WO2019153801A1 - 一种ofdm-im系统频偏估计方法 - Google Patents

一种ofdm-im系统频偏估计方法 Download PDF

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WO2019153801A1
WO2019153801A1 PCT/CN2018/112821 CN2018112821W WO2019153801A1 WO 2019153801 A1 WO2019153801 A1 WO 2019153801A1 CN 2018112821 W CN2018112821 W CN 2018112821W WO 2019153801 A1 WO2019153801 A1 WO 2019153801A1
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frequency offset
ofdm
subcarriers
subcarrier
sub
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PCT/CN2018/112821
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陈芳炯
杨智斌
刘靖
季飞
余华
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华南理工大学
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H04L27/266—Fine or fractional frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2657—Carrier synchronisation
    • H04L27/2659—Coarse or integer frequency offset determination and synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2669—Details of algorithms characterised by the domain of operation
    • H04L27/2672—Frequency domain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2675—Pilot or known symbols
    • 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
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H04L5/001—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT the frequencies being arranged in component carriers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0014—Carrier regulation
    • H04L2027/0024—Carrier regulation at the receiver end
    • H04L2027/0026—Correction of carrier offset
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier 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
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver

Definitions

  • the present invention relates to the field of OFDM, serial number modulation and digital communication and parameter estimation, and in particular to a frequency offset estimation method for an OFDM-IM system.
  • Orthogonal Frequency Division Multiplexing is a multi-carrier modulation technology used by many existing wireless communication systems. The most typical representative is the wireless LAN technology under the IEEE 802.11 standard. Fi and 4G LTE, the fourth-generation mobile communication system that is now in commercial use. OFDM has high spectrum utilization and data transmission rate, and can effectively resist channel frequency-domain selective fading and channel multipath by dividing the wideband signal into a series of narrow-band signals with near-flat fading and increasing the cyclic prefix. effect.
  • OFDM technology includes the following aspects: sensitive to frequency offset and phase noise. Power peak-to-average ratio (PAPR) is large; load algorithms and adaptive modulation techniques increase system complexity. The use of load algorithms and adaptive modulation techniques increases the complexity of the transmitter and receiver.
  • PAPR Power peak-to-average ratio
  • Orthogonal Frequency Division Multiplexing with Index Modulation (OFDM-IM) technology is a novel OFDM technology proposed in the past two years.
  • OFDM-IM draws on the idea of spatial domain modulation technology and uses the positional freedom of the activated subcarrier to carry part. To transmit information, the receiving end obtains this part of information by detecting the location of the activated subcarrier.
  • the OFDM-IM system has more performance advantages than the conventional OFDM system, and can also flexibly configure the spectrum rate of the system by selecting different numbers of activated subcarriers.
  • the subcarriers of the present invention employing OFDM-IM are partially activated. This means that in addition to the initially set null subcarriers, the energy of the inactive subcarriers can be utilized.
  • the present invention utilizes inactive subcarriers to optimize the estimation of Doppler shift.
  • the main idea is to use OFDM-IM null carrier to improve the performance of frequency offset estimation.
  • the number of subcarriers in the OFDM-IM system is N, and the system uses the MPSK modulation scheme. Except for the pilot, the guard interval, and the preset N null null subcarriers, the system includes multiple OFDM subblocks, and each subblock has N. A total of subcarriers, where N active is an activated subcarrier, the position and symbol of the pilot are known, and the position of the pre-set null subcarrier is known.
  • the invention provides a frequency offset estimation method for an OFDM-IM system, which comprises the following steps:
  • step 2 the sum of the energy of the null subcarriers is used as a cost function:
  • y is the discrete baseband received signal with frequency offset 0
  • ⁇ is the remaining normalized frequency offset
  • S N is the empty subcarrier set
  • f m is the mth column of the inverse Fourier transform matrix
  • ⁇ ( ⁇ ) Frequency offset matrix (.) H is the conjugate operation
  • T c is the sampling interval.
  • the signal z 1 compensated by the preliminary estimation of the ⁇ is specifically calculated as:
  • the position of the inactive subcarrier in the OFDM-IM system is estimated from the signal after the frequency offset compensation, and the subcarrier satisfying the following criteria is determined to be an inactive subcarrier:
  • the subsequent steps use up to N max subcarriers that meet the above criteria.
  • the estimated subcarriers are arranged in descending order of P side size.
  • the larger the subcarrier energy of the P side is assigned a larger weight, and the weight of each subcarrier constitutes a diagonal matrix W.
  • the energy of the estimated subcarriers is added to the cost function according to different weights, and the cost function is modified as:
  • the final estimate of ⁇ is obtained by one-dimensional search of ⁇ Final compensation signal
  • step S2 the position of the inactive subcarrier is estimated by power detection using the initially compensated signal.
  • step S3 the energy estimated to be an inactive subcarrier is added to the final cost function according to different weights.
  • the subcarriers of the present invention employing OFDM-IM are partially activated. This means that in addition to the initially set null subcarriers, the energy of the inactive subcarriers can be utilized.
  • the present invention utilizes inactive subcarriers to optimize the estimation of Doppler shift.
  • Figure 1 is a flow chart of the method of the present invention
  • Figure 2 and Figure 3 are different The trend of the mean square error as a function of signal to noise ratio.
  • the present invention provides an OFDM sequence modulation method based on multiple modes.
  • the number of subcarriers in the OFDM-IM system is 128, and the system uses the QPSK modulation method. Except for the pilot, guard interval and pre-set 4 null subcarriers, the system contains 28 OFDM sub-blocks, each sub-block has 4 sub-carriers, 3 of which are activated sub-carriers.
  • the position and symbol of the pilot are known, and the position of the pre-set empty subcarrier is known.
  • step 2 the sum of the energy of the null subcarriers is used as a cost function:
  • y is the discrete baseband received signal with frequency offset 0
  • ⁇ is the remaining normalized frequency offset
  • S N is the empty subcarrier set
  • f m is the mth column of the inverse Fourier transform matrix
  • ⁇ ( ⁇ ) Frequency offset matrix (.) H is the conjugate operation
  • T c is the sampling interval.
  • the criteria are:
  • the subsequent steps use up to 8 subcarriers that meet the above criteria.
  • the estimated subcarriers are arranged in descending order of P side size, and the larger the P side , the greater the weight of the subcarrier energy, and the subcarrier with the sequence number k
  • the weights of the respective subcarriers form a diagonal matrix W.
  • the energy of the estimated subcarriers is added to the cost function according to different weights, and the cost function is modified as:
  • the final estimate of ⁇ is obtained by one-dimensional search of ⁇ Final compensation signal
  • the mean square error is a measure of the performance of the above method. As shown in Fig. 2 and Fig. 3, the simulation results in the figure are from the top to the bottom of the method 123 respectively. The trend of the mean square error as a function of signal to noise ratio.
  • simulation results show that the performance of 2 is slightly better than that of 1,3, which is better than 1 and 2. At high signal-to-noise ratio, the performance advantage of 3 is more obvious. Simulation results verify the effectiveness of the method of the present invention.

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  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
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Abstract

本发明提供一种OFDM-IM系统频偏估计方法。该方法包括：S1、对于受到非均匀频偏的接收信号，使用两步方法进行初步的频偏补偿：(1)重采样及下变频；(2)剩余频偏ε的统一补偿。第(2)步中使用空子载波的能量之和作为代价函数，通过一维搜索得到ε的初步估计值，并进行初步补偿；S2、利用初步补偿的信号估计OFDM-IM系统中非激活子载波位置；S3、对估计的子载波赋予一定的权值，估计的子载波的能量按照不同的权重加入到代价函数中，通过对ε的一维搜索得到ε的最终估计值，并进行再次补偿。本发明采用OFDM-IM的子载波是部分激活的。这意味着除了初始设置的空子载波外，还有非激活的子载波的能量可以加以利用。因此，本发明利用非激活的子载波来优化多普勒频移的估计。

Description

一种OFDM-IM系统频偏估计方法 技术领域
本发明涉及OFDM、序号调制和数字通信和参数估计领域，特别涉及一种针对OFDM-IM系统的频偏估计方法。
背景技术
正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术是一种多载波调制技术，被现有的很多无线通信系统所采用，最典型的代表为在IEEE 802.11标准下的无线局域网技术Wi-Fi和现在已经投入商用的第四代移动通信系统4G LTE。OFDM具有较高的频谱利用率和数据传输速率，而且通过将宽带信号划分为一系列的近乎平坦衰落的窄带信号和增加循环前缀，能分别有效地对抗信道频域选择性衰落和信道的多径效应。
OFDM技术的不足之处包括以下方面：对频偏和相位噪声比较敏感。功率峰值与均值比(PAPR)大；负载算法和自适应调制技术会增加系统复杂度。负载算法和自适应调制技术的使用会增加发射机和接收机的复杂度。
序号调制(Orthogonal Frequency Division Multiplexing with Index Modulation,OFDM-IM)技术是近两年来提出的一种新颖的OFDM技术，OFDM-IM借鉴空域调制技术的思想，利用激活子载波的位置自由度来携带部分传输信息，接收端通过检测激活子载波的位置来获取这部分信息。OFDM-IM系统相对于传统OFDM系统更具有性能优势，并且还能通过选择不同的激活子载波个数灵活地配置系统的频谱率。
本发明采用OFDM-IM的子载波是部分激活的。这意味着除了初始设置的空子载波外，还有非激活的子载波的能量可以加以利用。因此，本发明利用非激活的子载波来优化多普勒频移的估计。
发明内容
本发明的目的是提供一种针对OFDM-IM系统的频偏估计方法。其主要思路是利用OFDM-IM空载波来改善频偏估计性能。本发明中，OFDM-IM系统子载波数为N，系统使用MPSK调制方式，除去导频、保护间隔以及预先设置的N null个空子载波外，系统含有多个OFDM子块，每个子块有N total个子载波，其中N active个为激活的子载波，导频的位置以及符号已知，预先设置的空子载波的位置已知。
本发明提供的一种针对OFDM-IM系统的频偏估计方法，包含以下的步骤：
S1、对于受到非均匀频偏的接收信号，使用两步方法进行初步的频偏补偿：1、重采样及下变频，得到离散基带接收信号z＝Γ(ε)y；2、剩余频偏的统一补偿。第2步中使用空子载波的能量之和作为代价函数：
Figure PCTCN2018112821-appb-000001
其中，y为频偏为0时的离散基带接收信号，ε为剩余的归一化频偏，S N为空子载波集合，f m为傅里叶逆变换矩阵的第m列，Γ(ε)为频偏矩阵
Figure PCTCN2018112821-appb-000002
(.) H为取共轭操作，T c为采样间隔。
通过对ε的一维搜索得到ε的初步估计值
Figure PCTCN2018112821-appb-000003
S2、利用所述ε的初步估计补偿的信号z 1，具体计算为：
Figure PCTCN2018112821-appb-000004
从经过频偏补偿后的信号估计OFDM-IM系统中非激活子载波位置，满足以下准则的子载波判定为非激活子载波：
①当前子载波功率P null较小；
②两个相邻子载波中功率较大者P side较大；
③比值P side/P null足够大；
对本系统而言，后续步骤至多利用N max个符合以上准则的子载波。
S3、对估计的子载波按P side大小降序排列，P side越大的子载波能量赋予越大的权值，各个子载波的权值组成对角矩阵W。
估计的子载波的能量按照不同的权重加入到代价函数中，代价函数修改为：
Figure PCTCN2018112821-appb-000005
其中
Figure PCTCN2018112821-appb-000006
为估计的非激活子载波集合。
通过对ε的一维搜索得到ε的最终估计值
Figure PCTCN2018112821-appb-000007
最终补偿信号
Figure PCTCN2018112821-appb-000008
进一步地，步骤S2中，利用初步补偿的信号，通过功率检测估计非激活子载波的位置。
进一步地，步骤S3中，将估计为非激活子载波的能量按照不同权重加入到最终的代价函数。
与传统的OFDM技术相比，本发明采用OFDM-IM的子载波是部分激活的。这意味着除了初始设置的空子载波外，还有非激活的子载波的能量可以加以利用。因此，本发明利用非激活的子载波来优化多普勒频移的估计。
附图说明
图1为本发明方法的流程图；
图2、图3分别为不同
Figure PCTCN2018112821-appb-000009
的均方误差随信噪比变化的趋势图。
具体实施方式
下面结合附图和具体实施例对本申请作进一步详细说明，单本发明的实施和保护不限于此，需指出的是，以下若有未特别详细说明之过程，均是本领域技术人员可参照现有技术实现或理解的。
本发明提供一种基于多种模式的OFDM序号调制方法。其中OFDM-IM系统子载波数为128，系统使用QPSK调制方式。除去导频、保护间隔以及预先设置的4个空子载波外，系统含有28个OFDM子块，每个子块有4个子载波，其中3个为激活的子载波。导频的位置以及符号已知，预先设置的空子载波的位置已知。具体实施方式步骤如下：
S1、对于受到非均匀频偏的接收信号，使用两步方法进行初步的频偏补偿：1、重采样及下变频，得到离散基带接收信号z＝Γ(ε)y；2、剩余频偏的统一补偿。第2步中使用空子载波的能量之和作为代价函数：
Figure PCTCN2018112821-appb-000010
其中，y为频偏为0时的离散基带接收信号，ε为剩余的归一化频偏，S N为空子载波集合，f m为傅里叶逆变换矩阵的第m列，Γ(ε)为频偏矩阵
Figure PCTCN2018112821-appb-000011
(.) H为取共轭操作，T c为采样间隔。
通过对ε的一维搜索得到ε的初步估计值
Figure PCTCN2018112821-appb-000012
S2、利用初步补偿的信号
Figure PCTCN2018112821-appb-000013
估计OFDM-IM系统中非激活子载波位置，准则为：
①当前子载波功率P null小于非激活子载波功率的平均值
②两个相邻子载波中功率较大者P side大于激活子载波功率的平均值
③比值P side/P null>16
对本系统而言，后续步骤至多利用8个符合以上准则的子载波。
S3、对估计的子载波按P side大小降序排列，，P side越大的子载波能量赋予越大的权值，序号为k的子载波
Figure PCTCN2018112821-appb-000014
各个子载波的权值组成对角矩阵W。
估计的子载波的能量按照不同的权重加入到代价函数中，代价函数修改为：
Figure PCTCN2018112821-appb-000015
其中
Figure PCTCN2018112821-appb-000016
为估计的非激活子载波集合。
通过对ε的一维搜索得到ε的最终估计值
Figure PCTCN2018112821-appb-000017
最终补偿信号
Figure PCTCN2018112821-appb-000018
S6、对以上方法进行蒙特卡洛仿真。对以下3种情景进行仿真，如表1所示。
表1
方法 调制方式 用于估计的空载波数
①Li的方法 OFDM QPSK 4
②Li的方法 OFDM-IM QPSK 4
③本发明的方法 OFDM-IM QPSK 初始：4追加：不大于8
仿真通过比较估计值
Figure PCTCN2018112821-appb-000019
的均方误差来衡量以上方法的性能。如图2、图3，仿真结果图中图例从上到下分别为方法①②③的
Figure PCTCN2018112821-appb-000020
的均方误差随信噪比变化的趋势图。
仿真结果表明，②的性能要稍好于①，③的性能优于①和②，在高信噪比下，③的性能优势更加明显。仿真结果验证了本发明方法的有效性。
以上所述的具体实施仅为本发明的一种实现方式，并不用于限制本发明的专利范围，凡是利用本发明精神和原则及附图内容所作的等效结构或等效流程变换，均应包括在本发明的专利保护范围内。

Claims (3)

  1. 一种OFDM-IM系统频偏估计方法，其特征在于包括以下步骤：
    S1、对于受到非均匀频偏的接收信号，使用两步方法进行初步的频偏补偿：(1)重采样及下变频，得到离散基带接收信号z＝Γ(ε)y；(2)剩余频偏的统一补偿；第(2)步中使用空子载波的能量之和作为代价函数：
    Figure PCTCN2018112821-appb-100001
    其中，y为频偏为0时的离散基带接收信号，ε为剩余的归一化频偏，S N为空子载波集合，f m为傅里叶逆变换矩阵的第m列，Γ(ε)为频偏矩阵
    Figure PCTCN2018112821-appb-100002
    (.) H为取共轭操作，T c为采样间隔；
    通过对ε的一维搜索得到ε的初步估计值
    Figure PCTCN2018112821-appb-100003
    S2、利用所述ε的初步估计补偿的信号
    Figure PCTCN2018112821-appb-100004
    基于补偿后的信号估计OFDM-IM系统中非激活子载波位置，准则为：
    ①当前子载波功率P null较小；
    ②两个相邻子载波中功率较大者P side较大；
    ③比值P side/P null足够大；
    S3、对估计的子载波按P side大小降序排列，P side越大的子载波能量赋予越大的权值，各个子载波的权值组成对角矩阵W；
    估计的子载波的能量按照不同的权重加入到代价函数中，代价函数修改为：
    Figure PCTCN2018112821-appb-100005
    其中
    Figure PCTCN2018112821-appb-100006
    为估计的非激活子载波集合；
    通过对ε的一维搜索得到ε的最终估计值
    Figure PCTCN2018112821-appb-100007
    最终补偿信号
    Figure PCTCN2018112821-appb-100008
    其中OFDM-IM系统子载波数为N，系统使用MPSK调制方式，除去导频、保护间隔以及预先设置的N null个空子载波外，系统含有多个OFDM子块，每个子块有N total个子载波，其中N active个为激活的子载波，导频的位置以及符号已知，预先设置的空子载波的位置已知。
  2. 如权利要求1所述的一种OFDM-IM系统频偏估计方法，其特征在于步骤S2，利用初步补偿的信号，通过功率检测估计非激活子载波的位置。
  3. 如权利要求1所述的一种OFDM-IM系统频偏估计方法，其特征在于步骤S3，将估计为非激活子载波的能量按照不同权重加入到最终的代价函数。
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