CN102647226A

CN102647226A - Carrier Frequency Offset Compensation Method for Received Signals in High-speed Railway Environment

Info

Publication number: CN102647226A
Application number: CN2012101050865A
Authority: CN
Inventors: 熊箭; 邱晨; 归琳; 刘勃; 侯金鑫
Original assignee: Shanghai Jiao Tong University
Current assignee: Shanghai Jiao Tong University
Priority date: 2012-04-11
Filing date: 2012-04-11
Publication date: 2012-08-22

Abstract

A method for the carrier frequency offset compensation of receiving signals under high-speed rail environment comprises the steps of obtaining the position information of a current train by a high-speed rail train, calculating the horizontal distance between the train and a base station; calculating a carrier frequency offset value fd needing to be compensated currently; and conducting direct carrier frequency offset compensation on the signals received by a receiver of the high-speed rail train. According to the method, the carrier frequency offset value can be calculated without channel estimation, and the simplicity and the high efficiency are achieved.

Description

Carrier Frequency Offset Compensation Method for Received Signals in High-speed Railway Environment

技术领域： Technical field:

本发明涉及无线通信技术领域，特别是一种高速铁路环境下基站向高铁列车进行下行通信时，高铁列车对接收信号进行载波频偏补偿的方法。The invention relates to the technical field of wireless communication, in particular to a method for the high-speed train to compensate the carrier frequency offset of the received signal when the base station performs downlink communication to the high-speed train in a high-speed railway environment.

背景技术： Background technique:

我国铁路经过几次大幅度的提速后，列车运行速度越来越快。目前正在运行的高速铁路列车速度已经达到并超过了350km/h，对高速环境下通信服务的种类和质量的要求也越来越高，这无疑对铁路无线通信提出了更为苛刻的要求。After my country's railways have undergone several substantial speed increases, the trains are running faster and faster. The speed of the currently running high-speed railway trains has reached and exceeded 350km/h, and the requirements for the type and quality of communication services in the high-speed environment are getting higher and higher, which undoubtedly puts forward more stringent requirements for railway wireless communication.

在高速移动通信中，多普勒频移是影响系统性能的重要因素之一。当电磁波发射源与接收机发生相对运动的时候，会导致接收到的传播频率发生改变。当运动速度达到一定阀值时，引起传输频率的明显改变，这称之为多普勒频移。在多径环境下，接收信号的频谱结构中会产生不同的多普勒频移，造成多普勒扩展。当多普勒扩展大于信号带宽时，信道会出现时间选择性衰落，对系统的误码性能造成非常大的影响。In high-speed mobile communication, Doppler frequency shift is one of the important factors affecting system performance. When the electromagnetic wave transmitter and the receiver move relative to each other, the received propagation frequency will change. When the motion speed reaches a certain threshold, the transmission frequency will change obviously, which is called Doppler frequency shift. In a multipath environment, different Doppler frequency shifts will occur in the spectrum structure of the received signal, resulting in Doppler spread. When the Doppler spread is larger than the signal bandwidth, the channel will appear time-selective fading, which will have a great impact on the bit error performance of the system.

目前，解决多普勒频移问题的方法一般主要有两种：补偿法和反馈法。前者由接收机采用信道估计计算出频偏值，然后再用均衡或者同步的方法进行频率偏差的补偿，该方法不需要控制信道的帮助；后者由接收机将估计得到的频率偏差反馈至发射端，由发射端自动调整其发射信号的频率。然而这些方法都需要准确的信道估计，在接收机移动速率很大，信道处于快衰落的情况下，要实现快速信道估计非常困难。At present, there are generally two methods to solve the problem of Doppler frequency shift: compensation method and feedback method. The former uses channel estimation to calculate the frequency offset value by the receiver, and then compensates the frequency offset by means of equalization or synchronization, which does not require the help of a control channel; the latter feeds back the estimated frequency offset to the transmitter by the receiver. end, the transmitter automatically adjusts the frequency of its transmitted signal. However, these methods all require accurate channel estimation, and it is very difficult to achieve fast channel estimation when the receiver moves at a high rate and the channel is in fast fading.

发明内容： Invention content:

针对现有技术存在的问题，本发明的目的在于提出一种高速铁路下对接收信号进行载波频偏补偿的方法，该方法能够快速的估计出频率偏差值，通过接收机直接补偿的方式解决由于列车高速移动引起的多普勒频移。Aiming at the problems existing in the prior art, the purpose of the present invention is to propose a method of carrier frequency offset compensation for received signals under high-speed railways. This method can quickly estimate the frequency offset value and solve the problem of Doppler frequency shift caused by train moving at high speed.

本发明的主要想法是：由于高铁列车能够通过GPS定位或轮轨定位等技术获取当前列车的位置信息，因此可以使用位置信息而不是信道估计的方式计算出当前需补偿的载波频偏值，保证载波频偏补偿的实时性。The main idea of the present invention is: since the high-speed rail train can obtain the position information of the current train through technologies such as GPS positioning or wheel-rail positioning, the current carrier frequency offset value to be compensated can be calculated by using the position information instead of channel estimation, ensuring Real-time performance of carrier frequency offset compensation.

根据上述想法，本发明采用下述技术方案：According to above-mentioned idea, the present invention adopts following technical scheme:

一种高速铁路下对接收信号进行载波频偏补偿的方法，其特征在于，该方法包括如下具体步骤：A method for carrier frequency offset compensation of a received signal under a high-speed railway, characterized in that the method comprises the following specific steps:

(1)在高速铁路通信系统当中，高铁列车能够通过GPS定位或轮轨定位等技术获取当前列车的位置信息。当高铁列车接收到基站发来的下行通信数据的第i个符号y_i时，根据当前列车的位置信息计算出此时列车与基站的水平距离d_i；(1) In the high-speed railway communication system, the high-speed train can obtain the position information of the current train through technologies such as GPS positioning or wheel-rail positioning. When the high-speed train receives the i-th symbol y _i of the downlink communication data sent by the base station, the horizontal distance d _i between the train and the base station is calculated according to the position information of the current train;

(2)计算当前需补偿的载波频偏值f_d，计算式为：(2) Calculate the current carrier frequency offset value f _d to be compensated, the calculation formula is:

${f f}_{d d} = = f f \cdot &Center Dot; \frac{v v}{c c} \cdot &Center Dot; \frac{{d d}_{i i}}{\sqrt{{d d}_{i i}^{22} + + {h h}_{i i}^{22}}} - - - - - - ((11))$

其中，f表示接收信号的中心频点，v表示当前列车的行驶速度，d_i表示列车与基站的水平距离，h_i表示当前基站的高度，c表示光速。当列车行驶方向为面向基站时，v取正值，此时载波频移为正，接收频率上升，当列车行驶方向为背向基站时，v取负值，此时载波频移为负，接收频率下降；Among them, f represents the center frequency point of the received signal, v represents the speed of the current train, d _i represents the horizontal distance between the train and the base station, h _i represents the height of the current base station, and c represents the speed of light. When the train is traveling in the direction facing the base station, v takes a positive value, at this time the carrier frequency shift is positive, and the receiving frequency increases; when the train is traveling in the direction away from the base station, v takes a negative value, at this time the carrier frequency shift is negative, and the receiving frequency frequency drop;

(3)根据得到的载波频偏值f_d，高铁列车的接收机对接收到的信号进行直接载波频偏补偿：(3) According to the obtained carrier frequency offset value f _d , the receiver of the high-speed train performs direct carrier frequency offset compensation on the received signal:

${\overset{^^}{s the s}}_{i i} = = {s the s}_{i i} \cdot &Center Dot; {e e}^{- - j j 22 π π {f f}_{d d} {T T}_{s the s}} - - - - - - ((22))$

其中，表示直接补偿后的接收序列，s_i表示直接补偿前的接收序列，f_d表示当前的载波频偏值，T_s表示接收信号的采样周期。in, Indicates the receiving sequence after direct compensation, s _i indicates the receiving sequence before direct compensation, f _d indicates the current carrier frequency offset value, and T _s indicates the sampling period of the received signal.

与传统的载波频偏补偿方法相比，本发明方法能够不需信道估计就计算出载波频偏值，且计算方法简单高效，计算所需的参数如列车位置信息与列车当前行驶速度都能够在列车端实时获得，使得本发明的载波频偏补偿方法即使在高速移动的环境下也能够获得良好的性能。Compared with the traditional carrier frequency offset compensation method, the method of the present invention can calculate the carrier frequency offset value without channel estimation, and the calculation method is simple and efficient, and the parameters required for calculation, such as the train position information and the current speed of the train, can be The train end obtains it in real time, so that the carrier frequency offset compensation method of the present invention can obtain good performance even in a high-speed moving environment.

附图说明： Description of drawings:

图1基站到高铁列车的载波频偏计算示意图。Figure 1 Schematic diagram of carrier frequency offset calculation from base station to high-speed train.

具体实施方式： Detailed ways:

下面结合附图和具体实施例对本发明做进一步的描述。本实施例在以本发明技术方案为前提下进行实施，给出了详细的实施方式和具体的操作过程，但本发明的保护范围不限于下述的实施例。The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

如图1中所示，本发明的一种用于高速铁路环境下的载波频偏补偿方法，其具体步骤如下：As shown in Figure 1, a kind of carrier frequency offset compensation method that is used in the high-speed railway environment of the present invention, its specific steps are as follows:

(1)在高速铁路通信系统当中，高铁列车通过GPS定位或轮轨定位等技术获取当前列车的位置信息，当高铁列车接收到基站发来的下行通信数据的第i个符号y_i时，根据当前列车的位置信息计算此时列车与基站的水平距离d_i。(1) In the high-speed railway communication system, the high-speed train obtains the position information of the current train through technologies such as GPS positioning or wheel-rail positioning. When the high-speed train receives the i-th symbol _y of the downlink communication data sent by the base station, according The current position information of the train calculates the horizontal distance d _i between the train and the base station at this time.

列车与基站的水平距离d_i的计算方法，由于高铁列车的定位方法不同而有所区别，本实施例中仅列举通过GPS定位和轮轨定位方法获取当前列车的位置信息的两种情况，其他多种定位方法，在此不一一累述。The calculation method of the horizontal distance _di between the train and the base station is different due to the different positioning methods of the high-speed rail train. In this embodiment, only enumerate two situations in which the position information of the current train is obtained by GPS positioning and wheel-rail positioning methods. Others There are various positioning methods, which will not be described one by one here.

如果通过GPS定位技术计算d_i，首先列车通过GPS设备获取当前的三维坐标(x_i，y_i，z_i)，该坐标即为当前列车的位置信息，然后结合事先已保存在列车接收机内的基站的三维坐标(x′_i，y′_i，z′_i)由高铁列车的位置信息计算出此时列车与基站的水平距离If d _i is calculated by GPS positioning technology, first the train obtains the current three-dimensional coordinates (xi _, y _i , _zi ) through the GPS device, which is the position information of the current train, and then combined with the information previously saved in the train receiver The three-dimensional coordinates (x′ _i , y′ _i , z′ _i ) of the base station are calculated from the position information of the high-speed rail train to calculate the horizontal distance between the train and the base station at this time

${d d}_{i i} = = \sqrt{{(({x x}_{i i}^{' '} - - {x x}_{i i}))}^{22} + + {(({y the y}_{i i}^{' '} - - {y the y}_{i i}))}^{22} + + {(({z z}_{i i}^{' '} - - {z z}_{i i}))}^{22}};;$

如果通过轮轨定位技术计算d_i，首先列车通过轮轨定位设备获取当前列车行驶距离l_i，该距离即为当前列车的位置信息，然后通过顺序搜索存储在列车上的查找表(d_i，l_i)获取列车与基站的水平距离d_i；If d _i is calculated by the wheel-rail positioning technology, firstly, the train obtains the current train travel distance l _i through the wheel-rail positioning equipment, which is the position information of the current train, and then sequentially searches the look-up table stored on the train (d _i , l _i ) obtain the horizontal distance d _i between the train and the base station;

其中，f表示接收信号的中心频点，v表示当前列车的行驶速度，d_i表示列车与基站的水平距离，h_i表示当前基站的高度。当列车行驶方向为面向基站时，v取正值，此时载波频移为正，接收频率上升，当列车行驶方向为背向基站时，v取负值，此时载波频移为负，接收频率下降；Among them, f represents the center frequency point of the received signal, v represents the speed of the current train, d _i represents the horizontal distance between the train and the base station, and h _i represents the height of the current base station. When the train is traveling in the direction facing the base station, v takes a positive value, at this time the carrier frequency shift is positive, and the receiving frequency increases; when the train is traveling in the direction away from the base station, v takes a negative value, at this time the carrier frequency shift is negative, and the receiving frequency frequency drop;

(3)根据得到的载波频偏值f_d，列车接收机对接收到的信号进行直接载波频偏补偿：(3) According to the obtained carrier frequency offset value f _d , the train receiver performs direct carrier frequency offset compensation on the received signal:

其中，

表示直接补偿后的接收序列，s_i表示直接补偿前的接收序列，f_d表示当前的载波频偏值，T_s表示接收信号的采样周期。in,

Indicates the receiving sequence after direct compensation, s _i indicates the receiving sequence before direct compensation, f _d indicates the current carrier frequency offset value, and T _s indicates the sampling period of the received signal.

Claims

1. a kind of method that receiving signal is carried out carrier frequency offset compensation under high-speed railway, it is characterized in that, this method comprises following concrete steps:

(1) In the high-speed railway communication system, the high-speed train obtains the position information of the current train. When the high-speed train receives the i-th symbol y _i of the downlink communication data sent by the current base station, it calculates this according to the position information of the current train. The horizontal distance d _i between the train and the base station;

(2) Calculate the current carrier frequency offset value f _d to be compensated, the calculation formula is:

{f f}_{d d} = = f f \cdot \cdot \frac{v v}{c c} \cdot &Center Dot; \frac{{d d}_{i i}}{\sqrt{{d d}_{i i}^{22} + + {h h}_{i i}^{22}}} - - - - - - ((11))

Among them, f represents the center frequency point of the received signal, v represents the speed of the current train, d _i represents the horizontal distance between the train and the base station, h _i represents the height of the current base station, and c represents the speed of light. When the train is traveling in the direction facing the base station, v takes a positive value, at this time the carrier frequency shift is positive, and the receiving frequency increases; when the train is traveling in the direction away from the base station, v takes a negative value, at this time the carrier frequency shift is negative, and the receiving frequency frequency drop;

(3) According to the obtained carrier frequency offset value f _d , the receiver of the high-speed train performs direct carrier frequency offset compensation on the received signal:

{\overset{^^}{s the s}}_{i i} = = {s the s}_{i i} \cdot &Center Dot; {e e}^{- - j j 22 π π {f f}_{d d} {T T}_{s the s}} - - - - - - ((22))

in, Indicates the receiving sequence after direct compensation, s _i indicates the receiving sequence before direct compensation, f _d indicates the current carrier frequency offset value, and T _s indicates the sampling period of the received signal.