Sharif Digital Repository

A new achievable rate based on a partial decoding scheme is proposed for the multilevel relay network. A novel application of regular encoding and backward decoding is presented to implement the proposed rate. In our scheme, the relays are arranged in feed-forward structure from the source to the destination. Each relay in the network decodes only part of the transmitted message by the previous relay. The proposed scheme differs from general parity forwarding scheme in which each relay selects some relays in the network but decodes all messages of the selected relays. It is also shown that in some cases higher rates can be achieved by the proposed scheme than previously known by Xie and... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

In this letter, we propose a new accurate approach for target localization in multiple-input multiple-output (MIMO) radars, which exploits the sparse spatial distribution of targets to reduce the sampling rate. We express the received signal of a MIMO radar in terms of the deviations of target parameters from the grid points in the form of a block sparse signal using the expansion around all the neighbor points. Applying a block sparse recovery method, we can estimate both the grid-point locations of targets and these deviations. The proposed approach can yield more accurate localization with higher detection probability compared with its counterparts. Moreover, the proposed approach can... 

This paper studies the placement of antennas in presence of mountains for widely separated multiple-input multiple-output (MIMO) radar. One of the challenges in this configuration is proper placement of the receive antennas in order to achieve good performance. We derived Neyman-Pearson decision rule for target detection. Via several scenarios we show that proper placement of receivers can provide better performance  

This paper presents the first silicon-proven implementation of a lattice reduction (LR) algorithm, which achieves maximum likelihood diversity. The implementation is based on a novel hardware-optimized due to the Lenstra, Lenstra, and Lovász (LLL) algorithm, which significantly reduces its complexity by replacing all the computationally intensive LLL operations (multiplication, division, and square root) with low-complexity additions and comparisons. The proposed VLSI design utilizes a pipelined architecture that produces an LR-reduced matrix set every 40 cycles, which is a 60% reduction compared to current state-of-the-art LR field-programmable gate array implementations. The 0.13-μm CMOS... 

This paper introduces a novel scalable pipelined VLSI architecture for a 4×4 64-QAM hard-output multiple-input-multiple-output (MIMO) detector based on K-best lattice decoders. The key contribution is a means of expanding the intermediate nodes of the search tree on-demand, rather than exhaustively, along with three types of distributed sorters operating in a pipelined structure. The proposed architecture has a fixed critical path independent of the constellation size, on-demand expansion scheme, efficient distributed sorters, and is scalable to higher number of antennas. Fabricated in 0.13 μCMOS, it occupies 0.95 μ mm} 2 core area. Operating at 282 MHz clock frequency, it dissipates 135 mW... 

In this paper we analyze and investigate the bit error rate (BER) performance of multiple-input multiple-output underwater wireless optical communication (MIMO-UWOC) systems. In addition to exact BER expressions, we also obtain an upper bound on the system BER. To effectively estimate the BER expressions, we use Gauss-Hermite quadrature formula as well as approximation to the sum of log-normal random variables. We confirm the accuracy of our analytical expressions by evaluating the BER through photon-counting approach. Our simulation results show that MIMO technique can mitigate the channel turbulence-induced fading and consequently, can partially extend the viable communication range,... 

In this paper, a sparsity-aware target localization method in multiple-input-multiple-output (MIMO) radars by utilizing time difference of arrival (TDOA) measurements is proposed. This method provides a maximum likelihood (ML) estimator for target position by employing compressive sensing techniques. Also, for fast convergence and mitigating the mismatch problem due to grid discretization, we address a block-based search coupled with an adaptive dictionary learning technique. The Cramer-Rao lower bound for this model is derived as a benchmark. Simulations results are included to verify the localization performance  

Multiple-input multiple-output (MIMO) radars offer higher resolution, better target detection, and more accurate target parameter estimation. Due to the sparsity of the targets in space-velocity domain, we can exploit Compressive Sensing (CS) to improve the performance of MIMO radars when the sampling rate is much less than the Nyquist rate. In distributed MIMO radars, block CS methods can be used instead of classical CS ones for more performance improvement, because the received signal in this group of MIMO radars is a block sparse signal in a basis. In this paper, two new methods are proposed to improve the performance of the block CS-based distributed MIMO radars. The first one is a new... 

In this paper the Multiple Relay Channels (MRC) with delays, with and without channel state information (CSI) are investigated from an information theoretic point of view. For the MRC with unlimited look ahead where the relays can use the whole received block to encode, upper and lower bounds on the capacity are derived which are tight for the degraded case. For the MRC without-delay where the relays have access to the present received symbols in addition to the past symbols, the capacity of the degraded channel is established using Shannon's strategy for the channels with side information. Then we introduce the state dependent MRC with unlimited look ahead and derive a lower bound on the... 

An algebraic closed-form solution for locating a moving target using a distributed multiple-input multiple-output radar system is proposed. The position and velocity of the target are estimated by presenting a two-stage weighted least squares algorithm. In contrast to existing research, the proposed estimator is shown analytically to be approximately unbiased and its variance is equal to the Cramer-Rao lower bound. Numerical simulations corroborate the theoretical studies and demonstrate the superiority of this algorithm over the existing methods. © 1997-2012 IEEE  

Elliptic localization is an active range-based positioning technique that employs multiple transmitter-receiver pairs, each of which is able to provide separate bistatic range (BR) measurement. In this letter, an algebraic closed-form method for locating a single target from BR measurements using a distributed multiple-input multiple-output (MIMO) radar system is proposed. First, a set of linear equations is established by eliminating the nuisance parameters, and then, a weighted least squares estimator is employed to obtain the target position estimate. To refine the localization performance, the error in the initial solution is estimated in the sequence. The proposed method is shown... 

This study considers the detector design and performance analysis in a statistical multiple-input-multiple-output radar. The authors studied this subject under some assumptions such as single point target, Swerling scattering models for radar cross-section and Gaussian interference. The target is assumed to move in a piecewise linear trajectory and multi-scan data is stored. So, the target cell may have changed during the time. A three-dimensional data signal space is generated that involved in observations from multiple scans, then a generalised likelihood ratio test detector is derived that employs consecutive observations in a central unit. Then a sub-optimum detector is introduced in... 

In this letter, the problem of target localization from bistatic range (BR) measurements in distributed multiple-input multiple-output radar systems is investigated. By introducing nuisance parameters, a pseudolinear set of BR equations is established. Then, a closed-form localization algorithm is developed, based on this pseudolinear set of equations and multistage weighted least squares estimation. This solution is shown analytically to attain the Cramer-Rao lower bound under the small Gaussian noise assumption. Simulations are included to support the theoretical studies. Unlike the existing studies where the variance of BR measurements is assumed to be independent of the corresponding... 

In this study, an algebraic closed-form method for jointly locating the target and refining the antenna positions in multiple-input-multiple-output radar systems is proposed. First, a set of linear equations is formed by non-linear transformation and nuisance parameters elimination, and then, an estimate of the target position is obtained by employing a weighted least-squares estimator. To jointly refine the target and antenna positions, the associated error terms are estimated in the sequence. The proposed method is shown analytically and confirmed by simulations to attain the Cramér-Rao lower bound performance under small-error conditions. Numerical simulations are given to support the... 

In this paper, an algebraic solution for elliptic localization in multiple-input multiple-output (MIMO) radar systems is proposed by taking the uncertainties in antenna positions and their clock parameters into account. Through nonlinear transformation and multi-stage processing, the target position is estimated in closed-form by successively utilizing the weighted least squares estimator. Theoretical analysis demonstrates that the proposed method is able to attain the Cramer-Rao lower bound (CRLB) performance under mild Gaussian error. The conditions for achieving the CRLB are derived as well. The numerical simulations confirm the analytical results and demonstrate significant performance... 

A phase-coherent technique for multiple all-digital phase-locked loops (ADPLLs) is presented and developed in this paper to target a 57-63-GHz multiple-input multiple-output (MIMO) transmitter (TX) with a digital beam-steering capability. The ADPLL TX chains are first fabricated in nanoscale CMOS and then time-synchronized and frequency-phase locked by a field-programmable gate array (FPGA) evaluation board. The calibration approach for phase alignment is carried out using a cancellation method to acquire the out-of-phase state within two ADPLLs. The accuracy of beam steering and phase alignment is investigated and analyzed based on a time-domain model for ADPLL to consider the impact of... 

In this paper, we focus on the moving target localization problem in a multiple-input multiple-output radar with widely separated antennas. By exploiting jointly different types of information including time delay, Doppler shift and azimuth and elevation angles of arrival, we develop an algebraic closed-form two-stage weighted least squares solution for the problem. The proposed algorithm is shown analytically to attain the CramerRao lower bound accuracy under the small Gaussian noise assumption. Numerical simulations are included to examine the algorithm's performance and corroborate the theoretical developments  

The authors deal with the robust design of multiple-input-multiple-output (MIMO) space-time transmit code (STTC) and space-time receive filter (STRF) for a point-like target embedded in signal-dependent interference. Specifically, they assume that the radar exploits knowledge provided by dynamic environmental database, to roughly predict the actual scattering scenario. Then, they devise an iterative method to optimise the (constrained) STTC and the (constrained) STRF which sequentially improves the worst-case (over interfering scatterers statistics) signal-to-interference-plus-noise ratio (SINR). Each iteration of the algorithm is handled via solving two (hidden) convex optimisation... 

An optimal soft multiple-input multiple-output (MIMO) detector is proposed with linear complexity for a general spatial multiplexing system with two transmitting symbols and NR 2 receiving antennas. The computational complexity of the proposed scheme is independent of the operating signal-to-noise ratio and grows linearly with the constellation order. It provides the soft maximum-likelihood solution using an efficient log-likelihood ratio calculation method, avoiding the exhaustive search on all the candidate nodes. Moreover, an efficient pipelined hardware implementation of the detection algorithm is proposed, which is fabricated and fully tested in a 130-nm CMOS technology. Operating at...