Sharif Digital Repository

In this paper a novel form of the familiar E-shaped patch antenna is presented. In the presented approach, by using the genetic algorithm (GA) based on fuzzy decision-making, some modifications have been implemented to the incorporated slots which lead to even more enhancement in the antenna bandwidth. The MOM (Method of Moment) is employed for analysis at the frequency band of 1.8GHz-2.6GHz by the optimization parameters of supply locations and slot dimensions. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters like recombination to produce the next generation. Fuzzy inference system (FIS) is used for the control of GA parameters. The design... 

A new time-hopping ultrawideband (TH-UWB) CDMA scheme for indoor wireless communications is presented. In the proposed method, the duration of each bit is divided into Ns1 frames, each one containing Ns2 subframes. Two pseudorandom sequences are assigned to each user. During each bit interval, based on the output of a super-orthogonal encoder and the user's first dedicated pseudorandom sequence, the transmitter selects one of the Ns1 frames and then transmits Ns2 narrow pulses in that frame, one in each of the Ns2 subframes. The location of the pulse in each subframe is determined by the user's second dedicated PN sequence. Four different detection techniques are considered at the receiver... 

Adaptive modulation with the goal of minimizing the average transmit power is investigated. This is the dual problem of the well-known problem of maximizing the average spectral efficiency. This is desirable in power limited systems such as mobile and sensor networks. Two main cases are considered: adapting only transmit power and adapting only rate. Appropriate expressions for rate or power control policies are derived for different cases. For rate adaptation, we consider both continuous and discrete rate policies. Then, we will apply these methods to a special case of M-QAM modulation over Rayleigh fading channel. We will show that by using rate or power adaptation schemes, between 7dB and... 

Cooperation of nodes for routing and packet forwarding is inevitable in a mobile ad hoc network. Selfishness in such networks is a significant challenge and can cause network performance to noticeably degrade. In this paper, we propose some new selfishness models elicited from psychological behavior of human beings. We also evaluate performance of MANET in the presence of different percentages of selfish nodes that act based on our selfishness models. Results show that energy-based selfishness is a serious problem that could affect performance depends on mobility of nodes, density of network, and time of simulation. This kind of selfishness needs a comprehensive mechanism to cope with and we... 

A well known method to reduce the intrinsic complexity of Multiple Input Multiple Output (MIMO) systems is to choose a subset of available antennas which have stronger links than the others, in order to perform the specified MIMO algorithm. The data resulted from the antenna selection process (at the receiver side) is sent back to the transmitter side via a feedback channel. There seems to be a need to reduce the number of feedack bits, specially when the number of antennas is not small. In this paper, we investigate the problem of reducing the number of feedback bits in antenna selection techniques. We've proposed two methods using vector quantization techniques to perform feedback bit... 

With the advance of multimedia systems and wireless mobile communications, there has been a growing need to support multimedia services (such as mobile teleconferencing, mobile TV, telemedicine, and distance learning) using mobile multimedia technologies. Despite the research done in the field of mobile multimedia, delivery of real-time interactive video over noisy wireless channels is still a challenge for researchers. This paper presents a method for prioritising data partitioned MPEG-4 video in a way suitable for transmission over a mobile network. The effectiveness of the technique is demonstrated by examing its performance when the transport of the prioritized video streams can be... 

Wireless sensor networks consist of small nodes with sensing, computation, and wireless communicationr capabilities. Many routing protocols have been specifically designed for WSNs where energy awareness is an essential design issue. Routing protocols in WSNs might differ depending on the application and network architecture. In this article, a fault-tolerant and energy efficient routing protocol for wireless sensor networks is proposed This protocol is called Directed Flooding, and is a descendant of the Flooding routing protocol, which consumes less energy, while maintaining high levels of fault-tolerance. This is done by Tending data in a specific aperture instead of broadcasting, which... 

In this paper an optimized E-shaped patch antenna is presented, the bandwidth of the E-shaped microstrip antenna is optimized using the genetic algorithm (GA) based on fuzzy decision-making. In the implemented fuzzy system, inputs are parameters like population, and outputs are parameters such as recombination to produce the next generation. Fuzzy inference system is used for the control of the parameters of the genetic algorithm. Simulation results show the high ability of genetic optimization based on fuzzy system for about 33% BW. Dimensions of the slots have been optimized with the novel design approach presented herein. A prototype element is also constructed in order to validate the... 

In this paper, we consider the call admission problem in cellular networks that support several classes of calls. In the first part of this paper, we first introduce a multi-threshold guard channel policy and study its limiting behavior under the stationary traffic. Then we give an algorithm for finding the optimal number of guard channels that minimizes the blocking probability of calls with lowest level of QoS subject to constraints on blocking probabilities of other calls. In the second part of the paper, we give an algorithm for finding the minimum number of channels subject to constraints on blocking probabilities of calls. Finally, we propose a prioritized channel assignment algorithm... 

In this paper, a new transport layer method is proposed utilizing a diversity scheme to make an end to end communication reliable and consequently reduce power consumption in large scale sensor networks. Sensor networks are composed of large number of battery powered nodes. Energy consumption is the most important design objective in sensor networks while delay and throughput are taken less into account. Wireless transmission is the other important characteristic of these networks. Small-scale fading decreases wireless communication performance. In a fading channel higher SNRs is needed and consequently more energy is consumed. In addition to error occurred because of poor communication... 

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  

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 complex dielectric constants of building materials are present in the reflection, transmission and diffraction coefficients of the ray tracing formulation. Any deviation of the dielectric constants included in ray tracing simulation from the actual material properties may be a source of inaccuracy of the simulation results. This paper explores the sensitivity of ray tracing results to the inaccuracy of the dielectric constants of building materials. To do this, the real and imaginary parts of the dielectric constants are considered as random variables to account for the present uncertainty. The propagation of uncertainty in the ray tracing simulation is then obtained by means 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... 

Femtocell has appeared as a solution to increase both coverage and capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. In this paper, we deal with the problem of joint subband, rate, and power allocation in OFDMA based two-tier femtocell networks. It is assumed that for macrocell users, spectrum allocation is accomplished through Fractional Frequency Reuse (FFR). Our objective is to maximize the femtocell user's throughput while maintaining as little as possible reduction in the macrocell users' performance. Our proposed algorithm is decentralized, and needs to be done only when femtocell access point is...