• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.362-374
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• 2000

In this paper, trellis coded 16 QAM Multi-Carrior CDMA system is proposed, Using the equivalent signal-to-noise plus interference Power ratio (SNIR) of Multi-Carrier CDMA system in the reverse link, capacity and BER performance of trellis coded 16 QAM Multi-Carrier CDMA system are analyzed taking into account the number of multi-carrier, the number of multiple access user, the number of SC/MRC diversity branch, and Rician fading parameter in multiuser interference and Rician fading channel. And the capacity and the BER performance of trellis coded 16 QAM Multi-Carrier CDMA system using selection combining (SC) and maximal ratio cabining (MRC) diversity are numerically compared. Obtained results show that the capacity of proposed system depends on the number of multi-carrier. ti is found that the trellis coded 16 QAM Multi-Carrier CDMA system with SC/MRC antenna diversity scheme is efficient to combat multipath fading and to increase the maximum number of users in high speed data communication. With the results of analysis. MRC diversity technique provides the performance fro high speed data communications. Finally, we present a numerical approach to derive the capacity and the BER performance and to find the maximum number of multiple access user for Multi-Carrier system in multiuser interference and Rician fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.293-300
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• 2015

Recently, multiuser diversity(MUD) technique is used to improve the performance of OFDM transmission systems. With STBC antenna diversity technique, the performance of OFDM systems can be also improved. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of MUD STBC OFDM systems using pilot symbol, gauged by the bit error rate, is analyzed considering the channel estimation error. Result shows that MUD can improve the required power by a factor of approximately 5 dB for users number 32.

• 전자공학회논문지 IE
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• v.43 no.2
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• pp.75-79
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• 2006

Blind techniques without the help of training sequences are able to detect the information signal which has the minimal information of desired user. In this paper, we proposed the blind multiuser detector using the hybrid cost function to cancel the multiple user interference in direct sequence code division multiple access systems. The cost function of proposed blind multiuser detector is the hybrid type which joints both least mean square(LMS) algorithm and least mean fourth(LMF) algorithm. We evaluate the bit error rate(BER) performance of proposed blind multiuser detector under additive white Gaussian noise channel. Simulation results show that the proposed blind detector has an about 3dB of signal to noise ratio more than blind minimum output energy(MOE) multiuser detector under existing active user 20.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.762-772
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• 2016

This paper studies the problem of precoding and post-coding design for multicell multiuser downlink transmissions in the absence of perfect channel state information (CSI). Using statistical information of imperfect CSI, an iterative multiuser multicell transceiver design is formulated by minimizing the mean squared error (MSE) cost function of signal and leakage interference under per-base station power constraint (PBPC). The convergence of the iterative precoding and postcoding algorithm is verified by analytical and empirical results. The proposed precoding and postcoding algorithm offers a low computational complexity and robustness against CSI imperfection.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1223-1228
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• 2006

Closed-form expressions for capacity bounds of multiuser diversity combined with maximum ratio transmission (MRT) and maximum ratio combining (MRC) at each link are presented under the assumption of independent and quasi-static flat multiple-input multiple-output (MIMO) Rayleigh fading channels. The analysis results precisely agree with the numerical verification results and clearly show the impact of MRT/MRC on multiuser diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10A
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• pp.1540-1547
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• 2000

In this paper, the performance of the MMSE multiuser detector is compared with the conventional detector with respect to the signal-to-noise ratio, the number of users and the Nakagami parameter under AWGN as well as Nakagami fading channel. The results show that the MMSE multiuser detector is superior to the conventional detector with respect to cancelling the multiple access interference. However, its drawback is the hardware's complexity. To solve this drawback, the advanced MMSE multiuser detector is presented, and its performance is analyzed. The number of taps in the advanced MMSE multiuser are independent of the processing gain. Thus, the system engineer can choose the appropriate number of taps in the detector to achieve a optimal trade-off between the hardware complexity and the performance of system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4B
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• pp.298-307
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• 2002

This paper concentrates on developing and analyzing an advanced space-time multiuser receiver for WCDMA forward link. Through exploring the interference caused by co-channel users and delayed multipaths in CDMA, a constrained linear adaptive filter is adopted to cancel the interference. Furthermore, by utilizing the space-time diversity, an optimum diversity receiver, called a constrained adaptive space-time interference canceller (C-ASTIC), is proposed. For comparison, the statistical analysis of multiuser performance for WCDMA system with space-time diversity is described. The result of the simulation showed that C-ASTIC performs better than both the space-time diversity combining maximal ratio combiner (MRC) and the single-antenna adaptive interference canceller in a multipath fading channel. Also, the efficiency of the C-ASTIC in the multimedia communication environment is investigated under the multiuser, multi-transmit antenna, and multirate WCDMA system in a multipath fading channel. From the results, the C-ASTIC was validated to be useful for multi-rate WCDMA system through improving the performance gain by more than 3 dB at BER of 10$\^$-3/ in a half or more loaded system.

• Journal of Korea Society of Digital Industry and Information Management
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• v.8 no.4
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• pp.99-105
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• 2012

Recently, there are many user selection algorithms in multi user multiple-input multiple-output (MU-MIMO) systems. One of well-known user selection methods is Semi orthogonal user selection (SUS). It is an algorithm maximizing channel capacity. However, it is applicable only when user's antenna is one. We propose a generalized user selection algorithm regardless of the number of user's antennas. In the proposed scheme, Base station (Bs) selects the first user who has the highest determinant of channel and generates a user group that correlation with first user's channel is less than allowance of correlation. Then, each determinant of channels made up of first user's channel and a user's channel in the generated group is calculated and BS selects the next user who has the highest determinant of that. BS selects following users by repeating above procedure. In this paper, we get better performance because of selecting users who have the highest determinant of channel as well as allowance of correlation optimally calculated through matrix operations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.353-361
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• 2000

The performance of a multi-carrier CDMA system is analyzed considering frequency selective multipath fading and Near/Far effects. The number of multicarrier, multiuser, and arms of RAKE receiver, and the decay ratio of frequency selective multipath fading are used as a parameter for the performance analysis. More over, the distribution and the strength of multiuser interference are also considered. To evaluated the Near/Far effects in a multi-carrier CDMA system, three distribution models are assumed. In the first model. interference to carrier Ratio, I/C, ranges form -4 dB to 4dB, and at each 2 dB interval 20 % of multiuser is assumed to be uniformly distributed. In the second one, I/C ranges from -2 dB to 2 dB, and 33.3% of multiuser is assumed to be equally dispersed at each 2dB interval. The third model is 0 dB of I/C, that is, with perfect power control, multiuser are assumed to be evenly located. In this paper, multi-carrier CDMA system adoption RAKE receiver is proposed to mitigate the frequency selective multipath fading. Form the results, the third model(i.e. perfect power control)shows the best performance, and the narrower range of I/C causes the less effects to the desired signal, which reads to the better performance.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.175-185
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• 2008

In this paper, we investigate the effect of cooperative and selection relaying schemes on multiuser diversity in downlink cellular systems with fixed relay stations (RSs). Each mobile station (MS) is either directly connected to a base station (BS) and/or connected to a relay station. We first derive closed-form solutions or upper-bound of the ergodic and outage capacities of four different downlink data relaying schemes: A direct scheme, a relay scheme, a selection scheme, and a cooperative scheme. The selection scheme selects the best access link between the BS and an MS. For all schemes, the capacity of the BS-RS link is assumed to be always larger than that of RS-MS link. Half-duplex channel use and repetition based relaying schemes are assumed for relaying operations. We also analyze the system capacity in a multiuser diversity environment in which a maximum signal-to-noise ratio (SNR) scheduler is used at a base station. The result shows that the selection scheme outperforms the other three schemes in terms of link ergodic capacity, link outage capacity, and system ergodic capacity. Furthermore, our results show that cooperative and selection diversity techniques limit the performance gain that could have been achieved by the multiuser diversity technique.