The Experts below are selected from a list of 4950 Experts worldwide ranked by ideXlab platform
Joon Ho Cho - One of the best experts on this subject based on the ideXlab platform.
-
An Optimal Full-Duplex AF Relay for Joint Analog and Digital Domain Self-Interference Cancellation
IEEE Transactions on Communications, 2014Co-Authors: Young Yun Kang, Byung-jae Kwak, Joon Ho ChoAbstract:In this paper, a full-duplex (FD) amplify-and-forward (AF) relay is designed to compensate for the duplexing loss of the half-duplex (HD) AF relay. In particular, when there is no direct link between a source and a destination, joint analog domain self-interference suppression and digital domain residual self-interference cancellation is considered with an FD-AF relay having Single Receive Antenna but multiple transmit Antennas. Unlike previous approaches, a nonconvex quadratically constrained quadratic programming problem is formulated to find the optimal solution. The end-to-end spectral efficiency or, equivalently, the end-to-end signal-to-interference-plus-noise ratio from the source to the destination is chosen as the objective function to be maximized subject to the average transmit power constraint at the relay. In addition, an average power constraint is imposed on the output of the relay's Receive Antenna to avoid the nonlinear distortion in the low noise amplifier and the excessive quantization noise in the analog-to-digital converter. Through the systematic reduction and the partitioning of the constraint set, the optimal solution is derived in a closed algorithmic expression and shows how it allocates the transmission power not only in the direction of maximal performance improvement but also in the orthogonal direction in order to balance the system performance and the amount of self interference. It is shown that the optimal FD-AF relay significantly outperforms the optimal HD-AF relay even with the hardware limitations in the RF chain of the relay's Receiver being well taken into account.
Georgios B Giannakis - One of the best experts on this subject based on the ideXlab platform.
-
quantifying the power loss when transmit beamforming relies on finite rate feedback
IEEE Transactions on Wireless Communications, 2005Co-Authors: Shengli Zhou, Zhengdao Wang, Georgios B GiannakisAbstract:Transmit beamforming achieves optimal performance in systems with multiple transmit Antennas and a Single Receive Antenna from both the capacity and the Received signal-to-noise ratio (SNR) perspectives but ideally requires perfect channel knowledge at the transmitter. In practical systems where the feedback link can only convey a finite number of bits, transmit beamformer designs have been extensively investigated using either the outage probability or the average SNR as the figure of merit. In this paper, we study the symbol error rate (SER) for transmit beamforming with finite-rate feedback in a multi-input Single-output setting. We derive an SER lower bound that is tight for good beamformer designs. Comparing this bound with the SER corresponding to the ideal case, we quantify the power loss due to the finite-rate constraint across the entire SNR range.
-
space time block coded multiple access through frequency selective fading channels
IEEE Transactions on Communications, 2001Co-Authors: Georgios B GiannakisAbstract:Mitigation of multipath fading effects and suppression of multiuser interference (MUI) constitute major challenges in the design of wide-band third-generation wireless mobile systems. Space-time (ST) coding offers an effective transmit-Antenna diversity technique to combat fading, but most existing ST coding schemes assume flat fading channels that may not be valid for wide-band communications. Single-user ST coded orthogonal frequency-division multiplexing transmissions over frequency-selective channels suffer from finite-impulse response channel nulls (fades). Especially multiuser ST block-coded transmissions through (perhaps unknown) multipath present unique challenges in suppressing not only MUI but also intersymbol/chip interference. In this paper, we design ST multiuser transceivers suitable for coping with frequency-selective multipath channels (downlink or uplink). Relying on symbol blocking and a Single-Receive Antenna, ST block codes are derived and MUI is eliminated without destroying the orthogonality of ST block codes. The system is shown capable of providing transmit diversity while guaranteeing symbol recovery in multiuser environments, regardless of unknown multipath. Unlike existing approaches, the mobile does not need to know the channel of other users. In addition to decoding simplicity, analytic evaluation and corroborating simulations reveal its flexibility and performance merits.
Vincent K. N. Lau - One of the best experts on this subject based on the ideXlab platform.
-
optimal downlink space time scheduling design with convex utility functions multiple Antenna systems with orthogonal spatial multiplexing
IEEE Transactions on Vehicular Technology, 2005Co-Authors: Vincent K. N. LauAbstract:It is well known that link level throughput could be significantly increased by using multiple Antennae at the transmitter and Receiver without increasing the bandwidth and power budget. However, optimizing the link level performance of multiple-Antenna systems does not always imply achieving system level optimization. Therefore, cross-layer optimization across the link layer and the scheduling layer is very important to fully exploit the temporal and spatial dimensions of the communication channel. In this paper, we consider the optimal downlink space-time scheduling design for a general class of convex utility functions. The access point or base station is equipped with n/sub T/ transmit Antennas. There are K mobiles in the system with a Single Receive Antenna. For practical reasons, we assume zero-forcing processing at the physical layer of the base station and mobile. We will apply the design framework to two common utility functions, namely the maximum throughput and the proportional fair. The cross-layer scheduling design is a mixed convex and combinatorial optimization problem and the search space of the optimal solution is enormous. Greedy algorithm, which has been widely used in today's wireless data systems (3G1X, high data rate system (HDR), Universal Mobile Terrestrial Service), is optimal when n/sub T/=1. However, we found that there is a large performance penalty of greedy algorithms (relative to optimal performance) when n/sub T/>1 and this motivates the search for more efficient heuristics. In this paper, we will address genetic-based heuristics and discuss their complexity-performance tradeoff.
-
optimal downlink space time scheduling design with convex utility functions multiple Antenna systems with orthogonal transmit beamforming
International Conference on Communications, 2004Co-Authors: Vincent K. N. LauAbstract:We consider the optimal downlink MISO scheduling design framework for a general class of convex utility functions. The access point or base station is equipped with n/sub T/ transmit Antennas. There are K mobiles in the system with Single Receive Antenna. For practical reasons, we constraint the physical/link layer of the base station and mobile devices to linear processing complexity in signal transmission/reception respectively. We shall apply the design framework to two common utility functions, namely the maximum throughput and the proportional fair. The scheduling problem is a mixed nonlinear integer programming problem and therefore, the complexity of the optimal solution is enormous. Greedy algorithms is widely used in today's wireless data systems (3GIX, HDR, UMTS) and is optimal when n/sub T/ = 1. However, we found that there is a large performance penalty of greedy algorithms (relative to optimal performance) when n/sub T/ > 1 and this motivates the search for more efficient heuristics. In this paper, we address genetic-based heuristics and discuss their complexity-performance tradeoff.
-
On the Design and Tradeoff of Wireless Downlink Space Time Scheduler on Network Capacity and Coverage
2004Co-Authors: Vincent K. N. LauAbstract:It is well-known that wireless scheduling algorithm could exploit multi-user diversity to enhance the network capacity of wireless systems. However, the advantage of scheduling with respect to network coverage is a relatively unexplored topic. We consider a wireless system with an access point or base station equipped with transmit Antennas as well as mobiles with Single Receive Antenna. With multiple transmit Antenna, there are additional degrees of freedom which could deliver either spatial multiplexing gain and/or spatial diversity gain. The spatial multiplexing allows simultaneous transmission to multiple clients at the same time and frequency and therefore contributes to network capacity gain. On the other hand, the spatial diversity offers robustness to channel fading and contributes to the network coverage. With cross layer scheduling, there is also multi-user selection diversity which contributes to both network capacity and coverage. In this paper, we propose a common analytical design framework for both capacity-optimized scheduler and coverage-optimized scheduler design. We show that both problems could be cast into a common optimization problem with an adjustable parameter . We found that tradeoff in the space time scheduler is required only for users close to the base station. For example, the space time scheduler should exploit spatial multiplexing ( ) and spatial diversity ( ) to optimize the network capacity and network coverage respectively. On the other hand, for users that are far from the base station, the space time scheduler should always exploit spatial diversity ( ) nomatter it is target for network coverage or network capacity. Due to huge complexity involved for the optimal solution, we propose two heuristic space-time schedulers, namely the greedy algorithm and the genetic algorithm, that allows flexible tradeoff between network capacity and network coverage. We show that the greedy algorithm, which has been widely used in today’s wireless data systems (3G1X, HDR, UMTS), offers the optimal coverage performance ( ). When , there is a large performance gap between the greedy algorithm and the optimal result. On the other hand, the genetic scheduler could fill in most of the performance gap at reasonable complexity.
Young Yun Kang - One of the best experts on this subject based on the ideXlab platform.
-
An Optimal Full-Duplex AF Relay for Joint Analog and Digital Domain Self-Interference Cancellation
IEEE Transactions on Communications, 2014Co-Authors: Young Yun Kang, Byung-jae Kwak, Joon Ho ChoAbstract:In this paper, a full-duplex (FD) amplify-and-forward (AF) relay is designed to compensate for the duplexing loss of the half-duplex (HD) AF relay. In particular, when there is no direct link between a source and a destination, joint analog domain self-interference suppression and digital domain residual self-interference cancellation is considered with an FD-AF relay having Single Receive Antenna but multiple transmit Antennas. Unlike previous approaches, a nonconvex quadratically constrained quadratic programming problem is formulated to find the optimal solution. The end-to-end spectral efficiency or, equivalently, the end-to-end signal-to-interference-plus-noise ratio from the source to the destination is chosen as the objective function to be maximized subject to the average transmit power constraint at the relay. In addition, an average power constraint is imposed on the output of the relay's Receive Antenna to avoid the nonlinear distortion in the low noise amplifier and the excessive quantization noise in the analog-to-digital converter. Through the systematic reduction and the partitioning of the constraint set, the optimal solution is derived in a closed algorithmic expression and shows how it allocates the transmission power not only in the direction of maximal performance improvement but also in the orthogonal direction in order to balance the system performance and the amount of self interference. It is shown that the optimal FD-AF relay significantly outperforms the optimal HD-AF relay even with the hardware limitations in the RF chain of the relay's Receiver being well taken into account.
Robert W. Heath - One of the best experts on this subject based on the ideXlab platform.
-
Spatial Channel Covariance Estimation for the Hybrid MIMO Architecture: A Compressive Sensing Based Approach
IEEE Transactions on Wireless Communications, 2018Co-Authors: Sungwoo Park, Robert W. HeathAbstract:Spatial channel covariance information can replace full knowledge of the entire channel matrix for designing analog precoders in hybrid multiple-input-multiple-output (MIMO) architecture. Spatial channel covariance estimation, however, is challenging for the hybrid MIMO architecture because the estimator operating at baseband can only obtain a lower dimensional pre-combined signal through fewer radio frequency (RF) chains than Antennas. In this paper, we propose two approaches for covariance estimation based on compressive sensing techniques. One is to apply a time-varying sensing matrix, and the other is to exploit the prior knowledge that the covariance matrix is Hermitian. We present the rationale of the two ideas and validate the superiority of the proposed methods by theoretical analysis and numerical simulations. We conclude the paper by extending the proposed algorithms from narrowband massive MIMO systems with a Single Receive Antenna to wideband systems with multiple Receive Antennas.
-
Multiuser MIMO in distributed Antenna systems with out-of-cell interference
IEEE Transactions on Signal Processing, 2011Co-Authors: Robert W. Heath, Young Hoon Kwon, Tao Wu, A.c.k. Anthony C K SoongAbstract:Distributed Antenna systems (DAS) augment the base station's transmit capability by adding multiple remote radio units, connected to the base station via a high bandwidth and low latency link. With DAS, the base station operates as if it had multiple Antennas, but the Antennas happen to be in different geographic locations. DAS have been shown to enhance coverage and capacity in cellular systems, in a variety of different configurations. This paper proposes, analyzes, and compares several downlink multiuser multiple input multiple output (MIMO) DAS strategies in terms of per-user throughput and area spectral efficiency. Zero-forcing transmit beamforming is used for transmission, the remote radio units may have one or more Antennas, and the subscriber has a Single Receive Antenna. Techniques considered include beamforming across all remote radio units (full transmission), using the same beamforming vector for each remote radio unit (simplified transmission), and selecting a subset of remote radio units. To facilitate rapid simulation and design space exploration, approximations of the ergodic rate are proposed for each technique assuming path-loss, small-scale Rayleigh fading, and out-of-cell interference. Simulations accounting for multiple interfering cells are used to compare the different transmission techniques. Full transmission is found to have the best performance even accounting for out-of-cell interference, though gains diminish for higher numbers of active users. Simplified transmission improves over no DAS but performance degrades with more active remote radio units.
-
using higher order cyclostationarity to identify space time block codes
Global Communications Conference, 2008Co-Authors: M R Deyoung, Robert W. Heath, B L EvansAbstract:Research in cognitive radios has renewed interest in tools, such as spectrum estimation and modulation identification, to characterize the radio frequency (RF) environment. The use of multiple Antennas for multiple-input multiple-output (MIMO) communications presents a new challenge in detecting and classifying signals. In this paper, we propose a cyclostationarity-based statistical test to detect space-time block codes, focusing on the two transmitter Alamouti space-time block code (STBC). Our test exploits a new characterization of the Alamouti code using fourth order cyclic frequencies. The test requires only a Single Receive Antenna, and does not require any symbol synchronization.
