The Experts below are selected from a list of 94173 Experts worldwide ranked by ideXlab platform
Jinho Choi - One of the best experts on this subject based on the ideXlab platform.
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On generalized downlink Beamforming with NOMA
Journal of Communications and Networks, 2017Co-Authors: Jinho ChoiAbstract:Recently, nonorthogonal multiple access (NOMA) has been studied to increase the spectral efficiency of downlink in a multiuser system by exploiting the notion of superposition coding with successive interference cancellation (SIC). NOMA can be employed with downlink Beamforming for downlink transmissions from a base station (BS) equipped with an antenna array, which results in NOMA Beamforming. In this paper, we formulate a multiuser NOMA Beamforming problem as a semidefinite programming (SDP) problem and generalize it in order to include the conventional (multiuser) Beamforming. A low-complexity approach to decide SIC sets for the generalized NOMA Beamforming is studied using the correlation between channel vectors for better performance. From analysis and simulation results, we show that the (generalized) NOMA Beamforming can outperform the conventional Beamforming, especially under limited scattering environments.
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Minimum Power Multicast Beamforming With Superposition Coding for Multiresolution Broadcast and Application to NOMA Systems
IEEE Transactions on Communications, 2015Co-Authors: Jinho ChoiAbstract:Multicast Beamforming with superposition coding (SC) is studied for multiresolution broadcast where both data streams of high priority (HP) and low priority (LP) are to be transmitted for a user close to a base station (BS), while only data stream of LP is to be transmitted to a user not close to the BS (e.g., a cell-edge user). Using SC, a minimum total transmission power Beamforming problem has been formulated to find Beamforming vectors and powers for both users. For given normalized Beamforming vectors, a closed-form expression for the optimal power allocation is derived from which an iterative algorithm is considered to find Beamforming vectors. The proposed multicast Beamforming with SC is applied to nonorthogonal multiple access (NOMA) systems to support multiple users as a two-stage Beamforming method.
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ICC - Opportunistic Beamforming with Single Beamforming Matrix for Virtual Antenna Arrays
2011 IEEE International Conference on Communications (ICC), 2011Co-Authors: Jinho ChoiAbstract:Opportunistic Beamforming is a promising technique for downlink channels in cellular systems. When opportunistic Beamforming is to support multiple users at a time, beams should be formed to avoid interference and this requires the feedback of channel state information (CSI) from users to a base station (BS). With limited feedback, to minimize the impact of interference, the best Beamforming matrix can be selected from a set of multiple Beamforming matrices. Thus, when a different set of users are to be supported by a scheduler, a new Beamforming matrix has to be selected, which may require excessive complexity. To avoid this problem, in this paper, we propose an opportunistic Beamforming approach with single Beamforming matrix. In addition, we show that the proposed approach suits for a virtual antenna array where multiple BS units form a transmit antenna array.
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Opportunistic Beamforming With Single Beamforming Matrix for Virtual Antenna Arrays
IEEE Transactions on Vehicular Technology, 2011Co-Authors: Jinho ChoiAbstract:Opportunistic Beamforming is a promising technique for downlink channels in cellular systems. When opportunistic Beamforming is to support multiple users at a time, it is important to form multiple beams with as little interference as possible. In the conventional approach with limited feedback of channel state information from users, the best Beamforming matrix can be selected from a set of multiple Beamforming matrices. Thus, at each time when a different set of users are selected by a scheduler, a new Beamforming matrix has to be found, which may require excessive complexity. To avoid this problem, in this paper, we propose an opportunistic Beamforming approach with a single fixed Beamforming matrix for stationary users. Since the beams are fixed, we only need to perform user selection (and power allocation if necessary). It is also shown that the proposed approach is suited for a distributed virtual antenna array built by multiple base station or access point units, since the intercorrelation between the users' channel vectors in this case allows effective opportunistic Beamforming based on user classification in conjunction with a single Beamforming matrix.
Jiandong Li - One of the best experts on this subject based on the ideXlab platform.
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Hybrid Beamforming for Broadband Millimeter Wave Massive MIMO Systems
IEEE Vehicular Technology Conference, 2018Co-Authors: Rui Chen, Lina Zhu, Changle Li, Hui Xu, Jiandong LiAbstract:MmWave systems with most prior work focused on its narrowband hybrid analog/digital precoding, however, will likely operate on wideband channels with frequency selectivity. Therefore, in this paper we investigate wideband angular Beamforming schemes for mmWave massive MIMO-OFDM systems. First, for the RF analog Beamforming, the optimal Beamforming of an unconstrained antenna array (UAA) is given as the performance benchmark. Then, the optimal angular Beamforming (OAB) and a simple dominant angular Beamforming (DAB) of a shared antenna array (SAA) are compared in received SNR and implementation cost. Second, for the baseband digital precoding, the space-frequency vector perturbation (SFVP) precoding is proposed to collect both spatial and multi-path diversity. Finally, analytical and simulation results show that: a) DAB is a cost- effective RF Beamforming scheme under LOS channel environment; b) the proposed hybrid DAB-SFVP Beamforming scheme achieves the array gain equaling the number of transmit antennas $N_t$ and diversity gain equaling the product of the number of RF chains $K$ and the number of temporal resolvable clusters ℒ.
Michele Zorzi - One of the best experts on this subject based on the ideXlab platform.
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EuCNC - Context information based initial cell search for millimeter wave 5G cellular networks
2016 European Conference on Networks and Communications (EuCNC), 2016Co-Authors: Waqas Bin Abbas, Michele ZorziAbstract:Millimeter wave (mmWave) communication is envisioned as a cornerstone to fulfill the data rate requirements for fifth generation (5G) cellular networks. In mmWave communication, Beamforming is considered as a key technology to combat the high path-loss, and unlike in conventional microwave communication, Beamforming may be necessary even during initial access/cell search. Among the proposed Beamforming schemes for initial cell search, analog Beamforming is a power efficient approach but suffers from its inherent search delay during initial access. In this work, we argue that analog Beamforming can still be a viable choice when context information about mmWave base stations (BS) is available at the mobile station (MS). We then study how the performance of analog Beamforming degrades in case of angular errors in the available context information. Finally, we present an analog Beamforming receiver architecture that uses multiple arrays of Phase Shifters and a single RF chain to combat the effect of angular errors, showing that it can achieve the same performance as hybrid Beamforming.
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Context Information Based Initial Cell Search for Millimeter Wave 5G Cellular Networks
arXiv: Information Theory, 2016Co-Authors: Waqas Bin Abbas, Michele ZorziAbstract:Millimeter wave (mmWave) communication is envisioned as a cornerstone to fulfill the data rate requirements for fifth generation (5G) cellular networks. In mmWave communication, Beamforming is considered as a key technology to combat the high path-loss, and unlike in conventional microwave communication, Beamforming may be necessary even during initial access/cell search. Among the proposed Beamforming schemes for initial cell search, analog Beamforming is a power efficient approach but suffers from its inherent search delay during initial access. In this work, we argue that analog Beamforming can still be a viable choice when context information about mmWave base stations (BS) is available at the mobile station (MS). We then study how the performance of analog Beamforming degrades in case of angular errors in the available context information. Finally, we present an analog Beamforming receiver architecture that uses multiple arrays of Phase Shifters and a single RF chain to combat the effect of angular errors, showing that it can achieve the same performance as hybrid Beamforming.
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towards an appropriate Beamforming scheme for initial cell discovery in mmw 5g cellular networks
arXiv: Information Theory, 2016Co-Authors: Waqas Bin Abbas, Michele ZorziAbstract:Beamforming is an essential requirement to combat high pathloss and to improve signal-to-noise ratio during initial cell discovery in future millimeter wave cellular networks. The choice of an appropriate Beamforming is directly coupled with its energy consumption. The energy consumption is even of more concern at a battery limited mobile station (MS). In this work, we provide an energy consumption based comparison of different Beamforming schemes while considering both a low power and a high power analog-to-digital converter (ADC) for a millimeter wave based receiver at the MS. We analyze both context information (CI) (GPS positioning based) and non context information based schemes, and show that analog Beamforming with CI (where mobile station’s positioning information is already available) can result in a lower energy consumption, while in all other scenarios digital Beamforming has a lower energy consumption than analog and hybrid Beamforming. We also show that under certain scenarios recently proposed phase shifters network architecture can result in a lower energy consumption than other Beamforming schemes. Moreover, we show that the energy consumption trend among different Beamforming schemes is valid irrespective of the number of ADC bits. Finally, we propose a new signaling structure which utilizes a relatively higher frequency sub-carrier for primary synchronization signals compared to other signaling, which allows a further reduction in initial cell search delay and energy consumption of the MS.
Robert W. Heath - One of the best experts on this subject based on the ideXlab platform.
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Hybrid precoding for millimeter wave cellular systems with partial channel knowledge
2013 Information Theory and Applications Workshop (ITA), 2013Co-Authors: Ahmed Alkhateeb, O. El Ayach, Geert Leus, Robert W. HeathAbstract:Next-generation cellular standards may leverage the large bandwidth available at millimeter wave (mmWave) frequencies to provide gigabit-per-second data rates in outdoor wireless systems. A main challenge in realizing mmWave cellular is achieving sufficient operating link margin, which is enabled via directional Beamforming with large antenna arrays. Due to the high cost and power consumption of high-bandwidth mixed-signal devices, mmWave Beamforming will likely include a combination of analog and digital processing. In this paper, we develop an iterative hybrid Beamforming algorithm for the single user mmWave channel. The proposed algorithm accounts for the limitations of analog Beamforming circuitry and assumes only partial channel knowledge at both the base and mobile stations. The precoding strategy exploits the sparse nature of the mmWave channel and uses a variant of matching pursuit to provide simple solutions to the hybrid Beamforming problem. Simulation results show that the proposed algorithm can approach the rates achieved by unconstrained digital Beamforming solutions.
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interpolation based transmit Beamforming for mimo ofdm with limited feedback
IEEE Transactions on Signal Processing, 2005Co-Authors: Jihoon Choi, Robert W. HeathAbstract:Transmit Beamforming and receive combining are simple methods for exploiting spatial diversity in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. Optimal Beamforming requires channel state information in the form of the Beamforming vectors for each OFDM subcarrier. This paper proposes a limited feedback architecture that combines Beamforming vector quantization and smart vector interpolation. In the proposed system, the receiver sends a fraction of information about the optimal Beamforming vectors to the transmitter and the transmitter computes the Beamforming vectors for all subcarriers through interpolation. A new spherical interpolator is developed that exploits parameters for phase rotation to satisfy the phase invariance and unit norm properties of the transmitted Beamforming vectors. The Beamforming vectors and phase parameters are quantized at the receiver and the quantized information is provided to the transmitter. The proposed quantization system provides only a moderate increase in complexity versus over comparable approaches. Numerical simulations show that the proposed scheme performs better than existing diversity techniques with the same feedback data rate.
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interpolation based transmit Beamforming for mimo ofdm with limited feedback
International Conference on Communications, 2004Co-Authors: Jihoon Choi, Robert W. HeathAbstract:Transmit Beamforming with receive combining is a simple method for exploiting the significant diversity provided by multiple-input multiple-output (MIMO) systems, and the use of orthogonal frequency division multiplexing (OFDM) enables low complexity implementation of this scheme over frequency selective MIMO channels. This paper proposes a Beamforming technique that reduces feedback requirements for optimal Beamforming. In the proposed architecture, the receiver sends back quantized versions of select Beamforming vectors and the transmitter reconstructs the missing Beamforming vectors through interpolation. Since a Beamforming vector is phase invariant and has unit norm, a new spherical linear interpolator is proposed that exploits additional parameters for phase rotation. These parameters are determined at the receiver in the sense of maximizing the minimum channel gain or capacity, and sent back to the transmitter along with the quantized Beamforming vectors. Simulation results show that the proposed Beamforming method requires much less feedback information than optimal Beamforming with only slight diversity loss.
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Grassmannian Beamforming for multiple-input multiple-output wireless systems
IEEE Transactions on Information Theory, 2003Co-Authors: David James Love, Robert W. Heath, Thomas StrohmerAbstract:Transmit Beamforming and receive combining are simple methods for\nexploiting the significant diversity that is available in multiple-input\nmultiple-output (MIMO) wireless systems. Unfortunately, optimal performance\nrequires either complete channel knowledge or knowledge of the optimal\nBeamforming vector; both are hard to realize. In this article, a\nquantized maximum signal-to-noise ratio (SNR) Beamforming technique\nis proposed where the receiver only sends the label of the best Beamforming\nvector in a predetermined codebook to the transmitter. By using the\ndistribution of the optimal Beamforming vector in independent and\nidentically distributed Rayleigh fading matrix channels, the codebook\ndesign problem is solved and related to the problem of Grassmannian\nline packing. The proposed design criterion is flexible enough to\nallow for side constraints on the codebook vectors. Bounds on the\ncodebook size are derived to guarantee full diversity order. Results\non the density of Grassmannian line packings are derived and used\nto develop bounds on the codebook size given a capacity or SNR loss.\nMonte Carlo simulations are presented that compare the probability\nof error for different quantization strategies.
Wan Choi - One of the best experts on this subject based on the ideXlab platform.
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Machine Learning-Based Beamforming in Two-User MISO Interference Channels
2019 International Conference on Artificial Intelligence in Information and Communication (ICAIIC), 2019Co-Authors: Hyung Jun Kwon, Jung Hoon Lee, Wan ChoiAbstract:As the demand for data rate increases, interference management becomes more important, especially in small cell environment of emerging wireless communication systems. In this paper, we investigate the machine learning-based Beamforming design in two-user MISO interference channels. To see the possibilities of machine learning in Beamforming design, we consider simple Beamforming, where each user chooses one between two popular Beamforming schemes, which are the maximum ratio transmission (MRT) Beamforming and the zero-forcing (ZF) Beamforming. We first propose a machine learning structure that takes transmit power and channel vectors as input and then recommends two users' choices between MRT and ZF as output. The numerical results show that our proposed machine learning-based Beamforming design well finds the best Beamforming combination and achieves the sum-rate more than 99.9% of the best Beamforming combination.
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Achievable degrees-of-freedom of (n, K)-user interference channel with distributed Beamforming
2015 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2015Co-Authors: Seong Ho Chae, Bang Chul Jung, Wan ChoiAbstract:A distributed Beamforming technique at each user pair (transmitter-receiver) is proposed in a (n, K)-user interference channel where K user pairs are allowed to simultaneously communicate with each other among n user pairs (K ≪ n). Each transmitter sends a single spatial stream and each user pair minimizes generating interference to the scheduled receivers and the received interference from the scheduled transmitters via transmit Beamforming and receive Beamforming, respectively. We analyze scaling of n to achieve K degrees-of-freedom (DoF) with high probability via the proposed Beamforming technique. This results show that the proposed Beamforming reduces the required network size (i.e., scaling of n) compared to the previous results on (n, K)-user interference channel.
