• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.967-975
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• 1998

This paper presents a system to cancel the multi-user interference of synchronous DS/CDMA systems by using the estimation circuit and the reference correlator. In the code-division multiple access(CDMA) scheme, the spectrum of the user's signal is directly spreaded by means of the Simplex coed or the phase offsetted PN code. It is interesting for the Simplex code and the PN code to have a similar correalation property. It these codes are used in DS/CDMA systems, the number of acceptable users can be increased in comparison with conventioal DS/CDMA systems. This thesis presents a interference cancellation model to cancel the multi-use interference in DS/CDMA systems by using Simples code of PN code as a spreading sequence. In AWGN environment, we analyze interference generated from other users and compare the resulting performance with that of the conventioanl receiver in same user side.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.53-59
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• 2009

In multi-user MIMO systems, a base station transmits multiple data to multi-user simultaneously in order to improve performance and bandwidth efficiency. When the base station transmits multiple data to multi-user simultaneously, multi-user interference occurs severely. In this paper, we define a post-processing leakage as the total power leaked from desired user to all other users after combining at the output of each user. Using concept of the post-processing leakage, we also define a performance metric, the so called signal-to-post-processing-leakage-plus-noise ratio (SPPLNR). Assuming that the receiver is the minimum mean square error (MMSE) receiver, we propose an iterative SPPLNR-based beamforming that determines beamforming vectors and combining vectors by using an iterative method. The proposed scheme does not impose a condition on the relation between the number of transmit antennas for the base station and the number of receive antennas for users. Simulation results show that the proposed scheme outperforms a beamforming scheme perfectly eliminating the multi-user interference when channel estimation error exists.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.4
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• pp.350-359
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• 2013

In this paper, Inter user interference elimination algorithm based on Block Diagonal Geometric Mean Decomposition(BD-GMD) for eliminating inter user interference apply to Zero-Forcing in the Successive Signal to Leakage plus Noise Ratio(SSLNR) in Coordinated Multi-Point Coordinated Beamforming system(CoMP CB). As a result, the leakage power is eliminated. The inter user interference elimination algorithm, however, cannot guarantee the enough desired signal power therefore we perform the channel ordering to overcome this disadvantage and increase the desired signal power. The simulation results show that the proposed scheme provides the improved Bit Error Rate(BER) performance compared with existing SSLNR-Zero-Forcing-Tomlinson Harashima precoding(SSLNR-ZF-THP).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.4
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• pp.180-187
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• 2014

In this paper, a extension of a fixed-complexity sphere decoder (FSD) to perform interference signal detection and cancelling is proposed for downlink multiuser multiple input-multiple output (MIMO) communication system. It is based on the application of channel matrix expansion on generalized sphere decoder (GSD), and modification of the channel matrix ordering scheme to a FSD algorithm for interference detection. A Monte Carlo simulation shows that the proposed algorithm improves the receiver performance by 3 dB as compared to maximum likelihood detection without interference cancelling at 10% packet error rate in configuration of 702 Mbit/s datarate for four users respectively on IEEE802.11ac.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.116-123
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• 2003

In this paper, we address the problem of designing multirate codes for a multiple-input and multiple-output (MIMO) system by restricting the receiver to be a successive decoding and interference cancellation type, when each of the antennas is encoded independently. Furthermore, it is assumed that the receiver knows the instantaneous fading channel states but the transmitter does not have access to them. It is well known that, in theory, minimummean- square error (MMSE) based successive decoding of multiple access (in multi-user communications) and MIMO channels achieves the total channel capacity. However, for this scheme to perform optimally, the optimal rates of each antenna (per-antenna rates) must be known at the transmitter. We show that the optimal per-antenna rates at the transmitter can be estimated using only the statistical characteristics of the MIMO channel in time-varying Rayleigh MIMO channel environments. Based on the results, multirate codes are designed using punctured turbo codes for a horizontal codedMIMOsystem. Simulation results show performances within about one to two dBs of MIMO channel capacity.

• Journal of Broadcast Engineering
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• v.21 no.1
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• pp.109-112
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• 2016

This paper analyzes the outage performance of a two-way relay network in the presence of interference from multiple interferers. We investigate a two-way relay network where a single user communicates with a selected other user via a relay during three phases. We propose a user selection scheme and analyze an outage probability. Numerical results verify our analysis by comparison with computer simulation and show effects of the number of users and the number of interferers on its the outage probability.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.410-414
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• 2006

In the present, Orthogonal Frequency Division Multiple Access (OFDMA) that wireless access scheme for high speed data transmission is noticed in mobile communication market and OFDMA/TDD scheme will be used combining Time Division Duplex (TDD) scheme based on OFDMA. The Base Station's receiver synchronizes the symbol timing to anyone user's symbol and the other user's symbols have some Symbol Timing Offset (STO). Linear phase shift is occurred by each user's STO in an OFDMA symbol and the Multiple Access Interference (MAI) caused by the summation of each user's linear phase shift degrades the performance of ranging code detection. In this paper, we analyze the ranging code detection performance for each users STO in OFDMA/TDD system. Simulation results show that the more users access and mobile speed increase, the more ranging code detection performance degrades.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.347-350
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• 2007

Adaptive arrays have been proposed as an effective means of mitigating Multiple Access Interference (MAI) and improving the performance of existing and future wireless communication systems. In this paper, we apply the analytical method proposed to analyse the theoretical Mean Bit Error Rate (BER) of an uncoded IS-95 based CDMA system with an array antenna at the BS in a Ricean fading environment. We present a modified expression for the Signal to Interference plus Noise (SINR) ratio as a function of the number of users, number of antennas and noise levels. We also verify the analytical results by means of simulations by considering different user and channel scenarios.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.8A
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• pp.601-611
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• 2012

In this paper, we first study the spatial multiplexing gain for the 3-cell interfering broadcast channels (IFBC) where all base stations and mobile users are equipped with multiple antennas. Then, we present the IA scheme in conjunction with user selection which outperforms the TDMA technique in the IFBC environment. The optimal scheduling method utilizes multiuser diversity to achieve a significant fraction of sum capacity by using an exhaustive search algorithm. To reduce the computational complexity, a suboptimal scheduling method is proposed based on a coordinate ascent approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11A
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• pp.892-902
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• 2011

The opportunistic spatial orthogonalization (OSO) scheme, proposed by Cong Shen and Michael P. Fitz, allows the existence of secondary users during the period in which the primary user is occupying all licensed bands. This paper introduces an active secondary user selection algorithm which mitigates the interference from the primary user transmitter to the secondary user receiver based on single-input multi-output system without altering a primary user's transmission strategy. A proposed algorithm guarantees the minimum average throughput of the primary user and overcomes the average sum throughput of a conventional OSO. We have numerically analyzed the average throughput under various constraints.