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131.
This paper studies the frequency offset correction technique which can be applied in optical OFDM systems. Through theoretical analysis and computer simulations, we can observe that our proposed scheme named pilot self-coding (PSC) has a distinct influence for rectifying the frequency offset, which could mitigate the OFDM performance deterioration because of inter-carrier interference and common phase error. The main approach is to assign a pilot subcarrier before data subcarriers and copy this subcarrier sequence to the symmetric side. The simulation results verify that our proposed PSC is indeed effective against the high degree of frequency offset. 相似文献
132.
Ronald Y. Chang Zhifeng Tao Jinyun Zhang C.‐C. Jay Kuo 《Wireless Communications and Mobile Computing》2013,13(1):12-27
A graph‐based framework is proposed in this paper to implement dynamic fractional frequency reuse (D‐FFR) in a multicell Orthogonal Frequency Division Multiple Access (OFDMA) network. FFR is a promising resource‐allocation technique that can effectively mitigate intercell interference (ICI) in OFDMA networks. The proposed D‐FFR scheme enhances the conventional FFR by enabling adaptive spectral sharing as per cell‐load conditions. Such adaptation has significant benefits in practical systems where traffic loads in different cells are usually unequal and time‐varying. The dynamic adaptation is accomplished via a graph framework in which the resource‐allocation problem is solved in two phases: (1) constructing an interference graph that matches the specific realization of FFR and the network topology and (2) coloring the graph by use of a heuristic algorithm. Various realizations of FFR can easily be incorporated in the framework by manipulating the first phase. The performance improvement enabled by the proposed D‐FFR scheme is demonstrated by computer simulation for a 19‐cell network with equal and unequal cell loads. In the unequal‐load scenario, the proposed D‐FFR scheme offers significant performance improvement in terms of cell throughput and service rate as compared to conventional FFR and previous interference management schemes. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
133.
The long symbol duration makes Orthogonal Frequency Division Multiplexing (OFDM) robust against frequency-selective fading, and also makes OFDM sensitive to time-selective fading. First, this paper deduces the Inter-subCarrier Interference (ICI) caused by time-selective fading, and then analyzes in detail how time-selective fading affects the performance of OFDM system, e.g. Bit-Error Rate (BER) and the channel capacity of each subcarrier. At last, some simulation figures are given. 相似文献
134.
Jiang?Zhu Abraham?O.?FapojuwoEmail author 《International Journal of Wireless Information Networks》2005,12(2):109-121
This paper proposes a hybrid OFDM/TDMA (Orthogonal Frequency Division Multiplexing/Time Division Multiple Access) scheduling
method to obtain fine bit-rate granularity in wireless personal area networks (WPANs). A new blind adaptive receiver structure
that combats the effects of inter-carrier interference (ICI) caused by users’ frequency offsets is also proposed to improve
the system throughput. The proposed blind adaptive receiver is based on constant modulus (CM) criterion and requires no more
knowledge of the frequency offsets of interferers’ signals than the conventional receiver. The advantage of our countermeasure
is that frequency-guard or redundant data is not needed, thus the throughput performance will not degrade, and estimation
of the frequency offset is also no longer necessary. In order to make the adaptive receiver realizable, we develop a soft-constraint-satisfaction
(SCS) based algorithm to achieve faster convergence. Simulation results show that our proposal is capable of significantly
reducing the influence of ICI. 相似文献
135.
Katsutoshi?KusumeEmail author 《International Journal of Wireless Information Networks》2005,12(4):225-233
This work addresses the severe performance degradation for OFDM systems when long channel delays exceed the guard interval. Such long delays can be seen as an interference source on the one hand and also as a valuable frequency diversity source on the other hand. Instead of simply suppressing such long delays, e.g. by beamforming at the transmitter, we propose a new precoding scheme, which attempts to find an optimum trade-off between the interference suppression and the diversity gain. An optimization problem is formulated by exploiting only long-term channel state information instead of instantaneous one. Then, it is solved based on the minimum mean square error criterion with a constraint on the transmit power. Computer simulation results show that the proposed scheme outperforms the conventional beamforming scheme. 相似文献
136.
探测器灵敏度及其能量响应特性在探测器的设计和研制过程中占有十分重要的地位.从理论和实验两个方面研究了ICI探测器的γ灵敏度及其γ射线能量响应特性.在60 Co 1.25MeV γ辐射源装置上进行实验测量得到ICI探测器的单位γ灵敏度为1.8×10-20 (±5%)C·cm2 ,理论计算的单位γ灵敏度为1.78×10-20 C·cm2 (γ能量1.25MeV),理论和实验结果符合得较好.研究结果表明,入射γ射线能量在1~10MeV范围内变化时,ICI探测器具有平坦的γ灵敏度响应曲线. 相似文献
137.
以系统和速率最大化为目标,将协同基站群的分簇问题建模为带权连通图的最大利益树生成问题,提出了一种基于协同度的最大利益树分簇算法。定义了利益树的协同度,并选择了协同度最大的两裸利益树进行合并的方式来并行生成多个规模动态的协同分簇,从而解决了传统顺序分簇导致的系统性能受限的问题,提高了系统的分簇性能。仿真结果表明,本算法的系统频谱效率优于现有的动态分簇算法,并且算法为线性复杂度。 相似文献
138.
Volkan Kumbasar 《Computers & Electrical Engineering》2010,36(3):397-403
In this work, better wavelet packet tree structures are searched to reduce the sum of ISI and ICI powers (integrated power) in Daubechies wavelet-based OFDM system over a practical two path low-voltage powerline channel or two way multipath channel. Better wavelet tree structures are obtained by using a brute-force algorithm. Results show that better wavelet packet tree structures perform better than conventional Mallat structures for the same bandwidth occupancy. 相似文献
139.
LI Ying-shan RYU Heung-Gyoon LI Jun-wen SUN Dong-yan LIU Hai-yuan ZHOU Li-jie WU Yue 《通讯和计算机》2008,5(12):32-38
In MISO-OFDM system, ICI which is caused by frequency offset and phase noise breaks down orthogonality between sub-carriers and degrades system performance. In this paper, to compensate integrated effect of frequency offset and phase noise, several ICI self-cancellation methods are proposed; and CPE, ICI and CIR are derived theoretically in MISO-OFDM system. As results, by choosing several ICI self-cancellation methods appropriately, considerable performance improvement can be achieved in the MISO-OFDM system which affected by frequency offset and phase noise. 相似文献
140.