Sharif Digital Repository

Interworking in heterogeneous wireless networks is one of the key objectives in the Next Generation Networks (NGN). Handoff between cellular and Wireless Local Area Networks (WLANs) can help achieve this aim. In this paper, a new method for decision-making on vertical handoff initiation is proposed which is on the basis of road topology information and mobility prediction. The main distinction between the proposed algorithm and previous research is exploitation of road topology map of the destination hotspot within a cellular network. Mobile terminal speed, WLAN dynamic traffic in the destination hotspot, and topology information are used to decide on suitability of vertical handoff... 

The noise exists in almost all environments such as cellular mobile telephone systems. Various types of noise can be introduced such as speech additive noise which is the main factor of degradation in perceived speech quality. At some applications for example at the receiver of a telecommunication system, the direct value of interfering noise is not available and there is just access to noisy speech. In these cases the noise cannot be cancelled totally but it may be possible to reduce the noise in a sensible way by utilizing the statistics of the noise and speech signal. In this paper the proposed method for noise reduction is Bayesian recursive state-space Kalman filter, which is a method... 

Mobile value-added services have drawn the attention of researchers and practitioners recently, due to the rapid development of the mobile telecommunications market. Various mobile-based services and applications have therefore been introduced in order to satisfy mobile phone subscribers' needs. Facing intensive competition, service providers are eager to persuade mobile phone subscribers into using the mobile value-add services in the hope to expand market share and ultimately raise revenues. This study therefore intends to investigate the factors that influence mobile phone subscribers' intention to use mobile value-added services in Iran by incorporating quality factors and perceived... 

We consider a cellular wireless system including several interfering multi-user multi-antenna uplink channels, where the base station of each cell has to locally recover the messages of its corresponding users. We use a linear Wyner model, where each base station experiences interference only from the users in the two neighboring cells. Each base station is connected to the two nearby base stations through a backhaul link. The objective is to achieve the maximum degrees of freedom per cell, with minimum aggregated load in the backhaul. We propose a successive cooperative alignment scheme, in which each base station forms backhaul messages by combining the previous received backhaul messages... 

Sudoku puzzle is a logical game which has recently got very popular. Every day various mass media print these puzzles. As a result these puzzles are a suitable alternative for hidden data transfer. SMS (short message service) is one of the popular mobile-phone services. In this service people can write short messages and send it to each other through mobile phones. In this paper a method has been presented for Steganography (hiding data) in Sudoku puzzles and through SMS. In this method after hiding data in a Sudoku puzzle, the puzzle is sent in a way that it does not attract any attention. Steganography algorithm is based on order of place of numbers 1 through 9 in one of the specified row... 

Using an in-house developed software the signal level, the best server cells, and the amount of interference using standard propagation models are determined in a cellular environment. The program is also able to assign the frequency channels automatically to the TRXs taking into account the carrier to interference and the traffic distribution using a genetic algorithm. In this paper, the cost function is based on the total Carrier to Interference ratio (C/I) and the traffic density of the serving area. The software by means of a genetic algorithm approaches a frequency assignment which increases the overall quality of service throughout the cellular network. The package has been used in a... 

Network survivability is one of the main design challenges in wireless sensor networks (WSN). Survivability is the ability of the network to provide essential services in the presence of attacks and/or failures, and recover full service in a timely manner. To the best knowledge of us, survivability for WSN has never been studied considering failure effects on network. We consider the network survivability as a composite measure consisting of both network failure duration and failure impact on the network. In this paper we model network survivability in steady state. In this state, network is affected by predicted failures. This modeling is based on network connectivity and coverage, when an... 

Nowadays m-banking (mobile banking) is widely used in many banks. It has embarked upon supply of various services based on different systems and with the aid of various services such as the Short Message Service (SMS). However in developing countries such as Iran, m-banking is facing some challenges. One of these challenges is the issue of language of this system, because the main language of this system, in both side of bank system and customer mobile phone, is English. Also one of the main issues in m-banking services is the security of the systems. For solvin g the above problems, we proposed a method in this paper. By this method we send secure banking messages as well as Persian SMS for... 

In this paper, we compute lower and upper bounds for the throughput capacity of an ad hoc network overlaid on a cellular network. The ad hoc network is comprised of a specific number of wireless cognitive nodes that opportunistically exploit the inactive frequency channels in the cellular network. In this respect, we employ a model recently proposed for single-channel mobile ad-hoc network after some minor modifications. The proposed framework consists of two queueing networks, a closed BCMP queueing network comprised of M/G/∞nodes capable of mobility modeling, and an open BCMP queueing network comprised of symmetric M/G/1 nodes capable of modeling the packet transmission process. By... 

There are many websites specially designed for mobile phones. Some hackers write automated programs to abuse these website services and waste the website resources. Therefore, it is necessary to distinguish between human users and computer programs. Methods known for achieving this are known as CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart). CAPTCHA methods are mainly based on the weaknesses of OCR (Optical Character Recognition) systems and ask the user to type a word. So using them is difficult in tools such as PDAs (Personal Digital Assistant) or mobile phones that lack a complete keyboard. In this paper, a new CAPTCHA system is proposed for... 

A5/1 is the strong version of the encryption algorithm on GSM (Global System for Mobile communications) used in many countries. It is constructed of a combination of three LFSRs (Linear Feedback Shift Registers) with irregular clocking manner. One of the most practical attacks against this algorithm is time-memory trade-off attack, which is based on birthday paradox. The goal of this attack is to find any intersection between precomputed LFSRs states set and set of states generating the output bits in the actual execution of the algorithm. In order to increase feasibility of this attack, the biased birthday attack was introduced. In this attack special states producing a specific pattern in... 

We study the problem of power optimization for object tracking using distributed Wireless Sensor Networks (WSNs). The accuracy of the object tracking is dependent on the tracking time interval. Smaller tracking time interval increases the accuracy of tracking a moving object. However, this increases the power consumption significantly. This paper proposes a modified adaptive sleep time management scheme called Modified Predict and Mesh (MPaM) to adapt tracking time interval such that it minimizes power consumption while keeping an acceptable tracking accuracy. Also a quantitative analysis to compare the performances of the conventional PaM and proposed Modified PaM (MPaM) schemes is... 

This paper presents a new model of call admission control which consists of a few key elements for protecting the network in different conditions of workload in a manner that, calls blocking /dropping are kept under desired level. This model consists of two traffic classes of voice and data. In order to give a priority to handoff call over new call, some parameters in this model are adjusted in a manner that handoff dropping is reduced to the least probability in the target cell and the adjacent cells. Some channels are reserved for voice and data calls in each cell to guarantee the quality of service requirements in the network. Limited fractional guard channel is used to have an optimized... 

A solution to channel assignment problem in cellular networks is self-organizing channel assignment algorithm with distributed control. In this paper, we propose three cellular learning automata based dynamic channel assignment algorithms. In the first two algorithms, no information about the status of channels in the whole network will be used by cells for channel assignment whereas in the third algorithm, the additional information regarding status of channels may be gathered and then used by cells in order to allocate channels. The simulation results show that by using the proposed channel assignment algorithms the micro-cellular network can self-organize itself. The simulation results... 

In this paper, a DCT-based blind watermarking scheme based on spread spectrum communications is proposed. We perform block-based DCT on the host image; then using the DC coefficients of each block, we construct a low-resolution approximation image. We apply block-based DCT on this approximation image, then watermark is embedded by adding a pseudo random noise sequence into its high frequencies. In detection stage, we extract the approximation image from the watermarked image, then the same pseudo random noise sequence is generated, and its correlation is computed with high frequencies of the watermarked approximation image. In our method, higher robustness is obtained because of embedding... 

Considering a multihop cellular system with one relay per sector, an effective modeling for the joint base-station/relay assignment, rate allocation, and routing scheme is proposed and formulated under a single problem for the downlink. This problem is then formulated as a multidimensional multichoice knapsack problem (MMKP) to maximize the total achieved throughput in the network. The well-known MMKP algorithm based on Lagrange multipliers is modified, which results in a near-optimal solution with a linear complexity. The notion of the infeasibility factor is also introduced to adjust the transmit power of base stations and relays adaptively. To reduce the complexity, and in order to... 

Mobile banking (M-Banking) has been welcomed in most of the countries as a new branch in electronic banking (E-Banking). In developing countries such as Iran mobile banking is limited to fields such as SMS due to lack of infrastructure and because of high costs. In this paper we present a method for developing banking services through mobile phone in the bank area. In our method a server which is capable to be connected through bluetooth is installed in the bank and offered banking services. Customers inside the bank and also around the bank are connected to the bank system through bluetooth technology and handle their banking operations through their mobile phones. This way they won't pay... 

In this paper, the problem of content caching in 5G cellular networks relying on social-aware device-to-device communications (DTD) is investigated. Our focus is on how to efficiently select important users (IUs) and how to allocate content files to the storage of these selected IUs to form a distributed caching system. We aim at proposing a novel approach for minimizing the downloading latency and maximizing the social welfare simultaneously. In particular, we first model the problem of maximizing the social welfare as a many-to-one matching game based on the social property of mobile users. We study this game by exploiting users' social properties to generate the utility functions of the... 

In this paper, we analyze the effect of applying leaky bucket as a well known traffic shaper on data users in a variable spreading gain CDMA (VSG-CDMA) uplink wireless cellular network. To this end, we model the effect of leaky bucket mechanism on a typical data user, with a closed product form queueing network. Each node in this queueing network corresponds to a specific processing gain or equivalently transmission rate and power. By solving such a queueing network we obtain the steady state probability with which a typical data user will exist at each node. By aggregating the effects of all data users we compute the mean and variance of interference and obtain the throughput and average... 

Recently Mobile Learning (M-Learning) has attracted much attention. Due to advantages of SMS (Short Messaging Service) on mobile phones we present a safe and protected method for taking multiple-choice quizzes by using the SMS on mobile phones in this paper. In this method questions of quiz are sent to students along with their answers through some SMS messages. The students will receive their grades immediately after answering the questions and this grade is also sent to the instructor or professor along with the student's answers through an SMS Picture Message. Answers of questions and the student's grade are hidden in SMS picture message through stenography and then they are sent. The...