We revisit the problem of systems consisting of buffered terminals accessing a common receiver over the collision channel by means of the standard ALOHA protocol. We find that in the slotted ALOHA system queues have insta- bility based on their individual average arrival rates and transmission probabilities. If a queue is stable, then the queue with lower instability is stable as well. The instability is used to intelligently set up the dominant systems. And the inner and outer bounds can be found by bounding the idle probability of some queues in the dominant system. Through analyzing those dominant systems one by one, we are able to obtain inner and outer bounds for stability. These bounds are tighter than the known ones although they still fail to identify the exact region for cases of . The methodology used is new and holds promise for successfully addressing other similar problems. have stability ranks. By using this property, we intelligently set up the dominant system and obtain the improved bounds. The system we consider is a discrete-time slotted ALOHA system with terminals. Each terminal has a buffer of infinite capacity to store the incoming packets. Time is slotted. Transmission time of a packet is one slot. The packet arrival process at each terminal is Bernoulli, 1 and arrival processes at different terminals are independent. In each slot, the terminal attempts to transmit the packet with probability , if its buffer is not empty. If two or more terminals transmit in the same slot, a collision occurs. The packets involved in the collision wait to be retransmitted in the next slot with the same respective probabilities. In Section II, we briefly set up the problem and describe the mathematical foundations which our later discus- sions are based on. In Section III, we investigate the problem. We use the concept of dominance to derive a lower bound in Section III-A. In Section III-B, we identify the relative rank of of the individual queues, and we obtain an upper bound. In Section III-C, we proceed to obtain the inner and outer regions by using the ranking technique, and we obtain an improved lower bound. Finally, in Section III-D, numerical results show the improvement of our bound over the previously obtained ones.
This dissertation is devoted to the design and analysis of multiuser interference avoidance and suppression schemes in wireless communication networks. We focus on two contention based medium access schemes: random multiple access and DS-CDMA.
The thesis has four major parts. In the first part, the stability region of slotted ALOHA with finite number of queues is upper and lower bounded by using a new ranking technique. This technique can be used to intelligently set up the useful dominant systems. In the second part, we consider the capture effect on throughput and energy efficiency of random multiple access. Number of power levels, transmission power and packet length are optimized to increase the throughput of the multiple-power-level random access system under the system average power constraint. It is proved that under a mild condition on decodability threshold, a single-power-level system achieves the maximum achievable throughput. Analysis of multiuser detection in DS-CDMA system is performed in the third and fourth part. We show new graphic properties of indecomposable error sequences in the third part. Those properties are used to upper bound the error probability of the maximum likelihood multiuser detection. In the fourth part, we analyze the energy efficiency of the power controlled system using multiuser detection. It is shown that the use of nonlinear detection has fundamental impact on power control schemes of the system.
As an important tool to help users filter Internet information, recommender system has played a very important role wherever in academia or in industrial area.During the past years, different recommendation approaches based on the social network have been proposed with the rapid development of online social networks.Different from the traditional ones which assume all the users are independent and identically distributed, these approaches follow the intuition that a person's implicit or explicit social network will affect his behaviors on the Web.In this paper, on the basis of the existing work, we fuse a baseline predictor model with an improved social recommendation model and propose a social recommendation algorithm based on probability matrix factorization.The experimental result shows that our method outperforms the existing approaches in accuracy.
Key predistribution schemes (KPSs) have played an important role in security of wireless sensor networks (WSNs). Due to comprehensive and simple structures, various types of combinatorial designs are used to construct KPSs. In general, compared to random KPSs, combinatorial KPSs have higher local connectivity but lower resilience against a node capture attack. In this paper, we apply two methods based on hash chains on KPSs based on transversal designs (TDs) to improve the resilience and the expressions for the metrics of the resulting schemes are derived.
The potential of near-infrared spectroscopy (NIRS) was investigated for its ability to rapidly discriminate the various brands of fermented Cordyceps mycelium powder. Relationship between mycelium powder varieties and the absorbance spectra was well established with the spectra region of 12500-4000 cm-1. Spectra preprocessing was performed using 1st derivative. Principal component analysis (PCA) was adopted for the clustering analysis and re-expressing of the hyper spectral data, and then, the obtained principal components (PCs) were used as the input of back-propagation artificial neural network (BPANN) to build PCA-BPANN model for the variety discrimination. The unknown samples in prediction set were precisely identified with the correlation coefficient R of 0.9959 and root-mean-square error of prediction (RMSEP) of 0.1007, which suggests that the NIR spectroscopy, if coupled with appropriate pattern recognition method, is very promising for rapid and nondestructive discrimination of fermented Cordyceps mycelium powder.
Aiming at the contradiction between fast changing needs of applications and slow response of software development,according to SOA and metadata,by encapsulating business logic in software component,this paper implementes a new rapid development platform using workflow technology to control the process.Test results show that the new platform can speed up software development and enhance software’s quality,and it can be applied in a wide range.
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