CN108540167B - A Spectrum Shaping Method Based on Spreading Shaping Code - Google Patents

Abstract

A spectrum shaping method based on spread spectrum shaping codes, comprising the following steps: 1) collecting channel status information; 2) constructing a code word according to the channel status information; The device encodes the original information to complete the shaping of the signal spectrum, and then sends the code word through the designated spatial channel; 4) Receive the code word information, and obtain the original information through direct sampling or decode it through the decoder to obtain the original information. The present invention can move the frequency spectrum of the baseband signal to the high frequency band and complete the shaping only by precoding at the sending end without using a modulator or any other device.

Description

A Spectrum Shaping Method Based on Spreading Shaping Code

technical field

The invention relates to the technical field of communication, in particular to a frequency spectrum shaping method.

Background technique

In a communication system, it is necessary to shift the spectrum of the baseband signal and modulate it to a specific frequency band for transmission. As shown in Figure 1, the traditional method of shifting the signal spectrum is to use a modulator.

For example, in optical communication systems, optical modulators are used; in wireless and microwave communication systems, modulation antennas are used. In a traditional chip communication system, since the transmission channel is a baseband low-pass channel, the baseband signal is directly sent without using a modulator. In addition to directly using the modulator, digital signal processing (DSP) technology can also be used to realize up-conversion in the digital domain. In this case, a mixer needs to be used to generate sine or cosine waves for signal up-conversion or down-conversion, as shown in Figure 2.

Figure 3 describes the principle of direct sequence spread spectrum technology: the message signal d (t) is multiplied by the random spread sequence c (t), s (t) = d (t) · c (t) to complete the information spread. The element c(t) of the spreading sequence is called a chip (chips), the chip duration is defined as T _c , the chip rate is 1/T _c , and the signal period is T _s , then S=T _s /T _c is defined as the spreading factor. Usually, the chips of the direct spread spectrum technology are pseudo-random codes and bipolar codes, that is, c _k ∈ {±1}. With traditional spread spectrum technology, the main lobe of the signal spectrum is extended from [-1/T _s , 1/T _s ] to [-1/T _c , 1/T _c ], corresponding to S _ss (f ) is shown by the dotted line.

The downsides of using modulators are:

1. In terms of power consumption, the modulator consumes energy;

2. In terms of signal quality, the bandwidth limitation of the modulator will introduce distortion on the signal;

3. In the implementation circuit, the use of modulators requires the introduction of additional devices, resulting in difficulties in circuit integration and miniaturization;

4. In terms of cost, modulators are not cheap, especially high-speed modulators;

5. In some application scenarios, such as next-generation chip communication products, there is a transmission requirement for a bandpass channel, but due to limitations in chip space and power consumption, it is impossible to use a modulator;

6. The modulator can only move the signal spectrum, but cannot shape the signal spectrum.

The disadvantages of using a digital frequency converter are:

1. In terms of power consumption, the mixer consumes more energy;

2. In terms of realizing the circuit, it is difficult to highly integrate and miniaturize the circuit;

3. In some application scenarios, such as next-generation chip communication products, there is a transmission requirement for a bandpass channel, but due to limitations in chip space and power consumption, the feasibility of using a digital frequency converter is very small.

Contents of the invention

The purpose of the present invention is to provide a spectrum shaping method based on spread spectrum shaping codes, which can move the baseband signal spectrum to the high frequency band and complete the shaping without using a modulator or any other devices, and only relying on the precoding at the sending end.

The purpose of the present invention is realized by such technical scheme, and concrete steps are as follows:

1) collecting channel status information of the spatial channel to be transmitted;

2) according to the channel condition information collected in step 1), construct codeword, determine chip c (t) parameter, chip c (t) parameter includes spreading factor S and chip combination c _k ;

3) According to the chip c(t) parameter determined in step 2), the original information is encoded by the encoder to complete the shaping of the signal spectrum, and then the code word is sent through the designated spatial channel;

4) Receive the codeword information sent in step 3), and obtain the original information by direct sampling or decode by a decoder to obtain the original information.

Further, step 2) described in construction code word, the concrete steps of determining chip c (t) parameter are as follows:

2-1) Determine the channel status information of the spatial channel to be transmitted, determine the acceptable spreading factor S, specify the symbol period T _s0 , and list all possible chip combinations c _k ∈ {±1};

2-2) Calculate the spectrum shaping effect corresponding to each possible chip combination;

2-3) If the spectrum shaping effect meets expectations, then output the best parameters S and c _k under the current conditions, these parameters determine the chip c(t) structure of the encoder; if the above conditions are not met, then change the spread spectrum Combination of factor S and chip, return to step 2-2).

Further, the specific method for calculating the spectrum shaping effect corresponding to each possible chip combination described in step 2-2) is:

Calculate the spectrum shaping effect cost function corresponding to each possible chip combination, that is, f _SRC

Among them, ∫|s(t)*h(t)| ² dt is the received signal power after transmission through the specified channel h(t), h(t) is the time-domain impulse response of the specified channel to be transmitted, ∫|s (t)| ² dt is the transmitted signal power, ∫|s(t)*h(t)| ² dt can be rewritten as ∫|s(t)*h(t)| ⁿ dt, ∫|s(t) | ² dt can be rewritten as

Further, the specific steps for judging whether the spectrum shaping effect meets expectations in step 2-3) are as follows:

If the calculated cost function is greater than the specified value, that is, f _SRC >P ₀ , then output the best parameters S, _ck , f _SRC under the current conditions, these parameters determine the coder chip c(t) structure; if If the above conditions are not met, increase the spreading factor S=S+1, and return to step 2-2).

Further, the specific steps for judging whether the spectrum shaping effect meets expectations in step 2-3) are as follows:

If the calculated cost function satisfies the specified value, that is, f _SRC >P ₀ , or S>S _max , then output the best parameters S,c _k ,f _SRC under the current conditions, these parameters determine the encoder chip c (t) structure; if the above conditions are not met, increase the spreading factor S=S+1, and return to step 2-2).

Further, the specific method for calculating the spectrum shaping effect corresponding to each possible chip combination described in step 2-2) is:

When transmitting certain random information, measure the bit error rate BER value of the receiving end, which is defined as:

In the formula, d′ _{(1, N)} is the received N bits, and d _{(1, N)} is the N bits sent. When the BER is lower than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Further, the specific method for calculating the spectrum shaping effect corresponding to each possible chip combination described in step 2-2) is:

When transmitting certain random information, measure the eye opening O _eye of the receiving end, which is defined as:

Among them, E _{i, c} and E _{i, f} respectively represent the highest and lowest amplitude values at the maximum opening of the inner eye of the eye diagram, and E _{o, c} and E _{o, f} respectively represent the highest amplitude at the maximum opening of the outer eye of the eye diagram and the lowest amplitude value; when the eye opening O _eye is greater than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Further, the specific method for calculating the spectrum shaping effect corresponding to each possible chip combination described in step 2-2) is:

The degree of matching between the signal spectrum and the channel transfer function after shaping M _SRC

Among them, ∫|S(f)·H(f)| ⁿ df is the spectrum distribution feature of the signal received after transmission through the specified channel H(f), ∫|S(f)| ⁿ df is the spectrum distribution feature of the transmitted signal , when the matching degree M _SRC is higher than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Further, the specific method for calculating the spectrum shaping effect corresponding to each possible chip combination described in step 2-2) is:

Correlation between received signal and transmitted signal XOOR _TxRx

Among them, X and Y represent the sent and received signal sequences respectively, and E(X) is the mean value of the signal sequence X. When the correlation is higher than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Owing to adopting above-mentioned technical scheme, the present invention has following advantage:

The spectrum shaping method of the present invention does not use a modulator and demodulation, and only needs to encode at the transmitting end, so it does not have the above-mentioned many disadvantages of the traditional modulator and DSP frequency conversion method. Compared with the traditional method, the method of the present invention has low power consumption, does not introduce additional distortion to the signal, only needs an encoding circuit at the transmitting end, does not require demodulation at the receiving end, has low cost, high circuit integration, and can perform spectrum shaping of signals and chip communication. And the application difficulty of the bandpass channel scene is small and other advantages.

Other advantages, objects and features of the present invention will be set forth in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the investigation and research below, or can be obtained from It is taught in the practice of the present invention. The objects and other advantages of the invention will be realized and attained by the following description and claims.

Description of drawings

The accompanying drawings of the present invention are described as follows.

Fig. 1 is the working principle diagram of the modulation/demodulation system in the background technology of the present invention;

Fig. 2 is a working principle diagram of digital frequency conversion in the background technology of the present invention;

Fig. 3 is the schematic diagram of direct sequence spread spectrum technology;

Fig. 4 is the time-domain schematic diagram of spread spectrum shaping code transmission;

Fig. 5 is a schematic diagram of the transmission frequency domain of the spreading shaping code;

Fig. 6 is codeword construction algorithm embodiment one;

Fig. 7 is codeword construction algorithm embodiment two;

Figure 8 is an example diagram of the opening of the eye expansion diagram;

Fig. 9 is a schematic diagram of a waveform in Embodiment 1;

Fig. 10 is a schematic diagram of the waveform of Embodiment 2;

Fig. 11 is a schematic diagram of the signal spectrum of Embodiment 1 SRC1 and Embodiment 2 SRC2 of the spread spectrum shaping code;

Figure 12 is a schematic diagram of the performance test results of the spread spectrum shaping code SRC2;

Fig. 13 is a schematic diagram of the performance test results of the spread spectrum shaping code SRC2;

Fig. 14 is a schematic flow chart of the present invention.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

The parameter definitions of the present invention employ terminology of direct sequence spread spectrum techniques. Figure 3 has described the principle of direct sequence spread spectrum technology: multiply the message signal d(t) by the random spread sequence c(t), s(t)=d(t)·c(t) to complete the information spread spectrum. The element c(t) of the spreading sequence is called a chip (chips), the chip duration is defined as T _c , the chip rate is 1/T _c , and the signal period is T _s , then S=T _s /T _c is defined as the spreading factor. Usually, the chips of the direct spread spectrum technology are pseudo-random codes and bipolar codes, that is, c _k ∈ {±1}. With the traditional spread spectrum technology, the main lobe of the signal spectrum is extended from [-1/T _s ,1/T _s ] to [-1/T _c ,1/T _c ], as shown in Figure 5 corresponding to S _ss (f ) is shown by the dotted line.

A spectrum shaping method based on spreading shaping codes, based on an encoder, which sends encoded information based on a fixed chip c(t). Based on the optimization of the encoding algorithm, the present invention can reshape the original signal to the desired frequency band after spreading the original signal. The encoder is shown in Figure 4, and the signal spectrum is reshaped as shown by the solid line corresponding to S _ss (f) in Figure 5, and the spectrum is reshaped to as the center of the high-frequency position. In the example shown in Fig. 4, the signal spectrum is shaped to match the bandpass channel |H(f) ² |, which is centered at frequency f ₀ and has a bandwidth of B. The signal waveforms in Fig. 4 and Fig. 5 are square waves, and the present invention includes but not limited to square wave waveforms.

After spreading the spectrum, in order to shape the signal to the target frequency band, it is necessary to construct a special shaping codeword, that is, to construct a specific spreading factor S and chip combination c _k . The parameter spreading factor S and chip combination c _k will determine the pulse shape in each signal cycle, the most critical point is to find the best combination of spreading factor S and code sequence c _k . There are many kinds of corresponding codeword construction algorithms. From the point of view of the code word structure of the spread spectrum shaping code, the difference between the present invention and the direct spread spectrum sequence technology is that what is transmitted in this scheme is the code sequence of the deterministic code output by the construction algorithm, rather than the direct spread spectrum sequence technology using is a random code sequence.

At the receiving end, two methods can be used for decoding, and the decoder is shown in Figure 4. Due to the introduction of the spread spectrum shaping code, the receiving end will receive several pulses in each signal cycle, which corresponds to several sub-eye diagrams. The first decoding method is to select the position of the maximum vertical opening in the sub-eye diagram for direct sampling, that is, the direct detector in Figure 4. This method is simple and fast, and supports high throughput. However, if the vertical opening difference between the largest sub-eye and the other sub-eyes is large, the random noise tolerance of the code is reduced. The second decoding method method, as shown in Decoder in Figure 4:

This method makes full use of the information of all sub-eye diagrams, thus improving the random noise tolerance.

Let the waveform of the signal use the square wave shown in the legend, but the present invention includes but not limited to the square wave waveform, then the waveform of the spread spectrum shaping code can be expressed as:

where c _k ∈ {±1} is the combination of chips, and S is the spreading factor. The spectrum distribution of the waveform corresponding to formula (2) is:

It can be seen from formula (3) that G _t (f) is actually a sinc function, and multiple weighted combination. The sinc function will expand the spectrum of the original signal, and the expanded spectrum will cover the frequency band of [-1/T _c , 1/T _c ]; at the same time, due to The weighting of will produce a sin or cos function; and the weighted combination of sin and cos functions can reshape the expanded spectrum to the target frequency band.

An appropriate spread spectrum shaping codeword will determine the effect and complexity of spectrum shifting and shaping, so the codeword construction algorithm is very important. All codeword constructions of the present invention will be based on the following three steps as the core algorithm:

1. Specify the channel characteristics to be transmitted (such as the impulse response in the time domain or the channel transfer function in the frequency domain), determine the acceptable spreading factor S, specify the symbol period T _s0 , and list all possible chip combinations c _k ∈ {±1};

2. Analyze the spectrum shaping effect corresponding to each possible chip combination; this shaping effect can be measured based on different cost functions;

3. If the spectrum shaping effect meets expectations, output the best parameters S,c _k under the current conditions, and these parameters determine the chip c(t) structure of the encoder. If the above conditions are not satisfied, then change the spreading factor S and chip combination, and return to step 2.

If the specified channel is very stable, such as the chip interconnection scenario, once the encoding algorithm constructs the spread spectrum shaping code, this parameter can be fixed in the implementation circuit of the encoder, and the receiving end does not need a decoder. Therefore, this The implementation complexity of the invention is extremely low.

An example of the construction algorithm of the spread spectrum shaping codeword is listed below:

Codeword construction algorithm 1, as shown in Figure 6:

1. Specify the channel characteristics to be transmitted (such as the impulse response h(t) in the time domain or the channel transfer function H(f) in the frequency domain), and select the minimum acceptable spreading factor, Determine the symbol period T _s0 , and list all possible chip combinations c _k ∈{±1}.

2. Calculate the cost function corresponding to each possible chip combination, that is, f _SRC

Among them, ∫|s(t)*h(t)| ² dt is through the specified channel h(t), h(t) is the time-domain impulse response of the specified channel to be transmitted, the received signal power after transmission, ∫| s(t)| ² dt is the transmitted signal power. In this cost function, ∫|s(t)*h(t)| ² dt can be rewritten as ∫|s(t)*h(t)| ⁿ dt, ∫|s(t)| ² dt can be rewritten as The result obtained by the final codeword construction remains unchanged.

3. If the calculated cost function is greater than the specified value, and f _SRC >P ₀ , then output the best parameters S,c _k , f _SRC under the current conditions, and these parameters determine the chip c(t) structure of the encoder. If the above conditions are not satisfied, increase the spreading factor S=S+1, and return to step 2.

Codeword construction algorithm 2, as shown in Figure 7:

1. Specify the channel characteristics to be transmitted (such as the impulse response h(t) in the time domain or the channel transfer function H(f) in the frequency domain), and select the minimum acceptable spreading factor, Determine the symbol period T _s0 , and list all possible chip combinations c _k ∈{±1}.

2. Calculate the cost function corresponding to each possible chip combination, that is, f _SRC

Among them, ∫|s(t)*h(t)| ² dt is through the specified channel h(t), h(t) is the time-domain impulse response of the specified channel to be transmitted, the received signal power after transmission, ∫| s(t)| ² dt is the transmitted signal power. In this cost function, ∫|s(t)*h(t)| ² dt can be rewritten as ∫|s(t)*h(t)| ⁿ dt, ∫|s(t)| ² dt can be rewritten as The result obtained by the final codeword construction remains unchanged.

3. If the calculated cost function satisfies the specified value, f _SRC >P ₀ , or S>S _max , then output the best parameters S,c _k ,f _SRC under the current conditions, these parameters determine the chip of the encoder c(t) structure. If the above conditions are not met, increase the spreading factor S=S+1, and return to step 3.

Codeword construction algorithm 3:

This algorithm is consistent with the steps of the above algorithm 1 or 2, the only difference is that a different cost function is used. The cost function of this algorithm is: when a certain random information is transmitted based on Figure 4, measure the bit error rate BER value at the receiving end, defined as :

In the formula, d′ _{(1, N)} is the received N bits, d _{(1, N)} is the N bits sent, and the sending and receiving structure is shown in Fig. 4 . When the BER is lower than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Codeword construction algorithm 4:

This algorithm is consistent with the steps of Algorithm 1 or 2 above, the only difference is that a different cost function is used. The cost function of this algorithm is: when a certain random information is transmitted based on Figure 4, measure the eye opening O _eye at the receiving end, and define for:

Among them, E _{i, c} and E _{i, f} respectively represent the highest and lowest amplitude values at the maximum opening of the inner eye of the eye diagram, and E _{o, c} and E _{o, f} respectively represent the highest amplitude at the maximum opening of the outer eye of the eye diagram and the lowest amplitude value. As shown in Fig. 8, the inner eye E _i,c =0.8 and E _i,f =-0.8, the outer eye E _o,c =1 and E _o,f =-1, so O _eye =80%. When the eye opening O _eye is greater than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Codeword construction algorithm 5:

This algorithm is consistent with the steps of the above algorithm 1 or 2, the only difference is that a different cost function is used. The cost function of this algorithm is: the matching degree of the signal spectrum after shaping and the channel transfer function M _SRC

Among them, ∫|S(f)·H(f)| ⁿ df is the spectrum distribution feature of the signal received after transmission through the specified channel H(f), ∫|S(f)| ⁿ df is the spectrum distribution feature of the transmitted signal . When the matching degree M _SRC is higher than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

Codeword construction algorithm 6:

This algorithm is consistent with the steps of the above algorithm 1 or 2, the only difference is that a different cost function is used. The cost function of this algorithm is: when transmitting information based on Figure 4, the correlation between the received signal and the sent signal is XOOR _TxRx , There are many industry-recognized calculation formulas for this correlation. For example, there are four calculation formulas for Pearson correlation. Here is one of them as an example:

Among them, X and Y represent the sent and received signal sequences respectively, and E(X) is the mean value of the signal sequence X. When the correlation is higher than the specified value, the algorithm considers that the spectrum shaping has achieved the expected effect.

The primary application of the present invention is the chip interconnection scenario. In the current chip interconnection, only square waves can be sent. This is due to power and delay limitations. In the chip interconnection scenario, the sending end can only send voltages or currents of different magnitudes by turning on and off the relay to send digital (0/1) information. Therefore, this scenario can only generate square wave. Therefore, the examples in the present invention all use square wave waveforms.

Embodiment one, embodiment two:

Based on the above algorithm, the spread spectrum shaping codeword is constructed, and the parameters S, _ck are determined. Then the pulse shape in each signal period is determined by these parameters. The pulse shapes determined in Embodiment 1 and Embodiment 2 of the present invention are shown in FIG. 9 and FIG. 10 . The spread spectrum shaping parameter adopted in embodiment one is S=8, c _k =[-1 1 1 -1 -1 1 1 -1], called SRC1 (spreadreshaping code1); the spread spectrum shaping parameter adopted in embodiment two For S=4, c _k =[-1 1 -1 1], it is called SRC2 (spread reshaping code2).

Corresponding to formula (3), the spectral shape of the SRC1 code can be calculated by Fourier transform as

Corresponding to formula (3), the spectrum shape of SRC2 code is

The spectral shapes of equations (10) and (11) are shown in Fig. 11. It can be seen from FIG. 11 that the signal spectrums of the first embodiment SRC1 and the second embodiment SRC2 of the spread spectrum shaping code are respectively shaped to the spectrum shape and position described by the dotted line and the solid line in the figure. These two spectral shapes and positions are best matched to the transfer functions H ₁ (f) and H ₂ (f) of the target transmission channel, respectively.

Fig. 12 and Fig. 13 show the performance test results of the spreading shaping code SRC2 in the second embodiment. The curve corresponding to Tx in Figure 12 is the shaped signal spectrum at the sending end, the curve corresponding to channel is a typical transfer function of the next-generation chip interconnection channel, and the curve corresponding to Rx is the spectrum of the received signal. It can be seen that through the spectrum shaping of the SRC2 code, the main spectrum of the signal, that is, the main lobe of the spectrum, is shaped to the position that best matches the channel, and the corresponding transmission energy loss is minimized. Figure 13 is the corresponding eye diagram of the receiving end. It can be seen that the opening of the eye diagram has reached 30-40%. Based on this code, the first direct detection method (direct detector) in Figure 4 can be used at the receiving end. In the maximum eye diagram The opening is directly detected and restored to the original signal.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements, without departing from the spirit and scope of the technical solution, should be included in the scope of the claims of the present invention.

Claims (10)

1. a kind of spectral shaping method based on spread spectrum shaping code, which is characterized in that specific step is as follows:

1) channel condition information of space channel to be transmitted is acquired, channel condition information includes the pulse impulse response of time domain Information, the channel transfer functions information of frequency domain；

2) according to channel condition information collected in step 1), code word is constructed, determines chip c (t) parameter, chip c (t) parameter It include spreading factor S and chip combinations c_k；

3) according to chip c (t) parameter determined in step 2), coding is carried out to raw information by encoder and completes signal spectrum Shaping, then by designated space channel carry out code word transmission；

4) receiving step 3) in send codeword information, by directly sample obtain raw information or by decoder for decoding, obtain Obtain raw information.

2. the spectral shaping method as described in claim 1 based on spread spectrum shaping code, which is characterized in that structure described in step 2) Code word is made, determines that specific step is as follows for chip c (t) parameter:

The channel condition information for 2-1) determining space channel to be transmitted determines acceptable spreading factor S, designated symbols period T_s0, list all possible chip combinations c_k∈{±1}；

2-2) calculate the frequency spectrum shaping effect under corresponding each possible chip combinations；

It is expected if 2-3) frequency spectrum shaping effect meets, exports the optimal parameter S and c under conditions present_k, these parameters determine Chip c (t) structure of encoder；If above-mentioned condition is unsatisfactory for, change spreading factor S and chip combinations, return step 2-2).

3. the spectral shaping method as claimed in claim 2 based on spread spectrum shaping code, which is characterized in that step 2-2) described in Calculate the frequency spectrum shaping effect under corresponding each possible chip combinations method particularly includes:

Calculate frequency spectrum shaping effect the cost function, i.e. f under corresponding each possible chip combinations_SRC

Wherein, ∫ | s (t) * h (t) |²Dt is by designated channel h (t), wherein h (t) is the time domain impulse for specifying channel to be transmitted Response, the signal power received after transmission, ∫ | s (t) |²Dt be send signal power, ∫ | s (t) * h (t) |²Dt can be rewritten as ∫|s(t)*h(t)|ⁿDt, ∫ | s (t) |²Dt can be rewritten as

4. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that step 2-3) judgement frequency Whether spectrum shaping effect meets that expected specific step is as follows:

If calculating resulting cost function greater than designated value, i.e. f_SRC> P₀, then the optimal parameter S under conditions present is exported, c_k, f_SRC, these parameters determine chip c (t) structure of encoder；If above-mentioned condition is unsatisfactory for, increase spreading factor S=S + 1, return step 2-2).

5. the spectral shaping method as claimed in claim 4 based on spread spectrum shaping code, which is characterized in that step 2-3) described sentence Whether disconnected frequency spectrum shaping effect meets that expected specific step is as follows:

If calculating resulting cost function meets designated value, i.e. f_SRC> P₀Or S > S_max, then export under conditions present Optimal parameter S, c_k, f_SRC, these parameters determine chip c (t) structure of encoder；If above-mentioned condition is unsatisfactory for, increase Spreading factor S=S+1, return step 2-2).

6. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that step 2-2) described in Calculate the frequency spectrum shaping effect under corresponding each possible chip combinations method particularly includes:

When transmitting certain random information, the error rate BER value of receiving end is measured, is defined as:

D ' in formula_{(1, N)}It is the N number of bit, d received_{(1, N)}It is the N number of bit sent, when BER is lower than designated value, algorithm thinks frequency Spectrum shaping has reached desired effect.

7. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that step 2-2) described in Calculate the frequency spectrum shaping effect under corresponding each possible chip combinations method particularly includes:

When transmitting certain random information, the eye figure aperture O of receiving end is measured_eye, is defined as:

Wherein E_{I, c}And E_{I, f}Respectively represent the highest and lowest range value at the interior eye maximum opening of a figure, E_{O, c}And E_{O, f}Generation respectively Highest and lowest range value at the external eyes maximum opening of table eye figure；As eye figure aperture O_eyeWhen greater than designated value, algorithm thinks frequency Spectrum shaping has reached desired effect.

8. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that step 2-2) described in Calculate the frequency spectrum shaping effect under corresponding each possible chip combinations method particularly includes:

The matching degree M of signal spectrum and channel transfer functions after shaping_SRC

Wherein, ∫ | S (f) H (f) |ⁿDf is the signal spectrum distribution characteristics that receives after being transmitted by designated channel H (f), ∫ | S (f)|ⁿDf is the signal spectrum distribution characteristics sent, as matching degree M_SRCWhen higher than designated value, algorithm thinks that frequency spectrum shaping reaches Desired effect is arrived.

9. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that step 2-2) described in Calculate the frequency spectrum shaping effect under corresponding each possible chip combinations method particularly includes:

The degree of correlation XOOR of the signal and transmission signal that receive_TxRx

Wherein, X and Y respectively indicates the signal sequence that the sum of transmission receives, and E (X) is the mean value of signal sequence X, works as the degree of correlation When higher than designated value, algorithm thinks that frequency spectrum shaping has reached desired effect.

10. the spectral shaping method as claimed in claim 3 based on spread spectrum shaping code, which is characterized in that described in step 2) Constructing code word includes S=8, c_k=[- 11 1-1-1 1 1-1] and S=4, c_k=[- 1 1-1 1].