CN106656453B - Synchronization device in narrow-band wireless communication terminal - Google Patents
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Abstract
Description
Translated fromChinese技术领域technical field
本发明涉及移动通信领域，具体而言，涉及一种在未来的物联网网络中应用于窄带蜂窝通信终端的同步装置和方法。The present invention relates to the field of mobile communication, in particular, to a synchronization device and method applied to a narrowband cellular communication terminal in a future Internet of Things network.
背景技术Background technique
在最近的通信市场上IoT(物联网)成为行业亮点，诸多运营商和设备上展示了其最新创新成果和应用案例。其中，窄带无线通信技术(NB-Iot)是运营商进军物联网市场的关键。窄带无线通信系统自身具备的低功耗、广覆盖、低成本、大容量等优势，使其可以广泛应用于多种垂直行业，如远程抄表、资产跟踪、智能停车、智慧农业等。3GPP标准的首个版本预计在2016年6月发布，预计窄带无线通信会在LPWA市场的多个技术竞争中脱颖而出，成为领先运营商的最佳选择。IoT (Internet of Things) has become an industry highlight in the recent communication market, and its latest innovations and application cases have been displayed on many operators and devices. Among them, narrowband wireless communication technology (NB-Iot) is the key for operators to enter the IoT market. The advantages of the narrowband wireless communication system itself, such as low power consumption, wide coverage, low cost, and large capacity, make it widely used in various vertical industries, such as remote meter reading, asset tracking, smart parking, and smart agriculture. The first version of the 3GPP standard is expected to be released in June 2016, and narrowband wireless communication is expected to stand out from the competition among multiple technologies in the LPWA market and become the best choice for leading operators.
首个版本的窄带无线通信支持3种运营模式(standalone，in-band，guard-band)，包括：The first version of narrowband wireless communication supports 3 operating modes (standalone, in-band, guard-band), including:
■Standalone：利用现有GERAN系统的频谱，取代一个或多个GSM载波Standalone: Utilize the spectrum of the existing GERAN system to replace one or more GSM carriers
■Guard-band：利用LTE载波保护间隔内未利用的资源块Guard-band: Utilize unused resource blocks within the LTE carrier guard interval
■In-band：利用普通LTE载波内资源块。■In-band: utilizes the resource blocks within the normal LTE carrier.
在窄带无线通信的网络部署中，基站可使用的带宽资源是宽泛的，但对于一个特定的窄带无线通信终端设备来说，其上、下行带宽最大都只占有180kHz(即一个PRB)，当与传统的LTE共用带宽部署时，窄带无线通信系统的下行同步导频只能在特定的PRB上发送，这些特定的PRB与100kHz栅格点相差为固定的2.5kHz或者7.5kHz，称为锚定PRB。In the network deployment of narrowband wireless communication, the bandwidth resources available to the base station are wide, but for a specific narrowband wireless communication terminal device, its uplink and downlink bandwidths only occupy a maximum of 180kHz (that is, a PRB). When the traditional LTE shared bandwidth is deployed, the downlink synchronization pilot frequency of the narrowband wireless communication system can only be sent on specific PRBs. The difference between these specific PRBs and the 100kHz grid point is a fixed 2.5kHz or 7.5kHz, which is called anchor PRB. .
窄带无线通信系统的下行同步导频包括主、辅同步导频两种，主同步信号用于获取网络的时间、频域同步，辅同步信号用于确定小区ID，本发明所涉及的技术方案是窄带无线通信系统的主同步序列的检测。3gpp首个版本的窄带无线通信系统中主同步导频(NPSS)的特性包括：The downlink synchronization pilot of the narrowband wireless communication system includes two kinds of primary and secondary synchronization pilots. The primary synchronization signal is used to obtain the time and frequency domain synchronization of the network, and the secondary synchronization signal is used to determine the cell ID. The technical scheme involved in the present invention is as follows: Detection of primary synchronization sequences for narrowband wireless communication systems. Features of the Primary Synchronization Pilot (NPSS) in the first release of 3gpp's narrowband wireless communication system include:
■NPSS传输周期是一个无线帧长(10ms)■NPSS transmission period is one radio frame length (10ms)
■NPSS使用每个无线帧中子帧5的后11OFDM符号，并且占用各个符号上的11个子载波传输，从子载波0到子载波10NPSS uses the last 11 OFDM symbols of
■NPSS在每个OFDM符号采用相同的ZC序列作为基序列，ZC根序列为u＝5，在频域生成，ZC序列有良好的时域和频域相关性■NPSS uses the same ZC sequence as the base sequence in each OFDM symbol, the ZC root sequence is u=5, generated in the frequency domain, and the ZC sequence has good correlation in the time domain and frequency domain
■NPSS在不同的OFDM符号之间采用随机图样的二进制加扰序列。■ NPSS employs a random pattern of binary scrambling sequences between different OFDM symbols.
由于窄带无线通信的终端设备必须具备低成本的特点，晶振精度较低，因此带来较大的初始频偏，此外如上所述，在和传统LTE同网络部署模式下，窄带无线通信系统下行同步导频所在的锚定PRB和100kHz的扫频栅格间存在着2.5/7.5kHz的频偏，两种因素的叠加导致在窄带无线通信终端设备在初始同步时最多可能达到25kHz以上的初始频偏。Because the terminal equipment of narrowband wireless communication must have the characteristics of low cost, the crystal oscillator precision is low, so it brings a large initial frequency offset. In addition, as mentioned above, in the same network deployment mode as traditional LTE, the downlink synchronization of the narrowband wireless communication system There is a frequency offset of 2.5/7.5kHz between the anchor PRB where the pilot frequency is located and the 100kHz sweep frequency grid. The superposition of the two factors leads to the initial frequency offset of more than 25kHz at most when the narrowband wireless communication terminal equipment is initially synchronized. .
并且，窄带无线通信终端设备往往部署在极低的低信噪比网络环境中，如何在强噪声背景中检测到同步信号也是需要克服的技术难题。In addition, narrowband wireless communication terminal equipment is often deployed in an extremely low and low signal-to-noise ratio network environment, and how to detect a synchronization signal in a strong noise background is also a technical problem that needs to be overcome.
传统LTE系统中的主同步检测方法，例如申请号为20101038021的发明《一种3GPPLTE下行初始主同步检测方法》，或者是申请号为2013103796348的发明《一种用于TD-LTE小区切换的快速下行主同步方法》，以及申请号为201010111963的发明《一种LTE系统中LTE主同步信号检测与序列生成方法及装置》，其所披露的都是通过将接收到的序列与本地生成的序列互相关的方法来检测(或者判断)同步信号的存在。针对窄带无线通信的系统，由于其同步序列较短且工作在极低信噪比以及较大初始频偏的环境下，应用传统LTE系统中使用的频域数据互相关的同步序列检测方法是根本无法找到相关峰的。The primary synchronization detection method in the traditional LTE system, such as the invention with application number 20101038021 "A 3GPPLTE Downlink Initial Primary Synchronization Detection Method", or the invention with application number 2013103796348 "A Fast Downlink for TD-LTE Cell Handover" Primary Synchronization Method", and the invention with application number 201010111963 "A method and device for LTE primary synchronization signal detection and sequence generation in an LTE system", which discloses the cross-correlation between the received sequence and the locally generated sequence method to detect (or judge) the existence of the synchronization signal. For the narrowband wireless communication system, due to its short synchronization sequence and working in the environment of extremely low signal-to-noise ratio and large initial frequency offset, it is fundamental to apply the synchronization sequence detection method of frequency domain data cross-correlation used in traditional LTE systems. No correlation peak could be found.
发明内容SUMMARY OF THE INVENTION
针对现有技术中存在的上述缺陷和不足，本发明的目的在于提供一种应用于物联网窄带蜂窝通信终端的同步装置和方法，在极低的信噪比以及较大的频偏环境下仍能较好地实现主同步信号的检测，并且其实现成本是较低的。In view of the above-mentioned defects and deficiencies in the prior art, the purpose of the present invention is to provide a synchronization device and method applied to the narrowband cellular communication terminal of the Internet of Things, which can still The detection of the primary synchronization signal can be better realized, and the realization cost is lower.
根据本发明的一个方面，提供了一种用于窄带蜂窝通信终端的同步装置，包括以下各模块，如图1所示。According to an aspect of the present invention, a synchronization apparatus for a narrowband cellular communication terminal is provided, which includes the following modules, as shown in FIG. 1 .
M101降采样模块，用于将采样率为1.92MHz的时域采样信号降采样为240kHz的信号。The M101 downsampling module is used to downsample the time domain sampling signal with a sampling rate of 1.92MHz to a signal of 240kHz.
所述降采样模块将每1ms(一个子帧长度)的1920个采样点分成14个OFDM符号时长，第1和第7个OFDM符号时长内的降采样图案为{10,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}，其它OFDM符号长度内的降采样图案为{9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}。The downsampling module divides 1920 sampling points of every 1ms (one subframe length) into 14 OFDM symbol durations, and the downsampling patterns in the first and seventh OFDM symbol durations are {10,8,8,8, 8,8,8,8,8,8,8,8,8,8,8,8,8}, the downsampling pattern in other OFDM symbol lengths is {9,8,8,8,8,8, 8,8,8,8,8,8,8,8,8,8,8,8}.
M201滑动自相关模块，用于初步确定主同步序列存在和初步的位置。The M201 sliding autocorrelation module is used to preliminarily determine the existence and preliminary position of the main synchronization sequence.
所述滑动自相关模块还包括一个数据缓存器，缓存上一个10ms无线帧最后11个OFDM时长的降采样后的数据，因此滑动自相关模块一次处理的总数据长度是当前10ms无线帧以及上一10ms无线帧最后11个OFDM符号的和。The sliding autocorrelation module also includes a data buffer, which buffers the down-sampled data of the last 11 OFDM durations of the previous 10ms radio frame, so the total data length processed by the sliding autocorrelation module at one time is the current 10ms radio frame and the previous 10ms radio frame. The sum of the last 11 OFDM symbols of a 10ms radio frame.
所述滑动自相关模块将处理窗口内的采样点数据逐位移动作为起始位置t，并取出时长为11个OFDM符号的降采样后数据，作为一个滑动窗口，然后将滑动窗口内的采样点分成11组，间隔两组之间的采样点乘以对应的加扰序列后，进行相关累加，并对多个10ms无线帧处理窗口的多组滑动自相关结果进行alpha滤波，最后对各滑动窗的滑动自相关结果进行功率归一化。The sliding autocorrelation module moves the sampling point data in the processing window bit by bit as the starting position t, and takes out the down-sampled data with a duration of 11 OFDM symbols as a sliding window, and then takes the sampling points in the sliding window. Divide into 11 groups, multiply the sampling points between the two groups by the corresponding scrambling sequence, perform correlation accumulation, and perform alpha filtering on multiple groups of sliding autocorrelation results of multiple 10ms wireless frame processing windows. Finally, each sliding window is The sliding autocorrelation results are power normalized.
若存在一个滑动窗的滑动自相关结果大于预设值的门限值，则启动差分互相关模块。If there is a sliding window whose sliding autocorrelation result is greater than the preset threshold value, the differential cross-correlation module is activated.
进一步地，所述滑动自相关模块还包含有小数倍的频偏估计和校准子模块，根据获得的滑动自相关结果的相位值进行小数倍频偏估计和校准，所述的小数倍频偏估计按照下式进行估算,Further, the sliding autocorrelation module also includes a fractional frequency offset estimation and calibration sub-module, and performs fractional frequency offset estimation and calibration according to the phase value of the obtained sliding autocorrelation result. The frequency offset estimation is estimated according to the following formula,
其中，arctan{At}表示对滑动自相关的结果取相位值，1.92MHz是初始时域数据的采样率，137是一个OFDM符号时长的采样点数。Among them, arctan{At } represents the phase value of the result of the sliding autocorrelation, 1.92MHz is the sampling rate of the initial time domain data, and 137 is the number of sampling points for one OFDM symbol duration.
M301差分互相关模块，用于进一步确定是否存在NPSS信号。The M301 differential cross-correlation module is used to further determine whether there is an NPSS signal.
所述差分互相关模块的处理数据对象是从滑动自相关模块获得的一个滑动窗口内的187个点的采样序列，将所述的187点采样序列差分成近似等长的两段，例如，第一段长度为97点，第二段长度为98点，或者，第一段长度为98点，第二段长度为97点，所述的两段序列分别与本地生成的NPSS时域序列进行共轭乘累加后，将两段结果进行相关合并，若相关合并结果大于预设定的门限值，则确认NPSS存在。The processing data object of the differential cross-correlation module is a sampling sequence of 187 points in a sliding window obtained from the sliding autocorrelation module, and the 187-point sampling sequence is differentially divided into two segments of approximately equal length, for example, the first The length of one segment is 97 points, the length of the second segment is 98 points, or, the length of the first segment is 98 points, and the length of the second segment is 97 points, and the two sequences are shared with the locally generated NPSS time domain sequence. After the yoke multiplication and accumulation, the results of the two sections are correlated and combined, and if the correlated combined result is greater than the preset threshold value, it is confirmed that the NPSS exists.
进一步地，所述相关合并还包括对每个10ms无线帧内的合并结果进行功率归一化。Further, the correlation combining further includes performing power normalization on the combining result in each 10ms radio frame.
较优地，在差分相关模块中还包括对接收序列进行整数倍的频偏估计和校准的子模块，所述整数倍的频偏估计和校准子模块在频偏范围内枚举出所有可能的整数倍频偏值，尝试每一种所述整数倍频偏值对本地生成的NPSS时域序列进行调制，并使用调制后的本地NPSS序列进行差分相关，找出使得差分互相关结果的最大值，其对应的整数倍频偏值即为估计值。然后，综合所述的小数倍频偏估计值和整数倍频偏估计值之和为总频偏估计值，按照采样点的采样时刻进行相位校准。Preferably, the differential correlation module also includes a sub-module for performing integer multiple frequency offset estimation and calibration on the received sequence, and the integer multiple frequency offset estimation and calibration sub-module enumerates all possible frequency offsets within the frequency offset range. Integer frequency offset value, try to modulate the locally generated NPSS time-domain sequence with each of the integer frequency offset value, and use the modulated local NPSS sequence to perform differential correlation to find the maximum value that makes the differential cross-correlation result , and its corresponding integer frequency offset value is the estimated value. Then, the sum of the fractional frequency offset estimate and the integer frequency offset estimate is a total frequency offset estimate, and phase calibration is performed according to the sampling time of the sampling point.
更优地，在差分相关模块中还包括定时估计的子模块，即先产生高采样率的所述本地NPSS时域序列，然后尝试不同的初始采样点偏移并进行下采样，生成所述的本地NPSS时域序列，然后进行所述的差分互相关，并找出使得差分互相关值最大的初始偏移值，作为估计的定时偏移量。More preferably, the differential correlation module also includes a timing estimation sub-module, that is, the local NPSS time-domain sequence with a high sampling rate is first generated, and then different initial sampling point offsets are tried and down-sampled to generate the described local NPSS time domain sequence. The local NPSS time-domain sequence, and then the differential cross-correlation is performed, and the initial offset value that maximizes the differential cross-correlation value is found as the estimated timing offset.
本发明装置的有益效果是：为窄带无线通信终端实现在低信噪比、大初始频偏环境下仍能正确检测到主同步序列提供了解决方案，区别于传统的将接收信号与本地序列相关的方案，本发明提供的方案性能更优，由于采样本发明方案能获得多个10ms无线帧之间的合并增益，在具体的工程实践中就可以用更长的同步时间来换取同步接入的准确率，因此适应于窄带无线通信低时延敏感、高恶劣环境下接入的性能要求。在较优配置下，本发明所公开的装置在检测NPSS信号的过程中还执行了小数倍和整数倍频偏的估计和校准，这就进一步提高了抗大频偏的性能。更优配置下，本发明所公开的装置还能进行初步的定时估计，这就为后续的下行数据接收创造了更好的条件，提升了接收机的整体性能。本发明装置已经进行了多次仿真实验和评估，根据3gpp协议约定，按照3gpp约定的仿真配置，使用本发明所公开的装置可以获得95％以上的检测成功率，在较优配置下可以达到定时同步在4Tsamp以内(其中Tsamp对应1.92MHz采样间隔)，频率同步误差在50Hz范围内。The beneficial effect of the device of the present invention is that it provides a solution for the narrowband wireless communication terminal to correctly detect the primary synchronization sequence under the environment of low signal-to-noise ratio and large initial frequency deviation, which is different from the traditional correlation between the received signal and the local sequence. The performance of the solution provided by the present invention is better. Since the combination gain between multiple 10ms wireless frames can be obtained by sampling the solution of the present invention, in specific engineering practice, a longer synchronization time can be used in exchange for synchronous access. Therefore, it is suitable for the performance requirements of narrowband wireless communication with low delay sensitivity and high harsh environment. Under the preferred configuration, the device disclosed in the present invention also performs the estimation and calibration of fractional and integer frequency offsets in the process of detecting the NPSS signal, which further improves the performance of resisting large frequency offsets. Under a better configuration, the device disclosed in the present invention can also perform preliminary timing estimation, which creates better conditions for subsequent downlink data reception and improves the overall performance of the receiver. The device of the present invention has been subjected to many simulation experiments and evaluations. According to the 3gpp protocol and the simulation configuration agreed by 3gpp, the device disclosed in the present invention can obtain a detection success rate of more than 95%, and the timing can be achieved under the optimal configuration. The synchronization is within 4Tsamp (where Tsamp corresponds to the 1.92MHz sampling interval), and the frequency synchronization error is within 50Hz.
根据本发明的另一个方面，提供了一种用于窄带蜂窝通信终端的同步检测方法，其包括以下若干过程。According to another aspect of the present invention, a synchronization detection method for a narrowband cellular communication terminal is provided, which includes the following procedures.
S101降采样过程，将1.92MHz采样率的时域信号以OFDM符号为单位长度，按照固定降采样图案降采样为240kHz采样率的信号；所述的固定降采样图案如本发明的装置部分的描述。S101 downsampling process, the time domain signal with a sampling rate of 1.92MHz is downsampled to a signal with a sampling rate of 240kHz according to a fixed downsampling pattern with an OFDM symbol as the unit length; the fixed downsampling pattern is as described in the device part of the present invention .
S201滑动自相关过程，将10ms无线帧处理窗长内的采样点数据逐位移动作为起始位置t，并以长度为11个OFDM符号时长作为滑动窗口，将所述滑动窗口内的采样点分成11组，间隔两组之间的采样点进行相关累加。S201 is a sliding autocorrelation process. The sampling point data within the 10ms wireless frame processing window is moved bit by bit as the starting position t, and the length of 11 OFDM symbols is used as the sliding window, and the sampling points in the sliding window are divided into There are 11 groups, and the sampling points between the two groups are correlated and accumulated.
较优地，所述的滑动自相关过程中还包括根据自相关结果进行小数倍频偏估计和校准的子过程。Preferably, the sliding autocorrelation process further includes a sub-process of performing fractional frequency offset estimation and calibration according to the autocorrelation result.
若所述滑动自相关过程计算获得的滑动自相关大于门限值，则启动差分互相关过程。If the sliding autocorrelation calculated by the sliding autocorrelation process is greater than the threshold value, the differential cross-correlation process is started.
S301差分互相关过程，将所述滑动自相关过程所获得的滑动窗口内的同步序列差分成等长两部分，并与本地生成的同步序列进行互相关累加。S301 is a differential cross-correlation process, which divides the synchronization sequence in the sliding window obtained by the sliding autocorrelation process into two parts of equal length, and performs cross-correlation accumulation with the locally generated synchronization sequence.
较优地，所述的差分互相关过程中还包括对整数倍频偏进行估计和校准的子过程。Preferably, the differential cross-correlation process further includes a sub-process of estimating and calibrating the integer frequency offset.
更优地，所述的差分互相关过程中还包括对定时的估计子过程。More preferably, the differential cross-correlation process also includes a timing estimation sub-process.
若所述差分互相关过程所获得的互相关结果大于门限值，则确认所检测出的序列是主同步序列。If the cross-correlation result obtained by the differential cross-correlation process is greater than the threshold value, it is determined that the detected sequence is the primary synchronization sequence.
附图说明Description of drawings
图1为本发明涉及的一种同步装置的模块结构示意图。FIG. 1 is a schematic structural diagram of a module of a synchronization device according to the present invention.
图2为降采样图案示意图。FIG. 2 is a schematic diagram of a downsampling pattern.
图3为实践中随机抽取1ms时间长度内实际子帧采样点和采样图案的对照关系示意图。FIG. 3 is a schematic diagram of a comparison relationship between sampling points and sampling patterns of actual subframes randomly selected within a time length of 1 ms in practice.
图4为NPSS序列物理映射示意图。Figure 4 is a schematic diagram of physical mapping of NPSS sequences.
图5为实践中存在的10ms处理窗口与实际无线帧位置对照示意图。FIG. 5 is a schematic diagram showing the comparison between the 10ms processing window and the actual radio frame position existing in practice.
图6为滑动自相关示意图。FIG. 6 is a schematic diagram of sliding autocorrelation.
图7为定时估计中尝试不同定时偏移的示意图。FIG. 7 is a schematic diagram of trying different timing offsets in timing estimation.
具体实施方式Detailed ways
以下通过特定的具体实例说明本发明的实施方式，此处所描述的具体实施例仅用以解释本发明，但并不用于限定本发明。本领域技术人员可由本说明书所揭露的内容轻易地了解本发明的其他优点与功效。The embodiments of the present invention are described below through specific specific examples. The specific embodiments described herein are only used to explain the present invention, but are not intended to limit the present invention. Those skilled in the art can easily understand other advantages and functions of the present invention from the content disclosed in this specification.
请参阅附图，NPSS检测装置所含的模块如图1所示，包括降采样模块，滑动自相关模块(AutoCorr)，粗互相关模块和细互相关模块。Please refer to the attached drawings. The modules included in the NPSS detection device are shown in FIG. 1 , including a downsampling module, a sliding autocorrelation module (AutoCorr), a coarse cross-correlation module and a fine cross-correlation module.
M101降采样模块M101 Downsampling Module
降采样模块实现从采样率1.92MHz到240K的降采样，降采样前每个子帧输入为1ms的1920＝(137*14+2)个采样点，降采样后每个子帧输出238＝(17*14)个采样点，并且按照下面的固定降采样图案进行：The downsampling module realizes downsampling from the sampling rate of 1.92MHz to 240K. Before downsampling, the input of each subframe is 1920=(137*14+2) sampling points of 1ms. After downsampling, each subframe outputs 238=(17* 14) sampling points, and follow the following fixed downsampling pattern:
将每个子帧的1920个采样点记成14组(14个OFDM符号)，第1组的采样点是138个，第2-6组的采样点是137个，第7组的采样点是138个，第8-14组的采样点是137个。第1-第6组记为时隙1(slot1)，第7-第14组记为时隙2(slot2)，每个时隙的第1组记为首个OFDM符号，剩余的组记为非首个OFDM符号。Record the 1920 sampling points of each subframe into 14 groups (14 OFDM symbols), the sampling points of the first group are 138, the sampling points of the second-6 groups are 137, and the sampling points of the seventh group are 138 There are 137 sampling points in groups 8-14. The 1st-6th group is recorded as time slot 1 (slot1), the 7th-14th group is recorded as time slot 2 (slot2), the first group of each time slot is recorded as the first OFDM symbol, and the remaining groups are recorded as non- The first OFDM symbol.
每个时隙的首个OFDM符号(即第1和第7组)降采样图案为{10,8,8,8,8,8,8,8,8，8,8,8,8,8,8,8,8}；如图2上半部分所示，先每隔10个点下采样1一个点，对剩余的采样点每隔8个点下采样1个点，并以此类推。The downsampling pattern of the first OFDM symbol (i.e. the 1st and 7th group) of each slot is {10, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 , 8, 8, 8}; as shown in the upper part of Figure 2, firstly downsample 1 point every 10 points, downsample the remaining
非首个OFDM符号(即第2-6组，第8-14组)采样图案为{9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}；如图2下半部分所示，先每隔9个点下采样1一个点，对剩余的采样点每隔8个点下采样1个点，并以此类推。The sampling pattern of the non-first OFDM symbol (ie the 2-6th group, the 8-14th group) is {9, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8 ,8,8,8}; as shown in the lower part of Figure 2, firstly downsample 1 point every 9 points, downsample the remaining
这样，每个OFDM符号降采样后的点数都是17个点，每个1ms时长内包含采样点数为238＝(17*14)。In this way, the number of points after downsampling of each OFDM symbol is 17 points, and the number of sampling points included in each 1ms duration is 238=(17*14).
图3所示为实践中随机抽取1ms时间长度内实际子帧采样点和采样图案的对照关系示意，假设随机抽取到的1ms时间窗起始位置对应的是上一子帧的最后一个OFDM符号，而第一组的采样图案为{10,8,8,8,8,8,8,8,8，8,8,8,8,8,8,8,8}，因此对应到子帧内前17个降采样后的数据是原始CP段内的第1点，数据段内第2,第10，…,第122点，接下来降采样窗口对应的是本子帧的第一个OFDM符号，采样图案是{9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}，因此对应到降采样后子帧内的17个数据是原始CP段内的第3点，数据段内第1,第9，…,第122点，第三个降采样窗口对应的是本子帧的第二个OFDM符号，采样图案仍然是{9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}，因此对应到子帧内降采样后的17个数据是原始CP段内的第2点，数据段内第1,第9，…,第122点，依次类推。Figure 3 shows a schematic diagram of the comparison between sampling points and sampling patterns of actual subframes randomly selected within a time length of 1ms in practice. It is assumed that the starting position of the randomly selected 1ms time window corresponds to the last OFDM symbol of the previous subframe. The sampling pattern of the first group is {10,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}, so it corresponds to the subframe The first 17 downsampled data is the first point in the original CP segment, the second, tenth, ..., 122nd point in the data segment, and the next downsampling window corresponds to the first OFDM symbol of this subframe, The sampling pattern is {9,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8}, so it corresponds to 17 in the subframe after downsampling The data is the 3rd point in the original CP segment, the 1st, 9th, ..., 122nd point in the data segment, the third downsampling window corresponds to the second OFDM symbol of this subframe, and the sampling pattern is still { 9, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8}, so the 17 data corresponding to the downsampling in the subframe are the original The 2nd point in the CP segment, the 1st, 9th, ..., 122nd point in the data segment, and so on.
由此可以看出，采用上述固定采样图案进行降采样可以保证在每个OFDM符号时间长度内降采样后的点数个数相同，并且保证原始OFDM符号降采样后采样位置间的误差保持在最大1个采样点，大部分OFDM采样位置无误差，从而一方面降低了后续滑动自相关的运算量，同时又最大限度减小了由于降采样给滑动自相关带来的性能下降。It can be seen from this that the use of the above fixed sampling pattern for downsampling can ensure that the number of points after downsampling is the same within the time length of each OFDM symbol, and that the error between the sampling positions after downsampling of the original OFDM symbol remains at a maximum of 1 There are many sampling points, and most of the OFDM sampling positions are error-free, which reduces the computational complexity of the subsequent sliding autocorrelation on the one hand, and at the same time minimizes the performance degradation caused by the downsampling to the sliding autocorrelation.
M201滑动自相关模块M201 Sliding Autocorrelation Module
图4所示如在协议[36.211]中的约定，窄带无线通信系统的主同步码NB-PSS序列在频域上是短序列，频域上占用11个RE，在时域上占用11个连续的OFDM符号并且经过加扰后发送。As shown in Figure 4, as agreed in the protocol [36.211], the primary synchronization code NB-PSS sequence of the narrowband wireless communication system is a short sequence in the frequency domain, occupying 11 REs in the frequency domain and 11 consecutive REs in the time domain. OFDM symbols are scrambled and sent.
经过降采样后1ms的采样点数是238个，滑动自相关模块的一次处理对象是每个无线帧(10ms)窗口时间内的接收时域数据，实际滑动自相关模块还包括一个数据缓存器，缓存上一个无线帧窗口内最后11个OFDM符合的数据，即11*17个采样点，因此，滑动自相关模块的实际一次处理对象包括一个无线帧降采样后的2380个采样点+11*17降采样点，共2567个降采样点的数据。After downsampling, the number of sampling points in 1ms is 238. The primary processing object of the sliding autocorrelation module is the received time domain data within the window time of each wireless frame (10ms). The actual sliding autocorrelation module also includes a data buffer. The last 11 OFDM-compliant data in the last wireless frame window, that is, 11*17 sampling points, therefore, the actual processing object of the sliding autocorrelation module includes 2380 sampling points after downsampling of a wireless frame + 11*17 downsampling. Sampling points, a total of 2567 down-sampling points.
增加滑动自相关模块中的数据缓存器的有益效果是防止数据漏检，如图5所示，可能存在的场景是，当前10ms处理窗口的起始位置正好位于真实发送NPSS子帧的帧内部，增加了11个OFDM符号时长的数据缓存就可以保证增长后的滑动自相关处理窗口内一定保存有至少一个完整的NPSS序列。The beneficial effect of adding the data buffer in the sliding autocorrelation module is to prevent data from being missed. As shown in Figure 5, a possible scenario is that the starting position of the current 10ms processing window is just inside the frame where the NPSS subframe is actually sent. Adding a data buffer of 11 OFDM symbol durations can ensure that at least one complete NPSS sequence must be stored in the increased sliding autocorrelation processing window.
如图6所示，将处理窗口内的采样点数据逐位移动作为起始位置t，并从长度为11个OFDM符号(即187个采样点)的时长窗口内取出采样点，作为一个滑动窗口。As shown in Figure 6, the sampling point data in the processing window is moved bit by bit as the starting position t, and sampling points are taken out from the time window with a length of 11 OFDM symbols (ie 187 sampling points) as a sliding window .
然后将一个滑动窗口内的187个采样点分成11组，每组17个采样点，如图6所示间隔两组之间的采样点进行相关累加，在相关累计中还需要乘以每个OFDM符号的加扰序列，如下式所示，Then, the 187 sampling points in a sliding window are divided into 11 groups, with 17 sampling points in each group. As shown in Figure 6, the sampling points between the two groups are correlated and accumulated, and each OFDM needs to be multiplied in the correlation accumulation. The scrambling sequence of symbols, as shown below,
上式中，
较优地，在工程实践中还包括对连续无线帧(10ms)窗口上自相关结果的alpha滤波运算Preferably, in the engineering practice, the alpha filtering operation of the autocorrelation result on the continuous radio frame (10ms) window is also included.
At＝a×At-1+(1-αNPSS,1)×AtAt =a×At-1 +(1-αNPSS,1 )×At
从而获得分集合并增益，进一步提高检测的准确程度。Thus, the diversity combining gain is obtained, and the detection accuracy is further improved.
然后，对滑动相关结果进行功率归一化，Then, power normalization is performed on the sliding correlation result,
判断归一化后的滑动自相关结果是否大于预定义的门限值，若大于则认为该无线帧窗口内含有NPSS，大致起始位置在第t个采样点，并转入下一个粗互相关模块，否则转到下一个无线帧窗口的判断。Determine whether the normalized sliding autocorrelation result is greater than the predefined threshold value, if it is greater than the radio frame window is considered to contain NPSS, the approximate starting position is at the t-th sampling point, and the next coarse cross-correlation is transferred. module, otherwise go to the judgment of the next radio frame window.
工程中较优地，还包括根据滑动自相关结果对降采样信号进行小数倍频偏估计和校准。Preferably in the project, it also includes performing fractional frequency offset estimation and calibration on the down-sampling signal according to the sliding autocorrelation result.
如上所述，由于初始采样率是1.92MHz，一个OFDM符号包含的采样点数是137个，因此一个OFDM符号时间长度是137/1.92MHz，在一个OFDM符号时间长度上由频偏所造成的相位旋转是：As mentioned above, since the initial sampling rate is 1.92MHz and the number of sampling points contained in one OFDM symbol is 137, the time length of one OFDM symbol is 137/1.92MHz, and the phase rotation caused by the frequency offset in the time length of one OFDM symbol Yes:
其中θ即是自相关结果的相位值。where θ is the phase value of the autocorrelation result.
因此，频偏的估计值：
需要指出的是，当真实的频偏值在一个OFDM符号上造成的相位旋转小于π，上式中的估计结果即是完整的频偏值，但在通常情况下，如背景技术所述，由于窄带无线通信系统非常大的初始频偏都会造成大于π的相位旋转，因此上式中的估计结果只是频偏值的小数部分，称为小数倍频偏值。It should be pointed out that when the phase rotation caused by the real frequency offset value on an OFDM symbol is less than π, the estimation result in the above formula is the complete frequency offset value. The very large initial frequency offset of a narrowband wireless communication system will cause a phase rotation greater than π, so the estimation result in the above formula is only the fractional part of the frequency offset value, which is called the fractional frequency offset value.
最后，按照估计出的小数倍频偏值对滑动窗内的降采样序列进行频偏校准，Finally, the frequency offset calibration of the down-sampling sequence in the sliding window is performed according to the estimated fractional frequency offset value,
其中，λi是第i个采样点的采样时刻。Among them, λi is the sampling time of the ith sampling point.
M301差分互相关模块M301 Differential Cross-Correlation Module
差分互相关模块仅在滑动自相关判断满足存在NPSS的条件下启动，作用是确认NPSS的存在以及估计和校准整数倍频偏，在优选情况下还包括消除定时偏差。The differential cross-correlation module is only activated when the sliding autocorrelation judgment satisfies the existence of NPSS. Its function is to confirm the existence of NPSS, estimate and calibrate the integer frequency offset, and in the preferred case, also includes eliminating the timing offset.
首先，按照协议规定生成无频偏的本地序列，记为di，di的采样率与降采样接收序列相同，并按照不同的整数倍频偏来调制di。First, a local sequence without frequency offset is generated according to the protocol, denoted as di , the sampling rate of di is the same as that of the down-sampling received sequence, and di is modulated according to different integer frequency offsets.
背景技术中介绍了窄带无线通信系统在小区搜索时遇到最大频偏为±25.5KHz，在这个范围内存在5种可能的整数频偏，分别是
采用枚举法，尝试上述假设中的每一种整数倍频偏对初始的本地序列进行调制。Using the enumeration method, try each of the above assumptions to modulate the initial local sequence with an integer octave offset.
然后，将调制后的本地序列与滑动自相关输出的采样序列相关，对11个OFDM符号时长内的NPSS序列分成近似等长的两段进行差分相关，即将长度为187点的本地序列以及接收采样序列均分成两段，第一段长度为94点，第二段长度为93点(或者也可以分割成第一段93点，第二段94点)，并将两者进行相关，Then, correlate the modulated local sequence with the sampling sequence output by the sliding autocorrelation, and divide the NPSS sequence within 11 OFDM symbols into two segments of approximately equal length for differential correlation, that is, the local sequence with a length of 187 points and the received samples. The sequence is divided into two segments, the length of the first segment is 94 points, and the length of the second segment is 93 points (or can also be divided into 93 points in the first segment and 94 points in the second segment), and the two are correlated,
其中*表示取共轭运算。Where * represents the conjugation operation.
在本领域的惯常技术方法中，求互相关多数是通过一个完整的接收序列和本地序列进行相关运算来获得的，但在本发明方案中，是将完整的同步序列拆分成近似等长的两段，再分别和本地序列进行相关而获得的。这是由于，按照协议规定，NPSS在不同的无线帧可以映射到不同的天线端口发送，因此如果采样惯常手段，对一个子帧长度(187点)的NPSS本地序列和接收序列进行直接相关就无法再在多个无线帧窗口间进行合并以获取合并增益；而本方案采用子帧内两段先差分再相关，一个子帧内部的天线端口是不变的，不同无线帧间差分相关的结果仍然可以合并，因此规避了无线帧间天线端口间切换的问题，从而获取合并增益。In the conventional technical methods in the art, most of the cross-correlation is obtained by performing a correlation operation on a complete received sequence and a local sequence, but in the solution of the present invention, the complete synchronization sequence is divided into approximately equal lengths. The two segments are obtained by correlating with local sequences respectively. This is because, according to the protocol, NPSS can be mapped to different antenna ports for transmission in different radio frames. Therefore, if the conventional method is sampled, it is impossible to directly correlate the NPSS local sequence and the received sequence with a subframe length (187 points). Then, multiple radio frame windows are combined to obtain the combined gain; however, in this scheme, two segments in a subframe are first differentiated and then correlated. The antenna ports within a subframe are unchanged, and the result of differential correlation between different radio frames is still the same. It can be combined, thus avoiding the problem of switching between antenna ports between wireless frames, so as to obtain combining gain.
将本10ms无线帧内的差分相关结果进行功率归一化，并将多个10ms无线帧窗口内的差分相关结果进行合并Normalize the power of the differential correlation results in the current 10ms radio frame, and combine the differential correlation results in multiple 10ms radio frame windows
其中，
若差分互相关结果大于门限值，则找出一个使得差分互相关结果最大的k值，If the differential cross-correlation result is greater than the threshold value, find a k value that maximizes the differential cross-correlation result,
认为差分互相关确认NPSS信号已经成功检测，其所对应的频偏值即是整数倍频偏估计结果。It is considered that the differential cross-correlation confirms that the NPSS signal has been successfully detected, and the corresponding frequency offset value is the result of integer frequency offset estimation.
总频偏估计结果是小数倍和整数倍频偏估计结果之和。The total frequency offset estimation result is the sum of the fractional multiple and integer multiple frequency offset estimation results.
对接收到的NPSS序列进行频偏校准，Perform frequency offset calibration on the received NPSS sequence,
其中，λi是第i个采样点的采样时刻。Among them, λi is the sampling time of the ith sampling point.
在工程中的较优情况下，差分互相关模块还包括初步定时估计的处理。如前面的描述，初始本地序列di的采样率与降采样接收序列相同(即为240kHz)。若需要初步估计定时的处理，则首先生成高采样率的本地序列，然后尝试多种的初始采样点偏移并进行下采样，例如生成的本地序列采样率为1.92MHz，如图7所示，尝试的采样点偏移分别是j＝0,1,2，….7点，下采样率为8，对应的下采样序列记为
其所对应的采样点偏移j即为初始的定时估计量。The corresponding sampling point offset j is the initial timing estimate.
按照3gpp约定的仿真配置(如表1)，使用本发明所公开的装置可以获得95％以上的检测成功率，在较优配置下可以达到定时同步在4Tsamp以内(其中Tsamp对应1.92MHz采样间隔)，频率同步误差在50Hz范围内。According to the simulation configuration agreed by 3gpp (as shown in Table 1), the detection success rate of more than 95% can be obtained by using the device disclosed in the present invention, and the timing synchronization can be achieved within 4Tsamp under the better configuration (wherein Tsamp corresponds to 1.92MHz sampling interval), the frequency synchronization error is within 50Hz.
表1性能仿真条件Table 1 Performance simulation conditions
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| CN201911187573.9AActiveCN111106892B (en) | 2017-02-05 | 2017-02-05 | Synchronous detection method in narrow-band wireless communication terminal |
| CN201911187338.1AActiveCN111106923B (en) | 2017-02-05 | 2017-02-05 | Synchronization device in narrow-band wireless communication terminal |
| CN201911187310.8AActiveCN110798304B (en) | 2017-02-05 | 2017-02-05 | Synchronization device in narrow-band wireless communication terminal |
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| CN201911187338.1AActiveCN111106923B (en) | 2017-02-05 | 2017-02-05 | Synchronization device in narrow-band wireless communication terminal |
| CN201911187310.8AActiveCN110798304B (en) | 2017-02-05 | 2017-02-05 | Synchronization device in narrow-band wireless communication terminal |
| CN201911187605.5AActiveCN111342948B (en) | 2017-02-05 | 2017-02-05 | Synchronous detection device applied to narrow-band wireless communication system terminal |
| CN201911187364.4AExpired - Fee RelatedCN111106924B (en) | 2017-02-05 | 2017-02-05 | Synchronous detection device applied to narrow-band wireless communication system terminal |
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| CN111342948A (en) | 2020-06-26 |
| CN111106892A (en) | 2020-05-05 |
| CN110932837B (en) | 2021-11-16 |
| CN111106923B (en) | 2021-11-19 |
| CN110798304B (en) | 2021-10-01 |
| CN110798304A (en) | 2020-02-14 |
| CN111106923A (en) | 2020-05-05 |
| CN111106924B (en) | 2022-03-04 |
| CN111106924A (en) | 2020-05-05 |
| CN106656453A (en) | 2017-05-10 |
| CN111106892B (en) | 2021-08-24 |
| CN111342948B (en) | 2022-01-28 |
| CN110932837A (en) | 2020-03-27 |
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