共查询到20条相似文献，搜索用时 46 毫秒
1.
This paper investigates the interference cancellation (IC) scheme for uplink cognitive radio systems, using the spectrum underlay
strategy where the primary users (PUs) and the secondary users (SUs) coexist and operate in the same spectrum. Joint MMSE-based
parallel interference cancellation (PIC) and Turbo decoding scheme is proposed to reduce the interference to the PUs, as well
as to the SUs, in which the minimum mean square estimation (MMSE) filter is only employed in the first iteration, regarded
as the “weakest link” of the whole detection process, to improve the quality of the preliminary detections results before
they are fed to the Turbo decoder. Simulation results show that the proposed scheme can efficiently eliminate the interference
to the PUs, as well as to the SUs. 相似文献
2.
Future mobile wireless communicationsystems demandhigh data rates and spectral efficiency in addition to ubiq-uitous coverage . To simultaneously meet these require-ments , a frequency band with higher central frequency(well above 2 GHz) has to be conside… 相似文献
3.
In this paper, a distributed compressive spectrum sensing scheme in wideband cognitive radio networks is investigated. An
analog-to-information converters (AIC) RF front-end sampling structure is proposed which use parallel low rate analog to digital
conversions (ADCs) and fewer storage units for wideband spectrum signal sampling. The proposed scheme uses multiple low rate
congitive radios (CRs) collecting compressed samples through AICs distritbutedly and recover the signal spectrum jointly.
A general joint sparsity model is defined in this scenario, along with a universal recovery algorithm based on simultaneous
orthogonal matching pursuit (S-OMP). Numerical simulations show this algorithm outperforms current existing algorithms under
this model and works competently under other existing models. 相似文献
4.
Reputation-based linear cooperation for spectrum sensing in cognitive radio networks 总被引：1，自引：0，他引：1
We propose a reputation-based cooperative spectrum sensing scheme in cognitive radio （CR） networks to solve the uncertainty resulting from the multipath fading and shadowing effect. In the proposed scheme, each cooperative CR user has a reputation degree that is initialized and adjusted by the central controller, and used to weight the sensing result from the corre- sponding CR user in the linear fusion process at the central controller. A simple method for adjusting the reputation degree of CR users is also presented. We analyzed and evaluated the detection performance of the reputation-based cooperative spectrum sensing scheme. Simulation results showed that our proposed scheme alleviates the problem of corrupted detection resulting from destructive channel conditions between the primary transmitter and the CR user. The performance of our proposed scheme was improved compared to the average-based linear cooperation scheme, and was similar to that of the optimal linear cooperation scheme with feasible computational complexity. Moreover, our proposed scheme does not require knowledge of channel statistics. 相似文献
5.
High-speed train communication system is a typical high-mobility wireless communication network. Resource allocation problem has a great impact on the system performance. However, conventional resource allocation approaches in cellular network cannot be directly applied to this kind of special communication environment. A multidomain resource allocation strategy was proposed in the orthogonal frequency-division multiple access （OFDMA） of high-speed. By analyzing the effect of Doppler shift, sub-channels, antennas, time slots and power were jointly consid- ered to maximize the energy efficiency under the constraint of total transmission power. For the purpose of reducing the computational complexity, noisy chaotic neural network algorithm was used to solve the above optimization problem. Simulation results showed that the proposed resource allocation method had a better performance than the traditional strategy. 相似文献
6.
为了改善主用户窄带干扰下的传输参考超宽带系统的性能,提出了一种认知传输参考超宽带系统.认知传输参考超宽带系统的发射机在检测主用户工作的频段后,采用在该频段陷波的椭球波发射脉冲以降低对主用户的干扰;接收机在相关接收处理前采用陷波滤波来降低主用户带来的窄带干扰.仿真结果表明:该系统在信干比为0dB的单个或2个窄带干扰影响下,误码性能接近于无窄带干扰下的系统性能;在信噪比为10dB且信干比在-20～10dB范围内变化时,误码性能变化不超过一个数量级.该系统具有极佳的抗窄带干扰能力,误码性能在不同信噪比下具有很强的健壮性,具有对同频段主用户更小的干扰. 相似文献
7.
黄建忠 《重庆大学学报(英文版)》2004,3(2):48-53
IntroductionAnidealstoragearchitecturewouldprovidestrongsecurity,datasharingacrossplatforms(i.e.operatingsystems),highperformance,andscalabilityintermsofthenumberofdevicesandclients.Today’sarchitecturesforcesystemdesignerstodecidewhichofthesefeaturesismostimportant,aschoosinganarchitectureinvolvesatrade-off.Thethreestoragearchitecturesincommonusetodayaredirect-attachedstorage(DAS),storageareanetworks(SANs),andnetwork-attachedstorage(NAS).Thefourtharchitecture,whichisoftencalledtheobjectst… 相似文献
8.
This paper proposes an analysis and a direct power control （DPC） design of a wind turbine driven doubly-fed induction generator （DFIG） under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions. 相似文献
9.
为了获得认知无线电系统更高的频谱利用效率,基于最小总错误概率准则推导了软判决协作频谱感知最优判决门限的闭合表达式,并且分析了各种频谱感知参数对最优判决门限的影响.理论分析表明,所提出的最优门限可以获得虚警概率和漏检概率2种性能指标的折中.从仿真结果可以看出,平均信噪比和软判决方案对最优判决门限影响较大,而样本数量对最优的判决门限几乎无影响.对于MRC和MDC两种软判决方案,随着协作用户数量的增加,最优判决门限值随之增加并且趋近于某一极限值.而对于EGC软判决方案,协作用户数对其最优门限值影响很小. 相似文献
10.
随着智能终端用户的大规模增长,迫切需要提高网络带宽和资源使用效率。5G网络中的认知D2D（device-to-device） 通信技术可直接通过通信设备建立通信链路,两个建立好链路的通信设备可直接通信,既能高效利用通信资源,又能满足爆发式增长的数据流量需求。如何进行通信资源管理及通信链路选择成为研究重点。基于5G网络的认知D2D通信技术提出了一种基于博弈论的信道分配方法,以解决资源分配问题,最大化D2D通信设备运行效率。将该方法与传统通信方法进行对比仿真,实验验证所提方法更加优越。 相似文献
11.
Spectrum sensing is the first step of cognitive radio (CR). In this area, previous researches mostly consider distributed
local nodes which are under identical channel conditions, hence uniform and fixed detection threshold is set with energy detector.
However, the distributions of nodes in real environments are not quite the same. In this paper, the optimal threshold to minimize
the total detection error over additive white Gaussion noise (AWGN) channel is derived firstly. Then the dynamic threshold
scheme is proposed to reduce the average total detection error. Simulations have shown that, with this scheme, sensing performance
is improved. 相似文献
12.
研究了多用户场景下多载波码分多址系统（MC—CDMA）的下行信道和功率分配,并将吞吐最大化问题建模成一个混合整数优化问题．为了简化分析,将问题分成2个低复杂度的子问题：功率分配和信道分配．这2个子问题可分别被一个次最优自适应功率分配算法（APA）和一个最优自适应信道分配算法（ACA）解决．通过联合APA和ACA算法,进一步提出了一个自适应信道和功率的分配方案．仿真结果表明：与传统的均匀功率分配算法相比,提出的APA算法更加适用于MC—CDMA系统;此外,提出的自适应信道和功率分配方案可以显著地提高系统吞吐量性能． 相似文献
13.
As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing （OFDM） has a high usage rate of spectrum and combats inter-symbol interference （ISI） in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference （ICI） is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named S1NR （signal-to-interference- and-noise ratio） is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair （OWCP） is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR. 相似文献
14.
INTRODUCTIONJPEG2 0 0 0 (LawsonandZhu ,2 0 0 2 )isanewlypublishedstillimage codinginternationalstandard .Itsintroductionmeantthatforthefirsttime,thediscretewavelettransform (DWT)wouldbeusedforthedecompositionandrecon structionofimagestogetherwithanefficientcod ingscheme.IntheJPEG2 0 0 0coder,beforeanywaveletdecompositionisperformed ,theimageispartitionedintonon overlappingtiles.Thesetilesareofequalsizeexceptpossiblyforthoseadjacenttotheimageboundary .Thenwavelettransformisappliedtotr… 相似文献
15.
对高速铁路下行MIMO-OFDM系统中的动态资源分配问题进行研究.联合考虑子载波、天线、时隙和功率,将多维资源分配问题建模为混合整数非线性规划问题.分析移动速度对多普勒频移的影响,并计算子载波间干扰功率.在总发射功率不超过一定阈值的约束条件下,将最大化系统吞吐量作为优化目标.为了降低求解最优化问题的计算复杂度,采用两步求解法得到次优解.首先,在等功率分配的前提下,将子载波、天线和时隙分配给不同用户.然后,根据第1步资源分配的结果,进行功率分配.仿真结果显示,提出的多维资源分配策略与已有策略相比在系统吞吐量方面具有较大的性能提高. 相似文献
16.
在使用波束成型传输数据的蜂窝系统中,为提高下行链路的频谱效率,需要多小区多用户之间协作地产生波束.以多小区多用户下行链路的数学模型为基础,计算了各用户波束发送滤波器、接收滤波器、发送功率三类变量的梯度,使这些变量不断沿梯度方向调整并投影至可行空间,从而提出了一种基于梯度投影的多小区多用户下行协作波束成型传输方案,并分析了该方案需要在相邻小区基站间交互的信息.仿真结果表明,该方案在典型场景与参数配置下可达到约5 bit/（s·Hz·cell）的平均频谱效率性能.因此,多小区多用户之间的有效协作有助于提高蜂窝系统频谱效率性能. 相似文献
17.
提出了一种优化的迭代降维算法求解混合交通网络设计问题. 混合(连续/离散) 交通网络设计问题常表示为一个带均衡约束的数学规划问题,上层通过新建路段和改善已有路段来优化网络性能,下层是一个传统的 Wardrop 用户均衡模型. 迭代降维算法的基本思想是降维,先保持一组变量(离散/连续) 不变,交替地对另一组变量(连续/离散) 实现最优化. 以迭代的形式反复求解连续网络设计和离散网络设计问题,直至最后收敛到最优解. 通过一个数值算例对算法的效果进行了验证. 相似文献
18.
19.
分别在平坦衰落和频率选择性衰落的无线信道模型中建立了基于多用户正交频分复用技术（OFDM）和分布式天线的认知无线电系统中子载波分配模型.该模型不再用＂干扰温度＂限制认知用户来保护主用户,而是规定主用户在其所有子载波上的吞吐量之和需要高于一定的门限.然后,根据不同信道模型的特点提出了最优子载波分配方案,该方案利用分支定界法和隐枚举法最大化系统的吞吐量.最后,利用Pegging算法提出了效率与公平折中的子载波分配方案.仿真证明,在不同场景中所提出的子载波分配方案与现有方案相比在吞吐量和公平性方面均具有较大的优势. 相似文献
20.
A novel architecture of wavelength-division multiplexing/optical code division multiplexing access-passive optical network
(WDM/OCDMA-PON) based on superstructure fiber Bragg grating (SSFBG) and wavelength re-modulation technology is proposed. In
this scheme, WDM is overlaid on OCDMA channel in a single network by virtue of a kind of SSFBG, and the total capacity of
hybrid PON can be extended by regulating the transmission power reasonably. Re-modulation technology is also a good method
to save wavelength-specific components at the optical network unit (ONU) and cost of wavelength management on the customer
side. In simulation system, 1.25 Gb/s up/downstream data are transported with good performance. In addition the crosstalk
penalties from adjacent wavelength channels (with the same OC) are found to be negligible in upstream and downstream transmissions. 相似文献