CN1707991A - 在发射前运用预旋转方法的码分多址系统 - Google Patents
在发射前运用预旋转方法的码分多址系统 Download PDFInfo
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- H04L2027/0022—Arrangements at the transmitter end using the carrier of the associated receiver of a transceiver
Abstract
一种在无线通信中计算从通信实体发出的接收信号在相位和频率方面的误差并在向该实体发射前对信号的相位和频率误差做预校正的数字扩频通信系统。
Description
背景技术
本发明主要涉及数字通信技术,特别涉及一种在发射前预旋转数字扩频信号的系统和方法,借此提高接收机准确率并改进接收机相位和频率信息的恢复还原状况。
许多现有通信系统都使用数字扩频调制或码分多址(CDMA)技术。数字扩频调制是一种通信技术,在此技术中,待发射数据与伪随机噪声信号相调制,并通过加宽的频带(扩频)将数据发射出去。用码分多址技术发射数据可以不受信号失真或发射路径中干扰频率的影响。
图1为码分多址通信系统的简图,所示通信系统包括一个具有给定带宽的单通信信道。该信道通过扩频编码混频,而此扩频编码重复伪随机噪声(pn)序列发生器生成的预定图形。数据信号与伪随机噪声序列相调制以生成数字扩频信号。载波信号与数字扩频信号相调制,用以建立前向链路并随后发射出去。接收机解调发射的内容以析取数字扩频信号。建立反向链路时也是如此。
在地面通信中,由于变化的地面、环境条件以及人为障碍,发射信号往往经由反射分布。其结果是单个发射信号生成为多个接收信号,而这些接收信号到达接收机时存在不同的时延。这一效应通常被称为多路失真。发生多路失真时,从不同的路径传来的信号以各自不同的振幅和载波相位延迟到达接收机。
在现有技术中,多路失真造成的误差通常由接收机加以纠正。此纠错过程在信号与匹配的伪随机噪声序列相关联且发射数据被再现后进行。这样,在关联完成的同时,信号中已含有误差。类似的多路失真也影响反向链路发射过程。法国第2767238号专利提出了一种用于估算接收到的信号的系统,其中采用预定函数来估算接收到的信号的相移。相移用于锁相环路,使系统会聚于零误差。
欧洲第0818892号和美国第5,499,236号专利提出了一种系统,其中由一个基站在下行传输中发送一个误差信号,表明要由终端站进行调整,以便进行反向线路发射。
因此,我们需要一种能够在发射过程中纠正所遇信号误差的系统。
发明内容
本发明涉及一种数字扩频通信系统,其在无线通信中计算通信实体发出的接收信号在相位和频率方面的误差,并在向该实体发射前对信号相位和频率方面的这些误差做预校正。
附图说明
图1所示为码分多址(CDMA)通信系统现有技术的简化框图。
图2所示为B-CDMATM通信系统的详细框图。
图3A所示为依照本发明使用伪随机导频信号的详细框图,载波偏移纠错在码片级进行。
图3B所示为瑞克(rake)接收机的框图。
图4所示为正交相移键控组上接收符号p0的示意图,该图显示了硬式决策过程。
图5所示为与指定符号对应的纠错角度示意图。
图6所示为应用与指定符号对应的纠错角度后合成符号的示意图。
图7所示为常规锁相环框图。
图8A所示为依照本发明较佳实施例的发射机简化框图。
图8B所示为依照本发明另一实施例的发射机简化框图。
图8C所示为依照本发明另一实施例的发射机简化框图。
具体实施方式
本发明较佳实施例现结合图示详细说明如下,相应数字始终代表相应元件。
如图2所示,码分多址通信系统25包括发射机27和接收机29,可以设置于基站或移动用户接收机上。发射机27包括信号处理器31,该处理器将音频信号及非音频信号按不同的速率编码成数据,例如按每秒八千字节、每秒十六千字节、每秒三十二千字节或每秒六十四千字节的数据速率。信号处理器31根据信号的种类或设定数据速率来选择具体的数据速率。
背景技术中,多路访问系统生成发射信号包括以下两步。第一步,输入数据33,经前向纠错(FEC)编码35进行编码。其中输入数据33可视为一种双相已调制信号。例如,如果使用r=1/2的卷积码,那么上述单个双相已调制数据信号变成了双变量或两个双相已调制信号。一个信号被指定在同相(I)信道41a。另一个信号被指定在正交(Q)信道41b。复数采用a+bj的形式,其中a和b是实数,且|j2=-1|。双相调制的I和Q信号常被称为正交相移键控(QPSK)。在较佳实施例中,约束长度k=7和卷积码速率r=1/2的拓扑生成多项式为G1=171|8|37和G2=133839。
第二步,上述两个双相已调制数据或符号41a、41b经复数伪随机噪声(pn)序列扩频。合成的145a和Q45b扩频信号与其它具有不同扩频编码的扩频信号(信道)相结合|于|53,并与载波信号51混频,随后发射55。此项发射包含具有不同数据速率的多个单体信道。
接收机29包括解调器57a、57b,该解调器将所发射的宽带信号55下变频为中频信号59a、59b。第二次下变频将信号降至基带。正交相移键控信号接着被过滤61,并经复数伪随机噪声(pn)序列43a、43b与63a、63b混频。其中复数伪随机噪声(pn)序列43a、43b与已发射复数编码的共轭相匹配。只有在发射机27上经同样编码扩频的原始波形被有效去扩频。其它波形以噪声形式出现于接收机29。数据65a、65b接着被送至信号处理器67,卷积编码的数据在信号处理器67处接受前向纠错解码。
当信号被接收并解调后,基带信号处于码片级。信号中的I和Q组成部分都经在扩频中使用过的伪随机噪声序列的共轭进行去扩频,并使信号回到符号级。然而,由于载波偏移,发射中发生的相位误差通过单个码片波形的改变反映出来。如果载波偏移纠错在码片级进行,那么由于码片级信号的固有卷积,整体准确度获得提高。载波偏移纠错也可在符号级进行,但整体准确度达不到那么高。然而,由于符号速率远不及码片速率,因此在符号级进行纠错时,整体处理速度较低。
图3A所示为依照本发明系统75和方法使用的接收机。构成同相和正交相位元件的复数基带数字扩频信号77经由自适应匹配滤波器(AMF)或其它自适应滤波方法被输入和过滤。自适应匹配滤波器79是一个横向滤波器(有限脉冲响应),该滤波器采用滤波系数81以使接收信号77的延迟复件相互覆盖,从而生成滤波后的信号输出83。该信号输出具有增大的信噪比(SNR)。自适应匹配滤波器79生成的输出83与多个信道去扩频器851、852、85n以及导频去扩频器87相连接。属于信号输出83的成分的导频信号经独立去扩频器87和伪随机噪声序列91进行去扩频,与此同时,发射数据77被指定到经伪随机噪声序列911、922、93n分别去扩频851、852、85n的信道。数据信道完成去扩频851、852、85n后,数据比特流951、952、95n与维特比解码器971、972、97n相连接并输出991、992、99n。
用于调整自适应匹配滤波器79的滤波系数81或加权通过多条单体多路传播路径的解调而获得。这一操作由瑞克接收机101完成。用瑞克接收机101来弥补多路失真的方法已为所属通信技术领域的技术人员所熟知。
如图3B,瑞克接收机101包括并行组合的路径解调器“指状元件”1030、1031、1032、103n,这些元件解调特定的多路元件。特定解调器的导频序列跟踪环路始于给定路径的时序估计,而此给定路径由伪随机噪声序列105决定。在现有技术中,伪随机噪声序列105可属于通信系统任一信道931。通常是使用具有最大接收信号的信道。
每个路径解调器都包括复数混频器1070、1071、1072、107n、加法器和锁存器1090、1091、1092、109n。对于每个瑞克元件而言,伪随机噪声序列105受到码片延迟τ1111、1112、111n并经基带扩频信号113与1071、1072、107n进行混频,从而对每个信号加以去扩频。每个倍增乘积都被输入至累加器1090、1091、1092、109n,并在完成下一个符号时钟循环后与原有乘积相加且锁存。瑞克接收机101为每个多路元件提供相对路径值。多个n维输出1150、1151、1152、115n提供了抽样脉冲信道响应的估计量,其包括0°、90°、180°或270°的相对相位误差。
参照前面的图3A,瑞克接收机生成的多个输出与n维复数混频器117相结合。经过与每个瑞克接收机101的混频,输出115是对抗衰落输出中相对相位误差的纠正。
导频信号是一个复数正交相移键控信号,但正交元件要设置为零。本发明的纠错119信号是由去扩频信道951通过对每个去扩频信号951的符号首先进行硬式决策121而导出的。硬式决策处理器121决定正交相移键控组最靠近去扩频符号值的位置。
如图4所示,硬式决策处理器121是一个欧几米德距离处理器以将信道1的接收符号p0比做四个正交相移键控组点x1,1,x-1,1,x-1,-1,x1,-1。由于在多路和射频的情况中发射55过程都存在噪声和失真的影响,因此有必要对每个接收符号p0进行检查。硬式决策处理器121计算从接收符号p0到每个象限的四个距离d1、d2、d3、d4,并选择最近距离d2,指定该符号定位x-1,1。原有符号坐标p0被废弃。
参照前面的图3A,在经过每次硬式符号决策121后,每个符号输出125的复共轭123被决定。复共轭是一对复数,其具有相同的实数部分,且虚数部分仅在记号上有所不同。如图5所示,通过首先决定指定符号坐标x-1,-1的复共轭来对符号解调或去旋转,并形成纠错信号119以除去抗衰落输出中的相对相位误差。这样,抗衰落输出通过硬式决策相关角度被有效地去旋转,且除去了相对相位误差。这一操作有效地提供了由导频信号驱动的抗衰落,而无需绝对相位参考。
参照前面的图3A,复共轭123生成的输出119与复数n维混频器117相连接,每个瑞克接收机101的输出115都与纠错信号119进行混频。如图6所示,合成乘积是脉冲信道响应的噪声估计量。图6所示的误差表明了同相轴上的弧度距离π/6。
参照前面的图3A,复数n维信道混频器117的输出129与n维估算器131相连接。信道估算器131是多个低通滤波器,每个滤波器都为一个多路元件的滤波而设。n维估算器131的输出81与自适应匹配滤波器79相连接。这些输出81用作自适应匹配滤波器79加权。自适应匹配滤波器79对基带信号加以过滤从而弥补由于在多路情况中没有大量使用导频信号而造成的信道失真。
瑞克接收机101与锁相环(PLL)133电路联合使用以除去载波偏移。载波偏移是由于发射机/接收机元件误配或其它射频失真而造成的。本发明75使用低级导频信号135,该信号是使用导频伪随机噪声序列91对基带信号77的导频信号进行去扩频87而产生的。如图7所示,导频信号与单个输入锁相环133相连接。锁相环133测量导频信号135与参考相位0之间的相位差。去扩频导频信号135是与锁相环133相连的实际误差信号。
锁相环133包括反正切分析仪136、复数滤波器137、积分器139以及相位复数转换器141。导频信号135是对锁相环133的误差信号输入,并与复数滤波器137相连接。复数滤波器137包括两个增益级143a、143b、一个积分器145和一个加法器147。复数滤波器137的输出与积分器139相连接。频率的积分是相位,该相位被输出140至转换器141。相位输出140与转换器141相连接,后者将相位信号转换成复数信号以便与基带信号77进行混频151。由于上行操作是可交换的,锁相环133的输出149也是进入系统75的反馈环。
如图8A所示,复共轭123的纠错信号119和锁相环133的输出信号149分别与位于发射器181里的混频器相连接,其目的是在发射前纠正信号。图8A中的发射机181与图2中的发射机27工作原理类似,只是前者的待发射信号在发射前已被预旋转。参照前面的图8A,数据1641、1642、1643通过使用前向纠错编码(FEC)35进行编码。两个双相调制的数据或符号41a、41b经复数伪随机噪声(pn)序列扩频,所得的145a和Q45b扩频信号与纠错信号119相混频,与载波信号51进行上变频,并将53与其它具有不同扩频编码的扩频信号相结合。结果信号55通过从接收机锁相环133发出的信号149接受再次纠错。已完成相位和频率预校正的信号56接着被发射。这样,本发明用图3A中的系统75生成的信号119、149对发射信号做预校正,从而减少接收机所得信号在相位和频率方面的误差。
参照前面的图8B,所示为依照本发明另一实施例所制的发射机183。这一实施例与图8A中的实施例类似,仅有的不同在于纠错信号119通过混频器157与基带数据信号混频。这样,基带数据在编码和扩频前已做预校正。当然,所属技术领域的技术人员应该意识到在纠错信号119与数据信号混频前还可能含有其它步骤。
参照前面的图8C,所示为依照本发明另一实施例所制的发射机188。在此实施例中,纠错信号119和载波偏移信号149被输入至组合器,该组合器在发射前将所述信号与单个预校正信号结合,并通过混频器169与加法器53的输出混频。
最后,请注意,载波偏移纠错和预旋转纠错是相互独立的纠错方法。各自可以被单独使用。例如,系统可以只对载波偏移误差做预校正而不使用预旋转。或者,系统进行预旋转,而不对载波偏移误差加以纠正。
虽然本文对本发明具体的实施例已做上述说明和描述,所属技术领域的技术人员在不离开本发明主旨和范围的前提下还可做很多调整和修改。以上描述仅以说明为目的,而非对本发明的某些方式方法加以限定。
Claims (11)
1.一种在发射一通信信号时通过一用户设备减少发射误差的方法,包括下列步骤:
在所述用户设备接收一射频通信信号;
分析所述接收信号的误差;
根据所述分析生成一纠错信号;以及
在从所述用户设备发射所述通信信号前,使用所述纠错信号纠正所述通信信号。
2.根据权利要求1所述的方法,还包括下列步骤:
使用一加权信号时将所述接收信号进行过滤以生成一滤波信号;
解调所述接收信号以在所述经接收信号中生成各多重路径元件的相对路径值:以及
将所述路径值与所述纠错信号进行混频以生成所述加权信号。
3.根据权利要求1所述的方法,其中所述误差包括相位误差,且在发射所述通信信号前,所述纠错信号对所述相位误差进行纠错。
4.根据权利要求1所述的方法,其中所述误差包括频率误差,且在发射所述通信信号前,所述纠错信号对所述频率误差进行纠错。
5.根据权利要求2所述的方法,其中所述分析步骤包括:
使用一导频信号对所述滤波信号进行去扩频;
在所述去扩频滤波信号中执行一硬式决策以生成符号输出;以及
决定所述符号输出的复共轭以生成所述纠错信号;
其中所述纠错信号将所述路径值中的相对相位误差移除。
6.一种用于发射与接收通信信号的用户设备,所述用户设备包括有一接收机与一发射机用于减少所述经发射信号的发射误差,所述接收机包括:
一天线,用于接收一通信信号;
一分析仪,用于分析所述接收信号的误差并根据所述分析以生成纠错信号;以及
一纠错单元,使用所述纠错信号对所述接收信号进行纠错;以及
所述发射机响应所述纠错单元,在发射前对所述发射信号进行纠错。
7.根据权利要求6所述的用户设备,所述接收器还包括一自适应匹配滤波器,用城使用一加权信号过滤所述经接收信号以生成一滤波信号。
8.根据权利要求7所述的用户设备,其中所述分析仪包括:
至少一去扩频器,使用一导频信号对所述滤波信号进行去扩频;
一处理器,用于在所述去扩频滤波信号中执行一硬式决策并生成符号输出;以及
一共轭器,用于决定所述符号输出的复共轭以生成所述纠错信号。
9.根据权利要求8所述的用户设备,其中所述纠错单元包括:
一瑞克接收器,用于解调所述经接收信号并生成所述接收信号的各多重路径元件的相对路径值;以及
一混频器。用于将所述路径值与所述纠错信号进行混频以生成所述加权信号。
10.根据权利要求6所述的用户设备,其中所述误差包括相位误差,且在发射所述通信信号前,所述纠错信号对所述相位误差进行纠错。
11.根据权利要求6所述的用户设备,其中所述误差包括频率误差,且在发射所述通信信号前,所述纠错信号对所述频率误差进行纠错。
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2002
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