WO2009030102A1 - Procédé de codage à l'avance et de planification pour utilisateurs multiples et station de base pour mettre en œuvre le procédé - Google Patents

Procédé de codage à l'avance et de planification pour utilisateurs multiples et station de base pour mettre en œuvre le procédé Download PDF

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Publication number
WO2009030102A1
WO2009030102A1 PCT/CN2008/001473 CN2008001473W WO2009030102A1 WO 2009030102 A1 WO2009030102 A1 WO 2009030102A1 CN 2008001473 W CN2008001473 W CN 2008001473W WO 2009030102 A1 WO2009030102 A1 WO 2009030102A1
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Prior art keywords
user
state information
channel state
base station
error
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PCT/CN2008/001473
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English (en)
French (fr)
Inventor
Keying Wu
Lei Wang
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Alcatel Shanghai Bell Co. Ltd.
Alcatel Lucent
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Application filed by Alcatel Shanghai Bell Co. Ltd., Alcatel Lucent filed Critical Alcatel Shanghai Bell Co. Ltd.
Priority to US12/675,208 priority Critical patent/US8464105B2/en
Priority to EP08800497.3A priority patent/EP2187533B1/en
Priority to JP2010522164A priority patent/JP5220859B2/ja
Priority to KR1020107006736A priority patent/KR101381130B1/ko
Publication of WO2009030102A1 publication Critical patent/WO2009030102A1/zh

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0456Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0652Feedback error handling
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0417Feedback systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0452Multi-user MIMO systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621Feedback content
    • H04B7/0626Channel coefficients, e.g. channel state information [CSI]
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W88/00Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08Access point devices
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W72/00Local resource management
    • H04W72/50Allocation or scheduling criteria for wireless resources
    • H04W72/54Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality

Definitions

  • the present invention relates to a wireless MIMO communication system, and more particularly to a multi-user precoding and scheduling method in which channel state information fed back from a user side is utilized (the channel state information may be inaccurate, and its inaccuracy may be From a variety of factors, such as feedback quantization, feedback delay, etc., and statistical characteristics of channel state information errors, a multi-user precoding matrix and scheduling scheme are generated for multi-user precoding and scheduling. Background technique
  • the MU-MIM0 Multi-User Multiple Input Multiple Output
  • MIM0 Multiple Input Multiple Output
  • the transmission processing of the MU-MIM0 system becomes complicated because each user must independently decode its own message and cannot operate with other users.
  • the core issue is how to resolve co-channel interference (CCI) between multiple users.
  • CCI co-channel interference
  • the MU MIM0 system uses multi-user precoding techniques to control or completely avoid co-channel interference between multiple users, so that each user is not subject to interference from other users or only limited interference from other users.
  • accurate CSI Channel State Information
  • CCI Channel State Information
  • completely accurate CSI is difficult to obtain, and inaccurate CSI is always used at the transmitter.
  • inaccurate CSI even with a zero-forcing precoding algorithm, cci between users cannot be completely avoided.
  • the interference suppression method such as maximum likelihood (ML) or minimum mean square error (SE) detection cannot suppress residual CCI due to inaccurate CSI at the receiver, the CCI can only be regarded as additive noise, and Its average power increases as the total transmit power increases. This feature of CCI greatly limits the performance of MU-MIM0, especially at high SNR.
  • the invention can provide a multi-user precoding and scheduling method, which uses the channel state information fed back by the user and the statistical characteristics of the channel state information error to generate a multi-user precoding matrix and a scheduling scheme for multi-user pre-processing. Coding and scheduling.
  • the precoding matrix and scheduling scheme designed in this way can better adapt to the situation that the channel information of the transmitting end is inaccurate, and reduce the residual CCI, thereby reducing the deterioration of the MU-MIMO performance by the inaccurate CSI.
  • a multi-user precoding and scheduling method including: feeding back channel state information and channel state information error statistical characteristics from a user equipment to a base station; the base station according to the fed back channel state information and Generating statistical characteristics of channel state information errors, generating a multi-user precoding matrix and scheduling scheme; and performing multi-user precoding and scheduling on user data using the generated multi-user precoding matrix and scheduling scheme.
  • the channel state information is an estimate of a channel matrix.
  • the statistical characteristic of the channel state information error is a covariance matrix of the error of the channel matrix estimate.
  • the multi-user precoding uses a minimum mean square error MMSE type algorithm.
  • the MMSE type algorithm is a continuous MMSE algorithm.
  • the multi-user scheduling adopts a maximum capacity standard.
  • the statistical characteristics of the channel state information error can be obtained by measuring channel estimation errors, feedback errors, and quantization errors.
  • the method is for a multi-user multiple input multiple output MU-MIM0 communication system.
  • a base station is further provided, comprising: receiving means, receiving channel state information fed back from a user equipment and statistical characteristics of channel state information errors; a multi-user precoding matrix and scheduling scheme generating means, according to the channel fed back State information and statistical characteristics of channel state information errors, generating a multi-user precoding matrix and scheduling scheme; and multi-user precoding and scheduling means for multi-user precoding of user data using the generated multi-user precoding matrix and scheduling scheme And scheduling.
  • FIG. 2 is a block diagram of a base station for implementing the multi-user precoding and scheduling method of the present invention
  • Figures 3 and 4 are graphs showing the performance comparison of the method of the present invention with prior art methods. detailed description
  • the transmitter When the transmitter has only inaccurate CSI, the transmitter cannot generate a multi-user precoding matrix that fully matches the multi-user channel. Such mismatches result in additional cci between users, which increases with transmit power and severely limits the performance of MU-MIM0, especially at high SNR. Interference suppression methods such as ML and MMSE detection cannot suppress CCI caused by CSI errors at the receiver. This has the effect similar to the additive noise increase.
  • the basic idea of the present invention is to study the relationship between such CCI power and precoding/scheduling results, and use this relationship to adjust the precoding and scheduling algorithms to better accommodate the inaccurate CSI environment.
  • a multi-user precoding and scheduling method will be proposed to better control the CCI power due to CSI errors and improve the performance of the recommended-MIM0 system when the CSI of the transmitting end is inaccurate.
  • the MMSE-like algorithm is usually used. This is because the algorithm balances interference and noise.
  • the CCI caused by the CSI error is regarded as AWGN (Additive White Gaussian Noise), and the relationship between the average power and the precoding/filtering matrix is established based on the covariance matrix of the CSI error.
  • the CCI power, precoding, and filtering matrix are then optimized according to the MMSE standard.
  • the maximum capacity standard can be employed and the user/mode subset with the largest and capacity can be selected.
  • the CCI as an AWGN when estimating the sum capacity of each user/mode subset, the relationship between CCI error related CCI power and user/mode selection can be established and used to adjust the scheduling operation.
  • N R receiving antennas per user N T transmit antennas at the base station (BS ) and K users receiving services from the same BS through the same time-frequency resources (here)
  • K is the number of users who are served in the same time slot and frequency band by spatial processing.
  • the total number of users in a cell can be much more than K).
  • the user's channel matrix The fading coefficient between the mth receive antennas.
  • the number of data streams dedicated to user k is represented by s k .
  • s k The number of data streams dedicated to user k is represented by s k .
  • the data vector Xk of the user k having the length Sk is multiplied by the N T x Sk precoding matrix T k , which is linearly transformed into a symbol vector of length ⁇ ⁇ to be transmitted from ⁇ ⁇ antennas.
  • the symbol vectors of the lengths of the users are linearly superimposed, and the superposed vectors are transmitted from the antenna array into the channel.
  • the elements of x k are independent and are equally distributed (independently distributed) with zero mean and unit variance.
  • the total transmit power is given by: For each user k, the received signal vector is:
  • the filter matrix B k can be obtained based on various criteria such as MMSE. According to formula (3), the maximum mutual information between x k and k is:
  • a class SE multi-user precoding algorithm can be employed (here, noise means CCI and AWGN noise due to CSI errors).
  • noise means CCI and AWGN noise due to CSI errors.
  • a continuous MMSE (S-MMSE) algorithm will be used, which is a simple implementation of the MMSE-type algorithm when each user has more than one receive antenna.
  • the basic principle of the ⁇ SE type algorithm is to find the set of the optimal ⁇ coding matrix ⁇ T k ⁇ and the filter matrix ⁇ B k ⁇ according to the MMSE standard.
  • Equation (6) involves optimization problems, and the acquisition of the optimal solution is usually very complicated.
  • the S-wake SE algorithm provides a simplified suboptimal solution to the problem through iterative operations:
  • Step 1 Generate a random s k xN R matrix to initialize each ⁇ -.
  • Step 3 Based on the ⁇ 1 ⁇ calculated as above, update the filter matrix ⁇ BJ according to the MMSE standard, as shown in the following equation:
  • Step 4 Repeat steps 2 and 3 until the ⁇ FJ and ⁇ BJ changed F norm falls below the preset threshold, or the number of iterations has reached a certain value.
  • Step 5 The array ⁇ TJ is normalized. Multi-user scheduling
  • indicates the total number of users in the communication system.
  • the scheduler selects a subset of users from among the users for multi-user transmission and also determines the number of data streams for each of the selected users. 7 (represents possible scheduling results.
  • the scheduler searches on the set of ?C, and according to the specific The standard choice of the best one, represented by ⁇ . For example, for the maximum capacity standard, the scheduler is selected according to the following equation,
  • the elements in ⁇ ⁇ are independent and identically distributed random variables with a mean of zero and a variance of 5 2 .
  • the generation of ⁇ ⁇ may have multiple factors, such as feedback quantization, feedback delay, and so on.
  • a value of 2 is available at the transmitter, which can be obtained at the receiving end by various means such as measuring channel estimation errors, feedback errors and quantization errors, and then fed back to the transmitter by the receiver.
  • ⁇ ") R W ⁇ ⁇ ⁇ ⁇ K X " T " H k + ⁇ I «I + ⁇ 2 /
  • ⁇ + ⁇ , (23) Moreover, ⁇ is defined in equation (9). Similarly, ⁇ is a CCI plus noise term, including CCI and AWGN due to CSI errors. In addition, (11 is approximated as a vector of complex Gaussian noise, which can be optimally generated by the following formula:
  • FIG. 1 is a flow chart of a multi-user precoding and scheduling method in accordance with the present invention.
  • step 101 channel state information is fed back from the user equipment to the base station.
  • the channel state information is an estimate of a channel matrix
  • the statistical characteristic of the channel state information error is a statistical property of an error matrix of the channel matrix estimate.
  • the estimation of the channel matrix may be ⁇
  • the statistical characteristic of the channel state information error may be a covariance matrix.
  • the multi-user precoding may employ an MMSE-like algorithm
  • the multi-user scheduling may employ a capacity maximization standard.
  • user data is multi-user precoded and scheduled using the generated multi-user precoding matrix and scheduling scheme.
  • the base station includes a receiving device 201, a multi-user precoding matrix and scheduling scheme generating device 203, and a multi-user precoding and scheduling device 205.
  • Receiving device 201 receives Channel state information fed back from the user equipment and statistical characteristics of channel state information errors.
  • the multi-user precoding matrix and scheduling scheme generating means 203 generates a multi-user precoding matrix and a scheduling scheme based on the fed back channel state information and the statistical characteristics of the channel state information error.
  • the multi-user precoding and scheduling device 205 performs multi-user precoding and scheduling of user data using the generated multi-user precoding matrix and scheduling scheme.
  • Figures 3 and 4 are graphs showing the performance comparison of the method of the present invention with prior art methods.
  • the CCI Estimation Assist MU-MIM0 policy in accordance with the present invention is compared to the original S-MMSE and MET (Multi-User Intrinsic Mode Transmission) algorithm based on the greedy scheduling policy.
  • four transmit antennas are employed at the base station, two receive antennas per user, and the total number of users is four.
  • the elements in the channel matrix ⁇ H k ⁇ are modeled as independent and identically distributed complex Gaussian variables with zero mean and unit variance.
  • the elements in the csi error matrix ⁇ ⁇ ⁇ are modeled as independent and identically distributed complex Gaussian white noise with zero mean and variance 5 2 .
  • the two are set to 0. 1 and 0.5.
  • the inventive scheme has better performance than MET and S- ⁇ SE with greedy scheduling, especially when CSI errors are high.
  • the present invention is flexible for different CSI error causes such as channel estimation errors, quantization errors, and feedback errors, and can be used for various recommended-MIM0 mechanisms such as based on sounding and user feedback.
  • MU-MIM0 operation is a hotspot in many broadband wireless communication standards such as IEEE 802.16 and 3GPP LTE standards because of its high probability of improving cell throughput, while CSI errors at the transmitter limit MU-MIM0 in practice.
  • the present invention provides an effective ending solution to this problem at the expense of a small amount of additional complexity at the BS, and can provide significant advantages.

Description

多用户预编码及调度方法和实现该方法的基站 技术领域
本发明涉及无线 MIMO通信系统, 更具体地, 涉及一种多用户预 编码和调度方法, 其中利用从用户侧所反馈的信道状态信息 (该信道 状态信息可能是不准确的, 其不准确性可能来自多种因素, 例如反馈 量化, 反馈延时等) 以及信道状态信息误差的统计特性, 生成多用户 预编码矩阵和调度方案以进行多用户预编码和调度。 背景技术
最近, 由于其在容量上的优势以及能与同时服务多个单天线用户 并仍然保持 MIM0 (多输入多输出)天线系统优点的特性, MU- MIM0 (多 用户多输入多输出) 系统已经引起了更多的关注。
与 SU- MIM0 (单用户多输入多输出) 系统相比, 由于每一个用户 必须独立地解码其各自的消息而无法与其他用户操作, MU-MIM0系统的 发射处理变得复杂。 其核心问题是如何解决多用户间的同道干扰 ( CCI ) o
为了解决该问题, MU MIM0系统使用了多用户预编码技术来控制 或完全避免多用户间的同道干扰, 从而使每一个用户不会受到来自其 他用户的干扰或仅仅受到来自其他用户的有限干扰。 为了完全避免或 有效控制 CCI , 在发射机处需要所有用户的准确 CSI (信道状态信息), 这是在真实系统中的不切实际的假定。实际上,完全准确的 CSI难以得 到, 而在发射机处总是使用不准确 CSI。 对于不准确 CSI , 即使使用迫 零类型的预编码算法,也无法完全避免用户间的 cci。由于通过诸如最 大似然 (ML) 或最小均方误差 (画 SE ) 检测等干扰抑制方法无法在接 收机处抑制由于不准确 CSI造成的残余 CCI, 该 CCI只能被看作加性噪 声,并且它的平均功率随着总发射功率增加而增加。 CCI的这一特性使 得它极大地限制了 MU- MIM0的性能, 特别是在高 SNR时。
发明内容
为了克服由于发送端不准确 CSI造成的残余 CCI对 MU-MIMO性 能的恶化, 本发明提出一种多用户预编码和调度方法, 它利用用户反 馈的信道状态信息以及该信道状态信息误差的统计特性, 来生成多用 户预编码矩阵和调度方案以进行多用户预编码和调度。 这样设计出来 的预编码矩阵和调度方案能更好的适应发射端信道信息不准确的情 况, 减小残余 CCI, 从而降低不准确 CSI对 MU-MIMO性能的恶化。
为了实现上述目的, 根据本发明, 提出了一种多用户预编码和调 度方法, 包括: 从用户设备向基站反馈信道状态信息以及信道状态信 息误差的统计特性; 基站根据所反馈的信道状态信息以及信道状态信 息误差的统计特性, 生成多用户预编码矩阵和调度方案; 以及利用所 生成的多用户预编码矩阵和调度方案对用户数据进行多用户预编码和 调度。
优选地, 所述信道状态信息为信道矩阵的估值。
优选地, 所述信道状态信息误差的统计特性为信道矩阵估值的差 错的协方差矩阵。
优选地, 所述多用户预编码采用最小均方误差 MMSE类算法。
优选地, 所述 MMSE类算法为连续 MMSE算法。
优选地, 所述多用户调度采用容量最大标准。
优选地, 所述信道状态信息误差的统计特性可以通过测量信道估 计差错、 反馈差错和量化差错来获得。
优选地, 所述方法用于多用户多输入多输出 MU- MIM0通信系统。 根据本发明, 还提出了一种基站, 包括: 接收装置, 接收从用户 设备反馈的信道状态信息以及信道状态信息误差的统计特性; 多用户 预编码矩阵和调度方案生成装置, 根据所反馈的信道状态信息以及信 道状态信息误差的统计特性, 生成多用户预编码矩阵和调度方案; 以 及多用户预编码和调度装置, 利用所生成的多用户预编码矩阵和调度 方案对用户数据进行多用户预编码和调度。 附图说明
通过参考以下结合附图对所采用的优选实施例的详细描述, 本发 明的上述目的、 优点和特征将变得显而易见, 其中: 图 1是根据本发明的多用户预编码和调度方法的流程图; 图 2是用于实现本发明的多用户预编码和调度方法的基站的方框 图;
以及
图 3和 4是用于显示本发明方法与现有技术方法的性能比较的曲 线图。 具体实施方式
当发射端只有不准确的 CSI时, 发射机无法产生与多用户信道完 全匹配的多用户预编码矩阵。 这样的不匹配导致了用户间的额外 cci, 该 CCI随着发射功率而增加而且严重地限制了 MU-MIM0的性能, 特别是 在高 SNR处。通过诸如 ML和 MMSE检测等干扰抑制方法无法在接收机处抑 制由 CSI差错所引起的 CCI。 这具有与加性噪声增加类似的效果。 本发 明的基本思想是研究这样的 CCI功率和预编码 /调度结果之间的关系, 并且使用该关系来调整预编码和调度算法使其更好地适应不准确 CSI 的环境。 这里, 根据本发明, 将提出一种多用户预编码和调度方法, 以更好地控制由于 CSI差错造成的 CCI功率,并改善当发送端 CSI不准确 时薦- MIM0系统的性能。
在本发明中, 总是假定 CSI差错的统计特性是在发射机处可得到 的。 对于多用户预编码, 通常采用了 MMSE类算法。 这是由于该算法能 够平衡干扰和噪声。 这里, 将由 CSI差错而引起的 CCI看作 AWGN (加性 高斯白噪声), 并且根据 CSI差错的协方差矩阵建立其平均功率和预编 码 /滤波矩阵之间的关系。 然后, 根据 MMSE标准对 CCI功率、 预编码和 滤波矩阵进行优化。
在本发明中, 对于多用户调度, 可以采用容量最大标准, 并选择 具有最大和容量的用户 /模式子集。 类似地, 通过在估计每一个用户 / 模式子集的和容量时将 CCI看作 AWGN,可以建立 CSI差错相关的 CCI功率 和用户 /模式选择之间的关系, 并且使用其来调整调度操作。 下面, 将详细解释根据本发明的多用户预编码和调度方法的原 理。
信道模型
考虑在基站(BS )处具有 NT个发射天线而 K个用户通过相同的时间 频率资源从相同的 BS接收服务的多用户 (每一个用户 NR个接收天线) MIM0系统的下行链路(这里, 需要注意的是, K是通过空间处理在相同 时隙和频带中得到服务的用户数量。 在小区中的用户总数可以远多于 K)。
假定所有用户的信道在频率上都是平坦衰落, 用户 的信道矩阵
Figure imgf000006_0001
的第 m个接收天线 之间的衰落系数。 由 sk来表示专用于用户 k的数据流的数量。 总是假定 sk<NR! 1 ≤ 。 首先将对用户 k的长度为 Sk的数据矢量 Xk乘以 NTxSk预 编码矩阵 Tk, 将其线性变换为长度为 Ντ的符号矢量, 以便从 Ντ个天线发 射。 然后, 将 Κ个用户的长度为 的符号矢量进行线性叠加, 将叠加后 的矢量从天线阵列发射到信道中。 这里, 总是假定 xk的元素是独立的, 并且以零均值和单位方差同一地分布(独立同分布)。于是, 总发射功 率由下式给出:
Figure imgf000006_0002
对于每一个用户 k, 接收到的信号矢量为:
Figure imgf000006_0003
其中 nk是具有零均值和方差为 σ2=Ν。/2的 AWGN过程的采样矢量。 每 一个用户 k通过将 yk与一个 skxNR滤波矩阵^相乘来产生 xk的估计值 , 如下式所示:
xk =Bkyk =Bk , τ,,χ,. +Bknk =BkH kTkxk +BkH k „x +Bknk (3) 在公式 (3)中,可以基于诸如 MMSE等各种标准来获得滤波矩阵 Bk。 根据公式 (3), 和 xk之间的最大互信息为:
4
Figure imgf000007_0001
其中 sinrk,s是 xk的第 s个元素的处理后信干噪比(¾), b ^ B r 的第 s列, 而 tk.s是 T的第 s列。 整个 MU- ΜΙΜ0系统的总的息于是等 于: ' c=∑ck (5) 下面, 将根据以上信道模型来设计根据本发明的多用 编码禾口 调度方法。为了清楚,将首先介绍在发射机处具有准确 csia 易研 的情形 (现有技术的情形), 然后针对具有不准确的 CSI的情 对本^: 明进行讨论。 利用准确 CSI的多用户预编码和调度 连续丽 SE (S-MMSE) 多用户预编码
如以上所提到的, 在本发明中, 由于其能够平衡千扰和噪声, 可 以采用匪 SE类多用户预编码算法(这里,噪声意味着由于 CSI差错所产 生的 CCI和 AWGN噪声)。 特别地, 将使用连续 MMSE ( S- MMSE) 算法, 这 是当每一个用户具有多于一个的接收天线时的 MMSE型算法的简单实 现。
匪 SE型算法的基本原理是根据 MMSE标准来找到最优顸编码矩阵 {Tk}和滤波矩阵 {Bk}的集合。
Figure imgf000007_0002
等式 (6)涉及优化问题, 其最优解的获得通常非常复杂。 而 S -醒 SE算法通过迭代运算提供了对该问题的简化的次优方案:
步骤 1 产生随机 skxNR矩阵来初始化每一个 Β-。
步骤 2 基于当前 {Bk}, 根据丽 SE标准来计算最优预编码矩阵 {TJ , 如下式所示: Γ,〜Γκ】=Η HS H (BHH ΗΒΗ+βΙ )- 其中,
以 )
Figure imgf000008_0001
步骤 3 基于如上所计算得到的 {1\}, 根据 MMSE标准来更新滤波 矩阵 {BJ, 如下式所示:
BK
Figure imgf000008_0002
步骤 4 重复步骤 2和 3, 直到 {TJ和 {BJ的变化的 F范数下降到预 设阈值之下, 或者迭代次数已经达到特定值为止。
步骤 5 以
Figure imgf000008_0003
阵 {TJ进行归一化。 多用户调度
Ν表示通信系统中的总用户数量。 调度器从 Ν个用户中选择用户子 集, 以进行多用户发射,并且还确定每一个所选用户的数据流的数量。 7(表示可能的调度结果。 Κ可以由三个部分来表示: 所选用户的数量 K( , 所选用户的索引集合 {nk(2 , k二 1〜K(7()} , 其中 l≤nk(7()≤N, 以及所选用户的数据流数量 {sk(?0, k=l~K(2()}。 调度器在 ?C的集合上 进行搜索, 并且根据特定的标准选择最优的一个, 由 ^来表示。 例如, 针对容量最大标准, 调度器根据以下等式来选择 ,
Figure imgf000008_0004
其中 调度器所要搜索的? C的集合, >Μ(κ ί (?ο是 s^)和 Ί τό 的第 s列, 其中 Bk(2() 和 Tk(?0是 7C中的第 k个用户的滤波和预编码矩 阵。 这里, 通过设置 K二 K(W, {sk} = {sk(?0}和 {Hk} = {ΗπΜ) , 根 3 据步骤 1到 5来获得 Bk(i0和 Tk ( 。 的大小取决于所使用的调度策略。 例如, 对于全搜索调度, 包括 的所有可能性。
一旦选择了 , 则通过预编码矩阵 { (ή^ι~^»的多用户预编码, 将 { (2^=1~^)}个数据流通过相同的时频资源传递到 )个用户。 根据本发明的利用不准确 CSI的多用户预编码和调度
用 表示在 BS处可得到的用户 k的不准确信道矩阵, 并且 ^=Wa— 表示用户 k的 CSI差错。 假定 { }中的元素是独立同分布的均 值为零, 方差为 52的随机变量。 { }的产生可能有多种因素, 例如反 馈量化, 反馈延时等。 还假定在发射机处可得到 2的值, 该值可以在 接收端通过诸如测量信道估计差错、 反馈差错和量化差错等各种手段 来获得, 然后由接收机反馈到发射机。
CCI估计辅助 S- MMSE预编码
对于不准确 CSI, 将等式 (3) 中的信道模型修改为如下所示: xk=Bk(Hk+Hk)†T,x,+Bknk (13) 对于具有给定 {TJ的滤波矩阵 {Bk}的优化, 可以将等式 (13) 重
(14)
Figure imgf000009_0001
,包括由于 CSI差错造成的 CCI 和 AWGN。 将7 近似为复高斯噪声的矢量, 则最优 {Bk}可以按如下方式 产生:
Figure imgf000009_0002
其中,
、 (a)
3] Π ")=R W κΤκχ KX"T"H k +σ I «I +σ2/
VV=1 (16)
Figure imgf000009_0003
在等式(16)中, (a)是通过将每个^ ^都近似为 1获得的, ved.A a ...aj-γ, 其中 是矩阵 的第 j列, "® "表示科罗内克积, 而
Figure imgf000010_0001
的协方差矩阵。
对于给定 {BJ的预编码矩阵 {Ί\}的优化, 以紧凑形式将等式 (13) 重写为:
χ=Β(Η +Η Jx+Bn =ΒΗ Γχ+ΒΗΤχ+Βη =ΒΗΤχ+μ (17) 中, =[ 1 Γ 2 Γ··· ^]Γ, (18)
Η =【 Η" ' . Ηχ τ]τ, (19) ?:^7^7"…?】7", (20) T= T 2 -TK], (21)
Figure imgf000010_0002
μ =ΒΗΤχ+Βη, (23) 而且, Β在等式 (9)中定义。 类似地, μ 是 CCI加噪声项, 包括 由于 CSI差错造成的 CCI和 AWGN。 另外, 将(11近似为复高斯噪声的矢量, 可以按以下公式来产生最优 :
Figure imgf000010_0003
Η)=ΕβΗΤχχΗΤΗΗ HBH)+a2trace(BBH)l
^ΡτΕβΗΗ ΗΒΗ) + a2trace(BB Η )/ (25)
= PTBRBH + a2trace{BBH)l 在等式(25)中, 通过以 ΡτΙ 来近似 ιν ·"来获得 (a), 并且 ^^/?Η)=Λ^2/ 是 的协方差矩阵, 可由信道状态信息误差的协方 差矩阵 { }计算得来。
由等式 (15) 和 (24) 来替换步骤 1〜5中的等式 (7) 和 (11), 可以获得根据本发明的 CCI估计辅助 S- MMSE预编码算法。
CCI估计辅助多用户调度
针对不准确 CSI将等式 (13) 中的信道模型重写为: x^BkH kxk +BkHk Tk.x„ +Βη k (26) 然后, 对于每一个用户 /模式子集 调度器通过将 Sin近似为复 斤噪声的矢量, 来估计容量, 如下式所示:
(16 ) 来
Figure imgf000011_0001
计算。 然后, CCI估计辅助调度算法根据以下标准来选择 。 7 =argmaxC (?) (28) 下面将结合附图来描述本发明的优选实施例。
图 1是根据本发明的多用户预编码和调度方法的流程图。
根据本发明, 在步骤 101 , 从用户设备向基站反馈信道状态信息
(该信道状态信息可能是不准确的, 其不准确性可能来自多种因素, 例如反馈量化, 反馈延时等) 以及信道状态信息误差的统计特性。 所 述信道状态信息为信道矩阵的估值, 所述信道状态信息误差的统计特 性为信道矩阵估值的误差矩阵的统计特性。 作为示例, 如上所示, 该 信道矩阵的估值可以是^, 信道状态信息误差的统计特性可以是协方 差矩阵 在步骤 103 , 基站根据所反馈的信道状态信息以及信道状 态信息误差的统计特性, 生成多用户预编码矩阵和调度方案, 如以上 所提到的, 所述多用户预编码可以釆用 MMSE类算法, 而所述多用户调 度可以采用容量最大化标准。最后, 在步骤 105, 利用所生成的多用户 预编码矩阵和调度方案对用户数据进行多用户预编码和调度。
图 2是用于实现本发明的多用户预编码和调度方法的基站的方框 图。 如图 2所示, 所述基站包括接收装置 201、 多用户预编码矩阵和调 度方案生成装置 203和多用户预编码和调度装置 205。接收装置 201接收 从用户设备反馈的信道状态信息以及信道状态信息误差的统计特性。 多用户预编码矩阵和调度方案生成装置 203根据所反馈的信道状态信 息以及信道状态信息误差的统计特性, 生成多用户预编码矩阵和调度 方案。多用户预编码和调度装置 205利用所生成的多用户预编码矩阵和 调度方案对用户数据进行多用户预编码和调度。
图 3和 4是用于显示本发明方法与现有技术方法的性能比较的曲 线图。 在图 3和 4中, 将根据本发明的 CCI估计辅助 MU-MIM0策略与基于 贪婪调度策略的原始 S-MMSE和 MET (多用户固有模式传输)算法进行比 较。 这里, 在基站处采用了 4个发射天线, 每一个用户两个接收天线, 并且总用户数为 4。将信道矩阵 {Hk}中的元素建模为具有零均值和单位 方差的独立同分布的复高斯变量。 将 csi差错矩阵{ ^} 中的元素建模 为具有零均值和方差 52的独立同分布的复高斯白噪声。 在本发明中, 分别在图 3和图 4中将 2 设置为 0. 1和 0. 5。 伺时考虑 MMSE和非 MMSE接 收机。 如所看到的, 对于 MMSE和非 MMSE接收机, 本发明的方案比具有 贪婪调度的 MET和 S-匪 SE具有更好的性能, 特别是当 CSI差错较高时。
本发明具有以下优点:
1、 根据本发明, 当在发射机处使用不准确 CSI时 (这是实际中的 真实情形), 极大地改善了 MU-MIM0系统的性能。
2、 根据本发明, 由于仅在 BS处带来了少量附加复杂度, 而在 UE (用户设备) 处几乎未带来附加复杂度。
3、 本发明对于诸如信道估计差错、 量化差错和反馈差错等不同 CSI差错原因而言具有灵活度, 并且可以用于诸如基于探测信号 (sounding)和用户反馈的各种薦 -MIM0机制。
总之, 由于其极有可能提高小区吞吐量, MU- MIM0操作是许多宽 带无线通信标准例如 IEEE 802. 16和 3GPP LTE标准中的热点, 而在发射 机处的 CSI差错是限制 MU-MIM0在实际系统中应用的主要实际问题之 一。 本发明以在 BS处的少量附加复杂度为代价给这一问题提供了一个 有效的结局方案, 并能带来明显的优势。
尽管以上已经结合本发明的优选实施例示出了本发明, 但是本领 域的技术人员将会理解, 在不脱离本发明的精神和范围的情况下, 可 以对本发明进行各种修改、 替换和改变。 因此, 本发明不应由上述实 施例来限定, 而应由所附权利要求及其等价物来限定。

Claims

权 利 要 求
1、 一种多用户预编码和调度方法, 包括:
从用户设备向基站反馈信道状态信息以及信道状态信息误差的 统计特性;
基站根据所反馈的信道状态信息以及信道状态信息误差的统计 特性, 生成多用户预编码矩阵和调度方案; 以及
利用所生成的多用户预编码矩阵和调度方案对用户数据进行多 用户预编码和调度。
2、 根据权利要求 1所述的方法, 其特征在于所述信道状态信息为 信道矩阵的估值。
3、 根据权利要求 1所述的方法, 其特征在于所述信道状态信息误 差的统计特性为信道矩阵估值的误差的协方差矩阵。
4、 根据权利要求 1所述的方法, 其特征在于所述多用户预编码釆 用最小均方误差匪 SE类算法。
5、 根据权利要求 4所述的方法, 其特征在于所述 M1SE类算法为连 续 MMSE算法。
6、 根据权利要求 1所述的方法, 其特征在于所述多用户调度采用 容量最大标准。
7、 根据权利要求 1所述的方法, 其特征在于所述信道状态信息误 差的统计特性通过在接收端测量信道估计误差、 反馈误差或量化误差 来获得, 然后由接收机反馈到发送机。
8、 根据权利要求 1所述的方法, 其特征在于所述方法用于多用户 多输入多输出 MU- MIM0通信系统。
9、 一种基站, 包括:
接收装置, 接收从用户设备反馈的信道状态信息以及信道状态信 息误差的统计特性;
多用户预编码矩阵和调度方案生成装置, 根据所反馈的信道状态 信息以及信道状态信息误差的统计特性, 生成多用户预编码矩阵和调 度方案; 以及 多用户预编码和调度装置, 利用所生成的多用户预编码矩阵和调 度方案对用户数据进行多用户预编码和调度。
10、 根据权利要求 9所述的基站, 其特征在于所述信道状态信息 为信道矩阵的估值。
11、 根据权利要求 9所述的基站, 其特征在于所述信道状态信息 误差的统计特性为信道矩阵估值误差的协方差矩阵。
12、 根据权利要求 9所述的基站, 其特征在于所述多用户预编码 采用最小均方误差 MMSE类算法。
13、 根据权利要求 12所述的基站, 其特征在于所述匪 SE类算法为 连续讓 SE算法。
14、 根据权利要求 9所述的基站, 其特征在于所述多用户调度采 用容量最大标准。
15、 根据权利要求 9所述的基站, 其特征在于所述信道状态信息 误差的统计特性通过在接收端测量信道估计误差、 反馈误差或量化误 差来获得, 然后由接收机反馈到发送机。
16、 根据权利要求 9所述的基站, 其特征在于所述基站用于多用 户多输入多输出 MU-MIM0通信系统。
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