CN103259757B - A kind of synchronous new method of Time And Frequency of effective MIMO-OFDM system - Google Patents

Abstract

The present invention is an effective new method for time and frequency synchronization of MIMO-OFDM system, which is characterized in that: there are many time-frequency synchronization methods in the technical field of synchronization of MIMO-OFDM system under wireless communication channel, but in MIMO-OFDM system Synchronization performance is not very good. Therefore, the present invention proposes a novel method for time and frequency synchronization of an effective MIMO-OFDM system. In this synchronization method, at the transmitting end, a time-orthogonal training sequence is inserted between the OFDM data symbols of each transmitting antenna, and the designed training sequence β factor value affects the autocorrelation of the sequence, thereby affecting the timing synchronization performance of the system; at the receiving end , the time synchronization and fractional frequency offset estimation are performed in the time domain, and the integer frequency offset estimation is also completed in the time domain, thus reducing the computational complexity of the system. Therefore, compared with the traditional synchronization algorithm, the algorithm proposed by the invention has the advantages of accurate timing, high detection probability and accurate frequency offset estimation in the MIMO-OFDM system.

Description

A New Method for Efficient Time and Frequency Synchronization of MIMO-OFDM Systems

technical field

The invention relates to the technical field of MIMO-OFDM, in particular to a novel method for synchronizing time and frequency of an effective MIMO-OFDM system.

technical background

With the rapid development of wireless communication technology, people have higher and higher requirements on the data transmission rate of mobile communication. For a single-input single-output (SISO, Single-Input Single-Output) system, the channel capacity is limited. According to the MIMO technology, the multipath component in propagation can be utilized, thereby reducing intersymbol interference, improving higher spatial diversity, and improving wireless communication channel capacity and spectrum utilization. The OFDM technology has the advantages of high spectrum utilization rate, strong capability of frequency selective fading, easy combination with multiple access schemes, and flexible support for multiple services. In addition, the OFDM system has a strong ability to resist multipath interference due to its low code rate and the addition of a time guard interval. The combination of MIMO technology and OFDM technology can well realize the effectiveness and reliability of the system. MIMO-OFDM integrates the advantages of MIMO and OFDM technology, using MIMO technology to double the capacity and spectrum utilization of the communication system without increasing the bandwidth, and improving the effectiveness of the system; using OFDM technology can make the frequency selective channel Converting to the characteristics of flat fading channel can realize the reliable application of MIMO technology in broadband wireless data transmission.

There are several technical difficulties in realizing the MIMO-OFDM system, including requiring the system to have high synchronization performance in the process of transmitting OFDM data information. Synchronization errors in MIMO-OFDM systems mainly include timing synchronization, frequency synchronization and sampling clock synchronization. Timing synchronization is divided into frame synchronization and symbol synchronization. The present invention completes the two processes in one step to reduce the amount of calculation in the system. Timing synchronization is to determine the initial position of the FFT window in the MIMO-OFDM signal demodulation process and realize information correct demodulation. Timing synchronization is to ensure the reliability of the entire system, and is an important guarantee for subsequent frequency offset estimation. Therefore, an effective new method for time and frequency synchronization of MIMO-OFDM systems is very important in high-speed MIMO-OFDM systems.

When studying the synchronization problem of the MIMO-OFDM system, according to the different network topology, it is usually divided into two different models for research, the centralized MIMO-OFDM synchronization model and the distributed MIMO-OFDM synchronization model. The invention is mainly applied to the centralized MIMO-OFDM synchronization model. There are two commonly used centralized MIMO-OFDM synchronization schemes: (1) The first one is to insert orthogonal training sequences at the same position of each receiving and transmitting antenna, and the ability of training sequences to resist multipath can be strengthened by multi-terminal repetition. However, the disadvantage of this method is that the time-domain orthogonal sequence is easily affected by the multipath fading channel, which weakens the orthogonality of the sequence. Therefore, the interference between antennas also increases, and the peak value of the sequence autocorrelation function will become blurred. , which causes the system synchronization error to increase. See literature: Mody.A.N, Stuber.G.L.Synchronization for MIMO-OFDMsystems.Global Telecommunications Conference.2001.GLOBECOM'01.IEEE.Volume:1,25-29Nov.2001Pages:509-513Vol.1. Mody.A.N,Stuber.G.L.Receiver Implementation for a MIMO-OFDM System.Global Telecommunications Conference.2002.GLOBECOM'02.IEEE.Volume:1.17-21.Nov.2002Pages:716-720Vol.1 The second method is to use time positive In the method of intersecting training sequences, the training sequences inserted on different transmitting antennas are staggered in time. However, the disadvantage of this synchronization algorithm is that as the number of antennas increases, the bandwidth occupied by the orthogonal training sequence increases accordingly, resulting in a decrease in frequency utilization and increasing the computational complexity of the system. See literature: T.C.W.Schenk, A.van Zelst. Frequency Synchronization for MIMO-OFDM Wireless LAN Systems. Proc. IEEE Vehicular Technology Conference Fall2003 (VTC Fall2003), Orlando (FL), 6-9October2003, paper05D-03. Allert van Zelst, Tim C.W. Schenk, Implementation of a MIMO OFDM-Based Wireless LAN System, IEEETRANSACTIONS ON SIGNAL PROCESSING, VOL.52, NO.2, pp.483-494FEBRUARY2004. FAN Hui-li, SUN Jing-fang, YANG Ping, LI Ding-shan, A Robust Timing and Frequency Synchronization Algorithm for HF MIMO OFDM Systems.IEEE CONFERENCEPUBLICATIONS.2010.

In order to overcome the deficiencies of existing methods in synchronization technology, the present invention proposes a new effective time and frequency synchronization method for MIMO-OFDM systems. The method belongs to the data-assisted synchronization method, can improve the channel capacity and spectrum utilization rate of the wireless communication system, and improves the effectiveness of the system.

Contents of the invention

The purpose of the present invention is to propose an effective new method for time and frequency synchronization of the MIMO-OFDM system, so as to overcome the deficiencies of the existing MIMO-OFDM system and its synchronization technology. The synchronization algorithm can improve the channel capacity and spectrum utilization of the wireless communication system, and improve the effectiveness of the system; at the same time, the designed training sequence has strong autocorrelation and weak cross-correlation, which can be cross-correlated with the locally transmitted data Finally, a single, sharp peak with almost no sidelobe is obtained, so that the receiving end can quickly and accurately realize system synchronization through threshold judgment, thereby ensuring correct demodulation of the transmitted information.

In order to achieve the above object, the present invention proposes a new method for time and frequency synchronization of an effective MIMO-OFDM system, which overcomes the deficiencies in existing MIMO-OFDM system synchronization technology, and the innovations of the present invention:

(1) A new training sequence T(n) proposed by the present invention proposes that the size of the β factor is within a certain range, and as the β factor increases, the autocorrelation of the training sequence can be enhanced to varying degrees.

(2) The timing synchronization and frequency synchronization algorithm proposed by the present invention can insert the training sequence between the transmitted OFDM data symbols, according to the cross-correlation between the training sequence and the data symbols, so that the objective function of timing synchronization has a side lobe Few, single, and sharp peaks allow the receiving end to quickly and accurately determine the initial position of timing synchronization by setting a specific threshold. On the basis of realizing system timing synchronization, frequency synchronization is performed to ensure the integrity of the transmitted data information. demodulated correctly.

A new method for time and frequency synchronization of an effective MIMO-OFDM system proposed by the present invention is to realize its process by transmitting and receiving antennas Nt×Nr, and both Nt and Nr are positive integers, which have:

Step 1: Construct a new training sequence T(n). As the value of β increases in the training sequence, its sequence autocorrelation increases, and its sequence T(n) has:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; j\&pi;r</span>}{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&beta;N</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, take r=N/2-1, gcd(r,N/2)=1, β∈(1,25);

Step 2: Take the T(n) sequence and repeat it once to construct a training sequence C ₁ (n) with a length of N, which is:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span>\\ \mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\right.$

Step 3: Take the T(n) sequence for anti-symmetry, and generate a new sequence T′(n), which has:

$\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Step 4: Construct the sequence T(n) and T′(n) into a sequence C ₂ (n) of length N, which has:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left\{\begin{array}{cc}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span>\\ {\mathrm{<span\; class="notranslate">\; T</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&rsqb;</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>\right.$

Step 5: At the receiving end, use the local training sequence C ₁ (n) to perform cross-correlation with the received signal to obtain timing synchronization. The synchronization timing measurement function can be expressed as:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them, Nt is the number of antenna lines at the transmitting end, Nr is the number of antenna lines at the receiving end, N is the length of an OFDM symbol not including the cyclic prefix, d is an integer value, and d represents the relative sliding position of the received sequence relative to the local sequence, n is the number of sampling points of the received signal, ()* indicates that the data in the brackets is conjugated, C _1,i (.) indicates the first training sequence inserted on each transmitting antenna, Indicates that the data signal transmitted on each receiving antenna is conjugated;

Step 6: By setting a simple threshold value, make the objective function M(d) exceed the threshold value d to determine the position of timing synchronization, that is, the synchronization moment:

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; estl</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\underset{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Step 7: Make a fractional frequency offset estimate:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\mathrm{<span\; class="notranslate">\; the\; angle</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; estl</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

In the formula $R\left({\mathrm{\&tau;}}_{\mathrm{estl}}\right)=\underset{j=0}{\overset{\mathrm{Nr}}{\mathrm{\&Sigma;}}}\underset{\mathrm{no}=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}({\mathrm{\&tau;}}_{\mathrm{estl}}+\mathrm{no})({\mathrm{\&tau;}}_{\mathrm{estl}}+\mathrm{no}+N/2)---\left(10\right)$

Among them, the fractional frequency offset estimation range ε _f ∈ (0,1);

Step 8: Perform integer frequency offset estimation after compensating the estimated fractional frequency offset. Integer frequency offset estimation is to directly estimate ε _i under the condition of time domain without FFT operation. The integer frequency offset estimation value is:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; est</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; esstl</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Ng</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; .</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; esst</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\underset{{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Wherein, Ng represents the length of the cyclic prefix, C _2,i ( ) represents the second training sequence inserted on each transmitting antenna, Indicates that the data signals transmitted on each receiving antenna take the conjugate operation, the search in equations (12) and (13) is centered on d′=τ _est1 +N+Ng, and the integer frequency offset estimation range ε _i ∈ (-N /4,N/4).

Description of drawings

In order to more clearly illustrate an effective new method for time and frequency synchronization of a MIMO-OFDM system, a brief introduction is given to the accompanying drawings of the present invention.

Fig. 1 is the MIMO-OFDM system basic block diagram that the present invention has Nt root transmitting antennas and Nr root receiving antennas;

In the figure, the MIMO-OFDM system block diagram is mainly composed of a transmitter and a receiver. At the transmitting end, it mainly includes: encoding 2, MIMO encoding 4, FFT modulation 6; at the receiving end, it mainly includes: timing synchronization and frequency synchronization 9, FFT demodulation 11, channel estimation 13, MIMO decoding 14, decoding 16, and sink 17.

Fig. 2 is a block diagram of the basic structure of the insertion training sequence of the present invention;

In the figure, the training sequence is inserted between the OFDM data symbols of each transmitting antenna in a time-orthogonal form.

Fig. 3 is a schematic diagram of the training sequence construction method of the present invention;

In the figure, C ₁ (n) takes the T(n) sequence and repeats it once to construct a training sequence of length N, and C ₂ (n) constructs a training sequence of length N from sequences T(n) and T′(n).

FIG. 4 is a schematic diagram of a method for timing synchronization and frequency synchronization in the present invention;

In the figure, cross-correlation is performed between the training sequence and the locally transmitted data information, the threshold value is set, the starting position of the FFT window is determined, and the frequency offset estimation is performed after determining the synchronization position.

Fig. 5 is the performance emulation figure of correct probability of β=10 timing synchronization algorithm of the present invention;

In the figure, the abscissa represents the signal-to-noise ratio (SNR), the ordinate represents the probability of correct synchronization, and β represents a factor affecting the probability of correct synchronization. It can be seen from the figure that the traditional algorithm and the improved algorithm have the same β factor, and the synchronization correct probability of the improved algorithm is far better than that of the traditional algorithm.

FIG. 6 is a performance simulation diagram of the decimal frequency offset estimation mean square error (MSE) of the present invention;

In the figure, the abscissa represents the signal-to-noise ratio (SNR), the ordinate represents the fractional frequency offset estimation mean square error (MSE), and β represents a probability factor affecting correct synchronization. It can be seen from the figure that under the same β factor between the traditional algorithm and the improved algorithm, the mean square error (MSE) of the frequency offset estimation of the improved algorithm is better than that of the traditional algorithm.

Fig. 7 is a simulation diagram of frequency offset estimation mean square error (MSE) performance of the present invention;

In the figure, the abscissa represents the signal-to-noise ratio (SNR), the ordinate represents the mean square error of frequency offset estimation (MSE), and β represents a probability factor affecting correct synchronization.

Fig. 8 is a performance simulation diagram of the correct probability of timing synchronization algorithms with different β factors of the present invention;

In the figure, the abscissa represents the signal-to-noise ratio (SNR), the ordinate represents the probability of correct synchronization, and β represents a factor affecting the probability of correct synchronization.

It can be seen from the figure that under the same signal-to-noise ratio, the larger the β factor, the higher the probability of correct synchronization of the system.

Detailed ways

The present invention is a new method for time and frequency synchronization of an effective MIMO-OFDM system, which will be further described in detail below in conjunction with specific implementation methods.

FIG. 1 is a basic block diagram of a MIMO-OFDM system with Nt transmitting antennas and Nr receiving antennas according to the present invention. An effective new method for time and frequency synchronization of MIMO-OFDM system mainly consists of a transmitter and a receiver. At the sending end, it mainly includes a data source module 1, an encoding module 2, a symbol mapping module 3, a MIMO encoding module, an insertion pilot module 5 on each transmitting antenna, an IFFT module 6, an insertion training sequence module 7, and an insertion guard interval Module 8. The receiving end mainly includes a timing synchronization and frequency synchronization module 9, a guard interval removal module 10 on each receiving antenna, an FFT module 11, a pilot extraction module 12, a channel estimation module 13, a MIMO decoding module 14, and a symbol demapping module 15 , a decoding module 16 , and a sink module 17 . Inserted training sequence module 7 at the receiving end, this training sequence module generates two training sequences with the same length as the data OFDM symbol. Prior to this, the MIMO coding module 4 is required, which applies spatial multiplexing or space diversity precoding technology, and the present invention mainly adopts spatial multiplexing and coding technology. Timing synchronization and frequency synchronization module 9 at the receiving end mainly determine the initial position of the FFT window to ensure that the data OFDM symbols can be demodulated correctly, and frequency synchronization mainly ensures mutual orthogonality between each subcarrier; channel estimation module 13 mainly uses The training sequence is used to estimate the time domain response of the multipath channel; then the MIMO decoding module 14 and decoding module 16 are implemented to demodulate the data OFDM symbols. Fig. 2 is a block diagram of the basic structure of the insertion training sequence of the present invention, the training sequence is inserted between OFDM symbols in the form of time orthogonality, but because it is a MIMO-OFDM system with multiple input and multiple output, the training sequence is time orthogonal The form is inserted between the OFDM data symbols of each transmit antenna.

FIG. 3 is a schematic diagram of the training sequence construction method of the present invention. For a MIMO-OFDM synchronization system, timing synchronization is particularly important if the receiving end is to accurately demodulate the data. Constructing a training sequence with good auto-correlation and weak cross-correlation is an important prerequisite to ensure timing synchronization of OFDM symbols at the receiving end. A method for constructing a training sequence with good autocorrelation: 301 constructing a new training sequence T(n), in the training sequence as the value of β increases, the sequence autocorrelation is enhanced; 302 takes the T(n) sequence and repeats it once Construct a training sequence C ₁ (n) with a length of N; 303 take the T(n) sequence for anti-symmetry to generate a new sequence T'(n); 304 form the sequence T(n) and T'(n) into a length is the sequence C ₂ (n) of N.

Example: When N=32 and β=10, the training sequence C ₁ (n) is the actual sequence

When N=32 and β=10, the actual sequence of the training sequence C ₂ (n).

Fig. 4 is a schematic diagram of the method of timing synchronization and frequency synchronization of the present invention, 401 is the received signal; 402 is the cross-correlation between the local training sequence C ₁ (n) of the receiving end and the received signal to obtain timing synchronization, and the synchronous timing measurement function can be expressed for:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

403 is to set the threshold value. When the objective function M(d) exceeds the threshold value d value, it is judged as the position of timing synchronization:

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; estl</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\underset{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

404 is to determine the synchronization position and perform frequency offset estimation. The objective function of frequency offset estimation is expressed as:

Make a fractional frequency offset estimate:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}\mathrm{<span\; class="notranslate">\; the\; angle</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; estl</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

In the formula $R\left({\mathrm{\&tau;}}_{\mathrm{estl}}\right)=\underset{j=0}{\overset{\mathrm{Nr}}{\mathrm{\&Sigma;}}}\underset{\mathrm{no}=0}{\overset{N/2-1}{\mathrm{\&Sigma;}}}{r}_j^{*}({\mathrm{\&tau;}}_{\mathrm{estl}}+\mathrm{no})r_j({\mathrm{\&tau;}}_{\mathrm{estl}}+\mathrm{no}+N/2)---\left(11\right)$

Wherein, the fractional frequency offset estimation range is ε _f ∈ (0,1).

405 is the integer frequency offset estimation of the frequency after the estimated fractional frequency offset is compensated, and 406 is the integer frequency offset estimation proposed by the present invention, which is directly estimated ε _i under the condition of the time domain, thus omitting the FFT operation. Integer frequency offset estimate:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; est</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; est</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; Ng</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nt</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; Nr</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; [</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; esst</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arg</span>}\underset{{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

Among them, Ng represents the length of the cyclic prefix, C _2,i (.) represents the second training sequence inserted on each transmitting antenna, r _j (.) represents the data signal transmitted on each receiving antenna, formula (13) and The search in (14) is centered on d′=τ _est1 +N+Ng. The range of integer frequency offset estimation ε _i ∈(-N/4,N/4).

Fig. 5 is a performance simulation diagram of the correct probability of the β=10 timing synchronization algorithm of the present invention. The main parameter settings of the simulation process of the present invention: the number of simulations is 10000 times, the number of antennas at the transmitting end is 2, the modulation method is BPSK, the number of subcarriers is N=1024, the length of the cyclic prefix is N/4, and the channel environment is selected in a multipath fading channel environment Next, the training sequence with β=10 is selected as the performance comparison of the synchronization accuracy probability between the traditional algorithm and the algorithm of the present invention. The traditional algorithm is: Allert van Zelst, Tim C.W.Schenk, Implementation of aMIMO OFDM-Based Wireless LAN System, IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL.52, NO.2, pp.483-494, FEBRUARY2004. As can be seen from the simulation diagram, the correct synchronization probability of the traditional algorithm reaches 90% and the signal-to-noise ratio is about 0dB. When the correct synchronization probability of the present invention reaches 90%, the signal-to-noise ratio is about -18dB. Therefore, the performance of the timing synchronization algorithm proposed by the present invention is far superior to the traditional algorithm.

Fig. 6 is a simulation diagram of the mean square error of fractional frequency offset estimation in the present invention. The main parameter settings of the simulation process of the present invention: the number of simulations is 10000 times, the number of antennas at the transmitting end is 2, the modulation method is BPSK, the number of subcarriers N=1024, the length of the cyclic prefix is N/4, and the channel environment is selected in a multipath fading channel environment Next, take the frequency offset ε _f =0.3, and choose the training sequence of β=10 as the traditional algorithm and the algorithm of the present invention to compare the performance of the synchronous fractional frequency offset estimation algorithm. As can be seen from the figure, when the mean square error of the traditional algorithm decimal frequency offset estimation is 10 ^-3 , the signal ^- to-noise ratio is about 0dB. About -10dB. Therefore, the performance of the frequency synchronization proposed by the present invention is better than that of the traditional algorithm.

Fig. 7 is a performance simulation diagram of mean square error (MSE) of frequency offset estimation in the present invention. The main parameter settings of the simulation process of the present invention: the number of simulations is 10000 times, the number of antennas at the transmitting end is 2, the modulation method is BPSK, the number of subcarriers N=1024, the length of the cyclic prefix is N/4, and the channel environment is selected in a multipath fading channel environment Next, the frequency offset ε=50.3 is taken. It can be seen from the simulation diagram that when the frequency offset estimation mean square error proposed by the present invention is 10 ^-3 , the SNR is about -6dB.

Fig. 8 is a performance simulation diagram of the correct probability of timing synchronization algorithms with different β factors in the present invention. The main parameter settings of the simulation process of the present invention: the number of simulations is 10000 times, the number of antennas at the transmitting end is 2, the modulation method is BPSK, the number of subcarriers N=1024, the length of the cyclic prefix is N/4, and the channel environment is selected in a multipath fading channel environment When the frequency offset ε _f =0.3, the β factor is selected to increase gradually, and the correct synchronization probability performance of the system is also enhanced. Under the same SNR condition -20dB, β=1, the probability of correct synchronization is 60%, β=5, the probability of correct synchronization is 70%, and β=10, the probability of correct synchronization is 80%. Therefore, different values of the β factor also affect the synchronization performance of the system.

Claims (2)

1. the synchronous new method of Time And Frequency of effective MIMO-OFDM system, this method is mainly used in centralized MIMO-OFDM synchronistic model, and its characteristic value is:

Step 1: construct new training sequence T (n), along with the increase of β value in training sequence, its sequence self correlation strengthens, and its sequence T (n), has:

$\begin{array}{cc}T\left(n\right)=\exp \left(\frac{2{\mathrm{j\&pi;rn}}^2}{\mathrm{\&beta;}N}\right)& n=0,1,\mathrm{...},N/2-1\end{array}---\left(1\right)$

Wherein, get r=N/2-1, gcd (r, N/2)=1, β ∈ (1,25);

Step 2: get T (n) sequence and repeat once to construct the training sequence C that length is N ₁n (), has:

$C_1\left(n\right)=\{\begin{array}{cc}T\left(n\right)& n\&Element;\&lsqb;0,N/2-1\&rsqb;\\ T(n-N/2)& n\&Element;\&lsqb;N/2,N-1\&rsqb;\end{array}---\left(2\right)$

Step 3: get T (n) sequence and carry out antisymmetry, generates a new sequence T ' (n), has:

T′(n)＝-T(N/2-n) n∈[0,N/2-1] (3)

Step 4: sequence T (n) and T ' (n) is formed the sequence C that length is N ₂n (), has:

$C_2\left(n\right)=\{\begin{array}{cc}T\left(n\right)& n\&Element;\&lsqb;0,N/2-1\&rsqb;\\ T^{\&prime;}(n-N/2)& n\&Element;\&lsqb;N/2,N-1\&rsqb;\end{array}---\left(4\right)$

Step 5: at receiving terminal, with local training sequence C ₁n () and Received signal strength carry out cross-correlation, obtain Timing Synchronization, synchronous timing measurements function can be expressed as:

$P\left(d\right)=\underset{i=1}{\overset{Nt}{\&Sigma;}}\underset{j=1}{\overset{Nr}{\&Sigma;}}\&lsqb;\underset{n=0}{\overset{N/2-1}{\&Sigma;}}{r}_j^{*}(d+n)C_{1,i}\left(n\right)\&rsqb;\&CenterDot;{\&lsqb;\underset{n=0}{\overset{N/2-1}{\&Sigma;}}{r}_j^{*}(d+n+N/2)C_{1,i}\left(n\right)\&rsqb;}^{*}---\left(5\right)$

$R\left(d\right)=\underset{i=1}{\overset{Nt}{\&Sigma;}}\underset{j=1}{\overset{Nr}{\&Sigma;}}\underset{n=1}{\overset{N/2-1}{\&Sigma;}}|C_{1,i}^{*}(n+d)\&CenterDot;C_{1,i}(n+d)|---\left(6\right)$

$M\left(d\right)=\frac{\left|P^2\left(d\right)\right|}{R^2\left(d\right)}---\left(7\right)$

Wherein, Nt is transmitting terminal sky number of lines, Nr is receiving terminal sky number of lines, N is the length not comprising Cyclic Prefix OFDM symbol, d is integer value, and d represents the relative sliding position of the sequence of reception relative to local sequence, and n is the sampling number of Received signal strength, () * represents that the data in bracket get conjugate operation, C _{1, i}() represents first training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation;

Step 6: by setting simple threshold value, target function M (d) is exceeded position that threshold value d value is judged to Timing Synchronization, i.e. synchronization point:

${\mathrm{\&tau;}}_{est1}=\underset{d}{\arg max}\left(M\right(d\left)\right)---\left(8\right)$

Step 7: carry out decimal frequency bias estimated value:

${\mathrm{\&epsiv;}}_f=\frac{1}{\mathrm{\&pi;}}angle\left(R\right({\mathrm{\&tau;}}_{est1}\left)\right)---\left(9\right)$

In formula $R\left({\mathrm{\&tau;}}_{est1}\right)=\underset{j=0}{\overset{Nr}{\&Sigma;}}\underset{n=0}{\overset{N/2-1}{\&Sigma;}}{r}_j^{*}({\mathrm{\&tau;}}_{est1}+n)r_j({\mathrm{\&tau;}}_{est1}+n+N/2)---\left(10\right)$

Wherein, decimal frequency bias estimation range ε _f∈ (0,1);

Step 8: carry out integer frequency bias estimation by after the fractional frequency migration estimated, it is direct estimation ε under the condition of time domain that integer frequency bias is estimated _i, eliminate FFT computing, integer frequency bias estimated value:

ε _i＝τ _est2-τ _est1-N-Ng+1 (11)

$Q\left(d^{\&prime;}\right)=\underset{i=1}{\overset{Nt}{\&Sigma;}}\underset{j=1}{\overset{Nr}{\&Sigma;}}\&lsqb;\underset{n=0}{\overset{N/2-1}{\&Sigma;}}{r}_j^{*}(d^{\&prime;}+n)C_{2,i}\left(n\right)\&rsqb;\&CenterDot;{\&lsqb;\underset{n=0}{\overset{N/2-1}{\&Sigma;}}{r}_j^{*}(d^{\&prime;}+N/2-n)C_{2,i}\left(n\right)\&rsqb;}^{*}---\left(12\right)$

${\mathrm{\&tau;}}_{est2}=\underset{d^{\&prime;}}{\arg max}\left(Q\right(d^{\&prime;}\left)\right)---\left(13\right)$

Wherein, Ng represents the length of Cyclic Prefix, C _{2, i}() represents second training sequence that each transmitting antenna inserts, represent that the data-signal that each reception antenna transmits gets conjugate operation, the search in formula (12) and (13) is with d '=τ _est1centered by+N+Ng, integer frequency bias estimation range ε _i∈ (-N/4, N/4).

2. the synchronous new method of Time And Frequency of a kind of effective MIMO-OFDM system according to claim 1, it is characterized in that: propose new training sequence T (n), according to the difference of the β factor, Timing Synchronization accuracy is with the increase of the β factor, and its timing net synchronization capability strengthens.