CN114465856A - Signal multi-system modulation method, demodulation method and equipment based on CDMA system - Google Patents
Signal multi-system modulation method, demodulation method and equipment based on CDMA system Download PDFInfo
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Abstract
The application discloses a signal multi-system modulation method, a demodulation method and a device based on a CDMA system, wherein the modulation method comprises the following steps: generating a whole-period pseudo-random PN code; carrying out multilevel coding on information through linear shift of a PN code, modulating a carrier wave by using a coded PN sequence, and generating a multilevel modulation signal based on a CDMA system; and transmitting the multilevel modulation signal to a satellite communication receiving device. The problems that the system capacity of satellite spread spectrum communication is low and the link margin is insufficient are solved.
Description
Technical Field
The present application relates to the field of satellite communications technologies, and in particular, to a signal multilevel modulation method, a signal multilevel demodulation method, and a signal multilevel demodulation device based on a CDMA system.
Background
Code Division Multiple Access (CDMA) is an address distinguished by different address codes. Each terminal is provided with different address codes, the carrier waves (same carrier waves) transmitted by a user are modulated by both baseband digital signals and the address codes, when receiving, only a receiver which is confirmed to be allocated with the address codes can demodulate corresponding baseband signals, and other receivers cannot demodulate the signals due to the different address codes. Typically, a pseudo-random code (PN code) is selected as the address code. Since the Code element width of the PN Code is much smaller than that of the Pulse Code Modulation (PCM) signal, the spectrum of the PN Code-added signal is much larger than that of the original baseband signal, and thus CDMA is also called spread spectrum multiple access. The CDMA technology is used in the low-orbit satellite communication because the CDMA is a spread spectrum technology, has strong anti-interference capability, adopts special spread spectrum code modulation, has strong confidentiality, has large Doppler of the low-orbit satellite communication, can seriously reduce the frequency spectrum efficiency by adopting a non-spread spectrum system, widens the frequency band by hundreds of times after the CDMA is adopted for spread spectrum, and greatly improves the frequency spectrum utilization rate. The defects of the traditional CDMA are obvious, the demodulation algorithm of the CDMA is complex, the consumed resources are more, the power consumption is high, and the pressure on energy use is caused to the satellite.
At present, a common Long Range Radio (LoRa) communication system in a ground internet of things system adopts multi-system spread spectrum modulation to perform continuous wave linear frequency modulation on signals, frequency shift is performed by using the initial frequency of the linear frequency modulation signals to realize symbol modulation, symbols with different initial frequencies have orthogonality, multi-system modulation is formed, a differential demodulator can be adopted, and the system is insensitive to Doppler and strong in anti-interference capability.
However, for CDMA, there may be multiple groups of spreading codes in a spread frequency band to increase system capacity, but Lora only has one group of chirp sequences in a spread frequency band, which causes modulation and spreading difficulty of CDMA signals, obviously, the system capacity is low and the link margin is insufficient.
Disclosure of Invention
In order to solve the problems of low system capacity and insufficient link margin of satellite communication, the application provides a signal multilevel modulation method, a signal multilevel demodulation method and signal multilevel demodulation equipment based on a CDMA system.
In a first aspect, the present application provides a signal multilevel modulation method based on a CDMA system, which adopts the following technical scheme:
generating a whole-period pseudo-random PN code;
carrying out multilevel coding on information through linear shift of a PN code, modulating a carrier wave by using a coded PN sequence, and generating a multilevel modulation signal based on a CDMA system;
and transmitting the multilevel modulation signal to a satellite communication receiving device.
By adopting the technical scheme, in satellite communication, CDMA signals are used, but different modulation and demodulation mechanisms are required to be used for different devices to match transmitting devices and receiving devices, linear shift is carried out through a PN code of a whole period during modulation, all information is coded to obtain a PN shift code of each information, due to the property of the PN code, the PN shift codes for carrying out linear shift have orthogonality, the PN shift codes corresponding to different information are different, one PN shift code corresponds to Nbit information, thus realizing multi-system modulation, one complete PN sequence length of the traditional CDMA can only represent 1 bit information, the multi-system modulation obviously improves the information rate under the same bandwidth, compared with Lora only having one group of linear frequency modulation sequences in a frequency spreading band, the CDMA system has the advantages that various PN sequences can be generated, the system capacity and the link margin of satellite communication are obviously improved.
Optionally, the generating a full-period PN code includes:
pre-configuring the period duration of the PN code;
determining the length of the code sequence of the PN code as M according to the period duration, wherein the value of M is 2N-1, N being a positive integer greater than 2, the M sequence elements in the code sequence having different phases;
and generating the PN code of one whole period according to the length of the code sequence.
Optionally, the performing multilevel coding on the information by linear shifting of the PN code, and modulating a carrier by using the coded PN sequence to generate a multilevel modulation signal based on a CDMA system includes:
using said PN code as a first code, a code sequence by said first code representing a kind of information;
performing linear cyclic shift on the code sequence of the first code by 1 phase to obtain a second code, wherein the second code also represents information;
similarly, repeating the previous step to obtain M kinds of codes, where the M kinds of codes represent M kinds of different information, and the information amount corresponding to each kind of code is Nbit;
and modulating the carrier wave through M codes to generate a multi-system modulation signal based on a CDMA system.
In a second aspect, the present application provides a signal multilevel demodulation method based on a CDMA system, which adopts the following technical scheme:
sampling a multi-system modulation signal of satellite communication to obtain a sampling signal;
acquiring all PN displacement codes;
and carrying out coherent demodulation on the sampling signal and all the PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code.
By adopting the technical scheme, in satellite communication, CDMA signals are used, but different modulation and demodulation mechanisms are required to be used for matching the transmitting equipment and the receiving equipment for different equipment, when demodulation is carried out, the modulation signals of the CDMA signals of the satellite communication are sampled to obtain sampling signals, preset PN codes of the sampling signals are obtained, all PN shift codes are determined according to the PN codes, coherent demodulation is carried out according to the sampling signals and all the PN shift codes to obtain target PN shift codes corresponding to the sampling signals, due to the property of the PN codes, orthogonality exists among the CDMA signals which carry out linear shift modulation, each modulation signal is different, so that demodulation can be realized through the PN shift codes, compared with the condition that only one group of linear frequency modulation sequences exists in a spread spectrum band by Lora, the multi-system modulation and demodulation mechanism obviously increases the spread spectrum range, the system capacity and the link margin of satellite communication are improved.
Optionally, the acquiring all PN offset codes includes:
the period duration of a pre-configured PN code of satellite communication sending equipment is known;
determining the length of the code sequence of the PN code as M according to the period duration, wherein the value of M is 2N-1, N being a positive integer greater than 2, the M sequence elements in the code sequence having different phases;
generating a whole period of the PN code according to the length of the code sequence;
using the PN code as a first PN shift code;
linearly shifting the first PN shift code by 1 sequence element to obtain a second PN shift code;
and carrying out successive processing by a linear shift principle until the M-1 PN shift code is linearly shifted by 1 sequence element to obtain the M PN shift code.
Optionally, the performing coherent demodulation on the sampling signal and all PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code includes:
respectively carrying out coherent accumulation on the sampling signal and all PN shift codes to obtain M accumulation results;
determining the maximum value of the M accumulation results, and taking the PN shift code corresponding to the maximum value as a target PN shift code used by the sampling signal;
and obtaining the information content of the multilevel modulation signal corresponding to the sampling signal according to the coding information corresponding to the target PN shift code.
In a third aspect, the present application provides a satellite communication transmitting device, which adopts the following technical solution:
the pseudo-random PN code generating module is used for generating a PN code of a whole period;
the multi-system modulation module is used for carrying out multi-system coding on information through linear displacement of the PN code, modulating a carrier wave by using a coded PN sequence and generating a multi-system modulation signal based on a CDMA system;
and the signal sending module is used for sending the multilevel modulation signal to satellite communication receiving equipment.
In a fourth aspect, the present application provides a satellite communication receiving device, which adopts the following technical solutions:
the signal receiving module is used for sampling a multi-system modulation signal of satellite communication to obtain a sampling signal;
the pseudo-random PN shift code acquisition module is used for acquiring all PN shift codes; (ii) a
And the coherent demodulation module is used for performing coherent demodulation on the sampling signal and all the PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code.
In summary, the present application includes the following beneficial technical effects:
in satellite communication, a CDMA signal is used, but for different devices, different modulation and demodulation mechanisms are required to be used for matching a transmitting device and a receiving device, and during modulation, linear shift is performed through a full-period PN code, so that all information is coded to obtain a PN shift code of each information, due to the properties of the PN codes, orthogonality is provided between the PN shift codes for performing linear shift, PN shift codes corresponding to different information are different, one PN shift code corresponds to Nbit information, so that multilevel modulation is realized, a complete PN sequence length of a traditional CDMA type can only represent 1 bit of information, multilevel modulation obviously improves the information rate under the same bandwidth, and compared with a set of chirp sequences only existing in a spread spectrum band, the CDMA system has the advantages that a plurality of PN sequences can be generated, the system capacity and the link margin of satellite communication are obviously improved. .
Drawings
Fig. 1 is a schematic flow chart of a signal multilevel modulation method based on a CDMA system according to the present application.
Fig. 2 is a schematic flow chart of the present application for performing multilevel modulation.
Fig. 3 is a flow chart illustrating a method for multilevel demodulation of signals based on a CDMA system according to the present application.
Fig. 4 is a schematic structural diagram of the satellite communication transmitting apparatus of the present application.
Fig. 5 is a schematic structural diagram of the satellite communication receiving apparatus of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
The embodiment of the application discloses a signal multilevel modulation method based on a CDMA system.
Referring to fig. 1, the method includes:
101, generating a PN code of a whole period.
In satellite communication, CDMA signals are used, but for different devices, different modulation and demodulation mechanisms need to be used for matching between the transmitting device and the receiving device, and a PN code generator may generate a full-period PN code, specifically:
presetting the period duration of a PN code generator when generating a PN code;
determining the length of the code sequence of the PN code as M according to the period duration, wherein the value of M is 2N1, N is a positive integer greater than 2, M sequence elements in the code sequence have different phases, e.g., assuming N is 8, then the code sequence length of the PN code is 255, i.e., 255 sequence elements;
a full period PN code is generated according to the length of the code sequence.
And 102, performing multilevel coding on information through linear shift of the PN code, modulating a carrier wave by using the coded PN sequence, and generating a multilevel modulation signal based on a CDMA system.
The specific steps of encoding information in multilevel by linear shift of PN code, modulating carrier wave by using the encoded PN sequence, and generating a multilevel modulation signal based on CDMA system include the following steps of fig. 2:
a PN code as a first code, a code sequence by the first code representing a kind of information 201;
202, performing linear cyclic shift on the code sequence of the first code by 1 phase to obtain a second code, wherein the second code also represents information;
203, repeating the action of the step 202 to obtain M kinds of codes, wherein the M kinds of codes represent M kinds of different information, and the information amount corresponding to each kind of code is Nbit;
performing multilevel modulation by a linear shift principle until M-1 sequence elements are linearly shifted for a code sequence of a first modulation code to obtain an Mth code, wherein if M is 255, 255 different codes can be formed by a PN code of one period;
and 204, modulating the carrier wave by M codes to generate a multilevel modulation signal based on a CDMA system.
And 103, transmitting the multilevel modulation signal to the satellite communication receiving device.
The implementation principle of the application is as follows: when modulation is carried out, linear shift is carried out through a PN code of a whole period, all information is coded, and a PN shift code of each information is obtained.
In the above embodiments shown in fig. 1 and fig. 2, a process of performing multilevel modulation by using a PN code is described, and a receiving party needs to receive correctly and needs to demodulate modulation to implement the process, as shown in fig. 3, a method for demodulating a signal based on a CDMA system according to the present application includes:
301, sampling the multilevel modulation signal of satellite communication to obtain a sampling signal.
In the embodiments shown in fig. 1 and fig. 2, after the CDMA signal is multi-system modulated by using the linear shift of the PN code, demodulation is required to be performed to sample the multi-system modulated signal of the satellite communication to obtain a sampled signal for correct reception.
302, all PN shift codes are acquired.
The method comprises the steps of knowing the period duration of a pre-configured PN code of satellite communication transmitting equipment, determining the length of a code sequence of the PN code to be M according to the period duration, wherein the value of M is 2N-1, N is a positive integer greater than 2, M sequence elements in the code sequence have different phases, a full-period PN code is generated according to the length of the code sequence, the PN code is used as a first PN shift code, the first PN shift code is linearly shifted by 1 sequence element to obtain a second PN shift code, and successive processing is performed by a linear shift principle until the M-1 PN shift code is linearly shifted by 1 sequence element to obtain an mth PN shift code.
303, performing coherent demodulation on the sampling signal and all the PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code.
Respectively carrying out coherent accumulation on the sampling signal and all PN shift codes to obtain M accumulation results, determining the maximum value of the M accumulation results, determining the coding information of the corresponding accumulation result as a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal corresponding to the sampling signal according to the coding information corresponding to the target PN shift code;
when M is 255, the formula for specifically calculating the bit error rate is as follows:
1 – (1 – 0.5*erfc((r/2)0.5) )255
where r is the signal-to-noise ratio, at higher signal-to-noise ratios, the above equation is about:
0.5*erfc((r/2)0.5)*255
differential coding is generally adopted in coding, so the error rate is multiplied by 2, and when the error rate is 10-6Then, r = 15.5db can be solved. Since M is 255 and one CDMA signal is equivalent to 8 bits, the actual signal-to-noise ratio r = 15.5-9 = 6.5 db;
it can be seen that the demodulation threshold for the unmodified CDMA is 10.8db, and the demodulation threshold for the present application is reduced to 6.5 db. If the length of the PN code is increased, when the length of the PN code is 4095, namely M is 4095, the demodulation threshold can be even reduced to 5db, the demodulation threshold is reduced, and the link margin of satellite communication is increased;
in addition, only M PN shift codes are needed to decode one sampling signal, so that the problem of phase lock loss during decoding does not exist, and even if the phase lock of one sampling signal is lost, the next sampling signal can be locked again. In the traditional CDMA, after the first sampling signal is captured, the full-phase search is not carried out in the subsequent demodulation process, and once the lock is lost, the phase can not be locked;
in addition, the demodulation threshold and the capture threshold are equal, so that phase search is not needed to be carried out on a plurality of sampling signals simultaneously during capture, only phase search is needed to be carried out on 1 sampling signal, and power consumption is greatly reduced.
As shown in fig. 4, the present application provides a satellite communication transmitting apparatus, comprising:
a PN code generating module 401, configured to generate a PN code of a whole period;
a multilevel modulation module 402, configured to perform multilevel coding on information through linear shift of a PN code, and modulate a carrier with a coded PN sequence to generate a multilevel modulation signal based on a CDMA system;
and a signal transmitting module 403, configured to transmit the multilevel modulation signal to a satellite communication receiving device.
The implementation principle of the application is as follows: when modulation is carried out, linear shift is carried out through a PN code of a whole period, all information is coded, and a PN shift code of each information is obtained.
As shown in fig. 5, the present application provides a satellite communication receiving apparatus, including:
the signal receiving module 501 is configured to sample a multilevel modulation signal of satellite communication to obtain a sampling signal;
a PN shift code obtaining module 502, configured to obtain all PN shift codes; (ii) a
The coherent demodulation module 503 is configured to perform coherent demodulation on the sampling signal and all PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtain information content of the multilevel modulation signal according to coding information corresponding to the target PN shift code.
The implementation principle of the application is as follows: during demodulation, modulation signals of CDMA signals of satellite communication are sampled to obtain sampling signals, preset PN codes of the sampling signals are obtained, all PN shift codes are determined according to the PN codes, coherent demodulation is carried out according to the sampling signals and all the PN shift codes, and target PN shift codes corresponding to the sampling signals are obtained.
The foregoing is a preferred embodiment of the present application and is not intended to limit the scope of the application in any way, and any features disclosed in this specification (including the abstract and drawings) may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.
Claims (8)
1. A signal multi-system modulation method based on CDMA system is characterized in that the method comprises the following steps:
generating a whole-period pseudo-random PN code;
carrying out multilevel coding on information through linear shift of a PN code, modulating a carrier wave by using a coded PN sequence, and generating a multilevel modulation signal based on a CDMA system;
and transmitting the multilevel modulation signal to a satellite communication receiving device.
2. The method according to claim 1, wherein said generating a full period PN code comprises:
pre-configuring the period duration of the PN code;
determining the length of the code sequence of the PN code as M according to the period duration, wherein the value of M is 2N-1, N being a positive integer greater than 2, the M sequence elements in the code sequence having different phases;
and generating the PN code of one whole period according to the length of the code sequence.
3. The method according to claim 2, wherein the multilevel modulation method for signals based on CDMA system is characterized in that the information is multilevel-coded by linear shift of PN code, and the carrier is modulated by using the coded PN sequence to generate the multilevel-modulated signals based on CDMA system, and comprises:
using said PN code as a first code, a code sequence by said first code representing a kind of information;
performing linear cyclic shift on the code sequence of the first code by 1 phase to obtain a second code, wherein the second code also represents information;
similarly, repeating the previous step to obtain M kinds of codes, where the M kinds of codes represent M kinds of different information, and the information amount corresponding to each kind of code is Nbit;
and modulating the carrier wave through M codes to generate a multi-system modulation signal based on a CDMA system.
4. A signal multi-system demodulation method based on CDMA system is characterized in that the method comprises the following steps:
sampling a multi-system modulation signal of satellite communication to obtain a sampling signal;
acquiring all PN displacement codes;
and carrying out coherent demodulation on the sampling signal and all the PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code.
5. The method according to claim 4, wherein said obtaining all PN shift codes comprises:
the period duration of a pre-configured PN code of satellite communication sending equipment is known;
determining the length of the code sequence of the PN code as M according to the period duration, wherein the value of M is 2N-1, N being a positive integer greater than 2, the M sequence elements in the code sequence having different phases;
generating a whole period of the PN code according to the length of the code sequence;
using the PN code as a first PN shift code;
linearly shifting the first PN shift code by 1 sequence element to obtain a second PN shift code;
and carrying out successive processing by a linear shift principle until the M-1 PN shift code is linearly shifted by 1 sequence element to obtain the M PN shift code.
6. The method according to claim 5, wherein the performing coherent demodulation on the sampled signal and all PN shifting codes to obtain a target PN shifting code corresponding to the sampled signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shifting code comprises:
respectively carrying out coherent accumulation on the sampling signal and all PN shift codes to obtain M accumulation results;
determining the maximum value of the M accumulation results, and taking the PN shift code corresponding to the maximum value as a target PN shift code used by the sampling signal;
and obtaining the information content of the multilevel modulation signal corresponding to the sampling signal according to the coding information corresponding to the target PN shift code.
7. A satellite communication transmitting device, comprising:
the pseudo-random PN code generating module is used for generating a PN code of a whole period;
the multi-system modulation module is used for carrying out multi-system coding on information through linear displacement of the PN code, modulating a carrier wave by using a coded PN sequence and generating a multi-system modulation signal based on a CDMA system;
and the signal transmitting module is used for transmitting the multilevel modulation signal to satellite communication receiving equipment.
8. A satellite communication receiving apparatus, comprising:
the signal receiving module is used for sampling a multi-system modulation signal of satellite communication to obtain a sampling signal;
the pseudo-random PN shift code acquisition module is used for acquiring all PN shift codes; (ii) a
And the coherent demodulation module is used for carrying out coherent demodulation on the sampling signal and all the PN shift codes to obtain a target PN shift code corresponding to the sampling signal, and obtaining the information content of the multilevel modulation signal according to the coding information corresponding to the target PN shift code.
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