CN105635026A - Location modulation and soft demodulation method in spread spectrum communication - Google Patents

Location modulation and soft demodulation method in spread spectrum communication Download PDF

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Publication number
CN105635026A
CN105635026A CN201510958629.1A CN201510958629A CN105635026A CN 105635026 A CN105635026 A CN 105635026A CN 201510958629 A CN201510958629 A CN 201510958629A CN 105635026 A CN105635026 A CN 105635026A
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sequence
modulation
bit
soft
spread spectrum
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CN201510958629.1A
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CN105635026B (en
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彭睿
张萌
田亚飞
高鹏
王婷
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Beijing Aerospace Science & Industry Century Satellite Hi-Tech Co Ltd
Beihang University
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Beijing Aerospace Science & Industry Century Satellite Hi-Tech Co Ltd
Beihang University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/3405—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
    • H04L27/3444—Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power by applying a certain rotation to regular constellations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
    • H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
    • H04L27/38—Demodulator circuits; Receiver circuits
    • H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
    • H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset

Abstract

The invention discloses a location modulation and soft demodulation method in spread spectrum communication, belongs to the wireless communication technical field. The method comprises two parts of a transmitting terminal algorithm and a receiving terminal algorithm; at the transmitting terminal, multiple different cyclic shift duplications are taken as a spread spectrum sequence; the multiple different cyclic shift duplications are obtained through shifting a certain original spread spectrum sequence; at the receiving terminal, a soft demodulation method is adopted; correlation is carried out to cyclic shifts of a receiving sequence and a local sequence; amplitude modulated data bit amplitude modulation value and location bit soft demodulation value are calculated according to correlation values at different locations and a demodulation algorithm; and decoding data are obtained through matching with the soft decision of the a decoder. According to the method of the invention, the traditional modulation mode and C band sequence location modulation are combined; the data carried by each modulation symbol can be improved by log2c bits; the spectrum efficiency is improved; the location bits are obtained through the soft demodulation method in the location demodulation; the method of the invention can be combined with a coded soft demodulation method; and the system error rate is reduced.

Description

Position modulation in a kind of spread spectrum communication and soft demodulating method
Technical field
The present invention relates to the position modulation in a kind of spread spectrum communication and soft demodulating method, belong to wireless communication technology field.
Background technology
In spread spectrum communication system, transmitting terminal is modulated much larger than the high speed pseudo noise code of signal bandwidth by a bandwidth, makes the bandwidth of former data signal be expanded, then through carrier modulation and send. Receiving terminal uses the bandwidth signal of identical pseudo noise code and reception to make relevant treatment, and namely narrow band signal broadband signal being changed into prime information data de-spreads, to realize information communication.
Sequence common in spreading code has m-sequence, Gold sequence etc. M-sequence is the cycle produced by n level linear shift register is 2nThe code sequence of-1, is the abbreviation of maximum length linear shift register sequence. This sequence has the advantageous feature such as cycle length, easily generation, randomness are good. Gold sequence is identical with speed with a pair cycle, but code word different m-sequence is preferably to obtaining after carrying out exclusive-OR. Preferably concentrating at m-sequence referring to, the absolute value of its cross-correlation function maximum is less than two m-sequence of certain two values. Gold sequence by m-sequence preferably to forming. The cross-correlation function of the m-sequence referring to two equal length is preferably had three values by m-sequence, and namely correlation only there will be three values:
Traditional spread spectrum system spectrum efficiency is low, if wanting to improve data transfer rate will adopt the modulation system of higher order. If improving data transfer rate under the premise not changing modulation coding mode, some information can be carried on sequence location, namely the sequence after spread spectrum is circulated displacement, is determined the figure place of displacement by position bit, so can improve data transfer rate when bandwidth is constant. Different displacement modes can make the spreading code after displacement different from the correlation of local spreading code, has thus resulted in the difference of receiver demodulation performance.
And in position demodulates, traditional demodulation method is to take turns doing relevant by receiving sequence from the local sequence through different displacements, by comparing the shift amount that the size of correlation several times finds the local sequence of peak value and correspondence thereof, this makes it possible to once solve whole position bit. But the method for this hard demodulation cannot with coding soft-decision with the use of, if correlation peak location is subject to influence of noise and changes, firmly demodulate the position data obtained and necessarily makes mistakes, control shift amount position bit it is possible to understand whole mistakes.
Summary of the invention
The method that the purpose of the present invention is to propose to the position modulation mode in a kind of spread spectrum communication and its soft demodulation, including transmitting terminal algorithm and receiving terminal algorithm two parts.
At transmitting terminal, the copy of the multiple different cyclic shifts that a certain original spreading sequence is obtained by the present invention after displacement, as frequency expansion sequence, transmits data by shift information. Owing to the cross correlation of Gold sequence has three values, namely remove correlation other correlations outer that cyclic shift is 0 place and only there will be the m-sequence with equal length preferably to 3 identical values:Therefore, during by position that frequency expansion sequence cyclic shift to correlation is-1, the step number namely shifted is corresponding to-1 position in the auto-correlation function of frequency expansion sequence. Higher transmission data rate can enable a system to obtain the minimum bit error rate, thus can be realized.
Concretely comprising the following steps of transmitting terminal position modulation: set the signal sequence that receives as r (n), local spread spectrum code sequence is s (n), and length is N, and position modulation system number is C, then can have 2CIndividual different shift value, during displacement, the sequence of reference is position sequence p (n), the element of position sequence p (n) is different shift value, known, frequency expansion sequence should be-1 according to after the element shift of p (n) with the correlation of former frequency expansion sequence, and the length of position sequence p (n) should be C. Each code element required displacement step number constitutes shift sequence pm(n). The step then modulated is as follows:
(1) by packet to be modulated, often group comprises M the bit for data modulation and log2C the bit for position modulation;
(2) M the bit for data modulation is mapped to the data on planisphere, and uses spreading code to carry out spread spectrum;
(3) by the log in each packet2C the bit for position modulation is scaled decimal scale displacement numbering, constitutes shift sequence pmThe nth elements of (n). If log2C the bit for position modulation is full 0, then do not shift;
(4) by shift sequence pmN () substitutes into position sequencep(n), form displacement step number sequence pstep(n), wherein, pstep(n)=p (pm(n));
(5) spread symbols that each packet is constituted being circulated and moved to right (or moving to left), displacement step number is pstepN code element corresponding in (), namely the n-th symbol cyclic moves to right (or moving to left) pstep(n) step.
At receiving terminal, the present invention adopts soft demodulating method, first do relevant by receiving sequence cyclic shift to local sequence, correlation again through various location, utilize demodulating algorithm, calculate the soft demodulation value of amplitude modulation data bit and the soft demodulation value of position bit, finally coordinate the soft-decision of decoder to obtain decoding data.
Specifically comprising the following steps that of demodulation
(1) frequency expansion sequence received is sequentially carried out ring shift left (or moving to right) according to the element of position sequence p (n), and carries out relevant to local spread spectrum code sequence s (n) after displacement every time. The cyclic shift of the cyclic shift of the frequency expansion sequence received and local spread spectrum code sequence is of equal value, i.e.
d ( k ) = Σ n = 0 N - 1 r [ ( n + k ) % N ] s * [ n ] ⇔ d ( k ) = Σ n = 0 N - 1 r [ n ] s * [ ( n + k ) % N ]
Wherein, %N represents N complementation, s*[n] represents the conjugation of local spread spectrum code sequence, carries out storing C correlation with a sequence d (k) after C displacement is correlated with;
(2) in C correlation, choose mould maximum, directly read correlation and its demodulation can be obtained M the bit for data modulation;
(3) utilizeObtaining the soft demodulation value of the kth bit of position data, | | represents modulus computing, k=1, and 2 ... log2C. Obtain whole log2C the soft demodulation value for the bit of position modulation;
(4) it is used for modulating soft demodulation value and the log of the bit of data by every M2C soft demodulation value 1 packet of composition for the bit of position modulation. Decoder is sent in all packets according to the order of sequence, namely completes to solve the decoding process that is in harmonious proportion.
It is an advantage of the current invention that:
(1) traditional modulation system is combined with the modulation of C system sequence location, make each modulation symbol more than enough can carry log2The data of C bit, improve the availability of frequency spectrum.
(2) on the basis of C system sequence location modulation, search out the modulation positions of best performance.
(3) method of soft demodulation is adopted to obtain position bit in position demodulates, it is possible to be combined with the soft demodulating method of coding and reduce error rate of system.
Accompanying drawing explanation
Fig. 1 is 63 Gold sequence auto-correlation function schematic diagrams.
Fig. 2 is the schematic diagram that sequence location modulates that correlation is-1 place.
Fig. 3 is the Performance comparision that sequence modulation arrives different correlation position.
Detailed description of the invention
Below in conjunction with drawings and Examples, the present invention is described in detail.
An embodiment of position modulation in the present invention a kind of spread spectrum communication and soft demodulating method be given below, the wherein position modulation of the generation of spreading code, sequence, including following steps:
(1) as it is shown in figure 1, adopt 63 long Gold sequence, original state being [010110], tap position is the m-sequence of [16] is [000101] with another original state, and the m-sequence that tap position is [1256] does mould 2 and produces.
(2) choice of modulation mode is the modulation of QPSK+ binary location, and displacement mode is ring shift right, and chnnel coding is the Turbo code of code efficiency R=1/2. Here our emulation location modulation positions performance at-1 place of correlation, emulation simultaneously is modulated in correlation except off peak higher value place and smaller value place (corresponding respectively for 63 long sequences be correlation is 15 places and-17 places) compares, such as Fig. 2, wherein position bit is that sequence is not shifted by 0 representative.
(3) frequency expansion sequence after the position modulation received is circulated according to the displacement step number of position modulation moves to left, and carry out relevant to local spread spectrum code sequence after displacement every time. Perform twice at after displacement is correlated with a sequence dQPSKN () stores the correlation of twice;
(4) choose that modulus value in twice correlation is big one group, directly reads the real part of correlation and imaginary part can obtain the QPSK data of 2 bits;
(5) utilize | dQPSK(1)|-|dQPSK(2) | obtaining the soft demodulation value of position bit, | | represents modulus computing;
(6) with position demodulating data, QPSK data being sent into turbo decoder, interpretation method adopts Viterbi decoding.
(7) bit error rate when contrast modulation is to diverse location, with signal to noise ratio change curve, finds the modulation positions that performance is best.
Simulation result is Fig. 3 such as, it can be seen that the performance modulating smaller value-17 position is significantly worse than two other position. Modulation is close to-1 position and modulation to the Performance comparision of higher value 15 position. When signal to noise ratio is relatively low, the performance being modulated at 15 positions is slightly better than-1 position, but when signal to noise ratio is higher, the performance that autocorrelation value is-1 position modulation is substantially better than 15 places, and signal to noise ratio is more big, effect more obvious (the curve BER=0 when SNR=-6 when modulation is to autocorrelation value-1 place in figure).

Claims (2)

1. the position modulation in spread spectrum communication and a soft demodulating method, including transmitting terminal algorithm and receiving terminal algorithm two parts, it is characterised in that:
At transmitting terminal, the copy of the multiple different cyclic shifts obtained after displacement by a certain original spreading sequence is as frequency expansion sequence, data are transmitted by shift information, during by position that frequency expansion sequence cyclic shift to correlation is-1, the step number namely shifted is corresponding to-1 position in the auto-correlation function of frequency expansion sequence; If the signal sequence received is r (n), local spread spectrum code sequence is s (n), and length is N, and position modulation system number is C, then have 2CIndividual different shift value, during displacement, the sequence of reference is position sequence p (n), the element of position sequence p (n) is different shift value, known, frequency expansion sequence should be-1 according to after the element shift of p (n) with the correlation of former frequency expansion sequence, and the length of position sequence p (n) should be C; Each code element required displacement step number constitutes shift sequence pm(n), then the step modulated is as follows:
(1) by packet to be modulated, often group comprises M the bit for data modulation and log2C the bit for position modulation;
(2) M the bit for data modulation is mapped to the data on planisphere, and uses spreading code to carry out spread spectrum;
(3) by the log in each packet2C the bit for position modulation is scaled decimal scale displacement numbering, constitutes shift sequence pmThe nth elements of (n); If log2C the bit for position modulation is full 0, then do not shift;
(4) by shift sequence pmN () substitutes into position sequence p (n), form displacement step number sequence pstep(n), wherein, pstep(n)=p (pm(n));
(5) spread symbols that each packet is constituted being circulated and moved to right (or moving to left), displacement step number is pstepN code element corresponding in (), namely the n-th symbol cyclic moves to right (or moving to left) pstep(n) step;
At receiving terminal, adopt soft demodulating method, first do relevant by receiving sequence cyclic shift to local sequence, correlation again through various location, utilize demodulating algorithm, calculate the soft demodulation value of amplitude modulation data bit and the soft demodulation value of position bit, finally coordinate the soft-decision of decoder to obtain decoding data.
2. the position modulation in a kind of spread spectrum communication according to claim 1 and soft demodulating method, it is characterised in that: what receiving terminal was soft demodulated specifically comprises the following steps that
(1) frequency expansion sequence received it is sequentially carried out ring shift left according to the element of position sequence p (n) or moves to right, and carrying out relevant to local spread spectrum code sequence s (n) after displacement every time; The cyclic shift of the cyclic shift of the frequency expansion sequence received and local spread spectrum code sequence is of equal value, i.e.
d ( k ) = Σ n = 0 N - 1 r [ ( n + k ) % N ] s * [ n ] ⇔ d ( k ) = Σ n = 0 N - 1 r [ n ] s * [ ( n + k ) % N ]
Wherein, %N represents N complementation, s*[n] represents the conjugation of local spread spectrum code sequence, carries out storing C correlation with a sequence d (k) after C displacement is correlated with;
(2) in C correlation, choose mould maximum, directly read correlation and its demodulation can be obtained M the bit for data modulation;
(3) utilizeObtain the soft demodulation value of the kth bit of position data,Represent modulus computing, k=1,2 ... log2C; Obtain whole log2C the soft demodulation value for the bit of position modulation;
(4) it is used for modulating soft demodulation value and the log of the bit of data by every M2C soft demodulation value 1 packet of composition for the bit of position modulation; Decoder is sent in all packets according to the order of sequence, namely completes to solve the decoding process that is in harmonious proportion.
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111490847A (en) * 2020-03-05 2020-08-04 熊军 Multi-address communication method and device for selecting pseudo-random code sequence to carry out spread spectrum

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Publication number Priority date Publication date Assignee Title
CN102932309A (en) * 2012-10-19 2013-02-13 西安电子科技大学 Carrier synchronization system and method of combining pilot frequency and iterative decoding
US20130058441A1 (en) * 2011-09-07 2013-03-07 Yun Zhang Signal Demodulation Method
CN103152074A (en) * 2013-02-17 2013-06-12 哈尔滨工程大学 Emitting and receiving method of direct sequence spread spectrum communication system
CN103152070A (en) * 2013-02-17 2013-06-12 哈尔滨工程大学 Variable beacon sequence-based spread spectrum communication method

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130058441A1 (en) * 2011-09-07 2013-03-07 Yun Zhang Signal Demodulation Method
CN102932309A (en) * 2012-10-19 2013-02-13 西安电子科技大学 Carrier synchronization system and method of combining pilot frequency and iterative decoding
CN103152074A (en) * 2013-02-17 2013-06-12 哈尔滨工程大学 Emitting and receiving method of direct sequence spread spectrum communication system
CN103152070A (en) * 2013-02-17 2013-06-12 哈尔滨工程大学 Variable beacon sequence-based spread spectrum communication method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111490847A (en) * 2020-03-05 2020-08-04 熊军 Multi-address communication method and device for selecting pseudo-random code sequence to carry out spread spectrum

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