初次考驾照是不是只能考C照吗?C1和C2的区别是什么?
初次考驾照是不是只能考C照吗?C1和C2的区别是什么?
09-03-17 &
次学车只能学习C照，C照分手动挡C1照与自动挡C2照，C1能驾驶自动挡车型， 但是C2不能驾驶手动挡车型。学C1可以选择小货或者小客，学C2只能选择小客。一般建议学 C1。现在C照取消年审，初次审领是6年有效期，到期换10年有效期的本。 驾照都是全国通用，可以在有效期到期时转到工作所在地，手续很简单，现在都是全国 联网，立等可换。费用很少。C1是小型汽车包括C2、C3（低速载货汽车和C4三轮车），但是C2就只是小型自动当汽车！！所以考驾照考C1就可以了！ A1大型客车和A3 B1 B2 A2牵引车和B1 B2 M A3城市公交和C1 B1中型客车和C1 M B2大型货车和C1 M C4三轮汽车 D普通三轮摩托车和E E普通二轮哦托车和F F轻便摩托车 M轮式自行机械车 N无轨电车 P有轨电车
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住宿旅店有高有低
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25以上可考b1,a2之类的. 手动挡C1照 自动挡C2照
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很炫很实惠 想买车的看过来　　几天前，小李有了购车的打算，但面对数十款车型，小李始终没有作出决定，想相信销售顾问的说法，却又不敢相信，自己一直犹豫。日前，又到了汽车销售旺季，像小李这样到处选车、看车的消费者很多，那么，如何在选车的过程中不走弯路，买到称心如意的车呢?此次，本报记者进行了相关采访，提醒想要购车的消费者千万别进入购车误区。　　购车技巧　　买车 三大误区请绕行　　误区一：只看车价　　对于大多数消费者而言，价格都是考虑的第一因素，但在购车过程中，往往会出现很多价格陷阱，有些看车的消费者被“车虫”盯上后，总是被“车虫”开出的低价所吸引买到不称心的车;还有的消费者在网上查找价格，选择风险较大的网购等途径进行购车。　　东风日产瑞孚专营店的市场部经理郑茂然告诉记者，在汽车卖场选车、经常会有“车虫”过来开出低价，但购车时千万别只考虑价格因素，“车虫”在上牌、装饰和保险等方面会有很多猫腻，一些小保险公司的理赔特别麻烦。还是应该通过正规的渠道选车、购车。事实上，有时4S店在售后服务方面开出的优惠政策也是值得消费者考虑的，因为，售后服务在养车的过程中是必不可少的，消费者需全方位对比、思考。　　误区二：低排量就代表低油耗　　目前，油价节节攀升，在很多消费者的心目中，都认为排量与油耗是成正比的，排量越大，油耗越高，因此，很多消费者在购车的过程中进入了选择的误区。　　“事实并非如此。”东风本田正泰服务店的副总经理高宇告诉记者：“排量与油耗确实有一定关系，但不是绝对的正比关系，油耗还与车的技术含量、汽车重量等因素有关，现在，排量为1.8L的车型可能比排量1.5L的车型还省油，主要因素就是技术含量高，消费者在判断油耗时除了排量因素还需要考虑技术因素和车的自重等因素。”　　误区三：高配置等于高性价比　　现在经销商都以性价比来吸引消费者，为了迎合消费者的需求，往往通过调高配置、增大内部空间、安装天窗、电视、倒车雷达等来吸引消费者的购买目光，但事实上，配置高、空间大并不能代表高品质。　　吉林省天骏达汽车销售服务有限公司的销售顾问董佳乐表示，在购车时，商家打出“性价比”牌，但请消费者要注意，高配置不代表卓越的性能和优良的品质，还要考虑到车的售后服务、维修保养价格等多种因素，只有在配置与性能完美结合的时候才能代表高性价比。　　试车　　这买车之前试车都该试点啥呢?试驾看似简单，但实际上却有很多学问。试驾不同于试衣服，它要求消费者在有限的时间内体验车辆的操控性能和功能，当然试驾中更要注意安全。那消费者在试驾时应该注意些什么?怎样才能在有限时间内体验到车辆的性能呢?　　要点一：速度不在快 安全就行　　所有4S店都有专门试驾车辆，但试驾时会有很多不可预料的因素，有可能因为驾驶员操作不当导致意外发生，所以试驾人员必须有C2(自动挡小型车驾照)及以上级别驾照，试驾必须签署试驾协议。东风悦达起亚长春瑞德专营店负责人表示：新手和很久不开车的人建议不要试驾车辆。试驾时，很多消费者感觉新鲜，上车并不是仔细观察车辆制造，也不关注车辆性能，而是不管试驾什么车型，上车就使劲踩油门，能开到一百多，特别是试驾自动挡车型，很多驾驶员恨不得把车“开飞”了，要不是工作人员阻拦很可能发生危险。为了保证试驾安全，试驾时服从陪驾人员安排，车速千万不可过快，更不能随意掉头、逆行，如无特殊情况不要猛踩油门、刹车;如驾驶者对中控台上的按钮不熟悉，可向陪驾人员咨询，否则违反试驾协议造成的后果都由试驾者自行负责。　　要点二：配置不在多 实用就行　　很多消费者买车偏好高配置的车型，实际上是受到试驾车的影响。因为4S店提供的试驾车往往都是该款车型的高配版，自动空调、真皮座椅、电动天窗等样样都有，消费者驾驶高配置试驾车时往往会被众多“新鲜”配置所吸引，因此买车时也喜欢选择高配置车型。　　长春市某汽车服务公司售后服务总监张勇师傅表示：普通工薪阶层消费者选车时没必要把“豪华”当作终极目标，舒适、实用才是关键。选车时多关注车上有几个气囊、有没有ABS(刹车防抱死)才是关键。另外，很多消费者喜欢真皮座椅，这的确让车子看上去有档次，但在使用过程中真皮座椅易脏，需要定期花钱打理，冬天真皮座椅坐上去又冰又凉很难受，所以需要真皮座椅的话最好再装上座椅加热系统。　　要点三：动力不在猛 节油就行　　还是要说一说4S店提供的试驾车，因为是高配车型，因此动力性也是最好的，潜移默化，对消费者选车也造成一定影响。长春市某汽车服务公司售后服务经理杨光师傅表示：其实车辆的动力性只是衡量车辆性价比的一方面，不能因为动力好、跑得快就说车子整体性能好，其实实用、节油才是选车的关键，毕竟家用轿车不是用来飙车的，况且车子在市内行驶走走停停，动力再好也发挥不出来，所以还是挑个动力性适中的，起步、加速、超车不“肉筋筋”，关键是省油就行。　　据长春市瑞德汽车销售有限公司品牌传播部经理梁爽介绍：试驾车辆时，不但要关注车辆动力性，还要测试车辆操控和制动性能。试驾最好选择车流较少、路面较好路段，着重测试车辆转向是否准确，刹车系统制动效果如何，当然如果您的驾驶技术很好，在确保安全前提下还可以适当做急转弯之类的“高难”动作，以体验车辆操控性能。试驾时还可以慢速通过小水坑，以测试车辆悬挂软硬度、是否有杂音，一般来说悬挂偏硬的车辆注重运动性，因此悬挂对路况反应更直接;在较好路况行驶时可以深踩油门感受车辆加速度。需要注意的是：试驾过程中要注意变速器换挡是否顺畅，挡位是否清晰，换挡时有无明显的机械噪声。　　再者，车辆的隔音效果也很重要，试驾时要关闭车窗以感受隔音效果，最好开到一个安静地方听听发动机怠速运转是否平稳，音响有没有杂音，打开发动机盖仔细听发动机怠速运转中是否有异响，观察转速表有没有“忽高忽低”现象，可以慢慢踩油门，正常情况下发动机声音应该是由弱到强平稳轰鸣。更多详细信息来源：
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&&机动车驾驶证申领和使用规定&&: 驾驶证准驾车型及代号如下. 大型客车 A1证可以开 大型载客汽车和 A3、B1、B2、C1、C2、C3、C4、M 牵引车 A2证可以开 重型、中型全挂、半挂汽车列车和 B1、B2、C1、C2、C3、C4、M 城市公交车 A3证可以开 核载10人以上的城市公共汽车和 C1、C2、C3、C4 中型客车 B1证可以开 中型载客汽车（含核载10人以上、19人以下的城市公共汽车）和 C1、C2、C3、C4、M 大型货车 B2证可以开 重型、中型载货汽车；大、重、中型专项作业车和 C1、C2、C3、C4、M 小型汽车C1证可以开手动档,自动档的9座(含9座)以下的 小型、微型载客汽车以及轻型、微型载货汽车(所有蓝牌的小货车)、轻、小、微型专项作业车 和小型自动挡汽车C2、低速载货汽车C3、三轮汽车C4. 小型自动挡汽车 C2证可以开 小型、微型自动挡载客汽车以及轻型、微型自动挡载货汽车 低速载货汽车 C3证可以开 低速载货汽车（原四轮农用运输车）和 C4 三轮汽车 C4证可以开 三轮汽车（原三轮农用运输车） 普通三轮摩托车 D证可以开 发动机排量大于50ml或者最大设计车速大于50km/h的三轮摩托车和 E、F 普通二轮摩托车 E证可以开 发动机排量大于50ml或者最大设计车速大于50km/h的二轮摩托车和 F 轻便摩托车 F证可以开 发动机排量小于等于50ml，最大设计车速小于等于50km/h的摩托车 轮式自行机械车 M 证可以开轮式自行机械车 无轨电车 N证可以开 无轨电车 有轨电车 P 证可以开有轨电车 详细的去这里看
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小儿的问题千万不要大惊小怪。我觉得
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我是觉得应该会很恐怖
请登录后再发表评论!邢台盛世房地产开发有限公司关于南大汪旧村改造项目C区项目C1、C2号楼房屋预测绘成果网上公告的通知_牛城晚报_邢台网
第02版：要闻
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邢台盛世房地产开发有限公司关于南大汪旧村改造项目C区项目C1、C2号楼房屋预测绘成果网上公告的通知
&&&&各位业主、相关利害关系人：&&&&我公司开发建设的坐落在冶金路与永祥街交叉口西南角南大汪旧村改造项目C区项目，其中C1、C2号楼已预测完毕。按照《房屋交易与产权管理工作导则》相关规定：预测绘成果中的预测绘面积是申请房屋预售、合同签约备案的主要依据。现该楼栋的房屋位置、预测绘建筑面积等信息已在网上公示，请各位业主及相关利害关系人登录http://www.（邢台房地产信息网），进入“交易管理→通知公告”查询。如对预测绘网上信息有异议，请于“公告”期内向邢台市房屋交易与产权管理中心提出书面意见。&&&&开发企业咨询电话：2116666&&&&邢台市房屋交易与产权管理中心咨询电话：2255016&&&&日当前位置：
＞＞＞如图，在△ABC中，∠ACB=90°，∠A=30°，BC=1．过点C作CC1⊥AB于C1，过..
如图，在△ABC中，∠ACB=90°，∠A=30°，BC=1．过点C作CC1⊥AB于C1，过点C1作C1C2⊥AC于C2，过点C2作C2C3⊥AB于C3，…，按此作发进行下去，则ACn=______．
题型：填空题难度：中档来源：不详
∵∠ACB=90°，∠A=30°，BC=1，∴AB=2 AC=3，∵CC1⊥AB于C1，∴32=AC1AC，∴AC1=32=(3)221，∵C1C2⊥AC，C2C3⊥AB，∴同理，AC2=334=(3)322，AC3=98=(3)423，∴ACn=(3)n+12n．故答案为(3)n+12n．
马上分享给同学
据魔方格专家权威分析，试题“如图，在△ABC中，∠ACB=90°，∠A=30°，BC=1．过点C作CC1⊥AB于C1，过..”主要考查你对&&直角三角形的性质及判定&&等考点的理解。关于这些考点的“档案”如下：
现在没空？点击收藏，以后再看。
因为篇幅有限，只列出部分考点，详细请访问。
直角三角形的性质及判定
直角三角形定义：有一个角为90°的三角形，叫做直角三角形。直角三角形可用Rt△表示，如直角三角形ABC写作Rt△ABC。 直角三角形性质：直角三角形是一种特殊的三角形，它除了具有一般三角形的性质外，具有一些特殊的性质：性质1:直角三角形两直角边a，b的平方和等于斜边c的平方。即。如图，∠BAC=90°，则AB2+AC2=BC2（勾股定理)性质2:在直角三角形中，两个锐角互余。如图，若∠BAC=90°，则∠B+∠C=90°性质3：在直角三角形中，斜边上的中线等于斜边的一半（即直角三角形的外心位于斜边的中点，外接圆半径R=C/2）。性质4:直角三角形的两直角边的乘积等于斜边与斜边上高的乘积。性质5:如图，Rt△ABC中，∠BAC=90°，AD是斜边BC上的高，则有射影定理如下：（1）（AD)2=BD·DC。（2）（AB)2=BD·BC。（3）（AC)2=CD·BC。性质6:在直角三角形中，如果有一个锐角等于30°，那么它所对的直角边等于斜边的一半。在直角三角形中，如果有一条直角边等于斜边的一半，那么这条直角边所对的锐角等于30°。性质7:如图，1/AB2+1/AC2=1/AD2性质8:直角三角形被斜边上的高分成的两个直角三角形和原三角形相似。性质9：直角三角形直角上的角平分线与斜边的交点D 则&&& BD:DC=AB:AC直角三角形的判定方法：判定1：定义，有一个角为90°的三角形是直角三角形。判定2：判定定理：以a、b、c为边的三角形是以c为斜边的直角三角形。如果三角形的三边a，b，c满足，那么这个三角形就是直角三角形。（勾股定理的逆定理）。判定3：若一个三角形30°内角所对的边是某一边的一半，则这个三角形是以这条长边为斜边的直角三角形。判定4：两个锐角互为余角（两角相加等于90°）的三角形是直角三角形。判定5：若两直线相交且它们的斜率之积互为负倒数，则两直线互相垂直。那么判定6：若在一个三角形中一边上的中线等于其所在边的一半，那么这个三角形为直角三角形。判定7：一个三角形30°角所对的边等于这个三角形斜边的一半，则这个三角形为直角三角形。（与判定3不同，此定理用于已知斜边的三角形。）
发现相似题
与“如图，在△ABC中，∠ACB=90°，∠A=30°，BC=1．过点C作CC1⊥AB于C1，过..”考查相似的试题有：
347634362111923863144668220948198505Radio channel model for ICI cancellation in multi-carrier systems
United States Patent 8811505
A channel modeling method for Inter Carrier Interference (ICI) cancellation in multi-carrier wireless communication systems comprises: describing the channel with a plurality of fixed matrices and an equal-numbered plurality
one-to-one pairing each of the described plurality of unfixed variables with one of described plurality of fixed matrices. Corresponding system is also provided. The method and system can compensate for the channel distortion of the Doppler Effect even if the Doppler Frequency Offset is relatively significant.
Inventors:
Zhang, Xiabo (Shanghai, CN)
Ma, Ni (Shanghai, CN)
Application Number:
Publication Date:
08/19/2014
Filing Date:
08/04/2008
Export Citation:
NXP, B.V. (Eindhoven, NL)
Primary Class:
Other Classes:
International Classes:
H04K1/10; H04L27/28
Field of Search:
View Patent Images:
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US Patent References:
7844018Tian et al.375/3467826517Kim et al.375/148Huang et al.375/260Yu et al.375/260Wu et al.375/260Swarts et al.370/342Koo et al.6970560Hench et al.Yun et al.375/260TanabeKolze et al.375/152Gorokhov et al.375/1486400761Smee et al.
Foreign References:
CN1514557AMethod and device of equalized fast fading channel in orthogonal frequency dirision multiplex systemCN1750527ASignal equalizing method in orthogonal frequency division multiplex systemEP1748612OFDM pilot symbols structure using Hadamard codesWOA1A METHOD FOR SIGNAL PROCESSING AND A SIGNAL PROCESSOR IN AN OFDM SYSTEMWOA2TIME AND FREQUENCY CHANNEL ESTIMATION IN AN OFDM SYSTEMWOA1A RADIO CHANNEL MODEL FOR ICI CANCELLATION IN MULTI-CARRIER SYSTEMS
Other References:
Zhao, Y., “Sensivity to Doppler Shift and Carrier Frequency Errors in OFDM Systems—The Consequences and Solutions”; IEEE 46th Vechcular Techn. Conf., Atlanta, GA, US; pp.
Jeon, Won Gi; “An Equalization Technique for Orthogonal Frequencydivision Multiplexing Systems in Time-Variant Multi-Path Channels”; IEEE Transactions on Communications, vol. 47, No. 1 (Jan. 1999).
Armstrong, J “Analysis of New and Existing Methods of Reducing Inter-Carrier Interference Due to Carrier Frequency Offset in OFDM”; IEEE Transations on Communications, vol. 47, No. 3; pp. 365-369 (Mar. 1999).
Choi, Yang-S “On Channel Estimation and Detection for Multicarrier Signals in Fast and Selective Rayleigh Fading Channels”; IEEE Transactions on Communications, vol. 49, No. 8; (Aug. 2001).
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Primary Examiner:
File, Erin
Attorney, Agent or Firm:
Intellectual Property and Licensing (NXP B.V.
411 East Plumeria Drive, MS41
SAN JOSE CA 95134)
What is claimed is:
A method for a channel model for a multi-carrier wireless communication system, comprising: in a receiver, cancelling interference in a received signal by describing the channel to include a plurality of fixed matrices and an equal-numbered plurality of unfixed variables, the fixed matrices being characterized as a at least a portion of a frequency-spectrum spread of the interference, the interference including inter-carrier interference (ICI); and pairing of each of the described plurality of unfixed variables, one-to-one with one of the described plurality of fixed matrices.
The method of claim 1, further comprising dividing the unfixed variables and fixed matrices into L groups such that every group includes T unfixed variables paired with T fixed matrices, wherein, L is the maximum multi-path number and T is a positive integer.
The method of claim 2, further comprising describing channel features of one path with one divided group.
The method of claim 3, further comprising defining the fixed matrices of the described one divided as a progressional spread of the interference, the interference including ICI.
The method of claim 4, wherein the multi-carrier wireless system is an orthogonal frequency division multiplexing (OFDM) and further comprising dividing a Doppler Spectrum spread range for the received signal into a plurality of segments each small enough such that the corresponding channel response can be treated as an impulse function in the frequency domain, and such for each segment, the received signal is: y(n)=∑l=0Lh(l)exp(jΔfn)s(n-l)+w(n) where Δf is the unitary frequency offset for the segmentation, h(l) is the time domain channel parameters within one OFDM symbol.
The method of claim 5, performing an FFT operation at a receiver in the system, the received frequency domain signal is: Y=∑l=0Lh(l)[ElX+CElX]EquationA where Y=[Y0Y1?YN-1] is the received signals in the frequency domain, X=[X0X1?XN-1] is the transmitted signals in the frequency domain, El[exp(-j2πl·0/N)0?00exp(-j2πl·1/N)?0????00?exp(-j2πl·(N-1)/N)] is the phase rotation matrix resulting from propagation delay and C=[0c1c2?cN-1c-10c1?cN-2c-2c-10?cN-3?????c-(N-1)c-(N-2)c-(N-3)?0] is the matrix representing ICI, in which cs is described in the following Equation B: cs≈∑t=0Tft(Δf)ctgt(πs/N)(ctg(πs/N)-j),EquationB the described one divided group defines the channel according to the following Equation C: Y=∑l=0L(h0(l)ElX+∑t=1Tht(l)CtElX)EquationC wherein, ht(l) represents the unfixed variables including the channel impulse response and Doppler frequency offset for a corresponding segment, Ct=[0c1tc2t?cN-1tc-1t0c1t?cN-2tc-2tc-1t0?cN-3t?????c-(N-1)tc-(N-2)tc-(N-1)t?0], cst=ctgt(πs/N)(ctg(πs/N)-j), the matrices CtEt(0≦t≦T) of the one path are the progressional spread of ICI, and t is the progressional rank.
The method of claim 5, further comprising increasing T to facilitate a more accurate determination of ICI via Equation C.
The method of claim 6, further comprising estimating the variables ht(l) using a linear estimation algorithm.
The method of claim 7, further comprising, in response to the variables of one OFDM symbol including at least (L+1)(T+1) pilot signals, using the linear estimation algorithm by: letting the data have a zero value to construct:
X=[P00 . . . 0P10 . . . 0 . . . P(L+1)(T+1)-1]T
where Ps is pilot signal, [ ]T is the transpose operator and the corresponding received signals are:
Y=[y00 . . . 0y10 . . . 0 . . . y(L+1)(T+1)-1]T
[ ]T is th and substituting X and Y into Equation C, achieving (L+1)(T+1) equations and determining the ht(l) variables by solving this set of simultaneous linear equations.
The method of claim 4, wherein the multi-carrier system is from the group consisting of OFDM, SC-FDMA, MC-CDMA.
For use in a multi-carrier wireless communication system having a maximum multi-path number of L and that includes a plurality of User Equipment (UE), a system comprising: a pilot assignment module configured and arranged to effect pilot allocation by high layers of L groups of pilots to each UE of said plurality of UEs; and a receiver configured and arranged to receive a signal via the wireless communication system and the receiving including a channel estimation module configured and arranged with a channel model that includes a plurality of fixed matrices and an equal-numbered plurality of unfixed variables paired one-to-one such that each of the plurality of unfixed variables is paired with a different one of the plurality of fixed matrices that are characterized as a at least a portion of a frequency-spectrum spread of interference in the received signal, the interference including inter-carrier interference (ICI).
The system of claim 11, wherein the unfixed variables and fixed matrices are divided into L groups such that every group includes T unfixed variables paired with T fixed matrices, wherein, T is a positive integer.
The system of claim 12, wherein channel features of one path are described by one divided group.
The system of claim 13, wherein the fixed matrices of the one divided group characterize a progressional spread of ICI.
The system of claim 14, wherein: the multi-carrier wireless system is an orthogonal frequency division multiplexing (OFDM) and the channel estimation module uses a Doppler spectrum spread range divided into a plurality of segments each small enough such that the corresponding channel response can be treated as an impulse function in the frequency domain, and such for each segment, the received signal is: y(n)=∑l=0Lh(l)exp(jΔfn)s(n-l)+w(n) where Δf is the unitary frequency offset for the segmentation and h(l) is the time domain channel parameters within one OFDM symbol.
The system of claim 15, including a receiver circuit configured and arranged to perform an FFT operation on the received frequency domain signal in accordance with Equation A as follows: Y=∑l=0Lh(l)[ElX+CElX]EquationA where Y=[Y0Y1?YN-1] is the received signals in the frequency domain, X=[X0X1?XN-1] is the transmitted signals in the frequency domain, El[exp(-j2πl·0/N)0?00exp(-j2πl·1/N)?0????00?exp(-j2πl·(N-1)/N)] is the phase rotation matrix resulting from propagation delay and C=[0c1c2?cN-1c-10c1?cN-2c-2c-10?cN-3?????c-(N-1)c-(N-2)c-(N-3)?0] is the matrix representing ICI, in which cs is described in the following Equation B: cs≈∑t=0Tft(Δf)ctgt(πs/N)(ctg(πs/N)-j),EquationB in which the described one divided group defines the channel according to the following Equation C: Y=∑l=0L(h0(l)ElX+∑t=1Tht(l)CtElX)EquationC wherein, ht(l) represents the unfixed variables including the channel impulse response and Doppler frequency offset for a corresponding segment, Ct=[0c1tc2t?cN-1tc-1t0c1t?cN-2tc-2tc-1t0?cN-3t?????c-(N-1)tc-(N-2)tc-(N-1)t?0], cst=ctgt(πs/N)(ctg(πs/N)-j), in which the matrices CtEl(0≦t≦T) of the one path are the progressional spread of ICI, and t is the progressional rank.
The system of claim 16, wherein the receiver circuit is configured and arranged to make T larger to facilitate a more accurate determination of ICI via Equation C.
The system of claim 17, wherein the receiver circuit further comprises a linear estimation module that estimates the variables ht(l) using a linear estimation algorithm.
The system of claim 18, wherein the receiver circuit is configured and arranged to, in response to the variables of one OFDM symbol including (L+1)(T+1) pilot signals or more, implement the linear estimation algorithm in accordance with the following: let the data have a zero value to construct:
X=[P00 . . . 0P10 . . . 0 . . . P(L+1)(T+1)-1]T
where Ps is pilot signal, [ ]T is the transpose operator and the corresponding received signals are:
Y=[y00 . . . 0y10 . . . 0 . . . y(L+1)(T+1)-1]T
[ ]T is th and substituting X and Y into Equation C to achieve (L+1)(T+1) equations and determining the ht(l) variables by solving this set of simultaneous linear equations.
The system of claim 11, wherein the multi-carrier system is from the group consisting of OFDM, SC-FDMA, MC-CDMA.
Description:
The present invention relates generally to communication systems and more particularly to a novel radio channel model for Inter Carrier Interference (ICI) cancellation in multi-carrier systems.In multi-carrier systems, a symbol duration is increased by splitting the high-rate serial data stream into many low-rate parallel streams. As illustrated in FIG. 1, in orthogonal frequency division multiplexing (OFDM), for example, a stream of signals are modulated on many equally spaced parallel subcarriers. Modulation and demodulation are implemented by means of Inverse Fast Fourier Transform (IFFT) 101 and its inverse (FFT) 102, respectively. The orthogonality of the signals, when transmitted over a radio channel, can only be maintained if the channel is flat and time-invariant. For time-varying channels self-interference occurs, among others, among signals at different subcarriers and is called Inter Carrier Interference (ICI). Some proposed solutions for ICI mitigation require a modification to the transmit format and are thus not suitable for existing standards. Others without this requirement cannot be used due to high speed of the user devices, e.g., when used in a vehicle, train or plane at their normal cruising speeds, while still others are too complex for a typical mobile user electronic device.As shown in FIG. 1 an OFDM system is an example of a multi-carrier system in which the frequency domain signals are transformed into a time domain by an IFFT module 101:s(n)=1N∑k=0N-1dkej2πnk/N(-(N-1)≤n≤N-1)Equation1
The received signal y(n) can be expressed as: y(n)=∑l=0Lh(n,l)s(n-l)+w(n)Equation2
Replacing s(n) with Equation 1, Equation 2 can be rewritten as: y(n)=1N∑k=0N-1dkHk(n)ej2πnk/N+w(n)Equation3
where Hk(n)=∑l=0Lh(n,l)e-j2πlk/N
and L is the maximum multipath number. The kth sub-carrier output from the FFT module 102 can be expressed as Yk=1N∑k=0N-1y(n)e-j2πnk/N=dkHk+αk+wk whereEquation4Hk=1N∑n=0N-1Hk(n)Equation5αk=1N∑m=0,m≠kN-1dm∑n=0N-1Hm(n)exp[j2πn(m-k)/N]Equation6wk=1N∑n=0N-1w(n)e-j2πnk/NEquation7
The dkHk is the expected received signal and the αk represents Inter-Carrier Interference (ICI) caused by the time-varying nature of the channel. wk is white Gaussian noise. Thus, ICI is structured according to the transmit standard. The ICI is a significant problem for multi-carrier systems, especially in a high mobility environment. As an inherent interference within OFDM-based systems, ICI results from incomplete orthogonality of the sub-carriers, which is caused by several factors, e.g., carrier frequency offset between transmitter and receiver, Doppler Effect, etc. The mobile radio channel brings the spectrum spread to the received signals. When a pure sinusoidal tone of frequency fc is transmitted, the received signal spectrum, called as Doppler spectrum, will have components in the range fc-fm to fc+fm, which is shown in FIG. 2.Considering one sub-carrier on the receiving side, the data on one sub-carrier is interfered with by the data on other sub-carriers, as described by the following Equations 8 and 9dl′=c0di+∑l=0-Nl≠icl-idiEquation8
where di is transmitted data, dl′ is the corresponding received data, cl-i is the ICI coefficient representing the ICI power level from the lth sub-carrier on the sub-carrier: cl-i=1Nsinπ(l-i+ΔfT)sinπ(l-i+ΔFTN)×expjπ(N-1)(l-i+ΔfT)NEquation9 A major reason that past proposed ICI cancellation schemes have not solved the ICI problem is the lack of a suitable channel model for addressing the ICI problem in multi-carrier wireless communication systems.Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.FIG. 1 illustrates a conventional OFDMFIG. 2 illustrates the spectrum shape of a DFIG. 3 illustrates segmentation of the Dop andFIG. 4 illustrates an OFDM system modified according to the present invention to include a linear estimation module that estimates the channel features, according to an exemplary embodiment of the present invention.A detailed description of the iterative channel estimation method and system to which this method is applied, are now provided.In the present invention a more accurate channel model is provided. This is a new model in which the basic idea is modelling the frequency domain channel features (ICI included) as having two parts: a first part comprising multiple fixed matrices and a part comprising unfixed variables. The unfixed variables are estimated via the pilots. The more fixed matrices that are used, the more accurately the channel is estimated. Moreover, the unfixed variables can be estimated by a linear algorithm.The Doppler spectrum spread (range from fc-fm to fc+fm) is divided into many small segments during which the channel impulse response remains almost the same. For each segment, the channel model in Equation 9 serves as a baseline. First, channel impulse response is described for every segment by employing fixed matrices and unfixed variables to approximate Equation 9. By combining all segments, the channel impulse response on the whole Doppler spectrum spread is achieved. If the segmented Doppler spread is small enough, the corresponding channel response can be treated as an impulse function in the frequency domain, as shown in FIG. 3.For each segment, the received signal is:y(n)=∑l=0Lh(l)exp(jΔfn)s(n-l)+w(n)
where Δf is the unitary frequency offset for the segmentation, and h(l) is the time domain channel parameters within one OFDM symbol. The unfixed variables and fixed matrices are divided into L groups, where L is the maximum multipath number and every group includes T variables/matrices. After the FFT operation at the receiver side, the received frequency domain signal is:Y=∑l=0Lh(l)[ElX+CElX]Equation10
where Y=[Y0Y1?YN-1]
is the received signals in frequency domain, X=[X0X1?XN-1]
is the transmitted signals in the frequency domain, El=[exp(-j2πl·0/N)0…00exp(-j2πl·1/N)…0????00…exp(-j2πl·(N-1)/N)]
is the phase rotation matrix resulting from propagation delay and C=[0c1c2…cN-1c-10c1…cN-2c-2c-10…cN-3?????c-(N-1)c-(N-2)c-(N-3)…0]
is the matrix representing ICI, in which cs is described in Equation 9. As derived in Appendix A, cs≈∑t=0Tft(Δf)ctg′(πs/N)(ctg(πs/N)-j)Equation11
where T is the rank number used to describe the ICI. The bigger T is, the more accurate Equation 11 is. Therefore, Equation 11 can be rewritten as: Y=∑l=0L(h0(l)ElX+∑t=1Thl(l)CtElX)Equation12
where ht(l) is the unfixed variables including the channel impulse response and Doppler frequency offset for a corresponding segment, Ct=[0c1tc2t…cN-1tc-1t0c1t…cN-2tc-2tc-1t0…cN-3t?????c-(N-1)tc-(N-2)tc-(N-1)1…0], and cst=ctg′(πs/N)(ctg(πs/N)-j).
The matrices CtEl(0≦t≦T) of one path are the progressional spread of ICI, and t is the progressional rank. Usually the variables corresponding to lower rank matrices are larger than the variables corresponding to the higher rank matrices, i.e., ht1(l)&ht2(l)(t1&t2). Combining all the segmentations of the Doppler spread, a practical channel model is achieved. The matrices Ct and El are fixed and only the ht(l)'s are altered along with segmentations. Therefore, the format of the proposed channel model on the whole Doppler spread is the same as Equation 12, the only difference lies in ht(l).In order to use Equation 12 to describe the channel features, a total of (L+1)(T+1) variables of (ht(l)) have to be estimated. A basic linear estimation algorithm is provided as an example only of how to obtain the variables ht(l), since other algorithms providing the same result can be used. This linear estimation algorithm can be used to estimate the variables if one OFDM symbol includes (L+1)(T+1) pilots signals (or more). The example of a basic linear estimation scheme is described below.Let the transmitted data have a zero value to construct:
X=[P00 . . . 0P10 . . . 0 . . . P(L+1)(T+1)-1]T
where Ps is a pilot signal and [ . . . ]T is the matrix transposition operator. Correspondingly, the received Pilot signals in the frequency domain are:
Y=[y00 . . . 0y10 . . . 0 . . . y(L+1)(T+1)-1]T
Substituting X and Y into Equation 12 results in a system of (L+1)(T+1) linear equations. Then the variables are derived by solving this set of linear equations, which means low processing delay and achievable performance, especially under high SNR condition. The present invention provides the above new channel model comprising multiple fixed matrices and unfixed variables, as shown in Equation 12 which describes the channel response, where a total of (L+1)(T+1) variables (ht(l)) are estimated.Referring now to FIG. 4, an exemplary embodiment of an OFDM system according to the present invention is illustrated in which the receiver comprises means to implement a channel estimation scheme that is diagrammatically shown by the block E 501. In the present invention an OFDM system transmit blocks of N symbols where the shape and size of the block processed on reception is free, in order to best match block size to the system architecture. Further, the OFDM system assigns L groups of pilots for each UE where L is the maximum multi-path delay, according to the distributed pilot allocation scheme of the present invention. Maximum rank number T is the number of variables/matrices included in each group.The purpose of the invention is to provide a radio channel model suitable for ICI estimation and cancellation in multi-carrier systems. FIG. 4 illustrates an exemplary embodiment of an OFDM system modified in accordance with the present invention. In order to perform the linear estimation algorithm to obtain the channel variables, the data parts of transmitted signals X are set to zero so that only pilot signals Xp are sent by the transmission side to the receiver side of the system and are received thereby as Yp.The channel estimation is conducted in module LE 401. The pilot format and position is assigned according to the UE mobility, and then the pilots are inserted into OFDM symbol before IFFT module PAM 402.The pilots are assigned to UEs by high layers Pilot Assignment Module 402 and the receiver side demodulates received pilot-only signals using the Fast Fourier Transform 102. Then, according to an exemplary embodiment, a linear estimation module LE 401 can be used to solve a system of (L+1)(T+1) equations, assuming that one OFDM symbol includes (L+1)(T+1) pilots signals (or more)). The example of a basic linear estimation scheme is described below.Let the transmitted data have a zero value to construct:
X=[P00 . . . 0P10 . . . 0 . . . P(L+1)(T+1)-1]T
where Ps is a pilot signal and [ . . . ]T is the matrix transposition operator. Correspondingly, the received Pilot signals in the frequency domain are:
Y=[y00 . . . 0y10 . . . 0 . . . y(L+1)(T+1)-1]T
Substituting X and Y into Equation 12 results in a system of (L+1)(T+1) linear equations. Then the variables to describe the channel features, a total of (L+1)(T+1) variables of (ht(l)) are derived by solving this set of linear equations, which means low processing delay and achievable performance, especially under high SNR condition. Module LE 401 solves these linear equations and outputs (ht(l)). While exemplary embodiments of the present invention have been provided, one skilled in the art will realize that the invention is not limited to the specific details and exemplary embodiments shown and described herein. Accordingly, various modifications may be made thereto without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.APPENDIX Acs=1N(1-jtgΔfTπN)sinπΔfTexp(-jπs/N)exp(jπΔfT)sin(sπ/N)+cos(sπ/N)tgΔfTπN=F(ΔfT,N)1-jtg(sπ/N)tg(sπ/N)+tgΔfTπN=F(ΔfT,N)ctg(sπ/N)-j1+tgΔfTπNctg(sπ/N)ctgΔfTπNctg(sπ/N)?1=F(ΔfT,N)(∑t=0∞(-1)ttgtΔfTπNctgt(sπ/N))(ctg(sπ/N)-j)=∑t=0∞ft(ΔfT,N)ctgt(sπ/N)(ctg(sπ/N)-j)
where F (ΔfT,N) is a function of ΔfT and N: ft(ΔfT,N)=1N(1-jtgΔfTπN)sinπΔfTexp(jπΔfT)(-1)ttgtΔfTπN
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