• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.469-474
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• 2006

In this paper, we develop a method that derive the average sector throughput of HSDPA system. This proposed method reflects the effects of AMC, scheduling and multi-code transmission, and is performed by simple calculation procedures such as link budget analysis. Link budget table is used to estimate a cell coverage in general. We modify the link budget table in order to calculate C/I of the user according to the location of the user in CDMA packet system employing AMC. Furthermore, we utilize the proposed method to analyze the effects of scheduling and multi-code transmission.

• Journal of Communications and Networks
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• v.12 no.4
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• pp.334-345
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• 2010

In this paper, we study optimal tradeoffs of achievable throughput versus consumed power in wireless ad-hoc networks formed by a collection of multiple antenna nodes. Relying on adaptive modulation and/or dynamic channel coding rate allocation techniques for multiple antenna systems, we examine the maximization of throughput under power constraints as well as the minimization of transmission power under throughput constraints. In our examination, we also consider the impacts of enforcing quality of service requirements expressed in the form of channel coding block loss constraints. In order to properly model temporally correlated loss observed in fading wireless channels, we propose the use of finite-state Markov chains. Details of fading statistics of signal-to-interference-noise ratio, an important indicator of transmission quality, are presented. Further, we objectively inspect complexity versus accuracy tradeoff of solving our proposed optimization problems at a global as oppose to a local topology level. Our numerical simulations profile and compare the performance of a variety of scenarios for a number of sample network topologies.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.413-419
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• 2014

Underwater acoustic channel has time-variability. Time varying channel which disturbs the continuous transmission of information data reduces the underwater acoustic communication performance. In this paper, we show the temporal coherence as time-variability of channel and indicate throughput efficiency in accordance with transmission time of information data. Then we analyzed influence of underwater channel time-variability on communication throughput efficiency. We confirmed that the throughput efficiency reduced when the time-variability of the channel increased via lake trial.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.9
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• pp.734-740
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• 2012

In this paper, we propose a method for throughput improvement in multirate multihop wireless networks with intra-session network coding. A multirate transmission supports several rates so that it has a tradeoff between transmission rate and transmission range, therefore multirate can cope with the performance degradation. We present the rate selection method with intra-session network coding in multirate nodes. The effective transmission rate is calculated by using intra-session network coding, and then its maximum effective transmission rate is selected. Concurrent transmission set is determined by selected transmission rate and then the linear programming is formulated for throughput calculation in multihop wireless networks. We evaluate the performance by using MATLAB and lp_solve programs in two topologies. It is shown that the throughput of the proposed method is improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5B
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• pp.338-347
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• 2012

In this paper, we propose the cooperative transmission scheme (CTS) for system throughput maximization in OFDMA based enterprise femtocell networks. In our scheme, the user equipment (UE) can receive the desired signal from serving femtocell BS (fBS) as well as an adjacent fBS. Thus, UE achieves an improved signal to interference plus and noise ratio (SINR) by the synchronized two signals. The performances of this strategy consider not only the call-level quality of service (QoS) but also the packet-level QoS. We first measure the call blocking probability and utilization for the downlink resources for various offered load in femtocell. Based on that, the outage probability and effective throughput of the system are simulated. Simulation results show that the proposed scheme can reduce the outage probability for enterprise femtocell compared with conventional systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1493-1499
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• 2007

Real-time applications in a wireless sensor network environment require real-time transmissions from sensing nodes to sink nodes. Existing congestion control mechanisms have treated congestion problems in sensor networks, but they only adjust the reporting frequency or the sending rate in intermediate nodes. They were not suitable for real-time applications from the transmission delays point of view. In this paper, we suggest a new mechanism that can reduce the transmission delay and can increase the throughput for real-time applications in sensor network. This mechanism classifies data on the real-time characteristics, processes the data maintaining the real-time characteristics prior to the other data such as the non real-time data or the data lost the real-time characteristics. A modified frame format is also proposed in order to apply the mechanism to IEEE 802.15.4 MAC layer. The simulation based on ns-2 is accomplished in order to verify the performance of the suggested scheme from transmission delay and throughput standpoints. The simulation results show that the proposed algorithm has a better performance specifically when It applies to the real-time applications in sensor networks.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.77-86
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• 2013

Cognitive radio (CR) has emerged as one of effective methods to enhance the utilization of existing radio spectrum. Main principle of CR is that secondary users (SUs) are allowed to use the spectrum unused by primary users (PUs) without interfering PU's transmissions. In this paper, PUs operate on a slot-by-slot basis and SUs try to exploit the slots unused by PUs. We propose OSA protocols in the single channel and we propose an opportunistic spectrum access (OSA) protocols in the multi-channel cognitive radio networks with one control channel and several licensed channels where a slot is divided into contention phase and transmission phase. A slot is divided into reporting phase, contention phase and transmission phase. The reporting phase plays a role of finding idle channels unused by PUs and the contention phase plays a role of selecting a SU who will send packets in the data transmission phase. One SU is selected by carrier sense multiple access / collision avoidance (CSMA/CA) with request to send / clear to send (RTS/CTS) mechanism on control channel and the SU is allowed to occupy all remaining part of all idle channels during the current slot. For mathematical analysis, first we deal with the single-channel case and we model the proposed OSA media access control (MAC) protocol by three-dimensional discrete time Markov chain (DTMC) whose one-step transition probability matrix has a special structure so as to apply the censored Markov chain method to obtain the steady state distribution.We obtain the throughput and the distribution of access delay. Next we deal with the multi-channel case and obtain the throughput and the distribution of access delay by using results of single-channel case. In numerical results, our mathematical analysis is verified by simulations and we give numerical results on throughput and access delay of the proposed MAC protocol. Finally, we find the maximum allowable number of SUs satisfying the requirements on throughput and access delay.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.5
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• pp.589-595
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• 2019

Recently, the mobile social networks, which consider both social relationship between users and mobile communication networks, have been received great attention. In this paper, we consider the trust degree of node as the social relationship for the cooperative communication networks. In contrast to the existing works that consider the case of the perfect trust degree information, for the case that transmitter has an imperfect trust degree information, we propose an imperfect trust degree based cooperative communication technique that maximizes a throughput. We first model the imperfect trust degree information as a probability distribution and derive the outage probability using the probability distribution. Then, we propose the transmission scheme that maximizes the throughput, which consider both outage probability and transmission rate. The simulation results show that the proposed cooperative transmission scheme outperforms the conventional scheme in terms of the throughput.

• Annual Conference of KIPS
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• 2006.05a
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• pp.1147-1150
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• 2006

Stream Control Transmission Protocol (SCTP) uses the 32-bit checksum in the common header, by which a corrupted SCTP packet will be regarded as a lost packet and then discarded. This may result in degradation of SCTP's throughput performance over wireless networks. This paper proposes a new chunk checksum scheme for SCTP, in which each data chunk contains its own checksum field and SACK chunk carry corresponding Transmission Sequence Number (TSN) with timestamp for every corruption event. The proposed chunk checksum scheme is introduced with the following three purposes: 1) to distinguish the chunk corruptions from the chunk losses; 2) to avoid the unnecessary halving of the congestion window (cwnd) in the case of chunk corruption; 3) to avoid the unwanted timeouts which can be induced in conventional SCTP in the case that the retransmitted data chunks are corrupted again in wireless networks. Simulation results show that the proposed chunk checksum scheme could improve the SCTP throughput in the wireless environments with a high bit error rate.

• Journal of Information Processing Systems
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• v.10 no.3
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• pp.459-470
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• 2014

In this paper, the average probability of the symbol error rate (SER) and throughput are studied in the presence of joint spectrum sensing and data transmission in a cognitive relay network, which is in the environment of an optimal power allocation strategy. In this investigation, the main component in calculating the secondary throughput is the inclusion of the spatial false alarms, in addition to the conventional false alarms. It has been shown that there exists an optimal secondary power amplification factor at which the probability of SER has a minimum value, whereas the throughput has a maximum value. We performed a Monte-Carlo simulation to validate the analytical results.