Farshad Eshghi

Performance analysis of ad hoc wireless LANs for real-time traffic

Compelling features of wireless local area networks (WLANs), put a variety of wireless service demands in place. In order to adjust system parameters to fulfill specific needs of different applications, a mathematical description of the system turns to be helpful. The inherent complexity of the wireless access, makes this description very challenging. We propose a new performance model for the IEEE 802.11 WLAN in ad hoc mode. The ad hoc mode has been chosen since we eventually aim at interconnected WLAN clusters where no base station exists. The model is based on the presentation of the system with a pair of one-dimensional state diagrams which can easily accommodate variations of many input parameters. The corresponding state variables are contention window size and buffer occupancy of each user in the system. The input parameters considered are: packet fragmentation factor, buffer size, and maximum allowable number of retransmissions. However, the approach taken is capable of ingesting many other probable parameters of interest. System performance criteria under study are: throughput, delay, and probability of fail to deliver. The last two are crucial for real-time applications.

Performance evaluation of multihop ad hoc WLANs

Ongoing technological advances in portable devices, coupled with the need for continuous connectivity while mobile, have made ad hoc networks a compelling research and development topic, particularly in a challenging multimedia multihop scenario. The ability of IEEE 802.11s ad hoc mode of operation, as a dominating wireless local area network (WLAN) protocol, to serve multihop networks requires thorough investigation. In this article, through considering crucial real-life physical phenomena and avoiding as many confining assumptions as possible, system performance measures such as delay and packet failure rate are evaluated. As a result, the importance of adequate selection of the system parameters toward performance improvement is underscored. Moreover, the simulation results imply that by complementing through priority provisions, coordination, route reservation, clustering, and optimum channel coding considerations, the IEEE 802.11 medium access control (MAC) protocol can survive in a multihop scenario. The custom simulation environment developed features modularity, comprising traffic generator, mobility, wireless channel, and IEEE 802.11 protocol modules, and is capable of accommodating many more of the physical phenomena involved.

Performance analysis of ad-hoc wireless LANs for real-time traffic

Compelling features of wireless local area networks (WLAN) put a variety of wireless service demands in place. In order to adjust system parameters to fulfill the specific needs of different applications, a mathematical description of the system tends to be helpful. The inherent complexity of wireless access makes this description very challenging. We propose a new performance model for the IEEE 802-11 WLAN in ad-hoc mode. The ad-hoc mode has been chosen since we eventually aim at interconnected WLAN clusters where no base station exists. The model is based on the presentation of the system with a pair of one-dimensional state diagrams which can easily accommodate variations of many input parameters. The corresponding state variables are contention window size and buffer occupancy of each user in the system. The input parameters considered are: packet fragmentation factor; buffer size; maximum allowable number of retransmissions. However, the approach taken is capable of ingesting any other probable parameters of interest. System performance criteria under study are: throughput; delay; probability of failure to deliver. The last two are crucial for real-time applications.

Error Performance of FH Wireless LANs in DS and Tone Interference

In this paper the bit error probability of the SFH/MFSK system in presence ofwideband and tone interference in a fading environment is evaluated.Simultaneous license-free operation of tone-like applications, FrequencyHopping (FH), and Direct Sequence (DS) based LAN clusters is assumed to be theprime interference facing the subject FH wireless LAN (of the IEEE 802.11standard). The wideband DS interference is considered to have asinc2() shape Power Spectral Density (PSD) centered at the middleof FH signal band and tone interferers are assumed to be spread over the wholeFH band of the intended signal. Assumptions of slow non-selective fading alongwith slow hopping justify a quasi-static treatment. Results shows that the FHsystem is more sensitive to tone interference and fading and less sensitiveto wideband interference variations. The paper sheds light on the performanceof wireless LAN operation in the unlicensed free band where many other LANsmay exist.

A New Lightweight Watchdog-Based Algorithm for Detecting Sybil Nodes in Mobile WSNs

Wide-spread deployment of Wireless Sensor Networks (WSN) necessitates special attention to security issues, amongst which Sybil attacks are the most important ones. As a core to Sybil attacks, malicious nodes try to disrupt network operations by creating several fabricated IDs. Due to energy consumption concerns in WSNs, devising detection algorithms which release the sensor nodes from high computational and communicational loads are of great importance. In this paper, a new computationally lightweight watchdog-based algorithm is proposed for detecting Sybil IDs in mobile WSNs. The proposed algorithm employs watchdog nodes for collecting detection information and a designated watchdog node for detection information processing and the final Sybil list generation. Benefiting from a newly devised co-presence state diagram and adequate detection rules, the new algorithm features low extra communication overhead, as well as a satisfactory compromise between two otherwise contradictory detection measures of performance, True Detection Rate (TDR) and False Detection Rate (FDR). Extensive simulation results illustrate the merits of the new algorithm compared to a couple of recent watchdog-based Sybil detection algorithms.

An EVEBO-Based BTS Localization Algorithm.

In this paper, we use EVEBO, an election-inspired optimization algorithm, to solve the BTS (i.e. transceiver) localization problem. The proposed method tries to solve the classic and very important problem of achieving maximum coverage with minimum number of BTSs in a specified geographical area. It also tries to reduce the over-coverage rate, one of the undesirable phenomena in cellular networks. The EVEBO’s merit in solving the problem is measured by a common fitness function, and speed of convergence. Simulation results show that EVEBO solves the problem in much less number of evaluations compared to the best results reported in the literature for square-coverage transceivers. We also show that it can be used in a scenario involving more challenging non-square-coverage (almost circular) transceiver type with satisfactory results.

VID: Virtual Information Desk

Organizations providing services to public, generally comprise three representative entities, staff, events, and processes. Since these entities involve in not-necessarily time-wise predictable phenomena, service delivery in such organizations is inherently fluid, particularly in specific-staff dependent service providers or organizations. To provide service receivers (clients) with satisfactory experience, keeping them informed regarding service parameters is of great importance. While traditional information systems serve an organization internally, systems that provide such information for clients (external to the organization), too, prove to be useful regarding service experience. Information by its nature can be divided into static and dynamic. Static information are less exposed to changes while dynamic information are more volatile. There might be situations where, in a specific organization, dynamic information override static information for a specific period of time. Dissemination methods for static and dynamic information are different. Thanks to ubiquitous and pervasive computing, advancements in communication technologies, and accessibility of processing power, the concept of real-time information systems, once unimaginable, has become a reality today. Focusing on dynamic information, and in particular last-minute change information, in this paper, we devise and present an implementation of VID system which is a new distributed information dissemination/update system for specific-staff dependent service providers or organizations such as educational institutions where events are very much dependent on specific peoples presence.

Bilateral localisation algorithm for wireless sensor networks with communication holes

Localisation is one of the vital services for many protocols and applications in wireless sensor networks. Although in most of the range base localisation algorithms an unknown node requires at least three anchor nodes to localise itself, some bilateration approaches can perform the task with only two anchors. These approaches lose their accuracy in cases when there is sparsity of nodes at some spot in the field. A communication hole is a problem that localisation algorithms face, causing their performance reduction. In this paper, we devise a new recursive approach, called non-directed bilateration position estimation NBPE that uses only two anchor nodes to calculate two possible positions and prune one of them using a specific criterion. To decrease error propagation a precedence mechanism is applied to select the proper anchors, which results in higher accuracy in networks with communication holes. NBPE is evaluated through simulation under various noise conditions and network densities.

QADC-MORE: A new QoS-aware dynamic credit MORE protocol for wireless mesh networks

Attracting much research attention recently, opportunistic routing and network coding are considered as extremely capable routing/coding schemes for boosting feasible throughput in wireless mesh networks featuring lossy links. Unfortunately, opportunistic routing schemes implicitly allow each individual flow to eagerly consume network resources without considering other concurrent flows. The selfish manner of an opportunistic flow leads to a poor performance in multi-flow scenarios. In this paper, we design a QoS-aware and application service priority level-dependent queuing mechanism to efficiently support multi-flow scenarios. We base our protocol on a well-known opportunistic routing protocol (MORE) which employs network coding as well. Our scheme significantly increases the overall throughput seen by each individual flow while considering their priorities.

Error performance of FH signals in DS and TDMA interfering wireless LAN clusters

In this paper the bit error probability of the SFH/MFSK system in presence of wideband and tone interference in a fading environment is evaluated. Simultaneous license-free operation of TDMA, and direct sequence (DS) based LAN clusters is assumed to be the prime interference facing the subject FH wireless LAN (of the IEEE 802.11 standard). The wideband DS interference is considered to have a sinc/sup 2/() shape psd centered at the middle of FH signal band and tone interferers are assumed to be spread over the whole FH band of the intended signal. Assumptions of slow non-selective fading along with slow hopping justify a quasi-static treatment. Results shows that the FH system is more sensitive to tone interference and fading and less sensitive to wideband interference variations. The paper sheds light on the performance of wireless LAN operation in the unlicensed free band where many other LANs may exist.