• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.3B
• /
• pp.304-310
• /
• 2009

In this paper, we evaluate the performance of VoIP in OFDMA-based relay systems with various capabilities of relays. We classify relays according to capability as "mid-capability (MC)" and "high-capability (HC)" relay. In system with HC relays, not only base station (BS) but also relay station (RS) performs scheduling at its ova whereas only BS performs scheduling in system with MC relays using the information reported by MS (i.e. the received signal-to-interference-plus-noise ratio (SINR) of mobile station (HS), the amount of MS traffic, etc). In system with MC relays, the controling overhead of BS is larger than that of system with HC relays. However, since BS has all MS information, efficient resource allocation and scheduling is possible. We derived the "average packet delay," "good packet ratio," and "cell goodput" in a VoIP environment. The simulation results demonstrate that the system with MC relays has better VoIP performance over that with HC relays.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.9A
• /
• pp.729-736
• /
• 2005

In this paper, we introduce a new approach for the design of uplink sub-channel allocation and power control in the High-speed Portable Internet system that is based on OmMAnDD scheme. In OFDMA system, because the number of allocated sub-channel in mobile station varies from one to the whole sub-channel as in base station while mobile station's transmit power is lower than that of base station, full loading range(FLR) constraint occurs where whole sub-channel can be used and the conventional open-loop power control scheme can not be used beyond FLR. We propose a new scheme that limits the maximum sub-channel allocation number and uses power concentration gain(PCG) depending on location of mobile station, which is based on ranging in OfDMA system. Simulation results show that the proposed scheme extends the uplink coverage to the entire cell service coverage area, provides solutions for optimum utilization of radio resource and enables open-loop power control beyond FLR without extra hardware complexity.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.12C
• /
• pp.1217-1224
• /
• 2003

In this paper, we propose an edge side-lobe suppressor (ESS) for the uplink of OFDMA systems, which mitigates the interference introduced by different frequency offsets between a desired user and the other users. We evaluate the proposed ESS scheme by measuring average signal to interference ratio (SIR) and average bit error rate (BER). The simulation results confirm that the proposed ESS scheme improves system performance by approximately 5∼10 dB SIR as compared to conventional OFDMA systems. Because the additional operations for the proposed scheme can be performed by a real-valued look-up table, the implementation of the ESS hardly requires increasing transmitter and receiver complexity.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.8A
• /
• pp.743-751
• /
• 2010

OFDMA femtocell becomes an effective solution to support indoor high data rate services instead of the macrocell systems. Although the advantage of the femtocell, the co-channel interference between the femocell and the macrocell is the most significant problem that reduces the system performance. Macrocell users who have no permission to access the femtocell suffer from interference of the downlink transmission of femtocell. Therefore, the femtocell should use transmission power as small as possible to reduce interference to macrocell users. In this paper, we define the margin adaptive power allocation problem for the femtocell and propose a heuristic power allocation algorithm to solve the problem. Simulation results show the performance of the proposed algorithm.

• 한국정보통신설비학회:학술대회논문집
• /
• 2006.08a
• /
• pp.57-61
• /
• 2006

As high speed internet users are tremendously increasing, three are keenly in need of development of high speed portable internet technology which can provide high quality wireless internet service cheaply even in the mobile. Unlike the FDD-CDMA, TDD-OFDMA has relatively poor wave environment with inducing interference, fading and delay because it agrees to multi-carrier modulation method and time-division radio telecommunication system. To solve this problem, it is necessary to develop repeater operating by digital signal processing method which have more strict wireless channel control and wave signal processing technology over TDD telecommunication equipments. This thesis is dealing with design and implementation of Digital RF Repeater which implemented 'Synchronization Acquisition Unit', 'TDD signal switching Unit', 'Feedback Signal Cancellation Unit'. Over this argument, we will develop digital RF repeater with more cheap, more adaptive in wave environment like oscillation control, adaptive wave monitoring and output increasing and having control function as a result it will be helpful for success in high speed portable internet service business.

• Journal of Internet Computing and Services
• /
• v.9 no.2
• /
• pp.25-33
• /
• 2008

In this paper we propose uplink packet transmission scheme based on Synchronized RA. The scheme can afford to support diverse QoS required from diverse multimeda traffics. In order to minimze the collision probability occurred in contention based channel access, we assign a reservation access channel additionally to the traffic channels. Access probability function for controlling collisions occurred in the reservation access channel is applied. Through assigning different access probability to each traffic user with respect to priority issued by his required QoS, the proposed scheme guarantees minimum throughput required by higher priority users in the whole range of system load.

• Journal of the Korea Society of Computer and Information
• /
• v.18 no.2
• /
• pp.59-68
• /
• 2013

Efficient resource management and hand-over schemes are necessary to maintain consistent QoS because it may be severely defected by some delay and information loss during hand-over in LTE-Advanced networks. This paper proposes a resource management scheme based on the load control to support consistent QoS for heterogeneous services during hand-over in OFDMA based systems. Various multimedia services with different requirements for resource are able to be serviced simultaneously because service continuity can be provided by our proposed scheme. Simulation results show that it provides better performances than the conventional one with the measure of hand-over failure rate and packet loss rate.

• Proceedings of the IEEK Conference
• /
• 2005.11a
• /
• pp.81-84
• /
• 2005

In this paper, we investigate the method for reducing the amount of feedback in multi-user downlink orthogonal frequency division multiple access (OFDMA) systems. The objective is to maximize the total throughput of the system under the constraints of transmit power. In previous methods, each user in a cell transmits channel quality information (CQI) of its all sub-bands to the base station, which requires extremely high feedback overhead. Thus, we propose an efficient sub-band allocation algorithm in which each user transmits partial CQI and one additional information to reduce the amount of feedback. Simulation results show that we can greatly reduce the amount of feedback than full feedback system.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.11
• /
• pp.3008-3025
• /
• 2012

In this paper, the downlink resource allocation of OFDMA system with decode-and-forward (DF) relaying is investigated. A non-convex optimization problem maximizing system throughput with users' satisfaction constraints is formulated with joint relay selection, subcarrier assignment and power allocation. We first transform it to a standard convex problem and then solve it by dual decomposition. In particular, an Optimal resource allocation scheme With Time-sharing (OWT) is proposed with combination of relay selection, subcarrier allocation and power control. Due to its poor adaption to the fast-varying environment, an improved version with subcarrier Monopolization (OWM) is put forward, whose performance promotes about 20% compared with that of OWT in the fast-varying vehicular environment. In fact, OWM is the special case of OWT with binary time-sharing factor and OWT can be seen as the tight upper bound of the OWM. To the best of our knowledge, such algorithms and their relation have not been accurately investigated in cooperative OFDMA networks in the literature. Simulation results show that both the system throughput and the users' satisfaction of the proposed algorithms outperform the traditional ones.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.12A
• /
• pp.1214-1222
• /
• 2006

In this paper, an efficient direction-r)f-arrival based adaptive beamforming algorithm for orthogonal frequency-division multiple-access smart antenna systems is proposed. The proposed algorithm provides a high performance by steering main beams to the directions of a desired signal, whereas steering nulls to the directions of the interference, using the estimated directions. The beamforming outputs obtained by steering the main beams to the distinct directions of resolvable multipath signals are combined in a maximal ratio manner to exploit angular diversity gain. The performance elf the proposed algorithm is finally evaluated in cellular mobile environments to verify its efficiency and is compared with that of least-squares beamforming algorithm, by taking the WiBro system as a target system.