Hyunhee Park

Performance analysis for contention adaptation of M2M devices with directional antennas

In the directional carrier sense multiple access-collision avoidance (directional-CSMA-CA) mechanism, the efficient channel access mechanism with a collision-controlled concept is one of the most challenging topics. Especially, in capillary machine-to-machine (M2M) where wireless personal area network (WPAN) is a key technology for its wireless connectivity, a contention-based medium access control (MAC) protocol is crucial to enable numerous M2M devices to concurrently access the channel. This paper presents an analytical model for the slotted directional-CSMA-CA mechanism of 802.15.3c networks under saturated environment. By presenting a multi-class approach of directional-CSMA-CA mechanism to reduce collision occurrences, we support an adaptive back-off exponent of M2M device on the required frame payload size. For the mathematical analysis, the discrete-time Markov chain model is applied with the features of PHY/MAC of millimeter Wave (mm-Wave) network and the effects of directional antennas. In addition, extensive simulations are performed to verify the analytical model. The obtained results of the analytic and simulation show that the collision probability of M2M device is reduced by differentially adapting the contention rate to each M2M device, and the fairness property can be improved because there are remarkable increases of opportunities to transmit short-frame payloads.

Modern trends in Class III orthognathic treatment: A time series analysis

OBJECTIVEnTo examine the current trends in surgical-orthodontic treatment for patients with Class III malocclusion using time-series analysis.nnnMATERIALS AND METHODSnThe records of 2994 consecutive patients who underwent orthognathic surgery from January 1, 2004, through December 31, 2015, at Seoul National University Dental Hospital, Seoul, Korea, were reviewed. Clinical data from each surgical and orthodontic treatment record included patients sex, age at the time of surgery, malocclusion classification, type of orthognathic surgical procedure, place where the orthodontic treatment was performed, orthodontic treatment modality, and time elapsed for pre- and postoperative orthodontic treatment.nnnRESULTSnOut of the orthognathic surgery patients, 86% had Class III malocclusion. Among them, two-jaw surgeries have become by far the most common orthognathic surgical treatment these days. The age at the time of surgery and the number of new patients had seasonal variations, which demonstrated opposing patterns. There was neither positive nor negative correlation between pre- and postoperative orthodontic treatment time. Elapsed orthodontic treatment time for both before and after Class III orthognathic surgeries has been decreasing over the years.nnnCONCLUSIONnResults of the time series analysis might provide clinicians with some insights into current surgical and orthodontic management.

Location-oriented multiplexing transmission for capillary machine-to-machine systems

This paper presents a location-oriented multiplexing transmission (LOT) strategy for use with a capillary machine-to-machine (M2M) system based on a millimeter wave (mmWave) wireless personal area network (WPAN). Omni-directional or directional antennas are used depending on the multicast groups and the data rate that is achievable in order to maximize the normalized throughput. Specifically, the devices that are closer to the access point (AP) are served with a high-rate omni-directional antenna. In contrast, devices that are distant to the AP are treated with a high-rate directional-antenna. We exploit the optimal transmission strategy with sum rate maximization to show that the normalized throughput can be maximized. The IEEE 802.15.3c WPAN standard is used to demonstrate that the LOT strategy improves the normalized throughput by 39–62xa0% relative to other multicast schemes.