Abstract-MAC layer protocols for wireless ad hoc networks typically assume that the network is homogeneous with respect to the transmit power capability of individual nodes in the network. The IEEE 802.11 MAC protocol has been popular for use in ad hoc networks. We investigate the performance of this protocol when it is used in a network with nodes that transmit at various power levels. We show that overall throughput is lower than the throughput of a network in which all nodes transmit at identical power levels. In addition, low power nodes have a disadvantage in accessing the medium due to higher levels of interference from the high power nodes. We consider propagating the control messages generated by a node wishing to initiate communication to distant nodes so that they may forbear transmissions for some time, thereby allowing clear access to the initiating node. We find that the overhead incurred due to the additional message transmissions outweighs the potential gain achieved by propagating these messages. This indicates that the signalling mechanism used in the IEEE 802.11 standard or the variants thereof are not sufficient to alleviate the loss in throughput and the lack of fairness engendered by networks that are heterogeneous with regard to the transmit power capabilities of individual nodes.
-The performance of the IEEE 802.11 MAC protocol has been shown to degrade considerably in an ad hoc network with nodes that transmit at heterogeneous power levels. The main cause of this degradation is the potential inability of high power nodes to hear the RTS/CTS exchanges between nodes when at least one node involved in communication is a low power node. The propagation of the CTS message beyond the one-hop neighborhood of two communicating low power nodes was considered in our prior work in an attempt to alleviate this effect. However, this resulted in excessive overhead and further degraded the performance at the MAC layer. In this paper we consider two techniques to reduce the overhead incurred due to the aforementioned propagation of the CTS message: (a) the use of an intelligent broadcast scheme and (b) the reservation of bandwidth for the sequential transmission of multiple data packets with a single RTS/CTS exchange (and propagation as needed). These techniques require changes only at the MAC layer. We find, by means of extensive simulations, that the techniques provide a significant improvement over the original 802.11 MAC protocol in the considered power heterogeneous ad hoc network. The overall throughput improves by as much as 12 % and the throughput of the low power nodes improves by up to 14 % as compared to the IEEE 802.11 MAC protocol. Furthermore, the schemes find applicability even in homogeneous networks as they reduce the number of false link failures that arise when the IEEE 802.11 MAC protocol is used, by about 20 %. We conclude that the schemes together offer a simple yet effective and viable means of performing medium access control in power heterogeneous ad hoc networks.
Advances in hyper spectral imaging sensors makes it possible to obtain high dimensional and high resolution data which poses challenges for computational cost and time. As the inter-band resolution is high in hyper spectral images, the spectral dimension could be reduced without significant loss of useful information. This requires careful application of dimensionality reduction techniques to reduce the dimension but preserve the original spectral characteristics. It is observed in the literature that filtering techniques can address some of the challenges concerning dimensionality reduction in hyper spectral imaging. In this paper a dimensionality reduction method adopting Discrete Wavelet Transform and Distance Classifier Correlation filter has been proposed for hyper spectral imaging. The experimental results show that the combination of ID-DWT with DCCF outperforms the other methods in dimensionality reduction and classification of given data set.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.