CN111294082A - Spread spectrum-based parallel transmission OFDM communication method and system - Google Patents
Spread spectrum-based parallel transmission OFDM communication method and system Download PDFInfo
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- CN111294082A CN111294082A CN202010085424.8A CN202010085424A CN111294082A CN 111294082 A CN111294082 A CN 111294082A CN 202010085424 A CN202010085424 A CN 202010085424A CN 111294082 A CN111294082 A CN 111294082A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
- H04B1/7075—Synchronisation aspects with code phase acquisition
- H04B1/708—Parallel implementation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
Abstract
The invention discloses a spread spectrum-based parallel transmission OFDM communication method and a spread spectrum-based parallel transmission OFDM communication system. The method comprises the following steps: at a sending end, performing serial-parallel conversion on data of an information source to obtain a data stream to be sent containing K bits at time t; generating a spread spectrum pseudo code sequence; each spreading pseudo code sequence has the same time delay delta t ═ G/K relative to the next spreading pseudo code sequence]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcIs the chip duration of the spreading code; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si(i-1) Δ t, i ═ 1,2,3, …, K; carrying out OFDM carrier modulation on the spread spectrum signal, and transmitting the carrier modulation signal to a receiving end through a channel; OFDM of received carrier modulated signal at receiving endCarrier demodulation; and respectively carrying out spread spectrum demodulation on the data streams after carrier demodulation by using the same spread spectrum pseudo code sequence as the transmitting end. The invention can improve the channel utilization rate and the data transmission efficiency in the OFDM communication system.
Description
Technical Field
The invention relates to the technical field of signal transmission, in particular to a parallel transmission OFDM communication method and system based on spread spectrum.
Background
At present, mobile communication can be said to be one of the most widely applied and fastest developing technologies in the current communication field. The OFDM modulation technique has been widely applied and developed in the fields of digital television, mobile communication, and the like. The core idea of the OFDM modulation technology is to divide a channel into a plurality of orthogonal sub-channels, convert a high-speed data signal into parallel low-speed self-data streams, and modulate the self-data streams onto each sub-channel for transmission.
The existing multi-carrier modulation technology OFDM has the characteristics of strong anti-fading capability, high frequency utilization rate and strong anti-intersymbol interference capability, but also has the defects of large modulation time delay, strict requirement on time-frequency synchronization and the like.
Therefore, the existing OFDM communication technology has the problems of large modulation delay, low transmission efficiency and the like. It is desirable to find a suitable modulation scheme to meet the requirements of high rate and low latency in 5G networks.
Disclosure of Invention
The invention provides a spread spectrum-based parallel transmission OFDM communication method and a spread spectrum-based parallel transmission OFDM communication system, which realize parallel transmission spread spectrum communication, and have higher channel utilization rate and higher data transmission efficiency.
A spread spectrum based parallel transmission OFDM communication method, the method comprising:
step one, carrying out serial-parallel conversion on data of an information source at a sending end to obtain a data stream to be sent { d) containing K bits at time t1(t),d2(t),…,dK(t)}；
Generating a spread spectrum pseudo code sequence, wherein the autocorrelation function of the spread spectrum pseudo code sequence is as follows:
wherein P represents the total number of sequence related elements, TcRepresents a chip duration;
step three, each spreading pseudo code sequence has the same time delay delta t relative to the next spreading pseudo code sequence [ G/K ═]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcIs the chip duration of the spreading code; for each numberThe bits being spread-spectrum modulated by the same spreading pseudo-code sequence, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K；
Step four, OFDM carrier modulation is carried out on the spread spectrum signal, and the carrier modulation signal is sent to a receiving end through a channel;
step five, OFDM carrier demodulation is carried out on the received carrier modulation signal at a receiving end;
and step six, respectively carrying out spread spectrum demodulation on the data stream after carrier demodulation by using the same spread spectrum pseudo code sequence as the transmitting end.
The channel in step four adopts a multipath channel.
The receiving end comprises a receiver which consists of k matched filters.
A spread spectrum based parallel transmission OFDM communication system, the system comprising:
a serial-to-parallel conversion module, configured to perform serial-to-parallel conversion on data of the information source at the sending end to obtain a data stream to be sent { d } containing K bits at time t1(t),d2(t),…,dK(t)}；
A spread spectrum sequence generating module, configured to generate a spread spectrum pseudo code sequence, where an autocorrelation function of the spread spectrum pseudo code sequence is:
wherein P represents the total number of sequence related elements, TcRepresents a chip duration;
a spread spectrum modulation module for spread spectrum modulation, wherein each spread spectrum pseudo code sequence has the same time delay delta t ═ G/K relative to the next spread spectrum pseudo code sequence]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcIs the chip duration of the spreading code; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K；
The signal modulation module is used for carrying out carrier modulation on the spread spectrum signal and sending the carrier modulation signal to a receiving end through a channel;
the signal demodulation module is used for carrying out OFDM carrier demodulation on the received carrier modulation signal at a receiving end;
and the de-spreading module is used for respectively carrying out spread spectrum demodulation on the data stream after carrier demodulation at the receiving end by using the same spread spectrum pseudo code sequence as the transmitting end.
The invention has the beneficial effects that:
the invention sets time delay between pseudo code sequences, adopts a plurality of modulation channels, and makes a sending signal arrive at any time after modulation is finished, thereby overcoming the problem of low transmission efficiency caused by the modulation time delay of the OFDM system and improving the data transmission efficiency and the channel utilization rate.
The OFDM system modulation has high requirement on synchronization, and the invention adopts the spread spectrum technology, can ensure data synchronization while transmitting in parallel.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further 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 invention and are not intended to limit the invention.
A spread spectrum modulation communication system, i.e. a spread spectrum communication system, refers to a communication system in which a spectrum of information to be transmitted is spread by a specific spreading function to form a wideband signal, and then the wideband signal is transmitted into a channel for transmission, and then the wideband signal is despread by a corresponding means, so as to obtain transmission information. The radio frequency bandwidth required for transmitting the same information is much wider than the bandwidth required by various familiar modulation modes. The bandwidth of the information symbol before spreading is much smaller than that of the spread code sequence after spreading, the information is no longer an important factor for determining the bandwidth of the modulation signal, and the bandwidth of the modulation signal is mainly determined by the spreading function. A commonly used spreading function is a pseudo-randomly coded signal. Compared with the conventional communication system, the spread spectrum system has strong anti-jamming, anti-narrowband jamming and anti-multipath capabilities, and also has the advantages of information hiding, multiple access secret communication and the like. However, the modulation time is prolonged in the system modulation process, and the channel utilization rate is low. Therefore, the invention provides a spread spectrum modulation method and a system for asynchronous transmission, which improve the channel utilization rate and the data transmission efficiency. FIG. 1 is a flow chart of the method of the present invention. The following description will be made by way of specific examples.
The first embodiment is as follows:
the OFDM communication method based on spread spectrum parallel transmission comprises the following steps:
step one, carrying out serial-parallel conversion on data of an information source at a sending end to obtain a data stream to be sent { d) containing K bits at time t1(t),d2(t),…,dK(t)}。
In a transmission system, information source data needs to be processed first to obtain a data slice or a data stream to be transmitted. Generally, to simplify the transmission system, each data stream is equal in length.
At the transmitting end, the data input by the source is sent to a serial-to-parallel converter. Setting n x K bits of source data, wherein n represents the length of each data stream, K represents the number of data bits, and taking the converted data as a data stream to be transmitted at t moment { d }1(t),d2(t),…,dK(t)}。
At this point, the preparation of the data stream to be transmitted is completed.
Generating a spread spectrum pseudo code sequence, wherein the autocorrelation function of the spread spectrum pseudo code sequence is as follows:
wherein P represents the total number of sequence related elements, TcIndicating the chip duration.
The m-sequence is a maximum length linear shift register sequence and is formed by adding feedback to a shift register. The m-sequence has equalization, run characteristics, and shift-add characteristics. The m-sequence has some randomness, especially the good properties of its autocorrelation function. The invention adopts m sequence as the pseudo code sequence of spread spectrum to modulate the spread spectrum of the signal.
Further, a chaotic sequence may be employed as the spreading sequence. When the processed data volume is large, the m sequence is used as a pseudo-random sequence, the pseudo-random sequence of code modulation is long, and the anti-interception performance is poor. Therefore, the chaotic sequence can be employed as a spreading sequence.
Specifically, the state equation of the chaotic system for generating the chaotic sequence is shown as the following formula:
xn+1＝uxn(1-xn)(n＝1,2,3,…)
wherein u is a branching parameter, xn∈(0,1)。
Step three, each spreading pseudo code sequence has the same time delay delta t relative to the next spreading pseudo code sequence [ G/K ═]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcIs the chip duration of the spreading code; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K。
In the spread spectrum modulation communication system, since time is required for spread spectrum modulation and carrier modulation processing, if only one modulation channel is provided, data is transmitted in a serial manner, and channel utilization and data transmission efficiency are very low. However, if a plurality of data are transmitted simultaneously by parallel transmission, the requirements on the channel capacity and the synchronization mode of the receiving end are very high. The invention sets the same time delay for each spread spectrum pseudo code sequence. On one hand, the modulation time delay can be fully utilized for data transmission, and the data transmission efficiency is improved; on the one hand, different data streams can be distinguished at a receiving end according to time delay.
And step four, carrying out OFDM carrier modulation on the spread spectrum signal, and sending the carrier modulation signal to a receiving end through a channel.
The modulation mode of the digital signal comprises frequency shift keying, amplitude keying and phase shift keying. Quadrature phase shift keying QPSK is a digital modulation scheme. The QPSK technology has the advantages of strong anti-interference performance, good error code performance, high frequency spectrum utilization rate and the like. The invention uses QPSK modulation to carry out carrier modulation on the spread spectrum signal. When a carrier modulation signal is transmitted to a receiving end through a channel, a multipath channel is used for transmission.
And step five, at the receiving end, carrying out carrier demodulation on the received carrier modulation signal.
At the receiving end, the carrier demodulation is firstly needed to be performed on the received carrier modulation signal, and the next step of spread spectrum demodulation is further performed.
And step six, respectively carrying out spread spectrum demodulation on the data streams by using the same spread spectrum pseudo code sequence as the transmitting end.
At the receiving end, the received signal is correlated with each of the local spreading sequences and the received combined spread signal is despread. The matched filter accumulates the signals corresponding to all the chips into the baseband complex signal corresponding to any chip in the sequence according to the spreading rule of the spreading pseudo code sequence, and the spreading demodulation processing of the spreading signals is completed.
Example two:
the invention also provides a spread spectrum based parallel transmission OFDM communication system, which comprises:
a serial-to-parallel conversion module, configured to perform serial-to-parallel conversion on data of the information source at the sending end to obtain a data stream to be sent { d } containing K bits at time t1(t),d2(t),…,dK(t)}；
A spread spectrum sequence generating module, configured to generate a spread spectrum pseudo code sequence, where an autocorrelation function of the spread spectrum pseudo code sequence is:
wherein P represents the total number of sequence related elements, TcRepresents a chip duration;
a spread spectrum modulation module for spread spectrum modulation, wherein each spread spectrum pseudo code sequence has the same time delay delta t ═ G/K relative to the next spread spectrum pseudo code sequence]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcCodes being spreading codesA patch duration; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K；
The signal modulation module is used for carrying out OFDM carrier modulation on the spread spectrum signal and transmitting the carrier modulation signal to a receiving end through a channel;
the signal demodulation module is used for carrying out carrier demodulation on the received carrier modulation signal at a receiving end;
and the de-spreading module is used for respectively carrying out spread spectrum demodulation on the data streams at the receiving end by using the same spread spectrum pseudo code sequence as the transmitting end.
Aiming at the problem that the modulation time delay in the OFDM system modulation process is large, the time delay between pseudo code sequences is set, a plurality of modulation channels are adopted, and after modulation is completed, a sending signal is transmitted along with the transmission, so that the data transmission efficiency is improved.
The invention combines the OFDM and the spread spectrum code, occupies less resources, has low realization complexity and certain engineering realizability, and lays a technical foundation for the development and the development of the spread spectrum OFDM baseband. Aiming at the problem that the modulation time delay in the modulation process of the OFDM system is large, the time delay between pseudo code sequences is set, a plurality of modulation channels are adopted, and after modulation is completed, a sending signal is transmitted at once, so that the problem of low transmission efficiency caused by the modulation time delay of the OFDM system is solved, and the data transmission efficiency and the channel utilization rate are improved. The OFDM system modulation has high requirement on synchronization, and the invention adopts the spread spectrum technology, and can ensure data synchronization while transmitting in parallel.
The above embodiments are merely preferred embodiments of the present invention, which should not be construed as limiting the present invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A spread spectrum based OFDM communication method for parallel transmission, comprising:
step one, data of a signal source at a transmitting endPerforming serial-parallel conversion to obtain data stream to be transmitted { d) containing K bits at time t1(t),d2(t),…,dK(t)}；
Generating a spread spectrum pseudo code sequence, wherein the autocorrelation function of the spread spectrum pseudo code sequence is as follows:
wherein P represents the total number of sequence related elements, TcRepresents a chip duration;
step three, each spreading pseudo code sequence has the same time delay delta t relative to the next spreading pseudo code sequence [ G/K ═]Tc，[]Denotes a rounding operation, G is the spreading code sequence length, TcIs the chip duration of the spreading code; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K；
Step four, OFDM carrier modulation is carried out on the spread spectrum signal, and the carrier modulation signal is sent to a receiving end through a channel;
step five, OFDM carrier demodulation is carried out on the received carrier modulation signal at a receiving end;
and step six, respectively carrying out spread spectrum demodulation on the data stream after carrier demodulation by using the same spread spectrum pseudo code sequence as the transmitting end.
2. The spread-spectrum based parallel transmission OFDM communication method of claim 1, wherein the channels in the fourth step employ multipath channels.
3. The spread spectrum based parallel transmission OFDM communication method of claim 1, wherein the receiving end includes a receiver, and the receiver is comprised of k matched filters.
4. A spread spectrum based parallel transmission OFDM communication system, comprising:
a serial-to-parallel conversion module, configured to perform serial-to-parallel conversion on data of the information source at the sending end to obtain a data stream to be sent { d } containing K bits at time t1(t),d2(t),…,dK(t)}；
A spread spectrum sequence generating module, configured to generate a spread spectrum pseudo code sequence, where an autocorrelation function of the spread spectrum pseudo code sequence is:
wherein P represents the total number of sequence related elements, TcRepresents a chip duration;
a spread spectrum modulation module for spread spectrum modulation, wherein each spread spectrum pseudo code sequence has the same time delay delta t ═ G/K relative to the next spread spectrum pseudo code sequence]Tc，[]Denotes a rounding operation, G is the length of the PN sequence, TcIs the chip duration of the spreading code; spread-spectrum-modulated by the same spreading pseudo-code sequence for each data bit, i.e. PNi(t)＝PN1(t+si),si＝(i-1)Δt，i＝1,2,3,…,K；
The signal modulation module is used for carrying out OFDM carrier modulation on the spread spectrum signal and transmitting the carrier modulation signal to a receiving end through a channel;
the signal demodulation module is used for carrying out carrier demodulation on the received carrier modulation signal at a receiving end;
and the de-spreading module is used for respectively carrying out spread spectrum demodulation on the data stream after carrier demodulation at the receiving end by using the same spread spectrum pseudo code sequence as the transmitting end.
5. The spread spectrum based parallel transmission OFDM communication system of claim 4 wherein the channel employs a multipath channel.
6. The spread spectrum based parallel transmission OFDM communication system of claim 4 wherein the receiving end comprises a receiver comprised of k matched filters.
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