• Journal of Communications and Networks
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• v.15 no.4
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• pp.338-351
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• 2013

Multiple-input multiple-output (MIMO) communication may provide high spectral efficiency through the deployment of a very large number of antenna elements at the base stations. The gains from massive MIMO communication come from the use of multi-user MIMO on the uplink and downlink, but with a large excess of antennas at the base station compared to the number of served users. Initial work on massive MIMO did not fully address several practical issues associated with its deployment. This paper considers the impact of channel aging on the performance of massive MIMO systems. The effects of channel variation are characterized as a function of different system parameters assuming a simple model for the channel time variations at the transmitter. Channel prediction is proposed to overcome channel aging effects. The analytical results on aging show how capacity is lost due to time variation in the channel. Numerical results in a multicell network show that massive MIMO works even with some channel variation and that channel prediction could partially overcome channel aging effects.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.842-845
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• 2009

Wireless ad hoc networks often suffer from rapidly degrading performance with the number of user increases in the network. One of the major reasons for this rapid degradation of performance is the fact that users are sharing a single channel. Obviously, the problem of using single shared channel schemes is that the probability of collision increases with the number of nodes. Fortunately, it is possible to solve this problem with multi-channel approaches. Due to the especial properties of multiple channels, using the multiple channels is more efficient than single channel because it enhances the capacity of the channel and reduces the error rate during data transmission. Some multi-channel schemes us one dedicated channel for control packets and one separate channel for data transmissions. On the other hand, another protocols use more than two channels for data transmissions. This paper summarizes six multiple channel protocols based on these two kinds of schemes. Then we compare them and discuss the research challenge of multiple channel protocols.

• 정보화사회
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• s.7
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• pp.48-51
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• 1988

• Journal of Advanced Navigation Technology
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• v.18 no.3
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• pp.223-228
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• 2014

Recently mobile communication systems have supported various multimedia services based on wideband code division multiple access (WCDMA). In November 2013, the statistics reported that the domestic subscriber number of mobile communication systems was totally 54 million 514 thousand 397 in using feature phones and smart phones. Therefore, the user number of mobile communication services has surpassed over 4 million rather than the whole number of population. The sharp increase of the mobile user number has made the network management and analysis for mobile communication services more important than before. Besides, the service quality has been studied in various ways. This paper has implemented the simulator calculating the channel capacity of mobile communication systems to support secure and stable services for both feature phones on CDMA and smart phones on WCDMA. By using the simulator, this paper has analyzed the characteristics of the various channel capacity in mobile communication environments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.77-83
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• 2012

In this paper, when interference caused by the primary user exists, the capacity performance of the mean value-based power allocation scheme is analyzed and evaluated under the outdated channel environment in spectrum sharing systems. When interference due to the primary transmitter affects the secondary receiver, we derive the upper bound of the ergodic capacity of the mean value-based power allocation scheme in a closed form. Furthermore, based on that, we investigate how interference due to the primary transmitter degrades the ergodic capacity of the secondary user. In simulation results, we show the performance degradation of the secondary user due to interference caused by the primary user. In addition, we show that the region where the mean value-based power allocation scheme outperforms the outdated channel information-based power allocation scheme is reduced as interference by the primary user increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.2B
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• pp.170-177
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• 2009

In this paper, we propose the structures of the NBTC (Narrow-Beam Trisector Cell) and the WBTC(Wide-Beam Trisector Cell) in which directional antennas both at the base station and at the relay station are used. We analyze and compare total capacity of the both systems taking the co-channel interference into consideration for two channel models. Through analysis, we find the effect of LOS (Lind of Sight) path to the total capacity of NBTC structure and that of WBTC structure. Our work may be useful as a guideline to control the interference for the next generation mobile communication and WiBro systems using multi-hop relays.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.9
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• pp.750-758
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• 2013

In this paper, we introduce the low-density parity-check (LDPC) coded orthogonal frequency division multiplexing (OFDM) subframe reordering scheme for achieving equal combined power allocation in type I hybrid automatic repeat request (H-ARQ) systems and analyze the performance improvement by using the channel capacity. Also, it is confirmed that the layered decoding for subframe reordering scheme in H-ARQ systems gives faster convergence speed. It is verified from numerical analysis that a subframe reordering pattern having larger channel capacity shows better bit error rate (BER) performance. Therefore the subframe reordering pattern achieving equal combined power allocation for each subframe maximizes the channel capacity and outperforms other subframe reordering patterns. Also, it is shown that the subframe reordering scheme for achieving equal combined power allocation gives better performance than the conventional Chase combining scheme without increasing the decoding complexity.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.2
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• pp.92-95
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• 2015

Capacity reflecting effects of quantized feedback information is evaluated through computer simulation for practical implementation of polarization angle estimation and compensation. In the dual-polarization antenna case, evaluated capacity values varies more than four times depending on accuracy of the polarization angle estimation and compensation. Using 6-bit the quantized feedback information, we can achieve 96.8 percentage of the capacity of the perfect feedback information case.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.5
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• pp.1-9
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• 2000

In this paper, for the reverse link of a imperfect power controlled DS/CDMA cellular system when a mobile radio channel is a Rayleigh distributed multipath fading channel, A extended DS/CDMA blocking probability formula considering both shadowing and multipath fading is derived. Erlang capacity and equivalent channel number considering shadowing are analyzed and compared with those considering both shadowing and multipath fading, respectively. The DS/CDMA blocking probability is calculated based on the analysis method that obtains Erlang capacity and ICF(interference correction factor) using the median value of $E_{b(i)}$/ $I_{0}$ corresponding to each reverse link user Assuming that the blocking probability set 2%, it is observed that the Erlang capacity is 19.97 Erlang at the data rate $R_{b}$=9.6 kbps and 11.67 Erlang at the data rate $R_{b}$=14.4 kbps and then is less 16% and 19% than the Erlang capacity considering shadowing only, respectively. It is also shown that the effect of multipath fading must not be ignored and then exact Erlang capacity and equivalent channel numbers that the DS/CDMA cellular system can support are provided.d.d.d.

• Korean Management Science Review
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• v.26 no.1
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• pp.161-169
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• 2009

A traffic analysis on the Internet has an advantage for obtaining the characteristics of transferred packets. There were many studies to understand the characteristics of the Internet traffic with mathematical statistical approach. The approach of this study is different from previous studies. We first introduced a virtual network concept to present the Internet as a simplified mathematical model. It also represents each traffic flowing on the Internet as a parallel Gaussian channel on the virtual network. We suggest the optimal capacity of each parallel Gaussian channel using some related studies on the Gaussian channel model.