• ETRI Journal
• /
• v.33 no.6
• /
• pp.831-840
• /
• 2011

This paper focuses on codebook-based precoding for space-division multiple access/orthogonal frequency-division multiple access (SDMA-OFDMA) systems aiming to guarantee high throughput for their users as well as to mitigate interference to fixed satellite service (FSS). A systematic design of SDMA codebook for subband-based OFDMA is proposed, which forms multiple orthogonal beams with common spatial null in the direction of a victim FSS earth station (ES). The design enables both transmitter and receiver to independently construct identical codebook by sharing only on the direction angle of an FSS ES, which takes fewer overhead bits than Gram-Schmidt process, a general method satisfying our design criterion. A system-level throughput evaluation shows that the proposed precoding provides superior performance over existing spectrum sharing method, that is, subband deactivation. The spectrum sharing analysis shows that the proposed precoding, even with an estimation error of the direction angles of an FSS ES, causes lower interference than existing precoding, knockdown precoding.

• ETRI Journal
• /
• v.34 no.5
• /
• pp.655-665
• /
• 2012

Based on wideband precoding (WBP) in the multiple-input multiple-output orthogonal frequency division multiplexing system, an adaptive nonuniform codebook is presented in this paper. The relationship between the precoder distribution and spatial correlation is analyzed at first. A closed-form expression based on overlapped isosceles triangles is proposed as an approximation of the precoder distribution. Then, the adaptive codebook design is derived with the approximate distribution to minimize quantization errors. The capacity and bit error rate performance demonstrate that the adaptive codebook with WBP outperforms the conventional fixed uniform codebook.

• Journal of Broadcast Engineering
• /
• v.28 no.1
• /
• pp.141-144
• /
• 2023

Recently, a joint channel estimation, channel quantization, feedback, and precoding system based on deep-neural network (DNN) was proposed. The corresponding system achieved a joint optimization based on deep learning such that it achieved a higher sum rate than the existing codebook-based precoding systems. However, this DNN-based procoding system is not directly applicable for the environments with many users such that a specific user selection can potentially increase the sum rate of the system. Thus, in this letter, we study an appropriate user selection method suitable for DNN-based precoding.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.4
• /
• pp.1292-1306
• /
• 2014

This paper proposes a space-polarization division multiple access (SPDMA) system that has limited feedback channels. The system simultaneously serves data streams to multiple mobile users through dual-polarized antenna arrays, by using pre-determined sets of precoding vectors that are orthogonal in both space and polarization domains. To this end, a codebook whose elements are sets of the precoding vectors is systematically designed based on the discrete Fourier transform (DFT) matrix and considering the power imbalance of polarized channels. Throughput of the SPDMA system is evaluated and compared to that of space division multiple access (SDMA) system, according to the various parameters including cross polarization discrimination (XPD). The results show that the throughput of SPDMA system outperforms that of SDMA in the environments of high XPD with many mobile users.

• ETRI Journal
• /
• v.36 no.1
• /
• pp.62-68
• /
• 2014

This paper presents a novel user selection method based on the signal-to-interference-plus-noise ratio (SINR), which is approximated using limited feedback data at the base stations (BSs) of multiple user multiple-input multiple-output (MU-MIMO) systems. In the proposed system, the codebook vector index, the quantization error obtained from the correlation between the measured channel and the codebook vector, and the measured value of the largest singular value are fed back from each user to the BS. The proposed method not only generates precoding vectors that are orthogonal to the precoding vectors of the previously selected users and are highly correlated with the codebook vector of each user but also adopts the quantization error in approximating the SINR, which eventually provides a significantly more accurate SINR than the conventional SINR-based user selection techniques. Computer simulations show that the proposed method enhances the sum rate of the conventional SINR-based methods by at least 2.4 (2.62) bps/Hz when the number of transmit antennas and number of receive antennas per user terminal is 4 and 1(2), respectively, with 100 candidate users and an SNR of 30 dB.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.4
• /
• pp.646-652
• /
• 2015

In this paper, the system-level performance is evaluated for the feedback scheme on the pre-coding matrix index (PMI) and channel quality indication (CQI), which are required for user selection in the multi-user MIMO system. Our analysis demonstrates that the number of users, the number of selected users, and codebook size are the key factors that govern the performance of the best companion grouping (BCG)-based user scheduling. Accordingly, we have confirmed that the probability of forming the co-scheduled user group is determined by these factors, which implies that the number of PMI's and codebook size can be dynamically determined so as to maximize the average system throughput as the number of users varies in the cell.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.7
• /
• pp.723-731
• /
• 2016

A core technological base to provide enhanced data rates required by 5G mobile wireless communications is the improved bandwidth efficiency using massive multiple-input multiple-output (MIMO) transmission. MIMO transmission requires the channel estimation using the channel state information reference signaling (CSI-RS) and appropriate beamforming, thus the design of the codebook defining proper beamforming vectors is an important issue. In this paper, we propose a multi-rank codebook based on the discrete Fourier transform (DFT) matrix, by utilizing statistical properties of the channel generated by the spatial channel model (SCM). The proposed method includes a structural change of the precoding matrix indicator (PMI) by considering the phase difference distributions between adjacent antenna elements, as well as the selected codevector characteristics of each transmission layer. Performance gain of the proposed method is evaluated and verified by making the performance comparison to the 3GPP standard codebooks adopted by Long-Term Evolution (LTE) systems.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.49 no.3
• /
• pp.14-26
• /
• 2012

In this paper, a fast diagonal-weighted Jacket matrices (DWJMs) is proposed to have the orthogonal architecture. We develop the successive DWJM to reduce the computational load while factorizing the large-order DWJMs into the low-order sparse matrices with the fast algorithms. The proposed DWJM is then applied to the precoding multiple-input and multiple output (MIMO) wireless communications because of its diagonal-weighted framework with element-wise inverse characteristics. Based on the properties of the DWJM, the DWJM can be used as alternative open loop cyclic delay diversity (CDD) precoding, which has recently become part of the cellular communications systems. Performance of the DWJM-based precoding system is verified for orthogonal space-time block code (OSTBC) MIMO LTE systems.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.49 no.10
• /
• pp.54-59
• /
• 2012

Multiple antenna transmission and reception, whose principal merits are significant increase in spectral efficiency and/or reduction in error rate, lose much of their effectiveness in high levels of interference from other cells. Incorporating the other cell interference into advanced signal processing at transmitter and receiver is one of the key challenges for cell boundary users in cellular system. Since receiver can obtain exact knowledge of interference channels more easily than transmitter, an interference-aware multiple antenna receiver that can significantly attenuate interferences is considered. Based on the receiver, codebook-based coordinated precoding schemes are proposed. According to the level of cooperation, centralized and distributed schemes are proposed. We verified by the simulation results that even the distributed schemes, which have same amount of feedback and no cooperation between cells, have performance gain compared to the conventional non-coordinated scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.17 no.12 s.115
• /
• pp.1224-1230
• /
• 2006

In this paper, for spatial multiplexing with limited feedback, a precoding scheme is proposed based on the joint use of minimal instantaneous feedback and long-term feedback of a small number of bits, wherein the long-term feedback is used to convey a selected preceding matrix within a precodercodebook consisting of a number of unitary matrices, and the active column vectors of the selected unitary matrix are conveyed to the transmitter using instantaneous feedback. Focusing on the case of dual multi-input multi-output(MIMO) systems, precoder codebook design for maximizing the average throughput of a spatial multiplexing system with a zero-forcing(ZF) receiver is proposed. It is shown that the proposed scheme provides a considerable throughput enhancement over multi-mode antenna selection and multi-mode basis selection only with the additional long-yterm feedback of a small number of bits. For example, the throughput increases by 11.5 % than antenna selection and 5.1% than basis selection, respectively, when SNR=20 dB.