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41.
42.
A variational principle is formulated which enables the mean value and higher moments of the solution of a stochastic nonlinear differential equation to be expressed as stationary values of certain quantities. Approximations are generated by using suitable trial functions in this variational principle and some of these are investigated numerically for the case of a Bernoulli oscillator driven by white noise. Comparison with exact data available for this system shows that the variational approach to such problems can be quite effective. 相似文献
43.
Resource allocation in multiuser OFDM systems is a complex nonlinear optimization problem. In order to avoid direct solution,
based on the analytical results of the problem of minimizing the total transmit power, a two-step subcarrier allocation algorithm
is presented. The algorithm reduces the total transmit power by reducing the achievable minimum transmit power value required
by each user. Subcarriers are allocated in the algorithm according to the data rate required by users and the channel characteristics.
The required number of subcarriers allocated to users does not need to be known in advance. The allocation process consists
of two steps: basic subcarrier allocation and residual subcarrier allocation. Numerical results demonstrate that the proposed
algorithm can reduce the total transmit power effectively.
Handong Gong was born in 1974. He received the B.S. degree in auto control and the M.S. degree in physical electronic, and the Ph.D. degree
in communication and information system from South China University of Technology in 1996, 2002 and 2006 respectively. He
is now a lecturer in Shenzhen Institute of Information Technology. His main research interest include OFDM signal process,
linearization technique for amplifier and mobile communication technologies.
Wu Ye was born in 1938. Now he is a professor and Ph. D. advisor at South China University of Technology. His research interests
include queuing theory and its application in communication networks, mobile communication technologies and video process.
Suili Feng was born in 1955. Now he is a professor and doctor supervisor at South China University of Technology. His research interests
include theory and technology of communication network, key technologies of mobile communication and embedded system.
Hui Song was born in 1980. She received doctor’s degree from South China University of Technology in communication and information
system in 2005. Now she is a lecturer in South China Normal University. Her research interests include signal process, flow
control and optimization. 相似文献
44.
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46.
Orthogonal frequency division multiplexing (OFDM) is an important technique to support high speed transmission of broadband
traffic in wireless networks, especially broadband wireless local area networks (LANs). Based on OFDM, a new multiple access
scheme, called OFDM-TDMA with subcarrier allocation (OFDM-TDMA/SA), is proposed in this paper. It provides more flexibility
in resource allocation than other multiple access schemes such as OFDM-TDMA, OFDM-frequency division multiple access (OFDM-FDMA),
and orthogonal frequency division multiple access (OFDMA). With OFDM-TDMA/SA, a medium access control (MAC) is designed for
broadband wireless LANs. It optimizes bit allocation in subcarriers so that maximum bits are transmitted in each OFDM symbol
under a frequency selective fading environment. The OFDM-TDMA/SA MAC protocol also supports three classes of traffic such
as guaranteed, controlled-load, and best effort services. Based on the optimum subcarrier bit-allocation algorithm and considering
heterogeneous QoS constraints of multimedia traffic, a hierarchical scheduling scheme is proposed to determine the subcarriers
and time slots in which a mobile terminal can transmit packets. In such a way, the OFDM-TDMA/SA MAC protocol significantly
increases system throughput in a frequency selective fading environment and guarantees QoS of multimedia traffic. Computer
simulation is carried out to evaluate the performance of the OFDM-TDMA/SA MAC protocol. Results show that the new MAC protocol
outperforms other MAC protocols for OFDM-based wireless LANs.
This work was supported by the State of Georgia Yamacraw Project (E21-105). 相似文献
47.
网络操作、管理与维护(OAM)在公用网中非常重要,它能够提高网络可靠性,简化操作,降低网络运行成本。本讨论了在MPLS(多协议标记交换)网络中通过OAM数据包来实现OAM功能的方法,并在分析网络管理需求的前提下,提出了几种在MPLS层实现OAM功能的方案,展望了MPLS OAM标准的发展方向。 相似文献
48.
Bin Han Mugen Peng Yuwei Jia Wenbo Wang 《Wireless Communications and Mobile Computing》2015,15(1):30-42
This paper studies optimal resource allocation for multiple network‐coded two‐way relay in orthogonal frequency division multiplexing systems. All the two‐way relay nodes adopt amplify‐and‐forward and operate with analog network coding protocol. A joint optimization problem considering power allocation, relay selection, and subcarrier pairing to maximize the sum capacity under individual power constraints at each transmitter or total network power constraint is first formulated. By applying dual method, we provide a unified optimization framework to solve this problem. With this framework, we further propose three low‐complexity suboptimal algorithms. The complexity of the proposed optimal resource allocation (ORA) algorithm and three suboptimal algorithms are analyzed, and it is shown that the complexity of ORA is only a polynomial function of the number of subcarriers and relay nodes under both individual and total power constraints. Simulation results demonstrate that the proposed ORA scheme yields substantial performance improvement over a baseline scheme, and suboptimal algorithms can achieve a trade‐off between performance and complexity. The results also indicate that with the same total network transmit power, the performance of ORA under total power constraint can outperform that under individual power constraints. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
49.
MIAO Tingting WANG Ning YANG Hongwen YANG Dachcng 《中国通信》2014,(11):34-43
In orthogonal frequency division multiplexing (OFDM) based multihop communications, the conventional decodeand-forward (DF) relay scheme severely suffers from the error propagation problem. This drawback is serious in multihop networks as errors made by any relay node may fail the decoder at the destination in great chance. In this paper, we propose a bit error rate (BER) modified DF protocol (BMDF) which can be applied to systems where error correction channel coding and M-ary modulation are used. By modeling all links except the last one as a binary symmetric channel (BSC), we derive a log likelihood ratio (LLR) modification function relying only on the accumulated BER of all previous links to be applied to the output of the soft demapper. Furthermore, to reduce the computational complexity and signaling overhead, the modification function is simplified from its original exponential expression and less BERs are delivered between nodes by making successive subcarriers share the same BER. In addition, for situations where the channel state information (CSI) of forward link is available, the proposed BMDF can be further enhanced by combining with subcarrier pairing (SP) and power allocation (PA), where a sorted-channel gain SP scheme and a greedy PA algorithm are proposed. The simulation results verify thesignificant performance improvement to the conventional DF. 相似文献
50.
本文介绍了一种用于副载波复用(subcarriermultiplexingSCM)光通信系统的副载波复合/解复合器电路组件的结构及设计方法,其中就组件内各子电路的特性分析与设计用基本理论进行了简要叙述。最后给出了典型硬件样品的几组实测特性结果。 相似文献