CN101345733B - Multi-user OFDM Modulation Method Based on Embedded Training Sequence and BICM - Google Patents

Abstract

The invention discloses a multi-user OFDM modulation method based on embedded training sequence and BICM, which comprises the following steps: 1) each user uniformly inserts zeros into the training sequence of the user to form an FFT discrete training sequence block; 2) each user forms an FFT bit interleaving coding modulation data block after carrying out multi-code rate puncturing convolution coding, bit interleaving and code element modulation on the bit stream of the input data of the user; 3) directly superposing the FFT discrete training sequence block and the FFT bit interleaving coding modulation data block to form an FFT embedded training sequence bit interleaving coding modulation data block; 4) adopting IFFT to transform the FFT embedded training sequence bit interleaving coding modulation data block into a time domain discrete sample value block; 5) inserting the cyclic prefix as a guard interval into the time domain discrete sample value block to form a signal frame; 6) shaping the signal frame pulse by using a square root raised cosine roll-off filter; 7) the baseband signal is up-converted to a carrier wave.

Description

Multi-user OFDM Modulation Method Based on Embedded Training Sequence and BICM

technical field

The invention belongs to the field of wireless communication, and more specifically relates to a multi-user OFDM (Bit Interleaved Coded Modulation, BICM; Orthogonal Frequency Division Multiplexing, OFDM) based on embedded training sequences and BICM modulation method.

Background technique

Wireless communication is one of the most important infrastructures in the modern information society. It has become a basic requirement for national progress and social development, and plays an important role in sustainable economic development and modern military defense construction. However, in the field of wireless communication, on the one hand, spectrum resources are limited; on the other hand, with the increase in the number of users and the expansion of business scope (especially the emergence of various high-speed data services) With the growth of broadband wireless communication, it plays an increasingly important role in modern social life, and related technologies of broadband wireless communication have become research hotspots in today's international academic circles and industrial circles.

Due to the rapid development of digital signal processing technology and integrated circuit technology, the system realization of Orthogonal Frequency Division Multiplexing (OFDM) technology becomes easier and easier. Because OFDM multi-carrier transmission technology has many advantages such as simple structure, high spectrum utilization rate, and anti-frequency selectivity and channel time variation, it has attracted much attention and has been deeply researched and applied in Xdsl, broadband mobile communication, broadband wireless local area network, It is widely used in many fields such as digital TV terrestrial broadcasting.

In the actual communication environment, the performance of OFDM communication system is affected by factors such as synchronization time, clock jitter, channel fading, and multi-user co-channel interference. Channel coding technology and modulation method are the key technologies to realize reliable OFDM communication.

Channel coding is an important part of digital communication systems. With the rapid development of modern information technology, channel coding technology has become an indispensable technology in the field of modern communication. Redundant code elements are embedded in the information sequence, and channel coding technology reduces signal errors during transmission through the role of redundant code elements, thereby improving the reliability of the communication system.

Under multipath fading channel, the optimal design of coding, interleaving and modulation scheme can achieve the largest possible signal diversity order, so as to obtain independent fading in the symbol sequence equal to or exceeding the minimum free distance. BICM technology (Bit Interleaved Coded Modulation, BICM) uses a bit interleaver and makes the encoding and modulation processes relatively independent, so that the diversity order can be expanded from different multi-ary symbols to different binary bits , that is to say, its diversity order L is the minimum Hamming distance between binary codeword sequences. Because the BICM technology makes the order of diversity significantly improved, it makes the communication system have good bit error characteristics under the multipath fading channel.

Based on the above background, the present invention proposes a multi-user OFDM modulation method based on embedded training sequence and BICM for the actual communication environment, which can meet the needs of high data rate wireless multi-user communication.

For a more in-depth understanding of the patent background, please refer to the following literature:

L.J. Cimini, "Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing," IEEE Trans. Commun., vol. COM-33, pp.665-675, July 1985.

R.V.Nee, R.Prasad. "OFDM for wireless multimedia communications". Boston: Artech House, 2000.

A.R.S.Bahai and B.R.Saltzberg. "Multi-Carrier Digital Communications: Theory and Applications of OFDM". KluwerAcademic/Plenum, 1999.

E. Zehavi, "8-PSK trellis codes for a rayleigh channel," IEEE Trans. Commun., vol.40, no.5, pp.873-884, May 1992.

G.Caire, G.Taricco, E.Biglieri, "Bit-interleaved coded modulation," IEEE Trans.Information Theory, vol.44, no.3, pp.927-946, May 1998.

X.Li, A.Chindapol and J.A.Ritchey, "Bit-interleaved coded modulation with iterative decoding and 8 PSK signaling," IEEE Trans. Commun., vol.50, pp.1250-1257, 2002.

J. Hagenauer, "Rate-compatible punctured convolutional codes and their applications," IEEE Trans. Commun., vol.36, no.4, pp.389-400, April 1988.

X.Li and J.A.Ritcey, "Bit-interleaved coded modulation without iterative decoding," IEEE Commun. Lett., vol.1, pp.169-171, Nov.1997.

A.Chindapol and J.A.Ritcey, "Design, analysis, and performance evaluation for BICM-ID with square QAM constellations in Rayleigh fading channels," IEEE J.Select.Areas Commun., vol.19, no.5, pp.944-957, May 2001.

U. Wachsmann, R. Fischer, and J. Huber, "Multilevel codes: theoretical concepts and practical design rules," IEEE Trans. Inform. Theory, vol.45, no.5, pp.1361-1391, July 1999.

S. Benedetto, D. Divsalar, G. Montorsi, and F. Pollara, "Serial concatenation of interleaved codes: performance analysis, design, and iterative decoding," IEEE Trans. Inform. Theory, vol.44, no.3, pp. 909-925, May 1998.

Contents of the invention

Aiming at the problem of high data rate wireless multi-user communication, the present invention proposes a multi-user OFDM (Bit Interleaved Coded Modulation, BICM; Orthogonal Frequency Division Multiplexing) based on embedded training sequence and BICM , OFDM) modulation method.

A kind of multi-user OFDM modulation method based on embedding training sequence and BICM that the present invention proposes is characterized in that it comprises the following steps:

1) Each user inserts zeros into the user's own training sequence according to the uniform discrete rule to form an FFT discrete training sequence block, wherein the number of zeros is K-X, the length of the training sequence is X, and FFT stands for Fast Discrete Fourier Transform , the length of the FFT discrete training sequence block is K;

2) Each user further forms an FFT bit-interleaved coded modulation data block after multi-code rate punctured convolutional coding, bit interleaving, and symbol modulation of the input data bit stream, wherein the FFT bit-interleaved coded modulation data block length is K;

3) directly superimposing the FFT discrete training sequence block and the FFT bit-interleaved coded modulation data block to form an FFT embedded training sequence bit-interleaved coded modulated data block;

4) Transforming the FFT embedded training sequence bit-interleaved coded modulation data block into a time-domain embedded training sequence bit-interleaved coded modulated data block by using IFFT, wherein IFFT represents inverse fast discrete Fourier transform;

5) inserting the cyclic prefix as a guard interval into the time-domain embedded training sequence bit interleaving coded modulation data block obtained through IFFT transformation to form a signal frame, wherein the length of the cyclic prefix is C;

6) using a square root raised cosine roll-off filter to shape the signal pulse of the signal frame;

7) Up-convert the baseband signal to the carrier.

According to the above-mentioned multi-user OFDM modulation method based on embedding training sequence and BICM, it is characterized in that: in the signal frame of each user, there is a time-domain embedded training sequence bit interleaving coding modulation data block; the length X of the training sequence of each user is One of 32, 64, 256, 512, and 1024; the training sequence of each user has pseudo-random characteristics; the training sequences of different users are orthogonal; the input data is encoded by multi-rate punctured convolutional encoding The rate is one of 1/4, 1/2, 5/8, 3/4, and 7/8; the bit interleaving adopts random interleaving; the symbol modulation is one of QPSK, 16QAM, 32QAM, and 64QAM, and the symbol Constellation diagram mapping adopts Gray code mapping; FFT embedded training sequence bit interleaving code modulation data block is composed of subcarriers, the number of subcarriers K is one of 128, 256, 1024, 2048 and 4096; the frequency interval of subcarriers is 2KHz, 4KHz One of , 16KHz, 64KHz and 128KHz; the cyclic prefix length C is one of 1/2, 1/4, 1/8, 1/16 and 1/32 of the length K of the FFT bit interleaved coding modulation data block.

Features of the present invention:

The invention is a modulation scheme of mixing time domain and frequency domain. The training sequence of each user has pseudo-random characteristics, and the training sequences of different users are orthogonal. The FFT embedded training sequence bit-interleaved coded modulation data block is directly superimposed by the FFT discrete training sequence block and the FFT bit-interleaved coded modulation data block. Formed, these ensure that each user can achieve fast and accurate frame synchronization, frequency synchronization, time synchronization, channel transmission characteristic estimation, and reliable tracking of phase noise and channel transmission characteristics. Using BICM to perform bit-interleaved coding and modulation on the input data improves the diversity order and makes the communication system have good bit error characteristics in multi-path fading channels. The cyclic prefix is inserted as a guard interval into the time-domain embedded training sequence bit interleaved coded modulation data block obtained by IFFT transformation to form a signal frame, which can reduce the interference effect between adjacent signal frames. The modulation method of the invention has many advantages such as short synchronization time, small clock jitter, anti-channel fading, anti-multi-user interference, and the like.

Description of drawings

FIG. 1 is a schematic diagram of an embodiment of a multi-user OFDM modulation method based on embedded training sequences and BICM for a user among multiple users according to the present invention.

Fig. 2 is a schematic diagram of an embodiment of the structure of a signal frame obtained by a certain user of the multi-user OFDM modulation method based on embedded training sequence and BICM according to the present invention.

Fig. 3 is a schematic diagram of an embodiment of an uplink of a multi-user mobile communication based on a multi-user OFDM modulation method embedded in training sequences and BICM according to the present invention.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

According to the embodiment of the multi-user OFDM modulation method based on embedded training sequence and BICM proposed by the present invention to a certain user in the multi-user (such as: a certain user n in the multi-user), as shown in Figure 1, follow the steps conduct:

1) A certain user n in the multi-user inserts zeros into the user's own training sequence according to the uniform discrete rule respectively to form a FFT fast discrete Fourier transform discrete training sequence block, wherein the number of zeros is K-X, and the length of the training sequence Be X, X is one of 32, 64, 256, 512 and 1024, the length of the FFT discrete training sequence block is K, and K is one of 128, 256, 1024, 2048 and 4096;

2) A certain user n in the multi-user further forms an FFT bit-interleaved coded modulation data block after the multi-rate punctured convolutional encoding, bit interleaving, and symbol modulation of the input data bit stream, wherein, the FFT bit-interleaving The length of the encoded modulation data block is K;

3) directly superimposing FFT discrete training sequence blocks and FFT coded data blocks to form FFT embedded training sequence bit interleaving coded modulation data blocks;

4) Transforming the FFT embedded training sequence bit-interleaved coded modulation data block into a time-domain embedded training sequence bit-interleaved coded modulated data block by using IFFT fast discrete Fourier inverse transform;

5) Inserting the cyclic prefix as a guard interval into the time-domain embedded training sequence bit interleaved coded modulation data block obtained by IFFT transformation to form a signal frame, wherein the length of the cyclic prefix is C, and C is 1/2 of the size of K, One of 1/4, 1/8, 1/16 and 1/32;

6) using a square root raised cosine roll-off filter to shape the signal pulse of the signal frame;

7) Up-convert the baseband signal to the carrier.

According to an embodiment of the structure of a signal frame obtained by a certain user (such as: a certain user n in the multi-user) of the multi-user OFDM modulation method based on the embedded training sequence and BICM of the present invention, as shown in Figure 2, The specific implementation is as follows:

Firstly, the FFT discrete training sequence block is formed in the frequency domain after being zero-interpolated according to the uniform discrete rule, and the FFT bit-interleaved coded modulation data block after multi-code rate punctured convolutional coding, bit interleaving, and symbol modulation is formed; then, the FFT The discrete training sequence block and the FFT bit-interleaved coded modulation data block are directly superimposed to form an FFT embedded training sequence bit-interleaved coded modulated data block.

As each user's training sequence has pseudo-random characteristics, the training sequences of different users have orthogonality. The training sequence satisfying the above characteristics can be realized by a special type of shifted m-sequence as a pseudo-random number sequence and Walsh sequence, Hadamard sequence or orthogonal sequence generated by other methods as an orthogonal sequence.

The FFT embedded training sequence bit interleaving coded modulation data block is composed of subcarriers, the number of subcarriers is one of 128, 256, 1024, 2048 and 4096; the frequency interval of subcarriers is one of 2KHz, 4KHz, 16KHz, 64KHz and 128KHz.

A guard interval is inserted into the time domain embedding training sequence bit interleaving coded modulation data block obtained by IFFT transformation to form a signal frame. There are 5 working modes for the guard interval, which are defined as one of 1/2, 1/4, 1/8, 1/16 and 1/32 of the FFT bit interleaving code modulation data block size. The last segment of sampling of the time-domain embedded training sequence bit-interleaved coded modulation data block obtained by IFFT transformation is used as a guard interval. A coding rate of 1/4, 1/2, 5/8, 3/4, and 7/8 is used for performing multi-rate punctured convolutional coding on the input data.

The baseband signal of the signal frame according to the present invention is an Orthogonal Frequency Division Multiplexing (OFDM) block embedded with a training sequence and bit-interleaved coded modulation of input data using BICM. An OFDM block can be further divided into a guard interval and an IFFT block. Since the guard interval in the signal frame of the present invention is the last sampling of the time-domain embedded training sequence bit interleaving coded modulation data block obtained through IFFT transformation, the signal frame of the present invention conforms to the cyclic prefix OFDM (CP-OFDM) some features.

For a more in-depth understanding of CP-OFDM involved in the patent, please refer to the following literature: B.Muquet, Z.Wang, G.B.Giannakis, M.de Courville, and P.Duhamel, "Cyclic-Prefixed or Zero-Padded Multicarrier Transmissions?," IEEE Transactions on Communications, vol.50, pp.2136-2148, Dec.2002.

The signal of the signal frame is pulse-shaped using a square root raised cosine roll-off filter. The roll-off coefficient of the square-root raised cosine roll-off filter for pulse-shaping the signals of the signal frame is one of 0.1, 0.05 and 0.025.

According to the embodiment of the upload link of the multi-user mobile communication of the multi-user OFDM modulation method based on the embedded training sequence and BICM of the present invention, as shown in Figure 3, the specific implementation is as follows:

1) Each mobile communication user in the multi-user inserts zero into the user's own training sequence according to the uniform discrete rule respectively to form a FFT fast discrete Fourier transform discrete training sequence block, wherein the number of zeros is K-X, and the number of training sequences The length is X, and X is one of 32, 64, 256, 512 and 1024, the length of the FFT discrete training sequence block is K, and K is one of 128, 256, 1024, 2048 and 4096;

2) Each mobile communication user in the multi-user further forms an FFT bit-interleaved coded modulation data block after undergoing multi-rate punctured convolutional coding, bit interleaving, and symbol modulation of its input data bit stream, wherein, the FFT bit The length of the interleaved coding modulation data block is K;

3) Each mobile communication user in the multi-user directly superimposes the FFT discrete training sequence block and the FFT bit-interleaved coded modulation data block to form an FFT embedded training sequence bit-interleaved coded modulated data block;

4) Each mobile communication user in the multi-user transforms the FFT embedded training sequence bit-interleaved coded modulation data block into a time-domain embedded training sequence bit-interleaved coded modulated data block by using IFFT fast discrete Fourier inverse transform;

5) Each mobile communication user in the multi-user inserts the cyclic prefix as a guard interval into the time-domain embedded training sequence bit interleaved coded modulation data block obtained by IFFT transformation to form a signal frame, wherein the length of the cyclic prefix is C, C is one of 1/2, 1/4, 1/8, 1/16 and 1/32 of the size of K;

6) Each mobile communication user in the multi-user uses a square root raised cosine roll-off filter to shape the signal pulse of the signal frame;

7) Each mobile communication user in the multi-user up-converts the baseband signal to the carrier;

8) At the base station side of the uplink, multi-antennas are used to perform receiver signal processing such as synchronization, channel estimation, and equalization on the signals of each mobile communication user among the multi-users.

The specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and those skilled in the art can make various modifications without departing from the spirit and scope of the claims of the application modify or remodel.

Claims (9)

1. a multi-user OFDM modulation method based on embedded training sequence and BICM, is characterized in that it comprises the following steps: 1) Each user inserts zeros into the user's own training sequence according to the uniform discrete rule to form an FFT discrete training sequence block, wherein the number of zeros is K-X, the length of the training sequence is X, and FFT stands for Fast Discrete Fourier Transform , the length of the FFT discrete training sequence block is K; 2) Each user further forms an FFT bit-interleaved coded modulation data block after multi-code rate punctured convolutional coding, bit interleaving, and symbol modulation of the input data bit stream, wherein the FFT bit-interleaved coded modulation data block length is K; 3) directly superimposing the FFT discrete training sequence block and the FFT bit-interleaved coded modulation data block to form an FFT embedded training sequence bit-interleaved coded modulated data block; 4) Transforming the FFT embedded training sequence bit-interleaved coded modulation data block into a time-domain embedded training sequence bit-interleaved coded modulated data block by using IFFT, wherein IFFT represents inverse fast discrete Fourier transform; 5) inserting the cyclic prefix as a guard interval into the time-domain embedded training sequence bit interleaving coded modulation data block obtained through IFFT transformation to form a signal frame, wherein the length of the cyclic prefix is C; 6) using a square root raised cosine roll-off filter to shape the signal pulse of the signal frame; 7) Up-convert the baseband signal to the carrier. 2. by the multi-user OFDM modulation method based on embedding training sequence and BICM of claim 1, it is characterized in that: described each user inserts zero into this user's own training sequence by uniform discrete rule, wherein, the number of zero is K-X, the length of the training sequence is X, and X is one of 32, 64, 256, 512 and 1024. 3. The multi-user OFDM modulation method based on embedding training sequence and BICM according to claim 2, characterized in that: the training sequence as each user has a pseudo-random characteristic. 4. by the multi-user OFDM modulation method based on embedding training sequence and BICM of claim 2, it is characterized in that: there is orthogonality between the training sequences of described different users. 5. by the multi-user OFDM modulation method based on embedding training sequence and BICM of claim 1, it is characterized in that: each user of described adopts multi-code rate punctured convolution coding that input data is encoded, and input data is multiplexed The coding rate of punctured convolutional coding is one of 1/4, 1/2, 5/8, 3/4 and 7/8; the bit interleaving adopts random interleaving; the symbol modulation is QPSK, 16QAM, 32QAM One of 64QAM and 64QAM, the symbol constellation mapping method adopts Gray code mapping. 6. by the multi-user OFDM modulation method based on embedding training sequence and BICM according to claim 1, it is characterized in that: said FFT embedding training sequence bit interleaving coding modulation data block is made up of subcarriers, and subcarrier number K is 128,256,1024 , 2048 and 4096 in one. 7. The multi-user OFDM modulation method based on embedded training sequence and BICM according to claim 6, characterized in that: the frequency interval of the subcarriers is one of 2KHz, 4KHz, 16KHz, 64KHz and 128KHz. 8. The multi-user OFDM modulation method based on embedded training sequence and BICM according to claim 1, characterized in that: the length of the guard interval of the signal frame is C. 9. by the multi-user OFDM modulation method based on embedding training sequence and BICM of claim 1, it is characterized in that: the length C of the cyclic prefix as the guard interval is 1/2 of the FFT bit interleaving coding modulation data block length K size , 1/4, 1/8, 1/16 and 1/32 in one.

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