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A modified sphere decoding (SD) scheme is proposed for multiple-input multiple-output (MIMO) communication systems in this paper. The conventional SD goes from the lower dimension to the higher dimension to examine whether a lattice point lies inside the sphere of some radius, which remains fixed for all dimensions. Since the sphere radius directly affects the search range and thus the complexity,...
A novel generalized iterative approach is proposed for designing the MMSE MIMO processors (precoders, relay processors and decoders) for two amplify-and-forward relaying schemes: two-hop (2Hop) and cooperative (Coop) relaying schemes. The MMSE design can be achieved for communication links with two end nodes and multiple relay nodes (all nodes with multiple antennas) subject to either the per-node...
In this paper, we propose an efficient link adaptation scheme for the 3GPP Long Term Evolution Advanced (LTEA) uplink with turbo successive interference cancelation (Turbo-SIC) receiver and imperfect channel estimation. Link adaptation for non-linear MIMO receivers such as Turbo SIC is not straightforward because the soft-outputs of such receiver cannot be simply modeled using a scalar Gaussian channel...
Turbo equalization schemes based on minimum mean square error (MMSE) criteria available in the literature for multiple-input multiple-output (MIMO) systems are computationally expensive, as they require a relatively large matrix inversion. In this paper, we propose a low complexity turbo equalization (TE) scheme with successive interference cancellation for orthogonal frequency division multiplexing...
In previous works, MIMO beamforming in multiuser wireless systems is typically formulated in two ways: one is minimizing the total transmit power with individual signal-to-interference-plus-noise ratio (SINR) constraints for each user; and the other one is maximizing the minimum SINR among all the users with a total transmission power constraint. However, although the total transmit power is optimized,...
In this paper, we apply vector perturbation (VP) precoding to a network multiple-input multiple-output (MIMO) scheme, in which downlink transmissions from base stations are coordinated. We propose a multi-cell VP by introducing a common power scaling factor for all base stations in order to satisfy per base station power constraint. In our scenario, we consider multiple-antenna users with heterogeneous...
The virtual MIMO (V-MIMO) and coordinated multipoint transmission (CoMP) are adopted by the LTE system to extend the uplink spectral efficiency. V-MIMO makes use of spatial multiplexing to increase system throughput while CoMP by means of mitigating inter cell interference (ICI) significantly achieve the same effect. In this paper, we present an orthogonality based proportional fair scheduling (OPF)...
Channel reciprocity is regarded as one of the most important advantages of TDD systems. However, the RF front-ends contribute to the channel experienced, and their TX/RX mismatches might cause reciprocity error, and thus degrade system throughput. Therefore, channel reciprocity calibration is a crucial issue. Among the existing calibration methods, Over-the-air (OTA) calibration is a promising approach...
MIMO, OFDMA and cooperative relaying are the key technologies in future wireless communication systems. However, under the usage of these technologies, resource allocation becomes a more crucial and challenging task. In multi-user MIMO-OFDMA relay-enhanced cellular networks, we formulate the optimal instantaneous resource allocation problem including user group selection, path selection, power allocation,...
In this paper, we investigate the joint effects of high-power amplifier (HPA) nonlinearity, in-phase/quadrature-phase (I/Q) imbalance and crosstalk, on the performance of multiple-input multiple-output (MIMO) transmit beamforming (TB) systems, and propose a compensation method for the three impairments together. The performance of the MIMO TB system equipped with the proposed compensation scheme is...
Antenna gain mismatch between transmitter and receiver circuits has been regarded as an obstacle for exploiting channel reciprocity between uplink and downlink channels in time-division duplex (TDD) multiple-input multiple-output (MIMO) systems. To the best knowledge of the authors, little work to date has been on about the impact of antenna mismatches on the precoding vector. Motivated by this fact,...
Mobile broadcasting MIMO systems differ in several essential ways from conventional MIMO applications, especially when they are operating in single-frequency networks. There are certain channel features, like the imbalance of received average powers, which should be taken into account in system design. In this paper, space-time coding that allows reduced complexity maximum likelihood decoding of the...
Not only the minimum Euclidean distance but also the number of neighbors providing the dmin in the received constellation has an important role in reducing the error probability when Maximum Likelihood detection is considered. Assuming that the channel-state-information is available at the transmitter, a new precoder in which the rotation parameter has no influence is proposed for two independent...
A unified Bit-based Probabilistic Data Association (B-PDA) detection approach is proposed for Multiple-Input Multiple-Output (MIMO) systems employing high-order Quadrature Amplitude Modulation (QAM). The new approach transforms the symbol detection process of QAM to a bit-based process by introducing a Unified Matrix Representation (UMR) of QAM. Both linear natural and nonlinear Gray bit-to-symbol...
In this paper, throughput of cognitive multiple-input multiple-output (MIMO) systems operating under quality-of-service (QoS) constraints is studied. It is assumed that transmission power and the covariance of the input signal vector are varied depending on the sensed activities of primary users in the system. Considering the reliability of the transmission and channel sensing results, a state-transition...
An interference management method for coordinating downlink transmission in a Multiple-Input Multiple-Output (MIMO) cellular network is proposed. The problem is to efficiently manage inter-cell interference in a multi-cell environment, by so-called transmitter cooperation, in order to reduce the diminishing effects of interference on the networks performance. To allow for application in deployable...
In downlink Multiuser Multiple-Input Multiple-Output (MU-MIMO) systems, the zero-forcing (ZF) transmission is a simple and effective technique for separating users and data streams of each user at the transmitter side, but its performance depends greatly on the accuracy of the available channel state information (CSI) at the transmitter. Due to the existence of the CSI delay and channel estimation...
Double space-time transmit diversity (DSTTD) is currently one of the promising techniques for realizing both spatial diversity and multiplexing gains concurrently. In this paper, in contrast to previous work [6], we consider the performance of double space time transmit diversity (DSTTD) system with multi-user transmitter preprocessing (MUTP) over correlated and uncorrelated frequency-selective fading...
Multi-cell MIMO technique theoretically promises large improvement in spectral efficiency and fairness in cellular networks and is regarded as the key enabling technique for solving the troublesome issue of inter-cell interference. To evaluate its practical performance in the cellular network, we have implemented the real-time downlink multi-cell MIMO trial system operating over bandwidth of 20 MHz...
The MIMO system convincingly promises a better bit rate in comparison with a SISO system. The system gets even efficient when OFDM is amalgamated with MIMO to obtain better data rates even in hostile channel environment. Research establishes OFDM as a potential candidate for use in MIMO systems for the reasons like inherent FFT, waveform adaptation, advanced antenna techniques, multiple access, interoperability,...
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