Current Issue : October - December Volume : 2011 Issue Number : 4 Articles : 5 Articles
The IEEE community is working on the wireless access in vehicular environments as a main technology for vehicular ad hoc networks. The medium access control (MAC) protocol of this system known as IEEE 802.11p is based on the distributed coordination function (DCF) of the IEEE 802.11 and enhanced DCF of the IEEE 802.11e that have low performance especially in high-density networks with nodes of high mobility. In this paper, we propose a novel MAC protocol where nodes dynamically organize themselves into clusters. Cluster heads are elected based on their stability on the road with minimal overhead since all clustering information is embedded in control channel's safety messages. The proposed MAC protocol is adaptable to drivers' behavior on the road and has learning mechanism for predicting the future speed and position of all cluster members using the fuzzy logic inference system. By using OFDMA, each cluster will use a set of subcarriers that are different from the neighboring clusters to eliminate the hidden terminal problem. Increasing the system reliability, reducing the time delay for vehicular safety applications and efficiently clustering vehicles in highly dynamic and dense networks in a distributed manner are the main contributions of our proposed MAC protocol....
Throughput maximization is one of the main challenges in multi-hop wireless mesh network (WMN). Throughput of the multi-hop WMN network seriously degrades due to the presence of the hidden node. In order to avoid this problem, we use a combination of the high-sensitive sensing function and beacon signalling at the routing. The purpose of this sensing function is used to avoid the hidden node during route formation in the self flow. This function is considered to construct a route from the source node to the destination node without any hidden node. In the proposed method, high-sensitive sensing device is utilized in both route selection and in the media access. The accuracy of our proposed method is verified by numerical analysis and by computer simulations. Simulation results show that our proposed method improves the network performance compared with the conventional systems which do not take account of the hidden node....
In this paper, the minimum-length scheduling problem in wireless networks is studied, where each source of traffic has a finite amount of data to deliver to its corresponding destination. Our objective is to obtain a joint scheduling and rate control policy to minimize the total time required to deliver this finite amount of data from all sources. First, networks with time-invariant channels are considered. An optimal solution is provided by formulating the minimum-length scheduling problem as finding a shortest path on a single-source directed acyclic graph. However, finding the shortest paths is computationally hard since the number of vertices and edges of the graph increases exponentially in the number of network nodes, as well as in the initial traffic demand values. Toward this end, a simplified version of the problem is considered for which we explicitly characterize the optimal solution. Next, our results are generalized to time-varying channels. First, it is shown that in case of time-varying channels, the minimum-length scheduling problem can be formulated as a stochastic shortest path problem and then an optimal policy is provided that is based on stochastic control. Finally, our analytical results are illustrated with a set of numerical examples....
A considerable number of studies have been performed recently on mobile peer-to-peer networks (MOPNETs), as the number of services based on mobile devices has increased. However, existing studies still reveal numerous shortcomings, such as bandwidth overhead, and redundant transmission in terms of multi-broadcast between peers. Especially, owing to the characteristics of MOPNETs, it is extremely important to determine broadcast size and to disseminate data within the limited environment of the network. The mechanism directly affects how well resource information in a mobile device is discovered and how data are transmitted. In this context, it is vital to efficiently disseminate data to be able to arrange hierarchal sequences of resource information of each mobile device for better search performance. Especially, it is also vital to determine the broadcast size, considering the consumption patterns of mobile users. In this article, we propose an adaptable algorithm that determines weighted values and disseminates data using the high-order Markov chain (HoMC). We apply weighted values in consideration of the MOPNET environment. In addition, the proposed HoMC-based Mobile User-preference-based Data Dissemination algorithm was simulated with a Qualnet simulator. Results show that the proposed algorithm performs 17.3% better, on average, in terms of data dissemination, than the existing dissemination methods....
In this article, we have studied the statistical properties of the instantaneous channel capacitya of spatially correlated Nakagami-m channels for two different diversity combining methods, namely maximal ratio combining (MRC) and equal gain combining (EGC). Specifically, using the statistical properties of the instantaneous signal-to-noise ratio, we have derived the analytical expressions for the probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the instantaneous channel capacity. The obtained results are studied for different values of the number of diversity branches and for different values of the receiver antennas separation controlling the spatial correlation in the diversity branches. It is observed that an increase in the spatial correlation in the diversity branches of an MRC system increases the variance as well as the LCR of the instantaneous channel capacity, while the ADF of the channel capacity decreases. On the other hand, when EGC is employed, an increase in the spatial correlation decreases the mean channel capacity, while the ADF of the instantaneous channel capacity increases. The presented results are very helpful to optimize the design of the receiver of wireless communication systems that employ spatial diversity combining techniques. Moreover, provided that the feedback channel is available, the transmitter can make use of the information regarding the statistics of the instantaneous channel capacity by choosing the right modulation, coding, transmission rate, and power to achieve the capacity of the wireless channelb....
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