Sharif Digital Repository

In this paper, we study the problem of secret communication over a Compound Multiple Access Channel (MAC). In this channel, we assume that one of the transmitted messages is confidential that is only decoded by its corresponding receiver and kept secret from the other receiver. For this proposed setting (compound MAC with confidential messages), we derive general inner and outer bounds on the secrecy capacity region. Also, as examples, we investigate 'Less noisy' and 'Gaussian' versions of this channel, and extend the results of the discrete memoryless version to these cases. Moreover, providing numerical examples for the Gaussian case, we illustrate the comparison between achievable rate... 

The authors study the problem of secret communication over a multiple-access channel with a common message. Here, the authors assume that two transmitters have confidential messages, which must be kept secret from the wiretapper (the second receiver), and both of them have access to a common message which can be decoded by the two receivers. The authors call this setting as multiple-access wiretap channel with common message (MAWC-CM). For this setting, the authors derive general inner and outer bounds on the secrecy capacity region for the discrete memoryless case and show that these bounds meet each other for a special case called the switch channel. As well, for a Gaussian version of... 

In this paper, we study the problem of secret communication over a compound Multiple Access Channel (MAC). In this channel, we assume that one of the transmitted messages is confidential, which is only decoded by its corresponding receiver and kept secret from the other receiver. We call this proposed setting the compound MAC with a confidential message. For this model, we derive general inner and outer bounds for both imperfect and perfect secrecy conditions for the second receiver. Also, as examples, we investigate less noisy and Gaussian versions of this channel, and extend the results of the discrete memoryless version to these cases. Moreover, providing numerical examples for the... 

In this paper, the extension of cooperative communication to the context of TH-UWB is investigated. In particular, the average bit error probability (BEP) is provided for cooperative TH-UWB systems with decode-and-forward relaying protocol. In the considered relay network, UWB links among the nodes are modeled according to IEEE 802.15.4a standards. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. We use Gaussian quadrature numerical method to approximate the CF of interference component appeared in decision variable term. This technique permits to predict the system performance in different IEEE 802.15.4a defined... 

In this paper, we present the average bit error probability (BEP) of a decode-and-forward relay network employing UWB links, developed by IEEE 802.15.4a standards, between its nodes. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. Numerical results show that significant improvement in the BEP of impulse radio UWB system is obtained by adding a relay node. The analytical expressions are also validated by computer simulations which confirm the accuracy of the approximations used in obtaining the BEP  

This paper suggests to use a Block MAP-LMS (BMAP-LMS) adaptive filter instead of an Adaptive Filter called MAP-LMS for estimating the sparse channels. Moreover to faster convergence than MAP-LMS, this block-based adaptive filter enables us to use a compressed sensing version of it which exploits the sparsity of the channel outputs to reduce the sampling rate of the received signal and to alleviate the complexity of the BMAP-LMS. Our simulations show that our proposed algorithm has faster convergence and less final MSE than MAP-LMS, while it is more complex than MAP-LMS. Moreover, some lower bounds for sparse channel estimation is discussed. Specially, a Cramer-Rao bound and a Bayesian... 

Linear controllers have been widely used for controlling Active Power Filters (APFs). However, due to their limitations, a tradeoff between the bandwidth of the current control loop (CCL) and the voltage control loop (VCL) need to be made to remain stable in all conditions. This tradeoff leads to imperfect usage of the APF's capacity. Nonlinear controllers can eliminate such limitations and simultaneously remain stable in all conditions. In this paper, a new nonlinear controller for controlling the output current and the DC voltage (Vdc) of an APF is proposed. Feedback linearization method is applied on the CCL and the VCL is controlled via indirect method. In this method, an auxiliary... 

Lattice Reduction (LR) has been proposed as a method to enhance the performance of MIMO detectors such as ZF, MMSE and V-BLAST. Until recently, the application of LR to the superior K-Best tree-search detection algorithm was not practical due to the significant increase in complexity of K-Best as a result of the distortion of tree symmetry caused by LR. However, in our recently published work we developed an innovative K-Best algorithm to accommodate tree-asymmetry with no additional complexity. In this work, we build on this result and perform a detailed analysis of the effect of various LR algorithms on the performance of LR-aided K-Best. We show that LLL and Seysen provide equivalent... 

We study the capacity region of the two-user binary fading (or erasure) interference channel, where the transmitters have no knowledge of the channel state information. We develop new inner bounds and outer bounds for this problem. We identify three regimes based on the channel parameters: weak, moderate, and strong interference regimes. Interestingly, this is similar to the generalized degrees of freedom of the two-user Gaussian interference channel, where transmitters have perfect channel knowledge. We show that for the weak interference regime, treating interference as erasure is optimal while for the strong interference regime, decoding interference is optimal. For the moderate... 

This article takes a theoretical approach to focus on the algorithmic properties of hardware/software partitioning. It proposes a method with polynomial complexity to find the global optimum of an NP-hard model partitioning problem for 75% of occurrences under some practical conditions. The global optimum is approached with a lower bound distance for the remaining 25%. Furthermore, this approach ensures finding the 2-approximate of the global optimum partition in 97% of instances where technical assumptions exist. The strategy is based on intelligently changing the parameters of the polynomial model of the partitioning problem to force it to produce (or approach) the exact solution to the... 

A secure channel coding (joint encryption-channel coding) scheme provides both data security and reliability in one combined process to achieve faster processing and/or more efficient implementation. The issue of using quasi-cyclic low-density parity-check (QC-LDPC) codes in a symmetric-key secure channel coding scheme is addressed. A set of this class of LDPC codes has recently been recommended by the NASA Goddard Space Flight Center for near-earth and deep-space communications. The proposed scheme provides an efficient error performance, an acceptable level of security and a low-complexity practicable implementation. The results indicate that the proposed scheme can efficiently employ... 

Fuzzy sliding mode control (FSMC) as a robust and intelligent nonlinear control technique is proposed to control processes with severe nonlinearity and unknown models. The performance of the proposed method has been evaluated for both single input single output (SISO) and MIMO nonlinear systems through its application in three severely nonlinear processes that are frequently used as benchmarks of nonlinear process control strategies. The evaluation shows that, despite its lack of dependence on the process model, the proposed method performs almost the same as conventional sliding mode control alternatives that utilize all the information that exists in the mathematical model of the process.... 

In this letter, we consider two problems of sending a bivariate Gaussian source through a two-user Gaussian non-orthogonal multiple-access channel. We provide a new distortion outer bound for the considered joint source-channel coding problems, which significantly reduces the gap between inner and outer bounds of the distortion for correlation coefficients below a threshold. Furthermore, numerical results show, that under some conditions, our proposed outer bound matches with the inner bound obtained via the separate source-channel coding scheme, which proves the optimality of this scheme. © 1997-2012 IEEE  

In this paper, we consider the problem of sending a bivariate correlated Gaussian source through a two-user Gaussian orthogonal multiple-access channel (MAC), where each encoder observes a noisy version of one of the source components, and the receiver aims at reconstructing each source component. The estimation quality is measured by mean-squared error (MSE) distortion criterion. Different components of the source have their own fidelity requirements instead of total or average distortion measure. It is easy to verify that for this problem, digital communication has an optimal performance. However, it is not explicit that when there is a constraint on the total power budget, what power... 

In this paper we study the sum modulo two problem proposed by Körner and Marton. In this source coding problem, two transmitters who observe binary sources X and Y, send messages of limited rate to a receiver whose goal is to compute the sum modulo of X and Y. This problem has been solved for the two special cases of independent and symmetric sources. In both of these cases, the rate pair (H(X|Y), H(Y|X)) is achievable. The best known outer bound for this problem is a conventional cut-set bound, and the best known inner bound is derived by Ahlswede and Han using a combination of Slepian-Wolf and Körner-Marton's coding schemes. In this paper, we propose a new outer bound which is strictly... 

In this paper, the impact of a small variations in the channel gains on the secrecy rate of the wiretap channel is studied, in which it is assumed that the imperfect channel knowledge is available at the transmitter. First, we consider general additive noise model for both legitimate and eavesdropper channels in the wiretap channel, and compute the variation of the secrecy rate resulting from the small variations in the channel gains. Then, we focus on the Gaussian wiretap channel, as a special case and calculate the sensitivity of the secrecy capacity to the channel gains with imperfect channel knowledge. Interestingly, it is shown that in some situations the effect of the channel variation... 

We extend the result by Tse and Verdú on the optimum asymptotic multiuser efficiency of randomly spread code division multiple access (CDMA) with binary phase shift keying input. Random Gaussian and random binary antipodal spreading are considered. We obtain the optimum asymptotic multiuser efficiency of a K-user system with spreading gain N when K and N → ∞ and the loading factor, (K/N) , grows logarithmically with K under some conditions. It is shown that the optimum detector in a Gaussian randomly spread CDMA system has a performance close to the single user system at high signal-to-noise ratio when K and N → ∞ and the loading factor, (K/N), is kept less than (log3 K/2). Random binary... 

This paper introduces a new method for the least significant bit (LSB) steganography in spatial domain. The new method, called one-third LSB embedding, reduces the probability of change per pixel to one-third without sacrificing the embedding capacity, as compared to previous LSB steganography techniques. This improvement results in a better imperceptibility and higher robustness against well known LSB detectors. Each bit of the message is carried through a function of three adjacent cover pixels and it is shown that no significant improvement is achieved by increasing the length of the pixel sequence employed. ©2009 IEEE  

Many studies have shown that the imbalance of network channel traffic is of critical effect on the overall performance of multicomputer systems. In this paper, we analytically model the traffic rate crossing the network channels of a hypercube network under different working conditions. The effect of different parameters on the shaping of non-uniformity and traffic imbalance over network channels, are considered and analytical models for each case are proposed. © Springer-Verlag Berlin Heidelberg 2006  

Remote observation of the state trajectory of nonlinear dynamic systems over limited capacity communication channels is studied. It is shown that two extreme cases are possible: Either the system is fully observable or the error in estimation blows up. The key observation is that such behavior is determined by the relationship between the Shannon capacity and the Lyapunov exponents; the well-known characterizing parameters of a communication channel on one side, and a dynamic system from the other side. In particular, it is proved that for nonlinear systems with initial state x0, the minimum capacity of an additive white Gaussian noise channel required for full observation of the system in...