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A pair of secondary (cognitive, unlicensed) users is communicating in the presence of multiple primary (licensed) user pairs. The cognitive transceiver is implementing beamforming and orthogonal space-time block coding in the presence of external interference, induced by the primary system transmission, that has to be properly handled. Moreover, the cognitive link nodes, both the transmitter and the receiver, are supplied with different levels of network side information (NSI), i.e. primary messages and partial channel side information (CSI). We investigate how this side information can be taken into account in the cognitive system design and how interference affects the behaviour of the beamforming solution. Through numerical simulations, we illustrate the impact of partial CSI on system performance and discuss its implications on the feasibility of cognitive systems., QC 20121218

We consider a pair of secondary nodes (SU) coupled, in Z-topology, with multiple pairs of primary nodes (PU). The secondary (cognitive) transmitter is combining beamforming with orthogonal space-time block coding (BOSTBC) and operates under Quality-of-Service (QoS) constraints that must be guaranteed for the primary receivers (PURx). The cognitive link is designed assuming imperfect channel state information (CSI) for all links, available at the SU transmitter (SUTx). Under this premise we characterize the optimal design in terms of CSI quality and interference and evaluate their impact on the performance of BOSTBC transmission in underlay cognitive networks., QC 20130116

Compressive Sampling Matching Pursuit (CoSaMP) is one of the popular greedy methods in the emerging field of Compressed Sensing (CS). In addition to the appealing empirical performance, CoSaMP has also splendid theoretical guarantees for convergence. In this paper, we propose a modification in CoSaMP to adaptively choose the dimension of search space in each iteration, using a threshold based approach. Using Monte Carlo simulations, we show that this modification improves the reconstruction capability of the CoSaMP algorithm in clean as well as noisy measurement cases. From empirical observations, we also propose an optimum value for the threshold to use in applications., QC 20130226

The two-user discrete memoryless state-dependent multiple-access channel with cooperating encoders is considered. It is assumed that the channel is controlled with two independent states such that each of the channel state information is noncausally available at one encoder. Moreover, based on the intrinsic characteristic of wireless networks, it is assumed that each encoder strictly causally receive a noisy version of the transmitted signal of the other encoder. Hence, the encoders can cooperate in transmitting the message to the receiver. An achievable rate region for the channel is derived by use of rate splitting, block Markov encoding and Gelfand-Pinsker multilevel encoding along with partial decoding at the encoders and backward decoding at the receiver. Finally, for a Gaussian channel model the proposed achievable rate region is evaluated and discussed., QC 20130118

This paper studies the asymptotic sum-rate of the primary network within the relay-assisted multi-antenna cognitive radio system performing amplify-and-forward relaying. The achievable sum-rates are derived in the large-system limit by means of the replica method. A closed-form expression for the sum-rate of the primary network is obtained for large antenna arrays as a function of parameters obtained by solving a set of fixed-point equations. Numerical simulations confirm the validity of the results even for systems with only a few antennas at each terminal., QC 20121219

A secret key agreement setup between three users is considered in which each pair of them wishes to agree on a secret key hidden from the remaining user. The three users observe i.i.d. outputs of correlated sources and there is a noiseless public channel from each user for communication to the others. In this setup, inner and outer bounds of the secret key capacity region is derived. Moreover, some special cases are obtained in which the inner bound coincides the explicit outer bound. Also a binary-erasure example is presented through which the results are examined., QC 20130115

We consider the source coding problem of computing functions of correlated sources, which is an extension of the Slepian - Wolf coding problem. We observe that all the discrete functions are in fact restrictions of polynomial functions over some finite field. Based on this observation, we demonstrate how to use Elias' Lemma to enlarge the coding rate region (compared to the Slepian - Wolf region) for a certain class of polynomial functions. We present a classification result about polynomial functions regarding this coding problem. The result is conclusive in the two-sources scenario and, in fact, gives another interpretation of a result by Han and Kobayashi [1, Theorem 1]., QC 20121115

In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms., QC 20120227

In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms., QC 20120227

In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms., QC 20120227

In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms., QC 20120227

In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms., QC 20120227

For compressive sensing, we endeavor to improve the atom selection strategy of the existing orthogonal matching pursuit (OMP) algorithm. To achieve a better estimate of the underlying support set progressively through iterations, we use a least squares solution based atom selection method. From a set of promising atoms, the choice of an atom is performed through a new method that uses orthogonal projection along-with a standard matched filter. Through experimental evaluations, the effect of projection based atom selection strategy is shown to provide a significant improvement for the support set recovery performance, in turn, the compressive sensing recovery., QC 20120803

In this work the multiantenna bidirectional broadcast channel under channel uncertainty is studied. This problem is motivated by the broadcast phase of the decode-and-forward bidirectional relaying protocol, where a relay node establishes a bidirectional communication between two other nodes while having only imperfect channel state information available. Different uncertainty models are investigated, where the nominal channels experience either a multiplicative or additive perturbation based on a spectral norm constraint. For these uncertainty models the corresponding capacity regions of the multiantenna bidirectional broadcast channel are analyzed. Further, robust transmit strategies are characterized and worst-case perturbations are identified., QC 20120625

A secret key agreement setup between three users is considered in which each of the users 1 and 2 intends to share a secret key with user 3 and users 1 and 2 are eavesdroppers with respect to each other. The three users observe i.i.d. outputs of correlated sources and there is a generalized discrete memoryless multiple access channel (GDMMAC) from users 1 and 2 to user 3 for communication between the users. The secret key agreement is established using the correlated sources and the GDMMAC. In this setup, inner and outer bounds of the secret key capacity region are investigated. Moreover, for a special case where the channel inputs and outputs and the sources form Markov chains in some order, the secret key capacity region is derived. Also a Gaussian case is considered in this setup., QC 20130115

We study secret-key agreement over a non-coherent block-fading multiple input multiple output (MIMO) wiretap channel. We give an achievable scheme based on training and source emulation and analyze the rate in the high SNR regime. Based on this analysis we find the optimal number of antennas to use for training. Our main result is that if the sum of the number of antennas at Alice and Bob is larger than the coherence time of the channel, the achievable rate does not depend on the number of antennas at Eve. In this case source emulation is not needed, and using only training is optimal. We also consider the case when there is no public channel available. In this case we show that secret-key agreement is still possible by using the wireless channel for discussion, giving the same number of secure degrees of freedom as in the case with a public channel., QC 20130220

We consider a lossless multi-terminal source coding problem with one transmitter, two receivers and side information. The achievable rate region of the problem is not well understood. In this paper, we characterise the rate region when the side information at one receiver is conditionally less noisy than the side information at the other, given this other receiver's desired source. The conditionally less noisy definition includes degraded side information and a common message as special cases, and it is motivated by the concept of less noisy broadcast channels. The key contribution of the paper is a new converse theorem employing a telescoping identity and the Csiszár sum identity., QC 20130219

We consider a lossless multi-terminal source coding problem with one transmitter, two receivers and side information. The achievable rate region of the problem is not well understood. In this paper, we characterise the rate region when the side information at one receiver is conditionally less noisy than the side information at the other, given this other receiver's desired source. The conditionally less noisy definition includes degraded side information and a common message as special cases, and it is motivated by the concept of less noisy broadcast channels. The key contribution of the paper is a new converse theorem employing a telescoping identity and the Csiszár sum identity., QC 20130219

We consider a lossless multi-terminal source coding problem with one transmitter, two receivers and side information. The achievable rate region of the problem is not well understood. In this paper, we characterise the rate region when the side information at one receiver is conditionally less noisy than the side information at the other, given this other receiver's desired source. The conditionally less noisy definition includes degraded side information and a common message as special cases, and it is motivated by the concept of less noisy broadcast channels. The key contribution of the paper is a new converse theorem employing a telescoping identity and the Csiszár sum identity., QC 20130219

We consider a lossless multi-terminal source coding problem with one transmitter, two receivers and side information. The achievable rate region of the problem is not well understood. In this paper, we characterise the rate region when the side information at one receiver is conditionally less noisy than the side information at the other, given this other receiver's desired source. The conditionally less noisy definition includes degraded side information and a common message as special cases, and it is motivated by the concept of less noisy broadcast channels. The key contribution of the paper is a new converse theorem employing a telescoping identity and the Csiszár sum identity., QC 20130219

We consider a lossless multi-terminal source coding problem with one transmitter, two receivers and side information. The achievable rate region of the problem is not well understood. In this paper, we characterise the rate region when the side information at one receiver is conditionally less noisy than the side information at the other, given this other receiver's desired source. The conditionally less noisy definition includes degraded side information and a common message as special cases, and it is motivated by the concept of less noisy broadcast channels. The key contribution of the paper is a new converse theorem employing a telescoping identity and the Csiszár sum identity., QC 20130219

Orthogonal Matching Pursuit (OMP) is a popular greedy pursuit algorithm widely used for sparse signal recovery from an undersampled measurement system. However, one of the main shortcomings of OMP is its irreversible selection procedure of columns of measurement matrix. i.e., OMP does not allow removal of the columns wrongly estimated in any of the previous iterations. In this paper, we propose a modification in OMP, using the well known Subspace Pursuit (SP), to refine the subspace estimated by OMP at any iteration and hence boost the sparse signal recovery performance of OMP. Using simulations we show that the proposed scheme improves the performance of OMP in clean and noisy measurement cases., QC 20130226

We propose a new unequal error protection (UEP) scheme for Luby Transform (LT) codes over additive white Gaussian noise (AWGN) channels. In contrast to the state-of-the-art UEP scheme for LT codes where the effective code rates are exploited for UEP, we characterize the variable-node degree distribution to achieve UEP for LT codes. For performance analysis, we compare the lower bounds on bit error rate for our proposed scheme and a conventional UEP-based LT codes over AWGN channels for various parameters. Moreover, it is demonstrated through numerical examples that our proposed UEP scheme has better performance than the conventional UEP-based LT codes over a wide range of code rates and channel conditions., QC 20130116

Well-known standard hybrid coding techniques utilize the concept of motion-compensated predictive coding in a closed-loop. The resulting coding dependencies are a major challenge for packet-based networks like the Internet. On the other hand, subband coding techniques avoid the dependencies of predictive coding and are able to generate video streams that better match packet-based networks. An interesting class for subband coding is the so-called motion-compensated orthogonal transform. It generates orthogonal subband coefficients for arbitrary underlying motion fields. In this paper, a theoretical signal model based on Gaussian distributions is discussed to construct a cost function for efficient rate allocation. Additionally, a rate-distortion efficient video coding scheme is developed that takes advantage of motion-compensated orthogonal transforms. The scheme combines multiple types of motion-compensated orthogonal transforms, variable block sizes, and half-pel accurate motion compensation. The experimental results show that this adaptive scheme outperforms individual motion-compensated orthogonal transforms by up to 2 dB., QC 20120807

In this paper, we propose an iterative algorithm to jointly design codes and trainingsequences for frequency-selective block fading channels with partial channel state information (CSI) at the receiver. After showing that the maximum-likelihood (ML) decoding metric over channels with partial CSI can be well approximated by the joint maximum-likelihood (JML) decoding metric for combined channel estimation and data detection, we propose to use the JML criterion to search for good codes and training sequences in an iterative fashion. Simulations show that the code and training sequence found by our method can outperform a typical system using a channel code with a separately designedtraining sequence, in particular when codes of low rates are considered., QC 20120207

A class of semi-deterministic relay channels is introduced and it is shown that for channels in the class capacity can be achieved using an instantaneous relaying scheme. Applications to Gaussian channels are then discussed., QC 20120203

This paper proposes a method to optimize the performance of tandemsource–channel coding with respect to the mean-squared error by exploiting the unequal error protection coding. More specifically,we formulate a combination of linear programming and gridsearch to optimize degree distributions for unequal error protected rateless channel codes. An asymptotic upper bound for the meansquared error of the cascaded system is also derived. By optimizing the corresponding degree distributions of the rateless codes using unequal error protection principles, the proposed scheme has shown promising performance at high resolution region of sourcecoding., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111121

This paper proposes a method to optimize the performance of tandemsource–channel coding with respect to the mean-squared error by exploiting the unequal error protection coding. More specifically,we formulate a combination of linear programming and gridsearch to optimize degree distributions for unequal error protected rateless channel codes. An asymptotic upper bound for the meansquared error of the cascaded system is also derived. By optimizing the corresponding degree distributions of the rateless codes using unequal error protection principles, the proposed scheme has shown promising performance at high resolution region of sourcecoding., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111121

This paper proposes a method to optimize the performance of tandemsource–channel coding with respect to the mean-squared error by exploiting the unequal error protection coding. More specifically,we formulate a combination of linear programming and gridsearch to optimize degree distributions for unequal error protected rateless channel codes. An asymptotic upper bound for the meansquared error of the cascaded system is also derived. By optimizing the corresponding degree distributions of the rateless codes using unequal error protection principles, the proposed scheme has shown promising performance at high resolution region of sourcecoding., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111121

This paper proposes a method to optimize the performance of tandemsource–channel coding with respect to the mean-squared error by exploiting the unequal error protection coding. More specifically,we formulate a combination of linear programming and gridsearch to optimize degree distributions for unequal error protected rateless channel codes. An asymptotic upper bound for the meansquared error of the cascaded system is also derived. By optimizing the corresponding degree distributions of the rateless codes using unequal error protection principles, the proposed scheme has shown promising performance at high resolution region of sourcecoding., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111121

This paper proposes a method to optimize the performance of tandemsource–channel coding with respect to the mean-squared error by exploiting the unequal error protection coding. More specifically,we formulate a combination of linear programming and gridsearch to optimize degree distributions for unequal error protected rateless channel codes. An asymptotic upper bound for the meansquared error of the cascaded system is also derived. By optimizing the corresponding degree distributions of the rateless codes using unequal error protection principles, the proposed scheme has shown promising performance at high resolution region of sourcecoding., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111121

We investigate the error floor performance of Luby Transform (LT) codes over the additive white Gaussian noise channel. We first derive a lower bound on the bit error rate for an LT code, which we subsequently use to show that the corresponding error floor is predominantly caused by low-degree variable nodes. Based on this observation, we propose a modified encoding scheme for LT codes that provides a lower error floor with no increase in encoding and decoding complexities. The convergence behavior of the proposed scheme is analyzed using extrinsic information transfer charts, and shown to be similar to the original LT code. Numerical examples demonstrate the improvements of the modified LT code as a stand-alone code and as a component code of a Raptor code., QC 20120206

We study network coding for wireless networks with finite channel state information (CSI) at intermediate nodes (relays). Based on the CSI of the relay-sink channels, we adapt the network codes at the relays. For a specific network with two sources, four relays and two sinks, the analytic results show that one bit CSI of all relay-sink channels (global CSI) can reduce complexity (field size), and simultaneously decrease the erasure probability. Then, we generalize the results to relay networks with M users, N relays and J sinks. We show that fixed network codes without CSI cannot achieve instantaneous min-cut, i.e., min-cut under current channel state. We also show that with one bit global CSI, we can achieve instantaneous min-cut by adapting the network codes using an alphabet size L, where L is the number of sinks connecting to a relay. Yet, the fixed MDS network codes use an alphabet size L(M-1N-1). For the networks with perfect or imperfect source-relay channels, adaptive network codes with one bit global CSI have lower erasure probability than the codes without CSI. Thus, one bit global CSI can reduce the erasure probability, and simultaneously reduce coding complexity., QC 20120416

Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111026

Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111026

Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111026

Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111026

Considering a single-antenna M-user interferencechannel with symmetrically distributed channel gains, when thechannel state information (CSI) is globally available, applyingthe ergodic interference alignment scheme, each transmitterreceiverpair achieves a rate proportional to 1⁄2 of a single user’sinterference-free achievable rate. This is substantially higher thanthe achievable rate of the conventional orthogonal transmissionschemes such as TDMA. Since the rigid requirement on theCSI may be difficult to realize in practice, in this paper weinvestigate the performance of applying the ergodic interferencealignment scheme when the estimation of each channel gain ismade globally known through exploiting only a limited feedbacksignal from the associated receiver of that channel. Under a blockfading environment, we provide a lower bound on the achievableaverage throughput of the network. Our results imply that thebetter performance of interference alignment over TDMA maystill exist even without the assumption of perfect CSI. Also, thetrade off between allocating feedback rate of each receiver tothe desired channel or the interference channels at deferent SNRregion investigated., © 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20111026

In distributed storage systems reliability is achieved through redundant storage nodes distributed in the network. Then a data collector can recover source information even if some nodes fail. To maintain reliability, an autonomous and efficient protocol should be used to reconstruct the failed node. Therepairprocess causes traffic in the network. Recent results in e.g., [1], [2] found the optimal traffic-storage tradeoff, and proposed regenerating codes to achieve the optimality. We investigate the link costs and the impact of network topologies during therepairprocess. We formulate the minimum costrepairproblem in joint and decoupled methods. We investigate the required field size for the joint method. For the decoupled method, we show that the optimization problem is linear for the linear cost. We further show that the cooperation of surviving nodes could efficiently exploit the network topology and reduce therepaircost. The numerical results in tandem, star and grid networks show the benefits of our methods in term of the repair cost., QC 20120208

In this paper, we investigate the wiretap channel in the presence of a cooperative helping node. We derive a closed-form expression for the secrecy outage probability for the decode-and-forward (DF) relaying and cooperative jamming (CJ) strategies for the Rayleigh slow fading channel. We investigate the power allocation at the source and helping node, and compare the secrecy outage performance of the two schemes., QC 20111208

In this paper, we investigate the wiretap channel in the presence of a cooperative relay node. We analyze and compare the outage performance of three cooperatives schemes: cooperative jamming (CJ), decode-and-forward (DF), and amplify-and-forward (AF) for the Rayleigh slow fading channel. In particular, we derive a closed-form expression for the outage probability for the DF and CJ strategies, which allows an optimal strategy selection in terms of outage performance. We compare the three cooperative schemes through numerical simulations., QC 20111208

We consider a base-station broadcasting a set of order-insensitive packets to a user population over packet-erasure channels. To improve efficiency we propose a relay-aided transmission scheme using instantaneously-decodable binary network coding. Our proposed scheme ensures that a coded packet can be immediately decoded at the user side without delay. Moreover, only binary operations are required in the encoding and decoding processes, which decrease the computational complex. We further analyze the performance of the resulting broadcast scheme, and show that significant improvements in transmission efficiency are obtained as compared to previously proposed ARQ and network-coding-based schemes., QC 20120228

In this paper, we consider network coded (NCed)Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressionfor NCed HARQ with arbitrary number of users in i.i.d. channels.We apply the result to Rayleigh fading channels for incrementalredundancy (IR) and chase combining (CC) based NCed HARQ.We verify the analytical approach with simulations. We observesubstantial SNR improvements over regular ARQ with networkcoding as well as classical (H)ARQ. The SNR gains in the highand low throughput regimes are mainly due to the networkcoding and HARQ aspects, respectively. For low SNRs, NCedHARQ with IR surpasses the CC performance., © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Qc 20120203

In this paper, we consider network coded (NCed)Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressionfor NCed HARQ with arbitrary number of users in i.i.d. channels.We apply the result to Rayleigh fading channels for incrementalredundancy (IR) and chase combining (CC) based NCed HARQ.We verify the analytical approach with simulations. We observesubstantial SNR improvements over regular ARQ with networkcoding as well as classical (H)ARQ. The SNR gains in the highand low throughput regimes are mainly due to the networkcoding and HARQ aspects, respectively. For low SNRs, NCedHARQ with IR surpasses the CC performance., © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Qc 20120203

In this paper, we consider network coded (NCed)Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressionfor NCed HARQ with arbitrary number of users in i.i.d. channels.We apply the result to Rayleigh fading channels for incrementalredundancy (IR) and chase combining (CC) based NCed HARQ.We verify the analytical approach with simulations. We observesubstantial SNR improvements over regular ARQ with networkcoding as well as classical (H)ARQ. The SNR gains in the highand low throughput regimes are mainly due to the networkcoding and HARQ aspects, respectively. For low SNRs, NCedHARQ with IR surpasses the CC performance., © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Qc 20120203

In this paper, we consider network coded (NCed)Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressionfor NCed HARQ with arbitrary number of users in i.i.d. channels.We apply the result to Rayleigh fading channels for incrementalredundancy (IR) and chase combining (CC) based NCed HARQ.We verify the analytical approach with simulations. We observesubstantial SNR improvements over regular ARQ with networkcoding as well as classical (H)ARQ. The SNR gains in the highand low throughput regimes are mainly due to the networkcoding and HARQ aspects, respectively. For low SNRs, NCedHARQ with IR surpasses the CC performance., © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Qc 20120203

In this paper, we consider network coded (NCed)Hybrid-ARQ (HARQ) for multiple unicast flows. The main contribution of the paper is the derivation of throughput expressionfor NCed HARQ with arbitrary number of users in i.i.d. channels.We apply the result to Rayleigh fading channels for incrementalredundancy (IR) and chase combining (CC) based NCed HARQ.We verify the analytical approach with simulations. We observesubstantial SNR improvements over regular ARQ with networkcoding as well as classical (H)ARQ. The SNR gains in the highand low throughput regimes are mainly due to the networkcoding and HARQ aspects, respectively. For low SNRs, NCedHARQ with IR surpasses the CC performance., © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Qc 20120203

The bidirectional broadcast channel denotes a broadcast channel with two receivers where each receiver knows the message intended for the other. We consider streaming sources where messages of each user arrive as bit-stream to the encoder. Thus our main quantity of interest is the bit error probability. By extending Sahai's argument to bidirectional broadcast channel, we show that under maximum-likelihood decoding the bit error probability decays exponentially in delay with positive exponent for all the rate pairs inside the capacity region. We also show existence of deterministic codes which achieve exponentially decaying bit error probability with delay., QC 20111216

We design non-codebook-based Multiple-Input Multiple-Output (MIMO) precoding schemes using multiple cell-specific reference signals patterns for the time division duplex (TDD) mode of LTE, where channel reciprocity can be exploited. Previously proposed non-codebook-based precoding schemes typically use UE specific reference signals for demodulation. Cell specific reference signals are however always allocated for the transmission of common control signalling, mobility measurements and downlink channel quality measurements. In order to save the resources occupied by UE specific reference signals, and to simplify UE implementation, a precoder-estimation scheme and a codebook-assisted scheme are designed. The codebook-assisted scheme has the novelty of using a codebook in equalization. Link throughput simulations indicate that the codebook-assisted scheme is preferable compared to the precoder-estimation scheme and the scheme using UE specific reference signals in scenarios with moderate UE velocity., QC 20140901

In this paper, we consider the problem of the joint optimization of encoder-controller for closed-loop control with state feedback over a binary-input Gaussian channel (BGC). The objective is to minimize the expected linear quadratic cost over a finite horizon. Thisencoder-controller optimization problem is hard in general, mostly because of the curse of dimensionality. The result of this paper is a synthesis technique for a computationally feasible suboptimal controller which exploits both the soft and hard information of thechannel outputs. The proposed controller is efficient in the sense that it embraces measurement quantization, error protection and control over a finite-input infinite-output noisy channel. How to effectively implement this controller is also addressed in the paper. In particular, this is done by using Hadamard techniques. Numerical experiments are carried out to verify the promising gain offered by the combined controller, in comparison to the hard-information-based controller., QC 20120124