WO2015085820A1 - 一种导频排布确定方法及基站 - Google Patents

一种导频排布确定方法及基站 Download PDF

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WO2015085820A1
WO2015085820A1 PCT/CN2014/087947 CN2014087947W WO2015085820A1 WO 2015085820 A1 WO2015085820 A1 WO 2015085820A1 CN 2014087947 W CN2014087947 W CN 2014087947W WO 2015085820 A1 WO2015085820 A1 WO 2015085820A1
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Prior art keywords
pilot
pilot arrangement
arrangement
subcarriers
base station
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PCT/CN2014/087947
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English (en)
French (fr)
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戚晨皓
吴艺群
张舜卿
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华为技术有限公司
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Priority to EP14870031.3A priority Critical patent/EP3068065B1/en
Publication of WO2015085820A1 publication Critical patent/WO2015085820A1/zh
Priority to US15/178,405 priority patent/US9794041B2/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0014—Three-dimensional division
    • H04L5/0023—Time-frequency-space
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0037—Inter-user or inter-terminal allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices

Definitions

  • the present application relates to the field of communications technologies, and in particular, to a pilot arrangement determining method and a base station.
  • Multi-Input Multi-Output (MIMO) technology can achieve considerable diversity gain and multiplexing gain, thereby improving the reliability and transmission rate of wireless communication systems.
  • the technology has been widely used in various wireless communication systems, such as a Long Term Evolution (LTE) system, a Worldwide Interoperability for Microwave Access (WiMax) system, and the like.
  • LTE Long Term Evolution
  • WiMax Worldwide Interoperability for Microwave Access
  • 3GPP 3rd Generation Partnership Project
  • 3GPP 3rd Generation Partnership Project
  • FIG. 1 is a schematic diagram of multipath transmission of a MIMO system.
  • the number of pilots is usually increased, but this will reduce the spectrum utilization and limit the performance of the MIMO system.
  • LS Least Squares
  • the number of pilots is greater than the maximum delay spread sample value of the channel, which usually requires a large pilot overhead.
  • CIR channel impulse response
  • CS Compressed Sensing
  • the commonly used pilot arrangement determination scheme has the following two types:
  • the prior art 1 is an equally spaced pilot arrangement, which is commonly used in LTE systems, and the pilot arrangement is evenly distributed in the frequency domain and the time domain.
  • many research literatures show that the pilot arrangement determined by this method for sparse channels is not optimized.
  • the second technique of the prior art is a random pilot arrangement. For example, for a MIMO system with 2 transmit antennas and 256 Orthogonal Frequency Division Multiplexing (OFDM) subcarriers, if each transmit antenna uses 12 subcarriers as pilot subcarriers, then 256 are used. 24 randomly available OFDM subcarriers, and 12 of the selected 24 are allocated to the transmitting antenna 1, and the remaining 12 are allocated to the transmitting antenna 2, so that the pilot subcarriers of different transmitting antennas are orthogonal to each other. Two transmitting antennas can simultaneously transmit data, and can effectively distinguish signals transmitted by two different antennas when performing sparse channel estimation at the receiving end. However, this approach still does not guarantee that the optimized pilot arrangement is determined.
  • OFDM Orthogonal Frequency Division Multiplexing
  • the embodiment of the present application provides a method for determining a pilot arrangement and a base station, which are used to solve the problem that the existing pilot allocation determination method cannot determine an optimized pilot arrangement for a sparse channel of the MIMO system.
  • a method for determining a pilot arrangement including:
  • the selected set of subcarriers G is selected.
  • the first optimized pilot arrangement P1 specifically includes:
  • the pilot number of subcarriers are taken out from the G each time in an arrangement or a random manner as an initial pilot arrangement;
  • the initial pilot that minimizes the function value of the objective function is arranged as the P1.
  • the cyclic shifting of the P1 includes:
  • the P1 can be cyclically shifted by the following formula:
  • Pi is a pilot arrangement obtained by cyclically shifting the ith antenna
  • N is the number of elements in the original subcarrier set.
  • the pilots of any two transmit antennas are arranged in The frequency domain is orthogonal.
  • a base station including:
  • a transmitting antenna for transmitting a pilot arrangement of each of the transmitting antennas obtained by the processing unit.
  • the processing unit is configured to select a first optimized pilot arrangement P1 from the available set of subcarriers G, specifically for:
  • the pilot number of subcarriers are taken out from the G each time in an arrangement or a random manner as an initial pilot arrangement;
  • the initial pilot that minimizes the function value of the objective function is arranged as the P1.
  • the processing unit is configured to cyclically shift the P1, specifically:
  • the P1 can be cyclically shifted by the following formula:
  • Pi is a pilot arrangement obtained by cyclically shifting the ith antenna
  • N is the number of elements in the original subcarrier set.
  • the pilots of any two transmit antennas are arranged
  • the frequency domain is orthogonal.
  • the solution has strong versatility and flexibility, is simple, fast, and has low complexity, and can be arranged in the first optimized pilot. Based on the pilot arrangement of the subsequent antennas, it is ensured that the optimized pilot arrangement is determined for the sparse channels of the MIMO system.
  • FIG. 1 is a schematic diagram of multipath transmission of a MIMO system in the prior art
  • FIG. 2 is a flowchart of a method for determining a pilot arrangement in an embodiment of the present application
  • FIG. 3 is a schematic diagram of comparison of pilot arrangements for a sparse channel for a MIMO system determined by using the prior art 2 and the embodiment of the present application;
  • FIG. 4 is a schematic diagram of a method for determining a pilot arrangement in the embodiment of the present application, which is compared with the prior art 1 and the prior art;
  • FIG. 5 is a schematic structural diagram of a first type of base station according to an embodiment of the present application.
  • FIG. 6 is a schematic structural diagram of a second base station according to an embodiment of the present application.
  • the existing pilot allocation determination method cannot determine the optimization for the sparse channel of the MIMO system.
  • the problem of the pilot arrangement is as follows.
  • the embodiment of the present application provides a method for determining a pilot arrangement. The process of the method is shown in FIG. 2, and the steps are as follows:
  • the base station has N t root transmit antennas, and within the coverage of the base station, there are N u mobile stations, and each mobile station has one antenna, thereby constructing a multi-user of N t ⁇ N u .
  • MIMO system There are many propagation paths from the base station to the mobile station. In addition to the direct path and several reflection paths, the multipath propagation effect is significant. It is assumed that the system uses OFDM for signal transmission, the mobile station uses sparse channel estimation, and the number of OFDM subcarriers is N, which constitutes a set of original subcarriers.
  • the number of edge subcarriers and DC subcarriers totals N 0 , and NN 0 available subcarriers constitute a set of available subcarriers.
  • Selecting a first optimized pilot arrangement P 1 ⁇ k 1 , k 2 , . . . , k m ⁇ from the set of available subcarriers, indicating that the k 1 , k 2 , . . . , k m subcarriers are Used to transmit pilot symbols, 1 ⁇ k 1 ⁇ k 2 ⁇ ... ⁇ k m ⁇ N.
  • the scheme has strong versatility and flexibility, is simple, fast, and has low complexity, and can obtain the pilot arrangement of the subsequent antennas on the basis of the first optimized pilot arrangement, ensuring a sparse channel for the MIMO system. All that is determined is the optimized pilot arrangement.
  • the first optimized pilot arrangement P1 is selected from the available subcarrier sets G in the foregoing S20, and specifically includes:
  • the number of pilots is taken out of G each time in a permutation or random manner.
  • the destination subcarrier is arranged as the initial pilot;
  • the initial pilot that minimizes the function value of the objective function is arranged as P1.
  • the OFDM channel estimation problem can be expressed as:
  • the superscript "T" indicates vector transposition.
  • the line numbers of F are k 1 , k 2 , . . . , m m and the first L columns of F, forming a D ⁇ submatrix F M ⁇ of M ⁇ L dimensions.
  • A(m) represents the mth row of the matrix A
  • ⁇ a, b> represents the inner product of the vector a and the vector b.
  • the power of each pilot symbol is the same, ie:
  • the optimal pilot arrangement that is, the pilot arrangement for minimizing the cross-correlation of matrix A is:
  • the cyclic shifting of P1 in the foregoing S21 includes:
  • P1 can be cyclically shifted by the following formula:
  • Pi is a pilot arrangement obtained by cyclically shifting the ith antenna
  • N is the number of elements in the original subcarrier set.
  • This operation can be quickly implemented by a cyclic shift register.
  • the method in the present application makes the pilots of all transmitting antennas of the base station orthogonal in the frequency domain, and any mobile station can effectively distinguish when receiving signals simultaneously transmitted by different base station antennas.
  • FIG. 3 is a schematic diagram showing the comparison of the pilot arrangement of the sparse channel for the MIMO system determined by the prior art 2 and the embodiment of the present application.
  • the edge subcarriers and the DC subcarriers on both sides are removed, and among the remaining available OFDM subcarriers, the optimal pilot arrangement suitable for the sparse channel is determined.
  • Figure 3 The half is the uniform pilot arrangement obtained by the prior art 2, that is, the equally spaced pilot arrangements are used, and the pilots of different transmit antennas are orthogonal to each other in the frequency domain; and the lower half of FIG. 3 is the embodiment of the present application.
  • the pilot arrangement determined in the medium is not necessarily equally spaced, and the pilot arrangement of the base station transmitting antenna 2 can be obtained by cyclically shifting the pilot arrangement of the base station transmitting antenna 1.
  • the base station has four transmit antennas, and within the coverage of the base station, there are two mobile stations, and each mobile station has one antenna, thereby constructing A 4 x 2 multi-user MIMO system.
  • the number of OFDM subcarriers is 1024, wherein the number of side edge subcarriers and DC subcarriers is 421, the number of pilots is 24; the cyclic prefix length of OFDM is 64, and the channel impulse response is 60 after sampling.
  • the preferred pilot arrangement for the two transmit antennas is denoted as p 2 .
  • p 2 The preferred pilot arrangement for the two transmit antennas.
  • the last three pilot subcarriers of p 1 and p 2 are very close, and then the shift of p 1 is continued, and the obtained pilots are arranged as ⁇ 211, 225, 228, 236, 252, 312.
  • p 3 ⁇ 211, 212, 213, 238, 280, 336, 345, 363, 375, 390, 491, 501, 561, 568, 589, 611, 666, 716, 752, 756, 797, 801, 809, 810 ⁇ , assigned to the third transmit antenna of the base station
  • p 4 ⁇ 214, 215, 216, 217, 252, 267, 274, 303, 392, 403, 466, 478, 489, 508, 580 , 628, 641, 676, 690, 706, 781, 792, 807, 808 ⁇ , assigned to the fourth transmit antenna of the base station.
  • any mobile station (mobile station 1 or mobile station 2)
  • signals from the base station transmit antenna 1, transmit antenna 2, transmit antenna 3, and transmit antenna 4 are simultaneously received, since the four transmit antennas are respectively orthogonal in the frequency domain.
  • the pilots are arranged p 1 , p 2 , p 3 and p 4 , the channel parameters of the transmitting antenna 1 to the mobile station can be estimated using p 1 , and the channel parameters of the transmitting antenna 2 to the mobile station can be estimated using p 2 , using p 3 transmit antennas 3 estimated channel parameters to the mobile station, using the estimate of the transmit antenna 4 p 4 to the mobile station channel parameters.
  • the method for determining the pilot arrangement of the sparse channel of the MIMO system in the embodiment of the present application can improve the Mean Square Error (MSE) performance of the sparse channel estimation of the MIMO system.
  • MSE Mean Square Error
  • the method for determining the pilot arrangement in the embodiment of the present application is compared with the two methods in the background.
  • the pilot arrangement of the transmitting antenna 2 Q 2 ⁇ 211, 237, 263, 289, 315, 341, 367, 393, 419, 445,471,497,523,549,575,601,627,653,679,705,731,757,783,809 ⁇
  • the pilot arrangement of the transmitting antenna 3 Q 3 ⁇ 212, 238, 264, 290 , 316,342,368,394,420,446,472,498,524,550,576,602,628,654,680,706,732,758,784,810 ⁇
  • pilot arrangement of the transmitting antenna 4 Q 4 ⁇ 213,239,265,291,3
  • 96 subcarriers are randomly selected from 603 available subcarriers, and 24 subcarriers are sequentially selected as the pilot arrangement of the transmitting antenna 1, the transmitting antenna 2, the transmitting antenna 3, and the transmitting antenna 4, respectively.
  • R 1 , R 2 , R 3 and R 4 ensure that there is no overlap between the four sets of pilot arrangements, and then substitute the objective function to obtain g(R 1 ), g(R 2 ), g(R 3 ). And g(R 4 ). Repeat the above pilot design steps 1000 times, and obtain the objective functions after 1000 times of averaging.
  • the channel is sparse, that is, the L taps of the channel are mostly zero and only a few are non-zero.
  • the number of multipaths of the channel is 5.
  • the mainstream OMP algorithm is used for sparse channel estimation.
  • the channel is randomly generated 10,000 times, and the average of 10,000 results is averaged.
  • channel estimation it is assumed that the number of non-zero taps of the channel is unknown, the position of the non-zero tap is unknown, and the value of the non-zero tap coefficient is unknown.
  • the MSE performance of the randomly generated pilot arrangement is finally averaged 1000 times.
  • the solutions of the present application, the prior art 1 and the prior art 2 are compared under the same channel parameter conditions.
  • the mobile station uses the pilots from the transmit antenna 1, the transmit antenna 2, the transmit antenna 3, and the transmit antenna 4 to perform four link-independent sparse channel estimations, and average the MSEs of the four channels.
  • the embodiment of the present application provides a base station, and the structure of the base station is as shown in FIG. 5, and includes:
  • the transmitting antenna 51 is configured to transmit a pilot arrangement of each transmitting antenna obtained by the processing unit.
  • the processing unit 50 is configured to select the first optimized pilot arrangement P1 from the available set of subcarriers G, specifically for:
  • the number of pilot subcarriers is extracted from the G in a permutation combination or in a random manner as an initial pilot arrangement;
  • the initial pilot that minimizes the function value of the objective function is arranged as P1.
  • the processing unit 50 is configured to perform cyclic shift on P1, specifically for:
  • P1 can be cyclically shifted by the following formula:
  • Pi is a pilot arrangement obtained by cyclically shifting the ith antenna
  • N is the number of elements in the original subcarrier set.
  • the pilots of any two transmit antennas are orthogonal in the frequency domain.
  • the embodiment of the present application provides a base station, and the structure of the base station is as shown in FIG. 6, and includes:
  • the transceiver 61 is configured to transmit a pilot arrangement of each of the transmitting antennas obtained by the processing unit.
  • the processor 60 and the transceiver 61 are connected by a bus.
  • the processor 60 is configured to select a first optimized pilot arrangement P1 from the available set of subcarriers G, specifically for:
  • the number of pilot subcarriers is extracted from the G in a permutation combination or in a random manner as an initial pilot arrangement;
  • the initial pilot that minimizes the function value of the objective function is arranged as P1.
  • the processor 60 is configured to perform cyclic shift on P1, specifically for:
  • P1 can be cyclically shifted by the following formula:
  • Pi is a pilot arrangement obtained by cyclically shifting the ith antenna
  • N is the number of elements in the original subcarrier set.
  • the pilots of any two transmit antennas are orthogonal in the frequency domain.

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Abstract

本申请公开了一种导频排布确定方法及基站，该方法包括：S1、从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；S2、对所述P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；令G1＝G1-Pi，i＝i+1，重复执行S2，直到i等于发射天线的个数。该方案确保了针对MIMO系统的稀疏信道确定出的都是优化导频排布。

Description

一种导频排布确定方法及基站
本申请要求在2013年12月12日提交中国专利局、申请号为201310687413.7、发明名称为“一种导频排布确定方法及基站”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及通信技术领域，尤指一种导频排布确定方法及基站。
背景技术
多输入多输出(Multi-Input Multi-Output，MIMO)技术能获得可观的分集增益和复用增益，从而提高无线通信系统的可靠性和传输速率。该技术目前已被广泛应用于各种无线通信系统，例如长期演进(Long Term Evolution，LTE)系统、全球微波互联接入(Worldwide Interoperability for Microwave Access，WiMax)系统等。然而，随着发射端和接收端天线数目的增加，未知的信道数目也越来越多，例如，第三代移动通信标准化伙伴项目(3rd Generation Partnership Project，3GPP)版本(Release)11支持下行8×8的MIMO架构，接收端在进行信号解调前要获取8×8＝64条信道的信道状态信息(Channel State Information，CSI)，若发射端还需进行MIMO波束成型，接收端还要将CSI反馈给发射端，因此，CSI的准确程度将直接决定MIMO系统的性能。图1为MIMO系统多径传输示意图。
为提高CSI的准确性，通常会增加导频数目，但这样会降低频谱利用率，反而限制MIMO系统性能的提升。对于最小二乘(Least Squares，LS)信道估计，导频数目要大于信道的最大时延扩展采样值，通常需要较大的导频开销。针对该问题，提出了稀疏信道估计(Sparse Channel Estimation)，采用稀疏恢复的思想对信道冲击响应(Channel Impulse Response，CIR)进行重建，能充分发掘无线信道的稀疏性，发挥压缩感知(Compressed Sensing，CS)信 号处理技术的优势。与LS信道估计相比，稀疏信道估计能显著降低导频开销，提高频谱利用率。
为提高稀疏信道估计性能，需要确定稀疏信道的最优导频排布。目前，常用的导频排布确定方案有如下两种：
现有技术一为等间隔分布的导频排布方式，这种方式常用于LTE系统，导频排布在频率域和时间域上均匀分布。但是很多研究文献表明，该方式针对稀疏信道确定出的导频排布并不是优化的。
现有技术二为随机的导频排布方式。例如，对于2根发射天线、256个可用正交频分复用(Orthogonal Frequency Division Multiplexing，OFDM)子载波的MIMO系统，若每根发射天线采用12个子载波作为导频子载波，则从256个可用OFDM子载波中随机选取24个，再从选中的24个中任选12个分配给发射天线1，剩下12个分配给发射天线2，这样，不同发射天线的导频子载波相互正交，2根发射天线可同时发送数据，在接收端进行稀疏信道估计时能有效区分2根不同天线发射的信号。但是，这种方式仍然无法保证确定出的是优化导频排布。
发明内容
本申请实施例提供一种导频排布确定方法及基站，用以解决现有导频排布确定方法不能针对MIMO系统的稀疏信道确定出优化导频排布的问题。
第一方面，提供一种导频排布确定方法，包括：
S1、从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；
S2、对所述P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；
令G1＝G1-Pi，i＝i+1，重复执行S2，直到i等于发射天线的个数。
结合第一方面，在第一种可能的实现方式中，从可用子载波集合G中选 取第一优化导频排布P1，具体包括：
确定导频数目后，以排列组合方式或者随机方式每次从所述G中取出所述导频数目的子载波作为初始导频排布；
将选取的每个初始导频排布代入目标函数中；
使得所述目标函数的函数值最小的初始导频排布为所述P1。
结合第一方面或者第一方面的第一种可能的实现方式，在第二种可能的实现方式中，对所述P1进行循环移位，具体包括：
可通过下列公式对所述P1进行循环移位：
Pi＝(P1+i-1)mod N；
其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
结合第一方面、第一方面的第一种可能的实现方式或者第一方面的第二种可能的实现方式，在第三种可能的实现方式中，任意两根发射天线的导频排布在频域正交。
第二方面，提供一种基站，包括：
处理单元，用于从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；对所述P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；令G1＝G1-Pi，i＝i+1，重复对所述P1进行循环移位，直到i等于发射天线的个数；
发射天线，用于发射所述处理单元得到的每根发射天线的导频排布。
结合第二方面，在第一种可能的实现方式中，所述处理单元，用于从可用子载波集合G中选取第一优化导频排布P1，具体用于：
确定导频数目后，以排列组合方式或者随机方式每次从所述G中取出所述导频数目的子载波作为初始导频排布；
将选取的每个初始导频排布代入目标函数中；
使得所述目标函数的函数值最小的初始导频排布为所述P1。
结合第二方面或者第二方面的第一种可能的实现方式，在第二种可能的实现方式中，所述处理单元，用于对所述P1进行循环移位，具体用于：
可通过下列公式对所述P1进行循环移位：
Pi＝(P1+i-1)mod N；
其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
结合第二方面、第二方面的第一种可能的实现方式或者第二方面的第二种可能的实现方式，在第三种可能的实现方式中，任意两根发射天线的导频排布在频域正交。
根据第一方面提供的导频排布确定方法或者第二方面提供的基站，该方案具有很强的通用性和灵活性，简单、快速、复杂度低，并且可以在第一优化导频排布的基础上得到后续天线的导频排布，确保了针对MIMO系统的稀疏信道确定出的都是优化导频排布。
附图说明
图1为现有技术中MIMO系统多径传输示意图；
图2为本申请实施例中导频排布确定方法的流程图；
图3为采用现有技术二和本申请实施例确定的针对MIMO系统的稀疏信道的导频排布的对比示意图；
图4为本申请实施例中导频排布确定方法与现有技术一、现有技术二两种方案进行对比的示意图；
图5为本申请实施例中第一种基站的结构示意图；
图6为本申请实施例中第二种基站的结构示意图。
具体实施方式
针对现有导频排布确定方法不能针对MIMO系统的稀疏信道确定出优化 导频排布的问题，本申请实施例提供一种导频排布确定方法，该方法的流程如图2所示，执行步骤如下：
S20：从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1。
如图1所示，基站有Nt根发射天线，在基站覆盖范围内，有Nu个移动台，每个移动台均有1根天线，由此构建了一个Nt×Nu的多用户MIMO系统。从基站到移动台的传播路径有多条，除了直达径还有若干反射径，多径传播效应显著。假设该系统采用OFDM进行信号传输，移动台采用稀疏信道估计，OFDM子载波数目为N，组成原始子载波集合。边缘子载波和直流子载波数目共计N0，N-N0个可用子载波构成可用子载波集合。从可用子载波集合中选取第一优化导频排布P1＝{k1，k2，...，km}，表示第k1，k2，...，km号子载波被用于传输导频符号，1≤k1＜k2＜...＜km≤N。
选出P1后，要将G与P1做差集，从G中除去P1，得到G1。
S21：对P1进行循环移位，并判断移位后得到的Pi是否为G1的子集，若是，执行S22；否则，执行S23。
S22：Pi作为第i根发射天线的导频排布，执行S24。
S23：在G1中选取Pi，作为第i根发射天线的导频排布，执行S24。
S24：令G1＝G1-Pi，i＝i+1，i为大于或等于2的自然数，判断i是否等于发射天线的个数，若是，执行S25；否则，执行S21。
每次选出Pi后，都需要更新G1，执行G1＝G1-Pi。
S25：流程结束。
该方案具有很强的通用性和灵活性，简单、快速、复杂度低，并且可以在第一优化导频排布的基础上得到后续天线的导频排布，确保了针对MIMO系统的稀疏信道确定出的都是优化导频排布。
具体的，上述S20中的从可用子载波集合G中选取第一优化导频排布P1，具体包括：
确定导频数目后，以排列组合方式或者随机方式每次从G中取出导频数 目的子载波作为初始导频排布；
将选取的每个初始导频排布代入目标函数中；
使得目标函数的函数值最小的初始导频排布为P1。
若导频数目为M，发射天线发送的导频符号为X(k1)，X(k2)，...，X(kM)，接收到的导频符号记为Y(k1)，Y(k2)，...，Y(kM)，则OFDM信道估计问题可表示为：
Figure PCTCN2014087947-appb-000001
其中，h＝[h(1)，h(2)，…，h(L)]T为等效的离散信道冲击响应函数，长度为L。上标“T”表示向量转置。η＝[η(1)，η(2)，…，η(M)]T为噪声向量，其每一个元素独立同分布，满足均值为0、方差为σ2的复高斯分布。对于标准的N维DFT方阵F，取F的行号为k1，k2，...，km的M行和F的前L列，构成M×L维的DFT子矩阵FM×L。设y＝[Y(k1)，Y(k2)，…，Y(kM)]T，X＝diag{X(k1)，X(k2)，…，X(kM)}为由发射导频符号X(k1)，X(k2)，...，X(kM)构成的对角阵，并设方阵X与FM×L的乘积为A＝X·FM×L(A也称为观测矩阵)，则可将式(1)进一步写为：
y＝A·h+η。
h＝[h(1)，h(2)，…，h(L)]T是稀疏的，即L个元素中，大多数为零，而仅有少数非零。因此，信道估计问题本质上是在噪声项η未知的情况下，由已知的y和A来估计h，并充分利用h稀疏这一先验信息。若导频排布为p，一旦p确定，则FM×L也确定了，相应的A也就确定了。
定义矩阵A的互相关为：
Figure PCTCN2014087947-appb-000002
其中，A(m)表示矩阵A的第m行，<a，b>表示向量a和向量b的内积。通常每个导频符号的功率相同，即：
|X(k1)|2＝|X(k2)|2＝…＝|X(kM)|2＝W；
则目标函数：
Figure PCTCN2014087947-appb-000003
最优的导频排布即最小化矩阵A的互相关的导频排布为：
popt＝arg minpg(p)。
不难发现，若p偏移一个常数位置c，其目标函数的函数值并不发生改变，即：
Figure PCTCN2014087947-appb-000004
因此，若p为该参数条件下的一组优化导频排布，则对p进行循环移位以后得到的p+c也是优化导频排布，且两者对应的目标函数的函数值相同，即g(p)＝g(p+c)。
具体的，上述S21中的对P1进行循环移位，具体包括：
可通过下列公式对P1进行循环移位：
Pi＝(P1+i-1)mod N；
其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
该操作可通过循环移位寄存器快速实现。本申请中的方法使基站所有发射天线的导频在频域正交，任一移动台在收到不同基站天线同时发送的信号时，能有效进行区分。
图3给出了采用现有技术二和本申请实施例确定的针对MIMO系统的稀疏信道的导频排布的对比示意图。除去两侧的边缘子载波和直流子载波，在剩余可用的OFDM子载波中，确定适用于稀疏信道的最优导频排布。图3上 半部分为采用现有技术二得到的均匀导频排布，即采用等间隔的导频排布，不同发射天线的导频在频域相互正交；而图3下半部分为本申请实施例中确定的导频排布，不一定等间隔，通过对基站发射天线1的导频排布循环移位即可获得基站发射天线2的导频排布。
下面以一个具体实例说明本申请中导频排布确定方法，假设基站有4根发射天线，在基站覆盖范围内，有2个移动台，每个移动台均有1根天线，由此构建了一个4×2的多用户MIMO系统。OFDM子载波个数为1024，其中两侧边缘子载波和直流子载波的个数共计421，导频数目为24；OFDM的循环前缀长度64，信道冲击响应经过采样以后长度为60。除去OFDM直流子载波和边缘子载波，由603个可用子载波构成可用子载波集合G＝{209，210，...，510，511，513，514，...811，812}，假设获取的第一优化导频排布p1＝{209，223，226，234，250，310，348，382，396，420，456，469，542，581，590，638，656，710，740，766，798，802，804，811}，将p1作为基站第1根发射天线的导频排布，第2根发射天线的导频排布p2可通过对p1进行循环移位获得pi′＝(p1+i-1)mod 1024＝(kM+i-1)mod 1024，当i＝1时，仍然为p1，当i＝2，可计算得到p2′＝{210，224，227，235，251，311，349，383，397，421，457，470，543，582，591，639，657，711，741，767，799，803，805，812}，作为第二根发射天线的优选导频排布，记为p2。但同时也发现，p1和p2的最后3个导频子载波十分接近，再继续对p1进行移位，得到的导频排布为{211，225，228，236，252，312，350，384，398，422，458，471，544，583，592，640，658，712，742，768，800，804，806，813}，其中，804在p1中已经使用过，813并不是可用子载波集合中的子载波，所以无法通过循环移位获得基站第3根和第4根发射天线的导频排布。于是，重新选取p3＝{211，212，213，238，280，336，345，363，375，390，491，501，561，568，589，611，666，716，752，756，797，801，809，810}，分配给基站第3根发射天线，将p4＝{214，215，216，217，252，267，274，303，392，403，466，478，489，508，580， 628，641，676，690，706，781，792，807，808}，分配给基站第4根发射天线。对于任一移动台(移动台1或移动台2)，同时收到来自基站发射天线1、发射天线2、发射天线3和发射天线4的信号，由于4根发射天线分别采用频域正交的导频排布p1、p2、p3和p4，可利用p1估计发射天线1至该移动台的信道参数，利用p2估计发射天线2至该移动台的信道参数，利用p3估计发射天线3至该移动台的信道参数，利用p4估计发射天线4至该移动台的信道参数。
本申请实施例中针对MIMO系统的稀疏信道的导频排布确定方法，能够提升MIMO系统的稀疏信道估计的均方误差(Mean Square Error，MSE)性能。
定义均方误差为：
Figure PCTCN2014087947-appb-000005
其中，
Figure PCTCN2014087947-appb-000006
为h的信道估计结果，||·||2表示向量的l2范数。
下面将本申请实施例中导频排布确定方法与背景技术中的两种方式进行对比。
继续沿用上例，将p1、p2、p3和p4分别代入目标函数，得到g(P1)＝g(P2)＝8.0233，g(P3)＝8.0291，g(P4)＝8.0667。
采用现有技术一的方案得到基站发射天线1的导频排布Q1＝{210，236，262，288，314，340，366，392，418，444，470，496，522，548，574，600，626，652，678，704，730，756，782，808}，发射天线2的导频排布Q2＝{211，237，263，289，315，341，367，393，419，445，471，497，523，549，575，601，627，653，679，705，731，757，783，809}，发射天线3的导频排布Q3＝{212，238，264，290，316，342，368，394，420，446，472，498，524，550，576，602，628，654，680，706，732，758，784，810}，发射天线4的导频排布Q4＝{213，239，265，291，317，343，369，395，421，447，473，499，525，551，577，603，629，655，681，707，733，759，785，811}，分别代入目标函数，得到g(Q1)＝g(Q2)＝g(Q3)＝g(Q4)＝21.8929。
采用现有技术二的方案，从603个可用子载波中随机选取96个子载波，从中依次任选24个子载波分别作为发射天线1、发射天线2、发射天线3和发射天线4的导频排布R1、R2、R3和R4，保证4组导频排布之间不存在任何重叠，然后分别代入目标函数，得到g(R1)、g(R2)、g(R3)和g(R4)。重复以上导频设计步骤1000次，得到经过1000次平均后的目标函数分别为
Figure PCTCN2014087947-appb-000007
Figure PCTCN2014087947-appb-000008
Figure PCTCN2014087947-appb-000009
Figure PCTCN2014087947-appb-000010
假设信道是稀疏的，即信道的L个抽头大多数为零而仅有少数非零。信道的多径数目为5。每次信道生成方式为，从L＝60个抽头里任选5个抽头作为非零抽头，这5个抽头位置上的抽头系数服从均值为0、方差为1的复高斯分布。对每一次随机生成的信道，均采用主流的OMP算法进行稀疏信道估计。信道随机生成10000次，最后对10000次结果取平均。在信道估计时，假设信道的非零抽头个数未知、非零抽头位置未知、非零抽头系数数值未知。对于背景技术中的第二种方案，最后要对随机生成的导频排布的MSE性能进行1000次平均。如图4所示，在相同的信道参数条件下对比了本申请方法、现有技术一和现有技术二的方案。移动台分别使用来自发射天线1、发射天线2、发射天线3和发射天线4的导频进行4条链路独立的稀疏信道估计，并对4条信道的MSE求平均。可看到，本申请实施例中的方法(采用P1、P2、P3和P4)优于现有技术二(采用R1、R2、R3和R4)，并且远优于现有技术一(采用Q1、Q2、Q3和Q4)，从而大幅提升了MIMO系统的稀疏信道估计的性能。
基于同一发明构思，本申请实施例提供一种基站，该基站的结构如图5所示，包括：
处理单元50，用于从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；对P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；令G1＝G1-Pi，i＝i+1，重复对P1进行循环移位，直到i等于发射天线的个数；
发射天线51，用于发射处理单元得到的每根发射天线的导频排布。
具体的，上述处理单元50，用于从可用子载波集合G中选取第一优化导频排布P1，具体用于：
确定导频数目后，以排列组合方式或者随机方式每次从G中取出导频数目的子载波作为初始导频排布；
将选取的每个初始导频排布代入目标函数中；
使得目标函数的函数值最小的初始导频排布为P1。
具体的，上述处理单元50，用于对P1进行循环移位，具体用于：
可通过下列公式对P1进行循环移位：
Pi＝(P1+i-1)mod N；
其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
具体的，任意两根发射天线的导频排布在频域正交。
基于同一发明构思，本申请实施例提供一种基站，该基站的结构如图6所示，包括：
处理器60，用于从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；对P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；令G1＝G1-Pi，i＝i+1，重复对P1进行循环移位，直到i等于发射天线的个数；
收发器61，用于发射所述处理单元得到的每根发射天线的导频排布。
上述处理器60与收发器61之间通过总线连接。
具体的，上述处理器60，用于从可用子载波集合G中选取第一优化导频排布P1，具体用于：
确定导频数目后，以排列组合方式或者随机方式每次从G中取出导频数目的子载波作为初始导频排布；
将选取的每个初始导频排布代入目标函数中；
使得目标函数的函数值最小的初始导频排布为P1。
具体的，上述处理器60，用于对P1进行循环移位，具体用于：
可通过下列公式对P1进行循环移位：
Pi＝(P1+i-1)mod N；
其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
具体的，任意两根发射天线的导频排布在频域正交。
显然，本领域的技术人员可以对本申请进行各种改动和变型而不脱离本申请的精神和范围。这样，倘若本申请的这些修改和变型属于本申请权利要求及其等同技术的范围之内，则本申请也意图包含这些改动和变型在内。

Claims (8)

  1. 一种导频排布确定方法，其特征在于，包括：
    S1、从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；
    S2、对所述P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；
    令G1＝G1-Pi，i＝i+1，重复执行S2，直到i等于发射天线的个数。
  2. 如权利要求1所述的方法，其特征在于，从可用子载波集合G中选取第一优化导频排布P1，具体包括：
    确定导频数目后，以排列组合方式或者随机方式每次从所述G中取出所述导频数目的子载波作为初始导频排布；
    将选取的每个初始导频排布代入目标函数中；
    使得所述目标函数的函数值最小的初始导频排布为所述P1。
  3. 如权利要求1-2任一所述的方法，其特征在于，对所述P1进行循环移位，具体包括：
    可通过下列公式对所述P1进行循环移位：
    Pi＝(P1+i-1)mod N；
    其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
  4. 如权利要求1-3任一所述的方法，其特征在于，任意两根发射天线的导频排布在频域正交。
  5. 一种基站，其特征在于，包括：
    处理单元，用于从可用子载波集合G中选取第一优化导频排布P1，作为第一根发射天线的导频排布，令G1＝G-P1；对所述P1进行循环移位，若移位后得到的Pi为G1的子集，则Pi作为第i根发射天线的导频排布，i为大于或 等于2的自然数；若移位后得到的Pi不是G1的子集，则在G1中选取Pi，作为第i根发射天线的导频排布；令G1＝G1-Pi，i＝i+1，重复对所述P1进行循环移位，直到i等于发射天线的个数；
    发射天线，用于发射所述处理单元得到的每根发射天线的导频排布。
  6. 如权利要求5所述的基站，其特征在于，所述处理单元，用于从可用子载波集合G中选取第一优化导频排布P1，具体用于：
    确定导频数目后，以排列组合方式或者随机方式每次从所述G中取出所述导频数目的子载波作为初始导频排布；
    将选取的每个初始导频排布代入目标函数中；
    使得所述目标函数的函数值最小的初始导频排布为所述P1。
  7. 如权利要求5-6任一所述的基站，其特征在于，所述处理单元，用于对所述P1进行循环移位，具体用于：
    可通过下列公式对所述P1进行循环移位：
    Pi＝(P1+i-1)mod N；
    其中，Pi为针对第i根天线进行循环移位后得到的导频排布，N为原始子载波集合中元素的个数。
  8. 如权利要求5-7任一所述的基站，其特征在于，任意两根发射天线的导频排布在频域正交。
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