scholarly journals Precoding Designs for Full-Duplex Multi-User MIMO Cognitive Networks with Imperfect CSI

2019 ◽  
Vol 9 (1-2) ◽  
Author(s):  
Xuan-Xinh Nguyen ◽  
Ha Hoang Kha
Keyword(s):  
Objective Function ◽  
Multiple Input Multiple Output ◽  
Cognitive Networks ◽  
Full Duplex ◽  
Linear Matrix ◽  
Interference Constraints ◽  
Input Multiple Output ◽  
Efficiency Performance ◽  
Sum Rate ◽  
The Difference

This paper studies a cognitive radio (CR) network which consists of a full-duplex (FD) multi-user (MU) multiple-input multiple-output (MIMO) secondary user (SU) networks operating within the coverage of multiple primary users (PUs). It is assumed that the channel state information (CSI) matrices associated with SU systems are perfectly known whereas the CSI ones from SUs to PUs are imperfectly estimated. The problem of interest is to design robust precoding matrices at the SUs to maximize the CR sum rate subject to the SU transmit power constraints and harmful interference restrictions at PUs. Due to non-concavity of the objective function and intractability of robust PU interference constraints, the design problem is non-convex and challenging to directly solve. We exploit the difference of two concave functions to recast the sum rate objective function as a lower bounded concave one. In addition, a linear matrix inequality (LMI) transformation is used to handle the semi-infinite robust interference constraints. Then, the sequential convex programming method is carried out to iteratively solve a convex optimization problem in each iteration. The simulation results are provided to investigate the CR sum-rate (spectral efficiency) performance and the robustness against the CSI uncertainty.

scholarly journals The Downlink Performance for Cell-Free Massive MIMO with Instantaneous CSI in Slowly Time-Varying Channels

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1552
Author(s):  
Tongzhou Han ◽  
Danfeng Zhao
Keyword(s):  
Power Control ◽  
Massive Mimo ◽  
Mimo Systems ◽  
Mimo System ◽  
Multiple Input Multiple Output ◽  
Time Varying ◽  
Input Multiple Output ◽  
Efficiency Performance ◽  
A Cell ◽  
Time Varying Channel

In centralized massive multiple-input multiple-output (MIMO) systems, the channel hardening phenomenon can occur, in which the channel behaves as almost fully deterministic as the number of antennas increases. Nevertheless, in a cell-free massive MIMO system, the channel is less deterministic. In this paper, we propose using instantaneous channel state information (CSI) instead of statistical CSI to obtain the power control coefficient in cell-free massive MIMO. Access points (APs) and user equipment (UE) have sufficient time to obtain instantaneous CSI in a slowly time-varying channel environment. We derive the achievable downlink rate under instantaneous CSI for frequency division duplex (FDD) cell-free massive MIMO systems and apply the results to the power control coefficients. For FDD systems, quantized channel coefficients are proposed to reduce feedback overhead. The simulation results show that the spectral efficiency performance when using instantaneous CSI is approximately three times higher than that achieved using statistical CSI.

scholarly journals Virtual MIMO Beamforming and Device Pairing Enabled by Device-to-Device Communications for Multidevice Networks

2017 ◽  
Vol 2017 ◽  
pp. 1-10
Author(s):  
Yeonjin Jeong ◽  
Jooheum Yoon ◽  
Sang Hyun Lee ◽  
Yun Hee Kim
Keyword(s):  
Multiple Input Multiple Output ◽  
Access Point ◽  
D2d Communications ◽  
Channel State ◽  
Multiple Input ◽  
Device To Device ◽  
Input Multiple Output ◽  
Sum Rate ◽  
Device Pairing ◽  
The Internet Of Things

We consider a multidevice network with asymmetric antenna configurations which supports not only communications between an access point and devices but also device-to-device (D2D) communications for the Internet of things. For the network, we propose the transmit and receive beamforming with the channel state information (CSI) for virtual multiple-input multiple-output (MIMO) enabled by D2D receive cooperation. We analyze the sum rate achieved by a device pair in the proposed method and identify the strategies to improve the sum rate of the device pair. We next present a distributed algorithm and its equivalent algorithm for device pairing to maximize the throughput of the multidevice network. Simulation results confirm the advantages of the transmit CSI and D2D cooperation as well as the validity of the distributive algorithm.

scholarly journals Optimal precoder designs for sum rate maximization in MIMO multiuser multicells

2015 ◽  
Vol 18 (3) ◽  
pp. 92-101
Author(s):  
Kha Hoang Ha ◽  
Long Dinh Nguyen ◽  
Tuan Hong Do
Keyword(s):  
Design Problem ◽  
Multiple Input Multiple Output ◽  
Base Station ◽  
Base Stations ◽  
Transmission Strategy ◽  
Difference Of Convex Functions ◽  
Input Multiple Output ◽  
Difference Of Convex ◽  
Sum Rate ◽  
User Interference

This paper is concerned with the joint linear precoder design problem for the multiuser multiple-input multiple-output (MIMO) heterogeneous networks (HetNets) in which multiple femto base stations (FBSs) coexist with a macro base station (MBS). To tackle the inter-user interference in the macrocell, we exploit the blockdiagonalization scheme and then use the convex optimization to maximize the sum rate of the macrocell. The FBS transmission strategy is to maximize the sum-rate of femtocells subject to the transmitted power constraints per FBS and restrictions on the cross-tier interference to macro-users (MUs). Such a design problem is typically nonconvex, and, thus, challenging to find the FBS precoders. We reformulate the design problem of the FBS precoders as a d.c. (difference of convex functions) programming, and develop an efficient iterative algorithm to obtain the optimal precoders. Numerical simulation results show that the proposed algorithm outperforms the other methods in terms of the total sum-rate of the HetNet.

scholarly journals Low complexity full duplex MIMO systems: Analog canceler architectures, beamforming design, and future directions

2021 ◽  
Vol 2 (2) ◽  
pp. 109-127
Author(s):  
George C. Alexandropoulos
Keyword(s):  
Communication Systems ◽  
Mimo Systems ◽  
Multiple Input Multiple Output ◽  
Low Complexity ◽  
Full Duplex ◽  
Hardware Complexity ◽  
Algorithmic Solution ◽  
Input Multiple Output ◽  
The One ◽  
Rate Optimization

The hardware complexity of the analog Self-Interference (SI) canceler in conventional full duplex Multiple Input Multiple Output (MIMO) designs mostly scales with the number of transmit and receive antennas, thus exploiting the benefits of analog cancellation becomes impractical for full duplex MIMO transceivers, even for a moderate number of antennas. In this paper, we provide an overview of two recent hardware architectures for the analog canceler comprising of reduced number of cancellation elements, compared to the state of the art, and simple multiplexers for efficient signal routing among the transceiver radio-frequency chains. The one architecture is based on analog taps and the other on AUXiliary (AUX) Transmitters (TXs). In contrast to the available analog cancellation architectures, the values for each tap or each AUX TX and the configuration of the multiplexers are jointly designed with the digital transceiver beamforming filters according to desired performance objectives. We present a general optimization framework for the joint design of analog SI cancellation and digital beamforming, and detail an example algorithmic solution for the sum-rate optimization objective. Our representative computer simulation results demonstrate the superiority, both in terms of hardware complexity and achievable performance, of the presented low complexity full duplex MIMO schemes over the relative available ones in the literature. We conclude the paper with a discussion on recent simultaneous transmit and receive operations capitalizing on the presented architectures, and provide a list of open challenges and research directions for future FD MIMO communication systems, as well as their promising applications.

scholarly journals Mitigating the Interference Caused by Pilot Contamination in Multi-cell Massive Multiple Input Multiple Output Systems Using Low Density Parity Check Codes in Uplink Scenario

2020 ◽  
Vol 37 (6) ◽  
pp. 1061-1074
Author(s):  
Lokesh Bhardwaj ◽  
Ritesh Kumar Mishra
Keyword(s):  
Mimo System ◽  
Multiple Input Multiple Output ◽  
Base Station ◽  
Low Density ◽  
Pilot Contamination ◽  
Parity Check ◽  
Low Density Parity Check ◽  
Multiple Input ◽  
Input Multiple Output ◽  
Sum Rate

The effects of pilot contamination (PC) on the performance of multi-cell multi-user massive multiple input multiple output (MC-MU-m-MIMO) system in uplink has been analyzed in this article. In a multi-cell scenario, the channel estimation (CE) at the desired cell using pilot reuse to avoid significant overhead results in poor CE due to PC. The improvement in degraded performance due to the effect of PC has been shown using low Density Parity Check (LDPC) codes. The comparative analysis of performance in terms of variation in bit error rate (BER) with the signal to noise ratio (SNR) for LDPC coded and uncoded information blocks of users has been shown when the number of cells sharing the same frequency band is varied. Further, the expression for sum-rate has been derived and its variation with the number of base station (BS) antennas has also been shown. The simulated results have shown that the LDPC coded scheme performs better than the uncoded counterpart and the sum-rate capacity increases when the strength of channel coefficients between the BS antennas of the desired cell and the users of remaining cells is less.

scholarly journals Sum-Rate of Multi-User MIMO Systems with Multi-Cell Pilot Contamination in Correlated Rayleigh Fading Channel

Entropy ◽  
2019 ◽  
Vol 21 (6) ◽  
pp. 573 ◽  
Author(s):  
Menghan Wang ◽  
Dongming Wang
Keyword(s):  
Rayleigh Fading ◽  
Gaussian Approximation ◽  
Mimo Systems ◽  
Mimo System ◽  
Multiple Input Multiple Output ◽  
Moment Generating Function ◽  
Base Station ◽  
Pilot Contamination ◽  
Input Multiple Output ◽  
Sum Rate

This paper presents some exact results on the sum-rate of multi-user multiple-input multiple-output (MU-MIMO) systems subject to multi-cell pilot contamination under correlated Rayleigh fading. With multi-cell multi-user channel estimator, we give the lower bound of the sum-rate. We derive the moment generating function (MGF) of the sum-rate and then obtain the closed-form approximations of the mean and variance of the sum-rate. Then, with Gaussian approximation, we study the outage performance of the sum-rate. Furthermore, considering the number of antennas at base station becomes infinite, we investigate the asymptotic performance of the sum-rate. Theoretical results show that compared to MU-MIMO system with perfect channel estimation and no pilot contamination, the variance of the sum-rate of the considered system decreases very quickly as the number of antennas increases.

scholarly journals Simultaneous Diagonalization Using Baseband Beamforming in mmWave MU-MIMO Systems

Electronics ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1944
Author(s):  
Ahmad Kamal Hassan ◽  
Ziaul Haq Abbas ◽  
Ghulam Abbas ◽  
Thar Baker
Keyword(s):  
Objective Function ◽  
Performance Metrics ◽  
Mimo Systems ◽  
Linear Optimization ◽  
Multiple Input Multiple Output ◽  
Ergodic Capacity ◽  
Simultaneous Diagonalization ◽  
Active Set ◽  
Multiple Input ◽  
Input Multiple Output

We consider the problem of simultaneous diagonalization of Hermitian matrices for the desired and co-channel interference terms of millimeter-wave (mmWave) multi-user multiple-input multiple-output systems. The joint unitary eigenvectors and the corresponding eigenvalues are known to assist in the mathematical tractability of key performance metrics, such as outage probability, ergodic capacity, and spectral efficiency. We formulate the signal-to-interference-plus-noise ratio in a canonical quadratic form and subsume the digital baseband beamforming vectors in the weight matrices of channels at the transmitter side. Next, a real scalar objective function is defined, which quantifies the correlation loss due to joint-diagonalization. The objective function is then maximized using baseband beamforming under the hardware constraints of the mmWave system. Through simulations, the proposed beamforming algorithm is evaluated by employing several non-linear optimization sub-routines, and it is shown that the “active-set” approach results in improved summary statistics both for the correlation metric and for the time complexity. We also reflect on the effect of optimization on the channel scatterers in mmWave systems.

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