Sharif Digital Repository

In this paper, we study the performance of optical code-division multiple access (CDMA) systems using various receivers structures. Two general classes of receivers based on required electronic bandwidth are studied. Optical orthogonal codes (OOCs) are utilized as signature sequences and the performance studied in this paper takes into account the effect of all major noise sources, i.e., quantum shot-noise, dark current noise, and Gaussian circuit noise. Furthermore, this paper introduces a generalized method of analyzing the performance of various optical CDMA receiver structures. Required mean number of photon count per chip time for reliable transmission of data bits for various receiver... 

This paper deals with the possibilities of cancellation of unwanted signals by steering nulls of the pattern in the direction of arrival of signal while keeping the main beam to the desired direction. New iterative adaptive digital beam forming technique is presented here to enhance the conventional effectiveness of beam forming in common commercial application. Simulation and measurement results confirm that this algorithm can achieve effective Co-Channel Interference (CCI) suppression, while increasing the strength of the desired signal  

The cooperative relay cognitive interference channel (RCIC) is a four-node network with two source nodes (primary source and cognitive source) and two destination nodes, in which sources try to communicate at certain rates with their corresponding destinations simultaneously through a common medium and each destination can act as a relay to assist the other one. In this paper, we study partially and fully cooperative state-dependent relay cognitive interference channels (RCICs) with perfect causal channel state information (CSI). For each of these channels, we investigate three different cases. For the first case, perfect causal CSI is available at both the source and relay nodes; for the... 

In this study, the three-user interference channel (IFC) with common information is considered, where each receiver decode not only the private message from the intended transmitter but also the common messages from the non-intended transmitters by applying a simultaneous decoding scheme. An achievable rate region is presented using rate splitting and superposition encoding at the transmitters and simultaneous joint decoding at the receivers in which the transmitters cooperatively send the split messages which allows the interference cancellation at the receivers. The implicit form of the achievable rate region is also extended to K-user IFC with common information. Finally the inner bound... 

In this paper, lattice based coding is used over two-user Gaussian state-dependent multiple access channel with common message for two channel models. First, it is assumed that the additive channel interference is noncausally known at both encoders. Exploiting a lattice encoding and decoding scheme, the effect of the interference is completely removed and the capacity region is achieved. Then, the multiple access channel with two additive interferences is considered in the case, where each interference is known noncausally to the associated transmitter. A pure lattice based encoding and decoding structure is proposed and an inner bound on the capacity region is derived which is valid for the... 

The performance of OFDM-based Wireless Local Area Networks (WLANs) is investigated by employing different smart antenna techniques at the receiver. The use of multiple antennas at the Access Point (AP) receiver in IEEE802.11a standard-compliant Single Input Multiple Output (SIMO) configuration, improves the physical layer performance in different channel scenarios and interference that may arise from other stations sharing the same frequency band. For this purpose, a comparative study of smart antenna architectures for IEEE802.11a WLAN system using pre-FFT and post-FFT array processing techniques is presented. Simulations are performed on a new model for IEEE802.11a system using a... 

We study the degrees of freedom of the three-user Gaussian interference channel under the circumstance where one or more transmitters are non-causally cognitive, meaning they are aware of the messages of one or more transmitters in a non-causal manner. Our focus is on the total degrees of freedom of the three-user cognitive interference channel. Our first case is when only one of the transmitters is fully cognitive and knows the messages of the other users. We prove that using interference alignment and interference cancellation, the achievable total degrees of freedom is 11/6 and does not coincide with the calculated total degrees of freedom upper bound which is 2. In the second and third... 

In this work, we consider the problem of communicating linear functions of correlated Gaussian sources over a two-user additive Gaussian noise multiple access channel (MAC) in the presence of known interference at the transmitter. The goal is to estimate a linear combination of two sources at the receiver with minimum average mean squared error (MSE) distortion. Here, a lattice-based coding scheme is presented and its achievable distortion is analyzed. In addition, two lower bounds on the achievable distortion are derived. The proposed lattice coding scheme can cancel channel interference completely  

In this paper, we consider a three-user cognitive radio network with two primary users and one cognitive radio. We concentrate on a three-user Interference Channel (IFC) where one of the transmitters has cognitive capabilities and non-causally knows the messages of the other two transmitters. Moreover, we assume that the cognitive transmitter does not cause any interference at the receivers of the primary users and we introduce three-user Cognitive Z-Interference Channel (C-ZIFC). We first obtain an inner bound on the capacity region of three-user C-ZIFC, where our coding scheme makes use of collaborative strategy by rate splitting and cooperative strategy by superposition coding. Moreover,... 

We define partial cognitive relay channel as a twotransmitter, two-receiver interference channel with a relay node such that one of the transmitters is a cognitive transmitter. As a more feasible assumption we assume that the cognitive transmitter has non-causally access to a part of the other transmitter's encoded message. The cognitive radio transmitter transmits simultaneously over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. We calculate the achievable rate region for partial cognitive relay channel based on the combination of partial decode-compress and forward for the relay, rate-splitting and Gel'fand and Pinsker coding. Numerical... 

In this letter, we explore blind interference alignment (BIA) for the K-user single-input and single-output interference channel. We show that if we implement the structure of reconfigurable antennas at the receivers, by increasing the number of reception modes, the chance of finding proper channel conditions to align most part of interference signals will increase. Throughout this letter, we use the antenna structure of media-based modulation as reconfigurable antenna structure of the receivers. In this method, the receivers try to find proper channel states to align interference signals in an opportunistic manner. The results of this letter show that our proposed method has higher capacity... 

Fundamental limits of communication is studied in a 4 × 4 interference network, in which the transmitters are equipped with cache memories. Each of the receivers requests one file from a library of N equal-size files. The caches at the transmitters are filled without the knowledge of the user demands, such that all possible demand combinations can be satisfied reliably over the interference channel. The achievable normalized delivery time (NDT) is studied under centralized cache placement. By combining the interference alignment (IA) and zero-forcing (ZF) techniques, a novel caching and transmission scheme is presented, and is shown to be optimal for all possible cache sizes; fully... 

An achievable rate region for the genie-aided cognitive radio channel is obtained using the celebrated HanKobayashi jointly decoding strategy for the interference channel and the Gel'fand-Pinsker coding scheme for channels with side information known at the transmitter. The achievable rate region is then simplified by Fourier-Motzkin elimination. The obtained achievable rate region (i) extends the Chong-Motani-Garg region for the interference channel to the cognitive channel and (ii) is a simplified description of the Devroye-Mitran-Tarokh rate region for the genie-aided cognitive radio channel. © 2009 IEEE  

We consider transmission of a Gaussian source over a Gaussian channel under bandwidth compression in the presence of an interference known only to the transmitter. We study hybrid digital-analog (HDA) joint source-channel coding schemes and propose two novel layered coding schemes that achieve the optimal mean-squared error (MSE) distortion. This can be viewed as the extension of results by Wilson ["Joint Source Channel Coding With Side Information Using Hybrid Digital Analog Codes," IEEE Trans. Inf. Theory, vol. 56, no. 10, pp. 4922-2940, Oct. 2010], originally proposed for sending a Gaussian source over a Gaussian channel in two cases: 1) Matched bandwidth with known interference only at... 

Resource allocation with quality of service constraints is one of the most challenging problems in elastic optical networks that is normally formulated as a mixed-integer nonlinear optimization program. In this paper, we focus on novel properties of geometric optimization and provide a heuristic approach for resource allocation that is much faster than its mixed-integer nonlinear counterpart. Our heuristic consists of two main parts for routing/traffic ordering and power/spectrum assignment. It aims at minimization of the transmit optical power and spectrum usage constrained to the quality of service and physical requirements. We consider three routing and three traffic ordering procedures... 

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... 

In this paper, we consider the problem of data transmission for {K}- user interference channel (IC) with no channel state information (CSI) at transmitters. Each pair of transceivers with the aid of a particular precoder and a switching pattern structure tries to place its desired signal in a subspace which is linearly independent of interference signals. We show that if the channel values are known only to the receivers, the sum degrees-of-freedom (DoF) of the linear interference alignment (IA) with reconfigurable antenna at receivers is rac {{ { Kr}}}{ {r}^{2}- {r}+ {K}} , where {r} = left lceil{ {rac {sqrt {1+4 {K}}-1}{2}} }ight ceil . For previous methods when 3 leq {K} leq 10^{4} , the... 

We consider the K-user Multiple Input Multiple Output (MIMO) Gaussian interference channel with M antennas at each transmitter and N antennas at each receiver. It is assumed that channel coefficients are constant real numbers and are available at all transmitters and at all receivers. The main objective of this paper is to characterize the number of Degrees of Freedom (DoF) of this channel. Using the real interference alignment technique introduced in [20], we show that MN/M+NK degrees of freedom can be achieved for almost all channel realizations. Also, a new upper-bound on the DoF of this channel is provided. This upper-bound coincides with our achievable DoF for K ≥ Ku≜M+N/gcd(M;N), where...