• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.27-35
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• 2011

Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.168-175
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• 2006

To cope with channel variation, wireless networks such as IEEE 802.11 WLAN provide multiple transmission rates by employing different channel modulation and coding schemes. However, the coexistence of different transmission rates degrades the total system performance of the network. In order to eliminate this performance abnormality and improve protocol capacity, we propose a new Packet transmission algorithm, the RAT(Rate-Adapted Transmission) scheme. The RAT scheme distributes the wireless channel fairly based on the channel occupancy time. Moreover, it efficiently transmits packets even in a single station using rate-based queue management. Therefore, the RAT scheme obtains not only the inter-rate contention gain among stations but also the intra-rate contention gain among connections in a single station.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.7
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• pp.1040-1046
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• 2022

In this paper, we consider a system with massive user equipments (UEs) in a cell and assume path loss and Rayleigh fading channels between the base station (BS) and UEs. In addition, it is assumed that the system bandwidth consists of multiple identical frequency subchannels. Under such assumptions, we propose a channel state information (CSI) feedback scheme and a resource allocation scheme for non-orthogonal multiple access (NOMA) transmission in order to reduce the feedback overhead of CSI generated by massive UEs and to reduce the complexity of resource allocation. In particular, for the proposed schemes, we analyze the sum data rate achievable by massive UEs in a cell and the outage probability with which the UEs in a cell do not meet the target data rate. Through the simulation results, we show that the proposed schemes can provide the superior outage probability, although it degrades the average sum data rate.

• The Transactions of the Korea Information Processing Society
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• v.7 no.5
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• pp.1536-1543
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• 2000

In this paper, we propose a multiple access scheme for efficient transmission of realtime and non-realtime data in IMT-2000 through cdma2000's CDMA MACD. On the contrast to the conventional circuit-based service, this framework is packet-oriented service. maximum number of simultaneous subscribers increases due to the statistical multiplexing based on variable transmission rate of realtime data. System performance is evaluated and compared with conventional circuit-based scheme considering transmission delay and channel utilization by computer simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.2
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• pp.40-46
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• 2010

Multi-user MIMO (Multiple-Input Multiple-Output) systems require collaborative PF schedulers to improve the performance of the log sum of average transmission rates. While the performance of single cell based conventional PF schedulers has been evaluated over various channel conditions, scheduling algorithms by multiple base stations which select multiple users over a given time frame and their performance require further investigations. In this paper, we apply a collaborative PF scheduler to the distributed multi-user MIMO system, which assigns radio resources to multiple users by exchanging user channel information from base stations located in three adjacent sectors. We further evaluate its performance in terms of the log sum of average transmission rates. The performance is compared to that of the full-search collaborative PF scheduler which searches over all possible combinations of user groups, and that of a parallel PF scheduler that determines users without channel information exchange among base stations. We show the log sum of average transmission rates of the collaborative PF scheduler outperforms that of the parallel PF scheduler in low percentile region. In addition, the collaborative PF scheduler exhibits a negligible performance degradation when compared to the full-search collaborative PF scheduler while a significant reduction of the computational complexity is achievable at the same time.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.102-103
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• 2012

본 논문에서는 다중 사용자 증폭재전송(amplify-and-forward) MIMO 중계 시스템을 위한 프리코딩(precoding) 기법을 제안한다. 제안된 프리코딩 기법에서는 블록 대각화(block diagonalization)를 통해 사용자간 간섭(inter-user interfereence)을 제거하고 기지국과 중계기에서의 전송전력(transmit power) 제한을 만족하면서 사용자 데이터 전송률(data rate)의 합이 최대화 되도록 한다. 모의실험결과를 통해 제안된 기법이 기존 기법에 비해 더 높은 사용자 데이터 전송률의 합을 달성함을 보이고 있다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.8
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• pp.1673-1678
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• 2009

Multicast can transmit data packet to multiple terminals by using only one transmission and enhances the system performance. However, the multicast transmission rate is fixed and the system performance is not optimized. In this paper, we propose an adaptive multicast rate control method. In the proposed method, orthogonal subcarrier is assigned to each terminal. Each terminal informs the channel status using the allocated subcarrier. Transmitter selects the optimal rate using the feedback information. With the proposed adaptive rate control method, the system performance is enhanced compared with the legacy multicast method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.680-687
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• 2013

We investigate a generalized combined power and rate adaptation scheme in direct-sequence (DS) code-division multiple-access (CDMA) communications over Nakagami fading channels. The transmission power allocated to user i is proportional to $G^p_i$, where $G_i$ is the channel gain of user i and p is a real number, and the data rate (i.e., spreading gain) is jointly adapted so that a desired QoS is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme provides a significant performance improvement over power-only and rate-only adaptation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.7
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• pp.1313-1319
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• 2017

In this paper, we evaluate the performance of multi-hop transmissions in IEEE 802.15.6 ultra wide band (UWB) wireless body area network (WBAN). The packet structure in the physical layer, and encoding and decoding are considered for multi-hop transmissions in IEEE 802.15.6 UWB WBAN. We analyze the data success rate and energy efficiency of multi-hop transmissions with considering the length of data payload, transmission power, and distances between the nodes in IEEE 802.15.6 UWB WBAN. Through simulations, we evaluate the data success rate and energy efficiency of multi-hop transmissions with varying the length of data payload, transmission power, and distances between the nodes in IEEE 802.15.6 UWB WBAN. Finally, we can select an energy-efficient multi-hop transmission in IEEE 802.15.6 UWB WBAN depending on the length of data payload, transmission power, and distances between the nodes.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.566-572
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• 2014

We propose a two-way multi-hop relaying scheme improving the throughput as well as enlarging the coverage for ship-to-ship communications in multi-ship marine networks. The proposed scheme reduces the time slots required for the data exchange by designing data transmission and network coding procedures in a sophisticated way based on two-phase digital network coding. Simulation results show that the proposed two-way multi-hop relaying scheme improves the throughput of the conventional one about 5/3 times.