CN1751484B - 时分双工通信系统的信道校准 - Google Patents

时分双工通信系统的信道校准 Download PDF

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CN1751484B
CN1751484B CN2003801067973A CN200380106797A CN1751484B CN 1751484 B CN1751484 B CN 1751484B CN 2003801067973 A CN2003801067973 A CN 2003801067973A CN 200380106797 A CN200380106797 A CN 200380106797A CN 1751484 B CN1751484 B CN 1751484B
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subscriber station
matrix
uplink channel
pilot tone
access point
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CN1751484A (zh
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M·华莱士
J·W·凯淳
R·J·沃尔顿
S·J·海华德
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Qualcomm Inc
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Abstract

用于校准下行链路和上行链路信道以考虑接入点和用户终端处发射和接收链频率响应差异的技术。在一实施例中,导频在下行链路和上行链路信道上被发送,且用于导出响应的下行链路和上行链路信道响应估计。两个纠正因子集合然后基于下行链路和上行链路信道响应估计而确定。校准下行链路信道通过使用下行链路信道的第一纠正因子集合而形成,且校准上行链路信道通过使用上行链路信道的第二纠正因子集合而形成。第一和第二纠正因子集合可以使用矩阵比计算或最小均方误差(MMSE)计算而确定。校准可以基于空气传输而实时实现。

Description

时分双工通信系统的信道校准
根据35U.S.C.§119的优先权声明
本申请要求于第60/421,462和第60/421,309美国临时申请的优先权,两个申请提交日期均为2002年10月25日,分别题为“Channel Calibration fora Time Division Duplexed Communication System”和“MIMO WLAN System”,两者均被转让给本发明的受让人并在此完全引用并入与此。
                             背景
领域
本发明一般涉及通信,尤其涉及在时分双工(TDD)通信系统内校准下行链路和上行链路信道响应的技术。
背景
在无线通信系统内,接入点和用户终端间的数据通信发生在无线信道上。取决于系统设计,相同或不同的频带可以用于下行链路和上行链路。下行链路(或前向链路)指从接入点到用户终端的传输,且上行链路(或反向链路)指从用户终端到接入点的传输。如果两个频带可用,则下行链路和上行链路可以使用频分双工(FDD)方式在分开的频带上发送。如果只有一个频带可用,则下行链路和上行链路可以使用时分双工(TDD)共享相同的频带。
为了获得高性能,经常需要知道无线信道的频率响应。例如,接入点可能需要下行链路信道的响应以为到用户终端的下行链路数据传输实现空间处理(如下所述)。下行链路信道响应可以由用户终端基于接入点发送的导频而估计。用户终端可以将信道估计发回接入点以使用。对于该信道估计方案,需要在下行链路上发送导频,且将信道估计发回接入点会需要附加延时资源。
对于带有共享频带的TDD系统,下行链路和上行链路信道响应可以被假设相互为倒数。即如果H表示从天线阵列A到阵列B的信道响应矩阵,则倒数信道指从阵列B到阵列A的耦合,给出为H T,其中M T表示矩阵M的转置。因此,对于TDD系统,一个链路的信道响应可以基于在其他链路上发送的导频而估计。例如,上行链路信道响应可以上行链路导频而估计,且上行链路信道响应估计的转置可以用作下行链路信道响应估计。
然而,接入点处的发射和接收链的频率响应一般不同于用户终端处的发射和接收链的频率响应。特别是,用于上行链路传输的发射/接收链的频率响应可能不同于用于下行链路传输的发射/接收链的频率响应。由于发射/接收链之差,“有效”下行链路信道响应(即包括发射/接收链)可以不同于有效上行链路信道响应倒数。如果为一个链路获得的信道响应估计倒数用于在其他链路上空间处理,则发射/接收链的频率响应内的任何差异会表示误差,即如果不被确定或不予以考虑会恶化性能的误差。
因此,领域内需要一种校准TDD通信系统内下行链路和上行链路信道的技术。
概述
在此提供校准下行链路和上行链路信道以考虑接入点和用户终端处发射和接收链的频率响应。在校准后,为一个链路获得信道响应的估计可以用于获得其他链路的信道响应估计。这可以简化信道估计和空间处理。
在一实施例中,提供一种方法用于在无线TDD多输入多输出(MIMO)通信系统内校准下行链路和上行链路信道的方法。根据该方法,导频在上行链路信道上发送,且用于导出下行链路信道响应估计。导频还在下行链路信道上发送且用于导出下行链路信道响应估计。然后基于下行链路和上行链路信道响应估计确定两个纠正因子集合。校准后的下行链路信道通过为下行链路信道使用第一纠正因子集合而形成,且校准后上行链路信道通过为上行链路信道使用第二纠正因子集合而形成。合适的纠正因子会在下行链路和上行链路信道相应的发射机处被使用。校准后下行链路和上行链路信道的响应由于两个纠正因子的集合而大致为倒数。第一和第二纠正因子集合可以使用矩阵比计算或最小均方误差(MMSE)计算确定,如下描述。
校准可以基于空气上传输而实时实现。系统内的每个用户终端可以为其本身使用而导出第二纠正因子。接入点的第一纠正因子集合可以由多个用户终端导出。对于正交频分复用(OFDM)系统,校准可以为第一子带集合使用以为集合内的每个子带获得两个纠正因子集合。其他“未经校准”的子带的纠正因子可以基于为“校准后”子带获得的纠正因子而内插。
本发明的各个方面和实施例在以下进一步描述。
附图的简要描述
通过下面提出的结合附图的详细描述,本发明的特征、性质和优点将变得更加明显,附图中相同的符号具有相同的标识,其中:
图1示出MIMO系统内接入点和用户终端处的发射和接收链;
图2说明应用纠正因子以考虑接入点和用户终端处发射/接收链之差;
图3示出校准TDD MIMO-OFDM系统内下行链路和上行链路信道响应的过程;
图4示出从下行链路和上行链路信道响应估计导出纠正向量估计的过程;
图5是接入点和用户终端的框图;以及
图6是TX空间处理器的框图。
详细描述
在此描述的校准技术可以用于各种无线通信系统。而且,这些技术可以用于单输入单输出(SISO)系统、多输入单输出(MISO)系统、单输入多输出(MISO)系统、单输入多输出(SIMO)系统和多输入多输出(MIMO)系统。
MIMO系统使用多个(NT)发射天线和多个(NR)接收天线进行数据传输。由NT个发射天线和NR个接收天线形成的MIMO信道可能被分解为NS个独立信道,其中NS≤min{NT,NR}。NS个独立信道的每个对应空间子信道且对应一维。如果利用多个发射和接收天线建立的附加维数,则MIMO信道可以提供改善的性能(例如增加传输容量和/或更大的可靠性)。这一般需要发射机和接收机之间准确的信道响应估计。图1示出MIMO系统内接入点102和用户终端104处的发射和接收链框图。对于该系统,下行链路和上行链路以时分复用方式共享相同的频带。
对于下行链路,在接入点102处,码元(用“发射”向量x dn表示)由发射链(TMTR)114处理并在无线信道上从Nap个天线116发送。在用户终端104处,下行链路信号由Nut个天线152接收并由接收链(RCVR)154处理以提供接收的码元(用“接收”向量r dn表示)。发射链114的处理一般包括数模转换、放大、滤波、上变频等。接收链154的处理一般包括下变频、放大、滤波和模数转换等。
对于上行链路,在用户终端104处,码元(用发射向量x up表示)由发射链164处理并在无线信道上从Nut个天线152发送。在接入点102处,上行链路信道由Nap个天线116处理并由接收链124处理以提供接收到码元(用接收向量r up表示)。
对于下行链路,用户终端处的接收向量可以表示为:
r dnR ut HT ap x dn                   等式(1)
其中x dn是带有N ap项的发射向量,以从接入点处的Nap个天线的发送码元;
r dn是带有Nut项的接收向量,以在用户终端处的Nut个天线的接收码元;
T ap是Nap×Nap对角矩阵,该项是与接入点处的Nap个天线的发射链相关联的复数增益;
R ut是Nut×Nut对角矩阵,该项是与用户终端处的Nut天线的接收链相关联的复数增益;以及
H是下行链路的Nut×Nap信道响应矩阵。
发射/接收链响应和无线信道一般是频率的函数。为了简洁,假设平缓衰落信道(即带有平缓频率响应)。
对于上行链路,接入点处的接收向量可以表示为:
r upR ap H T T ut x up                    等式(2)
其中x up是发射向量,以在用户终端处从Nut个天线的发送码元;
r up是接收向量,以在接入点处的Nap个天线的接收码元;
T ut是Nut×NutNut对角矩阵,其项是与用户终端处的Nut个天线的发射链相关联的复数增益;
R ap是Nap×Nap对角矩阵,其项是接入点处与Nap个天线的接收链相关联的复数增益;以及
H T是上行链路的Nap×Nut信道响应矩阵。
对于TDD系统,由于下行链路和上行链路共享相同频带,一般在下行链路和上行链路信道响应之间存在高度相关性。因此,下行链路和上行链路信道响应矩阵可以被假设互为倒数(即转置)并相应用HH T表示,如等式(1)和(2)示出。然而,接入点处的发射/接收链响应一般不等于用户终端处发射/接收链响应。差异导致以下不等性R apHT T ut≠(R ut H T ap)T
从等式(1)和(2),包括可应用的发射和接收链响应的“有效”下行链路和上行链路信道响应H dnH up可以表示为:
H dn =R ut HT ap 并且H up =R ap H T T ut    等式(3)
组合等式集合(3)内的两个等式,可以获得以下关系:
R ut -1 H dnT ap -1=(R ap -1 H upT ut -1)TT ut -1 H up TT ap -1    等式(4)
重新组合等式(4),可以获得以下结果:
H up TT ut R -1 ut H dnT ap -1 R ap=Kut -1 H dn K ap
H up=(Kut -1 H dnK ap )T    等式(5)
其中 K ‾ ut = T ‾ ut - 1 R ‾ ut K ‾ ap = T ‾ ap - 1 R ‾ ap 。等式(5)还可以表示为:
H upK ut =(H dnK ap )T    等式(6)
等式(6)的左边表示在上行链路上的校准信道响应,且右侧表示下行链路上校准后信道响应转置。如等式(6)示出,对有效下行链路和上行链路信道响应应用对角矩阵K utK ap使得下行链路和上行链路的校准后信道响应表示为相互的转置。接入点的Nap×Nap对角矩阵K ap是接收链响应与发射链响应R ap和发射链响应T ap之比(即 K ‾ ap = R ‾ ap T ‾ ap ),其中该比是每元素之比。同样地,用户终端的Nut×Nut对角矩阵K ut是接收链响应与发射链响应R ut和发射链响应T ut之比。
矩阵K apK ut包括考虑接入点和用户终端处的发射/接收链之差的值。这允许一个链路的信道响应由其他链路的信道响应表示,如等式(6)内示出。
可以实现校准以确定矩阵K apK ut。一般,真实的信道响应H和发射/接收链响应是位置的,且它们不能准确地或很容易地被确定。有效下行链路和上行链路信道响应H dnH up而是相应基于在下行链路和上行链路上发送的导频而估计的,如下所述。矩阵K apK ut的估计被称为纠正矩阵
Figure A20038010679700134
它们可以基于下行链路和上行链路信道响应估计
Figure A20038010679700136
Figure A20038010679700137
而导出,如下所述。矩阵
Figure A20038010679700138
包括考虑了接入点和用户终端处发射/接收链之差的纠正因子。
图2说明应用纠正矩阵
Figure A200380106797001311
以考虑接入点和用户终端处的发射/接收链之差。在下行链路上,发射向量x dn首先由单元乘以矩阵接着由发射链114和接收链154为下行链路进行的处理与图1内示出的相同。类似地,在上行链路上,发射向量x up首先由单元162乘以矩阵
Figure A200380106797001313
同样,发射链164和接收链124为上行链路进行的相继处理与图1内示出的相同。
用户终端和接入点观察到的“校准后”下行链路和上行链路信道响应可以被表示为: H ‾ cdn = H ‾ dn K ‾ ^ ap 以及 H ‾ cup = H ‾ up K ‾ ^ ut 等式(7)
其中H cdn TH cup是等式(6)内“真实”的校准后信道响应表达式。使用等式(6)内的表达式组合等式集合(7)内的两个等式,可以示出 H ‾ cup = H ‾ cdn T . 关系 H ‾ cup = H ‾ cdn T 的准确性取决于矩阵
Figure A20038010679700145
的准确性,这接着一般取决于下行链路和上行链路信道响应估计
Figure A20038010679700147
Figure A20038010679700148
的质量。
如上所述,校准可以在TDD系统内实现以根据接入点和用户终端处的发射/接收链响应确定差异。一旦发射/接收链经校准,为一个链路获得的校准后信道响应估计(例如)可以用于为其他链路确定校准后信道响应估计(例如
Figure A200380106797001410
)。
在此描述的校准还可以用于使用OFDM的无线通信系统。OFDM有效地将总系统带宽分成多个(NF个)正交子带,这还被称为频率区段或子信道。在OFDM中,每个子带与响应子载波相关,在其上可以调制数据。对于使用OFDM的MIMO系统(即MIMO-OFDM系统),每个本征模式的每个子带可以被视作独立传输信道。
校准可以以各种方式实现。为了清楚,以下为TDD MIMO-OFDM系统描述特定校准方案。对于该系统,每个无线链路的子带可以被假设为倒数。
图3是用于在TDD MIMO_OFDM系统内校准下行链路和上行链路信道响应的过程300实施例流图。开始时,用户终端使用为系统定义的获取过程获取接入点定时和频率(步骤310)。用户终端然后发送消息以初始与接入点的校准,或校准可以由接入点初始。校准可以由接入点并行地与用户终端的注册/验证实现(例如在呼叫设立期间),且还可以在任何被授权时实现。
校准还可以为所有可能被用于数据传输的子带实现(这还被称为“数据”子带)。不用于数据传输的子带(即保护子带)一般不需要被校准。然而,由于接入点和用户终端处的发射/接收链的频率响应一般在大多数所述频带上为平缓,且由于相邻子带可能相关,校准可以只为数据子带的一子集实现。如果校准少于所有子带的数据子带,则被校准的子带(还被称为“指定”子带)可以被信令到接入点(例如在发送以初始校准的消息内)。
对于校准,用户终端在指定子带上发送MIMO导频到接入点(步骤312)。MIMO导频的生成在以下详细描述。上行链路MIMO导频传输的持续时间取决于指定子带数。例如,如果为四个子带实现校准,则8个OFDM码元足以,且更多的子带可能需要更多的(例如20个)OFDM码元。总发射功率一般是固定的,因此如果MIMO导频在较少数量的子带上被发送,则可能这些子带的每个需要更高的发射功率量,且每个子带的SNR很高。相反,如果MIMO导频在大量子带上被发送,则可以为每个子带使用更少的发射功率,且每个子带的SNR会更糟糕。如果每个子带的SNR不足够高,则更多的OFDM码元可以为MIMO导频发送,且在接收机内整合以为子带获得更高的总SNR。
接入点接收上行链路MIMO导频并为每个指定的子带导出上行链路信道响应估计
Figure A20038010679700151
其中k表示子带索引。基于MIMO导频的信道估计如下描述。上行链路信道响应估计经量化并被发送到用户终端(步骤314)。每个矩阵内的项是第k个子带的上行链路Nut个发射和Nap个接收天线间的复数信道增益。所有矩阵的信道增益可以用特定比例缩放因子经比例缩放以获得期望的动态范围,该因子对于所有指定子带相同。例如,每个矩阵内的信道增益可以为指定子带用所有矩阵的最大信道增益经反向比例缩放,使得最大的信道增益幅度为一。由于校准目标是标准化下行链路和上行链路间的增益/相位差,则绝对信道增益不重要。如果12比特复数值(即带有12比特同相(I)和12比特正交(Q)分量)用于信道增益,则下行链路信道响应估计可以在3NutNapNsb字节内被发送到用户终端,其中“3”是为了用于表示I和Q分量的总共24个比特,Nsb是指定子带数。
用户终端还接收接入点发送的下行链路MIMO导频(步骤316)并基于接收到导频为每个指定子带导出上行链路信道响应的估计
Figure A20038010679700155
(步骤318)。用户终端然后为每个指定子带基于上行链路和下行链路信道响应估计
Figure A20038010679700157
确定纠正因子
Figure A20038010679700158
(步骤320)。
对于纠正因子的导出,每个子带的下行链路和上行链路信道响应被假设为倒数,带有增益/相位纠正以考虑接入点和用户终端处的发射/接收链之差,如下:
H up(k)K ut(k)=(H dn(k)K ap(k))T  其中k∈K               等式(8)
其中K表示带有所有数据子带的集合。由于只有有效下行链路和上行链路信道响应估计在校准期间可用于指定子带,等式(8)可以重写为:
H ‾ ^ up ( k ) K ‾ ^ ut ( k ) = ( H ‾ ^ dn ( k ) K ‾ ^ ap ( k ) ) T 其中k∈K                           等式(9)
其中K’表示带有所有指定子带的集合。纠正因子可以被定义为只包括
Figure A20038010679700161
的Nut个对角元素。同样地,纠正向量可以被定义为之包括
Figure A20038010679700163
的Nap个对角元素。
纠正因子
Figure A20038010679700165
可以从信道估计以各种形式被导出,包括通过矩阵比计算和最小均方误差(MMSE)计算。两种计算方法在以下详细描述。也可以使用其他计算方法,且这在本发明范围内。
A.矩阵比计算
图4是使用矩阵比计算从下行链路和上行链路信道响应估计中导出纠正向量
Figure A200380106797001610
Figure A200380106797001611
的过程320a实施例流图。过程320a可以用于图3内的步骤320。
开始时,为每个指定子带计算Nut×Nap矩阵C(k)(步骤412),如下:
C ‾ ( k ) = H ‾ ^ up T ( k ) H ‾ ^ dn ( k ) 其中k∈K′                        等式(10)
其中比为每元素之比。C(k)的每个元素因此可以被计算为:
c ‾ i , j ( k ) = h ^ upi , j ( k ) h ^ dni , j ( k ) 其中,i={1...Nut}而j={1...Nap},    等式(11)
其中
Figure A200380106797001615
分别是
Figure A200380106797001616
Figure A200380106797001617
的第i行第j列元素,且ci,j(k)是C(k)第i行第j列元素。
在一实施例中,接入点的纠正向量
Figure A200380106797001618
被定义为等于C(k)的标准化行的均值,且由框420内的步骤导出。C(k)的每行首先由对行内的Nap个元素的每个用行内的第一个元素进行比例缩放而标准化(步骤422)。因此,如果
c ‾ i ( k ) = c i , 1 ( k ) · · · c i , N ap ( k ) C(k)的第i行,则标准化行可以被表示为:
c ‾ ~ i ( k ) = [ c i , 1 ( k ) / c i , 1 ( k ) · · · c i , j ( k ) / c i , 1 ( k ) · · · c i , N ap ( k ) / c i , 1 ( k ) ] 等式(12)
标准化行的均值然后可以被确定为Nut个标准化行之和除以Nut(步骤424)。纠正向量被设定为等于该均值(步骤426),这可以被表示为:
k ‾ ^ ap ( k ) = 1 N ut Σ i = 1 N ut c i ‾ ~ ( k ) 其中k∈K′                  等式(13)
由于标准化,
Figure A200380106797001625
的第一元素为单位一。
在实施例中,用户终端的纠正因子被定义为等于C(k)的标准化列的倒数的均值,且由框430内的步骤导出。C(k)的第j列首先通过用向量
Figure A200380106797001627
的第j个元素对列内的每个元素进行比例缩放而标准化,这可以用Kap,j,j(k)表示(步骤432)。因此,如果 c ‾ j ( k ) = c 1 , j ( k ) · · · c N ut , j ( k ) T C(k)的第j列,则标准化列
Figure A20038010679700172
可以表示为:
Figure A20038010679700173
等式(14)
标准化列的倒数的均值然后被确定为Nap个标准化列的倒数和除以Nap(步骤434)。纠正向量被设定等于该均值(步骤436),可以表示为:
Figure A20038010679700175
其中k∈K′                        等式(15)
其中标准化列的反转按每元素实现。
B.MMSE计算
对于MMSE计算,纠正因子
Figure A20038010679700177
Figure A20038010679700178
从下行链路和上行链路信道响应估计
Figure A20038010679700179
中导出,使得校准后下行链路信道响应和校准后上行链路信道响应间的均方误差(MSE)最小化。该条件可以表示为:
min | ( H ‾ ^ dn ( k ) K ‾ ^ ap ( k ) ) T - H ‾ ^ up ( k ) K ‾ ^ ut ( k ) | 2 其中k∈K等式(16)
还可以被写为:
min | K ‾ ^ ap ( k ) H ‾ ^ dn T ( k ) - H ‾ ^ up ( k ) K ‾ ^ ut ( k ) | 2 其中k∈K
其中 K ‾ ^ ap T ( k ) = K ‾ ^ ap ( k ) , 因为是对角矩阵。
等式(16)受到一限制,即的主元素等于单位一(即 K ‾ ^ ap , 0,0 ( k ) = 1 )。无该限制,则可以通过将矩阵
Figure A200380106797001717
的元素设定为零获得平凡解。在等式(16)内,矩阵Y(k)首先通过 Y ‾ ( k ) = K ‾ ^ ap ( k ) H ‾ ^ dn T ( k ) - H ‾ ^ up ( k ) K ‾ ^ ut ( k ) 而获得。然后为矩阵Y(k)的Nap·Nut项的每个获得绝对值的平方。均方误差(或平方误差,由于忽略除以Nap·Nut)等于所有Nap·Nut个平方值之和。
为每个指定子带实现MMSE计算以获得该子带的纠正因子该一个子带的MMSE计算描述如下。为了简洁,子带索引k在以下描述中被省略。且为了简洁,下行链路信道响应估计
Figure A200380106797001722
的元素表示为{αij},上行链路信道响应估计的元素被表示为{bij},矩阵
Figure A200380106797001724
的对角元素被表示为{ui},且矩阵的对角元素表示为{vj},其中i={1...Nap},且j={1...Nut}。
均方误差可以从等式(16)中重写如下:
MSE = Σ j = 1 N ut Σ i = 1 N ap | a ij u i - b ij v j | 2 , 等式(17)
同样受到限制u1=1。最小均方误差可以通过对等式(17)关于u和v进行偏微分并设定偏微分为0而获得。这些操作的结果是以下等式集合:
Σ j = 1 N ut ( a ij u i - b ij v j ) · a ij * = 0 , i ∈ { 2 . . . N ap } , 以及等式(18a)
Σ i = 1 N ao ( a ij u i - b ij v j ) · b ij * = 0 , j ∈ { 1 . . . N ut } 等式(18b)
在等式(18a)中,u1=1,因此在该情况下没有偏微分,且索引i从2到Nap
等式集合(18a)和(18b)的(Nap+Nut-1)个等式集合可以更方便地用矩阵形式表示如下:
Ayz                                等式(19)
其中
A ‾ = Σ j = 1 N ut | a 2 j | 2 0 · · · 0 - b 21 a 21 * · · · - b 2 N ap a 2 N ut * 0 Σ j = 1 N ut | a 3 j | 2 0 · · · · · · · · · · · · · · · 0 · · · 0 0 · · · 0 Σ j = 1 N ut | a N ap j | 2 - b N ap 1 a N ap 1 * - b N ap N ut a N ap N ut * - a 21 b 21 * · · · - a N ap 1 b N ap 1 * Σ i = 1 N ap | b i 1 | 2 0 · · · 0 · · · · · · · 0 Σ i = 1 N ap | b i 2 | 2 0 · · · · · · 0 · · · 0 - a 2 N ap b 2 N ut * · · · - a N ap N ut b N ap N ut * 0 · · · 0 Σ i = 1 N ap | b iN ut | 2
y ‾ = u 2 u 3 · · · u N ap v 1 v 2 · · · v N ut z ‾ = 0 0 · · · 0 a 11 b 11 * a 12 b 12 * · · · a IN ut b IN ut *
矩阵A包括Nap+Nut-1行,前Nap-1行对应来自等式(18a)的Nap-1个等式,最后Nut行对应来自等式集合(18b)的Nut个等式。特别是,矩阵A的第一行从等式集合(18a)中用i=2生成,第二行用i=3生成等。矩阵A的第Nap行从等式集合(18b)用j=1生成等,且最后一行用j=Nut生成。如上示出,矩阵A的项和向量z的项可以基于矩阵
Figure A20038010679700191
内的项而获得。
纠正因子被包括在向量y内,它可以被表示为:
yA -1 z                 等式(20)
MMSE计算的结果是纠正矩阵
Figure A20038010679700193
它们可以最小化校准后下行链路和上行链路信道响应内的均方误差。由于矩阵
Figure A20038010679700195
Figure A20038010679700196
基于下行链路和上行链路信道响应估计
Figure A20038010679700197
而获得,纠正矩阵
Figure A20038010679700199
Figure A200380106797001910
的质量因此决定于信道估计
Figure A200380106797001912
的质量。MIMO导频可以在接收机处被平均以为
Figure A200380106797001913
Figure A200380106797001914
获得更准确的估计。
基于MMSE计算获得的纠正矩阵
Figure A200380106797001915
Figure A200380106797001916
一般好于基于矩阵比计算获得的纠正矩阵,特别是当一些信道增益很小且测量噪声会大大恶化信道增益时。
C.计算后(post computation)
不管选用的特定计算方法,在完成纠正矩阵计算后,用户终端将为所有指定子带的接入点纠正向量
Figure A200380106797001917
发送到接入点。如果为内的每个纠正因子使用12比特复数值,则所有指定子带的纠正向量
Figure A200380106797001919
可以在3Nut(Nap-1)·Nsb字节内被发送到接入点,其中“3”是用于I和Q分量的24个总比特,且(Nap-1)来自每个向量内的第一个元素等于单位一,因此不需要被发送。如果第一元素被设定为29-1=+511,则会有12dB的净空(headroom)(因为最大正12比特带符号值为211-1=+2047),这允许下行链路和上行链路间多达12dB的增益不匹配由12比特值容纳。如果下行链路和上行链路匹配在12dB内,且第一元素被标准化到值511,则其他元素应不大于绝对值511·4=2044,且可以用12比特表示。
为每个指定子带获得纠正向量
Figure A200380106797001921
Figure A200380106797001922
对。如果为少于所有数据子带的子带实现校准,则“未经校准”的子带的纠正因子可以通过内插指定子带获得纠正因子而获得。内插可以由接入点实现以获得纠正因子
Figure A200380106797001923
其中k∈K。同样地,可以由用户终端实现内插以获得纠正向量
Figure A200380106797001924
其中k∈K。
接入点和用户终端此后使用其相应的纠正向量
Figure A200380106797001925
Figure A200380106797001926
或对应的纠正矩阵
Figure A200380106797001928
以在无线信道上传输前对调制码元进行比例缩放,如下所述,其中k∈K。用户终端所见的有效下行链路信道是 H ‾ cdn ( k ) = H ‾ dn ( k ) K ‾ ^ ap ( k ) .
上述的校准方案允许在由不同用户终端实现校准时为接入点导出“可兼容”的纠正向量,其中为接入点和用户终端的每个获得纠正因子向量。
例如,如果两个用户终端同时实现校准过程,则这些终端的校准结果可能经平均以改善性能。然而,校准一般每次为一个用户终端实现。因此,第二用户终端用第一用户终端已经应用的纠正因子观察下行链路。在该情况下,旧纠正向量与第二纠正向量之积可以用作新纠正向量,或还可以使用“加权平均”(如下描述)。接入点一般为所有用户终端使用单个纠正向量,且为不同用户终端不使用不同纠正向量(虽然也可以这样实现)。来自多个用户终端的更新或来自一个用户终端的相继更新可以以相同方式处理。更新向量可以直接被应用(通过积操作)。或者,如果期望一些平均以减少测量噪声,则可以使用加权平均,如下描述。
因此,如果接入点使用纠正向量
Figure A20038010679700201
以发送MIMO导频,用户终端从该导频确定新纠正向量
Figure A20038010679700202
则更新后的纠正向量
Figure A20038010679700203
是当前和新纠正向量之积。纠正向量
Figure A20038010679700205
可以由相同或不同的用户终端导出。
在一实施例中,更新后的纠正向量被定义为 k ‾ ^ ap 3 ( k ) = k ‾ ^ ap 1 ( k ) · k ‾ ^ ap 2 ( k ) , 其中乘法是按每元素相乘原则。在另一实施例中,更新后的纠正向量可以被重新定义为 k ‾ ^ ap 3 ( k ) = k ‾ ^ ap 1 ( k ) · k ‾ ^ ap 2 α ( k ) , 其中α是用于提供加权平均的因子(例如0<α<1)。如果校准更新不频繁,则α接近一可能性能最佳。如果校准更新频繁但多噪声,则可能α值更小更佳。更新的纠正向量
Figure A20038010679700208
然后可以为接入点使用直到它们再次被更新。
如上所述,校准可以为少于所有数据子带的子带实现。例如,校准可以为每隔n个子带实现,其中n可以由发射/接收链的期望响应确定(例如n可以是2,4,6,8,16等)。校准还可以为不均匀分布的子带实现。例如,由于在带通边缘可能有更多的滤波器展开(roll-off),这可能导致发射/接收链不匹配,可能校准接近频带边缘的更多子带。一般,可以校准任何数量和任何分布的子带,且这在本发明的范围内。
在以上描述中,纠正向量
Figure A20038010679700209
Figure A200380106797002010
由用户终端导出,其中k∈K′,且向量被发送回接入点。该方案有利地将校准处理分布在多接入系统的用户终端之间。然而,纠正因子
Figure A200380106797002012
还可以由接入点导出,它然后将向量
Figure A200380106797002014
发送回用户终端,且这在本发明范围内。
在此描述的校准方案允许每个用户终端通过空气传输实时校准其发射/接收链。这使得带有不同频率响应的用户终端获得高性能而不需要严格的频率响应规范或在工厂实现校准。接入点可以由多个用户终端校准以提供改善的准确性。
D.增益考虑
校准还可以基于下行链路和上行链路信道的“标准化”增益实现,这是相对于接收机处的噪声底线的增益。使用标准化增益允许一个链路的特性(包括信道增益和每个本征模式SNR)在下行链路和上行链路经过校准之后基于另一链路的增益测量而获得。
接入点和用户终端可能开始时平衡其接收机输入水平,使得接入点和用户终端的接收路径上的噪声水平大致相等。平衡可以由估计噪声底线完成,即找到接收到TDD帧的一部分(即下行链路/上行链路传输单元),该部分由在特定持续时间上最小的平均功率(例如一个或两个码元周期)。一般,就在每个TDD帧开始之前的时间是无传输的,因为接入点需要接收任何上行链路数据,则在接入点在下行链路上发送之前需要接收/发送调转时间。取决于干扰环境,噪声底线可以基于多个TDD帧而确定。下行链路和上行链路信道响应然后相对于该噪声底线而测量。尤其是,给定发射/接收天线对的给定子带的信道增益首先可以例如作为接收到导频码元与该发射/接收天线对的子带的发送导频码元之比而实现。标准化增益则是测量的增益除以噪声底线。
接入点的标准化增益和用户终端的标准化增益之间较大差异可能导致用户终端的纠正因子大大不同于一。接入点的纠正因子接近单位一,因为矩阵
Figure A20038010679700211
的第一元素被设定为1。
用户终端的纠正因子大不同于一,则用户终端不能应用计算的纠正因子。这是因为用户终端对其最大发射功率有限制,且可能不能为较大的纠正因子增加其发射功率。而且,较小纠正因子的发射功率减少一般是不期望的,因为这会减少可获得的数据速率。
因此,用户终端可以使用计算的纠正因子的比例缩放后版本发送。经比例缩放的校准因子可以通过用特定比例缩放值对计算的纠正因子进行比例缩放而获得,这可能被设定为等于下行链路和上行链路信道响应间的增益区间(差或比)。该增益区间可以被计算为下行链路和上行链路的标准化增益间的差(或区间)的平均值。用于用户终端的纠正因子的比例缩放值(即增益区间)可以连同该接入点的计算纠正因子一起被发送到接入点。
在有纠正因子和比例缩放值或增益区间情况下,下行链路信道特性可以从测量的上行链路信道响应中被确定,反之亦然。如果接入点或用户终端处的噪声底线改变,则可以更新增益区间,且更新的增益区间可以在消息内被发送到其他实体。
在以上描述中,校准导致对于每个子带两个纠正因子集合(或向量或矩阵),一个由接入点用于下行链路数据传输,另一个由用户终端用于上行链路数据传输。校准的实现可以使得为每个子带提供两个纠正因子集合,一个由接入点用于上行链路数据接收,另一个由用户终端用于下行链路数据接收。校准的实现还可以使得为每个子带获得一个纠正因子集合,且该集合用于接入点或用户终端处。一般校准的实现使得校准后的下行链路和上行链路信道响应是倒是,而不管哪里应用纠正因子。
2.MIMO导频
为了校准,MIMO导频在上行链路上由用户终端发送以允许接入点估计上行链路信道响应,且MIMO导频在下行链路上由接入点发送以允许用户终端估计下行链路信道响应。对下行链路和上行链路可以使用相同或不同的MIMO导频,且使用的MIMO导频在接入点和用户终端处为已知的。
在一实施例中,MIMO导频包括特定OFDM码元(表示为“P”),它们从NT个发射天线的每个被发送,其中对于下行链路NT=Nap,且对于上行链路NT=Nut。对于每个发射天线,相同的P OFDM码元在为MIMO导频传输指定的每个码元时段内发送。然而,每个天线的P OFDM码元用分配给那个天线的不同的N码片Walsh序列覆盖,其中对于下行链路,N≥Nap,对于上行链路,N≥Nut。Walsh覆盖维持NT个发射天线间的正交性,且允许接收机区别单个发射天线。
P OFDM码元包括Nsb个指定子带的每个的一个调制码元。P OFDM码元因此包括Nsb个调制码元的特定“码字”,可以被接收机选用方便信道估计。该码字还可以被定义以最小化发送的MIMO导频内的峰平变化。这甚至可以减少发射/接收链生成的失真和非线性量,这可以改善信道估计的准确性。
为了清楚,以下为特定MIMO-OFDM系统描述了特定MIMO导频。对于该系统,接入点和用户终端每个有四个发射/接收天线。系统带宽被分成64个正交子带(即NF=64),它们被分配以-32到+31的索引。在这64个子带中,48个子带(例如索引为±{1,...,6,8,...,20,22,...,26})用于数据,4个子带(例如索引为±{7,21}可以用于导频以及可能的信令,不使用DC子带(索引为0),且不使用剩余子带,它们作为保护子带。该OFDM子带结构在IEEE标准802.11a且题为“Part 11:Wireless LAN Medium Access Control(MAC)and PhysicalLayer(PHY)specifications:High-speed Physical Layer in the 5GHz Band”(1999年9月)的文档内详细描述,这公开可用且在此包括作为参考。
P OFDM码元包括48个数据子带和4个导频子带的52个QPSK调制码元集合。该P OFDM码元可以给出如下:
P(real)=g·{0,0,0,0,0,0,-1,-1,-1,-1,1,1,1,-1,-1,1,-1,1,1,1,1,-1,-1,1,-1,1,-1,-1,-1,-1,1,-1,
       0,1,-1,-1,-1,-1,1,-1,-1,-1,-1,1,1,-1,-1,1,-1,-1,1,1,-1,1,-1,1,-1,1,-,0,0,0,0,0},
P(imag)=g·{0,0,0,0,0,0,-1,1,1,1,-1,-1,1,-1,1,1,1,-1,1,-1,-1,-1,-1,-1,-1,1,1,-1,1,1,-1,1,
       0,-1,-1,-1,-1,1,1,-1,1,-1,-1,1,-1,1,-1,1,1,1,-1,1,1,1,1,1,1,-1,-1,0,0,0,0,0},
其中g是导频的增益。{ }内的值为子带索引-32到-1(对于第一行)以及0到+31(对于第二行)给出。因此,P(real)和P(imag)的第一行表示码元(--j)在子带-26内被发送,码元(-1+j)在子带-25内被发送,依此类推。P(real)和P(imag)的第二行表示码元(1-j)在子带1内被发送,码元(-1-j)在子带2内被发送,依此类推。其他OFDM码元还可以用于MIMO导频。
在一实施例中,四个发射天线为MIMO导频被分配以Walsh序列,W1=1111,W2=1010,W3=1100,W4=1001。对于给定Walsh序列,值“1”指明发送P OFDM码元,且值“0”指明发送-P OFDM码元(即P内的52个调制码元的每个经反转)。
表格1列出为跨越四个码元周期的MIMO导频传输要从四个发射天线的每个发送的OFDM码元。
表格1
  OFDM码元   天线1   天线2   天线3   天线4
  1   +P   +P   +P   +P
  2   +P   -P   +P   -P
  3   +P   +P   -P   -P
  4   +P   -P   -P   +P
对于更长的MIMO导频传输,每个发射天线的Walsh序列被简单地重复。对于该Walsh序列集合,MIMO导频传输发生在四个码元周期的整数倍内以保证四个发射天线间的正交性。
接收机可以基于接收到的MIMO导频通过实现互补处理而导出信道响应估计。特别是,为了恢复从发射天线i发送并由接收天线j接收的导频,接收天线j接收的导频首先用分配给发射天线i的Walsh序列以与在发射机处实现的Walsh覆盖互补的方式处理。MIMO导频的所有Nps个码元周期的去覆盖OFDM码元然后经累加,其中累加为用于携带MIMO导频的52个子带的每个单独实现。累加的结果是
Figure A20038010679700241
其中K=±{1...26},这是52个数据和导频子带的从发射天线i到接收天线j的有效信道响应估计(即包括发射/接收链响应)。
可以实现相同的处理以在每个接收天线处恢复来自每个发射天线的导频。导频处理为52个子带的每个带提供了Nap·Nut个值,它们是有效信道响应估计
Figure A20038010679700242
Figure A20038010679700243
的元素。
上述的信道估计可以由接入点和用户终端在校准期间实现以相应获得有效上行链路的信道响应估计以及有效下行链路的信道响应估计
Figure A20038010679700245
这用于如上所述推出纠正因子。
3.空间处理
下行链路和上行链路信道响应间的相关可以被用于简化TDD MIMO和MIMO-OFDM系统的接入点和用户终端处的信道估计和空间处理。该简化在实现了校准之后可能用于考虑发射/接收链内差异。如上所述,校准后信道响应为:
H ‾ cdn ( k ) = H ‾ dn ( k ) K ‾ ^ ap ( k ) 对于下行链路,以及等式(21a)
H ‾ cup ( k ) _ = ( H ‾ dn ( k ) K ‾ ^ ap ( k ) ) T = H ‾ up ( k ) K ‾ ^ ut ( k ) 对于上行链路。等式(21b)
等式(21b)内的最后等号来自使用有效下行链路和上行链路信道响应间的关系 H ‾ up ( k ) = ( K ‾ ut - 1 ( k ) H ‾ dn ( k ) K ‾ ap ( k ) ) T
每个子带的信道响应矩阵H(k)可以“被对角线化”以获得该子带的NS个本征模式。这可以通过对信道响应矩阵H(k)实现奇异值分解或对H(k)的相关矩阵实现本征值分解而获得,相关矩阵为R(k)=H H(k)H(k)。
校准后下行链路信道响应矩阵H cup(k)的奇异值分解可以被表示为:
H ‾ cup ( k ) = U ‾ ap ( k ) Σ ‾ ( k ) V ‾ ut H ( k ) , 其中k∈K                        等式(22)
其中U ap(k)是H cap(k)的左本征向量的(Nap×Nap)酉阵;
(k)是H cup(k)的奇异值的(Nap×Nut)对角线矩阵;以及
V ut(k)是H cup(k)的右本征向量的(Nut×Nut)酉阵。
酉阵特性是M H MI,其中I是单位矩阵。相应地,校准下行链路信道响应矩阵H cdn(k)的奇异值分解可以被表示为:
H ‾ cdn ( k ) = V ‾ ut * ( k ) Σ ‾ ( k ) U ‾ ap T ( k ) , 其中k∈K                        等式(23)
其中矩阵V ut *(k)和U ap T(k)相应是H cdn(k)的左右本征向量的酉阵。矩阵V ut(k),V ut *(k),V ut T(k)和V ut H(k)是矩阵V ut(k)的不同形式,且矩阵U ap(k),U ap *(k),U ap T(k)和U ap H(k)是U ap(k)的不同形式。为了简化,以下描述内的矩阵U ap(k)和V ut(k)参考还可以指其各种其他形式。矩阵U ap(k)和V ut(k)相应地由接入点和用户终端用于空间处理并由其下标表示。
奇异值分解进一步在Gilbert Strang的书内详细描述,题为“Linear Algebraand Its Applications”,第二版,Academic Press,1980。
用户终端可以基于接入点发送的MIMO导频估计校准后下行链路信道响应。用户终端可以为校准下行链路信道响应估计
Figure A20038010679700251
实现奇异值分解,其中k∈K,以获得
Figure A20038010679700252
的左本征向量的对角矩阵以及矩阵V ut *(k)。该奇异值分解可以给出为 H ‾ ^ cdn ( k ) = V ‾ ut * ( k ) Σ ‾ ^ ( k ) U ‾ ap T ( k ) , 其中每个矩阵上的“^”表示是实际矩阵的估计。
类似地,接入点可以基于用户终端发送的MIMO信道估计校准后上行链路信道响应。接入点可以为校准后上行链路信道响应估计
Figure A20038010679700255
实现奇异值分解,其中k∈K,以获得的左本征向量的对角矩阵
Figure A20038010679700257
和矩阵
Figure A20038010679700258
该奇异值分解可以给出为 H ‾ ^ cup ( k ) = U ‾ ^ ap ( k ) Σ ‾ ^ ( k ) V ‾ ^ ut H ( k ) .
然而,由于倒数信道和校准,奇异值分解只需要由用户终端或接入点实现以获得
Figure A200380106797002510
如果由用户终端实现,则矩阵
Figure A200380106797002512
用于在用户终端处的空间处理,且矩阵
Figure A200380106797002513
可以被发送回接入点
接入点还能基于用户终端发送的操纵基准获得矩阵类似地,用户终端还能基于接入点发送的操纵基准获得矩阵
Figure A200380106797002516
Figure A200380106797002517
操纵基准在前述的临时美国专利申请序列号60/421309内描述。
矩阵
Figure A200380106797002519
还可以用于在MIMO信道的NS个本征模式上发送独立数据流,其中NS≤min{Nap,Nut}。以下描述杂下行链路和上行链路上发送多个数据流的空间处理。
A.上行链路空间处理
上行链路传输由用户终端进行的空间处理可以表示为:
x ‾ up ( k ) = K ‾ ^ ut ( k ) V ‾ ^ ut ( k ) s ‾ up ( k ) , 其中k∈K                等式(24)
其中x up(k)是第k个子带的上行链路的发射向量;以及
s up(k)是用于在第k个子带的NS个本征模式上发送的调制码元的多达NS个非零项的“数据”向量。
还可以在传输前对调制码元实现附加处理。例如信道反转可以被应用在数据子带上(例如对于每个本征模式)使得接收到的SNR大致等于所有数据子带。空间处理可以表示为:
x ‾ up ( k ) = K ‾ ^ ut ( k ) V ‾ ^ ut ( k ) W ‾ up ( k ) s ‾ up ( k ) , 其中k∈K                 等式(25)
其中W up(k)是带有(可选)上行链路信道反转的加权的矩阵。
信道反转还可以在调制发生前通过将发射功率分配给每个子带而实现,在该情况下向量s up(k)包括信道反转系数,且矩阵W up(k)可以从等式(25)中省略。在以下描述中,在等式内使用矩阵W up(k)指明信道反转系数不被包括在向量s up(k)内。在等式内缺少矩阵W up(k)可以指明(1)信道反转未被实现或(2)信道反转被实现且被包括在向量s up(k)内。
信道反转可以如前述的临时美国专利申请序列号60/421309和10/229209内描述的实现,后者题为“Coded MIMO Systems with Selective Channel InversionApplied Per Eigenmode”,提交于2002年8月27日,被转让给本发明的受让人并在此引入作为参考。
接入点处的接收上行链路传输可以被表示为:
r ‾ up ( k ) = H ‾ up ( k ) x ‾ up ( k ) + n ‾ ( k ) 其中k∈K               等式(26)
= U ‾ ^ ap ( k ) Σ ‾ ^ ( k ) s ‾ up ( k ) + n ‾ ( k )
r up(k)是第k个子带的上行链路的接收到向量;
n(k)是第k个子带的加性白高斯噪声(AWGN);以及
x up(k)如等式(24)示出。
接收到上行链路传输的接入点处空间处理(或匹配滤波)可以表示为:
s ‾ ^ up ( k ) = Σ ‾ ^ - 1 ( k ) U ‾ ^ ap H ( k ) r ‾ up ( k )
= Σ ‾ ^ - 1 ( k ) U ‾ ^ ap H ( k ) ( U ‾ ^ ap ( k ) Σ ‾ ^ ( k ) s ‾ up ( k ) + n ‾ ( k ) ) ,
= s ‾ up ( k ) + n ‾ ~ ( k ) 其中k∈K               等式(27)
其中 up(k)是用户终端在上行链路上发送的数据向量s up(k)的估计,且是处理后噪声。等式(27)假设在发射机处未实现信道反转,且接收到向量r up(k)如等式(26)内示出。
B.下行链路空间处理
下行链路传输的接入点处空间处理可以表示为:
x ‾ dn ( k ) = K ‾ ^ ap ( k ) U ‾ ^ ap * ( k ) s ‾ dn ( k ) , 其中k∈K                等式(28)
其中x dn(k)是发送向量,且s dn(k)是下行链路的数据向量。
同样附加处理(例如信道反转)也可以在传输前对调制码元实现。空间处理还可以表示为:
x ‾ dn ( k ) = K ‾ ^ ap ( k ) U ‾ ^ ap * ( k ) W ‾ dn ( k ) s ‾ dn ( k ) , 其中k∈K                 等式(29)
其中W dn(k)是带有(可选)下行链路信道反转的加权的矩阵。
用户终端处的接收下行链路传输可以被表示为:
r ‾ dn ( k ) = H ‾ dn ( k ) x ‾ dn ( k ) + n ‾ ( k ) , S基中k∈K              等式(30)
= V ‾ ^ ut * ( k ) Σ ‾ ^ ( k ) s ‾ dn ( k ) + n ‾ ( k )
其中x dn(k)是等式(28)示出的发射向量。
接收下行链路传输在用户终端处的空间处理(或匹配滤波)可以表示为:
s ^ dn ( k ) ‾ = Σ ‾ ^ - 1 ( k ) V ‾ ^ ut T ( k ) r ‾ dn ( k )
= Σ ‾ ^ - 1 ( k ) V ‾ ^ ut T ( k ) ( V ‾ ^ ut * ( k ) Σ ‾ ^ ( k ) s ‾ dn ( k ) + _ n ‾ ( k ) ) , 其中k∈K等式(31)
= s ‾ dn ( k ) + n ‾ ~ ( k )
等式(31)假设信道反转不在发射机处实现,且接收向量r dn(k)如等式(30)内示出。
表格2概述了用于数据传输和接收的在接入点和用户终端处的空间处理。表格2假设在发射机处由W(k)实现附加处理。然而如果该附加处理不实现,则W(k)可以被视为单位矩阵。
                               表格2
在上述描述和表格2内,纠正矩阵
Figure A20038010679700278
Figure A20038010679700279
相应被应用于接入点处和用户终端处的发射端。这可以简化总空间处理,因为调制码元可能需要经比例缩放(例如对于信道反转)且纠正矩阵
Figure A200380106797002711
还可以与加权矩阵W dn(k)和W up(k)组合以获得G dn(k)和G up(k),其中 G ‾ dn ( k ) = W ‾ dn ( k ) K ‾ ^ ap ( k ) , G ‾ up ( k ) = W ‾ up ( k ) K ‾ ^ ut ( k ) . 还可以实现该处理使得纠正矩阵用于接收空间处理(而不是发射空间处理)。
4.MIMO-OFDM系统
图5示出TDD MIMO-OFDM系统内的接入点502和用户终端504的实施例框图。为了清楚,以下假设接入点和用户终端每个备有四个发射/接收天线。
在下行链路上,在接入点502处,发射(TX)数据处理器510从数据源508接收话务数据(即信息比特)并从控制器530接收其他数据。TX数据处理器510对数据格式化、编码、交织以及调制(即码元映射)以提供调制码元。TX空间处理器520接收来自TX数据处理器510的调制码元并实现空间处理以提供四个发射码元流,每个天线一个流。TX空间处理器520还在导频码元内合适地进行天线(例如为了校准)。
每个调制器(MOD)522接收并处理相应发射码元流以提供对应OFDM码元流。每个OFDM码元进一步由调制器522内的发射链处理以提供对应的下行链路已调信号。来自调制器522a到522d的四个下行链路已调信号然后相应地从天线524a到524d被发送。
在用户终端504处,天线522接收下行链路已调信号,且每个天线向相应的解调器(DEMOD)554提供接收到信号。每个解调器554实现与在调制器522处实现的互补的处理并提供接收到码元。接收(RX)空间处理器560然后对来自所有解调器554的接收到码元实现空间处理以提供恢复的码元,这是接入点发送的调制码元估计。在校准中,RX空间处理器还基于接入点发送的MIMO导频而提供校准后下行链路信道估计
Figure A20038010679700281
RX数据处理器570处理(例如码元去映射、去交织并解码)恢复后码元以提供解码后数据。解码后数据可以包括恢复的话务数据、信令等,它们被提供给数据宿572以进行存储以及/或控制器580进行进一步处理。在校准期间,RX数据处理器570提供校准后上行链路信道估计
Figure A20038010679700282
这由接入点导出且在下行链路上被发送。
控制器530和580控制在接入点和用户终端处响应的各种处理单元操作。在校准期间,控制器580可以接收信道响应估计导出纠正矩阵
Figure A20038010679700285
将矩阵
Figure A20038010679700287
提供给TX空间处理器592进行上行链路传输,并将矩阵提供给TX数据处理器590以传送回接入点。存储器单元532和582相应存储控制器530和580使用的数据和程序代码。
上行链路的处理可以与下行链路的处理相同或不同。数据和信令由TX数据处理器590处理(例如编码、交错和调制),且进一步由TX空间处理器592进行空间处理,该处理器在校准期间在导频码元内多路复用。导频和调制码元进一步由调制器554处理以生成上行链路已调信号,它们然后通过天线522被发送到接入点。
在接入点110处,上行链路已调信号由天线524接收,由解调器522解调,并由RX空间处理器540和RX数据处理器542以与在用户终端处实现的互补的方式处理。在校准期间,RX空间数据处理器还基于用户终端发送的MIMO导频提供校准后上行链路信道估计
Figure A20038010679700291
矩阵由控制器530接收,然后提供给TX数据处理器510以发送回用户终端。
图6示出TX空间处理器520a的框图,且这可以用于图5内的TX空间处理器520和590。为了简洁,以下描述假设选用所有四个本征模式。
在处理器520a内,多路分解器632接收要在四个本征模式上发送的四个调制码元流(表示为s1(n)到s4(n)),将每个流多路分解为ND个数据子带的ND个子流,并向相应的TX子带空间处理器640提供每个数据子带的四个调制码元流。每个处理器640为一个子带实现等式(24)、(25)、(28)或(29)内示出的处理。
在每个TX子带空间处理器640内,四个调制码元子流(表示为s1(k)到s4(k))被提供给四个乘法器642a到642d,它们还为相关子带的四个本征模式接收增益g1(k),g2(k),g3(k)和g4(k)。对于下行链路,每个数据子带的四个增益是对应矩阵Gdn(k)的对角线元素,其中 G dn ( k ) = K ^ dn ( k ) G dn ( k ) = W dn ( k ) K ^ ap ( k ) . 对于上行链路,增益是矩阵Gup(k)的对角元素,其中 G up ( k ) = K ^ ut ( k ) G up ( k ) = W up ( k ) K ^ ut ( k ) . 每个乘法器642用其增益gm(k)对其调制码元进行比例缩放以提供经比例缩放的调制码元。乘法器642a到642d向四个波束成形器650a到650d分别提供四个经比例缩放的调制码元流。
每个波束成形器650实现波束成形以在一个子带的一个本征模式上发送一个码元子流。每个波束成形器650接收一个经比例缩放的码元子流sm(k)并使用相关本征模式的本征向量vm(k)实现波束成形。在每个波束成形器650内,经比例缩放的调制码元被提供给四个乘法器652a到652d,它们还接收相关本征模式的本征向量vm(k)的四个元素vm,1(k),vm,2(k),vm,3(k)和vm,4(k)。本征向量v m(k)是下行链路的矩阵
Figure A20038010679700297
的第m列,且是上行链路矩阵
Figure A20038010679700298
的第m列。每个乘法器652然后将经比例缩放的调制码元乘以其本征向量值vm,j(k)以提供“波束成形后”的码元。乘法器652a到652d向加法器660a到660d提供相应的四个波束成形的子流(还从四个天线被发送)。
每个加法器660接收并对每个码元时段的四个本征模式的四个波束成形码元求和以为相关发射天线提供经预调整码元。求和器660a到660d为四个发射天线向缓冲器/多路复用器670a提供相应的四个经预调整码元的四个子流。
每个缓冲器/多路复用670为ND个数据子带从TX子带空间处理器640接收导频码元以及经预调整码元。每个缓冲器/多路复用器670然后分别为导频子带、数据子带和未使用子带多路复用导频码元、预调整后码元和零以形成该码元周期的NF个发射码元序列。在校准期间,导频码元在指定子带上被发送。乘法器668a到668d用相应的分配给四个天线的Walsh序列W1到W4覆盖四个天线的导频码元,如上所述且如表格1示出。每个缓冲器/多路复用器670为一个发射天线提供发射码元流流xi(n),其中发射码元流包括NF个发射码元的链接序列。
空间处理和OFDM调制在前述的临时美国专利申请序列号60/421309内有详细描述。
在如上描述的本发明的各个实施例中,相同基本服务集合(BSS)或不同BSS内的各个用户终端(UT或SAT)间的对等通信可以如下描述地实现。用单个接入点(AP)校准的UT或STA是基本服务集合(BSS)成员。单个接入点是到BSS内所有UT的公共节点。如上描述的校准方法方便了以下类型的通信:
(i)BSS内的UT可以使用TX操纵以在上行链路(UL)上直接与AP通信,且AP可以使用TX操纵在上行链路(DL)上与UT通信。
(ii)BSS内的UT可以使用操纵直接与相同BSS内的另一UT通信。在该情况下,该对等通信必须自展(bootstrapped),因为没有UT知道它们之间的信道。在各个实施例中,自展过程如下:
-对等链路的初始是指派AP(DAP),且其他UT是被指派的UT(DUT)。
-DAP连同请求一起将MIMO导频发送到DUT以建立链路,所述请求包括BSS ID加上DAPI D。请求需要在公共模式内被发送(即TX分集)。
-DUT通过发送回操纵MIMO导频加上包含DUT ID、其BSS ID和一些DAP使用的速率指示符的确认而进行响应。
-DAP然后可以使用DL上的操纵,且DUT可以使用UL上的操纵。速率控制和跟踪可以通过将传输分为DL和UL分段而进行,且两个分段之间有充分时间以允许处理。
(iii)即使当每个用不同AP校准时,属于一个BSS(例如BSS1)的UT可以引导到属于领域BSS(例如BSS2)。然而在该情况下会由相位旋转岐义性(每子带)。这是因为如上所述的校准过程建立了对AP唯一的校准基准。该基准是一复数常量,
α ( k , j ) = g APTX ( 0 ) g APRX ( 0 )
其中k是子带索引,且j是AP索引,0是在AP上使用的基准天线的索引(例如天线0)。在一实施例中,该恒量对于给定BSS内的所有UT恒定,但对于不同的BSS是独立的。
作为结果,当来自BSS1的UT与BSS2内的UT通信时,操纵但不对该恒量进行纠正或补偿可能会导致相位旋转以及整个本征系统的幅度比例缩放。相位旋转可以通过使用导频(操纵和未经操纵的)而确定,且可以在每个相应的UT的接收机内被去除。在一实施例中,幅度纠正和补偿可以简单地是SNR比例缩放,且可以通过估计在每个接收机处的噪声底线而去除,这可能影响速率选择。
在各种实施例中,属于不同的BSS的UT间的对等交换可能如下进行:
-对等链路的初始(例如BSS1内的UT)是指派AP(DAP),且其他UT(例如BSS2内的UT)是被指派UT(DUT)。
-DAP连同请求一起将MIMO导频发送到DUT以建立链路,所述请求包括BSS ID加上DAP ID。请求需要在公共模式内被发送(即TX分集)。
-DUT通过发送回操纵MIMO导频加上包含DUT ID、其BSS ID和一些DAP使用的速率指示符的确认而进行响应。
-DAP接收机(Rx)可以估计上行链路(UL)上的相位旋转并对每个子带应用纠正常量。DAP然后可以使用下行链路(DL)上的操纵,但需要包括在至少第一操纵分组上的操纵基准的前同步码(preamble),以允许DUT接收机(Rx)纠正或补偿每个子带的DL上的相位旋转。相继DL传输可能不需要操纵基准前同步码。速率控制和跟踪可以通过将传输分为DL和UL分段而进行,且分段之间有充分时间以允许处理。
在此描述的校准技术可以用各种方式实现。例如,这些技术可以在硬件、软件或它们的组合内来实现。对于硬件实现而言,用于在接入点和用户终端出实现的技术可以在以下设备内实现:一个或多个专用集成电路(ASIC)、数字信号处理器(DSP)、数字信号处理设备(DSPD)、可编程逻辑器件(PLD)、现场可编程门阵列(FPGA)、处理器、控制器、微控制器、微处理器、设计成执行这里所述功能的其它电子单元、或者它们的组合。
对于软件实现而言,校准技术可以用执行这里所述功能的模块(例如过程、功能等等)来实现。软件代码可以被保存在存储器单元(例如图5中的存储器单元532或582)中,并可由处理器(例如控制器530或580)执行。存储器单元可以在处理器内实现或在处理器外实现,在后者情况下,它可以通过各种领域内已知的方式耦合到处理器。
这里包括的标题供引用,并且帮助定位特定的章节。这些标题并不限制其下所述概念的范围,这些概念可应用于整篇说明书中的其它章节。
上述优选实施例的描述使本领域的技术人员能制造或使用本发明。这些实施例的各种修改对于本领域的技术人员来说是显而易见的,这里定义的一般原理可以被应用于其它实施例中而不使用创造能力。因此,本发明并不限于这里示出的实施例,而要符合与这里揭示的原理和新颖特征一致的最宽泛的范围。

Claims (38)

1.一种在无线通信系统内校准下行链路和上行链路信道的方法,所述无线通信系统包括接入点、第一用户站和第二用户站,其特征在于,包括:
对于第一用户站和第二用户站的每一个,获得下行链路信道响应估计;
对于第一用户站和第二用户站的每一个,获得上行链路信道响应估计;
对于第一用户站和第二用户站的每一个,基于下行链路和上行链路信道响应估计确定第一和第二纠正因子集合;以及
基于第一和第二纠正因子集合的每一个,对于第一和第二用户站之间对等通信相应地校准下行链路信道和上行链路信道以形成校准后下行链路信道和校准后上行链路信道,从而可用于第一用户站和第二用户站之间而无需进一步校准。
2.如权利要求1所述的方法,其特征在于,所述第一纠正因子集合用于在下行链路信道上传输前对码元进行比例缩放,且所述第二纠正因子集合用于在上行链路信道上传输前对码元进行比例缩放。
3.如权利要求1所述的方法,其特征在于,所述第一纠正因子集合用于对在下行链路信道上接收到的码元进行比例缩放,且所述第二纠正因子集合用于对上行链路信道上接收到的码元进行比例缩放。
4.如权利要求1所述的方法,其特征在于,所述第一和第二纠正因子集合基于以下等式确定:
Figure F200380106797301C00011
其中
Figure F200380106797301C00012
是下行链路信道响应估计的矩阵;
是上行链路信道响应估计的矩阵,
Figure F200380106797301C00014
是第一纠正因子集合的矩阵,
是第二纠正因子集合的矩阵,以及
T”表示转置。
5.如权利要求4所述的方法,其特征在于,所述确定第一和第二纠正因子集合包括:
用矩阵
Figure F200380106797301C00021
与矩阵
Figure F200380106797301C00022
的每个元素之比计算矩阵C,以及基于矩阵C导出矩阵
Figure F200380106797301C00024
6.如权利要求5所述的方法,其特征在于,所述导出矩阵
Figure F200380106797301C00025
包括:
标准化矩阵C的多个行中的每一个;以及
确定矩阵C的多个标准化行的均值,且其中矩阵
Figure F200380106797301C00026
基于多个标准化行的均值形成。
7.如权利要求5所述的方法,其特征在于,所述导出矩阵
Figure F200380106797301C00027
包括:
标准化矩阵C的多个列中的每一个;以及
确定矩阵C的多个标准化列的逆的均值,且其中矩阵
Figure F200380106797301C00028
基于多个标准化列的逆的均值形成。
8.如权利要求4所述的方法,其特征在于,所述矩阵基于最小均方误差MMSE计算而导出。
9.如权利要求8所述的方法,其特征在于,所述MMSE计算最小化均方误差MSE,所述均方误差给出为:
。 
10.如权利要求1所述的方法,其特征在于,还包括:
确定指示下行链路信道响应估计和上行链路信道响应估计间平均差的比例缩放值。
11.如权利要求1所述的方法,其特征在于,所述下行链路和上行链路信道响应的估计经标准化以考虑接收机噪声底线。
12.如权利要求1所述的方法,其特征在于,所述确定在用户终端处实现。
13.如权利要求4所述的方法,其特征在于,为第一子带集合确定下行链路信道的第一纠正因子矩阵集合,所述方法还包括:
内插第一矩阵集合以便为第二子带集合的下行链路信道获得第二纠正因子矩阵集合。
14.如权利要求1所述的方法,其特征在于,所述下行链路和上行链路信道响应的估计各自基于从多个天线发射的导频而获得,并用多个正交序列经正交化。
15.如权利要求1所述的方法,其特征在于,所述上行链路信道响应估计是基于上行链路信道上发送的导频而获得,且其中下行链路信道响应估计基于下行链路信道上发送的导频而获得。
16.如权利要求1所述的方法,其特征在于,所述系统是多输入多输出MIMO系统。
17.如权利要求1所述的方法,其特征在于,所述系统使用正交频分复用OFDM。
18.一种在无线时分双工TDD多输入多输出MIMO通信系统内校准下行链路和上行链路信道的方法,所述通信系统包括接入点、第一用户站和第二用户站,其特征在于,包括:
对于第一用户站和第二用户站的每一个:
在上行链路信道上发送导频;
获得基于上行链路信道上发送的导频导出的上行链路信道响应的估计;
接收下行链路信道上的导频;
获得基于下行链路信道上接收到的导频导出的下行链路信道响应的估计;以及
基于下行链路和上行链路信道响应的估计确定第一和第二纠正因子集合,其中对于第一和第二用户站之间对等通信的校准后下行链路信道通过使用下行链路信道的第一纠正因子集合而形成,且对于第一和第二用户站之间对等通信的校准后上行链路信道通过使用上行链路信道的第二纠正因子集合而形成。
19.如权利要求18所述的方法,其特征在于,所述第一和第二纠正因子集合是基于最小均方误差MMSE计算而确定的。
20.如权利要求18所述的方法,其特征在于,所述第一和第二纠正因子集合基于矩阵比计算而确定。
21.如权利要求18所述的方法,其特征在于,所述第一纠正因子集合基于用多个用户终端校准而更新。
22.如权利要求18所述的方法,其特征在于,还包括:
在下行链路上传输之前用第一纠正因子集合对码元进行比例缩放。
23.如权利要求18所述的方法,其特征在于,还包括:
在上行链路上传输之前用第二纠正因子集合对码元进行比例缩放。
24.一种在无线时分双工TDD多输入多输出MIMO通信系统内的装置,其特征在于,包括:
对于第一用户站和第二用户站的每一个获得下行链路信道响应估计的装置;
对于第一用户站和第二用户站的每一个获得上行链路信道响应估计的装置;
对于第一用户站和第二用户站的每一个基于下行链路和上行链路信道响应的估计确定第一和第二纠正因子集合的装置,其中对于第一和第二用户站之间对等通信校准后下行链路信道通过使用下行链路信道的第一纠正因子集合而形成,且对于第一和第二用户站之间对等通信校准后上行链路信道通过使用上行链路信道的第二纠正因子集合而形成。
25.一种在无线时分双工TDD通信系统内的用户终端,其特征在于,包括:
TX空间处理器,用于在上行链路信道上发送第一导频;
RX空间处理器,用于在下行链路信道上接收第二导频,并基于接收到的第二导频导出下行链路信道响应估计,并接收基于发送的第一导频导出的上行链路信道响应的估计;以及
控制器,用于基于下行链路和上行链路信道响应估计确定第一和第二纠正因子集合,其中校准后下行链路信道通过使用下行链路信道的第一纠正因子集合而形成,校准后上行链路信道通过使用上行链路信道的第二纠正因子集合而形成,并且基于最小均方误差MMSE计算确定第一和第二纠正因子集合。
26.如权利要求25所述的用户终端,其特征在于,所述控制器还用于基于矩阵比计算确定第一和第二纠正因子集合。
27.无线系统内通信的方法,其特征在于,包括:
基于从与一个或多个通信链路相关联的信道响应估计导出的一个或多个纠正因子集合,校准多个用户站和一个或多个接入点之间的一个或多个通信链路,所述多个用户站包括第一用户站和第二用户站;以及
使用操纵来建立第一和第二用户站间的通信而不在第一和第二用户站间实行校准。
28.如权利要求27所述的方法,其特征在于,所述建立第一和第二用户站间的通信包括:
从第一用户站发送导频和请求以建立与第二用户站的通信链路;
响应于从第一用户站接收导频和请求而从第二用户站发送操纵导频和确认;
基于操纵导频使用操纵在第一和第二用户站之间发送信息。
29.如权利要求28所述的方法,其特征在于,所述建立通信的请求包括基本服务集合标识符以及第一用户站标识符,所述第一用户站属于所述基本服务集合。
30.如权利要求28所述的方法,其特征在于,所述确认包括第二用户站标识符、基本服务集合标识符和数据速率指示符,第二用户站属于所述基本服务集合。
31.如权利要求27所述的方法,其特征在于,所述一个或多个接入点包括与第一基本服务集合BSS相关联的第一接入点,以及与第二BSS相关联的第二接入点,其中所述第一用户站关于第一接入点校准,且第二用户站关于第二接入点校准,且其中建立第一和第二用户站间的通信包括:
从第一用户站发送导频和请求以建立与第二用户站的通信链路;
响应于从第一用户站接收导频和请求而从第二用户站发送操纵导频和确认;以及
使用经调整以补偿关于不同接入点的第一和第二用户站校准引起的相位旋转的操纵在第一和第二用户站间发送信息。
32.如权利要求31所述的方法,其特征在于,所述相位旋转基于从第二用户站接收的操纵导频而确定。
33.一种用于无线系统内通信的装置,其特征在于,包括:
基于从与一个或多个通信链路相关的信道响应估计导出的一个或多个纠正因子集合,校准多个用户站和一个或多个接入点之间的一个或多个通信链路的装置,所述多个用户站包括第一用户站和第二用户站;以及
使用操纵建立第一和第二用户站间的通信而不在第一和第二用户站之间进行校准的装置。
34.如权利要求33所述的装置,其特征在于,建立第一和第二用户站之间通信包括:
用于从第一用户站发送导频和请求以建立与第二用户站的通信链路的装置;
响应于从第一用户站接收导频和请求而从第二用户站发送操纵导频和确认的装置;
基于操纵导频使用操纵在第一和第二用户站间发送信息的装置。
35.如权利要求34所述的装置,其特征在于,所述建立通信的请求包括基本服务集合标识符以及第一用户站标识符,所述第一用户站属于所述基本服务集合。
36.如权利要求34所述的装置,其特征在于,所述确认包括第二用户站的标识符、基本服务集合标识符以及数据速率指示符,所述第二用户站属于所述基本服务集合。
37.如权利要求33所述的装置,其特征在于,所述一个或多个接入点包括与第一基本服务集合BSS相关联的第一接入点以及与第二BSS相关联的第二接入点,其中所述第一用户站关于第一接入点校准,且第二用户站关于第二接入点校准,且其中建立第一和第二用户站间的通信包括:
从第一用户站发送导频和请求以建立与第二用户站的通信链路;
响应于从第一用户站接收导频和请求而从第二用户站发送操纵导频和确认;以及
使用经调整以补偿关于不同接入点的第一和第二用户站校准引起的相位旋转的操纵在第一和第二用户站间发送信息。
38.如权利要求37所述的装置,其特征在于,所述相位旋转基于从第二用户站接收到的操纵导频而确定。
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