技术领域technical field
本发明涉及电子通信领域，特别涉及一种帧同步及载波频偏联合检测方法和装置。The invention relates to the field of electronic communication, in particular to a frame synchronization and carrier frequency offset joint detection method and device.
背景技术Background technique
在基于正交频分复用(Orthogonal Frequency Division Multiplexing，简称“OFDM”)的802.11b/g/n通信协议中，无论是传统模式，高吞吐量混合(HT-mixed)模式，还是高吞吐量绿野(HT-greenfield)模式，都需要从前导序列中准确提取帧同步及载波频偏信息。为了支持多天线传输，与802.11b/g协议不同，802.11n协议在不同天线发送的前导序列中加入了不同的循环移位(CSD)以避免非故意的波束成形效应。但是，加入CSD会在接收端产生假多径效应，使互相关检测产生多个峰值，严重地影响了已有的基于互相关检测的帧同步算法的准确性。基于自相关检测的帧同步算法虽然不受CSD的影响，但单独使用准确性不高。其它的帧同步算法，如频域帧同步，虽然也能消除CSD的影响，但有很多限制条件，如必须在载波频偏已被消除的情况下才使用，且计算复杂度高。In the 802.11b/g/n communication protocol based on Orthogonal Frequency Division Multiplexing ("OFDM"), whether it is the traditional mode, the high-throughput mixed (HT-mixed) mode, or the high-throughput The green field (HT-greenfield) mode needs to accurately extract frame synchronization and carrier frequency offset information from the preamble sequence. In order to support multi-antenna transmission, unlike the 802.11b/g protocol, the 802.11n protocol adds different cyclic shifts (CSD) to the preamble sent by different antennas to avoid unintentional beamforming effects. However, the addition of CSD will produce false multipath effects at the receiving end, causing multiple peaks in cross-correlation detection, which seriously affects the accuracy of existing frame synchronization algorithms based on cross-correlation detection. Although the frame synchronization algorithm based on autocorrelation detection is not affected by CSD, its accuracy is not high when used alone. Other frame synchronization algorithms, such as frequency domain frame synchronization, can also eliminate the influence of CSD, but there are many restrictions, such as it must be used only when the carrier frequency offset has been eliminated, and the calculation complexity is high.
发明内容Contents of the invention
本发明的目的在于提供一种帧同步及载波频偏联合检测方法和装置，使得帧同步及载波频偏的检测不受循环移位的影响，且帧同步及载波频偏两者联合检测，可以降低系统复杂度，提高精度。The purpose of the present invention is to provide a method and device for joint detection of frame synchronization and carrier frequency offset, so that the detection of frame synchronization and carrier frequency offset is not affected by cyclic shift, and the joint detection of frame synchronization and carrier frequency offset can achieve Reduce system complexity and improve accuracy.
为解决上述技术问题，本发明的实施方式提供了一种帧同步及载波频偏 联合检测方法，包含以下步骤：In order to solve the above technical problems, embodiments of the present invention provide a frame synchronization and carrier frequency offset joint detection method, comprising the following steps:
对接收到的数据包进行检测，获得短序列的重复模式；其中，所述数据包至少包含短训练序列中最后N个重复的短序列和长训练序列中2个重复的长序列；其中，所述N为大于2的自然数；Detecting the received data packet to obtain the repetition pattern of the short sequence; wherein the data packet contains at least the last N repeated short sequences in the short training sequence and 2 repeated long sequences in the long training sequence; wherein the Said N is a natural number greater than 2;
对短训练序列重复段进行不同间隔的自相关检测，获得载波频偏估计；Perform autocorrelation detection at different intervals on the short training sequence repeat segment to obtain carrier frequency offset estimation;
对长训练序列重复段进行自相关检测，用检测结果优化载波频偏估计；Carry out autocorrelation detection on the repeating segment of the long training sequence, and use the detection result to optimize the carrier frequency offset estimation;
根据估计得到的载波频偏，长训练序列的自相关值和短训练序列不同间隔的自相关值，获得帧同步点估计偏差函数；According to the estimated carrier frequency offset, the autocorrelation value of the long training sequence and the autocorrelation value of the short training sequence at different intervals, the frame synchronization point estimation deviation function is obtained;
找到所述帧同步点估计偏差函数的最大值点对应的采样点，并分别将查找得到的采样点及其对应的载波频偏估计作为最佳帧同步点和最佳载波频偏。Find the sampling point corresponding to the maximum point of the estimated deviation function of the frame synchronization point, and use the obtained sampling point and its corresponding carrier frequency offset estimation as the optimal frame synchronization point and the optimal carrier frequency offset respectively.
本发明的实施方式还提供了一种帧同步及载波频偏联合检测装置，包含：数据接收模块，短序列处理模块，长序列处理模块和结果输出模块；The embodiment of the present invention also provides a frame synchronization and carrier frequency offset joint detection device, including: a data receiving module, a short sequence processing module, a long sequence processing module and a result output module;
所述数据接收模块用于接收数据包；其中，所述数据包至少包含短训练序列中最后N个重复的短序列和长训练序列中的2个重复的长序列；其中，所述N为大于2的自然数；The data receiving module is used to receive data packets; wherein, the data packets include at least the last N repeated short sequences in the short training sequence and 2 repeated long sequences in the long training sequence; wherein, the N is greater than the natural number of 2;
所述短序列处理模块用于对接收到的数据包进行检测，获得短序列的重复模式；并对短训练序列重复段进行不同间隔的自相关检测，获得载波频偏估计；The short sequence processing module is used to detect the received data packets to obtain the repetition pattern of the short sequence; and perform autocorrelation detection at different intervals on the short training sequence repetition section to obtain carrier frequency offset estimation;
所述长序列处理模块用于对长训练序列重复段进行自相关检测，用检测结果优化载波频偏估计；并根据估计得到的载波频偏，长训练序列和长训练序列的相关值，获得帧同步点估计偏差函数；The long sequence processing module is used to perform autocorrelation detection on the long training sequence repeat segment, and use the detection result to optimize the carrier frequency offset estimation; and obtain the frame according to the estimated carrier frequency offset, the long training sequence and the correlation value of the long training sequence Synchronization point estimation bias function;
所述结果输出模块用于找到所述帧同步点估计偏差函数的最大值点对应的采样点，并分别将查找得到的采样点及其对应的载波频偏估计作为最佳 帧同步点和最佳载波频偏。The result output module is used to find the sampling point corresponding to the maximum point of the estimated deviation function of the frame synchronization point, and take the obtained sampling point and its corresponding carrier frequency offset estimation as the optimal frame synchronization point and the optimal frame synchronization point respectively. Carrier frequency offset.
本发明实施方式相对于现有技术而言，通过采用短训练序列的最后几个短序列和大部分的长训练序列进行帧同步和载波频偏估计，并且将帧同步估计和载波频偏估计联合起来形成了一个正反馈，即帧同步点估计偏差函数的值既是帧同步点估计偏差的函数，又是载波频偏估计偏差的函数，使得在帧同步和载波频偏估计中同时使用了短训练序列和长训练序列，可以提高估计运算的精度。而且，由于本实施方式没有使用基于互相关检测的帧同步算法，因此，在前导序列中加入CSD不会对本实施方式产生任何影响，从而本实施方式可以适用于802.11b/g/n等通信协议。进一步地，由于本实施方式可联合实现数据包检测，帧同步估计，及载波频偏估计，因此整体系统复杂度较低。Compared with the prior art, the embodiment of the present invention performs frame synchronization and carrier frequency offset estimation by using the last few short sequences of short training sequences and most of the long training sequences, and combines frame synchronization estimation and carrier frequency offset estimation Together, a positive feedback is formed, that is, the value of the frame synchronization point estimation deviation function is not only a function of the frame synchronization point estimation deviation, but also a function of the carrier frequency offset estimation deviation, so that the short training time is used in both frame synchronization and carrier frequency offset estimation. Sequences and long training sequences can improve the accuracy of estimation operations. Moreover, since this embodiment does not use a frame synchronization algorithm based on cross-correlation detection, adding CSD to the preamble will not have any impact on this embodiment, so this embodiment can be applied to communication protocols such as 802.11b/g/n . Furthermore, since this embodiment can jointly implement data packet detection, frame synchronization estimation, and carrier frequency offset estimation, the overall system complexity is relatively low.
另外，在所述对短训练序列进行不同间隔的自相关检测，获得估计载波频偏的步骤中，包含以下子步骤：In addition, in the step of performing autocorrelation detection at different intervals on the short training sequence and obtaining the estimated carrier frequency offset, the following sub-steps are included:
计算每一个间隔对应的短序列重复段的自相关值；Calculate the autocorrelation value of the short sequence repeat segment corresponding to each interval;
分别根据所述计算得到的短序列自相关值的相位，获得短序列频偏估计值；Obtain short sequence frequency offset estimation values according to the phases of the calculated short sequence autocorrelation values respectively;
对所述短序列频偏估计值进行相位展开，去除相位混淆度；performing phase unwrapping on the short sequence frequency offset estimation value to remove phase confusion;
对所述去除相位混淆度的短序列频偏估计值，引入第一修正因子，计算计入不同间隔的自相关值得到的载波频偏估计；其中，所述第一修正因子用于加权合并从不同间隔的自相关值得到的频偏估计，其取值根据N和短序列的间隔确定。For the short-sequence frequency offset estimation value of the phase ambiguity removal, a first correction factor is introduced to calculate the carrier frequency offset estimate obtained by taking into account the autocorrelation values of different intervals; wherein, the first correction factor is used for weighted combination from Frequency offset estimation obtained from autocorrelation values at different intervals, and its value is determined according to N and the interval of the short sequence.
另外，在所述根据估计得到的载波频偏，长训练序列的自相关值和短训练序列不同间隔的自相关值，获得帧同步点估计偏差函数的步骤中，包含以下子步骤：In addition, in the step of obtaining the estimated deviation function of the frame synchronization point according to the estimated carrier frequency offset, the autocorrelation value of the long training sequence and the autocorrelation value of the short training sequence at different intervals, the following substeps are included:
计算长序列重复段的自相关值；Calculation of autocorrelation values for long sequence repeats;
采用所述短序列的载波频偏估计，对所述长序列的自相关值的角度进行相位展开，去除相位混淆度；Using the carrier frequency offset estimation of the short sequence, phase unwrapping the angle of the autocorrelation value of the long sequence to remove the phase ambiguity;
对所述去除相位混淆度的长序列的相关值的角度，引入第二修正因子，计算计入长序列的自相关值得到的频偏估计；其中，所述第二修正因子用于加权合并从短序列得到的频偏估计和从长序列得到的频偏估计，其取值根据N确定；For the angle of the correlation value of the long sequence that removes the phase confusion, a second correction factor is introduced to calculate the frequency offset estimate that is included in the autocorrelation value of the long sequence; wherein, the second correction factor is used for weighting and merging from The frequency offset estimation obtained from the short sequence and the frequency offset estimation obtained from the long sequence are determined according to N;
根据所述加权合并后载波频偏估计将所述长序列的自相关值和所述短序列不同间隔的自相关值调整到实部，得到以短训练序列起始采样点为自变量的帧同步点估计偏差函数；其中，所述帧同步点估计偏差函数为所述经过载波频偏调整后的短序列不同间隔的自相关值与所述长序列的自相关值的实部乘以一加权系数的累加和；所述加权系数为计算长序列自相关值时的累加次数与计算短序列自相关值时的累加次数的比值。According to the carrier frequency offset estimation after the weighted combination, the autocorrelation value of the long sequence and the autocorrelation value of the short sequence at different intervals are adjusted to the real part, and the frame synchronization with the starting sampling point of the short training sequence as an independent variable is obtained. Point estimation deviation function; wherein, the frame synchronization point estimation deviation function is the real part of the autocorrelation value of the short sequence adjusted by the carrier frequency offset and the autocorrelation value of the long sequence multiplied by a weighting coefficient The cumulative sum; the weighting coefficient is the ratio of the cumulative times when calculating long sequence autocorrelation values to the cumulative times when calculating short sequence autocorrelation values.
另外，在所述得到以短训练序列起始采样点为自变量的帧同步点估计偏差函数的步骤之后，还包含以下步骤：In addition, after the step of obtaining the estimated deviation function of the frame synchronization point with the starting sampling point of the short training sequence as an independent variable, the following steps are also included:
对所述帧同步点估计偏差函数进行平均运算；performing an averaging operation on the estimated deviation function of the frame synchronization point;
在所述找到所述帧同步点估计偏差函数的最大值点对应的采样点的步骤中，查找所述进行平均运算后的帧同步点估计偏差函数的最大值点对应的采样点；In the step of finding the sampling point corresponding to the maximum value point of the estimated deviation function of the frame synchronization point, searching for the sampling point corresponding to the maximum value point of the estimated deviation function of the frame synchronization point after the averaging operation;
其中，进行平均运算所选取的帧同步点估计偏差函数的个数小于一预设值。Wherein, the number of estimated deviation functions of the frame synchronization points selected for the averaging operation is less than a preset value.
通过上述方法，在根据帧同步点估计偏差函数或者载波频偏估计偏差函数进行帧同步和载波频偏估计时，对偏差函数进行平均之后，再进行帧同步和载波频偏估计，可以提高估计算法的性能。Through the above method, when frame synchronization and carrier frequency offset estimation are performed according to the frame synchronization point estimation deviation function or carrier frequency deviation estimation deviation function, after the deviation function is averaged, frame synchronization and carrier frequency deviation estimation are performed, which can improve the estimation algorithm performance.
附图说明Description of drawings
图1是802.11b/g/n通信协议的前导序列示意图；Fig. 1 is a schematic diagram of the preamble sequence of the 802.11b/g/n communication protocol;
图2是根据本发明第一实施方式的帧同步及载波频偏联合检测方法的流程图；FIG. 2 is a flow chart of a frame synchronization and carrier frequency offset joint detection method according to a first embodiment of the present invention;
图3是根据本发明第三实施方式的帧同步及载波频偏联合检测装置的结构框图。Fig. 3 is a structural block diagram of an apparatus for joint detection of frame synchronization and carrier frequency offset according to a third embodiment of the present invention.
具体实施方式detailed description
为使本发明的目的、技术方案和优点更加清楚，下面将结合附图对本发明的各实施方式进行详细的阐述。然而，本领域的普通技术人员可以理解，在本发明各实施方式中，为了使读者更好地理解本申请而提出了许多技术细节。但是，即使没有这些技术细节和基于以下各实施方式的种种变化和修改，也可以实现本申请各权利要求所要求保护的技术方案。In order to make the object, technical solution and advantages of the present invention clearer, various embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that, in each implementation manner of the present invention, many technical details are provided for readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following implementation modes, the technical solution claimed in each claim of the present application can be realized.
本发明的第一实施方式涉及一种帧同步及载波频偏联合检测方法。该方法应用OFDM信号的前导序列的短训练序列的重复性和长训练序列的重复性，实现了帧同步及载波频偏的联合检测。The first embodiment of the present invention relates to a frame synchronization and carrier frequency offset joint detection method. The method utilizes the repeatability of the short training sequence and the long training sequence of the leading sequence of the OFDM signal to realize the joint detection of frame synchronization and carrier frequency offset.
在具体描述本实施方式之前，先介绍一下OFDM信号的特点。如图1所示，802.11b/g/n通信协议的前导序列包括一个短训练序列和一个长训练序列。当OFDM系统的采样速率为每秒20兆采样点时，短训练序列由一个0.8us(16个采样点)的短序列重复十次组成，长训练序列由一个3.2us(64个采样点)的序列重复2.5次组成。短训练序列的前半部分用于信号检测，自动增益控制，及分集选择；后半部分用于帧同步及载波频偏估计。在本实施方式中，采用最后N个短序列(16N个采样点)和大部分长训练序列(128个采样点)进行帧同步及载波频偏估计。Before describing this embodiment in detail, the characteristics of the OFDM signal are firstly introduced. As shown in Figure 1, the preamble sequence of the 802.11b/g/n communication protocol includes a short training sequence and a long training sequence. When the sampling rate of the OFDM system is 20 megasampling points per second, the short training sequence consists of a 0.8us (16 sampling points) short sequence repeated ten times, and the long training sequence consists of a 3.2us (64 sampling points) Sequences consisted of 2.5 replicates. The first half of the short training sequence is used for signal detection, automatic gain control, and diversity selection; the second half is used for frame synchronization and carrier frequency offset estimation. In this embodiment, the last N short sequences (16N sampling points) and most of the long training sequences (128 sampling points) are used for frame synchronization and carrier frequency offset estimation.
为了更好地说明本实施方式，采用如下一些标识来进行辅助说明。In order to better describe this embodiment, the following symbols are used for auxiliary description.
假设通信设备的发射机有T根天线，接收机有R根天线，在第r个接收天线，最后N个短序列中第n+k个采样点可采用如下公式表示：Assuming that the transmitter of the communication device has T antennas and the receiver has R antennas, at the rth receiving antenna, the n+kth sampling point in the last N short sequences can be expressed by the following formula:
式中，k为最后N个短序列(16N个采样点)中每一个采样点的时间索引，k在0,1,2,…,16N-1之中取值。In the formula, k is the time index of each sampling point in the last N short sequences (16N sampling points), and k takes a value among 0, 1, 2, ..., 16N-1.
htr(q)是从第t个发送天线到第r个接收天线的等效信道，其包括信道冲击响应和在第t个发送天线加入的循环移位(CSD)；其中，q是等效信道的时间索引，q＝0，1,2,…Q-1，Q是等效信道的总时间长度。htr (q) is the equivalent channel from the t-th transmit antenna to the r-th receive antenna, which includes the channel impulse response and the cyclic shift (CSD) added at the t-th transmit antenna; where q is the equivalent The time index of the channel, q=0, 1, 2, ... Q-1, Q is the total time length of the equivalent channel.
mod代表求余运算；θ是因载波频偏造成的每个采样点之间的相位差；Nn+k是采样点上叠加的高斯白噪声。mod represents the remainder operation; θ is the phase difference between each sampling point caused by the carrier frequency offset; Nn+k is the Gaussian white noise superimposed on the sampling point.
同理，128个采样点的长训练序列中的第n+16N+K+k个采样点可采用如下公式表示：Similarly, the n+16N+K+kth sampling point in the long training sequence of 128 sampling points can be expressed by the following formula:
式中，k为长训练序列中128个采样点的每一个采样点的时间索引，k在0,1,2,…,127之中取值；In the formula, k is the time index of each sampling point of 128 sampling points in the long training sequence, and k takes a value among 0, 1, 2, ..., 127;
K是本实施方式为了表示方便而设计的一个参数，K的取值应满足：K is a parameter designed for convenience in this embodiment, and the value of K should satisfy:
Q-1≤K≤GI (5)Q-1≤K≤GI (5)
式中，GI是OFDM数据块之间的保护间隔；GI的长度为8或16个采样点。K的建议值是GI。In the formula, GI is the guard interval between OFDM data blocks; the length of GI is 8 or 16 sampling points. The suggested value of K is GI.
从公式(1)至(4)可以看出，短训练序列的采样点每16个采样点重复一次，长训练序列的采样点每64个采样点重复一次。本实施方式正是应用这一信号特性进行帧同步及载波频偏的检测，即计算n和θ的取值。From formulas (1) to (4), it can be seen that the sampling point of the short training sequence Repeat every 16 sampling points, sampling points for long training sequences Repeat every 64 sampling points. In this embodiment, this signal characteristic is used to detect frame synchronization and carrier frequency offset, that is, to calculate the values of n and θ.
请参阅图2所示帧同步及载波频偏联合检测方法的流程图，本实施方式具体包含如下步骤：Please refer to the flow chart of the frame synchronization and carrier frequency offset joint detection method shown in Figure 2. This embodiment specifically includes the following steps:
步骤201，对接收到的数据包进行检测，获得短序列的重复模式。In step 201, the received data packet is detected to obtain a repeating pattern of a short sequence.
具体地说，对每根接收天线先计算采样点间隔为16的自相关，如下式表示：Specifically, for each receiving antenna, the autocorrelation with a sampling point interval of 16 is calculated first, as shown in the following formula:
式中，r为接收天线的索引，在1至R之间取值。In the formula, r is the index of the receiving antenna, which takes a value between 1 and R.
再将R根接收天线计算的自相关值进行累加：Then accumulate the autocorrelation values calculated by the R receiving antennas:
接着计算第r根天线的接收功率Pr,S(n)，并将R根天线的功率累加得到总接收功率PS(n)：Then calculate the received power Pr,S (n) of the rth antenna, and accumulate the power of the R antennas to obtain the total received power PS (n):
根据每一根天线在每一个n的自相关值，每一根天线的接收功率，以及R根天线的总接收功率计算得到一归一化值ρ(n)：According to the autocorrelation value of each antenna at each n, the received power of each antenna, and the total received power of R antennas, a normalized value ρ(n) is obtained:
式中，ρ(n)的取值范围在0到1之间：当没有802.11信号时，ρ(n)接近 于0；当存在802.11信号且没有噪声时，ρ(n)接近于1。如果连续NS次ρ(n)的值均大于设定的阈值AS，则认为检测到一个802.11数据包。In the formula, the value range of ρ(n) is between 0 and 1: when there is no 802.11 signal, ρ(n) is close to 0; when there is 802.11 signal and no noise, ρ(n) is close to 1. If the value of ρ(n) is greater than the set threshold AS for NS consecutive times, it is considered that an 802.11 data packet is detected.
步骤202，对短训练序列重复段进行不同间隔的自相关检测，获得载波频偏估计。Step 202, performing autocorrelation detection at different intervals on the repeating segment of the short training sequence to obtain carrier frequency offset estimation.
具体地说，在检测到802.11数据包后，对每一个n进行如下运算，直到连续NE次ρ(n)的值均小于设定的阈值AE，结束检测短训练序列。Specifically, after the 802.11 data packet is detected, the following operations are performed for each n, until the value of ρ(n) is smaller than the set threshold AE for NE consecutive times, and the detection of the short training sequence ends.
首先，对每个接收天线的采样点计算间隔为16i的自相关，再将R根接收天线计算的自相关值进行累加：First, calculate the autocorrelation interval of 16i for the sampling points of each receiving antenna, and then accumulate the autocorrelation values calculated by the R receiving antennas:
式中，16i为自相关的间隔，i在2至N-1之间取值。In the formula, 16i is the autocorrelation interval, and i takes a value between 2 and N-1.
分别根据计算得到的短序列不同间隔的自相关值的相位，获得短序列频偏估计值；具体地说，首先根据Y1(n)的相位进行频偏估计：According to the calculated phases of the autocorrelation values of the short sequences at different intervals, the estimated frequency offset of the short sequence is obtained; specifically, firstly, the frequency offset is estimated according to the phase of Y1 (n):
式中，∠表示取相位，TS是采样周期。In the formula, ∠ means to take the phase, and TS is the sampling period.
对Yi(n),i＝2,...,N-1,的相位进行相位展开(或者称为相位解缠，unwrapping)，去除相位混淆度：Perform phase unwrapping (or called phase unwrapping, unwrapping) on the phase of Yi (n), i=2,...,N-1, to remove phase confusion:
式中，round表示四舍五入运算。In the formula, round means rounding operation.
对去除相位混淆度的短序列频偏估计值，引入第一修正因子，计算计入不同间隔的自相关值得到的频偏估计：For the short-sequence frequency offset estimation value that removes the phase confusion, the first correction factor is introduced, and the frequency offset estimation obtained by calculating the autocorrelation values at different intervals is calculated:
式中，第一修正因子ai是本实施方式设计的一个参数，用于加权合并从不同间隔的自相关值得到的频偏估计，ai的建议值为：In the formula, the first correction factor ai is a parameter designed in this embodiment, which is used to weight and combine the frequency offset estimates obtained from the autocorrelation values of different intervals, and the suggested value of ai is:
在实际应用本方法时，需要保存n,Yi(n),i＝1,2,N-1,PS(n),及fN-1(n)，留待后续对长训练序列进行处理时使用。In the actual application of this method, it is necessary to save n, Yi (n), i=1, 2, N-1, PS (n), and fN-1 (n), and leave it for the subsequent processing of the long training sequence used when.
步骤203，对长训练序列重复段进行自相关检测，用检测结果优化载波频偏估计，并根据估计得到的载波频偏，长训练序列的自相关值和短训练序列不同间隔的自相关值，获得帧同步点估计偏差函数Step 203, performing autocorrelation detection on the long training sequence repeat segment, using the detection result to optimize carrier frequency offset estimation, and according to the estimated carrier frequency offset, the autocorrelation value of the long training sequence and the autocorrelation value of different intervals of the short training sequence, Get the frame sync point estimate bias function
具体地说，对每一个保存的n，当收到采样点zr,n+16N+K+127后，意味着长训练序列已收到。对长训练序列进行如下运算：Specifically, for each saved n, when the sampling point zr,n+16N+K+127 is received, it means that the long training sequence has been received. Perform the following operations on long training sequences:
首先，对每个接收天线的采样点计算间隔为64的自相关，再将R根接收天线计算的自相关值进行累加：First, calculate the autocorrelation with an interval of 64 for the sampling points of each receiving antenna, and then accumulate the autocorrelation values calculated by the R receiving antennas:
采用短序列的估计载波频偏fN-1(n)，对长序列自相关值的相位进行相位展开，去除相位混淆度；Using the estimated carrier frequency offset fN-1 (n) of the short sequence, the phase of the autocorrelation value of the long sequence is phase unwrapped to remove the phase confusion;
对去除相位混淆度的长序列重复段的自相关值的相位，引入第二修正因子，计算计入长序列的自相关值得到的频偏估计：For the phase of the autocorrelation value of the long-sequence repeat segment that removes the phase confusion, a second correction factor is introduced to calculate the frequency offset estimation that is included in the autocorrelation value of the long sequence:
式中，第二修正因子aL是本实施方式设计的一个参数,用于加权合并从短序列得到的频偏估计和从长序列得到的频偏估计，aL的建议值为：In the formula, the second correction factor aL is a parameter designed in this embodiment, and is used for weighted combination of the frequency offset estimation obtained from the short sequence and the frequency offset estimation obtained from the long sequence, and the suggested value of aL is:
根据加权合并后的频偏估计，将长序列的自相关值和短序列不同间隔的自相关值调整到实部，并加权合并得到以n为自变量的帧同步点估计偏差函数：According to the weighted combined frequency offset estimation, the autocorrelation value of the long sequence and the autocorrelation value of the short sequence at different intervals are adjusted to the real part, and weighted and combined to obtain the frame synchronization point estimation deviation function with n as the independent variable:
式中，帧同步点估计偏差函数为频偏调整后的短序列的自相关值与长序列的自相关值的实部乘以一加权系数的累加和。其中，Re[]表示取实部；加权系数ωL是本实施方式设计的一个参数，建议值为：In the formula, the frame synchronization point estimation error function is the accumulated sum of the autocorrelation value of the short sequence adjusted by the frequency offset and the real part of the autocorrelation value of the long sequence multiplied by a weighting coefficient. Wherein, Re[] means to take the real part; the weighting coefficient ωL is a parameter designed in this embodiment, and the suggested value is:
上式中，64为计算长序列自相关值时的累加次数，8N(N-1)是计算短序列自相关值时的累加次数。In the above formula, 64 is the number of accumulations when calculating the long-sequence autocorrelation value, and 8N(N-1) is the number of accumulations when calculating the short-sequence autocorrelation value.
步骤204，找到帧同步点估计偏差函数的最大值点对应的n，将该采样点作为最佳帧同步点，并将n对应的估计载波频偏作为最佳载波频偏。Step 204, find n corresponding to the maximum point of the estimated deviation function of the frame synchronization point, use this sampling point as the optimal frame synchronization point, and use the estimated carrier frequency offset corresponding to n as the optimal carrier frequency offset.
具体地说，从公式(20)可以看出，FS(n)为n的函数，当FS(n)取最大值时，对应得到一个n，本实施方式将这个n作为最佳帧同步点，用公式表示为:Specifically, it can be seen from formula (20) that FS (n) is a function of n, when FS (n) takes the maximum value, a corresponding n is obtained, and this embodiment uses this n as the optimal frame synchronization point, expressed as:
相应地，载波频偏为Correspondingly, the carrier frequency offset is
至此，本实施方式实现了帧同步及载波频偏的联合检测。So far, this embodiment realizes joint detection of frame synchronization and carrier frequency offset.
与现有技术相比，本实施方式的方法由于将帧同步估计和载波频偏估计联合起来形成了一个正反馈，即FS(n)的值既是帧同步点估计偏差的函数，又是载波频偏估计偏差的函数。当帧同步点远离最佳点时，载波频偏的估计也会出现较大偏差，此偏差与帧同步点的偏差一起会大幅降低FS(n)的值；反之， 当帧同步点接近最佳点时，载波频偏估计的准确性也会增加，从而大幅提高FS(n)的值。因此，本实施方式能够达到远高于现有基于自相关检测的帧同步算法的估计精度。而且，在帧同步和载波频偏估计中同时使用了短训练序列和长训练序列，相比于只使用了长训练序列的现有算法，可以提高估计运算的精度。Compared with the prior art, the method of this embodiment forms a positive feedback by combining frame synchronization estimation and carrier frequency offset estimation, that is, the value of FS (n) is not only a function of frame synchronization point estimation deviation, but also a function of carrier frequency offset estimation. Function of frequency offset estimation bias. When the frame synchronization point is far from the optimal point, the estimation of the carrier frequency offset will also have a large deviation, which together with the deviation of the frame synchronization point will greatly reduce the value of FS (n); on the contrary, when the frame synchronization point is close to the optimal point When the optimal point is reached, the accuracy of carrier frequency offset estimation will also increase, thereby greatly increasing the value of FS (n). Therefore, this embodiment can achieve an estimation accuracy much higher than that of the existing frame synchronization algorithm based on autocorrelation detection. Moreover, both the short training sequence and the long training sequence are used in the frame synchronization and carrier frequency offset estimation, which can improve the accuracy of the estimation operation compared with the existing algorithm that only uses the long training sequence.
此外，由于本实施方式没有使用基于互相关检测的帧同步算法，因此，在前导序列中加入CSD不会对本实施方式产生任何影响，从而本实施方式可以适用于802.11b/g/n等通信协议。进一步地，由于本实施方式可联合实现数据包检测，帧同步估计，及载波频偏估计，因此整体系统复杂度较低。In addition, since this embodiment does not use a frame synchronization algorithm based on cross-correlation detection, adding CSD to the preamble will not have any impact on this embodiment, so this embodiment can be applied to communication protocols such as 802.11b/g/n . Furthermore, since this embodiment can jointly implement data packet detection, frame synchronization estimation, and carrier frequency offset estimation, the overall system complexity is relatively low.
此外，值得说明的是，本实施方式应用于接收机中进行帧同步和载波频偏估计，而本领域技术人员应该了解，现有的帧同步和载波频偏估计为了实现快速检测，均是通过硬件电路实现的，所以本实施方式并不是单纯的数学计算方法，也是需要结合硬件实现的。In addition, it is worth noting that this embodiment is applied to the receiver for frame synchronization and carrier frequency offset estimation, and those skilled in the art should understand that in order to achieve fast detection, the existing frame synchronization and carrier frequency offset estimation are all performed by It is implemented by a hardware circuit, so this embodiment is not a pure mathematical calculation method, but also needs to be implemented in combination with hardware.
本发明的第二实施方式涉及一种帧同步及载波频偏联合检测方法。第二实施方式在第一实施方式基础上做了进一步改进，主要改进之处在于：在本发明第二实施方式中，在根据帧同步点估计偏差函数或者载波频偏估计偏差函数进行帧同步和载波频偏估计时，对偏差函数进行平均之后，再进行帧同步和载波频偏估计，可以提高估计算法的性能。The second embodiment of the present invention relates to a frame synchronization and carrier frequency offset joint detection method. The second embodiment is further improved on the basis of the first embodiment. The main improvement is that: in the second embodiment of the present invention, the frame synchronization and When carrier frequency offset is estimated, after the deviation function is averaged, frame synchronization and carrier frequency offset estimation are performed, which can improve the performance of the estimation algorithm.
具体地说，对帧同步点估计偏差函数进行平均运算，其中，进行平均运算所选取的帧同步点估计偏差函数的个数L小于一预设值。也就是说，对FS(n)进行如下平均运算：Specifically, an average operation is performed on the estimated deviation functions of the frame synchronization points, wherein the number L of estimated deviation functions of the frame synchronization points selected for the average operation is smaller than a preset value. That is, FS (n) is averaged as follows:
式中，L是本实施方式设计的一个参数，L的取值应满足：In the formula, L is a parameter designed in this embodiment, and the value of L should satisfy:
那么，在本实施方式中，最佳帧同步点为:Then, in this embodiment, the best frame synchronization point is:
相应的，载波频偏为Correspondingly, the carrier frequency offset is
上面各种方法的步骤划分，只是为了描述清楚，实现时可以合并为一个步骤或者对某些步骤进行拆分，分解为多个步骤，只要包含相同的逻辑关系，都在本专利的保护范围内；对算法中或者流程中添加无关紧要的修改或者引入无关紧要的设计，但不改变其算法和流程的核心设计都在该专利的保护范围内。The division of steps in the above methods is only for the sake of clarity of description. During implementation, they can be combined into one step or some steps can be split and decomposed into multiple steps. As long as they contain the same logical relationship, they are all within the scope of protection of this patent. ; Adding insignificant modifications or introducing insignificant designs to the algorithm or process, but not changing the core design of the algorithm and process are all within the scope of protection of this patent.
本发明第三实施方式涉及一种帧同步及载波频偏联合检测装置，如图3所示，包含：数据接收模块，短序列处理模块，长序列处理模块和结果输出模块。The third embodiment of the present invention relates to a frame synchronization and carrier frequency offset joint detection device, as shown in FIG. 3 , including: a data receiving module, a short sequence processing module, a long sequence processing module and a result output module.
其中，数据接收模块用于接收数据包。本实施方式中的数据包至少包含短训练序列中最后N个重复的短序列和长训练序列中的2个重复的长序列；其中，N为大于2的自然数。Wherein, the data receiving module is used for receiving data packets. The data packet in this embodiment includes at least the last N repeated short sequences in the short training sequence and 2 repeated long sequences in the long training sequence; wherein, N is a natural number greater than 2.
短序列处理模块用于对接收到的数据包进行检测，获得短序列的重复模式；并对短训练序列重复段进行不同间隔的自相关检测，获得载波频偏估计。The short sequence processing module is used to detect the received data packets to obtain the repetition pattern of the short sequence; and to perform autocorrelation detection at different intervals on the repetition of the short training sequence to obtain carrier frequency offset estimation.
短序列处理模块进一步包含：第一自相关子模块，频偏估计子模块，第一相位展开子模块，第一频偏修正子模块。第一自相关子模块用于计算每一个间隔对应的短序列重复段的自相关值。频偏估计子模块用于分别根据计算得到的短序列自相关值的相位，获得短序列频偏估计值。第一相位展开子模块用于对短序列频偏估计值进行相位展开，去除相位混淆度。第一频偏修正子模块用于对去除相位混淆度的短序列频偏估计值，引入第一修正因子，计算计入不同间隔的自相关值得到的载波频偏估计；其中，第一修正因子用于加权合并从不同间隔的自相关值得到的频偏估计，其取值根据N和短序列重 复段的间隔确定。The short sequence processing module further includes: a first autocorrelation submodule, a frequency offset estimation submodule, a first phase expansion submodule, and a first frequency offset correction submodule. The first autocorrelation submodule is used to calculate the autocorrelation value of the short sequence repeat segment corresponding to each interval. The frequency offset estimation sub-module is used to obtain short sequence frequency offset estimation values according to the phases of the calculated short sequence autocorrelation values respectively. The first phase unwrapping sub-module is used for phase unwrapping the short sequence frequency offset estimation value to remove the phase confusion. The first frequency offset correction sub-module is used to introduce the first correction factor to the estimated value of the short sequence frequency offset that removes the phase ambiguity, and calculate the carrier frequency offset estimate obtained by calculating the autocorrelation values at different intervals; wherein, the first correction factor It is used for weighted combination of frequency offset estimates obtained from autocorrelation values at different intervals, and its value is determined according to N and the interval of short sequence repeat segments.
长序列处理模块用于对长训练序列重复段进行自相关检测，用检测结果优化载波频偏估计；并根据估计得到的载波频偏，长训练序列的自相关值和短训练序列不同间隔的自相关值，获得帧同步点估计偏差函数。The long sequence processing module is used to perform autocorrelation detection on the long training sequence repeat segment, and optimize the carrier frequency offset estimation with the detection result; and according to the estimated carrier frequency offset, the autocorrelation value of the long training sequence and the autocorrelation value of the short training sequence at different intervals Correlation value, obtain frame sync point estimate bias function.
长序列处理模块进一步包含：第二自相关子模块，第二相位展开子模块，第二频偏修正子模块和偏差函数生成子模块。第二自相关子模块用于获取长序列重复段，计算长序列重复段的自相关值。第二相位展开子模块用于采用短序列的估计载波频偏，对长序列重复段的自相关值的相位进行相位展开，去除相位混淆度。第二频偏修正子模块用于对去除相位混淆度的长序列的自相关值的相位，引入第二修正因子，计算计入长序列的自相关值得到的频偏估计；其中，第二修正因子用于加权合并从短序列得到的频偏估计和从长序列得到的频偏估计，其取值根据N确定。偏差函数生成子模块用于根据加权合并后的载波频偏估计将长序列的自相关值和短序列不同间隔的自相关值调整到实部，得到以短训练序列起始采样点为自变量的帧同步点估计偏差函数；其中，帧同步点估计偏差函数为经过载波频偏调整后的短序列不同间隔的自相关值与长序列的自相关值的实部乘以一加权系数的累加和；加权系数为计算长序列自相关值时的累加次数与计算短序列自相关值时的累加次数的比值。The long sequence processing module further includes: a second autocorrelation submodule, a second phase unwrapping submodule, a second frequency offset correction submodule and a deviation function generation submodule. The second autocorrelation sub-module is used to obtain the long sequence repeating segment and calculate the autocorrelation value of the long sequence repeating segment. The second phase unwrapping sub-module is used to use the estimated carrier frequency offset of the short sequence to perform phase unwrapping on the phase of the autocorrelation value of the long-sequence repeat segment to remove the phase confusion. The second frequency offset correction sub-module is used to introduce a second correction factor to the phase of the autocorrelation value of the long sequence that removes the phase confusion, and calculate the frequency offset estimate that is included in the autocorrelation value of the long sequence; wherein, the second correction The factor is used to weight and combine the frequency offset estimation obtained from the short sequence and the frequency offset estimation obtained from the long sequence, and its value is determined according to N. The deviation function generation sub-module is used to adjust the autocorrelation value of the long sequence and the autocorrelation value of the short sequence at different intervals to the real part according to the weighted and combined carrier frequency offset estimation, and obtain the short training sequence starting sampling point as the independent variable A frame synchronization point estimation deviation function; wherein, the frame synchronization point estimation deviation function is the cumulative sum of autocorrelation values at different intervals of the short sequence and the real part of the long sequence autocorrelation value multiplied by a weighting coefficient after carrier frequency offset adjustment; The weighting coefficient is the ratio of the accumulation times when calculating long sequence autocorrelation values to the accumulation times when calculating short sequence autocorrelation values.
结果输出模块用于找到帧同步点估计偏差函数的最大值点对应的采样点，并分别将查找得到的采样点及其对应的载波频偏估计作为最佳帧同步点和最佳载波频偏。The result output module is used to find the sampling point corresponding to the maximum point of the estimated deviation function of the frame synchronization point, and use the obtained sampling point and its corresponding carrier frequency offset estimation as the optimal frame synchronization point and the optimal carrier frequency offset respectively.
不难发现，本实施方式为与第一实施方式相对应的系统实施例，本实施方式可与第一实施方式互相配合实施。第一实施方式中提到的相关技术细节在本实施方式中依然有效，为了减少重复，这里不再赘述。相应地，本实施方式中提到的相关技术细节也可应用在第一实施方式中。It is not difficult to find that this embodiment is a system embodiment corresponding to the first embodiment, and this embodiment can be implemented in cooperation with the first embodiment. The relevant technical details mentioned in the first embodiment are still valid in this embodiment, and will not be repeated here in order to reduce repetition. Correspondingly, the relevant technical details mentioned in this implementation manner can also be applied in the first implementation manner.
值得一提的是，本实施方式中所涉及到的各模块均为逻辑模块，在实际应用中，一个逻辑单元可以是一个物理单元，也可以是一个物理单元的一部分，还可以以多个物理单元的组合实现。此外，为了突出本发明的创新部分，本实施方式中并没有将与解决本发明所提出的技术问题关系不太密切的单元引入，但这并不表明本实施方式中不存在其它的单元。It is worth mentioning that all the modules involved in this embodiment are logical modules. In practical applications, a logical unit can be a physical unit, or a part of a physical unit, or multiple physical units. Combination of units. In addition, in order to highlight the innovative part of the present invention, units that are not closely related to solving the technical problems proposed by the present invention are not introduced in this embodiment, but this does not mean that there are no other units in this embodiment.
本发明第四实施方式涉及一种帧同步及载波频偏联合检测装置。第四实施方式在第三实施方式基础上做了进一步改进，主要改进之处在于：在本发明第四实施方式中，在根据帧同步点估计偏差函数或者载波频偏估计偏差函数进行帧同步和载波频偏估计时，对偏差函数进行平均之后，再进行帧同步和载波频偏估计，可以提高估计算法的性能。The fourth embodiment of the present invention relates to a frame synchronization and carrier frequency offset joint detection device. The fourth embodiment is further improved on the basis of the third embodiment. The main improvement is: in the fourth embodiment of the present invention, the frame synchronization and When carrier frequency offset is estimated, after the deviation function is averaged, frame synchronization and carrier frequency offset estimation are performed, which can improve the performance of the estimation algorithm.
具体地说，帧同步及载波频偏联合检测装置还包含平均运算模块。该平均运算模块用于对子模块得到的帧同步点估计偏差函数进行平均运算；其中，进行平均运算所选取的帧同步点估计偏差函数的个数小于一预设值。结果输出模块还用于查找进行平均运算后的帧同步点估计偏差函数的最大值点对应的采样点。Specifically, the device for joint detection of frame synchronization and carrier frequency offset also includes an average calculation module. The average operation module is used for performing average operation on the estimated deviation functions of the frame synchronization points obtained by the sub-modules; wherein, the number of estimated deviation functions of the frame synchronization points selected for the average operation is less than a preset value. The result output module is also used to search for the sampling point corresponding to the maximum point of the estimated deviation function of the frame synchronization point after the averaging operation.
由于第二实施方式与本实施方式相互对应，因此本实施方式可与第二实施方式互相配合实施。第二实施方式中提到的相关技术细节在本实施方式中依然有效，在第二实施方式中所能达到的技术效果在本实施方式中也同样可以实现，为了减少重复，这里不再赘述。相应地，本实施方式中提到的相关技术细节也可应用在第二实施方式中。Since the second embodiment corresponds to the present embodiment, the present embodiment can be implemented in cooperation with the second embodiment. The relevant technical details mentioned in the second embodiment are still valid in this embodiment, and the technical effects that can be achieved in the second embodiment can also be achieved in this embodiment, and in order to reduce repetition, details are not repeated here. Correspondingly, the relevant technical details mentioned in this embodiment mode can also be applied in the second embodiment mode.
本领域的普通技术人员可以理解，上述各实施方式是实现本发明的具体实施例，而在实际应用中，可以在形式上和细节上对其作各种改变，而不偏离本发明的精神和范围。Those of ordinary skill in the art can understand that the above-mentioned embodiments are specific examples for realizing the present invention, and in practical applications, various changes can be made to it in form and details without departing from the spirit and spirit of the present invention. scope.
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