Sharif Digital Repository

Selected mapping (SLM) is a well-known technique for peak-to-average-power ratio (PAPR) reduction of orthogonal frequency-division multiplexing (OFDM) systems. In this technique, different representations of OFDM symbols are generated by rotation of the original OFDM frame by different phase sequences, and the signal with minimum PAPR is selected and transmitted. To compensate for the effect of the phase rotation at the receiver, it is necessary to transmit the index of the selected phase sequence as side information (SI). In this paper, an SLM technique is introduced for the PAPR reduction of space-frequency-block-coded OFDM systems with Alamouti coding scheme. Additionally, a suboptimum... 

Clipping and filtering is a well-known technique used at the transmitter side of Orthogonal Frequency Division Multiplexing (OFDM) systems to reduce the Peak to Average Power Ratio (PAPR). In this paper, the extension of clipping and filtering to spatially multiplexed OFDM systems will be introduced. In the proposed scheme, the channel coding and clipping operations are performed at the transmitter branches independently. Based on this scheme, a receiver is proposed, which is based on the detection method of Nulling Cancellation (NC). In this method, the layer with the minimum average noise power over all subcarriers is selected and an iterative method is used to compensate for its clipping... 

In this paper, a metric based symbol predistortion method is introduced for Peak to Average Power Ratio (PAPR) reduction of the Space Frequency Block Coded (SFBC) Orthogonal Frequency Division Multiplexing (OFDM) systems with two transmitter antennas. In the proposed method, a metric is defined which shows the contribution of each frequency domain symbol to the time domain samples with high amplitude at both antennas. Then, the symbols with the highest metric values are chosen and predistorted such that the peak powers are reduced while the SFBC relationship between two antennas holds constant. Three variants of this method will be introduced. Then, this technique is extended to the general... 

In this paper, the Active Constellation Extension (ACE) technique is applied to Space Frequency Block Coded (SFBC) OFDM systems to reduce the Peak to Average Power Ratio (PAPR). For the extension of this technique to SFBC systems, it will be shown that the space frequency coded signals are the combination of several subframes and that the A CE method may be applied to these subframes. Using this model, an iterative ACE method, based on Projection Onto Convex Sets (POCS), is introduced. At each iteration, the time domain samples of the subframes are clipped based on their effect on the samples of all antennas. Then, the clipped subframes are filtered and the signals of the antennas are... 

Active Constellation Extension (ACE) is one of the techniques introduced for Peak to Average Power Ratio (PAPR) reduction of OFDM systems. In this technique, the constellation points are extended such that the PAPR is minimized but the minimum distance of the constellation points does not decrease. In this paper, an iterative ACE method is proposed for the PAPR reduction of OFDM systems with spatial diversity of Space Frequency Block Coding (SFBC). The proposed method is such that the PAPR is reduced simultaneously at all antennas, while the spatial encoding relationship still holds. In this method, at each iteration, the antenna with maximum PAPR is selected and the ACE algorithm is... 

In this paper, the performance of the gradient method based on Score Function Difference (SFD) in the separation of i.i.d. and periodic signals will be investigated. We will see that this algorithm will separate periodic signals better than i.i.d. ones. By using this experimental result and the fact that voiced frames of speech signals are approximately periodic, a modified algorithm named VDGaradient has been proposed for separation of speech signals in synthetic convolutive mixtures. In this method, voiced frames of speech signal will be used as the input to the gradient method, then the resulting separating system will be applied to separate sources completely  

In this paper, we propose a new method to recover band-limited signals corrupted by impulsive noise. The proposed method successively uses adaptive thresholding and soft decisioning to find the locations and amplitudes of the impulses. In our proposed method, after estimating the positions and amplitudes of the additive impulsive noise, an adaptive algorithm, followed by soft decision, is employed to detect and attenuate the impulses. In the next step, by using an iterative method, an approximation of the signal is obtained. This signal approximation is successively used to improve the noise estimate. The algorithm is analyzed and verified by computer simulations. Simulation results confirm... 

In this paper we propose a new method to recover bandlimited signals corrupted by impulsive noise. The proposed method uses CFAR adaptive thresholding and soft decision making to detect the locations of the impulsive noise. Then an iterative method cancels noise and reconstructs the signal. This estimate in turn will be used to make the approximation of the impulsive noise more accurate. Simulation results confirm the robustness of the proposed algorithm even when impulsive noise exceeds the theoretical reconstruction capacity. ©2008 IEEE  

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

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... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the...