CN104883229A - Code division multi-beam signal separation method based on FDMA system - Google Patents

Abstract

The invention relates to a code division multi-beam signal separation method based on an FDMA system, and belongs to the field of microwave signal measurement. In the method, priori information is used for superimposing the multi-channel parallel signals after mixing, and then through a low-pass filter and a matched filter of a common branch, the frequency division multiplexing signals are moved to a baseband; as beam signals corresponding to different frequency points have different coding sequences and respective autocorrelation functions can be used for distinguishing the beam signals, the matched multi-channel parallel code capture modules is used for correlation operation and correlation peak detection to obtain the correlation peak, and the correlation peak is used for solving the correlation operation to finally separate the signals. Compared with a conventional code division multi-beam signal separation method based on the FDMA system, the method provided by the invention simplifies the complex multi-channel parallel down-conversion module and the matched filter module through the introduction of solving the correlation operation, thereby significantly saving hardware resources, improving the operation efficiency and reducing the consumption of resources.

Description

A Code Division Multi-beam Signal Separation Method Based on FDMA System

technical field

The invention relates to a signal separation method, in particular to a code division multi-beam signal separation method based on an FDMA system, and belongs to the field of microwave signal measurement.

Background technique

In the actual system of the multi-beam network, factors such as the inconsistency of the amplitude and phase of the analog devices in the multi-beam network will cause the amplitude and phase relationship of each output beam between the array channels to deviate from the preset value. Therefore, it is of great practical significance to accurately separate the FDMA (Frequency Division Multiple Access) multi-beam signals of the antenna system, and to calculate the amplitude-phase relationship between the multi-beam signals based on the separated multi-beam signals. The inconsistency of channel amplitude and phase and compensation can ensure the quality of beamforming and make the multi-beam network work accurately and effectively. The traditional method of separating FDMA multi-beam signals only needs to pass the multi-beam signals through a parallel multi-channel down-conversion module and a multi-channel parallel matched filter module. The down-conversion module includes two parts: frequency mixing and low-pass filter. The method can completely separate the FDMA multi-beam signals.

In practical applications, multiple parallel down-conversion and multiple parallel matched filter modules need to consume a lot of FPGA resources, such as on-chip high-speed multiplier DSP48, logic resource Slice and so on. Therefore, in order to realize the separation of FDMA multi-beam signals, as the number of frequency points of parallel FDMA multi-beam signals increases, the resource consumption of traditional beam signal separation methods will be inestimable.

Contents of the invention

The purpose of the present invention is to solve the traditional FDMA multi-beam signal separation method hardware resource consumption is large, the problem of slow operation speed, proposes a kind of code division multi-beam signal separation method based on FDMA system, this method simplifies the system structure, reduces Resource consumption, reducing signal separation time.

The idea of the present invention is to use prior information, that is, the multi-beam signal of FDMA also satisfies the condition of code division at the same time, superimpose the signals after multi-channel parallel mixing, and then pass through the low-pass filter and matched filter of the common branch, Move the frequency-division multiplexed signals to the baseband; and because the beam signals corresponding to each frequency point have their own different code sequences, their respective autocorrelation functions can be used to distinguish each beam signal, so the matching multi-channel The parallel code capture module finally separates the signal after performing correlation calculation and correlation peak detection.

The present invention is achieved through the following technical solutions.

A kind of code division multi-beam signal separation method based on FDMA system, its main steps are as follows:

Step 1. The source generates FDMA signals, and the beams corresponding to each frequency point are not only frequency-divided, but also code-divided;

Step 2, the receiving end receives the FDMA multi-beam signal, performs multiple parallel frequency mixing operations, and moves the FDMA multi-beam signal from their respective frequency points to the baseband;

Step 3, superimposing the multi-channel parallel mixing results obtained in step 2, and filtering out high-frequency components through a low-pass filter after the superposition;

Step 4, the signal obtained in step 3 is matched and filtered through a matched filter to reduce inter-symbol crosstalk and improve the bit error rate;

Step 5. Pass the signal obtained in step 4 through multiple parallel code capture modules, perform correlation calculation and correlation peak detection on the input signal, and obtain the correlation peak signals output by each code capture module, and the obtained correlation peak signals are separated beam signal;

Step 6: Carry out de-correlation calculation on the correlation peaks obtained in step 5, and the signal obtained by de-correlation is the signal without multiple access interference after separation.

After the above seven steps, the beam separation of the code division multi-beam signal based on the FDMA system is completed.

Beneficial effect

The invention is a beam separation method of a code division multi-beam signal based on an FDMA system. The traditional FDMA multi-beam signal separation method requires multiple parallel frequency mixing modules, multiple parallel low-pass filter modules and multiple parallel matched filter modules. Multi-channel parallel operations will consume a lot of FPGA resources. For ordinary FPGA chip resource capacity requirements are relatively high. And adopt the method of the present invention, after the signal after the frequency mixing is superimposed, pass through low-pass filter and matched filter jointly, can reduce n-1 (n is frequency division signal after low-pass filter and matched filter are transferred to common branch The number of frequency points) combined modules of low-pass filter and matched filter significantly reduce resource consumption, improve computing efficiency, and reduce computing time. At the same time, since the coding sequences of the FDMA multi-beam signals are different, the multiple access interference caused by signal superposition can also be removed by decorrelation operations with little resource consumption, thereby separating all beams.

In summary, the present invention utilizes the FDMA multi-beam signal to satisfy the code division condition at the same time. Although the introduction of the de-correlation operation consumes a small amount of resources, it simplifies the complex multi-channel parallel down-conversion module and matched filter module. A large number of hardware resources are saved, and the computing speed is improved.

Description of drawings

Fig. 1 is a schematic flow chart of a conventional method for separating code-division multi-beam signals based on the FDMA system;

FIG. 2 is a schematic flow chart of a method for separating a code division multi-beam signal based on an FDMA system according to an embodiment of the present invention;

Fig. 3 is the traditional code division multi-beam signal separation method based on the FDMA system and the bit error rate comparison diagram of the separation method of the code division multi-beam signal based on the FDMA system of the present invention;

Fig. 4 is a time-consuming comparison diagram between the separation method of code division multi-beam signals based on FDMA system and the traditional separation method of code division multi-beam signals based on FDMA system according to the embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with accompanying drawing and embodiment, also described the technical problem and beneficial effect that the technical solution of the present invention solves simultaneously, it should be pointed out that described embodiment is only intended to facilitate the understanding of the present invention, and It has no limiting effect on it.

As shown in Figure 1, it is a schematic flow chart of the separation method of the traditional code-division multi-beam signal based on the FDMA system. The main method is to pass the frequency-division multi-beam signal sent by the source in parallel through multiple down-conversion modules and multiple parallel matched filters. module, wherein the down-conversion module includes two parts of frequency mixing and low-pass filter. Taking one down-conversion module as an example, the main function of the frequency mixing module is to move the FDMA multi-beam signal to the baseband and generate high-frequency signals at the same time; the function of the low-pass filter is to retain the baseband signal and filter out the high-frequency signal; The baseband signal is matched and filtered through multiple parallel matched filter modules to reduce inter-symbol crosstalk and improve the bit error rate; then use the good autocorrelation of the code sequence in the code division signal to perform correlation calculations through multiple parallel code capture modules Correlation peaks of each channel can be obtained through the detection of correlation peaks, and the result after beam separation can be obtained.

As shown in Figure 2, it is a schematic flow chart of the separation method of the code division multi-beam signal based on the FDMA system according to the embodiment of the present invention. The main method is to pass the code division multi-beam signal based on the FDMA system sent by the source in parallel through the multi-channel mixing module , the FDMA signal is moved to the baseband, and the aliasing of the signal spectrum will be generated at the same time, but it can be guaranteed that each beam is moved to the baseband. Add the multi-channel signals after frequency mixing, at this time, the signals are superimposed and the spectrum is aliased, but it can still ensure that the original signal remains unchanged in the baseband part of each beam. The superimposed signal is filtered through a low-pass filter to remove the high-frequency component of the aliased signal. At this time, the signal only retains the baseband component and part of the low-frequency component due to mixing, and the signal is further matched and filtered through the matched filter. . Then pass the signal through multiple parallel code capture modules to obtain the correlation peak signals of each channel. The code-divided multi-beam signal introduces multiple access interference in the superposition operation in the down-conversion module, so it needs to be processed after the code capture module. The decorrelation operation is performed to eliminate multiple access interference, and the multi-channel signal after the decorrelation operation is the final beam separation result.

Example

Taking a multi-beam amplitude-phase test system with 8 test users (ie 8 frequency points) and non-orthogonal codeword sequences as spreading codes as an example, the specific implementation process of the present invention will be described.

Step 1. Let the test users of the multi-beam amplitude and phase test system be 8 (that is, 8 groups of spreading codes), the source sends out 8 frequency division multiple access signals, and the beam signal corresponding to each frequency point also corresponds to 8 groups of spreading codes. One of the frequency codes. Spread spectrum code can choose Gold code, m sequence, ZCZ sequence, etc., and the spread spectrum code group selected in this example is m sequence. The frequency point can be set arbitrarily. In this example, the frequency points are 100MHz, 110MHz, 120MHz, 130MHz, 140MHz, 150MHz, 160MHz, and 170MHz.

Step 2: The receiving end performs parallel 8-channel mixing operation on the received multi-beam signals according to the known 8 frequency points, and moves the frequency-divided signals of the 8 frequency points to the baseband respectively. In the mixing process of each channel, only the corresponding frequency points, that is, in this example, the signals with frequencies of 100MHz, 110MHz, 120MHz, 130MHz, 140MHz, 150MHz, 160MHz, and 170MHz can be moved to the baseband (0MHz), such as the first channel In the frequency mixing operation, only the signal with a frequency of 100MHz is moved to the baseband, and the signals of the remaining 7 frequency points are all distributed near the baseband. This step will generate 8 channels of parallel signals, and each channel signal includes the baseband signal corresponding to the frequency point of the channel, the high frequency signal corresponding to the frequency point, and the corresponding mixing results of the remaining frequency points;

Step 3: Superimpose the multi-channel parallel signals obtained in Step 2. At this time, the obtained data includes baseband signals of 8 beams, and there are also aliased signals near the baseband after frequency mixing. The added signal passes through a low-pass filter to filter out high-frequency components, and completely retains the baseband signal. In this example, the low-pass filter is designed as a Kaiser window function, the filter bandwidth is set to 500KHz, and the sidelobe suppression is 40dBc. The tap coefficient of the filter is 144;

Step 4: Pass the signal obtained in Step 3 through the matched filter module. Wherein the matched filter can adopt root-raised cosine filter, square wave filter etc., select root-raised cosine filter in the present embodiment, the design of root-raised cosine filter is oversampling rate 16, roll-off coefficient is 1, filter The device tap coefficient is 482;

Step 5, carry out the code capture module of 8 parallel PN codes to the signal output by the matched filter, the code capture module can adopt sliding correlation capture method, digital matched filter (DMF) and fast capture method based on FFT. In the present embodiment, the code acquisition module selects a digital matched filter (DMF), and each parallel digital matched filter selects from 8 groups of superimposed code division signals using the known 8 groups of spreading codes in step 1. Any group of signals with a predetermined code pattern, other signals using different code patterns cannot be despread because they are different from the local code patterns generated by the receiver, and the 8-way superimposed codes can be separated by using the good autocorrelation of the m-sequence Multi-beam signal separation. If let r be the signal received by the receiver, For the original signal that is expected to be solved, A is the PN code group, A ^H is the transpose of the PN code group, and the operation formula of the digital matched filter is After the signal passes through the digital matched filter, the correlation peak of each output signal is obtained. Due to the introduction of multiple access interference by the superposition operation after frequency mixing, the 8 parallel correlation peak signals obtained at this time are still not completely separated;

Step 6. Use the calculation formula of the decorrelation matrix: h=(A ^H A) ^-1 , where A is the PN code group, A ^H represents the transposition of the PN code group, and "-1" in the upper right corner represents matrix inversion. The corresponding decorrelation matrix is obtained by operating the corresponding 8 groups of spreading code sequences. Jointly solve the correlation peak and decorrelation matrix output by the 8-way code capture module obtained in step 5, and the solution formula is: The separated signals without multiple access interference can be obtained.

Experimental results

For the above embodiment, the following table is a comparison of FPGA resource consumption using the traditional FDMA system-based code division multi-beam signal separation method and the FDMA system-based code division multi-beam signal separation method of this embodiment. The FPGA model used in this example For xc6vlx240t.

It can be seen from the above table that using the traditional multi-beam separation method will consume a lot of DSP48E1s and Slice resources, but the code division multi-beam signal separation method based on the FDMA system of the present invention greatly reduces the consumption of these two resources.

As shown in FIG. 3 , the bit error rate comparison between the separation method of the traditional code division multi-beam signal based on the FDMA system and the separation method of the code division multi-beam signal based on the FDMA system of the present invention is shown. It can be seen from Figure 3 that when the signal-to-noise ratio Eb/No changes from 1 to 11, the bit error rates of the two systems are all reduced, and the bit error rates of the two methods have the same trend with the change of the signal-to-noise ratio. It is proved that the modification of the structure of the traditional beam separation method by the present invention does not cause the increase of the bit error rate.

As shown in FIG. 4 , it is a time-consuming comparison chart of the separation method of the code division multi-beam signal based on the FDMA system of the present invention and the traditional separation method of the code division multi-beam signal based on the FDMA system. As can be seen from Figure 4, when the number of beams of the multi-beam signal is small, the time required for using the traditional multi-beam signal separation method is similar to that of the multi-beam separation method proposed in the present invention, but as the multi-beam signal As the number of beams of the signal increases, the number of frequency points increases accordingly, and the time-consuming difference between the two becomes larger. When the number of beams increases to 10, applying the method of the present invention to separate multi-beam signals can improve the efficiency by 100%. More than ten.

To sum up, applying the method of the present invention for signal separation can save a large amount of hardware resources, reduce resource consumption, and improve computing efficiency without changing the bit error rate.

The specific description above further elaborates the purpose, technical solution and beneficial effect of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not used to limit the protection of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (3)

1. a code division multi-beam signal separation method based on FDMA system, is characterized in that, comprises the steps: Step 1. The source generates FDMA signals, and the beams corresponding to each frequency point are not only frequency-divided, but also code-divided; Step 2, the receiving end receives the FDMA multi-beam signal, performs multiple parallel frequency mixing operations, and moves the FDMA multi-beam signal from their respective frequency points to the baseband; Step 3, superimposing the multi-channel parallel mixing results obtained in step 2, and filtering out high-frequency components through a low-pass filter after the superposition; Step 4, the signal obtained in step 3 is matched and filtered through a matched filter to reduce inter-symbol crosstalk and improve the bit error rate; Step 5, the CDMA signal that step 4 obtains is carried out correlation operation and the detection of correlation peak through multi-channel parallel code capture module, obtains the correlation peak signal that each code capture module outputs, to realize beam separation; Step 6: Carry out de-correlation calculation on the correlation peaks obtained in step 5, and the signal obtained by de-correlation is the signal without multiple access interference after separation. 2. a kind of code division multi-beam signal separation method based on FDMA system according to claim 1, is characterized in that: the operational formula of described code acquisition module is in, Represents the original signal expected to be solved, r represents the signal received by the receiving end, A represents the PN code group, and A ^H represents the transposition of the PN code group. 3. a kind of code division multi-beam signal separation method based on FDMA system according to claim 1, is characterized in that: described de-correlation operation is to multiply correlation peak and de-correlation matrix, and operational formula is as follows: $\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; ;</span>$ in, Indicates the original signal expected to be solved, r indicates the signal received by the receiving end, A indicates the PN code group, A ^H indicates the transposition of the PN code group, and "-1" in the upper right corner indicates matrix inversion.