Browsing by Subject "MIMO systems"

Now showing 1 - 14 of 14

Open Access
Capacity of printed dipole arrays in the MIMO channel
(Institute of Electrical and Electronics Engineers, 2008-10) Tunc, C. A.; Aktas, D.; Ertürk, V. B.; Altintas, A.
Moments performance of printed dipole arrays in the MIMO channel is investigated using a channel model based on the Method of solution of the electric-field integral equation. Comparisons with freestanding dipoles are given in terms of channel capacity. Effects of the electrical properties (such as the dielectric thickness and permittivity) on the MIMO capacity are explored. Various dielectric-substrate configurations yielding high-capacity MIMO arrays are presented.
Open Access
Low order controller design for systems with time delays
(2011-12) Gündeş, A. N.; Özbay, Hitay
Finite-dimensional controller synthesis methods are developed for some classes of linear, time-invariant, single-input single-output, or multi-input multi-output systems, which are subject to time delays. The proposed synthesis procedures give low-order stabilizing controllers that also achieve integral-action so that constant reference inputs are tracked asymptotically with zero steady-state error. © 2011 IEEE.
Open Access
Mode shift keying for reconfigurable MIMO antennas: performance analysis and antenna design
(IEEE, 2019-01) Hasan, M.; Bahçeci, İsrafil; Towfiq, Md. A.; Duman, Tolga M.; Çetiner, B. A.
Space-shift-keying (SSK) and spatial modulation (SM) enable multiple antenna transmission systems to convey information on antenna indices. While SSK/SM helps reduce the number of radio frequency (RF) chains, large numbers of antennas and low spatial correlations are required to achieve high data rates. This work investigates the use and design of multifunctional reconfigurable antennas (MRAs) for SSK/SM based transmission where a single-element MRA generates large numbers of modes. To enhance legacy SSK/SM performance while reducing RF hardware complexity, we propose single- and multi-carrier antenna mode-shift keying (MoSK) and mode modulation (MoM) schemes facilitated by MRAs. Based on an error probability analysis, we determine criteria for MRA design and mode set selection suitable for MoSK/MoM. We also develop two MRA designs and investigate their performances over Rayleigh fading channels. We argue that by creating MRA modes with low pattern correlations, channel correlations can be reduced to improve the detection performance. Extensive simulations demonstrate that MoSK/MoM performance exceeds that of SSK/SM along with significant complexity reduction. For instance, a single-carrier MoSK/MoM using a single MRA with 8 modes achieves about 2 dB gain compared to legacy SSK/SM requiring 8 antennas, and by multi-carrier MoSK/MoM using 4 subcarriers, an MRA with 32 modes can attain an error rate performance comparable to this single-carrier system.
Open Access
Multi-input multi-output deletion channel
(Institute of Electrical and Electronics Engineers, 2012) Wang F.; Duman, T. M.
We describe a new channel model suitable in certain applications, namely the multi-input multi-output (MIMO) deletion channel. This channel models the scenarios where multiple transmitters and receivers suffering from synchronization errors are employed. We then consider a coding scheme over such channels based on a serial concatenation of a low-density parity check (LDPC) code, a marker code and a layered space-time code. We design two detectors operating at the bit level which jointly achieve synchronization for the deletion channel (with the help of the marker code) and detection for the MIMO channel. Utilizing the proposed detector together with an LDPC code with powerful error-correction capabilities, we demonstrate that reliable transmission over a MIMO deletion channel is feasible.
Open Access
Multiple-resampling receiver design for OFDM over Doppler-distorted underwater acoustic channels
(2013) Tu, K.; Duman, T. M.; Stojanovic, M.; Proakis J. G.
In this paper, we focus on orthogonal frequency-division multiplexing (OFDM) receiver designs for underwater acoustic (UWA) channels with user-and/or path-specific Doppler scaling distortions. The scenario is motivated by the cooperative communications framework, where distributed transmitter/receiver pairs may experience significantly different Doppler distortions, as well as by the single-user scenarios, where distinct Doppler scaling factors may exist among different propagation paths. The conventional approach of front-end resampling that corrects for common Doppler scaling may not be appropriate in such scenarios, rendering a post-fast-Fourier-transform (FFT) signal that is contaminated by user-and/or path-specific intercarrier interference. To counteract this problem, we propose a family of front-end receiver structures that utilize multiple-resampling (MR) branches, each matched to the Doppler scaling factor of a particular user and/or path. Following resampling, FFT modules transform the Doppler-compensated signals into the frequency domain for further processing through linear or nonlinear detection schemes. As part of the overall receiver structure, a gradient-descent approach is also proposed to refine the channel estimates obtained by standard sparse channel estimators. The effectiveness and robustness of the proposed receivers are demonstrated via simulations, as well as emulations based on real data collected during the 2010 Mobile Acoustic Communications Experiment (MACE10, Martha's Vineyard, MA) and the 2008 Kauai Acomms MURI (KAM08, Kauai, HI) experiment.
Open Access
A new signaling scheme for Underwater Acoustic communications
(IEEE, 2013) Elmoslimany, A.; Zhou, M.; Duman, Tolga M.; Papandreou-Suppappola, A.
Underwater Acoustic (UWA) communications has attracted a lot of interest in recent years motivated by a wide range of applications. Different signaling solutions have been developed to date including non-coherent communications, phase coherent systems, multi-input multi-output (MIMO) solutions and multi-carrier based approaches. In this paper, we develop a novel UWA communications paradigm using biomimetic signals. In our scheme, digital information is mapped to the parameters of a class of biomimetic signal set and at the receiver an estimator to obtain the parameter values is utilized. To facilitate this, we develop analytical signal models with nonlinear instantaneous frequencies matching mammalian sound signatures in the time-frequency plane. We provide suitable receiver structures, and present decoding results using data recorded during the Kauai Acomms MURI 2011 (KAM11) UWA communications experiment. © 2013 MTS.
Open Access
On secrecy rate analysis of spatial modulation and space shift keying
(IEEE, 2015) Aghdam, Sina Rezaei; Duman, Tolga M.; Di Renzo, M.
Spatial modulation (SM) and space shift keying (SSK) represent transmission methods for low-complexity implementation of multiple-input multiple-output (MIMO) wireless systems in which antenna indices are employed for data transmission. In this paper, we focus our attention on the secrecy behavior of SSK and SM. Using an information-theoretic framework, we derive expressions for the mutual information and consequently compute achievable secrecy rates for SSK and SM via numerical evaluations. We also characterize the secrecy behavior of SSK by showing the effects of increasing the number of antennas at the transmitter as well as the number of antennas at the legitimate receiver and the eavesdropper. We further evaluate the secrecy rates achieved by SM with different sizes of the underlying signal constellation and compare the secrecy performance of this scheme with those of general MIMO and SIMO systems. The proposed framework unveils that SM is capable of achieving higher secrecy rates than the conventional single-antenna transmission schemes. However, it underperfoms compared to a general MIMO system in terms of the achievable secrecy rates.
Open Access
On the capacity of MIMO systems with amplitude-limited inputs
(IEEE, 2014) Elmoslimany, A.; Duman, Tolga M.
In this paper, we study the capacity of multiple-input multiple-output (MIMO) systems under the constraint that amplitude-limited inputs are employed. We compute the channel capacity for the special case of multiple-input singleo-utput (MISO) channels, while we are only able to provide upper and lower bounds on the capacity of the general MIMO case. The bounds are derived by considering an equivalent channel via singular value decomposition, and by enlarging and reducing the corresponding feasible region of the channel input vector, for the upper and lower bounds, respectively. We analytically characterize the asymptotic behavior of the derived capacity upper and lower bounds for high and low noise levels, and study the gap between them. We further provide several numerical examples illustrating their computation.
Open Access
On the capacity of multiple-antenna systems and parallel Gaussian channels with amplitude-limited inputs
(Institute of Electrical and Electronics Engineers Inc., 2016) Elmoslimany A.; Duman, T. M.
We propose upper and lower bounds on the capacity of multiple-input multiple-output (MIMO) systems with amplitude-limited inputs. The results are derived by considering an equivalent channel via singular value decomposition, and by enlarging and reducing the corresponding feasible region of the channel input vector, for the upper and lower bounds, respectively. We analytically characterize the asymptotic behavior of the derived bounds for high and low noise levels, and study the gap between them. We also consider parallel Gaussian channels with peak and average power-constrained inputs. For such channels, the capacity-achieving distribution has been reported in the literature to be discrete, which can be computed using numerical optimization techniques. However, there is no closed-form expression and finding the capacity-achieving distribution is computationally tedious. With this motivation, we derive approximate expressions for the capacity at low and high noise variance levels. We illustrate our findings on both MIMO channels and parallel Gaussian channels via several numerical examples. © 1972-2012 IEEE.
Open Access
On the capacity of printed planar rectangular patch antenna arrays in the MIMO channel: analysis and measurements
(IEEE, 2010) Tunc, C. A.; Olgun, U.; Ertürk, V. B.; Altintas, A.
Printed arrays of rectangular patch antennas are analyzed in terms of their MIMO performance using a full-wave channel model. These antennas are designed and manufactured in various array configurations, and their MIMO performance is measured in an indoor environment. Good agreement is achieved between the measurements and simulations performed using the full-wave channel model. Effects on the MIMO capacity of the mutual coupling and the electrical properties of the printed patches, such as the relative permittivity and thickness of the dielectric material, are explored.
Open Access
PID controller synthesis for a class of unstable MIMO plants with I/O delays
(Elsevier, 2006-07) Gündeş, A. N.; Özbay, Hitay; Özgüler, A. Bülent
Conditions are presented for closed-loop stabilizability of linear time-invariant (LTI) multi-input, multi-output (MIMO) plants with I/O delays (time delays in the input and/or output channels) using PID (Proportional + Integral + Derivative) controllers. We show that systems with at most two unstable poles can be stabilized by PID controllers provided a small gain condition is satisfied. For systems with only one unstable pole, this condition is equivalent to having sufficiently small delay-unstable pole product. Our method of synthesis of such controllers identify some free parameters that can be used to satisfy further design criteria than stability. Copyright © 2006 IFAC.
Open Access
Resilient PI and PD controllers for a class of unstable MIMO plants with I/O delays
(Elsevier, 2006-07) Özbay, Hitay; Gündeş, A. N.
Recently (Gündeş et al., 2006) obtained stabilizing PID controllers for a class of MIMO unstable plants with time delays in the input and output channels (I/O delays). Using this approach, for plants with one unstable pole, we investigate resilient PI and PD controllers. Specifically, for PD controllers, optimal derivative action gain is determined to maximize a lower bound of the largest allowable controller gain. For PI controllers, optimal proportional gain is determined to maximize a lower bound of the largest allowable integral action gain. Copyright © 2006 IFAC.
Open Access
Robust Smith predictor design with finite dimensional filters
(2024-01) Yeğin, Mustafa Oğuz
The time delay is a widely recognized inherent phenomenon present in practical control systems, and it has been a subject of extensive research over the past century. Unless managed appropriately, even a minor delay can deteriorate performance and potentially lead to instability. Therefore, incorporating a model for time delay and designing the controller to mitigate its effects are crucial steps to attain the desired robustness and performance criteria in control theory. Additionally, owing to its infinitedimensional structure, the majority of predictor-based controllers comprise finite impulse response filters, necessitating approximation with finite-dimensional transfer functions for seamless integration into physical systems. Controller designs based on the Smith predictor can effectively cancel out the impact of dead-time delay. This study introduces an extension of the Smith predictor to formulate stabilizing controllers for Linear Time Invariant (LTI) Single-Input SingleOutput (SISO) systems with multiple unstable modes and time delay. The main contribution of this approach lies in the streamlining of previous predictor-based control designs intended for unstable plants. The main contribution of this methodology lies in the simplification of previous predictor-based control designs tailored for unstable plants. The predictor filters are crafted by solving a Nevanlinna-Pick interpolation problem to attain optimal robust stability. The process also upholds the fundamental essence of the Smith predictor scheme, allowing the design of a controller based on the non-delayed nominal plant. Despite the susceptibility of Smith predictor-based designs to uncertain delays, the robustness of the proposed configuration surpasses that of the H∞ optimal controller design, as demonstrated in the relevant section. The proposed design is also extensible to a category of distributed parameter SISO systems and Multi-Input Multi-Output (MIMO) plants. For distributed parameter SISO systems, it is assumed that the plant’s transfer function can be expressed through coprime factorization. The fundamental idea underlying this approach is treating the infinite-dimensional inner factor of the plant as a “time delay,” and, in turn, determining the predictor structure accordingly. The modeling and controller design steps expounded here are exemplified using a flexible beam model. Regarding MIMO systems, provided specific conditions are met, the tangential Nevanlinna-Pick interpolation technique can be employed to derive the controller and filters according to the proposed configuration. While numerous studies have addressed model order reduction in the context of H∞-norm error, achieving optimal H∞ approximation remains a challenging and unresolved problem. This study introduces an alternative model reduction method that seeks to minimize the H∞ norm of the difference between the reduced model and the original Finite Impulse Response (FIR) structure. The proposed method essentially reduces the order of a given function by one with the minimum H∞-norm error, employ ing a high-order Pade approximation of the time-delay term. As the method reduces the order by one, an iterative algorithm is devised to recursively decrease the order of a given plant from n to a desired order of m, repeating the procedure (n − m) times following the outlined steps. The main contribution of the proposed technique is that it provides a new perspective against H∞-norm approximation by using Chebyshev equioscillation theorem on rational functions. Various examples are provided to elucidate the methodology of the suggested controller design and the robust stability condition in the context of approximating the infinite-dimensional predictor structure. Furthermore, the proposed model order reduction method is compared with the most recent state-of-the-art techniques within the literature. Finally, potential avenues for further research are deliberated, encompassing both the controller structure and H∞ approximation.
Open Access
Tangential Nevanlinna-Pick interpolation for strong stabilization of MIMO distributed parameter systems
(IEEE, 2012-12) Wakaiki, M.; Yamamoto, Y.; Özbay, Hitay
We study the problem of finding stable controllers that stabilize a multi-input multi-output distributed parameter system while simultaneously reducing the sensitivity of the system. The plants we consider have finitely many unstable transmission zeros, but they can possess infinitely many unstable poles. Using the tangential Nevanlinna-Pick interpolation with boundary conditions, we obtain both upper and lower bounds of the minimum sensitivity that can be achieved by stable controllers. We also derive a method to find stable controllers for sensitivity reduction. In addition, we apply the proposed method to a repetitive control system. © 2012 IEEE.