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Various flexible mechanisms related to quality of service (QoS) provisioning have been specified for uplink traffic at the
medium access control (MAC) layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme
can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These
two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those
applications, service differentiation (SD) is anticipated over the contention based bandwidth request scheme. In this paper
we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth
allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated
by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth
allocation priority, the SD performances will be better.
Foundation item: the National Basic Research Program (973) of China (No. 2005C13321804) 相似文献
2.
We describe a batch RSA digital signature scheme in which a signer can sign messages for multiple recipients simultaneously.
The construction is quite efficient due to the batch signing method. This is useful to improve the performance of a high-loaded
signing server, for example a secure electronic transaction (SET) gateway. Theoretical calculations and experimental results
show that the proposed scheme can improve the performance of the signing server significantly.
Foundation item: the National Basic Research Program (973) of China (No. 2005CB321804) 相似文献
3.
In this paper, we study an area localization problem in large scale underwater wireless sensor networks (UWSNs). The limited
bandwidth, the severely impaired channel and the cost of underwater equipment all make the underwater localization problem
very challenging. Exact localization is very difficult for UWSNs in deep underwater environment. We propose a range free method
based on mobile detachable elevator transceiver (DET) and 3D multi-power area localization scheme (3D-MALS) to address the
challenging problem. In the proposed scheme, the ideas of 2D multi-power area localization scheme (2D-ALS) and utilizing DET
are used to achieve the simplicity, location accuracy, scalability and low cost performances. The DET can rise and get down
to broadcast its position. And it is assumed that all the underwater nodes underwater have pressure sensors and know their
z coordinates. We evaluate the performances of 2D-ALS and our proposed 3D-MALS schemes under both ideal and non-ideal channel
propagation conditions, in terms of localization error and localization ratio. The simulation results show that our proposed
scheme is much more efficient than the 2D-ALS. 相似文献
4.
An improved scalar Costa scheme (SCS) was proposed by using improved Watson perceptual model to adaptively decide quantization step size and scaling factor. The improved scheme equals to embed hiding data based on an actual image. In order to withstand amplitude scaling attack, the Watson perceptual model was redefined, and the improved scheme using the new definition can insure quantization step size in decoder that is proportional to amplitude scaling attack factor. The performance of the improved scheme outperforms that of SCS with fixed quantization step size. The improved scheme combines information theory and visual model. 相似文献
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