Sharif Digital Repository

We consider the effect of caching in wireless networks where fading is the dominant channel effect. First, we propose a one-hop transmission strategy for cache-enabled wireless networks, which is based on exploiting multi-user diversity gain. Then, we derive a closed-form result for throughput scaling of the proposed scheme in large networks, which reveals the inherent trade-off between cache memory size and network throughput. Our results show that substantial throughput improvements are achievable in networks with sources equipped with large cache size. We also verify our analytical result through simulations  

Many applications in wireless networks impose locally distributed traffic on the network. We consider the effect of traffic localization on throughput of large wireless networks in the scaling sense. We show that by careful exploitation of traffic localization, one can enhance the throughput of various schemes in wireless networks. Also, the important case of Small World traffic distribution in wireless networks is addressed. In this type of traffic, in addition to the local traffic, a non-negligible amount of global traffic should be handled by the network. It is shown that a non-negligible amount of network-wide traffic can be tolerated by network without any performance degradation in the... 

In wireless body area networks (WBANs) it is necessary to devise an energy-efficient MAC scheduling mechanism which is capable of meeting strict QoS requirements. In this paper, special characteristics of WBAN channels, namely, the slow fading, the periodicity of fading, and the correlation among the channels have been exploited to formulate the sensor scheduling problem as a partially observable Markov decision problem (POMDP). Specific algorithms based on value iteration and pruning have been proposed in order to reduce the computational burden associated with the corresponding POMDP. The proposed scheduling mechanism is compared against a TDMA scheduling for a three-sensor network, and an... 

Considering the weaknesses of cryptography algorithms and the attacks performed against them, cryptography alone cannot guarantee the security of communication in a wireless network. With regard to the developments in wireless communication networks brought about by smart array antennas, security can be sought in the physical layer as well, aiming to restrict the access of the data in a wireless network and limit it to authorized users only in order to further restrain malicious data accesses. In this paper, we analysis a strategy for restricting data access using smart array antennas and present the results in security by a parameter called exposure region. For this strategy afterwards we... 

Network-on-Chip (NoC) as a promising design approach for on-chip interconnect fabrics could overcome the energy as well as synchronization challenges of the conventional interconnects in the gigascale System-on-Chips (SoC); The advantages of communication performance of traditional wired NoC will no longer be continued by the future technology scaling. Packets that travel between distant nodes of a large scale wired on-chip network significantly suffer from energy dissipation and latency due to the routing overhead at each hop. According to the International Technology Roadmap for Semiconductors annual report, the RFCMOS characteristics will be steadily improved by technology scaling. As the... 

The capacity of multiple-input multiple-output (MIMO) systems in vehicular communication is investigated throughout this paper. The goal is to consider a link between a vehicle-side and a road-side unit in presence of line-of-sight in a way that the road-side end uses all available antennas but the vehicle-side end chooses a subset of available antennas such that the link capacity becomes maximized. In order to maximize the channel capacity a criterion is derived that forces some circumstances about the configuration of antenna array in vehicle-side. If such circumstances are satisfied the channel capacity will be at its maximum. By proposing an antenna selection algorithm, the conditions... 

We study the asymptotic behavior of the capacity of erasure networks under a restricted class of network coding schemes, called spatial network coding. In spatial network coding, nodes are permitted to only combine data units received from distinct incoming links; multiple data units arriving on the same link may not be coded together. Elsewhere, it has been shown that the network capacity under spatial network coding is the statistical mean of the minimum cut value. In this paper, we come up with a new concept in the random graph theory referred to as typical min-cut family, which parallels the information theoretic notion of typical sequences, and use it to develop an analytical tool for... 

The achievement of our previously proposed space-time coding algorithm entitled full-rate linear-receiver space-time block code (FRLR STBC) has motivated us to propose, in this paper, a new class of high-rate space-time-frequency block codes (STFBCs) over frequency-selective Rayleigh fading channels. We have called these codes FRLR STFBCs with interleaving (FRLR STFBCs-I). FRLR STFBCs-I could achieve a full-diversity property over quasi-static channels. Simulation results also verify that the proposed schemes exhibit proper performances in comparison with the recently proposed STFBCs. The most outstanding characteristic of the newly introduced high-rate codes is the linear complexity of the... 

The plan of the environment used in a ray tracing simulation is not usually in exact accordance with the actual environment plan. Errors on the order of several centimeters may be present in describing the lateral wall positions. Such errors are comparable to the wavelength in indoor wireless applications and hence, can severely alter the phases of multipath components and lead to inaccurate electromagnetic field at the receiver. In this paper, the impact of this type of geometrical errors on the ray tracing results is investigated. Lateral wall positions are considered as random variables to account for possible geometrical errors. The statistical moments of some channel parameters are... 

Cell search is a crucial process in the synchronization procedure for the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system. In this paper, a high-speed, low-complexity and reliable architecture is proposed for both steps of cell search: sector ID and cell ID group detection. For the sector ID detection, two novel methods, sign-bit reduction and wise resource sharing, are proposed. In addition, for the cell ID group detection, we proposed an algorithm based on the Maximum Likelihood Sequence Detection (MLSD) called 'sign-bit MLSD'. Simulations show that the proposed methods result in more than 90% reduction in area compared to the state-of-the-art. We designed and... 

Sensor networks with sensing, data processing and communicating capabilities have a broad spectrum of applications. Based on application requirements, various network configurations can be designed. One such robust configuration is a hybrid wired-cum-wireless sensor network that is composed of a wireless sensor network and a wired backbone which are inter-connected via access points. In this paper, the joint problem of configuring a hybrid wired-cum-wireless sensor network, position-constrained cluster head and access point placement is proposed. The design considers real wireless communication limitations, optimum locations of access points and cluster heads, and hybrid transmission... 

Accurate modeling of sea clutter and detection of low observable targets within sea clutter are the major goals of radar signal processing applications. Recently, fractal geometry has been applied to the analysis of high range resolution radar sea clutters. The box-counting method is widely used to estimate fractal dimension but it has some drawbacks. We explain the drawbacks and propose a new fractal dimension based detector to increase detection performance in comparison with traditional detectors. Both statistically generated and real data samples are used to compare detector performance  

The prime shortcoming of Wireless Sensor Networks (WSNs) is their energy constraint. The main energy consumer in a sensor node is its radio transmitter. One of the most effective methods to reduce the data transmission rate is data prediction. By data prediction, the amount of transmitted data is reduced; which results in energy saving and the longevity of the network life. Environmental variations almost have similar effects on different sensor sources in a sensor device. So, considering the correlation between different sources reduces the noise impact and increases data prediction accuracy. In this paper, temporal and multi-source correlations are used, to reduce data transmission in... 

Recent demands toward high-speed wireless networks are growing. IEEE 802.11n, as the latest standard toward achieving higher speeds, aims to enhance IEEE 802.11 for higher throughputs. There are few works which analyze performance of this protocol in single-hop networks in terms of MAC layer-based parameters. Most of these works suggest disabling the RTS/CTS handshake to reduce MAC layer overheads. However, the effects of this protocol on the upper layers, especially the network layer, are still unknown. This paper deals with investigating performance of the network layer over IEEE 802.11n. Through extensive simulations performed in NS-2 we show that although network throughput is improved... 

A simulation tool, based on Ray Tracing method, has been developed and validated for millimeter-wave band. This tool helps for predicting the signal level as well as the delay characteristics of a propagation channel. Since the resultant of the received replicas of the transmitted signal at receiver point can experience a deep fade and consequently the quality degradation, a proper diversity method can effectively alleviate this drawback. Using this simulation tool and extracting the received wave characteristics in a street scenario, an analytical expression for predicting the space diversity gain for the Selection Combining technique and Maximal-Ratio Combining technique has been proposed  

Presently, the urgency of creating efficient system to tackle natural hazards such as tsunamis, earthquakes, landslides and floods to cite just a few, have originated that Wireless Sensor Networks (WSNs) play an increasingly important role in the natural hazards scenario as an efficient early warning system, sometimes in synergy with satellites-GMES (Global Monitoring Earth Systems) and also with mobile robotics. Their integration into the web scenario, giving rise to the sensor-web technology, provides even more power to the intrinsic strengths of WSNs. The WSNs application in post-disaster scenarios is also an emerging challenging issue. In this paper the fundamental technology concepts of... 

Routing methods and algorithms in "Wireless Sensor Networks" attract researchers' attention a lot recently. In order to find the optimal path in WSNs depending on their type and application, various algorithms are proposed. In this paper, an optimal path finding algorithm based on "Game Theory" is discussed and improved. This algorithm finds a path witch is optimizing network lifetime, load distribution, and path reliability simultaneously  

The focus of the paper is on cross-layer transmission based on rateless coding for relay networks. In the proposed method, rateless coding is used at the packet level and a separate physical layer coding is used at the physical layer. As rateless codes are originally designed and optimized for erasure channels, using these codes at the physical layer can lead to significant performance degradation. The proposed scheme has the advantage of a cross-layer design which uses a rateless code at the packet level modeled by an erasure channel. Based on the analysis and simulation results provided in this paper, the cross-layer scheme results in earlier successful decoding at the destination  

One of the most challenging problems in Opportunistic Spectrum Access (OSA) is to design channel sensing-based protocol in multi secondary users (SUs) network. Quality of Service (QoS) requirements for SUs have significant implications on this protocol design. In this paper, we propose a new method to find joint policies for SUs which not only tries to guarantee QoS requirements but also maximize network throughput. We use Decentralized Partially Observable Markov Decision Process (Dec-POMDP) to formulate interactions between SUs. Meanwhile, a tractable approach for Dec-POMDP is utilized to extract sub-optimum joint policies for large horizons. Among these policies, the QoS-aware joint... 

In this paper, we introduce a new cost function for SIR-Based uplink power control algorithms that takes into account transmission power level as well as target Signal-to-Interference Ratio (SIR) deviation. Existence of Nash equilibrium point, its uniqueness and the algorithm convergence are proved in the framework of so-called standard power control schemes. As shown through simulations, the proposed method results in significant transmit power reduction while achieving almost the same average SIR level. In addition, it is shown that the new scheme results in improved overall network fairness in comparison with another algorithm