CN1773977A

CN1773977A - MIMO-OFDM carrier frequency Synchronizing method based on pilot frequency design

Info

Publication number: CN1773977A
Application number: CN 200410088877
Authority: CN
Inventors: 姚瑶; 谢玉堂
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2004-11-08
Filing date: 2004-11-08
Publication date: 2006-05-17
Anticipated expiration: 2024-11-08
Also published as: CN1773977B

Abstract

The invention discloses a MIMO-OFDM carrier frequency synchronization method based on pilot frequency design in the field of wireless communication, which is applied to a MIMO-OFDM system with M transmitting antennas, N receiving antennas and Q sub-carrier frequencies, including the following steps: (1) Divide the entire Q sub-carrier frequency into M sub-bands, each sub-band occupies (see formula I) consecutive sub-carrier frequencies, correspondingly assigned to each transmitting antenna, and each sub-band ^sm only transmits the pilot frequency from the transmitter m symbol, while it is 0 in other transmitters; (2) at the end of each ^sm , several subcarrier frequencies are reserved as protection, that is, no information is transmitted; (3) at the end of each ^sm , the pilot frequency on the subcarrier frequency The symbols are equally spaced with 0, ^Nzero Nzero and ^Nguard are respectively 0 and the number of guarded sub-carrier frequencies in the sub-band, and the symbols are placed on the sub-carrier frequencies (see type II). The invention eliminates the multi-antenna interference in the MIMO system to the greatest extent, improves the carrier frequency offset estimation performance method, significantly improves the carrier frequency synchronization performance of the system, and has the characteristics of simple realization and the like.

Description

MIMO-OFDM Carrier Frequency Synchronization Method Based on Pilot Design

技术领域technical field

本发明涉及无线通信领域，尤其涉及一种无线通信系统中基于导频设计的MIMO-OFDM(多输入多输出，Multi-InputMulti-Output；正交频分复用，OrthogonalFrequencyDivisionMultiplexing)载频同步方法。The present invention relates to the field of wireless communication, in particular to a MIMO-OFDM (Multi-Input Multi-Output; Orthogonal Frequency Division Multiplexing) carrier frequency synchronization method based on pilot design in a wireless communication system.

背景技术Background technique

OFDM是一种多载波调制技术，发射端把数据调制到多个相互正交的子载波上同时发送，每个子载波都是窄带，具有很强的抗多径衰落能力，因而可以认为对每个子载波而言，信道是平坦衰落的。理论上来说，作为高速无线通信系统核心的OFDM技术，只要适当选择各载波的带宽和采用适当的纠错编码技术，多径衰落对系统的影响可以完全被消除。因此如果没有功率和带宽的限制，可以用OFDM技术实现任何传输速率。而其它技术就不具备这种特性，因为采用其它技术时，当数据速率增加到某一数值时，信道的频率选择性衰落会占据主导地位，此时无论怎样增加发射功率也无济于事，这正是OFDM技术适用于高速无线系统的原因。但从实际应用角度看，为了进一步增加系统的容量，提高系统传输速率，使用多载波调制技术的系统需要增加载波的数量，而这种方法会造成系统复杂度的增加，并增大系统的带宽，这对于带宽受限和功率受限的系统显然不很合适。而且OFDM系统存在对同步(载波、符号和定时同步)要求高，必须有效地控制峰均比等技术问题，当然，目前已经有许多解决办法，并已经达到实用的要求。另一方面，作为下一代无线通信系统(B3G/4G、WLAN、BWA、MBWA等)的关键技术，MIMO技术也得到了日益广泛的关注和应用，MIMO技术能在不增加带宽的情况下成倍地提高通信系统的容量和频谱利用率，因此将MIMO技术与OFDM技术相结合，能够很好地适应下一代系统发展趋势的要求。研究表明，在衰落信道环境下，OFDM系统非常适合使用MIMO技术来提高容量。MIMO-OFDM技术是通过在OFDM传输系统中采用阵列天线实现空间分集，提高了信号质量，是联合OFDM和MIMO而得到的一种新技术。它利用了时间、频率和空间三种分集技术，使无线系统对噪声、干扰、多径的容限大大增加。但其假设的应用环境是平坦衰落无线信道，这一假设往往存在于窄带通信系统中，在宽带通信系统中一般是不成立的。OFDM is a multi-carrier modulation technology. The transmitter modulates the data onto multiple mutually orthogonal sub-carriers and sends them simultaneously. Each sub-carrier is narrow-band and has strong anti-multipath fading capabilities. Therefore, it can be considered that each sub-carrier is As far as the carrier is concerned, the channel is flat fading. Theoretically speaking, as the core OFDM technology of high-speed wireless communication system, as long as the bandwidth of each carrier is properly selected and the appropriate error correction coding technology is adopted, the impact of multipath fading on the system can be completely eliminated. Therefore, if there is no limitation of power and bandwidth, any transmission rate can be realized with OFDM technology. But other technologies do not have this characteristic, because when other technologies are used, when the data rate increases to a certain value, the frequency selective fading of the channel will take the dominant position, and no matter how much the transmission power is increased at this time, it will not help. The reason why OFDM technology is suitable for high-speed wireless systems. But from the perspective of practical application, in order to further increase the capacity of the system and increase the transmission rate of the system, the system using multi-carrier modulation technology needs to increase the number of carriers, and this method will increase the complexity of the system and increase the bandwidth of the system , which is obviously not very suitable for bandwidth-constrained and power-constrained systems. Moreover, the OFDM system has high requirements for synchronization (carrier, symbol and timing synchronization), and technical problems such as peak-to-average ratio must be effectively controlled. Of course, there are many solutions at present, and they have already met the practical requirements. On the other hand, as the key technology of the next-generation wireless communication system (B3G/4G, WLAN, BWA, MBWA, etc.), MIMO technology has also received increasing attention and application. MIMO technology can double the bandwidth without increasing bandwidth. Therefore, the combination of MIMO technology and OFDM technology can well meet the requirements of the development trend of the next generation system. Studies have shown that in fading channel environments, OFDM systems are very suitable for using MIMO technology to increase capacity. MIMO-OFDM technology realizes space diversity by using array antenna in OFDM transmission system, improves signal quality, and is a new technology obtained by combining OFDM and MIMO. It utilizes time, frequency and space three kinds of diversity techniques, so that the tolerance of the wireless system to noise, interference and multipath is greatly increased. However, the assumed application environment is a flat fading wireless channel. This assumption often exists in narrowband communication systems, but generally does not hold true in broadband communication systems.

现有技术基本上是基于导频的OFDM载频频偏估计方法，一类是针对单纯的OFDM技术应用，如“Blindhigh-resolutionuplinksynchronizationofOFDM-basedmultipleaccessschemes，”(H.Bolcskei，1999，Proc.IEEEWorkshopSignalProcessingAdvancesinWirelessCommun.，Annapolis，MD，pp.166-169)、“CarrierfrequencyoffsetacquisitionandtrackingforOFDMsystems”(M.LuiseandR.Reggiannini，1996，IEEETrans.Commun.，vol.44，pp.1590-1598，Nov.)、“AnimprovedfrequencyoffsetestimatorforOFDMapplications”(M.MorelliandU.Mengali，1999，IEEECommun.Lett.，vol.3，pp.75-77，Mar.)、“RobustfrequencyandtimingsynchronizationforOFDM”(T.M.SchmidlandD.C.Cox，1997，IEEETrans.Commun.，vol.45，pp.1613-1621，Dec.)和“AhighefficiencycarrierestimatorforOFDMcommunications”(H.LiuandU.Tureli，1998，IEEECommun.Lett.，vol.2，pp.104-106，Apr.)所述的技术，但是上述技术全部都是针对纯粹的OFDM系统，因此不适合MIMO-OFDM系统下的同步。另一类是关于MIMO情况下OFDM的技术应用，如“OFDMblindcarrieroffsetestimation：ESPRIT，”(U.Tureli，H.LiuandM.D.Zoltowski，2000，IEEETrans.Commun.，vol.48，pp.1459-1461，Sep.)，这些方法并没有考虑MIMO系统的复杂性，从而在实际情况下并不适用。在现有技术中，导频位置通常是固定的，而且，O导频常常是连续布置的，不利于多天线干扰(MAI，Multi-Antenna-Interference)的消除，从而影响载频估计性能。The prior art is basically a pilot-based OFDM carrier frequency offset estimation method, and one class is aimed at pure OFDM technology applications, such as "Blind high-resolution uplink synchronization of OFDM-based multiple access schemes," (H.Bolcskei, 1999, Proc.IEEEWorkshopSignalProcessingAdvancesinWirelessCommun., Annapolis, MD, pp.166-169), "Carrier frequency offset acquisition and tracking for OFDM systems" (M. Luise and R. Reggiannini, 1996, IEEE Trans. Commun., vol. 44, pp. 1590-1598, Nov.), "An improved frequency offset testimator for OFDM applications" (M. 1999, IEEECommun.Lett., vol.3, pp.75-77, Mar.), "Robust frequency and timing synchronization for OFDM" (T.M.SchmidlandD.C.Cox, 1997, IEEETrans.Commun., vol.45, pp.1613-1621, Dec .) and the technology described in "AhighefficiencycarrierestimatorforOFDMcommunications" (H.LiuandU.Tureli, 1998, IEEECommun. Lett., vol.2, pp.104-106, Apr.), but the above-mentioned technologies are all aimed at pure OFDM systems, Therefore, it is not suitable for synchronization under the MIMO-OFDM system. The other category is about the technical application of OFDM in the case of MIMO, such as "OFDMblindcarrieroffsetestimation: ESPRIT," (U.Tureli, H.LiuandM.D.Zoltowski, 2000, IEEETrans.Commun., vol.48, pp.1459-1461, Sep.), these methods do not consider the complexity of the MIMO system, so they are not applicable in practical situations. In the prior art, the positions of the pilots are usually fixed, and the O-pilots are often arranged continuously, which is not conducive to the elimination of Multi-Antenna-Interference (MAI), thus affecting the performance of carrier frequency estimation.

发明内容Contents of the invention

本发明所要解决的技术问题是提供一种基于导频设计的MIMO-OFDM载频同步方法，以克服现有技术存在的系统实现复杂、MAI消除能力差等缺点。The technical problem to be solved by the present invention is to provide a MIMO-OFDM carrier frequency synchronization method based on pilot design, so as to overcome the disadvantages of complex system implementation and poor MAI elimination ability in the prior art.

本发明所述的基于导频设计的MIMO-OFDM载频同步方法，应用于具有M个发射天线、N个接收天线和Q个子载频的MIMO-OFDM系统，包括以下步骤：The MIMO-OFDM carrier frequency synchronization method based on pilot frequency design described in the present invention is applied to a MIMO-OFDM system with M transmitting antennas, N receiving antennas and Q sub-carrier frequencies, including the following steps:

(1)将整个Q个子载频分成M个子波段，每个子波段占

个连续的子载频，对应分派给每个发射天线。每个子波段S_m仅仅从发射机m传输导频符号，而在其它发射机为0；(1) Divide the entire Q sub-carrier frequencies into M sub-bands, and each sub-band occupies

Contiguous subcarrier frequencies are assigned to each transmit antenna. Each sub-band S _m only transmits pilot symbols from transmitter m and is 0 at other transmitters;

(2)在每个S_m的末尾，留数个子载频作为保护，即不传信息；(2) At the end of each S _m , several sub-carrier frequencies are reserved as protection, that is, no information is transmitted;

(3)在每个S_m的末尾，子载频上的导频符号等间隔置0。N_zero和N_guard分别为子波段内0和保护子载频数，在子载频(3) At the end of each S _m , the pilot symbols on the subcarrier frequencies are set to 0 at equal intervals. N _zero and N _guard are the number of 0 and guard sub-carrier frequencies in the sub-band, respectively, in the sub-carrier frequency

上置符号；其中，N_guard+N_zero＞L，L为多径延迟的最大值；

Upper symbol; where, N _guard +N _zero > L, L is the maximum value of multipath delay;

为进一步提高性能，导频位置按如下算法进行跳变：对第m个发射机，m＝1，2，…，M，其发射内容为：当b＝1时，为子波段S_m分派给第m个发射机；b＞1时，如果，(m+b-1)modM≠0，为S_(m+b)modM；否则，为S_M。In order to further improve the performance, the pilot position is hopped according to the following algorithm: for the mth transmitter, m=1, 2, ..., M, its transmission content is: when b=1, it is assigned to the sub-band S _m The mth transmitter; when b>1, if (m+b-1)modM≠0, it is S _(m+b)modM ; otherwise, it is S _M .

本发明所述的基于导频设计的MIMO-OFDM载频同步方法。针对MIMO与OFDM结合使用的情况下，OFDM的载波频偏估计比单纯OFDM系统更困难的特点，给出了一种载频位置按一定规律设置—子波段算法，从而最大限度消除MIMO系统中的MAI，提高载波频偏估计性能的方法，使系统载频同步性能显著提高。同时，本发明所述方法具有实现简单等特点。The MIMO-OFDM carrier frequency synchronization method based on pilot frequency design described in the present invention. In view of the fact that the carrier frequency offset estimation of OFDM is more difficult than that of a pure OFDM system when MIMO is used in combination with OFDM, a sub-band algorithm is given to set the carrier frequency position according to a certain rule, so as to eliminate the frequency offset in the MIMO system to the greatest extent. MAI, a method for improving the performance of carrier frequency offset estimation, significantly improves the system carrier frequency synchronization performance. At the same time, the method of the present invention has the characteristics of simple implementation and the like.

附图说明Description of drawings

图1是本发明所述方法的参考系统框图。Figure 1 is a block diagram of a reference system for the method of the present invention.

图2是本发明所述方法中子波段算法导频分布实例图。Fig. 2 is an example diagram of pilot frequency distribution of the sub-band algorithm in the method of the present invention.

图3是本发明所述方法中子波段算法导频跳变时分布实例图。Fig. 3 is an example diagram of the time distribution of sub-band algorithm pilot hopping in the method of the present invention.

具体实施方式Detailed ways

下面结合附图和具体实施方式对本发明所述方法作进一步说明。The method of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

本发明针对图1所示的系统，提出一种有效的载波位置跳变方法，如图3所示。与不跳变(即图2所示)的方法相比，可以获得更好的性能。Aiming at the system shown in FIG. 1 , the present invention proposes an effective carrier position hopping method, as shown in FIG. 3 . Better performance can be obtained compared to the method without jumping (ie shown in Figure 2).

本发明所应用的系统模型如图1所示，MIMO-OFDM系统具有M个发射天线、N个接收天线，Q个子载频。在发射端，第m个子天线，被发射符号的第b个数据块可以表示为：The system model applied in the present invention is shown in Fig. 1, the MIMO-OFDM system has M transmit antennas, N receive antennas, and Q sub-carrier frequencies. At the transmitting end, the mth sub-antenna, the bth data block of the transmitted symbol can be expressed as:

a_m，b＝[α_m，b(0)，α_m，b(1)，L，a_m，b(Q-1)]^T (1)a _{m, b} = [α _{m, b} (0), α _{m, b} (1), L, a _{m, b} (Q-1)] ^T (1)

发射前，通过一个Q点的IFFT运算完成OFDM调制，表示为：Before transmission, the OFDM modulation is completed through a Q-point IFFT operation, expressed as:

${s the s}_{m m,, b b} ((i i)) = = \frac{11}{\sqrt{Q Q}} {Σ Σ}_{q q = = 00}^{Q Q - - 11} {a a}_{m m,, b b} ((q q)) {e e}^{\frac{j j 22 πqi πqi}{Q Q}} i i = = 00,, K K,, Q Q - - 11 - - - - - - ((22))$

将调制的OFDM信号加上CP并进行上变频，然后通过一个准静态的、多径无线信道，在接收端经过相反的下变频、去CP后，在第n个接收机上接收到的基带信号表示为：The modulated OFDM signal is added with CP and up-converted, and then passed through a quasi-static, multipath wireless channel. After reverse down-conversion and CP removal at the receiving end, the baseband signal received on the nth receiver represents for:

${r r}_{n no,, b b} ((i i)) = = \frac{11}{\sqrt{Q Q}} {Σ Σ}_{m m = = 11}^{M m} {Σ Σ}_{q q = = 00}^{Q Q - - 11} {h h}_{m m,, n no} ((q q)) {a a}_{m m,, b b} ((q q)) {e e}^{\frac{j j 22 πqi πqi}{Q Q}} + + {η η}_{n no,, b b} ((i i)),, i i = = 00,, K K,, Q Q - - 11 - - - - - - ((33))$

这里，h_m，n(q)是发射机m到接收机n在第q个子载频时的冲击响应。η_n,b(i)是加性高斯白噪声(AWGN)，均值和方差为(0，σ²)。Here, h _m,n (q) is the impulse response from transmitter m to receiver n at the qth sub-carrier frequency. η _n,b (i) is additive white Gaussian noise (AWGN) with mean and variance (0, σ ² ).

由于收发频率源差异、信道多普勒频移等因素，实际接收信号为：Due to factors such as the difference in the transceiver frequency source, channel Doppler frequency shift, etc., the actual received signal is:

${r r}_{n no,, b b}^{' '} ((i i)) = = \frac{11}{\sqrt{Q Q}} {Σ Σ}_{m m = = 11}^{M m} {e e}^{} j j 22 π π {f f}_{V V}^{((m m,, n no))} ((i i + + ((b b - - 11)) ((Q Q + + K K)))) {Σ Σ}_{q q = = 00}^{Q Q - - 11} {h h}_{m m,, n no} ((q q)) {a a}_{m m,, b b} ((q q)) {e e}^{\frac{j j 22 πqi πqi}{Q Q}} + + {η η}_{n no,, b b} ((i i)) - - - - - - ((44))$

这里，f_v ^(m，m)从第m个发射机到第n个接收机的对子载波的归一化频偏。第q′个子载波的接收信号为：Here, _fv ^(m,m) is the normalized frequency offset to subcarriers from the mth transmitter to the nth receiver. The received signal of the q'th subcarrier is:

${R R}_{n no,, b b}^{' '} (({q q}^{' '})) = = \frac{11}{Q Q} {Σ Σ}_{i i = = 00}^{Q Q - - 11} [[{Σ Σ}_{m m = = 11}^{M m} {e e}^{} j j 22 π π {f f}_{V V}^{((m m,, n no))} ((i i + + ((b b - - 11)) ((Q Q + + K K)))) {Σ Σ}_{q q = = 00}^{Q Q - - 11} {h h}_{m m,, n no} ((q q)) {a a}_{m m,, b b} ((q q)) {e e}^{j j \frac{22 πi πi ((q q - - {q q}^{' '}))}{Q Q}}]] + + {ξ ξ}_{n no,, b b} (({q q}^{' '})) - - - - - - ((55))$

$= = \frac{11}{Q Q} {Σ Σ}_{m m = = 11}^{M m} {e e}^{j j 22 π π {f f}_{V V}^{((m m,, n no))} ((b b - - 11)) ((Q Q + + K K))} {h h}_{m m,, n no} (({q q}^{' '})) {a a}_{m m,, b b} (({q q}^{' '})) {I I}_{m m,, n no} (({f f}_{V V}^{((m m,, n no))}))$

$+ + \frac{11}{Q Q} {Σ Σ}_{m m = = 11}^{M m} {e e}^{j j 22 π π {f f}_{V V}^{((m m,, n no))} ((b b - - 11)) ((Q Q + + K K))} {Σ Σ}_{\underset{q q &NotEqual; &NotEqual; {q q}^{' '}}{q q = = 00}}^{Q Q - - 11} {h h}_{m m,, n no} ((q q)) {a a}_{m m,, b b} ((q q)) {I I}_{m m,, n no} (({f f}_{V V}^{((m m,, n no))} + + q q - - {q q}^{' '})) + + {ξ ξ}_{n no,, b b} (({q q}^{' '}))$

其中 $ξ_{n, b} (q^{'}) = \frac{1}{\sqrt{Q}} Σ_{i = 0}^{Q - 1} η_{n, b} (i) e^{- \frac{j 2 π q^{'} i}{Q}},$ 也是AWGN噪声，均值和方差为(0，σ²)。in $ξ_{no, b} (q^{'}) = \frac{1}{\sqrt{Q}} Σ_{i = 0}^{Q - 1} η_{no, b} (i) e^{- \frac{j 2 π q^{'} i}{Q}},$ It is also AWGN noise with mean and variance (0, σ ² ).

I_m，n(f_v ^(m，n)+q-q′)是从第m发到第n收的第q个子载波到第g′个子载波间的ICI系数：I _{m, n} (f _v ^{(m, n)} +qq′) is the ICI coefficient between the qth subcarrier and the g′th subcarrier from the mth transmission to the nth reception:

${I I}_{m m,, n no} (({f f}_{V V}^{((m m,, n no))} + + q q - - {q q}^{' '})) = = \frac{sin sin ((π π (({f f}_{V V}^{((m m,, n no))} + + q q - - {q q}^{' '}))))}{Q Q sin sin ((\frac{π π}{Q Q} (({f f}_{V V}^{((m m,, n no))} + + q q - - {q q}^{' '}))))} \cdot \cdot {e e}^{jπ jπ ((11 - - \frac{11}{Q Q})) (({f f}_{V V}^{((m m,, n no))} + + q q - - {q q}^{' '}))} - - - - - - ((66))$

当不存在频偏时，上式在q＝q′时最大，而在q≠q′时为0。但当存在频偏时，由于ICI的影响，即使q≠q′时仍然不为0。本发明就是通过设计适当的导频信号，有效地估计出{f_v ^(m，n)}。When there is no frequency offset, the above formula is maximum when q=q', and is 0 when q≠q'. However, when there is a frequency offset, due to the influence of ICI, even if q≠q' is still not 0. The present invention effectively estimates {f _v ^{(m, n)} } by designing appropriate pilot signals.

在MIMO情况下，载频频偏的估计变得复杂化。首先，由于每一对发射和接收天线的频偏都不一样，从而存在MAI：In the case of MIMO, the estimation of carrier frequency offset becomes complicated. First, since the frequency offset of each pair of transmitting and receiving antennas is different, there is MAI:

${T T}_{m m,, n no,, b b}^{' '} (({q q}^{' '})) = = \frac{11}{Q Q} {Σ Σ}_{\underset{{m m}^{' '} &NotEqual; &NotEqual; m m}{{m m}^{' '} = = 11}}^{M m} {e e}^{j j 22 π π {f f}_{V V}^{(({m m}^{' '} . . n no))} ((b b - - 11)) ((Q Q + + K K))} {Σ Σ}_{q q = = 00}^{Q Q - - 11} {h h}_{{m m}^{' '},, n no} ((q q)) {a a}_{{m m}^{' '},, b b} ((q q)) {I I}_{{m m}^{' '},, n no} (({f f}_{V V}^{(({m m}^{' '},, n no))} + + q q - - {q q}^{' '})) - - - - - - ((77))$

为了抑制MAI，首先将整个频段分成M个子波段，每个发射机在传输导频信号的时候只占用其中一个子带，在每个子波段的末尾保留若干个子载频，在这些子载频上不传输任何的信号，这种子波段的设置，不仅从理论上可以证明它可以有效地抑制MAI，也可以从仿真结果得到验证。In order to suppress MAI, the entire frequency band is first divided into M sub-bands, and each transmitter only occupies one of the sub-bands when transmitting pilot signals, and several sub-carrier frequencies are reserved at the end of each sub-band. Transmitting any signal, this kind of sub-band setting can not only prove that it can effectively suppress MAI in theory, but also can be verified from simulation results.

在每个子波段，采用周期性地在导频中插入0来取代[5]中连续性填0的方法。定义代价函数：In each sub-band, periodically insert 0 in the pilot to replace the continuous filling of 0 in [5]. Define the cost function:

这里，Q_z，m表示第m个发射机对应导频符号为0的子载频序号。仿真结果表明，与连续0方法相比，该方法对载频频偏的变化更敏感，从而更便于估计载频频偏。Here, Q _z,m represents the serial number of the subcarrier frequency corresponding to the pilot symbol 0 of the mth transmitter. The simulation results show that this method is more sensitive to the change of carrier frequency offset than the continuous zero method, so it is easier to estimate the carrier frequency offset.

为了进一步改善系统的同步性能，并考虑到在实际系统中，不仅仅需要估计载波频偏，信道参数也是影响整个系统性能的关键。在上述基础上，将导频位置分布按一定的规律跳变，从而使频偏估计不再依赖于每个子波段内0的分布，并能够有效地进行信道参数的估计。In order to further improve the synchronization performance of the system, and considering that in an actual system, not only the carrier frequency offset needs to be estimated, but the channel parameters are also the key to the overall system performance. On the basis of the above, the distribution of pilot frequency positions is hopped according to a certain rule, so that the frequency offset estimation no longer depends on the distribution of 0 in each sub-band, and the channel parameters can be estimated effectively.

本发明可总结为以下几个步骤：The present invention can be summarized as the following steps:

1、将整个Q个子载频分成M个子波段，每个子波段占

个连续的子载频，对应分派给每个发射天线。每个子波段S_m仅仅从发射机m传输导频符号，而在其它发射机为0；1. Divide the entire Q sub-carrier frequencies into M sub-bands, and each sub-band occupies

2、在每个S_m的末尾，留数个子载频作为保护，即不传信息；2. At the end of each S _m , several sub-carrier frequencies are left as protection, that is, no information is transmitted;

3、在每个S_m的末尾，子载频上的导频符号等间隔置0，N_zero和N_guard分别为子波段内0和保护子载频数，在子载频

上置符号；其中，N_guard+N_zero＞L，L为多径延迟的最大值；3. At the end of each S _m , the pilot symbols on the sub-carrier frequency are equally spaced to 0, N _zero and N _guard are respectively 0 and the number of guard sub-carrier frequencies in the sub-band, in the sub-carrier frequency

Superposition symbol; where, N _guard +N _zero > L, L is the maximum value of multipath delay;

下面结合附图2和附图3对本发明的子波段算法的具体实现方法描述如下：Below in conjunction with accompanying drawing 2 and accompanying drawing 3, the specific implementation method of the sub-band algorithm of the present invention is described as follows:

1)整个子载频的个数是64，发射天线为4个，将64个子载频分成4段，每一段包括了连续的16个子载频。在传输导频信号的时候，任何一个发射天线只在其中一个子波段发射导频符号，而在其他的子波段不传输信号。1) The total number of sub-carriers is 64, and the number of transmitting antennas is 4. The 64 sub-carriers are divided into 4 segments, and each segment includes 16 consecutive sub-carriers. When transmitting pilot signals, any transmit antenna only transmits pilot symbols in one of the sub-bands, and does not transmit signals in other sub-bands.

2)在每个子波段的末尾，保留4个子载频，在这些保护子载频上不传输信息。2) At the end of each sub-band, 4 sub-carrier frequencies are reserved, and no information is transmitted on these guard sub-carrier frequencies.

3)在每个子波段中，等间隔地将0放在其中的4个子载波上。3) In each sub-band, place 0s on four sub-carriers therein at equal intervals.

4)为进一步提高性能，每个天线所对应的子波段也随着不同的OFDM导频符号而变化，例如在第一个OFDM符号时，发射天线1对应第一个子波段；在第二个导频符号时，发射天线1对应于第二个子载波，依此类推。4) In order to further improve performance, the sub-band corresponding to each antenna also changes with different OFDM pilot symbols, for example, in the first OFDM symbol, transmitting antenna 1 corresponds to the first sub-band; When using pilot symbols, transmit antenna 1 corresponds to the second subcarrier, and so on.

Claims

1, a kind of MIMO-OFDM carrier frequency synchronization method based on pilot frequency design, be applied to the MIMO-OFDM system with M transmitting antennas, N receiving antennas and Q sub-carrier frequencies, it is characterized in that, comprises the following steps:

(1) Divide the entire Q sub-carrier frequencies into M sub-bands, and each sub-band occupies

consecutive sub-carrier frequencies, correspondingly assigned to each transmit antenna, each sub-band S _m only transmits pilot symbols from transmitter m, and is 0 at other transmitters;

(2) At the end of each S _m , several sub-carrier frequencies are reserved as protection, that is, no information is transmitted;

(3) At the end of each S _m , the pilot symbols on the sub-carrier frequency are equally spaced with 0, N _zero and N _guard are respectively 0 and the number of guard sub-carrier frequencies in the sub-band, and in the sub-carrier frequency

Symbol on top.

2. The MIMO-OFDM carrier frequency synchronization method based on pilot design according to claim 1, characterized in that in step (3), N _guard +N _zero >L, where L is the maximum value of multipath delay.

3. The MIMO-OFDM carrier frequency synchronization method based on pilot design according to claim 1, wherein the pilot position is hopped according to the following algorithm: for the mth transmitter, m=1, 2, ... , M, and its transmission content is: when b=1, the sub-band S _m is assigned to the mth transmitter; when b>1, if (m+b-1)modM≠0, then S _{(m+ b) mod} M; otherwise, S _M .

4. The MIMO-OFDM carrier frequency synchronization method based on pilot design according to claim 1, wherein when Q=64, M=4,

, including the following steps:

1) Any transmit antenna only transmits pilot symbols in one of the sub-bands, and does not transmit signals in other sub-bands;

2) At the end of each sub-band, 4 sub-carrier frequencies are reserved, and no information is transmitted on these guard sub-carrier frequencies;

3) In each sub-band, place 0s on four sub-carriers therein at equal intervals.

5. The MIMO-OFDM carrier frequency synchronization method based on pilot design according to claim 4, characterized in that, in the first OFDM symbol, transmitting antenna 1 corresponds to the first sub-band, and in the second pilot frequency symbol, transmit antenna 1 corresponds to the second subcarrier, and so on.