CN101321144B

CN101321144B - Multi-input multi-output orthogonal frequency division multiplexing system transmission method and transceiver

Info

Publication number: CN101321144B
Application number: CN2007101106342A
Authority: CN
Inventors: 王衍文; 郝东来; 张力
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2007-06-06
Filing date: 2007-06-06
Publication date: 2011-05-11
Anticipated expiration: 2027-06-06
Also published as: CN101321144A

Abstract

This invention discloses a transmission method of orthogonal frequency division multiplexing with multiple inputs and outputs, including: (1) an emitting end processes space-frequency coding to emitted data and processes space-time coding to the data, then processes serial/parallel transformation, inverse fast Fourier transform algorithmic transformation, adding cyclic prefix, parallel/serial transformation, then emits the data; (2) after receiving the data received from the emitting end, a receiving end respectively processes removing cyclic prefix, serial/parallel transformation, inverse fast Fourier transform algorithmic transformation and parallel/serial transformation to the received data in two symbol periods, then processes space-time decoding to the data, at last processes data combination. This invention further discloses a MIMO OFDM system coding emitter and a receiver, and an emitting method and a receiving method. This invention obtains an effective transreceiver suitable for adopting the MIMO OFDM system of space-time frequency coding and corresponding transmission method through adjusting a transreceiver mechanism under the condition of not increasing the transreceiver complexity.

Description

Transmission method of multi-input multi-output orthogonal frequency division multiplexing system and transceiver

Technical Field

The present invention relates to transceiver technology in the field of mobile communications, and in particular, to a transmission method for an MIMO (Multiple Input Multiple Output) OFDM (orthogonal frequency Division Multiplexing) system and a transceiver.

Background

MIMO systems can provide both diversity and multiplexing gains, and most existing MIMO techniques were originally designed to achieve maximum diversity or multiplexing gains. For example, Space-Time Codes (STC) -including Space-Time Block Code (STBC), Space-Frequency Code (SFBC), and Space-Time Trellis Code (STTC) -are designed to obtain maximum diversity gain; and the design of the Layered Space-Time code (BLAST) and the Vertical Layered Space-Time code (V-BLAST) is to obtain the maximum multiplexing gain.

A schematic diagram of a prior art OFDM system is shown in fig. 1, wherein a transmitting end includes a serial/parallel conversion unit, an IFFT (Inverse Fast Fourier Transform Algorithm) unit, a Cyclic Prefix (CP) adding unit, and a parallel/serial conversion unit; the receiving end includes a serial/parallel conversion unit, a CP removing unit, an FFT unit, and a parallel/serial conversion unit. Here, an OFDM system with N subcarriers is taken as an example. Dividing the information sequence S into data blocks of length N, the nth data block S (N) ([ S (nN), S (nN +1), …, S (nN + N-1)]^TWherein T is the period; then OFDM modulation is carried out, vector S (N) of dimension N multiplied by IFFT matrix F^HThis constitutes one OFDM data block. The frequency selective fading channel is represented as h: [ h (0), …, h (L) ] by an L-order FIR (Finite impulse response) filter]^TWhere h (l) denotes the l-th tap coefficient. In order to eliminate inter-block Interference (IBI) and inter-symbol Interference (ISI) caused by channel delay spread, a length L is added before each OFDM data block_CPL ≦ CP, and is removed in the corresponding received data block. This allows the FIR channel vector H to be represented by an N × N circulant matrix H with the element in the p-th row and q-th column of H being [ H ]]_p，qH ((P-q) mod P). The circulant matrix has a particular property: right multiplying the circulant matrix by F^HAfter left-multiplying by F, it can be converted to a diagonal matrix, given by:

D:＝diag(H(0)，…，H(N-1))＝FHF^H (1)

wherein,

k 0-N-1 corresponds to the frequency response of the channel on the kth subcarrier. Let y (N) ═ y (nN), …, y (nN + N-1)]^TRepresents an N × 1-dimensional received data block after FFT (fast fourier Transform Algorithm) at the receiving end,

representing an additive white Gaussian noise vector of dimension Nx 1 with a correlation matrix of

Wherein N is₀Is the power spectral density of the noise. The OFDM demodulated signal can be expressed as:

y(n)=DS(n)+η(n) (2)

wherein,

since the FFT matrix is unitary, η (n) is still white noise.

In the space-time processing, STBC coding is mostly adopted, and in the frequency domain, SFBC coding is adopted, and the mathematical principles of the two are the same. In the prior art, space frequency coding SFBC is adopted for design convenience. However, one significant characteristic of SFBC is that signals transmitted by each antenna are orthogonal, that is, a signal transmission matrix satisfies: GG (GG)^T＝||s₁|²+|s₂|²+…+|s_n|²I, where I is a unit matrix, S₁，S₂…S_nAre the signal points employed in the transmit matrix G. When the SFBC satisfies the orthogonality requirement, not only the maximum diversity gain can be guaranteed, but also the decoding complexity can be reduced. However, the introduction of the orthogonal relationship also brings the following problems: firstly, the coding gain of the SFBC is only related to the structure of the adopted signal constellation diagram, and no good coding gain optimization method exists at present; secondly, if 2 is adopted^bConstellation of signal points, SFBC band utilization can be achieved only when the transmitting end has two antennas_bit/(. s.Hz), the band utilization is the highest when the number of antennas increasesMost of all, 3/4 being the maximum. SFBC trades off coding gain and fractional band utilization, as it were, for maximum diversity gain and low coding complexity. Thirdly, the OFDM with cyclic prefix converts a frequency selective fading channel into N parallel flat fading sub-channels, but it is difficult to effectively suppress inter-group interference and multi-user interference.

Disclosure of Invention

The invention provides a transmission method and a transceiver of a multi-input multi-output orthogonal frequency division multiplexing system, which can obtain a high-efficiency transceiver suitable for a MIMO OFDM system adopting space-time-frequency coding and a corresponding transmission method by adjusting the structure of the transceiver under the condition of not increasing the complexity of the transceiver.

To solve the above technical problem, the present invention first provides a transmission method for a mimo-ofdm system, comprising the steps of:

(1) the transmitting terminal firstly carries out space-frequency coding processing on transmitted data, then carries out space-time coding processing on the processed data, then carries out serial/parallel transformation, inverse fast Fourier transform algorithm transformation, cyclic prefix adding and parallel/serial transformation processing, and then transmits the data;

(2) after receiving the data sent by the transmitting end, the receiving end respectively carries out cyclic prefix removal, serial/parallel conversion, fast Fourier transform algorithm conversion and parallel/serial conversion processing on the received data in two continuous symbol periods, then carries out space-time-space-frequency decoding processing on the processed data, and finally carries out data combination.

The method of the invention, wherein the step (1) comprises the following steps:

(1.1) when transmitting data, the transmitting terminal firstly performs space-frequency coding processing on an input signal;

(1.2) then the transmitting terminal carries out space-time coding processing on the processed data;

(1.3) transforming the space-time coded data into parallel data;

(1.4) after subcarrier distribution is carried out on the parallel data, inverse fast Fourier transform algorithm transformation is carried out;

(1.5) adding a cyclic prefix to the data which is subjected to the inverse fast Fourier transform algorithm transformation;

and (1.6) converting the converted data into serial data and then transmitting the serial data.

The method of the invention, wherein the step (2) comprises the following steps:

(2.1) the receiving end receives the data and removes the cyclic prefix of the received data;

(2.2) converting the data without the cyclic prefix into parallel data, and then performing fast Fourier transform algorithm conversion;

(2.3) converting the parallel data into serial data, and performing space-time space-frequency decoding on the obtained serial data;

and (2.4) after the space-time space-frequency decoding processing is carried out on the data, merging the decoded data and outputting the merged data to subsequent processing equipment.

The invention also provides a MIMO OFDM system coding transmitter, which comprises a serial/parallel conversion unit, an inverse fast Fourier transform algorithm unit, a cyclic prefix adding unit, a parallel/serial conversion unit, a transmitting antenna, a space-frequency coding unit and a space-time coding unit, wherein the space-frequency coding unit, the space-time coding unit, the serial/parallel conversion unit, the inverse fast Fourier transform algorithm unit, the cyclic prefix adding unit, the parallel/serial conversion unit and the transmitting antenna are connected in sequence; the space-frequency coding unit is used for carrying out space-frequency coding processing on the transmitted data, and the space-time coding unit is used for carrying out space-time coding processing on the data after the space-frequency coding processing and then sending the data to the serial/parallel conversion unit for subsequent processing.

The invention also provides a MIMO OFDM system code receiver, which comprises a receiving antenna, a cyclic prefix removing unit, a serial/parallel conversion unit, a fast Fourier transform algorithm unit, a parallel/serial conversion unit and a space-time space-frequency decoding unit, wherein the receiving antenna, the cyclic prefix removing unit, the serial/parallel conversion unit, the fast Fourier transform algorithm unit, the parallel/serial conversion unit and the space-time space-frequency decoding unit are connected in sequence; and the space-time space-frequency decoding unit is used for respectively carrying out space-time space-frequency decoding processing on the data sent by the parallel/serial conversion unit in two continuous symbol periods.

The invention also provides a transmitting method of the MIMO OFDM system, which comprises the following steps:

(6.1) when transmitting data, the transmitting end firstly carries out space-frequency coding processing on an input signal;

(6.2) then the transmitting terminal performs space-time coding processing on the processed data;

(6.3) transforming the space-time coded data into parallel data;

(6.4) after subcarrier distribution is carried out on the parallel data, inverse fast Fourier transform algorithm transformation is carried out;

(6.5) adding a cyclic prefix to the data which is subjected to the inverse fast Fourier transform algorithm transformation;

and (6.6) converting the converted data into serial data and then transmitting the serial data.

The invention also provides a receiving method of the multi-input multi-output orthogonal frequency division multiplexing system, which comprises the following steps:

(7.1) the receiving end receives the data and removes the cyclic prefix from the received data;

(7.2) converting the data without the cyclic prefix into parallel data, and then performing fast Fourier transform algorithm conversion;

(7.3) converting the parallel data into serial data, and performing space-time space-frequency decoding on the obtained serial data;

and (7.4) after the space-time space-frequency decoding processing is carried out on the data, merging the decoded data and outputting the merged data to subsequent processing equipment.

The scheme of the invention has the following advantages: firstly, the designed MIMO OFDM transceiver only adjusts the structure, does not need extra overhead and has simple structure; secondly, the method can simultaneously obtain 2-order space and 2-order time diversity gain; thirdly, the encoding and decoding processes of the method are based on linear processing, and the calculation is simple.

Drawings

FIG. 1 is a schematic diagram of a prior art OFDM system;

FIG. 2 is a schematic diagram of a transmitter in accordance with an embodiment of the present invention;

FIG. 3 is a schematic diagram of a receiver according to an embodiment of the present invention;

fig. 4 is a diagram illustrating simulation effects of a transmitter/receiver according to an embodiment of the present invention.

Detailed Description

The invention is described below in conjunction with the drawings and the detailed description, but not intended to be limiting.

The invention aims to adjust the structure of a transceiver to obtain a high-efficiency transceiver suitable for a MIMO OFDM system adopting space-time-frequency coding and a corresponding transmission method under the condition of not increasing the complexity of the transceiver. Compared with the traditional method, the method can simultaneously obtain 2-order space and 2-order time diversity gain, and the coding and decoding processes are based on linear processing and are simple in calculation.

The method suitable for the MIMO OFDM system comprises the following steps:

when the transmitting end transmits data:

step 101, let S (N) ([ S (nN)), S (nN +1), …, S (nN + N-1)]^TRepresenting an input data symbol with the length of N and the period of T, and carrying out SFBC space-frequency coding processing on an input signal by a transmitting terminal to obtain output:

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step 102, then space-time coding is carried out, two columns of S are taken as two continuous symbol vectors X₁And X₂Then, there are:

X₁＝[S(nN)-S^*(nN+1)…S(nN+N-2)-S^*(nN+N-1)]^T　　　　(2)

X₂＝[S(nN+1)S^*(nN)…S(nN+N-1)S^*(nN+N-2)]^T　　　(3)

mixing X₁And X₂For space-time coding, the equivalent space-time coding transmission matrix can be expressed as:

step 103, converting the data subjected to STBC space-time coding into parallel data;

104, performing IFFT transformation after subcarrier allocation on the parallel data;

step 105, adding a cyclic prefix CP to the data after IFFT;

and 106, converting the converted data into serial data and then transmitting the serial data.

When the receiving end receives data:

step 201, a receiving end receives data and removes CP from the received data;

step 202, converting the data without CP into parallel data, and then performing FFT;

order to

And

is four diagonal matrixes with diagonal elements being channels respectively

And

the frequency response on the corresponding sub-carrier. At time T and T + T, the symbol vectors after FFT are respectively represented as:

in conventional STBC-OFDM, the impulse response of the channel is assumed to remain unchanged for two symbol periods, i.e.

h_{1}^{t} = h_{1}^{t + T},

h_{2}^{t} = h_{2}^{t + T},

This sacrifices time diversity gain. It can be assumed that the complex channel gain remains constant on every two adjacent subcarriers, and our assumption is reasonable due to the very strong correlation between adjacent subcarriers. Namely:

step 203, converting the parallel data into serial data, and performing space-time-frequency decoding on the obtained serial data;

assuming that the channel information is accurately known (or the channel can be accurately estimated) by the receiving end, considering the first two symbols S (nN) and S (nN +1), the first two rows of equations (5) and (6) are rewritten as follows without loss of generality:

from equations (11) and (12), the decision quantities at times S (nN) and S (nN +1) at T and T + T, respectively, can be derived, given by the following two equations:

and step 204, after the space-time space-frequency decoding processing is performed on the data, merging the decoded data, and outputting the merged data to subsequent processing equipment.

Combining formulae (13) and (14) can yield:

wherein ω is₀And ω₁Are all noise terms.

Fig. 2 shows a schematic diagram of a transmitter for a MIMO OFDM system according to an embodiment of the present invention, which includes:

SFBC coding unit for obtaining two paths of data S by vector coding unit₁And S₂SFBC coding is respectively carried out to obtain matrixes shown in a formula (1);

STBC encoding unit using two columns of S as two continuous symbol vectors X₁And X₂And obtaining a space-time coding transmission matrix:

a serial/parallel conversion unit for converting the data obtained by the STBC coding unit into parallel data;

an IFFT unit for IFFT-converting the parallel data obtained by the serial/parallel conversion unit;

a CP adding unit which adds a cyclic prefix CP to the data after IFFT transformation;

a parallel/serial conversion unit for converting the parallel unit obtained by the IFFT unit into serial data;

and the transmitting antenna is used for transmitting the serial data obtained by the parallel/serial conversion unit.

Fig. 3 shows a schematic diagram of a receiver for a MIMO OFDM system according to an embodiment of the present invention, which includes:

the receiving antenna is used for receiving the data transmitted by the transmitter;

a CP removing unit, which is used for removing CP operation on the signal received by the receiving antenna;

a serial/parallel conversion unit for converting the data obtained by the CP removing unit into parallel data;

an FFT unit used for carrying out FFT conversion on the parallel data obtained by the serial/parallel conversion unit, and the obtained data are shown as formulas (5) and (6);

a parallel/serial conversion unit for converting the data obtained by the FFT conversion unit into serial data;

the space-time space-frequency decoding unit is used for carrying out space-time space-frequency decoding on the serial data obtained by the parallel/serial conversion unit; the decoding method is shown in formulas (13) and (14);

and the data merging unit is used for merging the data decoded by the space-time space-frequency decoding unit and outputting the merged data to subsequent processing equipment. This is partly in a conventional manner and is not directly given in the block diagram.

Fig. 4 is a diagram illustrating simulation effects of a transmitter/receiver according to an embodiment of the present invention. The conditions for the simulation were as follows: the channel is a frequency selective slow fading channel, the channel between a transmitting antenna and a receiving antenna is simulated by an FIR filter, the order v of the FIR filter is 4, tap coefficients are kept unchanged in one frame, and the frame-to-frame changes randomly. The length of each data block on each transmitting antenna is 256, the number of IFFT and FFT transformed points is 256, the length of the cyclic prefix is 5, the noise is 0 in average value, and the variance is

Complex gaussian random variables. The signal-to-noise ratio SNR is defined as

Wherein epsilon²Representing the energy of the signal, QPSK modulation is used. The figure shows the comparison of the performance of the proposed method of the present invention under two transmitting antennas and one receiving antenna with the performance of STBC under four transmitting antennas and one receiving antenna, and it can be seen that the two performances are very close, and both have 4 times diversity gain.

The above embodiment of the present invention is two channels, and the present invention can also be generalized to N (N is greater than 2) channels, where N is an integer.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A transmission method of a multiple-input multiple-output orthogonal frequency division multiplexing system is characterized by comprising the following steps:

(1) the transmitting terminal firstly carries out space-frequency coding SFBC processing on the transmitted data, then carries out space-time coding STBC processing on the processed data, then carries out serial/parallel transformation, inverse fast Fourier transform algorithm transformation, cyclic prefix addition and parallel/serial transformation processing, and then transmits the data;

2. The method of claim 1, wherein step (1) comprises the steps of:

(1.3) transforming the space-time coded data into parallel data;

3. The method of claim 1, wherein step (2) comprises the steps of:

4. A code transmitter of a multi-input multi-output orthogonal frequency division multiplexing system comprises a serial/parallel conversion unit, an inverse fast Fourier transform algorithm unit, a cyclic prefix adding unit, a parallel/serial conversion unit and a transmitting antenna, and is characterized by also comprising a space-frequency coding unit and a space-time coding unit, wherein the space-frequency coding unit, the space-time coding unit, the serial/parallel conversion unit, the inverse fast Fourier transform algorithm unit, the cyclic prefix adding unit, the parallel/serial conversion unit and the transmitting antenna are sequentially connected; the space-frequency coding unit is used for carrying out space-frequency coding SFBC processing on the transmitted data, and the space-time coding unit is used for carrying out space-time coding STBC processing on the data after the space-frequency coding SFBC processing and then sending the data to the serial/parallel conversion unit for subsequent processing.

5. A MIMO OFDM system code receiver comprises a receiving antenna, a cyclic prefix removing unit, a serial/parallel conversion unit, a fast Fourier transform algorithm unit, a parallel/serial conversion unit, and a space-time space-frequency decoding unit, wherein the receiving antenna, the cyclic prefix removing unit, the serial/parallel conversion unit, the fast Fourier transform algorithm unit, the parallel/serial conversion unit, and the space-time space-frequency decoding unit are connected in sequence; and the space-time space-frequency decoding unit is used for respectively carrying out space-time space-frequency decoding processing on the data sent by the parallel/serial conversion unit in two continuous symbol periods.

6. A transmitting method of a multiple-input multiple-output orthogonal frequency division multiplexing system is characterized by comprising the following steps:

(6.1) when transmitting data, the transmitting terminal firstly carries out space-frequency coding SFBC processing on an input signal;

(6.2) then the transmitting end carries out space-time coding (STBC) processing on the processed data;

(6.3) transforming the space-time coded data into parallel data;

7. A receiving method of a multiple-input multiple-output orthogonal frequency division multiplexing system is characterized by comprising the following steps: