Kaveh Ghaboosi

Modeling IEEE 802.11 DCF Using Parallel Space–Time Markov Chain

Many performance evaluations for the IEEE 802.11 Distributed Coordination Function (DCF) have been previously reported in the literature; most studies are based on saturation analysis, and a few models under a finite-load condition adopt an M/G/1 queuing system. However, using M/G/1 queuing only considers the first moment of the frame service time to derive the probability of the transmission queue being vacant. In this paper, we model the DCF using the parallel space-time Markov chain, where the frame arrivals are tracked by monitoring the transmission queue during transitions between successive states of the space-time Markov chain. The proposed framework provides the possibility of simultaneously modeling the contention phase, the backoff and post-backoff procedures, and the transmission queue status. The proposed framework is also validated by simulation results.

Interference avoidance via resource scheduling in TDD underlay femtocells

In this paper, we proposes a resource reuse scheme for femtocell networks. In this context, macrocells operate in a Frequency Division Duplexing mode while all femtocells employ the macrocellular uplink spectrum in a Time Division Duplexing mode. We propose two solutions. In the first one, a centralized scheduling is performed via list-coloring based on the overall conflict graph. The second solution is distributed and autonomously performed by each femto access point (FAP), based on local conflict graph. The two solutions are compared to a coordinated LTE-A compatible and a random allocation schemes in terms of spectral efficiency and activity factor in the superframe. Finally, given a target Quality of Service requirement, the proposed distributed scheme is evaluated. Results show that self-organizing femtocell operating in an uncoordinated way achieves a good tradeoff of performance when a limited feedback from femto users is exchanged.

Learning based mechanisms for interference mitigation in self-organized femtocell networks

We introduce two mechanisms for interference mitigation, inspired by evolutionary game theory and machine learning to support the coexistence of a macrocell network underlaid with self-organized femtocell networks. In the first approach, stand-alone femtocells choose their strategies, observe the behavior of other players, and make the best decision based on their instantaneous payoff, as well as the average payoff of all other femtocells. We formulate the interactions among selfish femtocells using evolutionary games and demonstrate how the system converges to an equilibrium. In contrast, in the Reinforcement-Learning (RL) approach, information exchange among femtocells is no longer possible and hence each femtocell adapts its strategy and gradually learns by interacting with its environment (i.e., neighboring interferers) through trials-and-errors. Our investigations reveal that through learning, femtocells are able to self-organize by relying only on local information, while mitigating the interference towards the macrocell network. Besides, a trade-off exists where faster convergence is obtained in the evolutionary case as compared to the RL approach, at the expense of more side information. Finally, it is shown that femtocells face an interesting tradeoff of exploration versus exploitation in their learning processes.

A Distributed Multi-channel Cognitive MAC Protocol for IEEE 802.11s Wireless Mesh Networks

In this paper, we propose a novel distributed frequency agile medium access control (MAC) extension to the IEEE 802.11s amendment for the next generation wireless mesh networks (WMNs). The proposed scheme has complete backward compatibility with the legacy IEEE 802.11 and the emerging 802.11s while, it is perfectly capable of multi-channel deployment of available frequency opportunities in order to coordinate concurrent multiple data transmissions. The root concept of the proposed enhancement is mainly based on the deployment of well-known ISM frequency bands, where the existing 802.11-based wireless equipments nowadays operate, as the common control channel in order to establish concurrent data transmissions. Here, we apply the aforementioned key concept to the IEEE 802.11s common channel framework (CCF) to attain two important goals: on one hand, the proposed scheme improves the channel utilization and capacity using the concept of cognitive radio and on the other hand, using the same concept it leads to lower access delay due to smarter decision making procedures exploited for link layer connection establishment. Through extensive simulations, which also take into account primary user (PU) appearance in non-ISM frequency opportunities, performance of the proposed medium access control (MAC) enhancement is evaluated showing its remarkable efficiency and better wireless medium access management.

Accuracy of RSS-Based RF Localization in Multi-capsule Endoscopy

In this paper, we derive and analyze cooperative localization bounds for endoscopic wireless capsule as it passes through the human gastrointestinal (GI) tract. We derive the Cramer-Rao bound (CRB) variance limits on location estimators which use measured received signal strength (RSS). Using a three-dimension human body model from a full wave simulation software and log-normal models for RSS propagation from implant organs to body surface, we calculate bounds on location estimators in three digestive organs: stomach, small intestine and large intestine. We provide analysis of the factors affecting localization accuracy, including various organ environments, external sensor array topology, number of pills in cooperation and the random variations in transmit power of sensor nodes. We also do localization accuracy analysis for the case when transmit power of the sensor is random with known priori distribution. The simulation results show that the number of receiver sensors on body surface has more influence on the accuracy of localization than the number of pills in cooperation inside the GI tract, The large intestine is affected the most with the transmit power randomness.

On Resource Reuse for Cellular Networks with Femto- and Macrocell Coexistence

This paper studies downlink resource reuse schemes for cellular networks with coexisting femtocells and macrocells. We examine two reuse schemes, termed split reuse and shared reuse. In this paper, we develop an analytical model of resource allocation based on random graphs. In our model, arbitrarily chosen communication links interfere with each other with a certain probability, which depends upon whether the links belong to femtocell or macrocell users. Using this model, we establish asymptotic bounds on the minimum number of resource blocks required to make an interference-free resource assignment for all the users in the network for large numbers of users. We assess these bounds using a simple greedy resource allocation algorithm to demonstrate that the bounds are reasonable in finite networks of plausible size. By applying the bounds, we establish the expected impact of femtocell networks on macrocell resource allocation under a wide variety of interference scenarios. Further, we assess the efficiency loss associated with split reuse, as an aid to determining whether resource allocators should use the simpler split reuse scheme or attempt to tackle the complexity and overhead associated with shared reuse.

Interference management for self-organized femtocells towards green networks

The femtocell concept is an emerging technology for deploying the next generation of the wireless networks, aiming at indoor coverage enhancement, increasing capacity and offloading the overlay macrocell traffic. One of the main challenges in short range femtocell networks is how to (re)configure the Home Node Bs (HNBs) in an autonomous manner so as to manage interference and diminish the energy consumption among nearby femtocells efficiently. In this paper, we investigate the indoor femtocell deployment making use of both the Frequency Division Duplexing (FDD) and the Time Division Duplexing (TDD) methods. In the FDD case, the HNBs share both the Uplink (UL) and Downlink (DL) channels with the macrocell without any cooperation to coordinate their access to the air interface. Conversely, in the TDD underlay case, femtocells only reuse the macrocell UL spectrum and cooperate with each other in order to minimize the interference among themselves, either with or without further coordination with the Macro User Equipment (MUE). The proposed solution is evaluated by means of system-level simulations using the Monte Carlo approach. Investigations have shown that the TDD underlay approach not only reduces the perceived interference levels, but also diminishes the outage probability.

Bio-inspired visual attention in agile sensing for target detection

In the context of surveillance, visual attention is referred to as an ability to rapidly locate the most salient or relevant target in biological or artificial vision systems. To support the basic research leading to determination of the principles on which humans and animals accomplish agile sensing, a survey of bio-inspired visual attention in target detection is presented in this paper. We first discuss some relevant fundamental concepts and techniques. Then several up-to-date algorithms and implementations are introduced in either bottom-up or top-down mechanisms. This paper also gives a tutorial for the existing researches and provides future challenges.

A survey of cyber crimes

With the advancement of computer and information technology, cyber crime is now becoming one of the most significant challenges facing law enforcement organizations. Cyber crimes are generally referred as criminal activities that use computers or networks. An understanding of the characteristics and nature of cyber crimes is important in helping research communities find ways to effectively prevent them. Most existing research focuses more on attacks and attack models, including either actual attacks or imaginary/possible attacks over all layers of networks or computers, but there has been less work carried out on a comprehensive survey of cyber crimes. This paper provides a survey of cyber crimes that have actually occurred. First, cyber crimes in the digital world are compared with crimes in the physical world. Then, cyber crimes are categorized according to the roles of computers or networks. Furthermore, we also notice that some cyber crimes are actually traditionally non-cyber crimes that are facilitated by computers or networks. It is surprising that there are so many recurrent cyber crimes. More efforts are needed to protect people from cyber crimes. Copyright

Joint admission control & interference avoidance in self-organized femtocells

In this paper, we consider a femtocell deployment scenario in which radio resources are shared among self-organized femtocells. We propose a distributed Admission Control Mechanism (ACM) for traffic load balancing among sub-carriers when there are multiple Quality of Service (QoS) classes. Furthermore, we propose a mechanism based on Reinforcement Learning (RL) for slot allocation to the traffic streams on different sub-carriers, which is employed by each Femto Access Point (FAP) to mitigate interference among femtocells and the underlaid macrocell. Through simulations, the performance of the proposed scheme is evaluated where it is shown that femtocells are able to coexist with the overlay macrocell network with no information exchange and by relying only on local information.