This paper present a novel performance enhancement for combined Code Division Multiple Access (CDMA) and Space Division Multiple Access (SDMA) scheme using SDMA grouping on top of code and spatial signatures. This pap...
详细信息
ISBN:
(纸本)9843233948
This paper present a novel performance enhancement for combined Code Division Multiple Access (CDMA) and Space Division Multiple Access (SDMA) scheme using SDMA grouping on top of code and spatial signatures. This paper is divided into two parts. In the first part, the system performance of combined CDMA- SDMA scheme is evaluated under Additive White Gaussian Noise (AWGN) channel for a single sectored cell. A fixed number of available codes L kept in a central pool can be utilized by K users, where, K>L. The same code can be assigned to a group of users according to their Angle of Arrival (which is known as SDMA group). Here, the analytical model of Bit Error Rate (BER) for any arbitrary number of users has been derived and evaluated. In the second part of this paper, a simple code assignment algorithm is proposed to assign a already used code to a new user by which, the orthogonality between users can be maximized. The results show that the system capacity is noticeably improved with the combined system compared to the pure CDMA system. Further enhancement can be obtained when SDMA grouping is considered with orthogonal code assignment to users those belongs to different SDMA groups. Finally, the code assignment algorithm shows that high number of users can be accommodated by a fixed small number of codes.
In mobile cellular systems the handover is a very important process to maintain the desired Quality of Service (QoS). Many handover algorithms are proposed in the literature. However, to make a better handover and kee...
详细信息
In mobile cellular systems the handover is a very important process to maintain the desired Quality of Service (QoS). Many handover algorithms are proposed in the literature. However, to make a better handover and keep the QoS in wireless networks is very difficult. In this paper, by using random walk model and fuzzy theory we propose a new handover system. The proposed system uses 3 parameters for handoff decision: signal strength from the present Base Station (BS), signal strength from the neighbor BS, and the distance between Mobile Station (MS) and BS. The performance evaluation via simulations shows that proposed system can avoid ping-pong effect and has a good handover decision.
This paper presents a new method on fault distribution modeling for stochastic prediction study of voltage sags in the distribution system. Two-dimensional stochastic models for fault modeling make it possible to obta...
详细信息
This paper presents a new method on fault distribution modeling for stochastic prediction study of voltage sags in the distribution system. Two-dimensional stochastic models for fault modeling make it possible to obtain the fault performance for the whole system of interest, which helps obtaining not only sag performance at individual locations but also system sag performance through system indices of voltage sag. By using bivariate normal distribution for fault distribution modeling, the paper estimates the influence of model parameters on system voltage sag performance. The paper also develops the modified SARFI{sub}X regarding phase loads that creates better estimation for voltage sag performance for distribution system.
Bolted joints are widely used in mechanical structures since the disassembly for maintenance is easy without high cost. However, vibration induced loosing due to dynamic loading has been unsolved subject for a long ti...
详细信息
Bolted joints are widely used in mechanical structures since the disassembly for maintenance is easy without high cost. However, vibration induced loosing due to dynamic loading has been unsolved subject for a long time. We have developed a new type of nut named 'hyper lock nut (HLN), which realizes anti-loosening performance without complicated tightening process and tool. In this study, we have investigated the mechanisms of bolted joint with HLN, and tightening behavior are analyzed by mean of three-dimensional finite element method. Results are compared with the experimental results for HLN. Good qualitative agreement is observed between analytical results and experiments with respect to displacement, tightening force and tightening torque. We found some new aspects and superior points for bolted-joint with HLN than that of standard nuts. It is found that tightening torque of HLN is higher than that of standard. It is also found that the anti-loosening performance can be realized by the thread contact force at the slit region and angular facing on bearing surface. Moreover, by mean of tensile and fatigue experiments, it is concluded that HLN involves sufficient strength in practical use.
Requirements traceability is becoming increasingly significant element in software engineering. It provides critical function in the development and maintenance of a software system. From the software evolution point ...
详细信息
This paper investigates the encryption efficiency of RC6 block cipher application to digital images, introducing a mathematical measure for encryption efficiency, which we will call the encryption quality instead of v...
详细信息
ISBN:
(纸本)142440892X
This paper investigates the encryption efficiency of RC6 block cipher application to digital images, introducing a mathematical measure for encryption efficiency, which we will call the encryption quality instead of visual inspection, The encryption quality of RC6 block cipher is investigated among its several design parameters such as word size, number of rounds, and secret key length and the optimal choices for the best values of such design parameters are given. Also, the security analysis of RC6 block cipher for digital images is investigated from strict cryptographic viewpoint. The security estimations of RC6 block cipher for digital images against brute-force, statistical, and differential attacks are explored. Experiments are made to test the security of RC6 block cipher for digital images against all aforementioned types of attacks. Experiments and results verify and prove that RC6 block cipher is highly secure for real-time image encryption from cryptographic viewpoint. Thorough experimental tests are carried out with detailed analysis, demonstrating the high security of RC6 block cipher algorithm. So, RC6 block cipher can be considered to be a real-time secure symmetric encryption for digital images.
Coherence multiplexing is a potentially inexpensive form of optical code-division multiple access, which is particularly suitable for short-range applications with moderate bandwidth requirements, such as access netwo...
详细信息
A problem to make a graph strongly connected is one of the most fundamental problems in graph theory. The known parallel algorithm[1] solves this problem in O(log n) time using O(n3) processors on a CRCW PRAM model. I...
详细信息
This paper concerns a swing-up control problem for a 3-link gymnastic planar robot in a vertical plane, whose first joint is passive (unactuated) and the rest are active (actuated). The objectives of this paper are: 1...
详细信息
ISBN:
(纸本)9781424414970;1424414970
This paper concerns a swing-up control problem for a 3-link gymnastic planar robot in a vertical plane, whose first joint is passive (unactuated) and the rest are active (actuated). The objectives of this paper are: 1) to design a controller under which the robot can be brought into any arbitrarily small neighborhood of the upright equilibrium point, where all three links of the robot remain in their upright positions;2) to attain a global analysis of the motion of the robot under the controller. To tailor the energy based control approach to achieve the above objectives, first, this paper considers the links 2 and 3 as a virtually composite link and proposes a coordinate transformation of the angles of active joints. Second, this paper constructs a novel Lyapunov function based on the transformation, and devises an energy based swing-up controller. This paper presents a necessary and sufficient condition for nonexistence of any singular points in the controller for the robot starting from any initial state. Third, this paper carries out a global analysis of the motion of the robot under the controller, and establishes some conditions on control parameters for achieving the swing-up control objective. To validate the theoretical results obtained, this paper provides simulation results for a 3-link robot whose mechanical parameters are obtained from a human gymnast.
暂无评论