Sharif Digital Repository

Non Line of Sight (NLOS) propagation is a challenging issue which the performance of network based wireless localization is limited by errors primarily caused by NLOS corruption. NLOS is inherently a dominant source of errors in metropolitan area wireless networks, like cellular one, so in this paper we discuss our proposed algorithm within cellular network terminology. This paper contributes two novel algorithms. The first one is to extract the NLOS state of base station (BS) and the second one is a correction algorithm to enhance the measurements accuracy. Our proposed algorithm discuses a novel localization technique to estimate true mobile terminal (MT) location from a set of possibly... 

Proper design of wireless personal and local area networks requires accurate characterization of radio wave propagation in indoor environments. The Shooting-and-Bouncing-Ray tracing (SBR) method, which uses Geometrical Optics (GO) approximation, has been widely used for indoor propagation modeling [1-2]  

Since DCF is the main protocol of accessing other mobile stations in ad hoc networks such as IEEE 802.11 WLANs, a self-controlling method for each station is necessary, called the backoff algorithm. An exponential backoff method has been used in WLANs and significant efforts have been made to analyze its throughput and other important properties such as delay and jitter. In this article, we propose a new backoff algorithm and model it with a discrete-time Markov chain; measuring its saturation throughput under several conditions and several set of parameters which are to be adjusted according to the network condition, with the aim of approaching maximum throughput when stations are... 

Hidden-terminal is one of the main problems in ad hoc wireless networks. In addition, there are scenarios where the desired destination is located in the range of other transmitters, so that the efforts on setting up communication with this terminal will fail due to collisions that may occur between transmitted control frames and undesired received control and data frames. This phenomenon becomes a bottleneck when most of data transmissions experience packet fragmentation. In such scenarios, the desired destination becomes unreachable during the data transfer of neighboring nodes. Using the same PHY of IEEE 802.11 and making slight modifications in its MAC, a new medium access control scheme... 

In this paper, we propose a data offloading algorithm in a network comprised of a macro base station and a few number of WiFi access points with overlapped coverage areas. The main goal of our algorithm is how to assign offloaded mobile stations (MSs) to access points (APs). Our approach in proposing the algorithm is based on mapping the problem onto finding a suitable matching algorithm, in order to minimize the average delay of the offloaded packets as one of the main QoS parameters on the one hand and to maximize the utility of the APs on the other hand. The utility of each AP is considered to be a combination of monetary benefit due to offloading service and the cost due to extra energy... 

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... 

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... 

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... 

In this letter, we examine the positioning in wireless networks in the presence of IRSs. We show that IRSs can be used to localize the user when there are not enough transmitters (Base Station). To this end, we consider a network of one transmitter, few IRSs, and one receiver, whose location should be determined. Our results indicate that we can achieve the accuracy required in the localization by controlling the number of elements of IRSs and properly selecting the location of IRSs for a given region. © 2012 IEEE  

Non Line of Sight (NLOS) propagation is a challenging issue which cause large errors in wireless localization systems. NLOS is especially a dominant source of errors in metropolitan area wireless networks like cellular ones. We discuss our algorithms within cellular network terminology. This paper contributes two novel algorithms. The first algorithm is to extract the NLOS state of base stations and the second one is a correction algorithm to enhance the measurements accuracy. Our introduced algorithms can easily operate with other wireless localization algorithms and reduced NLOS error. These algorithms are proposed for network-based localization because of the amount of calculation  

In this paper we propose and analyze the application of generalized optical orthogonal codes (GOOC) in the optical wireless local area networks (OWLAN). A system deploying GOOC can support more users and achieve better BER performance. We evaluate the system performance of GOOC noting practical constraints of OWLAN applications. We consider average and peak power limitations of free space infrared sources, arising from eye safety and device non-linearity restriction. We include the impact of various noises including background-light induced noise in system evaluation. Proper system design requires appropriate selection of GOOC code parameters. We analyze the influence of code parameters on... 

Optical Code Division Multiple Access has recently received considerable attention in wireless infrared communication. Previously introduced algorithms for wireless indoor infrared communication such as Advanced Infrared and IEEE 802.11 infrared standard use specific media access control (MAC) layer algorithms to coordinate transmission of multiple users. In this paper, we compare the multiple access performance of OCDMA with that of these algorithms and demonstrate the relative strengths and weaknesses of each algorithm. It is demonstrated that when MAC delay is an important issue, OCDMA provides a much better performance. Furthermore, OCDMA requires no coordination between users as they...