• Genomics & Informatics
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• v.2 no.4
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• pp.153-162
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• 2004

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1686-1694
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• 2001

In this paper, we analyze capacities of spectrum sharing scheme for both reverse link and forward link in hierachical CDMA cellular systems with Hot-spot microcell. Capacity analysis is performed through Monte-Carlo simulation by considering microcell radius, location of microcell. and transmission power ratio of microoell to macrocell. From simulation results, we analyzed these effects and derived a general design approach. In addition, the performance of spectrum sharing scheme for each link is analyzed in the capacity plane.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.3
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• pp.571-579
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• 1997

There are some transmission types on the reverse link of wideband DS-CDMA cellular system. The configurations of logical channels on the reverse link may be different dependent upon the transmission methods of reverse pilot or control signaling. In this paper, we present three transmission types on the wideband DS-CDMA reverse link; no-pilot system, pilot-channel aided system and pilot-symbol aided system. And we compare the performance of three systems in terms of capacity and cell coverage. The pilot-symbol aided system is shown to have the better performance than the pilot-channel aided system in both capacity and cell coverage.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.216-222
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• 2013

Handover is a technical methodology to support mobility of wireless communication users, which mainly affects the capacity of wireless communication systems and the quality of service (QoS) of link level signal. However, in OFDMA-based cellular systems, there are few published technical reports investigating handovers with respect to diversity gains and resource consumption depending on what handover technique is adopted. In this paper, we propose handover schemes exploiting transmit diversity and macro-diversity in order to increase capacity of OFDMA-based wireless communication systems, and analyze their performance. In cellular environments, depending on what handover scheme is selected, average signal-to-interference-and-noise ratio is calculated first for a handover user in order to evaluate the link level QoS. Through this technical evaluation for handover schemes, we conclude what handover scheme is suitable for OFDMA-based cellular systems.

• Journal of the Korea Society of Computer and Information
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• v.24 no.5
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• pp.19-26
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• 2019

In this paper, we consider the D2D Transmitter(Tx) and Receiver(Rx) pair assignment problem in the cellular system. Sharing the resource of the cellular system, D2D users may cause interference to the cellular system, though it is beneficial to improve the D2D user Capacity. Therefore, to protect the cellular users, D2D transmit power should be carefully controlled. Previously, optimal Tx-Rx assignment to minimize the total transmit power of users was investigated. Accordingly, the iterative algorithm to find the optimum Tx-Rx asignment was obtained. In this work, we consider the case where Tx group users becomes Rx group users, and Rx group users become Tx group users. We prove that the Tx-Rx assignment problem has the duality property. We present the numerical examples that show the duality between U-link and D-link.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.885-894
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• 2012

Currently, Demand of data traffic has rapidly increased by popular of smart device. It is very difficult to accommodate demand of data traffic by limited resource of base station (BS). To solve this problem, method has proposed that the Device-to-Device (D2D) reduce frequency overload of the BS and all of the user equipment (UE) inside the BS and neighbor BS don't allow communicating directly to BS. However, in LTE-Advance system cellular link and sharing radio resources of D2D link, the strong interference of the cellular network is still high. So we need to eliminate or mitigate the interference. In this paper, we use the transmission power control method and Soft Frequency Reuse (SFR) resource allocation method to mitigate the interference of the cellular link and D2D link. Simulation results show that the proposed scheme has high performance in terms of Signal to Noise Ratio (SINR) and system average throughput.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.7
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• pp.72-79
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• 2010

Device-to-device(D2D) links which share resources in a cellular network present a challenge in radio resource management due to the potentially severe interference they may cause to the cellular network. In this paper, a resource allocation scheme based on subset reuse methods is proposed to minimize the interference from the D2D links. We consider an adaptive group-wise subset reuse method to enhance the efficiency of frequency resource allocation for cellular and D2D links. A power optimization scheme is also proposed for D2D links if cellular links are interfered by adjacent D2D transmissions. The computer simulation results show that performance gain is obtained in link SINR, and total cell throughput increases as nearby traffic becomes more dominant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.395-402
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• 2003

The capacity of a CDMA cellular system is determined by the amount of interference, therefore the exact estimation of interference is important to evaluate the system performance. In this paper, we propose an approximated equation which calculates reverse link other cell interference in the CDMA cellular systems. The equation using Riemann-Zeta function has a property that it is useful in case of any radio propagation loss exponents. And we compare calculation results with simulation results in other to verify it's usefulness. The upper bound of system capacity calculated with the proposed approximated equation gives almost alike result with the simulation. The proposed interference bound is useful to calculate system capacity and to evaluate some algorithm in a hierarchical cellular system which must be considered various propagation exponents.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6B
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• pp.430-439
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• 2008

In this paper, we propose a sender-based TCP congestion control scheme for downward vertical handover (DVHO), in which mobile node moves from a cellular network to a wireless LAN. DVHO can give rise to severe performance problems in TCP throughput because it causes a drastic change of link characteristics. Particularly, TCP executes falsely congestion control by packet reordering, which is occurred from link delay difference between a cellular link and a wireless LAN link. Therefore, the congestion window is reduced. And unnecessary retransmissions wastes bandwidth. To solve these problems, we propose a method using estimated round-trip time in cellular link to process duplicated ACKs from reordering. Furthermore, the duplicated ACKs are used to the control congestion window size. Simulation result shows that the proposed scheme can solve problems. Moreover, the proposed scheme can have better performance than TCP New Reno and nodupack.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.429-438
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• 2016

In this paper, we investigate an interference mitigation scheme by antenna selection in device-to-device (D2D) communication underlaying downlink cellular networks. We first present the closed-form expression of the system achievable rate and its asymptotic behaviors at high signal-to-noise ratio (SNR) and the large antenna number scenarios. It is shown that the high SNR approximation increases with more antennas and higher ratio between the transmit SNR at the base station (BS) and the D2D transmitter. In addition, a tight approximation is derived for the rate and we reveal two thresholds for both the distance of the D2D link and the transmit SNR at the BS above which the underlaid D2D communication will degrade the system rate. We then particularize on the small cell setting where all users are closely located. In the small cell scenario, we show that the relationship between the distance of the D2D transmitting link and that of the D2D interfering link to the cellular user determines whether the D2D communication can enhance the system achievable rate. Numerical results are provided to verify these results.