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Network coding has been shown to be an effective approach to improve the wireless system performance. However, many security issues impede its wide deployment in practice. Besides the well-studied pollution attacks, there is another severe threat, that of wormhole attacks, which undermines the performance gain of network coding. Since the underlying characteristics of network coding systems are distinctly...
In this paper, we investigate the effect of channel estimation on the performance of a secondary network in a cognitive radio system. We focus on estimating the sensing-channel from the primary source to the secondary source which helps in determining the reliability of the sensing decision. The channel is estimated opportunistically when the secondary source senses the primary source to be active...
In DCF and EDCA schemes, the number of collisions increased caused the number of anomalous slots also increased. These conditions caused the average duration of collision will be much longer and result in a decreased network throughput. In this paper we have proposed SASA scheme to avoid anomalous slot after the collision. Simulation results show SASA scheme produces higher throughput compare to DCF...
In order to mitigate the problem of crowded radio spectrum, dynamic spectrum access (DSA) has become the solution and a research focal point. The number of works in wideband spectrum sensing is dramatically increasing recently due to its importance in cognitive radio (CR) networks. Most works assume that secondary users (SUs) are synchronous with the primary users' (PUs) network. However, in many...
In this paper, the problem of distributed multiuser Opportunistic Spectrum Access is studied based on Partially Observable Markov Decision Process (POMDP), where the channels are partially observed by secondary users (SUs) constrained by hardware and energy. Considering the similarity of spectrum environment, the decision of every secondary user may be the same, which leads to collisions. Comparing...
Analytical models of the Distributed Coordination Function (DCF) have numerous applications in the performance analysis of IEEE 802.11 networks. The model proposed in this paper distinguishes itself from existing approaches in that it allows throughput, delay, and frame loss ratio analysis under both saturation and non-saturation network conditions. It combines the Markov chain and the queuing theory...
Reliability prediction models for Service Oriented Architecture (SOA) based applications have thoroughly discussed system level & component level details. However, significant difference between applications based on service-oriented architecture and traditional distributed application is marshaling of remote web services, nonetheless, reliability of these web services have not been discussed...
Cooperative spectrum sensing (CSS) is capable to improve the performance of signal detection. It is one solution to overcome fading, shadowing, and uncertainty noises. Unlike centralized networks, Secondary User (SU) in decentralized networks independently senses license channel without forwarding the sensing result to central coordinator. This paper investigates the performance of Decentralized Multiuser...
With many improvements in both the physical and MAC layers, the IEEE 802.11n standard aims to achieve a data transmission rate of up to 600 Mbps. The most important 802.11n MAC enhancement is frame aggregation which significantly reduces the headers overheads of the legacy MAC by aggregating multiple frames into a single large frame. In this paper we drive an analytical model to study the impact of...
Bufferbloat is a phenomenon where excess buffers in the network cause high latency and jitter. As more and more interactive applications (e.g. voice over IP, real time video conferencing and financial transactions) run in the Internet, high latency and jitter degrade application performance. There is a pressing need to design intelligent queue management schemes that can control latency and jitter;...
In this paper a new mathematical model, describing the behavior of simplified Constrained Priority Countdown Freezing (CPCF) protocol, is introduced. The CPCF protocol sets constrains on DCF countdown mechanism and thus requires different mathematical model from those found in the literature. For this reason, the two-dimensional Markov chain analytical model is developed in order to accurately quantify...
Recently many prominent web sites face so called Distributed Denial of Service Attacks (DDoS). DDoS attacks are a virulent, relatively new type of attack on the availability of Internet services and resources. To avoid denigration most of the commercial sites do not expose that they were attacked that is the biggest challenges of the researchers. Network congestion caused by DDoS attack can be managed...
Rate adaptation varies the transmission rate of a wireless sender to match the wireless channel conditions, in order to achieve the best possible performance. It is a key component of IEEE 802.11 wireless networks. Minstrel is a popular rate adaptation algorithm due to its efficiency and availability in commonly used wireless drivers. However, despite its popularity, little work has been done on evaluating...
In this paper, we propose a relay selection method, Maximum Throughput Relay Selection Algorithm (MTRSA) for wireless networks. Based on the derivation of direct and cooperative communications, MTRSA takes both MAC overhead and collision into consideration for maximizing the system throughput. In addition, the analytical derivation and proposed relay selection algorithm support both amplify-and-forward...
A multirate cooperative MAC (MC-MAC) protocol is designed for networks with slowly-changing channels between nodes. In this protocol, the statistic channel state information is used to estimate the transmission rate and to select the relay nodes, and the work is done on the source side to avoid collision in the distributed relay nodes selection procedure. The final numerical simulation shows that...
This paper investigates the sensing order problem for multi-user and multi-channel cognitive radio networks. While most of the literature studies focus on the sensing order for a single user, we consider the scenario in which multiple secondary users sequentially sense and access the channel according to their individual sensing orders. In multi-user case, channel access collisions among secondary...
Cooperative sensing is one solution for fading, hidden node problems, and uncertainty noises in primary signal detection. In this case, each secondary user (SU) senses available channel and exchanges their local sensing results to decide which channel can be accessed. Subsequently, this technique is capable to reduce sensing errors and lead to the throughput improvement. In this paper, we investigate...
In this paper, we propose a novel CRN MAC, called MAX-PS-MAC. MAX-PS-MAC uses a probabilistic channel assignment mechanism that attempts at maximizing the packet success probability of each transmission by exploiting statistical information regarding availability durations and link quality conditions of idle channels. While most of previously proposed CRN MAC protocols account for PR channel dynamics...
In this paper, we consider channel access problem in cognitive radio networks. We assume ordered channel assignment policy in the primary network. Searching channels sequentially from the beginning, the first available channel is assigned when a request arrives from a primary user, leaving idle channels in the upper part of the spectrum. As secondary users have limited sensing capabilities, ordered...
In this paper, we compare the performance of two major spectrum information acquisition schemes in cognitive radio system, which are geo-location database based scheme and spectrum sensing based scheme. Although these two schemes are the major spectrum information acquisition schemes which are mainly considered in current researches on cognitive radio system, the comparison of two schemes has not...
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