• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.643-651
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• 2008

In this paper, we analyze the performance of normalized SNR based proportional fair scheduling with partial feedback information for multiuser MIMO-OFDMA systems. The closed form expression on the downlink capacity of the selective partial CQI feedback scheme is derived and its asymptotic behavior is investigated. From the performance analysis and numerical results, it is found that the optimal growth rate of downlink capacity can be achieved with bounded average feedback overhead irrespective of the number of users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1240-1248
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• 2006

In this paper, we present a new method for user selection, sub-band allocation, and power allocation in order to maximize the system throughput under the constraint of transmit power in multiuser downlink orthogonal frequency division multiple access (OFDMA) systems with partial channel quality information (CQI). In previous schemes, each user in one cell transmits CQI of all sub-bands to the base station, which requires enormous feedback overhead. Therefore, we proposed an efficient power allocation and modulation and coding selection scheme 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.617-626
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• 2006

In this paper, we propose an ASA(Aggressive Subchannel Allocation) algorithm, which is an effective dynamic channel allocation algorithm considering all user's channel state to maximize downlink sector throughput in OFDMA system. We compare an ASA algorithm with Round Robin, ACG(Amplitude Craving Greedy), RCG(Rate Craving Greedy) and GPF(General Proportional Fair) in the 2-tier environment of FRF(Frequency Reuse Factor) 1 and then analyze the performance of each algorithms, through compute simulation. Simulation results show that the proposed ASA algorithm gets 58 %, 190 %, 130 % and 8.5 % better sector throughput compared with the Round Robin, ACG, RCG and GPF respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7A
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• pp.768-775
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• 2008

In this paper, we consider downlink throughput performances of multiuser orthogonal frequency division multiplexing with reduced channel information feedback schemes. Specifically, two types of reduced feedback schemes, namely, 1-bit per sub-carrier and selective feedback scheme are considered and compared with each other in terms of average network throughput. Since the strict throughput comparison for given number of feedback bits per user is quite difficult, rather we compare their general behaviors in various system configurations with different system parameters, which can give us an insight into practical system design with those reduced feedback schemes.

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

• Journal of Communications and Networks
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• v.18 no.3
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• pp.387-396
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• 2016

Multiuser communication has been an important research area of underwater acoustic communications and networking. This paper studies the use of adaptive orthogonal frequency-division multiple access (OFDMA) in a downlink scenario, where a central node sends data to multiple distributed nodes simultaneously. In practical implementations, the instantaneous channel state information (CSI) cannot be perfectly known by the central node in time-varying underwater acoustic (UWA) channels, due to the long propagation delays resulting from the low sound speed. In this paper, we explore the CSI feedback for resource allocation. An adaptive power-bit loading algorithm is presented, which assigns subcarriers to different users and allocates power and bits to each subcarrier, aiming to minimize the bit error rate (BER) under power and throughput constraints. Simulation results show considerable performance gains due to adaptive subcarrier allocation and further improvement through power and bit loading, as compared to the non-adaptive interleave subcarrier allocation scheme. In a lake experiment, channel feedback reduction is implemented through subcarrier clustering and uniform quantization. Although the performance gains are not as large as expected, experiment results confirm that adaptive subcarrier allocation schemes based on delayed channel feedback or long term statistics outperform the interleave subcarrier allocation scheme.