技术领域technical field
本发明涉及一种NB-IoT系统下行链路中的小区搜索系统，主要涉及专利分类号H04电通信技术H04B传输H04B1/00不包含在H04B 3/00至H04B 13/00单个组中的传输系统的部件；不以所使用的传输媒介为特征区分的传输系统的部件H04B1/69扩频技术H04B1/707利用直接序列调制的H04B1/7073同步方面H04B1/7083小区搜寻，例如使用三级方法。The present invention relates to a cell search system in the downlink of NB-IoT system, mainly related to the transmission system of patent classification number H04 electric communication technology H04B transmission H04B1/00 not included in a single group H04B 3/00 to H04B 13/00 Components; components of transmission systems that are not characterized by the transmission medium used H04B1/69 Spread Spectrum Techniques H04B1/707 H04B1/7073 Synchronization Aspects with Direct Sequence Modulation H04B1/7083 Cell Search, e.g. using a three-level method.
背景技术Background technique
NB-IoT系统中，初始小区搜索过程是用户终端与基站之间建立下行通信链路的前提，其主要目的是实现下行链路在时间、频率上的同步和获取物理层小区标识(cellID)。NB-IoT系统下行采用正交频分复用(OFDM)技术，该技术的基本原理是将高速串行数据流经过串并转换后变成多路并行低速数据流，并调制到多个正交的子载波上传输，因为其要求子载波间满足正交性，因此与单载波系统相比，OFDM系统易受频率偏差的影响。由于发射机的载波频率与接收机本地振荡器间存在频率偏差，或由于多普勒效应，OFDM系统的子载波间的正交性会遭到破坏，从而导致子载波间干扰，所以频率同步要尽可能精确。时间同步是为了确定系统帧的起始位置和OFDM符号的起始位置，在多经信道中，时间同步不准确会造成符号间干扰，对系统性能影响很大，因此要求时间同步尽可能精确。In the NB-IoT system, the initial cell search process is the premise of establishing a downlink communication link between the user terminal and the base station. Its main purpose is to achieve downlink synchronization in time and frequency and to obtain the physical layer cell ID (cellID). The downlink of the NB-IoT system adopts Orthogonal Frequency Division Multiplexing (OFDM) technology. Compared with single-carrier systems, OFDM systems are susceptible to frequency deviations because they require orthogonality between sub-carriers. Due to the frequency deviation between the carrier frequency of the transmitter and the local oscillator of the receiver, or due to the Doppler effect, the orthogonality between the subcarriers of the OFDM system will be destroyed, resulting in interference between subcarriers, so the frequency synchronization must be Be as precise as possible. Time synchronization is to determine the start position of the system frame and the start position of OFDM symbols. In a multi-channel channel, inaccurate time synchronization will cause inter-symbol interference and have a great impact on system performance. Therefore, time synchronization is required to be as accurate as possible.
在现有技术中典型的NB-IoT系统采样时间Ts＝1/30720000秒，其时域结构如图1所示，每个系统帧时间为10毫秒(ms)，包含10个子帧，每个子帧时间为1ms，包含2个时隙，每个时隙时间为0.5ms，包含7个正交频分复用符号(symbol)，每个符号长度为2048个采样点并加上CP的长度，其中第0个symbol的CP长度为160个采样点，第1到第6个symbol的CP长度为144个采样点，所以每一个子帧包含14个symbol，长度为30720个采样点。npss信号位于系统帧的第5个子帧，nsss信号位于偶位系统帧的第9个子帧。In the prior art, the typical NB-IoT system sampling time Ts = 1/30720000 second, its time domain structure is shown in Figure 1, each system frame time is 10 milliseconds (ms), including 10 subframes, each subframe The frame time is 1ms, including 2 time slots, each time slot is 0.5ms, including 7 OFDM symbols (symbols), each symbol length is 2048 sampling points plus the length of the CP, The CP length of the 0th symbol is 160 sampling points, and the CP length of the 1st to 6th symbols is 144 sampling points, so each subframe contains 14 symbols, and the length is 30720 sampling points. The npss signal is located in the fifth subframe of the system frame, and the nsss signal is located in the ninth subframe of the even bit system frame.
发明内容Contents of the invention
针对现有npss信号检测技术在频偏较大情况下，时间同步不准的问题，本发明提出了一种可以抵抗较大频偏的npss信号检测系统，首先采用分段相关进行定时粗同步，然后采用模值相关的方法进行定时粗同步修正和定时细同步，模值相关方法的引入使得定时同步的抗频偏能力大大提高。Aiming at the problem of inaccurate time synchronization when the existing npss signal detection technology has a large frequency deviation, the present invention proposes an npss signal detection system that can resist a large frequency deviation. Then, the modulus correlation method is used to correct the coarse timing synchronization and the timing fine synchronization. The introduction of the modulus correlation method greatly improves the anti-frequency offset capability of the timing synchronization.
在储存本地npss信号时，本发明只需储存一个symbol的npss时域降采样信号和频域信号即可，而不需要将整个子帧的npss时域降采样信号和频域信号全部储存至本地，空间复杂度降低。When storing the local npss signal, the present invention only needs to store the npss time-domain downsampling signal and frequency-domain signal of a symbol, instead of storing all the npss time-domain downsampling signals and frequency-domain signals of the entire subframe locally , the space complexity is reduced.
进行频偏估计时，首先将本地npss信号乘以一定步长的频偏与接收到的主同步信号进行相关运算，求得粗频偏估计，粗频偏补偿后可以保证信号的频偏控制在一定步长以内；进行精频偏估计时，不是将一个symbol内的npss信号与本地信号共轭相乘后分为两段做相关，而是跨symbol进行，这样可以将精频偏估计范围减小至一定范围内，既满足了频偏估计的范围要求又最大限度的提高了精频偏估计的精度。When performing frequency offset estimation, the local npss signal is firstly multiplied by a frequency offset with a certain step length and the received primary synchronization signal is correlated with the received primary synchronization signal to obtain a rough frequency offset estimate. After the coarse frequency offset compensation, the frequency offset of the signal can be controlled within Within a certain step size; when performing fine frequency offset estimation, instead of multiplying the npss signal in a symbol and the local signal conjugate and dividing it into two segments for correlation, it is carried out across symbols, which can reduce the range of fine frequency offset estimation As small as a certain range, it not only satisfies the range requirement of frequency offset estimation but also maximizes the precision of fine frequency offset estimation.
进行nsss信号检测时，根据ZC序列的中心对称性，可在接收的nsss频域信号与本地nsss频域信号相关之前，先确定出nf和q的候选值，然后使用接收到的nsss频域信号与候选值内的本地nsss频域信号做相关，而无需与所有的本地nsss频域信号做相关，减小了时间复杂度。When performing nsss signal detection, according to the central symmetry of the ZC sequence, the candidate values of nf and q can be determined first before the received nsss frequency domain signal is correlated with the local nsss frequency domain signal, and then the received nsss frequency domain signal can be used The signal is correlated with the local nsss frequency domain signals within the candidate value, instead of all local nsss frequency domain signals, which reduces the time complexity.
附图说明Description of drawings
为了更清楚的说明本发明的实施例或现有技术的技术方案，下面将对实施例或现有技术描述中所需要使用的附图做一简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are only some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.
图1为本发明NB-IoT时域结构示意图Figure 1 is a schematic diagram of the NB-IoT time domain structure of the present invention
图2为本发明NB-IoT系统小区搜索功能模块图Figure 2 is a block diagram of the cell search function of the NB-IoT system of the present invention
图3为本发明npss信号检测功能模块图Fig. 3 is npss signal detection functional block diagram of the present invention
图4为本发明频率同步功能模块图Fig. 4 is a block diagram of the frequency synchronization function of the present invention
图5为本发明nsss信号检测功能模块图Fig. 5 is the nsss signal detection functional block diagram of the present invention
图6为本发明nf和cellID检测流程图Fig. 6 is the detection flowchart ofnf and cellID of the present invention
图7为本发明时偏估计对比图Figure 7 is a comparison chart of time offset estimation in the present invention
图8为本发明频偏估计对比图Figure 8 is a comparison chart of frequency offset estimation in the present invention
具体实施方式detailed description
为使本发明的实施例的目的、技术方案和优点更加清楚，下面结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚完整的描述：In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the embodiments of the present invention:
本发明使用的技术缩略语如下：The technical abbreviations used in the present invention are as follows:
NB-IoT Narrow Band Internet of Things窄带物联网NB-IoT Narrow Band Internet of Things
npss Narrowband primary synchronization signal主同步信号npss Narrowband primary synchronization signal main synchronization signal
nsss Narrowband secondary synchronization signal辅同步信号nsss Narrowband secondary synchronization signal secondary synchronization signal
CP Cyclic Prefix循环前缀CP Cyclic Prefix cyclic prefix
IFFT Inverse Fast Fourier Transformation快速傅里叶反变换IFFT Inverse Fast Fourier Transformation Fast Fourier Inverse Transform
OFDM Orthogonal Frequency Division Multiplexing正交频分复用OFDM Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing
cellID物理层小区标识cellID physical layer cell identifier
nf系统帧号nf system frame number
symbol正交频分复用符号symbol OFDM symbol
ε归一化频偏，即频偏与子载波间隔(15kHz)的比值ε normalized frequency offset, that is, the ratio of frequency offset to subcarrier spacing (15kHz)
如图1-6所示，一种NB-IoT系统下行链路中的小区搜索系统主要包括：As shown in Figure 1-6, a cell search system in the downlink of an NB-IoT system mainly includes:
npss信号检测单元npss signal detection unit
npss信号检测功能框图如图3所示，首先生成本地npss频域信号，变换至时域并进行降采样处理，然后对接收的21ms数据进行降采样处理，使用降采样后的数据进行定时粗同步，定时粗同步修正后使用未降采样的数据进行定时细同步，完成npss信号的检测。The block diagram of the npss signal detection function is shown in Figure 3. First, the local npss frequency domain signal is generated, converted to the time domain and down-sampled, and then the received 21ms data is down-sampled, and the down-sampled data is used for timing rough synchronization , after timing coarse synchronization correction, the non-downsampled data is used for timing fine synchronization to complete the detection of npss signal.
npss信号在频域是一个Zadoff-Chu序列，其生成表达式为：The npss signal is a Zadoff-Chu sequence in the frequency domain, and its generation expression is:
其中，根序列索引u＝5，l为symbol号，S(l)取值如表1所示：Wherein, the root sequence index u=5, l is the symbol number, and the value of S(l) is as shown in Table 1:
表1S(l)取值表Table 1 S(l) value table
可以发现，每个symbol的npss信号只相差一个符号位S(l)，为了减少空间复杂度，只需生成一个symbol的频域npss信号即可，其生成表达式为：It can be found that the npss signal of each symbol only differs by one symbol bit S(l). In order to reduce the space complexity, it is only necessary to generate a frequency-domain npss signal of a symbol. The generation expression is:
然后，将npss_loc_fre(n)变换至时域，生成一个symbol的时域npss信号：Then, transform npss_loc_fre(n) to the time domain to generate a symbol time domain npss signal:
为了减小计算量，对信号npss_loc_ti(n)进行16倍降采样处理，如式(4)所示，得到的信号记为npss_loc_ti_sam(n)，长度为128个采样点。In order to reduce the amount of calculation, the signal npss_loc_ti(n) is down-sampled by 16 times, as shown in formula (4), the obtained signal is recorded as npss_loc_ti_sam(n), and the length is 128 sampling points.
npss_loc_ti_sam(n)＝npss_loc_ti(16n),n＝0,1,...,127 (4)npss_loc_ti_sam(n)=npss_loc_ti(16n), n=0,1,...,127 (4)
npss信号位于系统帧的第5个子帧，则在接收到的21ms数据中，必包含两个子帧的npss信号。The npss signal is located in the fifth subframe of the system frame, so the received 21ms data must contain npss signals of two subframes.
npss信号检测实际使用前11ms数据，记为re(n)，长度为337920个采样点，对信号re(n)进行16倍降采样处理，得到的信号记为re_sam(n)，长度为21120个采样点。The npss signal detection actually uses the first 11ms data, which is recorded as re(n), and the length is 337920 sampling points. The signal re(n) is down-sampled by 16 times, and the obtained signal is recorded as re_sam(n), and the length is 21120. Sampling point.
用npss_loc_ti_sam(n)和re_sam(n)做滑动相关，每滑动一个点，从re_sam(n)中取出一个子帧的数据，记为re_sam_sf(m)，m＝0,1,…,M-1，M＝1920，则re_sam_sf(m)＝re_sam(n+m)，n＝0,1,…,19200，将re_sam_sf(m)分为14个symbol，第l个symbol的数据(不包含CP)记为re_saml(n)，n＝0,1,…,127，则re_saml(n)＝re_sam_sf(137l+10+(l≥7)+n)，l＝0,1,…,13，其中(l≥7)表示一个值，当l<7时，(l≥7)＝0，当l≥7时，(l≥7)＝1。对于npss信号，前3个symbol信号为0，使用后11个symbol信号re_saml(n)与本地信号npss_loc_ti_sam(n)做分段相关(段数取2，每段长度64)，并求和，如式(5)所示：Use npss_loc_ti_sam(n) and re_sam(n) for sliding correlation. For each point of sliding, take out the data of a subframe from re_sam(n), and record it as re_sam_sf(m), m=0,1,...,M-1 , M=1920, then re_sam_sf(m)=re_sam(n+m), n=0,1,...,19200, divide re_sam_sf(m) into 14 symbols, the data of the first symbol (excluding CP) Recorded as re_saml (n), n=0,1,...,127, then re_saml (n)=re_sam_sf(137l+10+(l≥7)+n), l=0,1,...,13, Wherein (l≥7) represents a value, when l<7, (l≥7)=0, and when l≥7, (l≥7)=1. For the npss signal, the first 3 symbol signals are 0, and the last 11 symbol signals re_saml (n) are used for segmentation correlation with the local signal npss_loc_ti_sam (n) (the number of segments is 2, and the length of each segment is 64), and summed, such as Formula (5) shows:
其中，n＝0,1,…,19200，即共滑动一帧的长度。求取corr(n)的最大值，其最大值对应的标号n即为定时粗同步位置，即Wherein, n=0,1,...,19200, that is, the length of one sliding frame in total. Find the maximum value of corr(n), and the label n corresponding to the maximum value is the timing coarse synchronization position, that is
因为频偏的影响，上述过程得到的定时粗同步有一定偏差，需要对其进行修正，在得到的粗同步位置coarse_start_time两侧各取20个点，用npss_loc_ti_sam(n)和re_sam(n)做滑动相关。Due to the influence of frequency offset, the timing coarse synchronization obtained by the above process has a certain deviation, which needs to be corrected. Take 20 points on both sides of the obtained coarse synchronization position coarse_start_time, and use npss_loc_ti_sam(n) and re_sam(n) for sliding relevant.
在使用信号npss_loc_ti_sam(n)与信号re_saml(n)做相关时，不再使用分段相关，而使用npss_loc_ti_sam(n)和re_saml(n)的模进行相关，以抵抗频偏对时偏的影响，如式(6)所示。When using the signal npss_loc_ti_sam(n) to correlate with the signal re_saml (n), segmental correlation is no longer used, but the modulus of npss_loc_ti_sam(n) and re_saml (n) is used for correlation to resist the effect of frequency offset on time offset Influence, as shown in formula (6).
其中，n＝coarse_start_time-20,coarse_start_time-19,…,coarse_start_time+20。求取corr_rev(n)的最大值，其最大值对应的标号n即为定时粗同步的修订值，即Among them, n=coarse_start_time-20, coarse_start_time-19,..., coarse_start_time+20. Find the maximum value of corr_rev(n), and the label n corresponding to the maximum value is the revision value of the timing coarse synchronization, that is
以上求取时偏的过程都是采用的16倍降采样信号，为了得到定时细同步，在得到start_time_rev后，The above process of obtaining the time offset is a 16-fold downsampling signal. In order to obtain fine timing synchronization, after getting start_time_rev,
首先将其乘以16变换至未降采样数据的时偏估计，然后在其两侧各取64个点，在未降采样的数据re(n)上进行滑动，每滑动一个点，从re(n)中取出一个子帧的数据，记为re_sf(n)，n＝0,1,…,N-1，N＝30720，然后再进行16倍降采样，得到的信号记为re_sam_sf'(n)，n＝0,1,…,N'-1，N'＝1920，第l个symbol的数据记为re_sam'l(n)，长度为128，对信号npss_loc_ti_sam(n)和re_sam'l(n)的模进行相关，如式(7)所示：First multiply it by 16 to transform it into the time offset estimation of the non-downsampled data, then take 64 points on both sides of it, and slide on the non-downsampled data re(n), and slide one point each time, from re( Take out the data of a subframe in n), record it as re_sf(n), n=0,1,...,N-1, N=30720, and then perform 16 times downsampling, and the obtained signal is recorded as re_sam_sf'(n ), n=0,1,...,N'-1, N'=1920, the data of the l symbol is recorded as re_sam'l (n), and the length is 128, for the signal npss_loc_ti_sam (n) and re_sam'l ( n) is correlated, as shown in formula (7):
其中，n＝start_time_rev*16-64,start_time_rev*16-15,…,start_time_rev*16+64。求取corr_acc(n)的最大值，其最大值对应的标号n即为定时细同步，即该值为npss信号开始的位置。Wherein, n=start_time_rev*16-64, start_time_rev*16-15,..., start_time_rev*16+64. Calculate the maximum value of corr_acc(n), and the label n corresponding to the maximum value is the timing fine synchronization, namely This value is where the npss signal starts.
频率同步单元frequency synchronization unit
频率同步功能框图如图4所示，根据start_time_acc可以得到接收到的npss信号，首先对信号进行16倍降采样，然后根据降采样的npss信号计算粗频偏估计，对信号进行粗频偏补偿，然后进行精频偏估计。The frequency synchronization function block diagram is shown in Figure 4. The received npss signal can be obtained according to start_time_acc. First, the signal is down-sampled by 16 times, and then the rough frequency offset estimation is calculated according to the down-sampled npss signal, and the rough frequency offset compensation is performed on the signal. Then perform fine frequency offset estimation.
将接收到的npss信号进行16倍降采样处理，记为npss_re_ti_sam(n)，则：The received npss signal is subjected to 16 times downsampling processing, which is recorded as npss_re_ti_sam(n), then:
npss_re_ti_sam(n)＝re(start_time_acc+16n),n＝0,1,...,N-1 (8)npss_re_ti_sam(n)=re(start_time_acc+16n), n=0,1,...,N-1 (8)
其中N＝1920，npss_re_ti_sam(n)为一个子帧的数据，将其分为14个symbol，第l个symbol的数据(不包含CP)记为npss_re_ti_saml(n)，n＝0,1,…,128-1，则npss_re_ti_saml(n)＝npss_re_ti_sam(137l+10+(l≥7)+n)，l＝0,1,…,13。Among them, N=1920, npss_re_ti_sam(n) is the data of a subframe, which is divided into 14 symbols, and the data of the first symbol (not including CP) is recorded as npss_re_ti_saml (n), n=0,1,... , 128-1, then npss_re_ti_saml (n)=npss_re_ti_sam(137l+10+(l≥7)+n), l=0,1,...,13.
本地npss降采样信号为npss_loc_ti_sam(n)，发生频偏时若忽略噪声的影响，则接收到第l个symbol的npss信号为：The local npss downsampling signal is npss_loc_ti_sam(n), and if the influence of noise is ignored when frequency offset occurs, the npss signal of the l-th symbol received is:
其中，ε为归一化频偏，△l＝137l+10+(l≥7)。将接收到的第l个symbol的npss降采样信号与本地npss降采样信号共轭相乘：Wherein, ε is the normalized frequency offset, △l =137l+10+(l≥7). Multiply the received npss downsampled signal of the l-th symbol by the conjugate of the local npss downsampled signal:
yl(n)＝S(l)npss_loc_ti_sam*(n)npss_re_ti_saml(n),n＝0,1,...,127 (10)yl (n) = S (l) npss_loc_ti_sam* (n) npss_re_ti_saml (n), n = 0,1,...,127 (10)
对yl(n)补偿频偏并求和，然后将后11个symbol的结果相加如式(11)所示。The frequency offset is compensated for yl (n) and summed, and then the results of the last 11 symbols are added as shown in formula (11).
其中ε为归一化频偏估计。求取y_sum(ε)的最大值，其最大值对应的标号ε即为粗频偏估计，即求得的粗频偏估计为对接收到的npss降采样信号npss_re_ti_sam(n)使用进行补偿，得到补偿后的npss信号为：where ε is the normalized frequency offset estimate. Find the maximum value of y_sum(ε), and the label ε corresponding to the maximum value is the rough frequency offset estimate, that is, the obtained rough frequency offset estimate is Use the received npss downsampled signal npss_re_ti_sam(n) After compensation, the npss signal after compensation is:
其中，N＝1920。Wherein, N=1920.
下面对信号进行精频偏估计。npss_cmp(n)为一个子帧的数据，将其分为14个symbol，第l个symbol的数据(不包含CP)记为npss_cmpl(n)，n＝0,1,…,128-1，则npss_cmpl(n)＝npss_cmp(137l+10+(l≥7)+n)，l＝0,1,…,13。对信号npss_cmpl(n)做如式(9)、式(10)相同操作，可得：Next, the precise frequency offset estimation is performed on the signal. npss_cmp(n) is the data of a subframe, which is divided into 14 symbols, and the data of the first symbol (excluding CP) is recorded as npss_cmpl (n), n=0,1,...,128-1, Then npss_cmpl (n)=npss_cmp(137l+10+(l≥7)+n), l=0,1,...,13. Perform the same operation as formula (9) and formula (10) on the signal npss_cmpl (n), and get:
其中，为精频偏估计，△l＝137l+10+(l≥7)。令y3'(n)与y5'(n)共轭相乘并相加：in, For precise frequency offset estimation, △l =137l+10+(l≥7). Conjugate multiplication of y3 '(n) with y5 '(n) and add:
其中，△＝△5-△3＝274。同理，对y4'(n)与y6'(n)、y7'(n)与y9'(n)、y8'(n)与y10'(n)、y11'(n)与y13'(n)做相同的操作，求出p值并求和，得到p_sum，求得的精频偏估计为：Among them, Δ=Δ5 −Δ3 =274. Similarly, for y4 '(n) and y6 '(n), y7 '(n) and y9 '(n), y8 '(n) and y10 '(n), y11 '( n) Do the same operation as y13 '(n), find the p value and sum it up to get p_sum, and the obtained fine frequency offset estimate is:
精频偏的估计范围为(-0.234,0.234)，粗频偏估计误差为(-0.2,0.2)，所以精频偏估计可以补偿粗频偏估计误差并最大限度的提高了频偏的估计精度。最终估计出的信号的频偏估计为The estimation range of the fine frequency offset is (-0.234, 0.234), and the estimation error of the coarse frequency offset is (-0.2, 0.2), so the fine frequency offset estimation can compensate the coarse frequency offset estimation error and maximize the estimation accuracy of the frequency offset . The frequency offset of the final estimated signal is estimated as
nsss信号检测单元nsss signal detection unit
nsss信号检测功能框图如图5所示，首先将降采样后的npss信号补偿频偏后变换至频域，根据本地生成的npss频域信号得到信道估计和nsss信号阈值，然后根据start_time_acc得到接收到的nsss信号，将信号降采样并补偿频偏后变换至频域，对nsss频域信号进行信道补偿，利用nsss信号自身特征确定帧号与cellID候选值，然后生成本地的nsss频域信号，与nsss频域接收信号做互相关，最终获取nf的低3bit信息与cellID。The block diagram of the nsss signal detection function is shown in Figure 5. First, the downsampled npss signal is compensated for frequency offset and transformed to the frequency domain. The channel estimation and nsss signal threshold are obtained according to the locally generated npss frequency domain signal, and then the received signal is obtained according to start_time_acc. The nsss signal, the signal is down-sampled and the frequency offset is compensated, and then converted to the frequency domain, the channel compensation is performed on the nsss frequency domain signal, and the frame number and cellID candidate value are determined by using the characteristics of the nsss signal itself, and then the local nsss frequency domain signal is generated. nsss receives signals in the frequency domain for cross-correlation, and finally obtains the low 3-bit information and cellID of nf .
接收到的npss降采样信号记为npss_re_ti_sam(n)，频偏估计为freoffset，按照式(12)将替换为freoffset计算补偿频偏后的npss信号记为npss_cmp(n)，将其分为14个symbol，第l个symbol的数据(不包含CP)记为npss_cmpl(n)，n＝0,1,…,127，则npss_cmpl(n)＝npss_cmp(137l+10+(l≥7)+n)，l＝0,1,…,13。将信号npss_cmpl(n)按照式(17)变换至频域，得到第l个symbol的npss的频域接收号npss_re_frel(k)。The received npss down-sampling signal is recorded as npss_re_ti_sam(n), and the frequency offset is estimated as freoffset. According to formula (12), the Replace it with freoffset to calculate the npss signal after compensating the frequency offset and record it as npss_cmp(n), divide it into 14 symbols, and record the data of the lth symbol (excluding CP) as npss_cmpl (n), n=0,1 ,...,127, then npss_cmpl (n)=npss_cmp(137l+10+(l≥7)+n), l=0,1,...,13. Transform the signal npss_cmpl (n) into the frequency domain according to formula (17), and obtain the frequency-domain reception number npss_re_frel (k) of npss of the l-th symbol.
其中l＝3,4,…,13。设npss信号频域的资源网格为npss_re_fre_vec(k,l)，其中k＝0,1,…,11，l＝0,1,…,13。资源网格表示信号的时-频分布，将npss_re_frel(k)按照l值和k值对应填入资源网格中即得到了接收到的npss信号的频域资源网格。where l=3,4,...,13. Let the resource grid of npss signal frequency domain be npss_re_fre_vec(k,l), where k=0,1,...,11, l=0,1,...,13. The resource grid represents the time-frequency distribution of the signal, and the npss_re_frel (k) is filled in the resource grid according to the l value and the k value correspondingly to obtain the frequency domain resource grid of the received npss signal.
由式(2)可得，一个symbol的本地npss频域信号为npss_loc_fre(n)，则第l个symbol的本地npss频域信号为S(l)npss_loc_fre(n)，将其填入资源网格中即得到了本地的npss频域资源网格npss_loc_fre_vec(k,l)，则得到的信道估计为如式(18)所示：From formula (2), it can be obtained that the local npss frequency domain signal of a symbol is npss_loc_fre(n), then the local npss frequency domain signal of the l-th symbol is S(l)npss_loc_fre(n), which is filled in the resource grid The local npss frequency domain resource grid npss_loc_fre_vec(k,l) is obtained, and the obtained channel estimation is shown in formula (18):
ce′(k,l)＝npss_re_fre_vec(k,l)/npss_loc_fre_vec(k,l) (18)ce'(k,l)=npss_re_fre_vec(k,l)/npss_loc_fre_vec(k,l) (18)
其中k＝0,1,…,10，l＝3,4,…,13。ce′(k,l)第l个symbol上的幅度均差为abs表示求模值运算，角度均差为angle表示求角度运算，采用典型内插算法将信道估计扩展，得到ce(k,l)，其中k＝0,1,…,10,11，l＝3,4,…,13，则ce(11,l)的幅度值为ce_mag(11,l)＝abs(ce′(10,l))+ce_mag′(l)，角度值为ce_ang(11,l)＝angle(ce′(10,l))+ce_ang′(l)，则ce(k,l)取值如式(19)所示。Where k=0,1,...,10, l=3,4,...,13. The average amplitude difference on the lth symbol of ce′(k,l) is abs represents the modulus operation, and the average angle difference is angle represents an angle calculation, using a typical interpolation algorithm to expand the channel estimate to obtain ce(k,l), where k=0,1,...,10,11, l=3,4,...,13, then ce( The amplitude value of 11,l) is ce_mag(11,l)=abs(ce'(10,l))+ce_mag'(l), and the angle value is ce_ang(11,l)=angle(ce'(10,l ))+ce_ang′(l), then the value of ce(k,l) is shown in formula (19).
将npss_re_fre_vec(k,l)和npss_loc_fre_vec(k,l)反资源网格映射，即按照资源网格映射的位置，依次取出每一个symbol中的数据，然后将数据串接，即可得到npss频域接收信号npss_re_fre(n)和频域本地信号npss_loc_fre(n)，长度为121。nsss信号阈值由频域npss信号得到，如式(20)所示：Map npss_re_fre_vec(k,l) and npss_loc_fre_vec(k,l) against the resource grid, that is, take out the data in each symbol in turn according to the position of the resource grid mapping, and then concatenate the data to obtain the npss frequency domain Receive signal npss_re_fre(n) and frequency domain local signal npss_loc_fre(n), the length is 121. The nsss signal threshold is obtained from the npss signal in the frequency domain, as shown in equation (20):
nsss信号位于偶数位系统帧的第9个子帧，则在21ms数据中，必存在一个子帧的nsss信号。The nsss signal is located in the ninth subframe of the even-numbered system frame, so there must be an nsss signal in one subframe in the 21ms data.
根据start_time_acc可以得到两个接收到的nsss信号，只有一个是实际存在的nsss信号，将其记为nsss_re_ti(n)，对信号nsss_re_ti(n)进行16倍降采样得到信号nsss_re_ti_sam(n)，对其按照上述操作进行频偏补偿并变换至频域，得到nsss信号资源网格nsss_re_fre_vec(k,l)，按照式(21)对其进行信道补偿，得到补偿后的nsss频域信号nsss_re_fre_vec_cmp(k,l)。According to start_time_acc, two received nsss signals can be obtained, only one is the actual nsss signal, which is recorded as nsss_re_ti(n), and the signal nsss_re_ti(n) is down-sampled by 16 times to obtain the signal nsss_re_ti_sam(n), which Perform frequency offset compensation according to the above operations and convert to the frequency domain to obtain the nsss signal resource grid nsss_re_fre_vec(k,l), perform channel compensation on it according to formula (21), and obtain the compensated nsss frequency domain signal nsss_re_fre_vec_cmp(k,l ).
nsss_re_fre_vec_cmp(k,l)＝nsss_re_fre_vec(k,l)/ce(k,l) (21)nsss_re_fre_vec_cmp(k,l)=nsss_re_fre_vec(k,l)/ce(k,l) (21)
将nsss_re_fre_vec_cmp(k,l)反资源网格映射，即可得到nsss频域信号nsss_re_fre(n)，长度为131。The nsss_re_fre_vec_cmp(k,l) is reversely mapped to the resource grid to obtain the nsss frequency domain signal nsss_re_fre(n), with a length of 131.
nsss本地信号在频域是一个Zadoff-Chu序列，其生成表达式为：The nsss local signal is a Zadoff-Chu sequence in the frequency domain, and its generation expression is:
其中in
n＝0,1,...,131n=0,1,...,131
n′＝nmod131n'=nmod131
m＝nmod128m=nmod128
mod表示取余操作。bq(m)如表2所示：mod represents the remainder operation. bq (m) is shown in Table 2:
表2bq(m)取值表Table 2bq (m) value table
对于接收信号，若忽略噪声影响，则：For the received signal, if the influence of noise is ignored, then:
对信号nsss_re_fre(n)补偿bq(m)得：Compensate bq (m) for signal nsss_re_fre(n):
由式(24)可得：From formula (24), we can get:
当nf＝0或4时，zc(n)具有中心对称性即zc(n)＝zc(130-n)。令q＝0,1,2,3，nf＝0,2,4,6，对nsss_re_fre(n)做补偿得：When nf =0 or 4, zc(n) has central symmetry, that is, zc(n)=zc(130-n). Let q=0,1,2,3, nf =0,2,4,6, make compensation for nsss_re_fre(n):
对其前后两部分共轭求和得：The conjugate summation of the two parts before and after it is:
定义corr(q,nf)最大值对应的nf为nf_max，q为q_max，则nf的候选值为(nf_max,(nf_max+4)mod8)，q的候选值为q_max。Define the nf corresponding to the maximum value of corr(q,nf ) as nf _max, and q as q_max, then the candidate value of nf is (nf _max,(nf _max+4)mod8), and the candidate value of q is q_max.
令nf＝0,2,4,6，cellID＝0,1,…,503，如式(22)所示生成本地nsss频域信号nsss_loc_fre(n,nf,cellID)保存至本地。根据start_time_acc按照前文所述方法从接收到的21ms数据中得到两个nsss频域补偿信号分别记为nsss_re_fre0(n)、nsss_re_fre1(n)，计算出的nf的候选值设为nf0、nf1，使用nsss_re_frei(n)与nsss_loc_fre(n,nf,cellID)进行相关运算如式(28)所示，检测流程如图6所示，当corrnsss>nsss_thresh时，本地信号对应的nf和cellID值即为计算得到的nf的低3bit信息与cellID。Set nf =0, 2, 4, 6, cellID = 0, 1, ..., 503, generate a local nsss frequency domain signal nsss_loc_fre(n, nf , cellID) as shown in formula (22) and save it locally. According to start_time_acc, two nsss frequency domain compensation signals are obtained from the received 21ms data according to the method described above, which are respectively denoted as nsss_re_fre0 (n) and nsss_re_fre1 (n), and the calculated candidate values of nf are set to nf0 , nf1 , use nsss_re_frei (n) and nsss_loc_fre(n,nf ,cellID) to perform correlation operations as shown in formula (28), and the detection process is shown in Figure 6. When corrnsss >nsss_thresh, the corresponding n of the local signal The values off and cellID are the calculated low 3-bit information and cellID of nf .
实施例1Example 1
为了验证本发明的有效性，进行了若干测试。实验输入为从接收天线接收到的21ms数据。In order to verify the effectiveness of the invention, several tests were carried out. The experimental input is 21ms data received from the receiving antenna.
图7为时偏估计对比图，使用分段相关法与本发明方法进行对比，对输入数据加入-1.8～1.8的归一化频偏，每个频偏对应的每种算法仿真100次，检测到的时偏的均方根误差(RMSE)如图所示，由图像可知本发明的时偏估计方法抗频偏能力较强，在大频偏情况下估计的时偏依然准确。图8为频偏估计对比图，使用将一个symbol内的npss信号与本地信号共轭相乘后分为两段做相关的方法(记为方法一)与本发明方法进行对比，在不同的信噪比(SNR)下，对数据随机加入(-1,1)范围的归一化频偏，每种信噪比下每种算法仿真100次，使用频率同步跟踪算法计算补偿过频偏后的数据的归一化频偏，再将其乘以15kHz作为估计频偏与实际频偏的差值，检测到的频偏的RMSE如图所示，由图像可知本发明的频偏估计结果更接近于实际频偏值，精度更高。表3为nsss信号检测时间对比表，使用直接相关的方法与本发明方法进行对比，数据表明本发明的nsss信号检测所用时间更少，时间复杂度降低。在储存本地npss信号时，本发明只需储存一个symbol的npss时域降采样信号和频域信号即可，空间复杂度降低。Figure 7 is a comparison diagram of time offset estimation, using the segmented correlation method to compare with the method of the present invention, adding a normalized frequency offset of -1.8 to 1.8 to the input data, simulating each algorithm corresponding to each frequency offset 100 times, and detecting The root mean square error (RMSE) of the obtained time offset is shown in the figure. It can be seen from the figure that the time offset estimation method of the present invention has a strong ability to resist frequency offset, and the estimated time offset is still accurate in the case of a large frequency offset. Fig. 8 is a comparison diagram of frequency offset estimation, using the method of dividing the npss signal in a symbol and the local signal conjugate into two sections for correlation (denoted as method 1) and comparing it with the method of the present invention, in different signals Under the noise ratio (SNR), a normalized frequency offset in the range (-1,1) is randomly added to the data, and each algorithm is simulated 100 times under each SNR, and the frequency synchronization tracking algorithm is used to calculate the frequency offset after compensation. The normalized frequency offset of the data is multiplied by 15kHz as the difference between the estimated frequency offset and the actual frequency offset. The RMSE of the detected frequency offset is shown in the figure. It can be seen from the image that the frequency offset estimation result of the present invention is closer to Compared with the actual frequency offset value, the accuracy is higher. Table 3 is a comparison table of nsss signal detection time. The direct correlation method is used to compare with the method of the present invention. The data shows that the nsss signal detection of the present invention takes less time and reduces time complexity. When storing the local npss signal, the present invention only needs to store the npss time-domain downsampling signal and frequency-domain signal of one symbol, and the space complexity is reduced.
表3nsss信号检测时间对比表Table 3 nsss signal detection time comparison table
以上所述，仅为本实施例较佳的具体实施方式，但本实施例的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本实施例揭露的技术范围内，根据本实施例的技术方案及其发明构思加以等同替换或改变，都应涵盖在本实施例的保护范围之内。The above is only a preferred specific implementation mode of this embodiment, but the scope of protection of this embodiment is not limited thereto. Anyone familiar with the technical field within the technical scope disclosed in this embodiment Any equivalent replacement or change of the technical solutions and the inventive concepts of the examples shall fall within the scope of protection of this embodiment.
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