• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10A
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• pp.935-942
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• 2006

The performance of ROF systems can be severely degraded due to nonlinear effects in the channel. Also, Orthogonal Frequency Division Multiplex(OFDM), as a standard for broadband wireless and mobile internet networks, is being proposed for deployment with ROF systems to facilitate the total performance of a system. In this paper, at first, the performance of the OFDM-based RoF system with a Mach-Zehnder(MZ) modulator distortion effects has been analyzed at 5.8GHz. Evaluation of mean-squared error of the proposed OFDM-RoF system was carried out to compare with the conventional single carrier system based RoF link after the modulator distortion case and also for fixed signal to noise ratio(SNR) of 20dB using undistorted OFDM signal. Nominal and offset baising pre-distortion techniques are applied in proposed system to linearize the OFDM-RoF link. Finally, a comparison between the aforementioned pre-distortion techniques applied showed important observation in terms of distortion-free dynamic range and SNR to choose offset pre-distortion technique for our proposed system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.9A
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• pp.790-795
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• 2011

The need for broadband wireless data networks such as IEEE 802.16e WiMAX systems increases as a variety of wireless information devices like smart phones are adopted rapidly in everyday life. Since most of mobile applications employ TCP as their transport layer protocol, the performance improvement of TCP in WiMAX systems is crucial. This paper proposes an efficient method to transmit uplink piggyback ACK packets by exploiting the uplink packet buffering which happens because of the resource allocation scheme of the WiMAX systems. The proposed method can support not only the ACK filtering but also the merging of the piggyback ACK packets. As a result, the bandwidth reduction in the piggyback ACK packet transmission leads to the improvement of the downlink throughput. The simulation results show that the bandwidth for the ACK packets reduces more than 90%, and the downlink throughput increases at least 30%.

• ETRI Journal
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• v.37 no.5
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• pp.877-887
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• 2015

This paper is a first-hand summary on our comprehensive live trial of cellular-assisted device-to-device (D2D) communications currently being ratified by the standards community for next-generation mobile broadband networks. In our test implementation, we employ a full-featured 3GPP LTE network deployment and augment it with all necessary support to provide realtime D2D connectivity over emerging Wi-Fi-Direct (WFD) technology. As a result, our LTE-assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real-world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE-assisted WFD solutions and associated operational ranges.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.199-204
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• 2013

Marine data communications still look for a novel data communication system at sea because of the restriction of bandwidths and costs of current carriers. In order to make the most efficient use of the broadband land carriers at sea, this paper proposes a routing scheme (MCS-NTC) at a marine MANET model. The routing scheme optimizes the route by choosing optimal nodes and carriers among the traditional and land carriers based on normalized transmission characteristics of applications and carriers. The performance is compared with the max-win method (OMH-MW) scheme considering the specific values of transmission characteristics. The result shows that our scheme derives more efficient routes than the previous one in terms of the transmission characteristics such as bandwidth, cost, delay, the number of hops and carriers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5B
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• pp.498-508
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• 2009

In wireless mobile environments, large bandwidth and high QoS (Quality of Service) are recently required to support the increased demands for multimedia services. LTE (Long Term Evolution) is one of the promising solutions for the next generation broadband wireless access systems. To efficiently use downlink resource and effectively support QoS, packet scheduling algorithm is one of the important features in LTE system. In this paper, we proposed DAPS (Delay-Aware Packet Scheduling) algorithm to consider QoS requirements of delays for various traffic classes as well as channel condition and fairness. To reflect delay experiences at scheduling instance, DAPS observes how queue waiting time of packet is closed to maximum allowable delay. The simulation results show that the DAPS algorithm yields better performance for delay experience by increasing the number of transmitted packets with satisfying the required delay time compared with existing scheduling algorithms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.10
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• pp.851-860
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• 2013

To overcome a scarcity of radio resources to mobile broadband service, the usage of TV white space gains much attraction around the world. This paper carries out an interference analysis either by performing realistic experiments or by executing statistical Monte-Carlo simulation to exploit interference probability. The results obtained from experiments are compared to those from simulations in order to clarify the coexistence of utilization of TV band devices (TVBD) in indoor circumstances. Along the execution of our experiment in the presence of DTV receiver, we apply to a variety of transmission parameters proposed in FCC for TVBD. According to experimental and simulation works, the allowable transmission powers of TVBD systems are exploited for the plausible which are coexist on the first as well as the second adjacent frequency bands. Throughout results, it can conclude that TVBD systems can be coexisted via achieving proper transmission powers depending on the locations of themselves without showing harmful interference to DTV reception.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6A
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• pp.445-457
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• 2009

Recently, there are growing interests in femto-cell for providing indoor users with various broadband multimedia services more efficiently. The technical issues regarding femto-cell such as interference management, self-organization, and resource allocation are now being intensively studied and investigated by researchers worldwide. In this paper, two novel schemes of neighboring cell list(NCL) management are proposed for the IEEE 802.16e system where a macro-cell and huge number of femto-cells coexist. The proposed schemes, named MS location-based neighboring cell list management and BS type-based neighboring cell list management, enable a mobile station(MS) to perform fast scanning and efficient handover by means of preselecting the candidate target femto-cells with high possibility for handover. The simulation result shows that the proposed schemes improve the MS's handover-related performance in terms of scanning power and scanning time compared with the conventional managements scheme of IEEE 802.16e system.

• Asia Pacific Journal of Business Review
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• v.3 no.1
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• pp.57-76
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• 2018

The "Internet of things" (IoT) is becoming an increasingly growing topic of conversation, it is a new emergent technology that can be present in almost every field and application. It's a concept that not only has the potential to impact how people live but also how people work. Broadband Internet and Mobile Internet are becoming more widely available, the cost of the service is decreasing, more devices are being created with Wi-Fi capabilities and sensors built into them, technology costs are going down, and smartphone penetration is growing so fast. All of these facts are creating the best environment for the IoT applications. In a country like Ecuador, is important to have a previous analysis about the feasibility of the implementation of this new technology in order to know what are the challenges the country has to face, and also to not stay behind as the other countries in the region are advancing. Currently, this kind of analysis does not exist. The Internet of Things is an innovation where business and technology models in Ecuador are relatively unexplored. The current infrastructure deployed in Ecuador and the available devices in the market are the central facts to initiate with the research, which is a starting point to show if Ecuador is ready to this technology, and if is not ready what is missing. This study shows the current telecommunications status in Ecuador, and its strengths and weaknesses to start the deployment of Internet of Things. Besides, it also will show the most likely applications that can be easily adopted for the Ecuadorian market with its respective availability, affordability, and adaptability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.2A
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• pp.152-161
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• 2007

IEEE 802.11 Wireless Local Area Network (WLAN) became a prevailing technology for the broadband wireless Internet access, and new applications such as Voice over WLAM (VoWLAN) are fast emerging today. For the battery-powered VoWLAN devices, the standby time extension is a key concern for the market acceptance while today's 802.11 is not optimized for such an operation. In this paper, we propose a novel Idle Mode operation, which comprises paging, idle handoff, and delayed handoff. Under the idle mode operation, a Mobile Host (MH) does not need to perform a handoff within a predefined Paging Area (PA). Only when the MH enters a new PA, an idle handoff is performed with a minimum level of signaling. Due to the absence of such an idle mode operation, both IP paging and Power Saving Mode (PSM) have been considered the alternatives so far even though they are not efficient approaches. We implement our proposed scheme in order to prove the feasibility. The implemented prototype demonstrates that the proposed scheme outperforms the legacy alternatives with respect to energy consumption, thus extending the standby time.

• Journal of KIISE:Information Networking
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• v.28 no.4
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• pp.527-539
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• 2001

The wireless asynchronous transfer mode (ATM) system has the advantage of providing the broadband services with various quality-of-service requirements to the mobile terminal efficiently by utilizing the ATM technology developed for the wired ATM system. The available bit rate (ABR) service among various ATM services utilizes the available bandwidth remaining in the ATM link, which allows the efficient bandwidth usage. During the handoff of the mobile terminal, however, the queue length in the access point (AP) which resides in the boundary of the wired ATM network and the wireless ATM network may increase abruptly. In this paper, we propose a scheme which prevents the buffer-overflow and buffer-underflow in the AP during the handoff of the wireless ABR connection in the wireless ATM system using binary feedback rate-based ABR traffic control. This scheme controls the source's cell generation rate during both handoff period and some time interval after the completion of the handoff procedure. The simulation results show that the proposed scheme prevents the buffer-overflow and buffer-underflow. The proposed scheme can contribute to increasing the throughput of the wireless ABR service during handoff by preventing the buffer overflow and underflow during handoff period.