CN1203003A - 用户端的频率漂移校正 - Google Patents

用户端的频率漂移校正 Download PDF

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CN1203003A
CN1203003A CN96198459A CN96198459A CN1203003A CN 1203003 A CN1203003 A CN 1203003A CN 96198459 A CN96198459 A CN 96198459A CN 96198459 A CN96198459 A CN 96198459A CN 1203003 A CN1203003 A CN 1203003A
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frequency
oscillator
error
base station
transmission
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CN1197376C (zh
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亚朗·伊凡斯
陈河伦
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Ai Kantor American Resources Inc.
Al Carter, American GP, Limited by Share Ltd.
Al Carter, American LP, Limited by Share Ltd.
Al Carter, American market, Limited by Share Ltd.
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Stanford Telecommunications Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/65—Arrangements characterised by transmission systems for broadcast
    • H04H20/71—Wireless systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H04N21/45—Management operations performed by the client for facilitating the reception of or the interaction with the content or administrating data related to the end-user or to the client device itself, e.g. learning user preferences for recommending movies, resolving scheduling conflicts
    • H04N21/462—Content or additional data management, e.g. creating a master electronic program guide from data received from the Internet and a Head-end, controlling the complexity of a video stream by scaling the resolution or bit-rate based on the client capabilities
    • H04N21/4622—Retrieving content or additional data from different sources, e.g. from a broadcast channel and the Internet
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H04N21/47—End-user applications
    • H04N21/478—Supplemental services, e.g. displaying phone caller identification, shopping application
    • H04N21/4782—Web browsing, e.g. WebTV
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/16—Analogue secrecy systems; Analogue subscription systems
    • H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/20—Adaptations for transmission via a GHz frequency band, e.g. via satellite
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards

Abstract

一种频率控制系统及方法,其是利用接收器频率偏移的估计值以推算基准振荡器的频率漂移的估计值,以补偿发送器局部振荡器的频率偏移。此使得可在用户远程通讯设备中使用低成本的晶体振荡器,而不会在基站或用户端的比特错误率性能造成劣化。

Description

用户端的频率漂移校正
发明背景：
对于传送至及传送出居住、办公及其他使用者的信息和数据量的需求持续增长得远比供给所能跟上的快。此信息需求是以多种形式来供给，包括各种形式的电话系统，电缆系统，混合光纤/电缆系统，以及无线系统。区域多点分配服务(LMDS)及多频道多点分配服务(MMDS)提供单向及双向宽频服务如广播电视，点播电视(video-on-demand)，多媒体能力，交互视频，高速远程LAN/Internet接达，电话，电算，速学，视频会议，电子销售/行销，远程医学，在家购物以及高速电脑数据链路。两种系统皆可提供无线基本结构以传送如区域TELCO中央局(CO)或有线“头端”
设备的宽频服务。图1显示一此种系统。此例示的系统包括二个基本的部份：头端设备，基站或中心站的系统，以及众多或复数个用户站。整个系统是由非重叠单元的地理结构所构成，其中各地理单元可具有由一个基站所支援的多数个用户站。复数个基站通过接口至单一头端。
如图1所示，头端收集所有信号以分配至整个系统，从而形成星形结构。头端在星形中心，基站环绕头端而用户围绕其各自的基站。作为所收集的信号例子，数字视频可经由卫星链路聚集，电话系统介面可经由五级开关提供，及/或高速率数字数据网络可经由高速率数据开关面接。送至/来自头端的数据分配至区域基站的系统，各基站是被指派以服务其用户站的地理单元。
在此种点对多点系统中，其中基站是从多个用户接收，减少从用户至基站的传输(其后称为上流方向)的频率不稳定度为有效的。举例而言，在脉冲群分时多重存取(TDMA)或分频多重存取(FDMA)连续模式中，窄频数据传输的频率不稳定度可包括多重频道，其造成用户与在相邻频道的另一用户相互干扰。为了避免此种频道间干扰，在相邻频道间常需要有一个大而不可使用的防护频带，导致无效率的频带使用。
在脉冲群模式(TDMA)宽频系统中，在每个脉冲群期间必须取得来自用户的信号。在脉冲群模式系统中，每个脉冲群典型地是由用于同步化的前导码，实际数据，以及防护频带所组成。一种频道效率的测量是数据对总脉冲群长度的比例。相较于调制符号速率的用户传输的频率不稳定度愈大，则脉冲群起头的同步化前导码必须愈长，因而降低了频道的效率。对于给定的用户局部振荡器稳定度而言，对于低成本振荡器典型为大约百万分之十(ppm)，用户传输频率误差的量是正比于载波射频(RF)。结果，此问题在目前供该等服务使用的较高频带变得尤其棘手-在10ppm的超高频(UHF)(0.3-3GHz)，特高频(SHF)(3-30GHz)以及极高频带(EHF)(30-300GHz)；UHF，SHF，及EHF对应的载波频率误差分别为3-30KHz，30-300KHz以及300-3000KHz。本发明对于在0.3-300GHz的范围中提供低成本的解决之道以解决用户频率误差问题尤其有用。
典型地，此问题是藉由确保在用户端的基准振荡器以百万分之几所测量的频率稳定度是非常小而加以解决。此导致使用具有特殊老化特性的昂贵振荡器，或使用热敏电阻网络或电热炉以补偿温度诱发的频率漂移。此等解决之道是比低成本消费者远程通讯设备所期望的贵上好几级。
另一种利用不昂贵的晶体振荡器的解决方法是使发送器局部振荡器经由锁相回路M/N频率合成器而从属于接收器局部振荡器，其中M/N是发送频率对接收器频率的比例。此为不符所需的，因为接收器载波回复锁相回路中的接收器热噪声造成对发送器局部振荡器的相位噪声，导致在头端接收到过度的相位噪声，因而产生劣化或较低的比特错误率性能。为了减少发送器局部振荡器的相位噪声，接收器锁相回路的噪声频宽必须非常小，其降低了接收器锁相回路追踪所接收的信号上的相位噪声的能力，导致用户比特错误率性能劣化。
本发明的目的是提供一种低成本的频率控制系统，其是以低价的晶体振荡器，确保用户传输的频率不稳定度非常小，而不会因过度的相位噪声牺牲比特错误率性能。
发明概述：
本发明是一种频率控制系统及方法，其是利用接收器频率偏移的估计值以推算基准振荡器的频率漂移的估计值，以补偿发送器局部振荡器的频率偏移。此使得可在用户远程通讯设备中使用低成本的晶体振荡器，而不会在基站或用户端的比特错误率性能造成劣化。
本发明是提供一种操作于0.3-300GHz频带的地面点对多点通讯系统(如MMDS及LMDS)中的唯一且有用的频率控制，从而减少用户端发送器局部振荡器误差，其是藉下列技术其中之一或两者：
1.利用来自基站的高频精确度的基准广播信号以及由测量用户接收器端中的频率误差所得的估计值以补偿用户发送器局部振荡器中的频率漂移/误差；及/或
2.由测量基站接收器载波回复中各用户的频率误差而获得个别的估计值，并转接至对应的用户发送器的局部振荡器。
附图说明
当连同下列说明及附图考虑时，本发明的上述及其他目的，优点及特征将更趋明显，图中：
图1为并入本发明的区域多点分配系统(LMOS)或多频道多点分配系统(MMDS)的概示方块图；
图2为并入本发明的用户频率控制系统的方块图；以及
图3为本发明的数字锁相回路的方块图。
特定实施例的说明
一个例示的用户端频率控制系统显示于图2。来自天线的RF输入是经由双工器1通至影像排斥滤波器2，其过滤任何用于低侧注入的在影像频率fLO-fIF的信号，其中fLO是接收器局部振荡器的频率，而fIF是中间频率。第一接收器混频器级3利用第一接收器局部振荡器4将输入信号降频转换至中间频率。第一接收器局部振荡器4将输入信号降频转换至中间频率。第一接收器局部振荡器是经由具有可编程的预定标器(prescaler)的锁相回路而从晶体振荡器基准5加以合成以实行调谐。来自第一接收器混频器而在fLO+fRF的影像是藉由第一接收器混频器影像滤波器6而移除，其中fRF是原始RF输入的频率。正交降频转换器级7将在中频的信号与从电压控制振荡器(VCO)8所推算的第二接收器局部振荡器混合成基频同相及正交相信号，其而后可由解调器9解调。
对于同调解调而言，载波相位需要藉由典型地经由正交降频转换器封闭锁相回路而加以回复。典型地，此是藉由使从第二接收器局部振荡器有输入信号间的相位误差推算的控制电压反馈至电压控制振荡器8而完成。有多种方法用于实行锁相回路。
举例而言，图3显示用于正交相移键控(QPSK)型调制的数字锁相回路实施，不过本发明同样可应用其他调制技术。如前，正交降频转换器21使同相及正交相基频模拟取样通至匹配的滤波器22，其输出是取样于符号纪(Symbol epochs)(未图示)。正交相移键控的决定导向相位检测器23形成相位误差估计值，其是由回路滤波器24过滤以达到用于解调之所需的回路噪声性能。回路滤波器的输出表示频率误差，当加至标称频率25时表示新的频率估计值，其可转换成适用于控制该电压控制振荡器26的电压。
在由接收器初始取得信号后，发送局部振荡器即立刻补偿基准晶体振荡器中的频率漂移。由于在基站中的频率基准是较用户端的基准晶体振荡器稳定好几阶，在用户载波相位回复中的任何测得的频率误差可假设成由用户的基准晶体振荡器所造成。在移除初始频率偏移之后，频率误差仅需被周期性更新。或许每分钟一次，起因于周围温度的变化。此频率漂移的缓慢本质使其可藉由低成本微控制器进行软件实施。
典型上，QPSK解调器数字集成电路将使频率误差可得。此可由如图3中所示的回路滤波器的累加器得之，或者该集成电路可采用独立的计算用以估计频率偏移。频率误差估计值可由微控制器，微处理器或数字信号处理器周期性读取且进而在软件处理以达到所需的噪声性能。微控制器，微处理器，或数字信号处理器而后可调整发送锁相回路合成器中的预定标分配器(prescale divider)以移除暂态局部振荡器(11，图2)中的频率误差。
本发明尤适用于上流为脉冲群模式之处，以致发送局部振荡器漂移/误差的控制可对来自所有用户及各用户的传输脉冲群间的所有脉冲群实行。一般而言，可使频率调整足够的小，故所感应的频率步阶是远小于基站载波回复计算的回路频宽，以避免基站解调器中的感应周期误失和比特错误。因为用户局部振荡器的频率漂移的缓慢本质，此小步阶调节为有效。
降低用户端的处理需求的另一种技术运作如下。各用户的传输中的频率误差是由CFE中基站计算，并转接回各用户以经由控制频道或下流数据中的频带内发讯传送频率校正或调整。此在脉冲群上流系统中可能很需要，其中基站中的解码器可于一频道中服务所有用户。在此结构中，各用户的发送频率误差是从基站载波回复计算中的误差计算。
变化：
A、硬件实施：
频率误差估计值的处理亦可完全在硬件实行而不需微控制器，微处理器，或数字信号处理器的介入及软件处理。实际上，此变成锁频回路，其中发送器局部振荡器频率是从属于接收器局部振荡器频率。
对于某些调制符号率或载波回复锁相回路频宽的意料之外组合而言，可连贯地使回复的载波于发送器局部振荡器转向。实际上，此造成一锁相回路，其中发送器局部振荡器是从属并锁相于接收局部振荡器。
B、数字实施：
在某些数字实施中，电压控制振荡器可由全部由数字数字控制的振荡器取代。此外，用于RF升转换的发送器局部振荡器可被固定，且调制器本身可含有数字控制的振荡器以实行频率漂移补偿并提供发送混频器一可变中频。
优点摘要：
根据本发明，藉由减少所有用户站的频率误差，在相邻FDMA频道间不需要有过度的频带，从而改进频谱的利用。甚且，藉由减少所有用户站的频率误差，可达到在基站迅速取得各用户的信号，从而允许有效的TDMA上流操作。
虽然本发明已就较佳实施例加以说明，应知其他实施例，适用及修改对于熟知此项技艺者是显而易知的。

Claims (7)

1.在一元线通讯系统中，其具有至少一基站于0.3-300千兆赫范围中从复数个相关的用户站发送及接收RF通讯信号，其特征在于包括一种用于降低从用户站至该基站的RF传输的频率不稳定度的系统，该系统包括：
所述用户站各具有附发送及接收频道的收发装置，于该发送频道的发送混频器以及于该接收频道的接收混频器，基准振荡器，连接至该基准振荡器的可控制发送及接收区域频率源，第一解调装置，将该第一解调器连接至该接收混频器的降频转换装置，连接至该降频转换器的电压控制振荡装置，连接该第一解调装置以用于供应载波相位误差校正信号至该电压控制振荡器的装置，以及将该发送频率源连接至该第一解调器以调整该发送频率源的频率的装置。
2.根据权利要求1所述的无线通讯系统，其特征在于：该基准振荡器是晶体振荡器。
3.根据权利要求1所述的无线通讯系统，其特征在于：该可控制发送及接收区域频率源是可编程锁相回路频率合成器。
4.根据权利要求1所述的无线通讯系统，其特征在于：该降频转换器是正交降频转换器。
5.根据权利要求1所述的无线通讯系统，其特征在于：包括将该接收混频器连接至该降频转换器的影像排斥滤波装置。
6.在一点对多点，星形结构的地上无线通讯系统中，其具有至少一基站于0.3-300千兆赫范围中从复数个相关的用户站发送及接收RF通讯信号，其特征在于包括一种用于降低从各用户站至该基站的RF传输的频率不稳定度，漂移或误差的系统，各用户站具有低成本的局部振荡器，该系统并入有用以实行以下一或以上项次的装置；
A)来自该基站的高频率精确度的基准广播信号，以及在用户站用于测量频率误差并补偿该用户站低成本局部振荡器中的频率漂移误差，
B)在基站中提供由测量各用户的频率漂移/误差所得的估计值，并将所测量的误差转接至对应的用户站以补偿用户的发送局部振荡器中的频率漂移/误差。
7.根据权利要求6所述的无线通讯系统，其特征在于：各用户站的该基准振荡器是低成本晶体振荡器。
CNB961984597A 1995-11-21 1996-11-19 在用户端具有频率漂移校正的无线通讯系统 Expired - Fee Related CN1197376C (zh)

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ATE350858T1 (de) 2007-01-15
EP0862834B1 (en) 2007-01-03
CA2237465A1 (en) 1997-05-29
AU1741997A (en) 1997-06-11
DE69636812T2 (de) 2007-12-13
US5794119A (en) 1998-08-11
JP2000512813A (ja) 2000-09-26
KR19990071470A (ko) 1999-09-27
KR100441240B1 (ko) 2004-11-12
EP0862834A4 (en) 2001-01-03
AU716711C (en) 2001-08-02
WO1997019557A1 (en) 1997-05-29
CN1197376C (zh) 2005-04-13
EP0862834A1 (en) 1998-09-09
AU716711B2 (en) 2000-03-02
US6240556B1 (en) 2001-05-29
DE69636812D1 (de) 2007-02-15
CA2237465C (en) 2006-03-14
MX9804013A (es) 1998-09-30
BR9611821A (pt) 1999-07-13
JP4354530B2 (ja) 2009-10-28

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