At an energy harvesting relay, securing residual harvested energy, net remaining energy after each receiving and forwarding cycle, is of importance for sustainable operation. However, there exists a tradeoff between the achievable rate and residual harvested energy, whereby understanding this tradeoff concretely is crucial for energy harvesting relay system design. This paper analyzes the rate-energy (R-E) region for achievable rate and residual harvested energy in two-way decode-and-forward (DF) relay systems with a power splitting based energy harvesting relay. In particular, we characterize R-E regions for multiple access broadcast (MABC) and time division broadcast protocols. Moreover, we propose a new energy harvesting relaying protocol, namely, information and energy signals multiple access broadcasts (IEBC), to improve the achievable R-E region. The boundary of the R-E regions is obtained by optimizing a power splitting factor in each protocol. Moreover, to have better analytic comparisons and useful insights on performance, we derive approximated R-E regions of all protocols for high and low signal-to-noise ratio cases. Based on the approximated R-E region, it is shown that if the required residual energy is large, the IEBC outperforms the others, but if the required residual energy is small, either the IEBC or MABC is preferred.

This paper studies secure transmissions in a bursty interference channel constructed by opportunistic user scheduling. To improve the physical layer security, we propose a signal-to-noise-plus-interference ratio (SINR) based opportunistic transmission scheme and mathematically analyze the ergodic secrecy rate per transmitter-receiver pair. In this scheme, a subset among$K$transmitter-receiver pairs is selected opportunistically, but each transmitter determines its activation state based on limited feedback of the SINR from its designated receiver only, without any information from other transmitters. For comparison, we also analyze the ergodic secrecy rates per transmitter-receiver pair for two benchmark schemes: non-opportunistic transmission and random transmission. Using derived analytical expressions, the achievable ergodic secrecy rates per transmitter-receiver pair are obtained by optimizing the activation probability for each scheme. To solve the non-convex optimization problem, we first show that the objective function is a sum of quasi-concave functions. Then, leveraging this fact, we propose a two-level iterative algorithm based on the damped Newton method. Furthermore, asymptotic behaviors of the achievable ergodic secrecy rate per transmitter-receiver pair are analyzed to offer insights behind the mathematical expressions. Our analytical and numerical results exhibit the gain of the proposed SINR based opportunistic transmission scheme compared to the benchmark schemes.

In this paper, we study time-varying channel estimation and optimal pilot design for multiple-input multiple-output two-way multi-relay systems in the sense of minimizing the total estimation mean square error (MSE) under the power constraints at two source nodes and multiple relays. A particularly challenging issue in the optimal pilot design is to completely eliminate the inter-link interference while most efficiently using the channel resource. To address this challenging issue, we consider a pilot design approach based on the phase rotation technique at multiple relays. First, we establish various optimality conditions for the pilot design in the sense of the minimum total MSE. Then, we propose the optimal pilot scheme by designing the pilot signals, phase rotations, and pilot symbol positions to satisfy the established optimality conditions. Finally, we propose the asymptotically optimal pilot scheme in the high signal-to-noise ratio (SNR) regime with low complexity. Simulation results show that the proposed schemes significantly outperform the existing schemes in terms of the channel estimation and the bit error rate, and the proposed asymptotically optimal scheme provides the near-optimal performance even in the low to moderate SNR range.

In this paper, we study a training design problem for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) amplify-and-forward (AF) two-way relay networks. Unlike the existing studies, we assume the spatially correlated fading and consider the nonreciprocal channel condition, which is a more practical assumption but makes the training problem more challenging. The equivalent channels of bidirectional relaying links, which consist of self-interfering channels and information-bearing channels, are estimated at each source node based on a linear minimum mean square error (LMMSE) approach. The total mean square error (MSE) of the channel estimation is minimized under the transmit power constraints at the source nodes and at the relay. To solve this problem, we first derive an optimal structure of the training signals, and then, convert the optimization problem into a tractable convex form, from which the optimal training scheme is designed efficiently. Furthermore, for a practical special case, the optimal training design is derived in semi-closed form, which provides useful insights. To reduce the required complexity, a low-complexity training scheme is also derived in closed-form. This scheme is shown to be asymptotically optimal in the high signal-to-noise ratio (SNR) regime and gives further insights into the optimal training. The performance of the proposed schemes is demonstrated through numerical simulations.

We propose the source and relay precoder designs to maximize sum rate under individual power constraints in two-way relay system with one relay and multiple sources. However, it is difficult to directly solve the sum rate maximization problem. For this reason, we establish the relationship between sum rate and weighted mean square error(WMSE), and show that the solution of the sum rate maximization problem can be also the solution of the WMSE minimization problem if the weight matrices are properly chosen. Then, based on the relationship between sum rate and WMSE, the sum rate maximization problem is equivalently formulated as the WMSE minimization problem. We finally propose an iterative algorithm for WMSE minimization problem. Simulation results show that the proposed scheme has better sum rate performance than conventional scheme at all SNR regimes.

This paper considers the problem of detecting the pilot contamination attack for multi-antenna secrecy systems. The detection problem is formulated as a binary hypothesis problem and the likelihood ratio or the generalized likelihood ratio is employed as a decision statistic for the detection of the pilot contamination. Using the Neyman-Pearson criterion, we then develop several detection methods under the different assumptions of the channel and noise statistics. To be specific, the cases of interest are as follows: (i) exact knowledge of all covariance matrices, (ii) exact knowledge of the legitimate channel and noise covariance matrices, but no knowledge of the jamming channel covariance matrix and (iii) no knowledge of all covariance matrices. The performance comparison of the proposed schemes with the conventional scheme is performed by simulations.

This letter proposes channel training designs for two-hop multi-relay networks, where a source, a destination and multiple amplify-and-forward (AF) relays are all equipped with multi-antenna, based on mean square error (MSE) and signal-to-noise ratio (SNR) criteria with taking into account spatial fading correlation between multiple-input multiple-output (MIMO) channel elements. The minimum MSE and maximum SNR channel estimators are initially derived and, then, optimal structures on source training signal and relay matrices are determined. An iterative and a closed-form power allocation solutions are proposed for both channel estimators. Simulation results show that the proposed schemes outperform the conventional schemes.

In this paper, a relay precoding problem is considered in a non-regenerative multiple-input multiple output (MIMO) relay system, when multiple interferers exist near the destination. The relay has the perfect channel state information (CSI) of the source-relay link and only the covariance information of the relay-destination link. Also, we assume that the training signals of the interferers are known at the destination, and thus, the covariance information of the channels from the interferers to the destination can be estimated at the destination and the information is fed back to the relay. For this scenario, the structure of the optimal relay precoder is derived to maximize the average capacity seen by the relay under a relay transmit power constraint. For the derivation of the optimal relay precoder, a new partial ordering result for the outage probability and the ergodic capacity of spatially correlated MIMO channels is derived. Numerical results demonstrate that the proposed scheme considerably improves the performance. Overall, the contributions of this paper are twofold: i) a new partial ordering result for MIMO channels is derived and ii) the structure of the optimal relay precoder is derived using the partial ordering result.

We consider a relay precoding problem in a non-regenerative multiple-input multiple-output (MIMO) relay system, where the relay has the perfect channel state information of the source-relay link and only the covariance information of the relay-destination link. The average capacity seen by the relay is maximized under a relay transmit power constraint. The relay precoding problem is transformed to its equivalent power allocation problem at the relay. The optimal power allocation solution is then derived by formulating the optimization problem via difference of convex (DC) functions programming. To reduce the computational complexity, we also propose a suboptimal scheme by modifying the naive Jensen method. Furthermore, we propose the maximum eigenmode relaying (MER) scheme, which allocates the relay transmit power only to the maximum eigenmode. A necessary and sufficient condition for the MER to be asymptotically optimal is derived in the high signal-to-noise ratio (SNR) regime of the source-relay link. The performance of the proposed schemes is investigated through extensive numerical simulations.

Use of the space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) is advantageous in high-mobility broadband wireless system but it is sensitive to the intercarrier interference (ICI) caused by phase noise (PHN). In this letter, the effect of PHN for Alamouti SFBC-OFDM system is analyzed and correlative coding (CC) is used to reduce ICI. Based on the expression of the ICI power for the Alamouti SFBC-OFDM system with CC, the optimal CC coefficients that minimize the ICI power are obtained. Numerical results show that optimum CC can effectively increase the carrier-to-interference ratio (CIR) and improve the bit error rate (BER) performance.

In this paper, we propose a precoder using a minimum mean-square error (MMSE) criterion for a non-regenerative relay system. It is assumed that the relay knows the channel covariance information (CCI) of the relay-destination link and the full channel state information (CSI) of the source-relay link. We start by assuming the precoder has a specified structure. We derive an upper-bound of the mean-square error (MSE) and obtain a closed form solution to minimize the upper-bound of the MSE. Although the proposed scheme is suboptimal, simulation results show that the proposed scheme has better performance in terms of the MSE and the bit error rate (BER) than the conventional schemes.

In this paper, the optimal power allocation problems are solved for hybrid distributed beamforming in wireless relay networks. The capacity of the source-destination link is maximized and the total transmit power of the source and the relays is minimized. The hybrid relaying which adapts relaying strategies such as amplify-and-forward (AF) and decode-and-forward (DF) to the channel condition can enhance the signal reliability. Three policies are used to determine the ordering of the relays for switching the relaying mode from AF to DF. Simulation results show that the performance of the proposed scheme is nearly optimal for both capacity maximization and power minimization with a few iterations.

A blind adaptive constrained minimum output energy (MOE) receiver has been proposed for the uplink multicarrier code-division multiple access (MC-CDMA) system in a multicell environment when some users, including the desired user, employ real-valued modulation such as binary phase-shift keying (BPSK) or amplitude-shift keying (ASK). Since the imaginary part of residual interference at the filter output does not affect the decision of the desired user's data in this case, the proposed receiver has been designed to perfectly eliminate the real part of residual in-cell interference using the information of the spreading sequence and to reduce the real part of residual intercell interference by minimizing the constrained output energy. Results of analysis and simulation show that the proposed blind adaptive algorithm converges faster and has a higher steadystate signal-to-interference and noise ratio (SINR) than those of conventional schemes.

We propose an efficient proportional fair (PF) scheduling algorithm for multi-user OFDMA systems employing fixed relays. An PF metric maximization problem is first formulated for relay enhanced OFDMA cellular systems. A two-step algorithm is then proposed to solve the problem; the user routing step and the resource allocation step. The simulation results confirm the near-optimal performance of the proposed algorithm in PF sense.

Multihop cellular networks (MCNs) is an extension of single hop cellular networks (SCNs) having benefits of a fixed base station and flexible ad hoc networks. The radio resource management becomes more complex to deal with the routing and resource allocation jointly. In this paper, we have proposed the algorithm which solves the joint subchannel allocation, routing and power allocation problem in OFDMA MCNs. Optimization problem has been decomposed into two subproblems: (1) subchannel allocation problem; (2) routing and power allocation problem, and solved by iterative two-step approach. The simulation results showed that the average total utility increases and the increment of the utility decreases as the number of hops increases.

We consider very general code-division-multiple- access (CDMA) systems, namely multiple-chip-rate CDMA systems, where signals can be transmitted at different chip rates, carrier frequencies, processing gains, and transmitted powers to satisfy the given quality of service (QoS) requirements. Also, nonzero and possibly different carrier frequency offsets are assumed for different users. For these systems, a closed-form bit error rate (BER) expression is derived based on the simplified improved Gaussian approximation. Numerical result demonstrates that the proposed method provides much more accurate BER values compared to the standard Gaussian approximation.

In the finite number of users, the proposed beam subset selection method improves the throughput performance of the orthogonal random beamforming (ORBF), which is a scheme to achieve asymptotic sum capacity for a downlink multiuser multiple-input/multiple output (MIMO) system using partial channel information in the infinite number of users. We show that there exists an optimal number of random beams to maximize the sum throughput for given number of users. When the number of random beams is less than the number of antennas, selecting the random beams to maximize signal- to-interference-plus-noise ratios (SINRs) provides additional SINR gain to ORBF. Through the simulation results, we show the performance improvement by the proposed beam subset selection.

In this paper, a low complexity subcarrier allocation scheme is proposed for multiuser MIMO-multiuser OFDM systems with zero-forcing beamforming (ZFBF) to minimize the total transmit power satisfying given target data rates of users. The ZFBF for multiuser MIMO makes multiple spatial channels by removing multiuser interference and the subcarrier allocation can be performed over spatial and frequency domain. Since the optimal method has very high computational complexity, the semi-orthogonal user selection (SUS) is employed to reduce the computational complexity. In numerical results, we show that the total transmit power satisfying the data rates of users is linearly decreased with the number of transmit antennas.

Many techniques exist for adapting videos to satisfy heterogeneous resource conditions or user preferences, whereas selection of the best adaptation operation among various choices usually is either ad hoc or inefficient. To provide a systematic solution, we present a conceptual framework based on utility function (UF), which models video entity, adaptation, resource, utility, and the relations among them. In order to support real-time video adaptation, we present a content-based statistical paradigm to facilitate the prediction of UF for real-time transcoding of live videos. Instead of modelling the UF through analytical models, as in the conventional rate-distortion framework, the proposed approach formulates the prediction as a classification and regression problem. Each video clip is classified into one of distinctive categories and then local regression is used to accurately predict the utility value. Our extensive experiment results based on MPEG-4 transcoding demonstrate that the proposed method achieves very promising performance - up to 89% accuracy in choosing the optimal transcoding operation (in both spatial and temporal dimensions) with the highest quality over a diverse range of target bit rates

We propose a joint channel and data estimation scheme which does not require the training data in multicarrier direct-sequence multiple access (MC-DS/CDMA) systems. In order to eliminate the multiple access interference (MAI), the minimum output energy (MOE) filter is first used on each subcarrier because it can be implemented without the knowledge of the channel coefficients. Then, the channel coefficients of the subcarriers are estimated using the MOE filter output signals, and they are used to combine the MOE filter output signals to maximize the output signal-to-interference plus noise ratio (SINR). Simulation results show that the proposed scheme is much superior to the previous schemes especially in the near-far environment.

Requantization is a key technology for reducing the bit rate of a previously compressed data. When recompression ratio is high, the requantizer may cause unacceptable quality degradation. To improve the quality of the requantized image, an optimization scheme for the requantization codebook has been proposed. The proposed scheme constructs an optimal requantization codebook in an iterative manner for a given original quantization codebook of transmitter. The construction of codebook is iteratively repeated until they reach a local optimum solution. Our approach can be applied not only to the scalar quantization, but to any method which employs vector quantization-based system. Simulation results show that the optimized system based on the proposed algorithm outperforms the conventional system which is made without consideration of requantization. The proposed algorithm enables a reliable image communication over heterogeneous networks.

An optimal power and antenna height determination over a wide range of incidence angles is proposed for in-orbit operations of the spaceborne stripmap synthetic aperture radar (SAR) with variable antenna height and variable radiating element power. The antenna height and the average transmitted radio-frequency power of a radiating element for each incidence angle are determined so that the mapping area can be maximized with the constraints on the signal-to-noise ratio, ambiguities, and swath width, given the SAR geometry (an altitude and incidence angles) and radar wavelength. With the receive-chain power consumption of one transmit/receive module (P/sub r/=10 mW) and the SAR instrument power consumption without the phased array antenna (P/sub I/=5 W), the illustrative design example shows that the mapping area of the proposed SAR for the maximum incidence angle (/spl eta//sup max/=75/spl deg/) is about 269.1% of that resulted from utilizing only the variable antenna height. The proposed optimization would have a more beneficial effect on applications that need the high-incidence-angle operations.

An optimum transmit power management scheme is proposed for wireless video service in code-division multiple-access systems. The scheme minimizes the transmit power subject to the constraint on the distortion resulted from the loss of each packet and the error propagation effect caused by the motion compensation. It implicitly controls the target bit-error rate (BER) of the video packet according to the importance of the packet. The more important the packet is, the more securely it is transmitted over noisy channel. Furthermore, the scheme adjusts the target BER as if the water filling concept is applied to the problem of minimizing the transmit power. The simulation results show that the proposed scheme considerably outperforms the conventional schemes.

Transmission bit rates are optimized for two-class traffic in variable spreading gain code-division multiple-access systems with antenna arrays. In an array antenna system, the interference levels experienced by the users belonging to different beams are not the same. Thus, it is not efficient to allocate the same rates to all the data users even though they belong to a cell. Considering this, an optimum rate allocation scheme is proposed for delay-tolerant data users. Additionally, we also propose the optimum rate allocation scheme for voice and data users when a packet scheduling scheme is considered. Numerical results show that, in array antenna systems, the proposed schemes considerably outperform the conventional scheme designed for omniantenna systems.

A power-distortion (P-D) optimized coding mode-selection scheme is proposed for variable bit rate videos in wireless code-division multiple-access (CDMA) systems. Unlike the conventional rate-distortion (R-D) optimized mode-selection methods, the proposed scheme takes into account time-varying channels. We show that the proposed optimization problem can be represented as the conventional R-D mode-selection problem, in which the Lagrangian multiplier depends on the channel conditions. In the proposed scheme, as the link gain of a user increases, the optimum mode for the user tends to be intramode rather than intermode, and vice versa. Numerical results show that, in CDMA systems, the proposed scheme consumes much less power at the same image quality compared with conventional R-D schemes.

An optimum power management scheme is proposed for intra-frame refreshed image sequences of the wireless video service in code-division multiple-access (CDMA) systems. The end-to-end distortion of H.263 video data is first modeled when the error concealment schemes are employed. This distortion model takes into account the error propagation effects caused by the motion compensation. Then, based on the model, the target bit-error rates (BERs) of the image frames are optimized in such a way that the consumed power could be minimized under the constraint of maximum distortion. To satisfy the specified target BER requirement, an optimum power management scheme is proposed. Simulation results show that the proposed scheme considerably outperforms the conventional scheme in the sense of the decoded image quality. Additionally, the effects of the imperfect power control on the performance are also investigated.

A new resource allocation scheme is proposed for video service over a Gaussian channel. For video quality rating, we introduce a suitable metric: the average peak signal-to-noise ratio (PSNR) or the average channel-induced PSNR degradation. Then, we model the end-to-end distortion considering the error propagation effect caused by motion compensation. On the basis of this model, we propose an efficient resource allocation scheme for real video service. Unlike conventional schemes, the new scheme satisfies the PSNR requirement of each video user by adjusting the bit-error rate level with the changes of image characteristics. Simulation results show that the proposed scheme utilizes the bandwidth more efficiently than conventional schemes.

We analyze the performance of the hybrid multiuser interference cancellation scheme when each user in the same group has different received signal power. On the basis of this analysis, it is shown that the conventional HIC which divides the active users into several groups of equal size experiences a performance degradation due to the large difference in received signal powers when the power control is not applied or imperfect. We propose a new improved HIC scheme that divides the active users into groups of variable size according to their received powers using a clustering algorithm. Numerical examples illustrate that the BER performance of the proposed HIC scheme is superior to that of the conventional HIC in the case of imperfect power control or no power control.

A joint design scheme has been proposed to optimize the source encoder and the modulation signal constellation based on the minimization of the end-to-end distortion including both the quantization error and channel distortion. The proposed scheme first optimizes the vector quantization (VQ) codebook for a fixed modulation signal set, and then the modulation signals for the fixed VQ codebook. These two steps are iteratively repeated until they reach a local optimum solution. It has been shown that the performance of the proposed system can be enhanced by employing a new efficient mapping scheme between codevectors and modulation signals. Simulation results show that a jointly optimized system based on the proposed algorithms outperforms the conventional system based on a conventional quadrature amplitude modulation signal set and the VQ codebook designed for a noiseless channel.

In this paper, an improved index assignment procedure is proposed to reduce the channel error effect in a communication system employing classified vector quantization (CVQ). The proposed algorithm consists of two parts: inner index assignment (IIA) and cross index assignment (CIA). The IIA reduces the distortion resulting from the error in order bits, presenting the identity of each code vector in a subcodebook. The CIA modifies the indexes assigned by the IIA in such a way that the effect of the channel error occurring in class bits, indicating the class information of the code vector can be minimized. Simulation results show that the proposed algorithms enable a reliable communication over noisy channels even without employing the channel encoding.

A differential index (DI) assignment scheme is proposed for the image encoding system in which a variable-length tree-structured vector quantizer (VLTSVQ) is adopted. Each source vector is quantized into a terminal node of VLTSVQ and each terminal node is represented as a unique binary vector. The proposed index assignment scheme utilizes the correlation between interblocks of the image to increase the compression ratio with the image quality maintained. Simulation results show that the proposed scheme achieves a much higher compression ratio than the conventional one does and that the amount of the bit rate reduction of the proposed scheme becomes large as the correlation of the image becomes large. The proposed encoding scheme can be effectively used to encode MR images whose pixel values are, in general, highly correlated with those of the neighbor pixels.

We present the estimation method of global motion parameters corresponding to 3-D camera motion in the non-stationary noisy situation. The total least squares problem is first formulated to represent the global motion parameters estimation procedure from the noise-corrupted image coordinates. Then, a recursive total least squares (RTLS) algorithm is proposed to estimate 3D camera motion parameters in image sequences. The algorithm is proposed based on a five camera parameter model: zoom, focal length, pan, tilt, and swing. In the experimental results, the efficiency of the proposed RTLS algorithm is shown by comparing its MSE and PSNR with those of the conventional linear algorithms.

In this paper, we describe a method for estimating and compensating 3D camera motion in image sequences for applications to the video coding system. To effectively estimate camera motion parameters (zoom, pan, tilt, swing, and focal length) from image sequences, we propose a new linear motion parameter equation and use the Kalman filtering method to solve it. Unlike the existing linear techniques, the proposed linear method accurately estimates the large rotation angles and the focal length. Experimental results show that the proposed method outperforms the conventional linear methods, especially for a large rotation angle.