Performance analysis of IEEE 802.11 DCF and 802.11e EDCA based on queueing networks

The authors propose a new analytical model based on BCMP closed queueing networks in order to evaluate the performance of IEEE 802.11 DCF MAC protocol when all nodes are in the transmission range of each other, that is, a single hop wireless ad hoc network. By the proposed model, some performance metrics such as saturation and non-saturation throughput, distributions of channel access delay and the number of packets in the MAC buffer are derived. An extension of the proposed model is used for the analysis of IEEE 802.11e EDCA and the same performance metrics are evaluated for this protocol. Analytical results on IEEE 802.11e prove that differentiation in service is possible and channel share for each service type may be well assigned by tuning the MAC protocol parameters. Simulation results show consistency with our analytical results.     

Nondestructive Identification of Knot Types in Hand-Made Carpet. Part I: Feature Extraction from Grey Images

Knot (pile) formation has a very important role in evaluation and rating of hand-made carpets. Visual identification of carpet structural elements is impossible even for expert people. This research presents a nondestructive method for recognition of carpet knotting structure. It is based on X-ray radiography (mammography). Available X-ray beams create visible images from the internal structure of object in two dimensions. Primary radiological images are taken by radiography from hand-made carpets. They are then converted to structural recognizable images by employing different image processing techniques. Considering that the 3-D structure of carpet is projected in 2-D images and understanding the effect of each structural element on the creation of X-ray images, common knot types (piles) including Farsi, Torky, Kaman-Shib, double Farsi, double Torky and double Kaman-Shib are considerably distinguishable.