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In wireless MIMO ad-hoc networks, channel reciprocity is assumed to optimize transmit and receive beamformers in conventional beamforming algorithms. But, when channels between nodes are not reciprocal, it is a huge burden to the feedback channel to inform a transmitting node of the channel state information. In this paper, we propose a distributed beamforming scheme with limited feedback for non-reciprocal...
Efficient pilot designs are vital as they improve system performance and resource utilization, especially in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Most of the existing pilot designs do not consider in-phase and quadrature (I/Q) imbalance whose detrimental effects become more severe since the technology and applications are pushing towards smaller...
In this treatise, we propose an iteratively decoded Bell-labs LAyered Space-Time (BLAST) scheme, which serially concatenates an IRregular Convolutional Code (IRCC), a UnityRate Code (URC) and a BLAST transmitter. The proposed scheme is capable of achieving a near capacity performance with the aid of our Extrinsic Information Transfer (EXIT) chart assisted design procedure. Furthermore, a Markov Chain...
This paper proposes a low-complexity algorithm to calculate log likelihood ratios (LLRs) of coded bits, which is necessary for channel decoding in coded MIMO-OFDM mobile communications. An approximate LLR needs to find a pair of transmitted signal candidates that can maximize the log likelihood function under a constraint that a coded bit be equal to either one or zero. The proposed algorithm can...
The distribution of the received signal power ?? of a multiple-input multiple-output system, with the associated 2 ?? 2 complex Wishart matrix having n degrees of freedom, is investigated under the channel inversion power allocation scheme. Exact closed-form expressions are derived for the probability density function and the cumulative distribution function of ??. The analysis covers systems with...
A wireless MIMO link is considered in a LOS configuration with multiple SISO wireless repeaters assisting. A theoretical analysis is presented in which repeater positions are considered and sufficient conditions proposed and evaluated for maximizing the MIMO multiplexing gain. The assisting repeaters would be useful when space constraints, for example, on a building top, would prohibit the wide element...
For downlink transmission in a multiuser multiple-input multiple-output (MIMO) communication system, quantized Channel State Information (CSI) is fed back to the base station in an uplink channel of finite rate. The quantized CSI is obtained via Channel Vector Quantization (CVQ) of the so-called composite channel vector, i.e., the product of the channel matrix and an estimation of the receive filter,...
This paper studies the computation of postprocessing signal-to-interference plus noise ratio (SINR) for maximum likelihood detector (MLD) in multiple-input and multiple output (MIMO)-orthogonal frequency division multiplexing (OFDM) spatial multiplexing systems. We derive an effective post-MLD SINR for each spatial stream, which is computed as post minimum mean-squared error (MMSE) SINR plus gain...
This paper presents a novel multi-functional MultipleInput Multiple-Output (MIMO) scheme that combines the benefits of the Vertical Bell Labs Layered Space-Time (V-BLAST) scheme, of SpaceTime Codes (STC) as well as of beamforming. To further enhance the attainable system performance and to maximise the coding advantage of the proposed transmission scheme, the system is also combined with multi-dimensional...
This paper studies the design of a decentralized multiuser MIMO system for spectrum sharing over a fixed bandwidth, where the coexisting users independently update their transmit covariance matrices for individual rate maximization via an iterative manner. This design problem was usually investigated in the literature by assuming that each user treats the co-channel interference from all the other...
This paper develops a joint maximum a posteriori (MAP) spatial filtering receiver by employing a joint parameter estimation approach for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) modulation systems, which can achieve promising bit-error-rate (BER) performance in the presence of co-channel interference (CCI). For a MAP receiver to suppress the CCI, conventionally,...
In this paper we propose time-varying decision feedback FIR equalization techniques for multiple-input multiple-output (MIMO) transmission over doubly selective channels. The doubly selective channel is approximated using the basis expansion model (BEM), and equalized by means of time-varying FIR filters. The time-varying FIR filters are modeled using the BEM. By doing so, the time-varying deconvolution...
This paper deals with the equalization of a nonirreducible multiple-input multiple-output (MIMO) finite-impulse-response (FIR) channel provided that the estimate of the channel matrix is available. An iterative method is developed to perform the channel equalization. The effectiveness of the proposed equalization method is demonstrated by simulation examples.
In this paper, we study the impact of antenna correlation at mobile units (MUs) on the capacity of multi-user multiple-input multiple-output (MIMO) systems with rate constraints. Both numerical results and asymptotic analyses show that antenna correlation can actually be regarded as a beneficial factor for such systems. It is also shown that the maximum eigenmode beamforming (MEB) based interleave-division...
In this work we consider the optimization of the power assigned to the user streams, in a coordinated base station downlink environment, when zero-forcing is employed to remove interference among users. Two schemes based on the waterfilling technique are proposed and compared to the optimal solution, which can be obtained numerically, by using convex optimization. We show that the proposed schemes...
This paper proposes a new hybrid structure for the practical MIMO receiver. The receiver operates in a QRMLD mode by default and achieves near-optimal performance. On the other hand, when the communication environment is not so favorable for a QR-MLD, it switches to a QR-MMSE mode and saves the mobile computing power. Using a common structure of QR decomposition from both receivers and the novel QR-MMSE...
Semi-blind space-time equalisation is considered for dispersive multiple-input multiple-output systems that employ high-throughput quadrature amplitude modulation signalling. A minimum number of training symbols, approximately equal to the dimension of the space-time equaliser (STE), are first utilised to provide a rough initial least squares estimate of the STE's weight vector. A gradient-Newton-type...
This paper proposes a novel receiver scheme for multiple-input multiple-output (MIMO) systems with hybrid-automatic-retransmission-request (HARQ) mechanism. The proposed scheme improves the decoding performance by characterizing and counteracting uncertainty of the soft decisions. Furthermore, the proposed scheme can make full use of the received signals and especially performs well when the prior...
In multiple-input multiple-output (MIMO) broadcast channels, the base station transmits information to multiple noncooperative users simultaneously. With perfect channel state information (CSI) at the base station, vector perturbation (VP) precoding technique achieves full diversity order. In this paper, we study the symbol error rate (SER) performance of such systems with quantized channel feedback...
In this paper, we address the robust linear transceiver design for dual-hop amplify-and-forward (AF) MIMO relay systems, where both transmitters and receivers have imperfect channel state information (CSI). With the statistics of channel estimation errors in the two hops being Gaussian, we formulate the robust linear-minimum-mean-square-error (LMMSE) transceiver design problem using the Bayesian framework,...
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