阅读说明：本技术 一种针对gmsk信号的单载波均衡方法 (Single carrier equalization method for GMSK signal ) 是由 熊军 杨林 解琦 田进 于 2019-06-28 设计创作，主要内容包括：本发明涉及无线通信技术领域,具体涉及一种针对GMSK信号的单载波均衡方法；本发明接收GMSK信号并对载波做同步头处理确定后面每一跳的起始位置和终止位置；然后对GMSK信号在训练序列附近滑动相关并做匹配滤波；并对GMSK信号相干解调和频域均衡；最终对GMSK信号进行软信息解扩和LDPC译码；本发明提出的GMSK/QPSK/BPSK循环信道估计算法装置,GMSK相干解调,单载波频域均衡算法,能够接近算法的理论极限,同时在复杂的多径信道下,能够准确的估计出各条路径的多径幅度信息,相位信息,时延信息。同时噪声被有效抑制,均衡采用MMSE算法,使得性能达到最佳,在郊区信道,城市信道,开阔地带等各种高速移动环境下都能够适应。具备抗复杂地形多径的效果,具有很强的创造性。(The invention relates to the technical field of wireless communication, in particular to a single carrier equalization method aiming at GMSK signals; the invention receives GMSK signal and processes the carrier wave to determine the initial position and end position of each jump; then, performing sliding correlation on the GMSK signal near the training sequence and performing matched filtering; coherent demodulation and frequency domain equalization are carried out on the GMSK signals; finally, soft information de-spread and LDPC decoding are carried out on the GMSK signal; the GMSK/QPSK/BPSK cyclic channel estimation algorithm device, GMSK coherent demodulation and single carrier frequency domain equalization algorithm provided by the invention can approach the theoretical limit of the algorithm, and can accurately estimate the multipath amplitude information, phase information and time delay information of each path under a complex multipath channel. Meanwhile, noise is effectively suppressed, MMSE algorithm is adopted for equalization, performance is optimal, and the method can be adapted to various high-speed mobile environments such as suburb channels, urban channels, open areas and the like. The method has the effect of resisting complex terrain multipath and has strong creativity.)

1. A method for single carrier equalization for GMSK signals, the method comprising the steps of:

s1 receiving GMSK signal and making synchronous head processing to carrier wave to determine the start position and end position of each following jump;

s2 performing sliding correlation and matched filtering on GMSK signals near the training sequence;

s3 coherent demodulation and frequency domain equalization of the GMSK signal in S2;

s4 performs soft information despreading and LDPC decoding on the GMSK signal in S3.

2. A single carrier equalization method for GMSK signals according to claim 1, wherein in S1, after receiving GMSK signals, frequency offset correction and signal correlation synchronization for carriers are performed, and a start position and an end position of each subsequent hop are determined.

3. A single carrier equalization method for GMSK signals according to claim 1, wherein in S2, the GMSK signals are subjected to sliding correlation near a forward-hop sequence and a backward-hop sequence, and matched filtering is performed after determining matched filter coefficients near a correlation peak.

4. The single-carrier equalization method for GMSK signals according to claim 1, wherein in S3, after matching filtering is performed on S2, coherent demodulation of GMSK signals is changed into symbol information, channel estimation is started, a multipath channel is estimated to obtain channel information h, and according to the channel information h, single-carrier frequency domain equalization/time domain equalization is performed to obtain equalized soft information.

5. Single carrier equalization method for GMSK signals according to claim 4, characterized in that in the estimation of the multipath channel, its received signal y_kAnd transmit signal x_kHave the following relationship therebetween

Wherein h is_lFor the channel response tap coefficient, ω_kIs variance of

6. Single carrier for GMSK signals according to claim 5The wave equalization method is characterized in that in the estimation of the multipath channel, the frequency domain equalization is carried out based on a data block with the length of L, the frequency domain equalization requires a system to be a minimum phase system, and h in channel response₀For a first received multipath signal;

h＝[h₀,h₁,…,h_M-1]^T(2)

the effect of the channel on a data block is regarded as a cyclic convolution of the whole data block, and a multipath channel model is rewritten into

y＝H_Cx+ω (3)

Wherein the content of the first and second substances,

y＝[y₀,y₁,…,y_L-1]^T(4)

x＝[x₀,x₁,…,x_L-1]^T， (5)

ω＝[ω₀,ω₁,…,ω_L-1]^T(6)

H_C＝Circ_L[h₀,h₁,…,h_M-1](7)

the channel estimation module calculates the estimation h of the channel by adopting a cyclic correlation method.

7. The single-carrier equalization method for GMSK signals according to claim 4, wherein, when performing single-carrier frequency domain equalization/time domain equalization, at a receiving end, first synchronizing received data, and finding an initial position of a training sequence using an autocorrelation characteristic of the training sequence; after synchronization, data is divided into two paths, 2048-point FFT (fast Fourier transform) is carried out on one path of data, channel estimation is carried out on the other path of data by means of the training sequence firstly according to the found training sequence position, the impulse response h of a channel is obtained, the obtained h is a sequence less than 63 long, zero padding is carried out, 2048 data are combined, the data enter an FFT (fast Fourier transform) module, the data are transformed to a frequency domain, and the weight w is obtained through substitution formula calculation₁Then, the two paths of data are subjected to point multiplication, and the result of the point multiplication enters an IFFT module and is converted into a time domain.

8. The single-carrier equalization method for GMSK signals according to claim 7, characterized in that IFFT-transformed data is divided into two paths, one path directly enters the adder, the other path enters the hard decision device, and then FFT transformation and weight multiplication are performed, the result after point multiplication is transformed into the time domain through IFFT, the result changes sign, one path of signal result after IFFT transformation of weight in the adder and adder, the result of summation of three paths of signals, the training sequence is removed, deinterleaving, and entering the decoding module for decoding.

9. The single-carrier equalization method for GMSK signals according to claim 4, wherein when performing single-carrier frequency domain equalization/time domain equalization, the simple forward linear equalizer is used to equalize the frequency domain received vector after FFT and CP removal, which can be expressed by the following equation:

where W ═ W (0), W (1), W (N-1)]^TIs the equalizer coefficient vector;

a zero-forcing equalizer:

MMSE equalizer:

let the variance of the noise be E (v)_n ²)＝σ²Let us orderIs provided with

Wherein

Order to

the balance part of the whole receiver comprises two weights, and the calculation formula is as shown in formula (4-4):

wherein w₁Is a feedforward coefficient, w₂Is the feedback coefficient; in the formula, σ²Is the noise power, is a fixed number, H is the vector containing 2048 numbers that has undergone FFT; and (4) division operation, namely generating a kernel from the table by adopting a list method, and inputting H to obtain a feedforward equilibrium coefficient and a feedback equilibrium coefficient.

Technical Field

The invention relates to the technical field of wireless communication, in particular to a single carrier equalization method for GMSK signals.

Background

With the development of modern communication technology, many excellent modulation techniques have been developed, wherein Gaussian Minimum Shift Keying (GMSK) is a more prominent binary modulation method in wireless communication, which has good power spectrum characteristics and good interference resistance, and is particularly suitable for wireless communication and satellite communication. Currently, GMSK technology is used in many communication standards, such as GSM, DECT, etc.

The data detection can adopt an MLSE (minimum mean square error) detection method, and the MLSE is realized by Viterbi equalization based on a modified Ungerboek algorithm.

And finding out the transmitted MSK symbol sequence at a receiving end, and mapping the MSK symbol sequence into binary information to finish the demodulation of the data. The function of the Viterbi detector (VA) is to estimate the sequence of MSK symbols sent into the mobile channel.

But the detection industry for GMSK signals commonly employs matched filtering and LMSE detection algorithms.

The LMSE detection algorithm is as follows

In the detection process, the detection system can be represented by a finite state machine, and each state of discrete time n is only corresponding to the first L in I_hThe MSK symbols are related. That is, the MSK symbol triggers a state transition of the state machine, and the next state is uniquely determined by the MSK symbol in the current I. The state of the state machine at time n is represented as:

σ[n]＝[I[n],I[n-1],……,I[n-(L_h-1)]]

the right side of the upper type is provided with L_hA symbol. In general, if I [ n ]]Is-j or a complex value of j, then I [ n +1 ]]It is a real value of-1 or 1, i.e., a real number alternates with a complex number. From the above, each state is associated with L_hOne MSK symbol is related, so the number of states M equals:

thus having σ n]∈{s₁,s₂,……,s_M}，s_mRepresenting the mth state. Sigma [ n ]]Belonging to one of the states in the set of states, numbered 1 to M. Because L is_hIf the number is less than or equal to 4, the number of states of the state machine is less than or equal to 32. In the implementation process, a mapping relation exists between the MSK symbol and the state number, a mapping table can be established, and the MSK symbol can be obtained at any time through the mapping table. According to the actual state transition relationship, the legal front state and back state of each state can be obtained, including the starting state and the stopping state.

After the concept of state is built, the problem of finding the most likely MSK symbol sequence translates into determining the best path through the entire state trellis. All states have two legal next states, namely:

i [ n ] ∈ {1, -1} or I [ n ] ∈ { j, -j }

Viterbi data detection is performed by finding the most probable path from the trellis diagram, and therefore the metric value of each branch path must be calculated, and the path with the larger metric value is taken as the survivor path. The path metric GAIN is calculated as follows:

wherein s is_aAnd s_bRespectively representing the state of the previous moment and the current state, described by the MSK symbol, Y n]Is the nth sample of Y. As can be seen from the equation, two legal states I n]Positive and negative, so that the path metric values of a state going to two next legal states are also positive and negative.

In addition, we can see some features beneficial to dsp processing from the state transition relationship diagram, for example, when Lh is 2, the state transition relationship is shown in fig. 7, and the following features can be seen from the state transition relationship diagram:

the switching relationship is composed of 2Lh +1/2 butterfly changes.

The next state of the butterfly-shaped upper branch is less than 2Lh +1/2, and the path metric values of the upper branch and the lower branch are in a positive-negative relationship.

The odd-even states alternate, i.e., the odd state can only transition to the even state and the even state can only transition to the odd state.

MSK sequence estimation I transmitted by survivor path_est. The MSK symbol sequence is converted to a non-return-to-zero binary sequence according to the following equation.

rx_burst[n]＝I_est[n]/(j·rx_burst[n-1]·I_est[n-1])

The above equation completes MSK demapping and differential decoding at the same time.

In this case, the LMSE detection algorithm generally aims at low-speed signals, and the time corresponding to one symbol point is long, for example, the GMSK signal rate in GSM is selected to be 270.833 kbit/sec. If the physical layer transmits 12Mbit/sec, the corresponding time of each sampling point is 1/40 of the time of the GSM sampling point, the number of the GSM states is 4, 160 states are needed corresponding to the high-speed data transmission state, and the corresponding multipath condition can be reflected, so that the detection by continuously adopting the LMSE algorithm is almost impossible aiming at the high-speed multipath channel. For this reason, a new detection algorithm is required to perform the detection of the GMSK signal at high speed.

Disclosure of Invention

Aiming at the defects of the prior art, the invention discloses a single carrier equalization method for GMSK signals, which is used for solving the technical problem.

The invention is realized by the following technical scheme:

a method for single carrier equalization for GMSK signals, the method comprising the steps of:

s1 receiving GMSK signal and making synchronous head processing to carrier wave to determine the start position and end position of each following jump;

s2 performing sliding correlation and matched filtering on GMSK signals near the training sequence;

s3 coherent demodulation and frequency domain equalization of the GMSK signal in S2;

s4 performs soft information despreading and LDPC decoding on the GMSK signal in S3.

Preferably, in S1, after receiving the GMSK signal, the frequency offset correction and the signal correlation synchronization for the carrier are performed, and the start position and the end position of each subsequent hop are determined.

Preferably, in S2, the GMSK signal is subjected to sliding correlation near the forward-hop sequence and the backward-hop sequence, and matched filtering is performed after the matched filter coefficients are determined near the correlation peak.

Preferably, in S3, after performing matching filtering on S2, coherent demodulation of the GMSK signal is changed into symbol information, channel estimation is started, a multipath channel is estimated to obtain channel information h, and single carrier frequency domain equalization/time domain equalization is performed according to the channel information h to obtain equalized soft information.

Preferably, in the estimating of the multipath channel, it receives the signal y_kAnd transmit signal x_kHave the following relationship therebetween

Wherein h is_lFor the channel response tap coefficient, ω_kIs variance of

Additive white Gaussian noise, M₁And M₂The length of the non-causal and causal parts of the channel response, respectively, and the total channel length is M-M₁+M₂+1。

Preferably, in the estimation of the multipath channel, the frequency domain equalization is performed based on a data block with a length L, and the frequency domain equalization requires that the system is a minimum phase system, i.e. h in the channel response₀For a first received multipath signal;

h＝[h₀,h₁,…,h_M-1]^T(2)

the effect of the channel on a data block is regarded as a cyclic convolution of the whole data block, and a multipath channel model is rewritten into

y＝H_Cx+ω (3)

Wherein the content of the first and second substances,

y＝[y₀,y₁,…,y_L-1]^T(4)

x＝[x₀,x₁,…,x_L-1]^T， (5)

ω＝[ω₀,ω₁,…,ω_L-1]^T(6)

H_C＝Circ_L[h₀,h₁,…,h_M-1](7)

the channel estimation module calculates the estimation h of the channel by adopting a cyclic correlation method.

Preferably, when single carrier frequency domain equalization/time domain equalization is performed, at a receiving end, synchronization is performed on received data first, and an initial position of a training sequence is found by using the autocorrelation characteristic of the training sequence; after synchronization, data is divided into two paths, 2048-point FFT (fast Fourier transform) is carried out on one path of data, channel estimation is carried out on the other path of data by means of the training sequence firstly according to the found training sequence position, the impulse response h of a channel is obtained, the obtained h is a sequence less than 63 long, zero padding is carried out, 2048 data are combined, the data enter an FFT (fast Fourier transform) module, the data are transformed to a frequency domain, and the weight w is obtained through substitution formula calculation₁Then, the two paths of data are subjected to point multiplication, and the result of the point multiplication enters an IFFT module and is converted into a time domain.

Preferably, the IFFT-transformed data is divided into two paths, one path directly enters an adder, the other path enters a hard decision device, then FFT transformation and weight value dot multiplication are carried out, the result after dot multiplication is transformed to a time domain through IFFT, the sign of the result is changed, the signal result after IFFT transformation of the weight value enters the adder and the adder, the result of summation of three paths of signals is obtained, a training sequence is removed, deinterleaving is carried out, and the signal result enters a decoding module for decoding.

Preferably, when single carrier frequency domain equalization/time domain equalization is performed, a simple forward linear equalizer is used to equalize the frequency domain received vector after FFT transformation and CP deletion, which can be expressed by the following formula:

wherein W is [ W (0), W (1),...,W(N-1)]^Tis the equalizer coefficient vector;

a zero-forcing equalizer:

MMSE equalizer:

let the variance of the noise be E (v)_n ²)＝σ²Let us order

Is provided with

Wherein

Order to

Obtaining an MMSE equalizer:

the balance part of the whole receiver comprises two weights, and the calculation formula is as shown in formula (4-4):

wherein w₁Is a feedforward coefficient, w₂Is the feedback coefficient; in the formula, σ²The noise power is a fixed number, 9dB is suggested, and H is a vector containing 2048 numbers which is subjected to FFT; and (4) division operation, namely generating a kernel from the table by adopting a list method, and inputting H to obtain a feedforward equilibrium coefficient and a feedback equilibrium coefficient.

The invention has the beneficial effects that:

the GMSK/QPSK/BPSK cyclic channel estimation algorithm device, GMSK coherent demodulation and single carrier frequency domain equalization algorithm can approach the theoretical limit of the algorithm, and meanwhile, under a complex multipath channel, multipath amplitude information, phase information and time delay information of each path can be accurately estimated. Meanwhile, noise is effectively suppressed, MMSE algorithm is adopted for equalization, performance is optimal, and the method can be adapted to various high-speed mobile environments such as suburb channels, urban channels, open areas and the like. The method has the effect of resisting complex terrain multipath.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic overall view of the present invention;

fig. 2 is a signal constellation diagram received by GMSK according to an embodiment of the present invention;

fig. 3 is a signal constellation diagram after GMSK coherent demodulation according to an embodiment of the present invention;

fig. 4 is a signal constellation diagram after GMSK coherent demodulation-frequency domain equalization according to an embodiment of the present invention;

FIG. 5 is a diagram of two paths for channel estimation according to an embodiment of the present invention;

fig. 6 is a graph comparing the performance of noise immunity after GMSK coherent demodulation-equalization according to an embodiment of the present invention.

Fig. 7 is a state relationship transition diagram in the background art.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.