Co-Channel Interference Cancellation in Cellular OFDM Networks

manar mohaisen,장경희 한국통신학회 2007 韓國通信學會論文誌 Vol.32 No.5

Boosting the Uplink Throughput of OFDM Systems by Creating Resolvable Interference

Manar Mohaisen,Bing Hui,KyungHi Chang 한국전자파학회JEES 2011 Journal of Electromagnetic Engineering and Science Vol.11 No.2

Multiple-input multiple-output with orthogonal frequency division multiplexing technology (MIMO-OFDM) is considered to be the ultimate solution for increasing system throughput and for enhancing communication reliability. In this paper, we propose to increase the uplink (UL) throughput by assigning the same UL resources to multiple single-antenna mobile stations. This leads to the loss of orthogonality among sub-carriers. Thus, at the base station (BS), MIMO-OFDM detection techniques are used to separate the streams of different users assigned the same UL resources. To obtain a realistic performance evaluation, different channel scenarios are applied with different correlation values among the antennas of the users. Simulation results show that the proposed MIMO-OFDM system linearly increases the uplink capacity of the OFDM system while maintaining a mobile station transmitter as simple as that used in a conventional OFDM system. For instance, when 4 users are assigned the same UL resources, the throughput of the proposed system is 3.07 times that achieved by a conventional single input single output OFDM system.

Fixed-Complexity Sphere Encoder for Multi-User MIMO Systems

Mohaisen, Manar,Chang, Kyung-Hi The Korea Institute of Information and Commucation 2011 Journal of communications and networks Vol.13 No.1

In this paper, we propose a fixed-complexity sphere encoder (FSE) for multi-user multi-input multi-output (MU-MIMO) systems. The proposed FSE accomplishes a scalable tradeoff between performance and complexity. Also, because it has a parallel tree-search structure, the proposed encoder can be easily pipelined, leading to a tremendous reduction in the precoding latency. The complexity of the proposed encoder is also analyzed, and we propose two techniques that reduce it. Simulation and analytical results demonstrate that in a $4{\times}4$ MU-MIMO system, the proposed FSE requires only 11.5% of the computational complexity needed by the conventional QR decomposition with M-algorithm encoder (QRDM-E). Also, the encoding throughput of the proposed encoder is 7.5 times that of the QRDM-E with tolerable degradation in the BER performance, while achieving the optimum diversity order.

Detection Techniques for MIMO Multiplexing: A Comparative Review

( Manar Mohaisen ),( Hongsun An ),( Kyunghi Chang ) 한국인터넷정보학회 2009 KSII Transactions on Internet and Information Syst Vol.3 No.6

Multiple-input multiple-output (MIMO) multiplexing is an attractive technology that increases the channel capacity without requiring additional spectral resources. The design of low complexity and high performance detection algorithms capable of accurately demultiplexing the transmitted signals is challenging. In this technical survey, we introduce the state-of-the-art MIMO detection techniques. These techniques are divided into three categories, viz. linear detection (LD), decision-feedback detection (DFD), and tree-search detection (TSD). Also, we introduce the lattice basis reduction techniques that obtain a more orthogonal channel matrix over which the detection is done. Detailed discussions on the advantages and drawbacks of each detection algorithm are also introduced. Furthermore, several recent author contributions related to MIMO detection are revisited throughout this survey.

Efficiency Improvement of the Fixed-complexity Sphere Decoder

( Manar Mohaisen ),( Kyunghi Chang ) 한국인터넷정보학회 2011 KSII Transactions on Internet and Information Syst Vol.5 No.2

In this paper, we propose two schemes to reduce the complexity of fixed-complexity sphere decoder (FSD) algorithm in the ordering and tree-search stages, respectively, while achieving quasi-ML performance. In the ordering stage, we propose a QR-decomposition-based FSD signal ordering based on the zero-forcing criterion (FSD-ZF-SQRD) that requires only a few number of additional complex flops compared to the unsorted QRD. Also, the proposed ordering algorithm is extended using the minimum mean square error (MMSE) criterion to achieve better performance. In the tree-search stage, we introduce a threshold-based complexity reduction approach for the FSD depending on the reliability of the signal with the largest noise amplification. Numerical results show that in 8 X 8 MIMO system, the proposed FSD-ZF-SQRD and FSD-MMSE-SQRD only require 19.5% and 26.3% of the computational efforts required by Hassibi`s scheme, respectively. Moreover, a third threshold vector is outlined which can be used for high order modulation schemes. In 4 X 4 MIMO system using 16-QAM and 64-QAM, simulation results show that when the proposed threshold-based approach is employed, FSD requires only 62.86% and 53.67% of its full complexity, respectively.

Downlink Macro-diversity Precoding-aided Spatial Modulation

Manar Mohaisen,Vitalii Pruks 한국통신학회 2018 Journal of communications and networks Vol.20 No.1

In this paper, a downlink macro-diversity precodingaidedspatial modulation (MD-PSM) scheme is proposed, in whichtwo base stations (BSs) communicate simultaneously with a singlemobile station (MS). As such, the proposed scheme achieved twicethe spectral efficiency of the conventional PSM scheme. To renderthe demodulation possible, the two signal constellation sets used atthe two BSs should be disjoint. Also, since the two BSs use the samespatial dimension, i.e., indices of receive antennas, the Minkowskisum of the two constellation sets should include unrepeated symbols. This is achieved through rotating the constellation set usedby the second BS, where the error rate is also minimized. Afterobtaining the optimal rotation angles for several scenarios, a reducedcomplexity maximum-likelihood receiver is introduced. Foran equal number of transmit and receive antennas of 4 and at a targetbit error rate (BER) of 10 4, the simulation results show thatthe proposed MD-PSM scheme outperforms the conventional PSMby about 17.3 dB and 12.4 dB while achieving the same and doublethe spectral efficiency, respectively. Also, due to the distributed natureof MD-PSM, it is shown that the diversity order of the novelMD-PSM scheme is twice that of the conventional PSM.

Transmit Antenna Selection for Multi-user MIMO Precoding Systems with Limited Feedback

Mohaisen, Manar The Korea Institute of Information and Commucation 2011 Journal of information and communication convergen Vol.9 No.2

Transmit antenna selection techniques are prominent since they exploit the spatial selectivity at the transmitter side. In the literature, antenna selection techniques assume full knowledge of the channel state information (CSI). In this paper, we consider that the CSI is not perfectly known at the transmitter; however, a quantized version of the channel coefficients is fed back by the users. We employ the non-uniform Lloyd-Max quantization algorithm which takes into consideration the distribution of the channel coefficients. Simulation results show that the degradation in the BER of the system with imperfect CSI at the transmitter is tolerable, especially when the transmit diversity order is high.

A Review of Fixed-Complexity Vector Perturbation for MU-MIMO

( Manar Mohaisen ) 한국정보처리학회 2015 Journal of information processing systems Vol.11 No.3

Recently, there has been an increasing demand of high data rates services, where several multiuser multipleinput multiple-output (MU-MIMO) techniques were introduced to meet these demands. Among these techniques, vector perturbation combined with linear precoding techniques, such as zero-forcing and minimum mean-square error, have been proven to be efficient in reducing the transmit power and hence, perform close to the optimum algorithm. In this paper, we review several fixed-complexity vector perturbation techniques and investigate their performance under both perfect and imperfect channel knowledge at the transmitter. Also, we investigate the combination of block diagonalization with vector perturbation outline its merits.

Co-Channel Interference Cancellation in Cellular OFDM Networks PART II: Co-Channel Interference Cancellation in Single Frequency OFDM Networks using Soft Decision MLE CCI Canceler

Mohaisen, Manar,Chang, Kyung-Hi The Korea Institute of Information and Commucation 2007 韓國通信學會論文誌 Vol.32 No.7a

본 논문에서는 OFDM 셀룰라 네트워크에서 셀 가장자리에 위치한 사용자를 위한 다운링크 동일채널간섭(CCI) 제거 기법을 소개한다. 기지국간의 협력적 심볼 전송은 동일 심볼을 다른 기지국에서 상이한 부반송파를 사용하여 전송함으로서 이루어진다. 단말기에서는 전송된 심볼을 추정하기 위하여 연판정 최대우도 동일채널간섭 제거기(soft decision maximum likelihood CCI canceler)와 수정된 최대비 합성법 (modified maximum ratio combining (M-MRC))을 적용하며, 합성법에 사용된 가중치는 협력 기지국과 단말기 사이의 채널 상수에 의해서 유도된다. 시뮬레이션 결과로부터 제안된 기법이 주파수 선택적 페이딩 채널과 주파수 비선택적 페이딩 채널에서 각기 9 dB와 6dB의 SIR 이득을 보임을 알 수 있다. In this paper, a new scheme of downlink co-channel interference (CCI) cancellation in OFDM cellular networks is introduced for users at the cell-edge. Coordinated symbol transmission between base stations (BS) is operated where the same symbol is transmitted from different BS on different sub-carriers. At the mobile station (MS) receiver, we introduce a soft decision maximum likelihood CCI canceler and a modified maximum ratio combining (M-MRC) to obtain an estimate of the transmitted symbols. Weights used in the combining method are derived from the channels coefficients between the cooperated BSs and the MS. Simulations show that the proposed scheme works well under frequency-selective channels and frequency non-selective channels. A gain of 9 dB and 6 dB in SIR is obtained under multipath fading and flat-fading channels, respectively.

Efficiency Improvement of the Fixed-Complexity Sphere Decoder

( Manar Mohaisen ),( Kyunghi Chang ) 한국인터넷정보학회 2011 KSII Transactions on Internet and Information Syst Vol.5 No.3

In this paper, we propose two schemes to reduce the complexity of fixed-complexity sphere decoder (FSD) algorithm in the ordering and tree-search stages, respectively, while achieving quasi-ML performance. In the ordering stage, we propose a QR-decomposition-based FSD signal ordering based on the zero-forcing criterion (FSD-ZF-SQRD) that requires only a few number of additional complex flops compared to the unsorted QRD. Also, the proposed ordering algorithm is extended using the minimum mean square error (MMSE) criterion to achieve better performance. In the tree-search stage, we introduce a threshold-based complexity reduction approach for the FSD depending on the reliability of the signal with the largest noise amplification. Numerical results show that in 8 X 8 MIMO system, the proposed FSD-ZF-SQRD and FSD-MMSE-SQRD only require 19.5% and 26.3% of the computational efforts required by Hassibi`s scheme, respectively. Moreover, a third threshold vector is outlined which can be used for high order modulation schemes. In 4 X 4 MIMO system using 16-QAM and 64-QAM, simulation results show that when the proposed threshold-based approach is employed, FSD requires only 62.86% and 53.67% of its full complexity, respectively.