Considering a multicell environment, a distributed user selection scheme for uplink multiuser multiple-input multiple-output (MU-MIMO) system is proposed. In the proposed scheme, each user determines their own transmit beamforming vector based on the locally available channel state information (CSI), and informs the associated base station (BS) of the amount of inter-cell interference (ICI) affecting adjacent cells and the resulting beamforming vector. With the identical first-order statistic between the ICI from adjacent cells and the ICI that affects adjacent cells, a set of users can be selected, which the BS will simultaneously serve based on either the achievable sum rate maximization or proportional fairness achievement. Simulation results show that compared with prior distributed user-selection schemes, the proposed method provides a significant improvement in terms of achievable sum rates.

In coordinated multi-point (CoMP) transmission systems, coordinated base stations (BSs) are geographically separated and have their own oscillators, thereby causing multiple carrier frequency offsets (CFOs) at the receiver. Therefore, perfect synchronization cannot be obtained at the mobile station (MS), resulting in severe interference. To resolve this problem, this study proposes a novel transceiver structure with improved robustness toward interference. With the knowledge of CFO and channel frequency response, a closed-form solution is derived for the sub-optimal CFO compensation value to minimize the approximated upper bound of the inter-carrier interference (ICI) plus noise power for environments with large-scale fading. The results reveal that the sub-optimal CFO compensation value is a function of both the degree of large-scale fading and the value of CFOs. Simulation results demonstrate that the proposed method significantly outperforms the existing structures and exhibits improved performance in terms of bit error rate.

In this paper, an amplify-and-forward cooperative single carrier-frequency domain equalizer system for spectrum sharing is proposed to improve the performance of the primary user (PU) and allow the secondary user (SU) to transmit its information simultaneously. To achieve this purpose, a modified data-dependent superimposed training (DDST) scheme is employed. In the original DDST scheme, a part of the frequency bins of the information signal is discarded to insert pilots. In the proposed approach, after receiving PU's data SU firstly serves as a relay and amplifies PU's data. Following, the modified DDST scheme is utilized to discard a part of the subcarriers to insert SU's data. The overall signals are transmitted to the destination. At the destination, the signals from PU and SU are combined for detection by maximizing the signal-to-noise ratio in the frequency domain. Furthermore, the signal-to-interference plus noise ratio of the primary system is analyzed. If the BER of the primary system is given, the number of subcarriers shared to the SU can be determined. The simulation results reveal that the proposed approach is more suitable for spectrum sharing compared with cooperative orthogonal frequency division multiplexing system.

This paper investigates the performance of a dual-hop amplify-and-forward relaying system with co-channel interference at both the relay and destination nodes. The source node is equipped with multiple antennas and adopts the orthogonal space-time block code to increase the system performance. Both the outage probability and the average bit error rate under the presence of multiple Rayleigh fading interferers are obtained in closed form for the variable and fixed-gain relaying schemes. Moreover, the effect of imperfect channel estimation on the variable-gain relaying scheme is also discussed. The effect of co-channel interference at both the relay and destination nodes are discussed. Simulation experiments are also conducted to verify the theoretical derivations.

The symbol interleaving scheme is one of the peak-to-average power ratio (PAPR) reduction schemes for the orthogonal frequency division multiplexing (OFDM) system. Compared with the selected mapping (SLM) and the partial transmit sequence (PTS) schemes, it does not require any extra complex multiplications to generate candidate signals aside from the complex multiplications of inverse fast Fourier transform (IFFT) operations. However, the interleaving scheme still has high computational complexity since it also requires a bank of IFFT operations. In this paper, two time-domain properties of IFFT operations are used to construct the proposed low-complexity PAPR reduction scheme. Simulation results show that the complementary cumulative distribution function (CCDF) of the proposed scheme is close to that of the traditional interleaving scheme when the given threshold γ <; 7.2 dB and N = 256 subcarriers. The CCDF of the proposed scheme is lower than that of the traditional interleaving scheme when γ ≥ 7.2 dB and N = 256 subcarriers.

This paper investigates the performance of a dual-hop amplify-and-forward relaying system with co-channel interference at the relay. The source node is equipped with multiple antennas and adopts the space-time block code to increase the diversity gain. Both the outage probability and the bit error rate in the presence of multiple Rayleigh fading interferers are obtained in closed-form. Simulation experiments are conducted to verify the theoretical derivations.

In data-dependent superimposed training (DDST) scheme, the data-induced interference in channel estimation is eliminated at the sacrifice of data distortion. Unfortunately, data distortion causes data identification problem (DIP) for DDST scheme, which results in error floor phenomenon in bit error rate (BER). Although some literatures have analyzed the DIP, the DIP is still an open problem without solution. In this work, we firstly review the data identification problem from the view of sub-space. The analysis result inspires us to introduce a precoding matrix for resolving the DIP in DDST scheme. In order to prevent the advantages in DDST scheme being reduced by the precoding matrix, we introduce several constraints on the precoding matrix. Subsequently, we derive the requirement of the precoding matrix for solving the DIP in DDST system by using singular value decomposition. Furthermore, an appropriate precoding matrix is developed based on Zadoff-Chu sequence, which is shown to satisfy all conditions derived in this work. Finally, simulation results are conducted to verify that the precoding matrix removes the error floor in BER for DDST scheme.

Relay selection for cooperative communications has been proposed as a technique to provide remarkable gains in multi-relay cooperative networks. Opportunistic relaying (OR) is a relay selection scheme used in dual-hop decode-and-forward cooperative networks, shown to be globally outage- optimal under an aggregate power constraint. However, due to channel fluctuations, the channel state information (CSI) used in the selection process may become outdated and differ from the CSI during the actual transmission of data. In this work, we analyze the effect of outdated CSI on the performance of OR over independent but not necessarily identically distributed Rayleigh fading channels. Particularly, we derive an exact expression for the average symbol error probability (SEP) of OR with outdated CSI. An approximate but tight closed-form SEP expression is also provided. We further study the asymptotic behavior of the SEP and show that the diversity order of OR reduces to one due to the outdated CSI. Finally, we perform Monte Carlo simulations to verify the analytical results.

A low-complexity blind data detector is proposed in this paper for orthogonal frequency division multiplexing (OFDM) systems, where the generalized likelihood ratio test (GLRT) approach is adopted. Traditional GLRT data detector (GDD) can be viewed as a combinatorial optimization problem, which suffers from prohibitively high computational complexity. The proposed scheme reduces the search space by exploiting the phase ambiguity. In addition, the computational complexity is further reduced by properly decoupling the GDD into several sub-group GDDs (SGDD). Mathematical analysis is adopted to evaluate the complexity of the proposed scheme. Simulation experiments are conducted to verify the system performance.

In wireless packet-forwarding networks, selfish nodes always want to maximize their utilities and do not like to help others forward data streams, thus causing severe network performance degradation. To solve the packet-forwarding problem, a novel coalitional game approach based on the selective decode-and-forward (SDF) relaying scheme is proposed. In the game-theoretic analysis, we study the properties and stability of the coalitions and prove that the cohesive behavior can be obtained by the aspect of outage probability. Simulation results show that the proposed SDF coalitional game can enforce cooperation and is beneficial in forming the cooperative groups.

Incremental opportunistic relaying (IOR) has been proposed to increase the spectral efficiency of the two-phase cooperative transmissions by exploiting limited feedback from the destination node. Specifically, the relaying process is activated only if the source-destination channel is of insufficient quality. In this case, the feedback instructs the best relay to forward the source message to the destination in order to exploit the spatial diversity. In this work, we analyze the effect of feedback delay on the performance of IOR with decode-and-forward strategy. Particularly, we derive an exact expression for the average symbol error probability (SEP) of IOR with feedback delay over independent but not necessarily identically distributed Rayleigh fading channels. An approximate but tight closed-form expression for the SEP is also provided. Finally, we perform Monte Carlo simulations to verify the analytical results. The results show that IOR is robust to the feedback delay at sufficiently high signal-to-noise ratio.

In this study, a semi-blind channel estimation algorithm for uplink multiuser orthogonal frequency division multiplexing with receiver diversity is proposed. The proposed algorithm combines simple multiuser channel estimates obtained from pilot subcarriers with subspace-based channel estimates to obtain accurate estimates for the multiuser channel gains. Minimum mean square error linear diversity combining is then performed based on the estimated channel. Simulation results show that a performance gain in excess of 1–2 dB is achievable by the proposed approach.

Orthogonal frequency division multiplexing (OFDM) systems that adopt the cyclic-delay diversity (CDD) scheme require only one inverse discrete Fourier transform (IDFT) operation at the transmitter. Therefore, the CDD provides a low-complexity means of increasing the transmission diversity in multiple-input multiple-output (MIMO) OFDM systems. However, the optimal pilot sequences which minimize the mean square error (MSE) of the channel estimate in traditional MIMO-OFDM systems are inapplicable to CDD-OFDM systems. Accordingly, this paper commences by deriving the criteria which yield the minimum MSE of both the least square (LS) channel estimate and the minimum mean square error (MMSE) channel estimate in CDD-OFDM systems. The derived criteria are then used to develop a general methodology for determining the optimal pilot sequence. Significantly, the proposed design methodology enables the status of the channel to be estimated using just one OFDM symbol. The simulation results confirm that the proposed pilot design minimizes the MSE of both the LS and the MMSE channel estimates.

Orthogonal frequency division multiplexing (OFDM) and interleave-division multiple-access (IDMA) are both attractive technique in modern wireless communication. In this paper, we study a multi-user system, which combines OFDM and IDMA, and fortunately, inherits many advantages. In order to improve system performance, low-density parity-check (LDPC) coding is further applied. And moreover, a turbo-type iterative receiver structure is investigated to mitigate multi-use interference (MUI). Simulation results are conducted to illustrate performance improvement. It is demonstrated that MUI is canceling efficiently by means of iterative multi-user detection algorithm. The proposed scheme provides an efficient solution to high-rate multiuser communications over multipath fading channels.

A 4-port antenna is designed for evaluating the performance of an MIMO system in indoor environment. Diversity gain, correlation coefficient and channel capacity are calculated and discussed in this paper. The selection diversity becomes more unapparent when using more antennas in MIMO system. Correlation in both rich scattering and high K-factor environment are found below 0.2 and 0.5 respectively. Channel capacity is 82% of the ideal case with uncorrelated channel. The above-mentioned results suggest the effectiveness of the proposed antenna.

Orthogonal frequency division multiplexing (OFDM) systems require the knowledge of signal-to-noise ratio (SNR) at the receiver in order to maximize the system performance. In general, the noise variance is required by the SNR estimator and the knowledge of noise variance also improves the performances of carrier frequency offset (CFO) and channel state estimations. This paper first investigates the maximum likelihood noise variance estimator (ML-NVE) in OFDM systems with imperfect frequency synchronization. Theoretical derivations show that both the mean and the variance of the ML-NVE are functions of the CFO. The mean and the variance of the SNR estimate are then derived by utilizing the derivation results of the ML-NVE. Finally, the validity of the theoretical observations is confirmed by simulation experiments.

State-of-the-art traffic-flow-detection technology includes the use of a looped vehicle detector, an infrared detector, an image detector, and a microwave detector. However, there are limitations that are associated with each detector. In this paper, we propose a channel awareness vehicle detector that can overcome these limitations. It employs only one pair of transmitter-receiver antennas to simultaneously perform the multilane and multivehicle identifications. By using the characteristics of channel variations, the proposed vehicle detector can determine the vehicle location, speed, and type. Our measurement results demonstrate its capabilities.

Orthogonal frequency division multiplexing (OFDM) systems require the knowledge of signal-to-noise ratio (SNR) at the receiver in order to optimize the system performance. In general, the noise variance is required by the SNR estimator and the knowledge of noise variance also improves the performance of carrier frequency offset (CFO) and channel state estimations. This paper commences by investigating the maximum likelihood noise variance estimator (ML-NVE) in OFDM systems with imperfect synchronization. Theoretical derivations show that both the mean and the variance of the ML-NVE are functions of the CFO and the advanced timing offset (ATO). In particular, it is demonstrated that the mean of the ML-NVE converges to a CFO-independent value as the ATO increases, while the variance converges to a CFO-dependent value. By exploiting the analytical results of the ML-NVE, we further investigate the SNR estimator. It is mathematically demonstrated that the SNR estimate is biased in the presence of CFO and ATO. Finally, the validity of the theoretical observations is confirmed by simulation experiments.

The performance of multiple-input multiple-output MIMO systems strongly depends on the correlation between antenna elements. In this paper, we propose a model for calculating the correlation between multi-polarized Rayleigh fading MIMO channels, which takes into account not only the gain patterns of both transmitting and receiving antennas, but also the polarization matrix of the propagation channel, array configurations and joint three-dimensional power angular spectrum on both transmitting and receiving side. The proposed model is then used to investigate the channel capacity for various 3×3 MIMO configurations in different propagation environments. It is found that when the antenna array size is limited, angular spread and cross-polarization ratio is small, the ergodic capacity of a multi-polarized configuration performs better than that of a single-polarized configuration.

The performance of multiple-input multiple- output (MIMO) systems strongly depends on the correlation between antenna elements. An analytical expression is given for the 3D spatial correlation (SC) coefficient of half-wavelength (¿/2) dipole antennas by using spherical mode expansion of plane waves. The mutual coupling (MC) effect is also considered using the concept of coupling matrix. Our results show that azimuth spread (AS) is the primary determinant of the SC of horizontally separated dipole antennas. The effect of MC on SC depends on the interelement spacing and richness of scattering.

To achieve efficient traffic control, Intelligent Transportation System (ITS) has been widely deployed in many regions such as America, Europe, Australia, Japan, and Taiwan. To prevent the unnecessary losses, ITS adopts the inter-vehicle communications to inform the drivers if there are accidents nearby. However, the ability of effective transmission distance of the emergency information depends notably on the percentage of the vehicles equipped with communication device and the characteristics of radio wave propagation. The vehicles which are not equipped with these communication devices will block the radio propagation and result in the undesirable shadowing attenuation. This paper surveys the impact of the shadowing effect for the inter-vehicle communications via the computer simulations and the field measurements. Besides, a modified three-ray shadowing model suitable for the inter-vehicle communication is proposed. With the proposed model, the influence of the showing effect on the effective transmission distance will be evaluated.

In orthogonal frequency division multiplexing (OFDM) systems, the equally-powered pilots (EPP) scheme is known to provide the best channel estimation performance when the channel status is unknown. In this study, it is shown that if we assume the channel correlation function (CCF) of a quasistatic channel is perfectly known at the receiver, all of the available pilot power should be allocated to the pilot sub-carrier with the maximum channel amplitude. In addition, a practical water-filling-type power allocation scheme, designated as the gain-powered pilots (GPP) scheme, is proposed for the case in which the CCF is subject to a certain amount of error. The simulation results indicate that the GPP scheme consistently outperforms the EPP method in terms of improving the performance of the linear minimum mean square error (LMMSE) channel estimator.

Bandwidth efficiency is a critical concern in wireless communications. To fully utilize the available bandwidth, this paper adopts the superimposed training (ST) scheme in orthogonal frequency division multiplexing (OFDM) systems without using cyclic prefix (CP) and guard interval (GI). If the pilot pattern is fixed, it is shown that the performance of the channel estimation using the ST scheme is the same for both the proposed architecture, denoted as OFDM-ST, and the OFDM system with CP and ST scheme, denoted as CP-OFDM-ST. In addition, since the CP is not adopted in the proposed system, the performances of channel estimation and data detection are degraded because of the inter-symbol interference (ISI) and the inter-carrier interference (ICI). Therefore, a novel data detector, which includes ICI cancellation, is proposed to improve the channel estimation in OFDM-ST systems. The simulation results show that the proposed algorithm substantially enhances the systems performance.

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. In a multiple-relay network, the opportunistic relay selection scheme has been shown to outperform any other strategy that involves the conventional all-participate scheme. The opportunistic relay selection scheme generally supposes the existence of a centralized entity to find out the best relay node. Unfortunately, when the number of relay nodes is increased, the resulting enormous overhead renders the centralized-based relay selection method to be impractical. Accordingly, we develop in this paper a decentralized relay selection algorithm, where each relay node decides to relay or keep silent according to its own instantaneous channel gain and a predefined threshold. Specifically, the proposed method can be considered as a process to eliminate the relay having the worse channel gain at each stage until the best relay node is determined. Simulation results illustrate that the proposed scheme has almost the same performance as that of the opportunistic relay selection method.

One of the major drawbacks of the orthogonal frequency division multiple access (OFDMA) system is the multi-user interference (MUI) induced by the carrier frequency offsets (CFOs). In sub-band based OFDMA systems, users occupy consecutive and non-overlapping frequency sub-bands. The pilots are usually placed on the edges of a sub-band for channel estimation. However, the channel estimation performance is seriously degraded by the MUI. Traditionally, the MUI is alleviated by inserting a guard sub-carrier between adjacent users. In this paper, a novel pilot architecture is proposed, where three pilots are placed on each edge of a sub-band and pilots of adjacent users are overlapped. The proposed architecture has the same bandwidth efficiency as that of the conventional guard sub-carrier insertion scheme and provides better channel estimation performance and MUI reduction.

Fourier transformation is a powerful analytical tool with wide-ranging applications in many fields. In certain cases, some of the inputs to the transformation function are zero, while the others are real or complex. For the case, where the nonzero inputs are complex, the transform decomposition (TD) method enables a significant reduction in the computational complexity. This letter proposes a modified TD (MTD) algorithm to further reduce the complexity when the nonzero input data are consecutive and real-valued. The analytical and numerical results confirm that the complexity of the MTD scheme is not only significantly lower than that of the original TD method, but also lower than that of the traditional split-radix fast Fourier transform (FFT) method when the length of the input sequence is short.

With single-carrier frequency-domain equalization, the carrier-frequency and sampling-frequency offsets are embedded in the phases of complex frequency-domain signal components. This paper proposes a sub-block processing to extract the phases and applies the least-squares regression to jointly estimate the offsets. The effectiveness of the proposed SC-FDE receiver is demonstrated on multipath fading channels.

With single-carrier frequency-domain equalization (SC-FDE), the carrier-frequency offset (CFO) and sampling-frequency offset (SFO) are embedded in the phase rotations of the complex frequency-domain signal components at the output of the fast Fourier transform (FFT). To extract the phase rotations and estimate the CFO and SFO, the frequency-domain signal components need to be known. However, they are, in general, not known to the receiver, since they are a mixture of the data and pilot symbols. To solve this difficulty sub-block processing is proposed, such that joint estimation of the CFO and SFO can be applied. For the joint estimation, both the linear least-squares (LLS) and simple weighted least-squares (SWLS) regressions are considered, where the latter is shown to be robust to the channel frequency-selectivity. Finally, the SC-FDE receiver with proposed closed-loop tracking algorithm is tested on both quasi-static and time-varying multipath fading channels and its effectiveness is demonstrated.

It is well-known that space-time block coded transmit diversity system suffers from a diversity penalty in the time-varying channel. Lately, based on the Alamouti two-input single-output (2ISO) antenna diversity system, Vielmon et al. investigated the impact of a time-varying channel on the bit-error-rate (BER) performance and also recommended three detectors to increase the system robustness for rapid channel variation. In this paper, we generalize these detectors and their BER expressions to the two-input multiple-output (2IMO) antenna configuration. Moreover, the bit-error-outages (BEOs) are also derived to provide a more objective judgment on the transmission quality within a fading environment. These generalized results can be easily extended to the orthogonal frequency-division multiplexing (OFDM) and code-division multiple-access (CDMA) systems with the 2IMO antenna configuration.

In this paper we discuss issues about the downlink wideband code division multiple access (WCDMA) in high-speed mobile environments. When the carrier synchronization is considered in the RAKE receiver, it may induce the over Doppler shifting (ODS) problem to the high-speed mobile in a rural area where more than one specular component for the multipath channels exist. This makes the receiver difficult to track the rapidly time-varying channel for the time-multiplexed pilot symbols. To fix this problem, we propose a Doppler shift compensation (DSC) method in the 2nd finger of the RAKE receiver to remove the residual frequency offset hence facilitate the channel tracking by linearly interpolating the pilot-aided channel estimates. It can be shown that the performance is improved tremendously for both coded and uncoded systems, especially when the specular component for the 2nd finger is strong.

This paper summarizes the different single-user detection techniques for the single-input multiple-output (SIMO) and the two-input multiple-output (2IMO) downlink multi-carrier code division multiple access (MC-CDMA) systems. The corresponding analytical bit error rates (BERs) for all the combining schemes are derived and compared in a unified fashion. The analytical solutions are verified by simulations. According to our derivation, we also find that even only one additional antenna is mounted at the transmitter or the receiver, the problem of noise amplification caused by the orthogonality restoring combining (ORC) scheme can be relieved

In this paper, a receiver algorithm for OFDM with receiver diversity is proposed.The proposed receiver uses a new multi-user generalization of the maximum a posteriori probability (MAP) selection diversity combining followed by successive interference cancellation with least-square projection for multi-user detection.Simulation results show that the proposed approach achieves near-maximal-ratiocombining performance with much lower complexity.

An iterative algorithm is proposed to estimate the maximum Doppler frequency in a line-of-sight (LOS) environment. While the autocorrelation function of a Rayleigh fading signal depends only on the maximum Doppler frequency, that of a Rician fading signal is also related to the K factor and the angle of arrival (AOA) of the LOS component. The performance of conventional Doppler spread estimators based on the Rayleigh fading assumption degrades in LOS environments due to the autocorrelation function mismatch. The proposed estimator estimates the Rician K factor first, then iteratively estimates the Doppler spread and the AOA of the LOS component. The performance degradation due to channel parameter variations is investigated by means of matching the autocorrelation functions. The simulation results indicate that the proposed estimator is not only superior to the conventional autocorrelation-based Doppler spread estimator but also robust to the channel parameter variation in both LOS and non-LOS environments

By applying the differential space-time block coding in wireless multicarrier transmission, Diggavi et al. proposed the two-input-multiple-output (2IMO) differentially space-time-time block coded OFDM (TT-OFDM) system. In this paper, we recommend three novel differentially transmit-diversity block coded OFDM (DTDBC-OFDM) systems, namely, the FT-, FF-, and TF-OFDM systems. For instance, the TF-OFDM stands for the differentially space-time-frequency block coded OFDM. Moreover, the noncoherent maximum-likelihood sequence detector (NSD), and its three special cases, namely, the noncoherent one-shot detector, linearly predictive decision-feedback (DF) detector, and linearly predictive Viterbi receiver are incorporated to the 2IMO DTDBC-OFDM systems

In this paper, a novel iterative algorithm for maximum Doppler frequency estimation is proposed. In line-of-sight (LOS) environments, it is known that the performance of the conventional maximum Doppler frequency estimator obtained by the Rayleigh fading assumption will degrade severely. Thus we propose an estimator that estimates the Rician K factor first, then iteratively estimate the Doppler spread and the angle of arrival (AOA) of the LOS component through the autocorrelation function. In addition, the Cramer-Rao bounds (CRB) for the K factor and maximum Doppler frequency estimations are also derived for comparison. Simulation results indicate that the proposed estimator is not only superior to the conventional estimator but also robust to the channel parameters variation.

Based on Alamouti code, Lee et al. proposed two-branch transmit diversity OFDM systems, namely, space-time block coded OFDM (STBC-OFDM) and space-frequency block coded OFDM (SFBC-OFDM). However, they employed the simple maximum-likelihood (SML) detector, which was designed under the assumption that the channel is static over the duration of a space-time/frequency codeword. Therefore, STB-COFDM/SFBC-OFDM suffers from the high time/frequency-selectivity of the wireless mobile fading channel. In our work, in addition to the original SML detector, three novel detectors, proposed by Vielmon et al., are applied to improve the two-branch TDBC-OFDM systems. Additionally, assuming sufficient cyclic prefix (CP), the performances of all systems in spatially uncorrelated time-varying multipath Rayleigh fading channels are evaluated by theoretical derivation and computer simulation, as well. Numerical results have revealed that significant performance improvement can be achieved even when the systems are operated in highly selective channels.

In this paper, a receiver algorithm for OFDM with receiver diversity is proposed. The proposed receiver uses a new multi-user generalization of the maximum a posteriori probability (MAP) selection diversity combining followed by successive interference cancellation with least-square projection for multi-user detection. Simulation results show that the proposed approach achieves near-maximal-ratio-combining performance with much lower complexity.

A receiver algorithm for OFDM with receiver diversity is proposed. The proposed receiver uses a new two-step blind channel estimation algorithm referred to as the subspace-MMSE channel estimator. Minimum mean square error linear diversity combining is then performed based on the estimated channel. Simulation results show that performance gain of 1-3 dB is achievable by the proposed approach.

The authors propose a simple algorithm to reconstruct the image of objects embedded in a finite-sized dielectric background. The algorithm is based on the concept that an undistorted image may be reconstructed if the true range profiles of the embedded object can be obtained. Neglecting the phenomena of multiple reflections and the bending effect of wave propagating in the dielectric, they propose a simple algorithm to compensate the electrical length of the wave traveling in the dielectric. Although the assumptions made are not precise, nevertheless, experimental results show that the proposed method is very time-efficient, and is effective in reconstructing a recognizable image of the object embedded in a background having moderate dielectric constant and smooth air-dielectric boundary shape.>