• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.462-483
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• 2016

The research on optimization of cellular network's energy efficiency (EE) towards environmental and economic sustainability has attracted increasing attention recently. In this survey, we discuss the opportunities, trends and challenges of this challenging topic. Two major contributions are presented namely 1) survey of proposed energy efficiency metrics; 2) survey of proposed energy efficient solutions. We provide a broad overview of the state of-the-art energy efficient methods covering base station (BS) hardware design, network planning and deployment, and network management and operation stages. In order to further understand how EE is assessed and improved through the heterogeneous network (HetNet), BS's energy-awareness and several typical HetNet deployment scenarios such as macrocell-microcell and macrocell-picocell are presented. The analysis of different HetNet deployment scenarios gives insights towards a successful deployment of energy efficient cellular networks.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.8
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• pp.1792-1798
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• 2010

Home Gateway is always on for continuous services of home networks. Ubiquitous home networks are extended. so power consumption of home gateways increases by geometric progression. Our algorithm is for home gateway to sleep, listen or wakeup according to network traffic adaptively, as well as to keep always-on service. To do this, it traces the accumulated average of previous sleep periods. In addition to this basic algorithm, we make the profiles for user's living pattern per the day to reflect network usages in detail and adaptively. As the simulation results by comparing with overall accumulated average and per-day accumulated average, in case of the overall accumulated average, the difference the estimation and real value is distributed from 0.43% to 4%. In contrast of this, in case of the per-day accumulated average is distributed from 0.06% to 2%. From this results, we know the profiling of per-day usage pattern can help reduce the difference of the real sleep period and the estimated sleep period.

• Sleep Medicine and Psychophysiology
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• v.20 no.1
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• pp.35-40
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• 2013

Objectives: The aim of this study is to evaluate the polysomnographic characteristics and prescription status of restless legs syndrome (RLS) patients in naturalistic setting. Methods: We reviewed medical record of the patients over 18 years olds who (i) satisfied the clinical RLS diagnostic criteria and (ii) had the polysomnography and got treatment related thereto. As a baseline, we evaluated the four diagnostic criteria of the International Restless Legs Syndrome Study Group (IRLSSG) and the International Restless Legs Scale (IRLS) of the subjects. Then the polysomnography and the suggested immobilization test (SIT) were conducted and, after one month of pharmacotherapy using dopamine agonist, the IRLS was evaluated again. Results: A total of 211 subjects participated in this analysis and 94 (44.5%) of them were male and the other 117 (55.5%) were female and the average age of the 211 subjects was $46.9{\pm}14.2$. Out of such 211 subjects, 136 subjects (64.5%) also had the obstructive sleep apnea (OSA), and 53 subjects (25.1%) also had the periodic limb movement disorder (PLMD). 185 subjects (87.7%) out of the 211 subjects had some other sleep disorders except RLS. The results of the polysomnography were as follows : 78.0% of sleep efficiency, 86.8 min of wake after sleep onset, and 3.4% of N3. More specifically, 12.4/h of the average apnea hypopnea index, 14.8/h of the periodic limb movement during sleep (PLMS), 41.2/h of the periodic limb movement during wake during SIT and 21.6/h of total arousal index during sleep. Out of the total subjects, 149 (70.6%) of them took the ropinirole and 47 (22.3%) of them took the pramipexole, and the average dosage of ropinirole was 0.9mg(dosage range 0.125-5 mg) while the average dosage of pramipexole was 0.5 mg (dosage range 0.125-4 mg). The dosage of the ropinirole showed a significant positive correlation with the age (r=0.25, p=0.002) and also with the IRLS (r=0.23, p=0.038). The IRLS at the baseline was 24.9 while the same was decreased down to 13.4 after one month. Conclusions: Analyzing the result of this study, a majority of clinical RLS subjects demonstrated comorbidity with some other sleep disorder such as the OSA or PLMD. 25.1% of the subjects showed a PLMD, which was less than in previous researches and the average PLMS was not very high as 14.8/h. The dosage of dopamine agonist taken was often a bit more than the amount recommended in Korea. A prospective research using a large scale controlled subjects will be necessary with respect to this topic.

• Journal of IKEEE
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• v.15 no.2
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• pp.134-142
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• 2011

This paper describes a tripple-mode high-efficiency DC-DC buck converter. The DC-DC buck converter operate in PWM(Pulse Width Modulation) mode at moderate to heavy loads(100mA~500mA), in PFM(Pulse Frequency Modulation)at light loads(1mA~100mA), and in LDO(Low Drop Out) mode at the sleep mode(<1mA). In PFM mode DPSS(Dynamic Partial Shutdown Strategy) is also employed to increase the efficiency at light loads. The triple-mode converter can thus achieve high efficiencies over wide load current range. The proposed DC-DC converter is designed in a CMOS 0.18um technology. It has a maximum power efficiency of 96.4% and maximum output current of 500mA. The input and output voltages are 3.3V and 2.5V, respectively. The chip size is 1.15mm ${\times}$ 1.10mm including pads.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.153-164
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• 2010

In this paper, we propose a multi-channel MAC protocol to improve the channel efficiency and network performance in wireless ad hoc networks. There are two main problems encountered in designing multi-channel MAC protocols. The first problem is the rendezvous problem and the second is multi-channel hidden node problem. In order to solve these problems, most of previous researches that have considered multi-channel MAC protocols use a common control channel to exchange control packets. However, they have a bottleneck problem at common control channel as increasing the number of data channels. The proposed MAC protocol solves the multi-channel hidden node problem using a TDMA scheme and increases the network throughput because transmitting and receiving data at the same time is possible. Also, since there is no common control channel, the network does not suffer from the common control channel saturation problem. Moreover, it achieves energy savings by allowing nodes that are not involved in communication to go into sleep mode. Simulation results show that the proposed MAC protocol improves the network throughput and channel efficiency and provides energy savings.

• Tuberculosis and Respiratory Diseases
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• v.48 no.6
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• pp.956-963
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• 2000

Backgrounds : Obstructive sleep apnea syndrome(OSA) can divided into two groups, positional(PP) and non-positional(NPP) obstructive sleep apnea syndrome, according to the body position while sleeping. In this study, we evaluated the differences of anthropometric data and polysomnographic recordings between the two types of sleep apnea syndrome. Materials : Fifty patients with OSA were divided two groups by Cartwright's criteria. The supine respiratory disturbance index (RDI) was at least two times higher than the lateral RDI in the PP group, and the supine RDI was less than twice the lateral RDI in the NPP group. This patients underwent standardized polysomnographic recordings. The anthropometric data and polysomnographic data were analyzed, statistically. Results : Of all 50 patients, 30% were found to be positional OSA. BMI was significantly higher in the PP group(p<0.05). Total sleep time was significantly longer in the PP group (350.6$\pm$28.2min, 333.3$\pm$46.0min, (p<0.05). Sleep efficiency was high in the PP group(89.6$\pm$6.4%, 85.6$\pm$9.9%, p<0.05). Deep sleep was significantly higher and light sleep was lower in the PP group than in the NPP group but no difference was observed in REM sleep between the two groups. Apnea index(AI) and RDI were significantly lower( 17.0$\pm$10.6, 28.5$\pm$13.3, p<0.05) and mean arterial oxygen saturation was higher in the PP group(92.7$\pm$1.8%. p<0.05) than in the NPP group. Conclusion : Body position during sleep has a profound effect on the frequency and severity of breathing abnormalities in OSA patients. A polysomnographic evaluation for suspected OSA patients must include monitoring of the body position. Breathing function in OSA patients can be improved by controlling their obesity and through postural therapy.

• Journal of Sleep Medicine
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• v.15 no.2
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• pp.37-42
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• 2018

Objectives: To assess the effect and safety of transcranial direct-current stimulation (tDCS) in primary chronic insomnia. Methods: A one-month, double-blind, randomized, sham-controlled trial was performed. A total of 7 patients with primary chronic insomnia received tDCS using anodal (n=3), cathodal (n=2), or sham stimulation (n=2). They were followed up at 1 week and 1 month after treatment. The primary outcome measures included improvement in total sleep time (TST), sleep latency (SL), and sleep efficiency (SE) at 1 month follow-up. Results: TST and SE were improved with tDCS at 1 month follow-up in all patients (100%) of the anodal group, one (50%) of the cathodal group, and one (50%) of the sham group. tDCS improved SL at 1 month follow-up in two patients (67%) of the anodal group, one (50%) of the cathodal group, and none (0%) of the sham group. With respect to adverse events, transient itching sensation occurred in one patient of the anodal group. None of the other groups reported adverse events. Conclusions: Our results suggest that tDCS may be effective and safe for treatment of primary chronic insomnia. A larger controlled study needs to be further investigated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.1
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• pp.105-122
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• 2011

The fundamental design goal of wireless sensor MAC protocols is to minimize unnecessary power consumption of the sensor nodes, because of its stringent resource constraints and ultra-power limitation. In existing MAC protocols in wireless sensor networks (WSNs), duty cycling, in which each node periodically cycles between the active and sleep states, has been introduced to reduce unnecessary energy consumption. Existing MAC schemes, however, use a fixed duty cycling regardless of multi-hop communication and traffic fluctuations. On the other hand, there is a tradeoff between energy efficiency and delay caused by duty cycling mechanism in multi-hop communication and existing MAC approaches only tend to improve energy efficiency with sacrificing data delivery delay. In this paper, we propose two different MAC schemes (ADS-MAC and ELA-MAC) using closed-loop control in order to achieve both energy savings and minimal delay in wireless sensor networks. The two proposed MAC schemes, which are synchronous and asynchronous approaches, respectively, utilize an adaptive timer and a successive preload frame with closed-loop control for adaptive duty cycling. As a result, the analysis and the simulation results show that our schemes outperform existing schemes in terms of energy efficiency and delivery delay.

• Journal of information and communication convergence engineering
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• v.15 no.1
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• pp.62-71
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• 2017

This paper presents a low-power voltage converter based on a reconfigurable capacitor array. Its energy recycling capacitor array stores the energy during a charge stage and supplies the voltage during an energy recycle stage even after the power source is disconnected. The converter reconfigures the capacitor array step-wise to boost the lost voltage level during the energy recycle stage. Its energy saving is particularly effective when most of the energy remaining in the charge capacitors is wasted by the leakage current during a longer sleep period. Simulations have been conducted using a voltage source of 500 mV to supply a $V_{DD}$ of around 800 mV to a load circuit consisting of four 32-bit adders in a 65-nm CMOS process. Results demonstrate energy recycling efficiency of 85.86% and overall energy saving of 40.14% compared to a conventional converter, when the load circuit is shortly active followed by a long sleep period.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.4
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• pp.1076-1089
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• 2012

Home automation networks are good environments for merging sensor networks and consumer electronics technologies. It is very important to reduce the energy consumption of each sensor node because sensor nodes operate with limited power based on a battery that cannot be easily replaced. One of the primary mechanisms for achieving low energy operation in energy-constrained wireless sensor networks is the duty-cycle operation, but this operation has several problems. For example, unnecessary energy consumption occurs during synchronization between transmission schedules and sleep schedules. In addition, a low duty-cycle usually causes more performance degradation, if the network becomes congested. Therefore, an appropriate control scheme is required to solve these problems. In this paper, we propose UDC (Unsynchronized Duty-cycle Control), which prevents energy waste caused by unnecessary preamble transmission and avoids congestion using duty-cycle adjustment. In addition, the scheme adjusts the starting point of the duty-cycle in order to reduce sleep delay. Our simulation results show that UDC improves the reliability and energy efficiency while reducing the end-to-end delay of the unsynchronized duty-cycled MAC (Media Access Control) protocol in sensor-based home automation networks.