CN101141185A - Multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving - Google Patents

Abstract

The multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving is a multi-user frequency division multiple access transmission method in the field of wireless communication, and belongs to the technical field of high-speed wireless transmission. The transmission method is divided into a transmission scheme and a reception scheme. In the sending scheme, OFDMA is performed among different users, and a sending method of interleaving in the frequency domain is adopted within each user. In the receiving scheme, an iterative detection or iterative detection decoding receiver is used. Specifically, when the sender uses error control coding, the receiver uses iterative detection and decoding; when the sender does not use error control coding, the receiver uses iterative detection. The implementation of this transmission scheme includes the traditional single carrier frequency division multiple access wireless transmission scheme, but the system bit error rate performance is better than the traditional single carrier frequency division multiple access transmission scheme.

Description

Multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving

Technical Field

The present invention relates to a broadband wireless communication transmission scheme for high-speed data transmission, and more particularly, to a multi-user frequency division multiple access transmission scheme.

Background

The Orthogonal Frequency Division Multiplexing (OFDM) transmission scheme solves the problem of frequency selective fading during broadband wireless transmission, can adopt a receiver with lower complexity at a receiving end, and is suitable for downlink transmission. The DFT-spread OFDM (DFT-S-OFDM), also known as single carrier frequency division multiple access (SC-FDMA), has the advantages of low peak-to-average ratio of transmitted signals, flexible multi-user subcarrier allocation, low complexity frequency domain at the receiving end, and the like, and is suitable for uplink transmission in wireless communication. In International organization for standardization 3 _gpp In the LTE release (e), the OFDM system is adopted as a downlink transmission scheme, and SC-FDMA is adopted as an uplink transmission scheme.

OFDM transmission does not achieve ideal performance in both uncoded systems and high rate error control coded systems due to the lack of frequency diversity. Conventional SC-FDMA also fails to achieve performance close to the matched filter bound in a codeless system. In future wireless communication systems, reliable transmission of information under error control coding conditions of different rates and different code rates needs to be supported. The iterative receiving method is a technology which is more and more concerned and emphasized in recent years, and by performing iteration between detection and decoding of a receiving end or performing iteration between detectors, compared with a traditional non-iterative receiver, the error rate performance of a system is greatly improved.

Aiming at the transmission of information transmission of various rate codes including a coding-free system in a broadband wireless environment, an efficient transmission scheme adopting an iterative receiving method is designed, and the method has important significance for the application realization of a broadband wireless communication system.

Disclosure of Invention

The technical problem is as follows: the invention aims to provide a multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving, which not only can realize flexible wireless resource allocation among multiple users, but also is used for improving the error rate performance of broadband wireless communication by an iterative detection method.

The technical scheme is as follows: the invention discloses a multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving, which not only supports an error control coding system, but also supports an error-free control coding system, and symbols after baseband mapping in a transmission scheme carry out multi-user frequency division multiple access modulation according to the following steps:

1.1 By N) signals for each user _b For length division into blocks, serial-to-parallel conversion is performed,

1.2 N) the serial-to-parallel converted signal _b The fast fourier transform of the point(s),

1.3 The resulting frequency domain signals are interleaved,

1.4 Map the interleaved signals of each user to N in a centralized or distributed manner _I On the basis of the number of sub-carriers,

1.5 Subjecting the signal obtained in step 1.4) to N _I Performing inverse fast Fourier transform on the points, and inserting cyclic prefix to obtain a baseband sending signal;

wherein N is _b For each user's occupied sub-carrier, N _I Is the total number of subcarriers in the system.

When the error-free control coding is adopted by the transmitting end, the receiver comprises the following steps:

2.1 Taking the received signal as a block unit, removing the cyclic prefix CP, then performing fast Fourier transform, and extracting the subcarrier signal occupied by the current user to obtain the length N of the current user _b The frequency domain of (a) receives a vector of signals,

2.2 ) reconstruct the mean of each signal

And the mean variance of all signalsInitialisation in the initial detection

2.3 Carry out N on a vector formed by signal means _b Point fast Fourier transform to obtain the signal mean value of the frequency domain, and then interweaving to generate the interweaved frequency domain signal

2.4 Performs interference cancellation at each carrier point in the frequency domain, performs frequency domain equalization on the signals obtained by the interference cancellation,

2.5 ) deinterleaves the frequency domain equalized signal,

2.6 N) the deinterleaved signal vector _b Inverse fast Fourier transform of the points to obtain a signal estimate

Equivalent channel coefficient

Wherein

h _k ^f Denotes the frequency domain channel parameter, σ, of the k-th carrier _z ² Representing an additive white gaussian noise variance,

2.7 Soft demodulation is performed based on the signal estimation value, the equivalent channel coefficient and the equivalent interference noise variance,

2.8 If the iteration is not finished, the step 2.2) is returned; and if the iteration is finished, the demodulated result is judged to obtain a receiving result.

When the transmitting end employs error control coding, the receiver comprises the steps of:

3.1 The received signal is divided into blocks, the cyclic prefix CP is removed, and then FFT is performed, so that the received signal is processed

Extracting the sub-carrier signal occupied by the current user to obtain the length N of the current user _b The frequency domain of (a) receives a vector of signals,

3.2 Based on the detectionOr the decoded result reconstructs the mean value of each signal

And the mean variance of all signals

Initialisation in primary detection

3.3 Carry out N on a vector formed by signal means _b Point fast Fourier transform to obtain the signal mean value of the frequency domain, and then interweaving to generate the interweaved frequency domain signal

3.4 Performs interference cancellation at each carrier point in the frequency domain, performs frequency domain equalization on signals obtained by the interference cancellation,

3.5 ) deinterleaves the frequency domain equalized signal,

3.6 N) the deinterleaved signal vector _b Inverse fast Fourier transform of the points to obtain a signal estimate

Equivalent channel coefficientWhereinh _k ^f Frequency representing the k carrier

Domain channel parameter, σ _z ² Representing an additive white gaussian noise variance,

3.7 Based on the signal estimation value, the equivalent channel coefficient and the equivalent interference noise variance, soft-demodulating, sending the result obtained by soft-demodulation to a soft-input and soft-output decoder,

3.8 The decoder performs soft-input soft-output decoding,

3.9 If the iteration is not finished, the step 3.2) is returned; and if the iteration is finished, the demodulated result is judged to obtain a receiving result.

Has the beneficial effects that: the invention provides a single-carrier frequency division multiple access transmitting and iteration receiving scheme based on frequency domain interleaving, which can support both error control coding and error-free control coding. And the wireless resource management can be realized through flexible subcarrier allocation among multiple users. The single user can obtain better error rate performance by adopting a frequency domain interleaving sending method through an iterative detection/iterative detection decoding receiving method. The realization structure compatible with the traditional single carrier frequency division multiple access is kept, and the frequency domain interleaving or the traditional single carrier frequency division multiple access transmission mode can be selected according to the requirements of the actual system. The frequency domain interference cancellation detection realized by the receiving end in the frequency domain has lower realization complexity.

Drawings

Fig. 1 is a transmission structure diagram of a single carrier frequency division multiple access wireless transmission scheme based on frequency domain interleaving.

Fig. 2 is a block diagram of an iterative reception of a single carrier frequency division multiple access wireless transmission scheme based on frequency domain interleaving.

Fig. 3 is a diagram of a frequency domain interference cancellation detection architecture.

The specific implementation mode is as follows:

the principle of multi-user FDMA transmission is to sum the total N _I N in subcarriers _b N assigned to each user _b One symbol is transmitted. Fig. 1 shows a transmission scheme of multi-user FDMA transmission based on frequency domain interleaving proposed by the present invention. The transmission information bit is processed by error control coding, bit interleaving and baseband symbol mapping to obtain baseband mapped symbol, and then processed by FDMA modulation and interpolation of frequency domain interleavingAnd obtaining a sending signal after entering a Cyclic Prefix (CP). The FDMA modulation realization process of frequency domain interweaving comprises the following steps: firstly, the signal is according to the length N _b Dividing into blocks, serial-to-parallel converting, and performing N on the signal vector _b Fast Fourier Transform (FFT) of the points, then the frequency domain signal obtained by the transform is interleaved once according to a predetermined interleaving pattern, and then N is processed according to a centralized or distributed mode _b Frequency domain signal mapping of points to N _I On each subcarrier, 0 is inserted into the rest subcarriers, and finally N is inserted _I Dimension Signal vector as N _I And point Inverse Fast Fourier Transform (IFFT) and parallel-serial transformation are carried out to complete FDMA modulation based on frequency domain interleaving. If the error control coding module and the interleaving module are omitted in fig. 1, the transmission scheme is degenerated to error-free control coding.

Figure 2 shows a reception scheme for multi-user FDMA transmission based on frequency domain interleaving. At the receiving end, CP is firstly removed, and N is carried out after serial-parallel conversion _I And point FFT, frequency domain interference cancellation equalization, and soft demodulation to obtain the likelihood ratio of the bit. If the transmission scheme adopts error control coding, the result after soft demodulation is interleaved and then sent into a decoder, the result obtained by the decoder is used for reconstructing symbol statistics (including mean value and variance) after interleaving, and then is fed back to frequency domain interference cancellation equalization to carry out iterative detection decoding; if the transmission scheme does not adopt error control coding, the result after soft demodulation is directly used for reconstructing symbol statistics and carrying out iterative detection with frequency domain interference cancellation balance. Error control coding in the transmitter, soft demodulation in the receiver, symbol statistic reconstruction, decoding and the like are used as common modules in the communication system, which are discussed in various documents, and are not described in this specification. In the following, we will describe FDMA modulation and frequency domain interference cancellation equalization algorithm in detail.

1. Multi-user FDMA modulation based on frequency domain interleaving

First, we assume that the total number of subcarriers in the system is N _I The number of subcarriers occupied by each user is N _b ， N _b ≤N _I . FDMA modulation comprises the steps of

1) Serial-parallel conversion: the symbol after the baseband mapping of a certain user is according to N _b Is divided into blocks for a unit.

2)N _b Point fast fourier transform.

3) Interweaving: and carrying out interweaving according to a preset interweaving pattern. The interleaving pattern may be generated by any method of pseudo-random interleaving.

4) Subcarrier mapping: n after interweaving _b The symbols are mapped to N in a centralized or distributed manner _I And (4) a subcarrier. Centralized mapping finger N _b Mapping of symbols to N _I N consecutive in sub-carriers _b 0 is inserted into each subcarrier and other subcarriers; distributed mapping refers to N _b Equispaced mapping of symbols to N _I N in sub-carriers _b 0 is inserted into each subcarrier and other subcarriers;

5)N _I point inverse fast fourier transform.

6) And (4) parallel-to-serial conversion.

2. Frequency domain interference cancellation detection

Suppose that the k sub-carrier channel parameter occupied by the current user is h _k ^f The variance of the noise is σ _z ² The channel parameters and the noise variance are generally obtained by a channel estimation method, and are not described in the present invention. Fig. 3 shows a schematic diagram of frequency domain interference cancellation detection, which includes the following specific steps:

1) Subcarrier extraction: the current user N is mapped according to the subcarrier mapping mode determined by the sending end _b Received signal of point from N _I Extracting the sub-carrier to obtain the frequency domain receiving signal y of the current user ₀ ，…，y _Nb-1 。

2) N of the reconstructed signal _b Point FFT and interleaving: mean value of the reconstructed signal

Carry out N _b The FFT point interweaves according to the interweaving pattern determined by the sending end to obtain an interweaved frequency domain reconstruction signal,

calculating the mean variance of the signal

v _i The reconstructed variance for the ith signal.

3) Frequency domain interference cancellation: for each subcarrier, according to the formula

And carrying out frequency domain interference cancellation.

4) Frequency domain equalization: for each subcarrier, calculating equalized frequency domain symbol

Wherein b is _k According to the formula

Is calculated, whereinIs the mean variance of the reconstructed signal.

5) And (3) reverse interleaving: and performing reverse interleaving on the signals after the frequency domain equalization according to the interleaving pattern determined by the sending end.

6)N _b Point IFFT: do N to the inversely interleaved signal _b And after point IFFT, obtaining a signal after frequency domain interference cancellation equalization.

7) Equivalent channel response ρ and equivalent noise μ: calculating out

Wherein

The equivalent noise variance is μ = ρ (1- ρ).

The invention provides a single carrier frequency division multiple access transmission technical scheme based on frequency domain interleaving, which meets the requirements of reliable multi-user and effective wireless transmission, and the specific implementation mode is as follows:

(1) Determining system parameters: under the given system bandwidth, according to the general rule designed by the orthogonal frequency division multiplexing system, the total subcarrier number N adopted in the system is determined according to the Doppler frequency offset and the implementation complexity _I And the number of subcarriers N per user _b (ii) a Determining the error control coding mode adopted by the system; determining the iteration times of an iterative receiver according to the requirements of the system on the error rate performance and the complexity; and determining an interleaving pattern and a subcarrier mapping mode.

(2) The sending method comprises the following steps: the transmitting end generates a transmitting baseband signal according to the technical scheme and the method shown in fig. 1, and transmits the transmitting baseband signal after carrier modulation. The method comprises the following specific steps:

and (2.1) coding the bits to be transmitted according to the determined error control coding mode.

And (2.2) carrying out bit interleaving on the coded bits. If the system adopts a no-coding system, the steps (2.1) and (2.2) are omitted.

And (2.3) mapping the interleaved coded bits to baseband symbols.

(2.4) mapping the symbols after baseband mapping according to the length N _b And performing serial-to-parallel conversion.

(2.5) performing N on the serial-to-parallel converted symbol _b And (6) point FFT.

And (2.6) interleaving the frequency domain symbols after the FFT.

And (2.7) carrying out subcarrier mapping in a centralized or distributed mode.

(2.8)N _I A point IFFT.

And (2.9) parallel-to-serial conversion.

And (2.10) inserting a cycle to obtain a transmission baseband signal.

(3) Receiving an overall scheme: when the transmitting end adopts error control coding, the receiver adopts a mode of iterative detection decoding. When the transmitting end does not adopt error control coding, the receiver adopts an iteration detection receiving mode. The concrete steps are shown in figure 2

(3.1) at the receiving end, CP is removed first, and N is performed _I And (6) point FFT.

And (3.2) carrying out soft-input soft-output frequency domain interference cancellation equalization.

And (3.3) carrying out likelihood ratio calculation according to the result of the frequency domain interference cancellation equalization in a symbol mapping mode.

And (3.4) if the error control coding is adopted by the sending end, the likelihood ratios obtained by detection are transmitted to a decoder for decoding after being inversely interleaved.

And (3.5) if the iterative detection decoding is not finished, using the decoding result to reconstruct the symbol statistic, feeding back to the detector, and returning to the step (3.2). And if the iteration is finished, judging the decoding result and taking the decoding result as the result of the receiver.

(4) And (3) frequency domain interference cancellation detection: the frequency domain interference cancellation detection calculates the signal estimation after the frequency domain interference cancellation detection, the equivalent channel coefficient rho and the equivalent noise variance mu according to the frequency domain receiving signal and the reconstructed symbol statistic, and the specific steps are as follows:

(4.1) subcarrier extraction: and extracting the received signals of the sub-carriers occupied by the current user according to the sub-carrier mapping mode determined by the sending end.

(4.2) reconstructing N of the signal _b Point FFT and interleaving: mean of the reconstructed signal

Carry out N _b Point FFT, interleaving according to the interleaving pattern determined by the sending end to obtain the interleaved frequency domain reconstruction signal

(4.3) frequency domain interference cancellation: for each subcarrier, according to the formula

And carrying out frequency domain interference cancellation.

(4.4) frequency domain equalization: for each subcarrier, calculating equalized frequency domain symbol

Wherein b is _k According to the formulaIs calculated, wherein

Is the mean variance of the reconstructed signal.

(4.5) reverse-interlacing: and performing reverse interleaving on the signals after the frequency domain equalization according to the interleaving pattern determined by the sending end.

(4.6)N _b Point IFFT: do N to the inversely interleaved signal _b After point IFFT, a signal with balanced frequency domain interference cancellation is obtained.

(4.7) equivalent channel response ρ and equivalent noise: calculating out

In whichThe equivalent noise variance is μ = ρ (1- ρ).

Claims (3)

1. A multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving, characterized in that the wireless transmission method both supports an error control coding system and an error-free control coding system, and the baseband mapping in the transmission scheme Symbols are modulated by multi-user frequency division multiple access according to the following steps: 1.1) divide the signal of each user into blocks according to the length of N _b , and perform serial-to-parallel conversion, 1.2) carry out the fast Fourier transform of N _b points to the signal after the serial-to-parallel transformation, 1.3) Interleave the obtained frequency domain signal, 1.4) Map the signal of each user after interleaving to _N1 subcarriers in a centralized or distributed manner, 1.5) the signal obtained in step 1.4) is carried out to the inverse fast Fourier transform of the _N1 point, and the baseband transmission signal is obtained after inserting the cyclic prefix; Among them, N _b is the subcarrier occupied by each user, and N _I is the total number of subcarriers in the system. 2. the multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving according to claim 1, is characterized in that when sending end adopts error-free control coding, receiver comprises the following steps: 2.1) Take the received signal as a unit, remove the cyclic prefix CP and perform fast Fourier transform, extract the subcarrier signal occupied by the current user, and obtain the frequency-domain received signal vector of the current user length _Nb , 2.2) Reconstruct the mean of each signal

and the average variance of all signals

, initialized in the first detection ${\stackrel{\‾}{\mathrm{the\; s}}}_i=0,$ $\stackrel{\‾}{v}=1,$ 2.3) Perform N _b- point fast Fourier transform on the vector formed by the mean value of the signal, obtain the mean value of the signal in the frequency domain, and then interleave to generate the interleaved frequency domain signal 2.4) Interference cancellation is performed at each carrier point in the frequency domain, and the signal obtained by interference cancellation is subjected to frequency domain equalization, 2.5) de-interleaving the frequency-domain equalized signal, 2.6) Carry out inverse fast Fourier transform of N _b points on the deinterleaved signal vector to obtain the estimated signal value

Equivalent Channel Coefficient $\mathrm{\ρ}=\frac{1}{N_b}\underset{k=0}{\overset{N_b-1}{\mathrm{\Σ}}}{d}_k,$ in $d_k=\frac{{\left|h_k^f\right|}^2}{({\left|h_k^f\right|}^2\stackrel{\‾}{v}+{\mathrm{\σ}}_z^2)}$ , h _k ^f represents the frequency-domain channel parameter of the kth carrier, σ _z ² represents the variance of additive white Gaussian noise, 2.7) Perform soft demodulation according to the estimated signal value, equivalent channel coefficient and equal interference noise variance, 2.8) If the iteration is not over, return to step 2.2); if the iteration is over, hard judge the demodulated result to obtain the receiving result. 3. the multi-user single carrier frequency division multiple access wireless transmission method based on frequency domain interleaving according to claim 1, is characterized in that when sending end adopts error control coding, receiver comprises the following steps: 3.1) Take the received signal as a unit, remove the cyclic prefix CP, and perform fast Fourier transform FFT, extract the subcarrier signal occupied by the current user, and obtain the frequency-domain received signal vector whose length is N _b for the current user, 3.2) Reconstruct the mean value of each signal according to the result of detection or decoding

and the average variance of all signals

Initialize on first detection ${\stackrel{\‾}{\mathrm{the\; s}}}_i=0,$ $\stackrel{\‾}{v}=1,$ 3.3) Perform N _b- point fast Fourier transform on the vector formed by the signal mean value, obtain the signal mean value in the frequency domain and then interleave to generate the interleaved frequency domain signal

3.4) Interference cancellation is performed at each carrier point in the frequency domain, and the signal obtained by interference cancellation is subjected to frequency domain equalization, 3.5) de-interleaving the frequency-domain equalized signal, 3.6) Carry out the inverse fast Fourier transform of N _b points to the signal vector after deinterleaving, and obtain the estimated value of the signal

Equivalent Channel Coefficient $\mathrm{\ρ}=\frac{1}{N_b}\underset{k=0}{\overset{N_b-1}{\mathrm{\Σ}}}{d}_k,$ in $d_k=\frac{{\left|h_k^f\right|}^2}{({\left|h_k^f\right|}^2\stackrel{\‾}{v}+{\mathrm{\σ}}_z^2)}$ , h _k ^f represents the frequency-domain channel parameter of the kth carrier, σ _z ² represents the variance of additive white Gaussian noise, 3.7) Perform soft demodulation according to the estimated signal value, equivalent channel coefficient and equivalent interference noise variance, and send the result obtained by soft demodulation to a decoder with soft input and soft output, 3.8) The decoder performs soft input and soft output decoding, 3.9) If the iteration is not over, return to step 3.2); if the iteration is over, hard judge the demodulated result to obtain the receiving result.

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