• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.717-727
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• 2003

The HIPERLAN/2(HIgh PERformance Local Area Network Type2) is one of the wireless LAN standards for providing raw data rates of up to 54 Mbps. The MAC protocol of HIPERLAN/2 is based on TDMA/TDD, and resources in one MAC frame can be allocated dynamically by Access Point(AP). The random channel(RCH) is defined for the purpose of giving a mobile terminal the opportunity to request transmission resources in the uplink MAC frames. It is desirable that the number of RCHs is dynamically adapted by the AP depending on the current traffic situation. Allocation of excessive RCHs may waste radio resources and insufficient RCHs compared to traffic loads may result in many collisions in access attempts. We propose an RCH allocation scheme based on split algorithm in HIPERLAN/2. The simulation and analytic results show that the proposed scheme achieves a higher channel throughput, lower access delay and delay jitter than previously proposed RCH allocation schemes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.8B
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• pp.910-920
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• 2011

In a heterogeneous wireless environment, a variety of Radio Access Technologies (RATs) coexist. Since the number of RATs is anticipated to increase in the near future, it is desirable to have radio and network resources managed in a cooperative manner using the Common Radio Resource Management (CRRM) strategy. In order to make RAT-specific radio resources manageable in CRRM, this paper proposes the Analytical Network Process (ANP) based resource management scheme that efficiently allocates resources among heterogeneous wireless networks. The proposed ANP-based method is flexible enough to be used in any network environment and can consider a multitude of decision factors. In addition, the proposed scheme uses a radio bandwidth model, which properly reflects transmission rates under given channel conditions, as the actual radio resources to be allocated. The model considers the AMC (Adaptive Modulation and Coding) scheme that is widely used in current broadband wireless access technologies, and thus, packet service characteristics, such as response time, can be analyzed. The effectiveness and flexibility of the proposed method are demonstrated by implementing a number of existing factors on heterogeneous networks environment.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.1
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• pp.59-65
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• 2008

In this paper, a new adaptive resource allocation scheme is proposed in orthogonal frequency-division multiple access(OFDMA) systems with rate proportionality constraints. The problem of maximizing the overall system capacity with constraints on bit error rate, total transmission power and rate-proportionality for user requiring different classes of service is formulated. Since the optimal solution to the constrained fairness problem is extremely complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. Firstly, the number of subchannels to be assigned to each user is determined based on the users' average signal-to-noise ratio and rate-proportion. Subchannels are subsequently distributed according to the modified max-min criterion. Lastly, based on the subchannel allocation, the optimal power allocation by solving the Language dual problem is proposed. Additionally, in order to reduce the computational complexity, iterative rate proportionality tracking algorithm is proposed for maximizing the capacity together with maintaining the rate proportionality constraint.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.451-458
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• 2006

In this paper, we propose a novel scheduling algorithm for downlink transmission which utilizes scarce wireless resource efficiently in an Orthogonal Frequency Division Multiple Access/Time Division Duplex system. Scheduling schemes which exploit channel information between a Base Station and terminals have been proposed recently for improved performance. Time series analysis is used to estimate the channel state of mobile terminals. The predicted information is then used for prioritized scheduling of downlink transmissions for improved throughput, delay and jitter performance. Through simulation, we show that the total throughput and mean delay of the proposed scheduling algorithm are improved compared with those of the Proportional Fairness and Maximum Carrier to Interference Ratio schemes.

• Proceedings of the Korea Society of Information Technology Applications Conference
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• 2003.06a
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• pp.67-68
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• 2003

IMT-2000에서 지원하는 멀티미디어 서비스는 실시간 데이터(Real-time data)와 비실시간 데이터(Non-relatime data)로 구분할 수 있는데 전송의 실시간성 VBR(Variable Bit Rate)이나 버스트성의 멀티미디어 데이터의 경우 자원의 이용률이 낮아 비효율적이다. 비실시간 데이터는 전송 지연에는 큰 영향을 받지 않으며 다만 오류 없이 전송될 것을 요구된다. 그러므로 채널의 이용률을 높일 수 있는 채널 공유방식에 적합하나 경쟁 시 충돌이 발생할 수 있으므로 이 문제를 해결할 것이 요구된다. 본 연구에서는 실시간 데이터를 위해 고정 액세스 방식으로 고유의 채널을 예약하여 사용하고, 전송 패킷이 없으면 우선 순위(Priority) 방식으로 비실시간 데이터를 전송하는 다중 액세스 방법을 제시한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.12C
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• pp.971-982
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• 2008

In this paper, we propose a new digital duplexing scheme, called SDD(Synchronous Digital Duplexing), which can increase data efficiency and flexibility of resource by transmitting uplink signal and downlink signal simultaneously. In order to transmit uplink data and downlink data simultaneously, the proposed SDD obtains mutual informations between AP(access point) and each SSs(subscriber station), SS and other SSs by mutual ranging procedure. These informations are used for selection of transmission time, decision of CS insertion, setting of CS length, and FFT duration resetting, etc. It is shown that the proposed SDD is appropriate for duplexing scheme in indoor environments over the conventional TDD(Time Division Duplexing) and FDD(Frequency Division Duplexing).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.11 s.353
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• pp.68-77
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• 2006

In accommodating the asymmetric traffic for future wireless multimedia services, the dynamic time division duplexing (D-TDD) scheme is considered as one of the key solutions. With the D-TDD mode, however, the inter-BS and inter-MS interference is inevitable during the cross time slot (CTS) period, and this interference seriously degrades the system performance. To mitigate such interference, we propose a region and time partitioning D-TDD architecture for OFDM systems. Each time slot in the CTS period is split into several minislots, and then each cell is divided into as many regions as the number of minislots per time slot. We then assign the minislots only to the users in its predefined corresponding region. On top of such architecture which inherently separates the interfering entities farther from each other, we design a robust time slot allocation scheme so that the inter-cell interference can be minimized. By the computer simulation, it has been verified that the proposed scheme outperforms the conventional time slot allocation methods in both the outage probability and the bandwidth efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.68-78
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• 2013

In this paper, we propose an early spectrum sensing(ESS) as an advance preparation for radio-access trial, which enables multi-mode terminals to access the most appropriate radio-access system in a cloud-conceptual base station system where multiple radio access technologies(RATs) coexist. Prior to a random access to one of RATs, a multi-mode terminal conducts a spectrum sensing over entire frequency bands of whole RATs, then select the RAT with the lowest sensing power, that is likely to have the most available spectrum. Thus, an access failure caused by that the selected RAT has no available radio spectrum could be avoidable in advance. In computer simulation, we consider as various RATs as possible. First, circuit and packet systems are taken into consideration. In addition, the packet systems are classified according to the feasibility of carrier aggregation(CA). In case of terminal, three modes are considered with circuit-only, packet-only, and multi-mode. Subsequently, packet traffic is classified into real-time and non-real-time traffic with three different tolerable delay levels. The simulation includes a call process starting with a call generation and ending up with a resource allocation reflecting individual user's QoS requirements and evaluates the proposed scheme in terms of the successful access probability, system access time, system balancing factor and packet loss probability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.5
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• pp.260-270
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• 2014

In this paper, we first analyze the delay performance of Dynamic Space-time Subframe (DSTS)-based frame structure which has been proposed to support the real-time service as well as non real-time service, using Ad hoc Self-Organizing Time Division Multiple Access (ASO-TDMA) MAC protocol, especially when transmitting a MAC SDU with two or more MAC PDUs, in a multi-hop ad-hoc maritime communication network. We propose two key transmission schemes: contiguous DSTS reservation which guarantees the end-to-end delay for the multiple PDUs, and adaptive transmission probability control schemes to maximize the system throughput. Our simulation results show that the proposed schemes outperform the system throughput of the existing transmission schemes, while supporting the real-time requirement.