Target Wake Time Scheduling Strategies for Uplink Transmission in IEEE 802.11ax Networks

Target wake time (TWT) has been introduced to provide the low power consumption mode for stations (STAs) with low traffic and periodic data transmissions in IEEE 802.11ax networks. The TWT operation starts with negotiating wake and doze periods between an access point (AP) and STAs. Thanks to the nature of wake and doze period negotiation, TWT operation enables time scheduled access, like time-division multiple access (TDMA) without modification overhead. In this paper, we demonstrate TWT scheduling issues that include scheduling requirements and results notifications from the AP to STAs, using standard-compliant methods. Then we establish TWT scheduling strategies by exemplifying two well-known schedulers, max-rate and proportional fairness schedulers. Through ns-3 simulation, we evaluate the performance of TWT scheduling and highlight the benefits of TWT for a large number of STAs from the fairness and power consumption perspective.N

Complementarity among Alternative Procurement Arrangements in the Pork Packing Industry

We estimate the economies of scale for a sample of pork packing plants and use these estimates together with two other performance measures (EBIT and gross margin) to examine whether the alternative procurement methods for live hogs are complementary. The results indicate that all procurement arrangements portfolios improve plant performance relative to the simple spot market purchases, but the portfolio coefficients in performance equations do not always monotonically increase with the portfolio order. However, looking at the price packers pay to procure their hogs, the results indicate that plants that use a combination of higher-order procurement arrangements on average pay lower prices relative to plants that use the spot market only. Comparing the magnitudes of the portfolio effects with the magnitudes of the individual procurement arrangement effects shows that individual practices have minimal additional impact on the procurement price, indicating that the procurement methods may be complementary.

Development and Quantitative Performance Evaluation of a Noninvasive EMG Computer Interface

This paper describes a noninvasive electromyography (EMG) signal-based computer interface and a performance evaluation method based on Fitts' law. The EMG signals induced by volitional wrist movements were acquired from four sites in the lower arm to extract users' intentions, and six classes of wrist movements were distinguished using an artificial neural network. Using the developed interface, a user can move the cursor, click buttons, and type text on a computer. The test setup was built to evaluate the developed interface, and the mouse was tested by five volunteers with intact limbs. The performance of the developed computer interface and the mouse was tested at 1.299 and 7.733 b/s, respectively, and these results were compared with the performance of a commercial noninvasive brain signal interface (0.386 b/s). The results show that the developed interface performed better than the commercial interface, but less satisfactorily than a computer mouse. Although some issues remain to be resolved, the developed EMG interface has the potential to help people with motor disabilities to access computers and Internet environments in a natural and intuitive manner

Graphic and haptic modeling of the oesophagus for VR-Based medical simulation

Abstract Background Medical simulators with vision and haptic feedback have been applied to many medical procedures in recent years, due to their safe and repetitive nature for training. Among the many technical components of the simulators, realistic and interactive organ modelling stands out as a key issue for judging the fidelity of the simulation. This paper describes the modelling of an oesophagus for a real-time laparoscopic surgical simulator