• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1982.10a
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• pp.37-39
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• 1982

In this paper, we deal with theoretical tools to improve the throughput efficiency of the conventional Go-Back-N ARQ system by performing block retransmission efficiently under high error rate, and two variations of the system is proposed.

• Journal of Communications and Networks
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• v.16 no.3
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• pp.293-300
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• 2014

As energy harvesting communication systems emerge, there is a need for transmission schemes that dynamically adapt to the energy harvesting process. In this paper, after exhibiting a finite-horizon online throughput-maximizing scheduling problem formulation and the structure of its optimal solution within a dynamic programming formulation, a low complexity online scheduling policy is proposed. The policy exploits the existence of thresholds for choosing rate and power levels as a function of stored energy, harvest state and time until the end of the horizon. The policy, which is based on computing an expected threshold, performs close to optimal on a wide range of example energy harvest patterns. Moreover, it achieves higher throughput values for a given delay, than throughput-optimal online policies developed based on infinite-horizon formulations in recent literature. The solution is extended to include ergodic time-varying (fading) channels, and a corresponding low complexity policy is proposed and evaluated for this case as well.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8B
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• pp.677-686
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• 2012

In the presence of a high power cellular network, picocells are added to a Macro-cell layout aiming to enhance total system throughput from cell-splitting. While because of the different transmission power between macrocell and picocell, and co-channel interference challenges between the existing macrocell and the new low power node-picocell, these problems result in no substantive improvement to total system effective throughput. Some works have investigated on these problems. Pico Cell Range Expansion (CRE) technique tries to employ some methods (such as adding a bias for Pico cell RSRP) to drive to offload some UEs to camp on picocells. In this work, we propose two solution schemes (including cell selection method, channel allocation and serving process) and combine new adaptive frequency partitioning reuse scheme to improve the total system throughput. In the simulation, we evaluate the performances of heterogeneous networks for downlink transmission in terms of channel utilization per cell (pico and macro), call blocking probability, outage probability and effective throughput. The simulation results show that the call blocking probability and outage probability are reduced remarkably and the throughput is increased effectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.6
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• pp.3012-3028
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• 2017

In this paper, we propose a joint power control strategy for both the uplink and downlink transmission by considering the energy requirements of the user equipments' uplink data transmissions in data and energy integrated communication networks (DEINs). In DEINs, the base station (BS) adopts the power splitting (PS) aided simultaneous wireless information and power transfer (SWIPT) technique in the downlink (DL) transmissions, while the user equipments (UEs) carry out their own uplink (UL) transmissions by exploiting the energy harvested during the BS's DL transmissions. In our DEIN model, there are M UEs served by the BS in order to fulfil both of their DL and UL transmissions. The orthogonal frequency division multiple access (OFDMA) technique is adopted for supporting the simultaneous transmissions of multiple UEs. Furthermore, a transmission frame is divided into N time slots in the medium access control (MAC) layer. The mathematical model is established for maximizing the sum-throughput of the UEs' DL transmissions and for ensuring their fairness during a single transmission frame T, respectively. In order to achieve these goals, in each transmission frame T, we optimally allocate the BS's power for each subcarrier and the PS factor for each UE during a specific time slot. The original optimisation problems are transformed into convex forms, which can be perfectly solved by convex optimisation theories. Our numerical results compare the optimal results by conceiving the objective of maximising the sum-throughput and those by conceiving the objective of maximising the fair-throughput. Furthermore, our numerical results also reveal the inherent tradeoff between the DL and the UL transmissions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1301-1318
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• 2017

In order to utilize the licensed channel of cognitive radio (CR) when the primary user (PU) is detected busy, a benefit-exchange access mode based on cooperative communication is proposed to allow secondary user (SU) to access the busy channel through giving assistance to PU's communication in exchange for some transmission bandwidth. A holistic joint optimization problem is formulated to maximize the total throughput of CR system through jointly optimizing the parameters of cooperative spectrum sensing (CSS), including the local sensing time, the pre-configured sensing decision threshold, the forward power of cooperative communication, and the bandwidth and transmission power allocated to SUs in benefit-exchange access mode and traditional access mode, respectively. To solve this complex problem, a combination of bi-level optimization, interior-point optimization and exhaustive optimization is proposed. Simulation results show that, compared with the tradition throughput maximizing model (TTMM), the proposed holistic joint optimization model (HJOM) can make use of the channel effectively even if PU is busy, and the total throughput of CR obtains a considerable improvement by HJOM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9B
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• pp.589-597
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• 2007

In this paper, a WDM metro ring consisting of access nodes with $FT-FR^n$ (Fixed Transmitter - n Fixed Receivers) is considered. A trade-off exists between node throughput and transmission fairness because the access nodes share wavelength channels. In order to eliminate the transmission unfairness and to increase throughput, the p-persistent medium access control (MAC) protocol is proposed: each node uses an empty optical slot to transmit a packet and make it available with the extraction of a transferred packet at the source access node, called source-stripping. The local empty slot can be used to transfer a head-of-line packet in the local buffer with probability p or it is used for the next downstream nodes with 1-p. The proposed MAC protocol provides better node throughput than the non-persistent protocol and exhibits better fairness index than the 1-persistent protocol in WDM ring networks. In addition, numerical analysis shows that the proposed MAC protocol maximizes the node throughput under uniform traffic conditions. For more detailed results, we use the network simulation under Poisson and self-similar traffic. Furthermore, unpredictable traffic constructed by the combination of the former and the latter is also considered. The reasonable probability of the p-persistent protocol for a given architecture can be determined through simulation.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.430-438
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• 2013

This paper addresses the issue of throughput-delay of one-to-many wireless multi-hop flows based on random linear network coding (RLNC). Existing research results have been focusing on the single-hop model which is not suitable for wireless multi-hop networks. In addition, the conditions of related system model are too idealistic. To address these limitations, we herein investigate the performance of a wireless multi-hop network, focusing on the one-to-many flows. Firstly, a system model with multi-hop delay was constructed; secondly, the transmission schemes of system model were gradually improved in terms of practical conditions such as limited queue length and asynchronous forwarding way; thirdly, the mean delay and the mean throughput were quantified in terms of coding window size K and number of destination nodes N for the wireless multi-hop transmission. Our findings show a clear relationship between the multi-hop transmission performance and the network coding parameters. This study results will contribute significantly to the evaluation and the optimization of network coding method.

• Journal of Computing Science and Engineering
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• v.8 no.2
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• pp.107-118
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• 2014

One interesting problem regarding wireless local area network (WLAN) ad-hoc networks is the effective mitigation of hidden nodes. The WLAN standard IEEE 802.11 provides request to send/clear to send (RTS/CTS) as mitigation for the hidden node problem; however, this causes the exposed node problem. The first 802.11 standard provided only two transmission rates, 1 and 2 Mbps, and control frames, such as RTS/CTS assumed to be sent at 1 Mbps. The 802.11 standard has been enhanced several times since then and now it supports multi-rate transmission up to 65 Mbps in the currently popular 802.11n (20 MHz channel, single stream with long guard interval). As a result, the difference in transmission rates and coverages between the data frame and control frame can be very large. However adjusting the RTS/CTS transmission rate to optimize network throughput has not been well investigated. In this paper, we propose a method to decrease the number of exposed nodes by increasing the RTS transmission rate to decrease RTS coverage. Our proposed method, Asymmetric Range by Multi-Rate Control (ARMRC), can decrease or even completely eliminate exposed nodes and improve the entire network throughput. Experimental results by simulation show that the network throughput in the proposed method is higher by 20% to 50% under certain conditions, and the proposed method is found to be effective in equalizing dispersion of throughput among nodes.

• ETRI Journal
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• v.41 no.5
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• pp.648-657
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• 2019

A cluster topology was proposed with the assumption of zero noise to improve the performance of wireless body area networks (WBANs). However, in WBANs, the transmission power should be reduced as low as possible to avoid the effect of electromagnetic waves on the human body and to extend the lifetime of a battery. Therefore, in this work, we consider a bit error rate for a cluster-based WBAN and analyze the performance of the system while the transmission of sensors and cluster headers (CHs) is controlled. Moreover, a hierarchical topology is proposed for the cluster-based WBAN to further improve the throughput of the system; this proposed system is called as the hierarchical cluster WBAN. The hierarchical cluster WBAN is combined with a transmission control scheme, that is, complete control, spatial reuse superframe, to increase the throughput. The proposed system is analyzed and evaluated based on several factors of the system model, such as signal-to-noise ratio, number of clusters, and number of sensors. The calculation result indicates that the proposed hierarchical cluster WBAN outperforms the cluster-based WBAN in all analyzed scenarios.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.53-56
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• 2015

In this paper, we want provide improved services with faster transmission, IEEE 802.11n was standardized. A-MPDU (Aggregation MAC Protocol Data UNIT) is a vital function of the IEEE 802.11n standard, which was proposed to improve transmission rate by reducing frame transmission overhead. In this paper, we show the problems of TCP retransmission with A-MPDU and propose a solution utilizing the property of TCP cumulative ACK. If the transmission of an MPDU subframe fails, A-MPDU mechanism allows selective re-transmission of failed MPDU subframe in the MAC layer. In TCP traffic transmission, however, a failed MPDU transmission causes TCP Duplicate ACK, which causes unnecessary TCP re-transmission. Furthermore, congestion control of TCP causes reduction in throughput. By supressing unnecessary duplicate ACKs the proposed mechanism reduces the overhead in transmitting redundant TCP ACKs, and transmitting only a HS-ACK with the highest sequence number. By using the RACK mechanism, through the simulation results, it was conrmed that the RACK mechanism increases up to 20% compared the conventional A-MPDU, at the same time, it tightly assures the fairness among TCP flows.