892 research outputs found
Does Massive MIMO Fail in Ricean Channels?
Massive multiple-input multiple-output (MIMO) is now making its way to the
standardization exercise of future 5G networks. Yet, there are still
fundamental questions pertaining to the robustness of massive MIMO against
physically detrimental propagation conditions. On these grounds, we identify
scenarios under which massive MIMO can potentially fail in Ricean channels, and
characterize them physically, as well as, mathematically. Our analysis extends
and generalizes a stream of recent papers on this topic and articulates
emphatically that such harmful scenarios in Ricean fading conditions are
unlikely and can be compensated using any standard scheduling scheme. This
implies that massive MIMO is intrinsically effective at combating interuser
interference and, if needed, can avail of the base-station scheduler for
further robustness.Comment: IEEE Wireless Communications Letters, accepte
Uplink Analysis of Large MU-MIMO Systems With Space-Constrained Arrays in Ricean Fading
Closed-form approximations to the expected per-terminal
signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral
efficiency of a large multiuser multiple-input multiple-output system are
presented. Our analysis assumes correlated Ricean fading with maximum ratio
combining on the uplink, where the base station (BS) is equipped with a uniform
linear array (ULA) with physical size restrictions. Unlike previous studies,
our model caters for the presence of unequal correlation matrices and unequal
Rice factors for each terminal. As the number of BS antennas grows without
bound, with a finite number of terminals, we derive the limiting expected
per-terminal SINR and ergodic sum spectral efficiency of the system. Our
findings suggest that with restrictions on the size of the ULA, the expected
SINR saturates with increasing operating signal-to-noise-ratio (SNR) and BS
antennas. Whilst unequal correlation matrices result in higher performance, the
presence of strong line-of-sight (LoS) has an opposite effect. Our analysis
accommodates changes in system dimensions, SNR, LoS levels, spatial correlation
levels and variations in fixed physical spacings of the BS array.Comment: 7 pages, 3 figures, accepted for publication in the proceedings of
IEEE ICC, to be held in Paris, France, May 201
Impact of Line-of-Sight and Unequal Spatial Correlation on Uplink MU-MIMO Systems
Closed-form approximations of the expected per-terminal
signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral
efficiency of a multiuser multiple-input multiple-output system are presented.
Our analysis assumes spatially correlated Ricean fading channels with
maximum-ratio combining on the uplink. Unlike previous studies, our model
accounts for the presence of unequal correlation matrices, unequal Rice
factors, as well as unequal link gains to each terminal. The derived
approximations lend themselves to useful insights, special cases and
demonstrate the aggregate impact of line-of-sight (LoS) and unequal correlation
matrices. Numerical results show that while unequal correlation matrices
enhance the expected SINR and ergodic sum spectral efficiency, the presence of
strong LoS has an opposite effect. Our approximations are general and remain
insensitive to changes in the system dimensions, signal-to-noise-ratios, LoS
levels and unequal correlation levels.Comment: 4 pages, 2 figures, accepted for publication in the IEEE Wireless
Communications Letters, Vol. 6, 201
Repeating Spatial-Temporal Motifs of CA3 Activity Dependent on Engineered Inputs from Dentate Gyrus Neurons in Live Hippocampal Networks.
Anatomical and behavioral studies, and in vivo and slice electrophysiology of the hippocampus suggest specific functions of the dentate gyrus (DG) and the CA3 subregions, but the underlying activity dynamics and repeatability of information processing remains poorly understood. To approach this problem, we engineered separate living networks of the DG and CA3 neurons that develop connections through 51 tunnels for axonal communication. Growing these networks on top of an electrode array enabled us to determine whether the subregion dynamics were separable and repeatable. We found spontaneous development of polarized propagation of 80% of the activity in the native direction from DG to CA3 and different spike and burst dynamics for these subregions. Spatial-temporal differences emerged when the relationships of target CA3 activity were categorized with to the number and timing of inputs from the apposing network. Compared to times of CA3 activity when there was no recorded tunnel input, DG input led to CA3 activity bursts that were 7× more frequent, increased in amplitude and extended in temporal envelope. Logistic regression indicated that a high number of tunnel inputs predict CA3 activity with 90% sensitivity and 70% specificity. Compared to no tunnel input, patterns of >80% tunnel inputs from DG specified different patterns of first-to-fire neurons in the CA3 target well. Clustering dendrograms revealed repeating motifs of three or more patterns at up to 17 sites in CA3 that were importantly associated with specific spatial-temporal patterns of tunnel activity. The number of these motifs recorded in 3 min was significantly higher than shuffled spike activity and not seen above chance in control networks in which CA3 was apposed to CA3 or DG to DG. Together, these results demonstrate spontaneous input-dependent repeatable coding of distributed activity in CA3 networks driven by engineered inputs from DG networks. These functional configurations at measured times of activation (motifs) emerge from anatomically accurate feed-forward connections from DG through tunnels to CA3
Incorporating Environmentally Compliant Manure Nutrient Disposal Costs into Least-Cost Livestock Ration Formulation
Livestock rations are formulated to minimize feed cost subject to nutritional requirements for a target performance level, which ignores the potentially substantial cost of disposing of nutrients fed in excess of nutritional requirements. We incorporate nutrient disposal costs into a modified least-cost ration formulation model to arrive at a joint least-cost decision that minimizes the sum of feed and net nutrient disposal costs. The method is demonstrated with phosphorus disposal costs on a representative dairy farm. Herd size, land availability and proximity, crop rotation, and initial soil phosphorus content are shown to be important in determining phosphorus disposal costs.environmental compliance, linear programming, livestock rations, manure disposal, Agribusiness, Environmental Economics and Policy, Livestock Production/Industries, C61, Q12, Q52,
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Chylous Leak During Posterior Approach to Juvenile Scoliosis Surgery: A Case Report.
CaseWe report the first documented case of chylous leak recognized intraoperatively during posterior spinal instrumentation and fusion for juvenile scoliosis in a female patient with a history of thoracotomy and decortication for an empyema.ConclusionsThoracic duct injury can lead to severe morbidity and mortality because of chylothorax formation. Although chylous leaks are a well-documented complication of the anterior approach to spine surgery, leaks during the posterior approach are rarely reported. When these chylous leaks are recognized intraoperatively, the likelihood of serious complications may be minimized by drain placement before closure
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