipments reporting their preferred beams, mostly in FDD operation. Massive MIMO in its originally conceived form uses the first strategy, with uplink pilots, whereas there is currently significant commercial interest in the second, grid-of-beams. It has been analytically shown that in isotropic scattering (independent Rayleigh fading) the first approach outperforms the second. Nevertheless there remains controversy regarding their relative performance in practice. In this contribution, the performances of these two strategies are compared using measured channel data at 2.6 GHz.Comment: Submitted to IEEE Transactions on Wireless Communications, 31/Mar/201

Initial Characterization of Massive Multi-User MIMO Channels at 2.6 GHz in Indoor and Outdoor Environments

The channel properties have a large influence on user separability in massive multi-user multiple-input multiple-output (massive MIMO) systems. In this paper we present spatio-temporal characteristics obtained from massive MIMO channel measurements at 2.6 GHz. The results are based on data acquired in both indoor and outdoor scenarios where a base station equipped with 64 dual-polarized antenna elements communicates simultaneously with nine single-antenna users. In the outdoor scenarios the base station is placed at two rooftops with different heights and the users are confined to a five-meter diameter circle and move rando mly at pedestrian speeds. In the indoor scenarios, the users are located close to each other in a lecture theater and the base station is placed at various locations in the room. We report on the observed distribution of the delay spreads and angular spreads. Furthermore, the multi-user performance in terms of singular value spread of the MU-MIMO channel is also reported. Finally, statistics of the coherence time and coherence bandwidth of the propagation channel in various scenarios are given. The results are important for the design and analysis of massive MU-MIMO systems, as well as in the development of realistic massive MU-MIMO channel models

Channel Hardening in Massive MIMO - A Measurement Based Analysis

Wireless-controlled robots, cars and other critical applications are in need of technologies that offer high reliability and low latency. Massive MIMO, Multiple-Input Multiple-Output, is a key technology for the upcoming 5G systems and is one part of the solution to increase the reliability of wireless systems. More specifically, when increasing the number of base station antennas in a massive MIMO systems the channel variations decrease and the so-called channel hardening effect appears. This means that the variations of the channel gain in time and frequency decrease. In this paper, channel hardening in massive MIMO systems is assessed based on analysis of measurement data. For an indoor scenario, the channels are measured with a 128-port cylindrical array for nine single-antenna users. The analysis shows that in a real scenario a channel hardening of 3.2-4.6 dB, measured as a reduction of the standard deviation of the channel gain, can be expected depending on the amount of user interaction. Also, some practical implications and insights are presented.Comment: Accepted to SPAWC 201

Spatial Separation of Closely-Spaced Users in Measured Massive Multi-User MIMO Channels

Fully-synchronous measurements of a massive multi-user multiple-input multiple-output (MU-MIMO) radio propagation channel are presented. We evaluate the ability of a massive MIMO system to spatially separate users located close to each other in line-of-sight (LOS) propagation conditions. The system consists of a base-station (BS) antenna array equipped with 64 dual-polarized antenna elements (128 ports) arranged in a cylindrical configuration, and eight single-antenna users. The users are confined to a five-meter diameter circle and move randomly at pedestrian speeds. The BS antenna array is located on top of a 20 m tall building and has LOS to the users. We examine user separability by studying singular value spread of the MU-MIMO channel matrix for several subsets of BS antenna array ports, along with sum-rate capacity and achievable sum-rates with both zero-forcing and matched-filtering linear precoders. We also analyze the performance of the user with the lowest rate. Finally, a comparison between the performance offered by the massive MIMO system and that of a conventional MU-MIMO system is provided. To the best of our knowledge, this is the first report of fully-synchronous dynamic measurements of a massive MIMO system. Our investigation shows that even users located close to each other in LOS propagation conditions can be spatially separated in a massive MIMO system

Parenteral Nutrition: Current Use, Complications, and Nutrition Delivery in Critically Ill Patients

Background: Parenteral nutrition (PN) is needed to avoid the development of malnutrition when enteral nutrition (EN) is not possible. Our main aim was to assess the current use, complications, and nutrition delivery associated with PN administration in adult critically ill patients, especially when used early and as the initial route. We also assessed the differences between patients who received only PN and those in whom EN was initiated after PN (PN-EN). Methods: A multicenter (n = 37) prospective observational study was performed. Patient clinical characteristics, outcomes, and nutrition-related variables were recorded. Statistical differences between subgroups were analyzed accordingly. Results: From the entire population (n = 629), 186 (29.6%) patients received PN as initial nutrition therapy. Of these, 74 patients (11.7%) also received EN during their ICU stay (i.e., PNEN subgroup). PN was administered early (<48 h) in the majority of patients (75.3%; n = 140) and the mean caloric (19.94 +/- 6.72 Kcal/kg/day) and protein (1.01 +/- 0.41 g/kg/day) delivery was similar to other contemporary studies. PN showed similar nutritional delivery when compared with the enteral route. No significant complications were associated with the use of PN. Thirty-two patients (43.3%) presented with EN-related complications in the PN-EN subgroup but received a higher mean protein delivery (0.95 +/- 0.43 vs 1.17 +/- 0.36 g/kg/day; p = 0.03) compared with PN alone. Once adjusted for confounding factors, patients who received PN alone had a lower mean protein intake (hazard ratio (HR): 0.29; 95% confidence interval (CI): 0.18-0.47; p = 0.001), shorter ICU stay (HR: 0.96; 95% CI: 0.91-0.99; p = 0.008), and fewer days on mechanical ventilation (HR: 0.85; 95% CI: 0.81-0.89; p = 0.001) compared with the PN-EN subgroup. Conclusion: The parenteral route may be safe, even when administered early, and may provide adequate nutrition delivery. Additional EN, when possible, may optimize protein requirements, especially in more severe patients who received initial PN and are expected to have longer ICU stays. NCT Registry: 03634943

Estimating the Cross-Correlation Properties of Large-Scale Parameters in Multilink Distributed Antenna Systems : Synchronous Measurements Versus Repeated Measurements

It is essential to capture the cross-correlation properties of large-scale parameters (LSPs) among different base station links in cooperative multilink systems in order to make realistic performance assessments. In this work, propagation measurements are used to study the cross-correlation properties of different LSPs, namely large-scale fading, delay spread, azimuth spread, and elevation spread of four links. The interlink cross-correlation coefficients of these LSPs are assessed based on two different measurement approaches: 1) synchronous measurements, where the values of the LSPs of the considered links are estimated from the same measurement run; and 2) repeated measurements, where the values of the LSPs of the considered links are estimated from different measurement runs. Repeated measurements are attractive because they are simpler and less expensive. In this paper, we address the following question: Can repeated measurements be used instead of synchronous measurements in order to estimate the LSPs' cross-correlation properties of different links? Based on analysis of wideband synchronous and repeated multilink measurements in a suburban microcell environment at 2.6 GHz, we found that: 1) the mean values of the cross-correlation coefficients are preserved with repeated measurements, and 2) the estimates of the cross-correlation coefficients from repeated measurements are less spread around the mean value than those from synchronous measurements. These findings are explained based on detailed investigation of specific measured cases and further supported by results obtained from Monte Carlo simulations