CN102857468B - SC-FDE (single carrier with frequency-domain equalization) system based on MAP (maximum a posterior) equalization and construction method of pilot frequency structure therein - Google Patents

Abstract

An SC-FDE system based on MAP equalization and a method for constructing a pilot structure in the system relate to an SC-FDE system and a method for constructing a pilot structure in the system. It solves the problem that the peak-to-average ratio of the transmitted signal of the OFDM system is high and is sensitive to frequency offset and phase noise. The mapping signal input end of the mapping unit is connected to the signal output end of the signal generating device, and the modulation signal output end of the modulator is connected to the signal input end of the channel; the signal output end of the channel is connected to the signal input end of the Fourier transform module; The transformed signal output end of the leaf transform module is connected with the transformed signal input end of the channel estimation and equalization unit; the signal output end of the channel estimation and equalization unit is connected with the signal input end of the inverse Fourier transform module; the demodulated signal of the demodulator The output end is connected to the demodulation signal input end of the decoder; the decoding signal output end of the decoder is connected to the decoding signal input end of the judging unit. It is used to eliminate multipath effects in single carrier systems.

Description

SC-FDE System Based on MAP Equalization and Construction Method of Pilot Structure in the System

technical field

The invention relates to a SC-FDE system and a pilot structure construction method in the system.

Background technique

The pilot structure of the communication system can also be called the frame structure, that is, the composition scheme of the data in transmission. As shown in Figure 1, the general pilot structure includes three parts, CP (Cyclic Prefixed), pilot and data. CP is a cyclic prefix, which is used to resist multipath delay, and usually copies the last segment of a frame of data to the front of the entire frame. The length of the CP should be determined according to the channel conditions, and it should usually be longer than the maximum multipath time, so as to ensure that the data behind the CP will not be affected by the intersymbol interference. The purpose of the pilot part is mainly for channel estimation and equalization at the receiving end. The equalization module at the receiving end has been proved by theory and practice that it can greatly improve the performance of the system, especially in the multipath fading channel environment. The data part is the actual content to be transmitted, and the CP and the pilot both play an auxiliary transmission role. However, since both CP and pilot are invalid data, in order to improve the transmission efficiency of the system, the CP and pilot are combined. At this time, the pilot will replace the role of CP. This solution has been maturely applied to many occasions. The pilot structure can be divided into two types, a serial frame structure and a block frame structure, in terms of shape.

The channel estimation and equalization methods at the receiving end of the system are very important to the performance of the single carrier system. Channel estimation can be roughly divided into blind estimation and non-blind estimation. Blind estimation does not depend on pilot transmission, which can save system resources and improve transmission efficiency. But blind estimation has the disadvantages of high complexity and limited precision. Channel estimation and equalization algorithms can solve the problem of multipath effects to a large extent, and different pilot structures are also an important factor affecting the performance of the frequency domain equalization system and communication efficiency. The general pilot structure design needs to rely on a specific channel estimation method or equalization method, because under different estimation and equalization algorithms, the change of pilot structure and the selection of pilot sequence will produce different effects.

Traditional single-carrier systems use time-domain equalization to eliminate multipath effects, but this is generally considered to be more complex. Orthogonal Frequency Division Multiplexing OFDM: The emergence of the Orthogonal Frequency Division Multiplexing system has solved the problem of high equalization complexity, but the OFDM system has the disadvantages of high peak-to-average ratio of transmitted signals and sensitivity to frequency offset and phase noise.

Contents of the invention

In order to solve the problems of high peak-to-average ratio of transmitted signals in OFDM system and sensitivity to frequency deviation and phase noise, the present invention proposes a SC-FDE system based on MAP equalization and a construction method of pilot frequency structure in the system.

SC-FDE system based on MAP equalization, the SC-FDE system is composed of a transmitter module, a channel mechanism and a receiver module; the transmitter module is composed of a mapping unit, a decoder and a modulator; the channel mechanism is composed of a channel ; The receiver module is composed of Fourier transform module, channel estimation and equalization degree unit, inverse Fourier transform module, demodulator, decoder and judgment unit; the mapping signal input terminal of the mapping unit and the signal The signal output terminal of the generating device is connected, the mapping signal output terminal of the mapping unit is connected with the mapping signal input terminal of the decoder, and the decoding signal output terminal of the decoder is connected with the decoding signal input terminal of the modulator; the modulator The modulated signal output end of the channel is connected with the signal input end of the channel; the signal output end of the channel is connected with the signal input end of the Fourier transform module; the transformation signal output end of the Fourier transform module is connected with the channel estimation and equalization unit The signal input end is connected; the signal output end of the channel estimation and equalization unit is connected to the signal input end of the inverse Fourier transform module; the transformed signal output end of the inverse Fourier transform module is connected to the transformed signal input of the demodulator The terminal is connected: the demodulation signal output terminal of the demodulator is connected with the demodulation signal input terminal of the decoder; the decoding signal output terminal of the decoder is connected with the decoding signal input terminal of the judging unit; The judgment signal output terminal of the judging unit is connected with the signal receiving port of the external signal receiving device.

Adopt the pilot structure construction method of above-mentioned SC-FDE system based on MAP equalization; Described construction method is finished by the following steps:

Step 1: Determine the multipath fading channel model, the fading channel model in the SC-FDE system is shown in formula 1;

Formula 1

The parameter N in formula 1 is the number of paths, the parameter ai and the parameter τi represent the amplitude attenuation coefficient and propagation delay of the i-th path respectively, and the parameter is the phase between the straight path and the transmitted path;

The parameter Tm represents the maximum multipath extension; That is, the maximum multipath time extension is the maximum value of the time delay of each path multiplied by the transmission rate; at the same time, the frame length T is determined according to the multipath channel model; the length of the frame length T must ensure that the channel state does not occur within the duration of one frame of data transmission Change;

Step 2: Extend T _m and frame length T when utilizing the maximum multi-path determined in step 1, and determine pilot length T _p and effective data length T _d in a frame of data of pilot structure in conjunction with MAP equalization mode; MAP equalization mode The relationship between the lower signal-to-noise ratio and the effective frame length is shown in formula 2;

${\mathrm{SNR}}_{\mathrm{MAP},\mathrm{eff}}=\frac{T-T_p}{T}\frac{d_{\min }^2}{4{\mathrm{\σ}}^2}{(1+\frac{L}{T_p-L+1})}^{-1}$ Formula 2

The parameter T _p in formula 2 is the pilot length, and the parameter Be the channel minimum distance, parameter L is the channel memory length, and parameter σ ² is the environmental noise power value; The length of described pilot length Tp is less than the length of frame length T; The Nash equilibrium equation in application game theory sees formula 3:

$J_i({T_p}^{*},T_d^{*})\&Greater\; Equal;J_i(T_{p_i},T_{d_i}),\∀i=\mathrm{1,2},\·\·\&Center\; Dot;,N.$ Formula 3

By deriving the Nash equilibrium equation, the ideal pilot length and data length obtained are respectively:

_Tp =T/4+ _Tm /2 and _Td =T/4- _Tm /2;

Step 3: According to the pilot length _Tp determined in step 2, generate a pilot whose pilot length is _Tp according to the formula of the Zadoff-Chu complex sequence x(n);

Step 4: The channel estimation and equalization unit 9 receives the data containing the pilot, and after extracting the pilot and effective data in the data, performs channel estimation according to the LS channel estimation algorithm, and outputs the estimated channel function said is an impact function;

Step 5: Obtain the impulse response function after LS channel estimation in step 4 Send this impulse response function to the MAP equalizer and use the relationship formula of the MAP equalizer for equalization processing;

Step 6: The data obtained after the MAP equalizer processing in step 5 is decoded and decoded by the decoder and decoder in the SC-FDE system to obtain the final valid data.

The SC-FDE system based on MAP equalization of the present invention has the advantages of low peak-to-average ratio of transmitted signals, insensitivity to frequency deviation and phase noise, low complexity, high precision and high transmission efficiency.

Description of drawings

FIG. 1 is a schematic diagram of an existing pilot structure;

FIG. 2 is a schematic diagram of the module structure of the MAP equalization-based SC-FDE system described in the present application.

Detailed ways

Specific embodiment 1: This embodiment is described in conjunction with FIG. 2 . The SC-FDE system based on MAP equalization described in this embodiment is composed of a transmitter module 1, a channel mechanism 2, and a receiver module 3; The transmitter module 1 is composed of a mapping unit 4, a decoder 5 and a modulator 6; the channel mechanism 2 is composed of a channel 7; the receiver module 3 is composed of a Fourier transform module 8, a channel estimation and equalization unit 9, An inverse Fourier transform module 10, a demodulator 11, a decoder 12 and a judgment unit 14 are composed; the mapping signal input end of the mapping unit 4 is connected with the signal output end of the signal generating device, and the mapping of the mapping unit 4 The signal output end is connected with the mapping signal input end of decoder 5, and the decoding signal output end of described decoder 5 is connected with the decoding signal input end of modulator 6; The modulated signal output end of described modulator 6 is connected with the signal of channel 7 The input end is connected; the signal output end of the channel 7 is connected with the signal input end of the Fourier transform module 8; the transformed signal output end of the Fourier transform module 8 is connected with the transformed signal input end of the channel estimation and equalization unit 9; The signal output end of the channel estimation and equalization unit 9 is connected to the signal input end of the inverse Fourier transform module 10; the transformed signal output end of the inverse Fourier transform module 10 is connected to the transformed signal input end of the demodulator 11 Connected: the demodulation signal output end of the demodulator 11 is connected with the demodulation signal input end of the decoder 12; the decoding signal output end of the decoder 12 is connected with the decoding signal input end of the judging unit 13 ; The judgment signal output terminal of the judging unit 13 is connected to the signal receiving port of the external signal receiving device.

In the transmitter module 1, firstly, the received signal data Sn is mapped and decoded, and then passed through the fading channel after modulation. Before the signal passing through the channel reaches the receiving end, noise Wn will be added. After receiving the data, the receiving end performs Fourier transform (FFT) first, and then performs channel estimation and equalization, in order to resist factors such as multipath interference in channel transmission. After equalization, it is an inverse Fourier transform (IFFT), and finally the desired data Rn can be obtained after demodulation and decoding. The SC-FDE system is the single carrier with frequency-domain equalization system, and the MAP equalization is the maximum a posterior equalization.

Specific embodiment two: this embodiment is described in conjunction with Fig. 2, and this embodiment is to adopt the pilot structure construction method of the SC-FDE system based on MAP equalization described in specific embodiment one; Described construction method is finished by the following steps:

Step 1: Determine the multipath fading channel model, the fading channel model in the SC-FDE system is shown in formula 1;

Formula 1

The parameter N in formula 1 is the number of paths, the parameter a _i and the parameter τ _i represent the amplitude attenuation coefficient and the propagation delay of the i-th path respectively, and the parameter is the phase between the straight path and the transmitted path;

The parameter Tm represents the maximum multipath extension; That is, the maximum multipath time extension is the maximum value of the time delay of each path multiplied by the transmission rate; at the same time, the frame length T is determined according to the multipath channel model; the length of the frame length T must ensure that the channel state does not occur within the duration of one frame of data transmission Change;

Step 2: Extend T _m and frame length T when utilizing the maximum multi-path determined in step 1, and determine pilot length T _p and effective data length T _d in a frame of data of pilot structure in conjunction with MAP equalization mode; MAP equalization mode The relationship between the lower signal-to-noise ratio and the effective frame length is shown in formula 2;

${\mathrm{SNR}}_{\mathrm{MAP},\mathrm{eff}}=\frac{T-T_p}{T}\frac{d_{\min }^2}{4{\mathrm{\σ}}^2}{(1+\frac{L}{T_p-L+1})}^{-1}$ Formula 2

The parameter T _p in formula 2 is the pilot length, and the parameter Be the channel minimum distance, parameter L is the channel memory length, and parameter σ ² is the environmental noise power value; The length of described pilot length Tp is less than the length of frame length T; The Nash equilibrium equation in application game theory sees formula 3:

$J_i({T_p}^{*},T_d^{*})\&Greater\; Equal;J_i(T_{p_i},T_{d_i}),\∀i=\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;,N.$ Formula 3

By deriving the Nash equilibrium equation, the ideal pilot length and data length obtained are respectively:

_Tp =T/4+ _Tm /2 and _Td =T/4- _Tm /2;

Step 3: According to the pilot length _Tp determined in step 2, generate a pilot whose pilot length is _Tp according to the formula of the Zadoff-Chu complex sequence x(n);

Step 4: The channel estimation and equalization unit 9 receives the data containing the pilot, and after extracting the pilot and effective data in the data, performs channel estimation according to the LS channel estimation algorithm, and outputs the estimated channel function said is an impact function;

Step 5: Obtain the impulse response function after LS channel estimation in step 4 Send this impulse response function to the MAP equalizer and use the relationship formula of the MAP equalizer for equalization processing;

Step 6: The data obtained after the MAP equalizer processing in step 5 is decoded and decoded by the decoder and decoder in the SC-FDE system to obtain the final valid data.

Specific embodiment three: the difference between this embodiment and specific embodiment two is that the pilot structure construction method based on the MAP equalized SC-FDE system, the formula of the Zadoff-Chu complex number sequence x (n) in step 3 is:

Formula 4

Wherein, n=1, 2, . . . , T _p , j is an imaginary number symbol. Other parameters and steps are the same as in the second embodiment.

Embodiment 4: The difference between this embodiment and Embodiment 2 is that the pilot structure construction method of the SC-FDE system based on MAP equalization, the formula of the LS channel estimation algorithm in step 4 is:

${\hat{h}}_{\mathrm{LS}}=x^{-1}\stackrel{\‾}{Y}={\left[(x_k/Y_k)\right]}^T,(k=\mathrm{0,1},...,N-1)$ Formula 5

Among them, the parameter is the impulse function output by channel estimation, the parameter X is the estimated value obtained after interpolating the known pilot data, and the parameter Y is the data obtained by Fourier transform in the receiving end module 3 . Other parameters and steps are the same as in the second embodiment.

Specific embodiment five: the difference between this embodiment and specific embodiment two is that the pilot structure construction method of the SC-FDE system based on MAP equalization, the relational expression of the MAP equalizer in step five is

$\underset{\‾}{\overset{^}{S}}\arg \underset{\underset{\‾}{u}}{\min }\left(\right||\underset{\‾}{x}-\mathrm{\τ}\left(\underset{\‾}{h}\right)\underset{\‾}{u}||:\underset{\‾}{u}\∈A^{T+L-1})$ Formula 6

Parameters in Equation 6 is the estimated value of the symbol transposition to be sought, the parameter argmin is the variable u value that minimizes the objective function, the parameter x is the input signal of the equalizer, the parameter h is the channel impulse function, the parameter τ is the Toeplitz matrix, and the parameter A is the corresponding modulation The data set of the mode uses BPSK modulation A={+1,-1}. Other parameters and steps are the same as in the second embodiment.

Claims (4)

1. The pilot structure construction method based on the MAP equalized SC-FDE system; The system based on the described construction method is an SC-FDE system based on MAP equalization, and the SC-FDE system consists of a transmitter module (1), a channel mechanism ( 2) and receiver module (3); said transmitter module (1) is made up of mapping unit (4), decoder (5) and modulator (6); said channel mechanism (2) consists of channel ( 7) constitute; the receiver module (3) is composed of Fourier transform module (8), channel estimation and equalization degree unit (9), inverse Fourier transform module (10), demodulator (11), translator Coder (12) and judging unit (14); The mapping signal input end of described mapping unit (4) is connected with the signal output end of signal generating device, and the mapping signal output end of described mapping unit (4) is connected with decoder The mapping signal input end of (5) is connected, and the decoding signal output end of described decoder (5) is connected with the decoding signal input end of modulator (6); The modulation signal output end of described modulator (6) is connected with channel ( 7) is connected to the signal input end; the signal output end of the channel (7) is connected to the signal input end of the Fourier transform module (8); the transformed signal output end of the Fourier transform module (8) is connected to the channel estimation and The transformed signal input end of the equalization unit (9) is connected; the signal output end of the channel estimation and equalization unit (9) is connected with the signal input end of the inverse Fourier transform module (10); the inverse Fourier transform module (10) conversion signal output end is connected with the conversion signal input end of demodulator (11): the demodulation signal output end of described demodulator (11) is connected with the demodulation signal input end of decoder (12) The decoding signal output end of the decoder (12) is connected with the decoding signal input end of the judgment unit (13); the judgment signal output end of the judgment unit (13) is connected with the signal receiving port of the external signal receiving device connected; It is characterized in that the construction method is completed by the following steps: Step 1: Determine the multipath fading channel model, the fading channel model in the SC-FDE system is shown in formula 1; Formula 1 The parameter N in formula 1 is the number of paths, the parameter a _i and the parameter τ _i represent the amplitude attenuation coefficient and the propagation delay of the i-th path respectively, and the parameter is the phase between the straight path and the transmitted path; The parameter T _m represents the extension during the maximum multipath; That is, the maximum multipath time extension is the maximum value of the time delay of each path multiplied by the transmission rate; at the same time, the frame length T is determined according to the multipath channel model; the length of the frame length T must ensure that the channel state does not occur within the duration of one frame of data transmission Change; Step 2: Extend T _m and frame length T when utilizing the maximum multi-path determined in step 1, and determine pilot length T _p and effective data length T _d in a frame of data of pilot structure in conjunction with MAP equalization mode; MAP equalization mode The relationship between the lower signal-to-noise ratio and the effective frame length is shown in formula 2; Formula 2 The parameter T _p in formula 2 is the pilot length, and the parameter Be the channel minimum distance, parameter L is the channel memory length, and parameter σ ² is the environmental noise power value; The length of described pilot length Tp is less than the length of frame length T; The Nash equilibrium equation in application game theory sees formula 3: Formula 3 By deriving the Nash equilibrium equation, the ideal pilot length and data length obtained are respectively: _Tp =T/4+ _Tm /2 and _Td =T/4- _Tm /2; Step 3: According to the pilot length _Tp determined in step 2, generate a pilot whose pilot length is _Tp according to the formula of the Zadoff-Chu complex sequence x(n); Step 4: The channel estimation and equalization unit (9) receives the data containing the pilot, and after extracting the pilot and effective data in the data, performs channel estimation according to the LS channel estimation algorithm, and outputs the estimated channel function said is an impact function; Step 5: Obtain the impact function after LS channel estimation in step 4 Send this impact function to the MAP equalizer and use the relationship formula of the MAP equalizer for equalization processing; Step 6: The data obtained after the MAP equalizer processing in step 5 is decoded and decoded by the decoder and decoder in the SC-FDE system to obtain the final valid data. 2. the pilot structure construction method based on the SC-FDE system of MAP equalization according to claim 1, it is characterized in that the formula of the Zadoff-Chu complex sequence x (n) in step 3 is: Formula 4 Wherein, n=1,2,...,T _p , and j is an imaginary number symbol. 3. the pilot structure construction method based on the MAP equalized SC-FDE system according to claim 1, it is characterized in that the formula of the LS channel estimation algorithm in the step 4 is: Formula 5 Among them, the parameter is the impact function output by channel estimation, the parameter X is the estimated value obtained after interpolating the known pilot data, and the parameter Y is the data obtained by Fourier transform in the receiving end module (3). 4. the pilot structure construction method based on the SC-FDE system of MAP equalization according to claim 1, it is characterized in that the relational expression of the MAP equalizer in step 5 is Formula 6 Parameters in Equation 6 is the estimated value of symbol transposition to be sought, the parameter argmin is the variable u value that minimizes the objective function, the parameter x is the input signal of the equalizer, the parameter h is the channel impact function, the parameter τ is the Toeplitz matrix, and the parameter A is the corresponding modulation mode The data set of , using BPSK modulation Α={+1,-1}.