Sharif Digital Repository

We study the quantum capacity of a continuous-variable dephasing channel, which is a notable example of a non-Gaussian quantum channel. We prove that a single-letter formula applies. The optimal input state is found to be diagonal in the Fock basis and with a distribution that is a discrete version of a Gaussian. We discuss how its mean and variance are related to the dephasing rate and input energy. We then show that by increasing the input energy, the capacity saturates to a finite value. We also show that it decays exponentially for large values of dephasing rates. © 2020 American Physical Society  

In general quantum operations, or quantum channels cannot be inverted by physical operations, i.e., by completely positive trace-preserving maps. An arbitrary state passing through a quantum channel loses its fidelity with the input. Given a quantum channel E, we discuss the concept of its quasi-inverse as a completely positive trace-preserving map Eqi which when composed with E increases its average input-output fidelity in an optimal way. The channel Eqi comes as close as possible to the inverse of a quantum channel. We give a complete classification of such maps for qubit channels and provide quite a few illustrative examples. © 2020 American Physical Society  

A central machine is interested in estimating the underlying structure of a sparse Gaussian Graphical Model (GGM) from a dataset distributed across multiple local machines. The local machines can communicate with the central machine through a wireless multiple access channel. In this paper, we are interested in designing effective strategies where reliable learning is feasible under power and bandwidth limitations. Two approaches are proposed: Signs and Uncoded methods. In the Signs method, the local machines quantize their data into binary vectors and an optimal channel coding scheme is used to reliably send the vectors to the central machine where the structure is learned from the received... 

Capacity has been found for degraded, reversely degraded, full feedback, semi-deterministic, orthogonal relay channels, also for a class of deterministic relay channels and a class of modulo sum relay channels. We indicate what the relay decodes and forwards with one auxiliary random variable having bounded cardinality and attempt to define a more general class of relay channels in order to unify most of known capacity theorems into one capacity theorem by considering additional assumptions imposed to the definition of those channels. In other words, the relay channel inputs are dependent as in multiple access channel with arbitrarily correlated sources and here we do for the relay channel... 

We introduce a new communication model consisting of two interfering broadcast channels with one cognitive transmitter, who knows the message transmitted by the other non-cognitive transmitter, in a non-causal manner. An achievable rate region is derived for this model. The region is computed based on the Marton region for the general broadcast channel and its extension by Steinberg to the broadcast channel with the states known at the transmitter. By using the region evaluated, an achievable rate for the Gaussian broadcast channel is derived. © 2008 IEEE  

Entanglement and entanglement assisted are useful resources to enhance the mutual information of the Pauli channels, when the noise on consecutive uses of the channel has some partial correlations. In this paper, we study quantum-communication channels in d -dimensional systems and derive the mutual information of the quantum channels for maximally entangled states and product states coding with correlated noise. Then, we compare fidelity between these states. Our results show that there exists a certain fidelity memory threshold, which depends on the dimension of the Hilbert space (d) and the properties of noisy channels. We calculate the classical capacity of a particular correlated noisy... 

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  

Considerable interest in the indoor applications of wireless local-area networks (WLANs) demands some powerful simulation methods of these systems. Proper modeling of the physical propagation channel is crucial in this context. A novel simulation method for indoor wideband multi-input multi-output (MIMO) channel at the operating frequency band of IEEE 802.11a, HIPERLAN/2, and the emerging IEEE 802.11n standards is presented in this paper which is suitable for performance analysis of MIMO techniques in these systems. The presented model is developed on the basis of a previously proposed channel representation at the same frequency band. Simulation results for MIMO channel capacity are... 

We consider the problem of recovering channel code parameters over a candidate set by merely analyzing the received encoded signals. We propose a deep learning-based solution that I) is capable of identifying the channel code parameters for several coding scheme (such as LDPC, Convolutional, Turbo, and Polar codes), II) is robust against channel impairments like multi-path fading, III) does not require any previous knowledge or estimation of channel state or signal-to-noise ratio (SNR), and IV) outperforms related works in terms of probability of detecting the correct code parameters. © 2012 IEEE  

We consider the fundamental limits of reliable communication over a two-state compound channel when the state of the channel needs to be masked. Our model is closely related to an area of study known as covert communication, a setting in which the transmitter wishes to communicate to legitimate receiver(s) while ensuring that the communication is not detected by an adversary. Our main contribution is the establishment of upper and lower bounds on the throughput-key length region when the constraint that quantifies how much the states are masked is defined to be the total variation distance between the channel output distributions of the two states. When length of the key is sufficiently... 

The voice channels present in cellular communication networks provide reliable, widespread and high priority communication mediums. Using these voice channels as a bearer for data transmission allows to deliver high Quality of Service data. But voice channels include vocoders that hinder the data flow by compressing the waveforms prior to transmission. Calculating vocoder channel capacity remains a challenging problem since no analytical model has been proposed for the vocoder channel so far. In this research, simplified models for the vocoder channel are proposed and bounds on vocoder channel capacity are derived based on them. In common cellular networks, the vocoder compression rate is... 

Reverberated speech signals in acoustical environments produces some problems such as reducing speech intelligibility, distinguishing speakers, locating source, quality for hands-free telephony, hearing aid, etc. Adaptive filters can be applied to reduce the reverberation effects or to dereverberate the received speech signals at microphone. In this paper a dereverberation method is proposed by applying an inverse filter to the received speech signals. Different values of the Room Impulse Response are used in the dereverberation procedure and the results are compared. The results show a significant improvement in the quality of the received signal for the desired reverberant environment.... 

Space-time block codes (STBCs) with orthogonal structures provide full-diversity reception and simple decoupled detection at the receiver. Rate-one orthogonal STBCs (OSTBC) for complex constellations have been found only for two transmit antennas. On the other hand, STBCs' designs are classically based on the assumption of independent and identically distributed (i.i.d.) fading channels. However, poor scattering conditions may have harmful effects on the performance of STBCs. In this paper, we first derive the average of received signal power at the receiver over Rician fading channel, when the signals are coded with linear dispersion code (LDC). Then by using a genetic algorithm (GA), we... 

In this paper, we consider a broadband secondary transmitter-receiver pair which interferes with N narrowband primary users and study the effect of cognition and cooperation on the maximum stable throughput. In our study we focus on four transmission protocols as well as two channel types, i.e., flat fading and frequency selective fading. In the cooperative protocols, the broadband transmitter relays the packets of the primary users which have not correctly decoded at the primary receiver. The analysis includes random packet arrivals at the transmitters which may impact on the maximum stable throughput. Moreover, sensing errors at the secondary user are considered. In this paper, we derive... 

In this paper, we consider the reliable transmission of correlated sources over the relay channel. The destination wishes to find a lossless reconstruction of both sources. We find the sufficient conditions under which the relay can partially cooperate with the sender to transmit the sources to the destination. The achievability scheme is based on regular encoding/backward decoding strategy. The proposed region includes the known region for multiple-access channel with correlated sources and the achievable rate of relay channel with partial decode-and-forward strategy, as special cases. A class of deterministic relay channels is considered. It is shown that the error-free transmission of... 

Polar codes are a new class of error correcting linear block codes, whose generator matrix is specified by the knowledge of transmission channel parameters, code length and code dimension. Moreover, regarding computational security, it is assumed that an attacker with a restricted processing power has unlimited access to the transmission media. Therefore, the attacker can construct the generator matrix of polar codes, especially in the case of binary erasure channels, on which this matrix can be easily constructed. In this paper, we introduce a novel method to keep the generator matrix of polar codes in secret in a way that the attacker cannot access the required information to decode the... 

In this paper, we propose an adaptive call admission algorithm based on learning automata. The proposed algorithm uses a learning automaton to specify the acceptance/rejection of incoming new calls. It is shown that the given adaptive algorithm converges to an equilibrium point which is also optimal for uniform fractional channel policy. To study the performance of the proposed call admission policy, the computer simulations are conducted. The simulation results show that the level of QoS is satisfied by the proposed algorithm and the performance of given algorithm is very close to the performance of uniform fractional guard channel policy which needs to know all parameters of input traffic.... 

In this paper, we consider a new scheme based on jointly network and rateless coding for a multiple-access relay channel. In the scheme, whenever the relay can decode multiple messages of the users, it jointly encodes them using a larger rateless code. This scheme is compared with direct transmission and the conventional relaying scheme in which the relay helps each user independently at orthogonal channels. The comparison is made by evaluating the throughput of different schemes. The analytical and the simulation results show that the proposed scheme outperforms the other ones at the cases considered  

We study the estimation of a Gaussian source by a Gaussian wireless sensor network (WSN) where L distributed sensors transmit noisy observations of the source through a fading Gaussian multiple access channel to a fusion center. In a recent work Gastpar, [ "Uncoded transmission is exactly optimal for a Simple Gaussian Sensor Network", IEEE Trans. Inf. Theory, vol. 54, no. 11, pp. 52475251, Nov. 2008] showed that for a symmetric Gaussian WSN with no fading, uncoded (analog) transmission achieves the optimal performance theoretically attainable (OPTA). In this correspondence, we consider an asymmetric fading WSN in which the sensors have differing noise and transmission powers. We first...