CN101345731B - Multi-user OFDM modulation method based on imbedded training sequence and LDPC code - Google Patents
Multi-user OFDM modulation method based on imbedded training sequence and LDPC code Download PDFInfo
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- CN101345731B CN101345731B CN2008100128673A CN200810012867A CN101345731B CN 101345731 B CN101345731 B CN 101345731B CN 2008100128673 A CN2008100128673 A CN 2008100128673A CN 200810012867 A CN200810012867 A CN 200810012867A CN 101345731 B CN101345731 B CN 101345731B
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Abstract
The invention discloses a multiuser OFDM modulation method based on embedded training sequence and LDPC coding, which includes the following steps: 1) each user inserting zero even in its own training sequence to form discrete FFT training sequence block; 2) each user performing LDPC coding to its own input data bit stream to further form an FFT coding data block; 3) directly superimposing the discrete FFT training sequence block and the FFT coding data block to form an FFT embedded training sequence coding data block; 4) adopting IFFT to switch the FFT embedded training sequence coding data block into a time-domain discrete sample block; 5) taking circulating prefix as guard interval to insert into the time-domain discrete sample block to from a signal frame; 6) using a Raised Cosine Roll-off Filter to perform pulse shaping to the signal frame; 7) upconverting the baseband signal to carrier. The method has advantages of short synchronization time, channel dwindle resistance and multiuser disturbance resistance and the like.
Description
Technical field
The invention belongs to wireless communication field, relate more specifically to a kind of based on the multi-user OFDM (low density parity check code, Low Density Parity Check, the LDPC that embed training sequence and LDPC coding; OFDM, Orthogonal Frequency Division Multiplexing, OFDM) modulator approach.
Background technology
Radio communication is one of most important infrastructure of advanced information society, has become the primary demand of country's progress and social development, in sustainable economic development and modern military national defense construction, is bringing into play important effect.But at wireless communication field, on the one hand, frequency spectrum resource is limited; On the other hand; The message volume explosive growth that is caused along with the increase of number of users and the expansion of the scope of business (appearance that particularly various high speed code rate datas are professional); It is more and more important to make that broadband wireless communications plays a part in the social life in modern times, and the broadband wireless communications correlation technique has become the research focus of current international academic community and industrial quarters.
Because the develop rapidly of Digital Signal Processing and integrated circuit technique, the system of OFDM (OFDM) technology realizes becoming more and more easier.Because of OFDM multi-carrier transmission technology has simple in structure; The availability of frequency spectrum is high, plurality of advantages such as becomes in the time of can resisting frequency selectivity and channel and extremely everybody concern and obtain deep research and the extensive use in numerous areas such as Xdsl, wide-band mobile communication, wideband wireless local area network, DTTB.
Chnnel coding is the important component part of digital communication system.Along with the develop rapidly of modern information technologies, channel coding technology has become the indispensable technology in modern communications field.In information sequence, embed redundancy symbol, the effect of channel coding technology through redundancy symbol reduces signal and in transmission course, makes a mistake, thereby improves the reliability of communication system.
Since Shannon had proposed famous channel coding theorem, scholars were devoted to construct error correcting capability near theoretical limit and the acceptable channel coding method of encoder complexity always.In 1993, people such as Berrou proposed Turbo code, and its superior performance has shocked coding circle, became the research focus on coding circle soon.Just along with the research that deepens continuously of Turbo code; People just find low density parity check code (the Low Density Parity Check of Turbo code and Gallager proposition in 1962; LDPC) many similarities are arranged; Both adopt the mode of random coded at coding side, all adopt the iterative decoding mode at the decoding end.Why Gallager did not find this characteristic of LDPC sign indicating number at that time; Main cause is that the simulation capacity when computer-chronograph is limited; Can't carry out The Realization of Simulation to the long LDPC sign indicating number of code word, be difficult in real system, be employed and so once out in the cold because the restriction of level of hardware at that time makes academia think that LDPC sign indicating number decoding algorithm is too complicated.Up to 1996, the LDPC sign indicating number had the performance of approaching the Shannon limit when MacKay and Neal proof adopted the BP iterative decoding algorithm, from then on made the research and the application of LDPC coding stride into a new stage.The LDPC sign indicating number is a kind ofly to be used in noise transmission channel transmission information and to carry out the error correcting code of forward error correction (FEC, ForwardError Correction).The LDPC code word can be regarded a kind of sign indicating number with binary parity check matrix as, and the element of parity matrix nearly all is zero.Although the LDPC coding can not guarantee errorless transmission with other error correction codings, the probability of loss of information can drop to required degree.LDPC coding be a kind of message transmission rate that can make near theoretical maximum, i.e. the encoding scheme of shannon limit.It is firm found the time to encode at LDPC, in most of the cases can't practical application because the amount of calculation of algorithm and encoder is excessive, thereby be not used widely.Yet, after LDPC sign indicating number in 1996 is re-recognized, in communication system, be used widely, such as: all considered to adopt of the application of LDPC sign indicating number in IEEE802.16e standard, the IEEE802.11n standard etc. as chnnel coding.
In the practical communication environment, the ofdm communication system performance receives the influence of factors such as lock in time, clock jitter, channel fading, multi-user's common-channel interference.Channel coding technology and modulator approach are to realize the key technology of reliable ofdm communication.
Just be based on above background, the present invention is directed to the practical communication environment and propose a kind of multi-user OFDM modulation method, can satisfy the needs of high-data-rate wireless multi-user communication based on embedding training sequence and LDPC coding.
Desire is done more deep understanding to the patent background can be with reference to following documents and materials:
L.J.Cimini，“Analysis?and?simulation?of?a?digital?mobilechannel?using?orthogonal?frequency?division?multiplexing，”IEEETrans.Commun.，vol.COM-33，pp.665-675，July?1985.
R.V.Nee，R.Prasad.“OFDM?for?wireless?multimediacommunications”.Boston：Artech?House，2000.
A.R.S.Bahai?and?B.R.Saltzberg.“Multi-Carrier?DigitalCommunications：Theory?and?Applica?tions?of?OFDM”.KluwerAcademic/Plenum，1999.
R.G.Gallager，“Low-density?parity-check?codes，”IRETrans.Inf.Theory，vol.IT-8，no.l，pp.21-28，Jan.1962.
D.J.C.MacKay，“Good?error-correcting?codes?based?on?verysparse?matrices，”IEEE?Trans.Inf.Theory，vol.45，no.2，pp.399-431，Mar.1999.
D.J.C.MacKay，S.T.Wilson，and?M.C.Davey，“Comparison?ofconstructions?of?irregular?Gallager?codes，”IEEE?Trans.Commun.，vol.47，no.10，pp.1449-1454，Oct.1999.
D.J.C.MacKay?and?R.M.Neal，“Near?Shannon?limit?performanceof?low?density?parity?check?codes，”IEE?Electron.Lett.，vol.32，no.18，pp.1645-1646，Aug.1996.
M.P.C.Fossorier，“Quasi-cyclic?low?density?parity?check?codesfrom?circulant?permutation?matrices，”IEEE?Trans.Inform.Theory，vol.50，pp.1788-1794，Aug.2004.
T.Richardson，A.Shokrollahi，and?R.Urbanke，“Design?ofcapacity?approaching?low?density?parity?check?codes，”IEEE?Trans.Inf.Theory，vol.47，no.2，pp.619-637，Feb.2001.
H.Tang，J.Xu，Y.Kou，S.Lin，and?K.Abdel-Ghaffar，“Onalgebraic?construction?of?Gallager?and?circulant?low?densityparity?check?codes，”IEEE?Trans.Inf.Theory，vol.50，no.6，pp.1269-1279，Jun.2004.
Z.Li，L.Chen，L.Zeng，S.Lin，W.Fong，“Efficient?encodingof?quasi-cyclic?low-density?parity-check?codes，”IEEE?Trans.Commun.，vol.54，no.1，pp.71-81，Jan.2006.
Summary of the invention
The present invention is directed to high-data-rate wireless multi-user communication problem, proposed a kind of based on the multi-user OFDM (low density parity check code, Low Density Parity Check, the LDPC that embed training sequence and LDPC coding; OFDM, Orthogonal Frequency Division Multiplexing, OFDM) modulator approach.
What the present invention proposed is a kind of based on the multi-user OFDM modulation method that embeds training sequence and LDPC coding, it is characterized in that it comprises the following steps:
1) each user respectively will zero (zero number is K-X) be inserted into by even discrete programming and forms the discrete training sequence piece of FFT (fast discrete Fourier conversion) (FFT disperse the length of training sequence piece be K) in this user's oneself training sequence (length of training sequence is X);
2) each user flows through the input data bit of oneself respectively and further forms FFT coded data block (length of FFT coded data block is K) after LDPC encodes;
3) the discrete training sequence piece of FFT, FFT coded data block are directly superposeed form FFT and embed the training sequence coded data block;
4) adopt IFFT (fast discrete Fourier inverse transformation) that FFT is embedded the discrete sample block (that is, time domain embeds the training sequence coded data block) that the training sequence coded data block is transformed to time domain;
5) Cyclic Prefix (length of Cyclic Prefix is C) is inserted the time domain that obtains through the IFFT conversion at interval as protection and embed the training sequence coded data block, to form signal frame;
6) adopt square root raised cosine filter that the signal pulse of signal frame is shaped;
7) with the baseband signal up-conversion to carrier wave.
The multi-user OFDM modulation method based on embedding training sequence and LDPC coding according to above-mentioned is characterized in that: have time domain in each user's the signal frame and embed the training sequence coded data block; The length X of each user's training sequence is in 32,64,256,512 and 1024; Each user's training sequence has pseudo-random characteristics; Has orthogonality between the training sequence of different user; The encoding rate that the input data is carried out the LDPC coding is in 1/4,1/2,5/8,3/4 and 7/8; FFT embeds the training sequence coded data block and is made up of subcarrier, and sub-carrier number (length K of FFT data block) is in 128,256,1024,2048 and 4096; The frequency interval of subcarrier is among 2KHz, 4KHz, 16KHz, 64KHz and the 128KHz; Circulating prefix-length C be FFT coded data block length K size 1/2,1/4,1/8,1/16 and 1/32 in one.
Characteristics of the present invention:
The present invention is the modulation scheme that a kind of time-domain and frequency-domain mixes.Each user's training sequence has pseudo-random characteristics; Has orthogonality between the training sequence of different user; FFT embeds the training sequence coded data block and is directly superposeed and formed by the discrete training sequence piece of FFT, FFT coded data block, and these have guaranteed that each user can realize that frame synchronization, Frequency Synchronization, time synchronized, channel transfer characteristic are estimated and phase noise and channel transfer characteristic are reliably followed the tracks of fast and accurately.Adopt the LDPC coding that the input data are carried out chnnel coding the error-correcting performance near shannon limit is provided.Cyclic Prefix is inserted the time domain that obtains through the IFFT conversion at interval as protection embed the training sequence coded data block, can reduce the interference effect between the adjacent signals frame to form signal frame.Modulator approach of the present invention has short, plurality of advantages such as clock jitter is little, anti-channel fading, resisting multi-user interference lock in time.
Description of drawings
Fig. 1 is based on the embodiment sketch map of the multi-user OFDM modulation method that embeds training sequence and LDPC coding to certain user among the multi-user according to of the present invention.
Fig. 2 is the embodiment sketch map according to the structure based on the signal frame that certain user obtained that embeds the multi-user OFDM modulation method that training sequence and LDPC encode of the present invention.
Fig. 3 is according to the embodiment sketch map of uploading link based on the multiuser mobile communication that embeds the multi-user OFDM modulation method that training sequence and LDPC encode of the present invention.
Embodiment
To combine accompanying drawing that specific embodiment of the present invention is described in detail below.
According to the present invention propose based on embed multi-user OFDM modulation method that training sequence and LDPC encode to certain user among the multi-user (such as embodiment certain the user n among the multi-user), as shown in Figure 1, follow these steps to carry out:
1) certain the user n among the multi-user respectively will zero (zero number is K-X) be inserted into this user's oneself training sequence by even discrete programming (length of training sequence is X; X is in 32,64,256,512 and 1024) the middle discrete training sequence piece of FFT (fast discrete Fourier conversion) (length of the discrete training sequence piece of FFT is K, and K is in 128,256,1024,2048 and 4096) that forms;
2) certain the user n among the multi-user flows through the input data bit of oneself respectively and further forms FFT coded data block (length of FFT coded data block is K) after LDPC encodes;
3) the discrete training sequence piece of FFT, FFT coded data block are directly superposeed form FFT and embed the training sequence coded data block;
4) adopt IFFT (fast discrete Fourier inverse transformation) that FFT is embedded the discrete sample block (that is, time domain embeds the training sequence coded data block) that the training sequence coded data block is transformed to time domain;
5) with Cyclic Prefix (length of Cyclic Prefix is C, C be K size 1/2,1/4,1/8,1/16 and 1/32 in one) insert the time domain that obtains through the IFFT conversion at interval as protection and embed the training sequence coded data block, to form signal frame;
6) adopt square root raised cosine filter that the signal pulse of signal frame is shaped;
7) with the baseband signal up-conversion to carrier wave.
According to of the present invention based on certain user of embedding the multi-user OFDM modulation method that training sequence and LDPC encode (such as the embodiment of the structure of a signal frame that certain the user n among the multi-user) is obtained, as shown in Figure 2, practical implementation is following:
At first form the discrete training sequence piece of FFT after quilt is pressed even discrete programming zero insertion, the FFT coded data block behind the LDPC coding at frequency domain; Then, the discrete training sequence piece of FFT, FFT coded data block are directly superposeed form FFT and embed the training sequence coded data block.
Training sequence as each user has pseudo-random characteristics, has orthogonality between the training sequence of different user.The training sequence that satisfies above-mentioned characteristic can be by realizing as one group of displacement m sequence of a kind of specific type of pseudo-random number sequence with as the walsh sequence of orthogonal sequence, hadamard sequences or by the orthogonal sequence that other modes produce.
FFT embeds the training sequence coded data block and is made up of subcarrier, and sub-carrier number is in 128,256,1024,2048 and 4096; The frequency interval of subcarrier is among 2KHz, 4KHz, 16KHz, 64KHz and the 128KHz.
In the time domain embedding training sequence coded data block that obtains through the IFFT conversion, insert protection and form signal frame at interval.Be separated with 5 kinds of mode of operations between protection, they be defined as FFT coded data block size 1/2,1/4,1/8,1/16 and 1/32 in one.The final stage sampling that the time domain that obtains through the IFFT conversion embeds the training sequence coded data block is used as protection at interval.The encoding rate that the input data is carried out the LDPC coding is in 1/4,1/2,5/8,3/4 and 7/8.
Baseband signal according to signal frame of the present invention is OFDM (OFDM) piece that embeds training sequence and adopt the LDPC coding that the input data are encoded.An OFDM piece can further be divided into protection interval and an IFFT piece.Owing to the protection in the signal frame of the present invention is spaced apart the final stage sampling that the time domain that obtains through the IFFT conversion embeds the training sequence coded data block, also just make signal frame of the present invention meet some characteristic of Cyclic Prefix OFDM (CP-OFDM).
Desire is done more deep understanding to the CP-OFDM that relates in the patent can be with reference to following documents and materials:
B.Muquet，Z.Wang，G.B.Giannakis，M.de?Courville，and?P.Duhamel，“Cyclic-Prefixed?or?Zero-Padded?Multicarrier?Transmissions?，”IEEETransactions?on?Communications，vol.50，pp.2136-2148，Dec.2002.
Adopt square root raised cosine filter that the signal of signal frame is carried out pulse shaping.The signal of signal frame is carried out the rolloff-factor of the square root raised cosine filter of pulse shaping and get in 0.1,0.05 and 0.025.
According to the embodiment that uploads link based on the multiuser mobile communication that embeds the multi-user OFDM modulation method that training sequence and LDPC encode of the present invention, as shown in Figure 3, practical implementation is following:
1) each mobile communication subscriber among the multi-user respectively will zero (zero number is K-X) be inserted into this user's oneself training sequence by even discrete programming (length of training sequence is X; X is in 32,64,256,512 and 1024) the middle discrete training sequence piece of FFT (fast discrete Fourier conversion) (length of the discrete training sequence piece of FFT is K, and K is in 128,256,1024,2048 and 4096) that forms;
2) each mobile communication subscriber among the multi-user is flowed through the input data bit of oneself respectively and is further formed FFT coded data block (length of FFT coded data block is K) after LDPC encodes;
3) each mobile communication subscriber among the multi-user directly superposes the discrete training sequence piece of FFT, FFT coded data block and forms FFT embedding training sequence coded data block;
4) each mobile communication subscriber among the multi-user adopts IFFT (fast discrete Fourier inverse transformation) that FFT is embedded the discrete sample block (that is, time domain embeds the training sequence coded data block) that the training sequence coded data block is transformed to time domain;
5) (length of Cyclic Prefix is C to each mobile communication subscriber among the multi-user with Cyclic Prefix; C be K size 1/2,1/4,1/8,1/16 and 1/32 in one) insert the time domain that obtains through the IFFT conversion at interval as protection and embed the training sequence coded data block, to form signal frame;
6) each mobile communication subscriber among the multi-user adopts square root raised cosine filter that the signal pulse of signal frame is shaped;
7) each mobile communication subscriber among the multi-user with the baseband signal up-conversion to carrier wave;
8) uploading the base station end of link, adopt many antennas to each the mobile communication subscriber signal among the multi-user carry out synchronously, receiver signals such as channel estimating, equilibrium, decoding handle.
Combine accompanying drawing that specific embodiment of the present invention is specified above, but the present invention is not limited to the foregoing description, under the spirit and scope situation of the claim that does not break away from the application, those skilled in the art can make various modifications or remodeling.
Claims (8)
1. one kind based on embedding the multi-user OFDM modulation method that training sequence and LDPC encode; LDPC is that low-density checksum is represented in the abbreviation of English Low Density Parity Check; OFDM is that OFDM is represented in the abbreviation of English Orthogonal Frequency Division Multiplexing, it is characterized in that it comprises the following steps:
1) each user respectively will zero be inserted into by even discrete programming and form the FFT training sequence piece that disperses in this user's oneself training sequence; Zero number is K-X; The length of training sequence is X, and FFT representes the fast discrete Fourier conversion, and the length of the discrete training sequence piece of FFT is K;
2) each user flows through the input data bit of oneself respectively and further forms the FFT coded data block after LDPC encodes, and the length of FFT coded data block is K;
3) the discrete training sequence piece of FFT, FFT coded data block are directly superposeed form FFT and embed the training sequence coded data block;
4) adopting IFFT that FFT is embedded the discrete sample block that the training sequence coded data block is transformed to time domain is that time domain embeds the training sequence coded data block, and IFFT representes the fast discrete Fourier inverse transformation;
5) Cyclic Prefix is inserted the time domain that obtains through the IFFT conversion at interval as protection and embed the training sequence coded data block, to form signal frame, the length of Cyclic Prefix is C;
6) adopt square root raised cosine filter that the signal pulse of signal frame is shaped;
7) with the baseband signal up-conversion to carrier wave.
2. press the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 1; It is characterized in that: said each user will zero be inserted into this user's oneself training sequence by even discrete programming, and the length X of training sequence is in 32,64,256,512 and 1024.
3. by the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 2, it is characterized in that: said training sequence as each user has pseudo-random characteristics.
4. by the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 2, it is characterized in that: have orthogonality between the training sequence of said different user.
5. press the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 1; It is characterized in that: described each user adopts the LDPC coding that the input data are encoded, and the encoding rate that the input data is carried out the LDPC coding is in 1/4,1/2,5/8,3/4 and 7/8.
6. press the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 1; It is characterized in that: said FFT embeds the training sequence coded data block and is made up of subcarrier, and sub-carrier number is in 128,256,1024,2048 and 4096.
7. by the multi-user OFDM modulation method based on embedding training sequence and LDPC coding of claim 6, it is characterized in that: the frequency interval of said subcarrier is among 128KHz, 64KHz, 16KHz, 4KHz and the 2KHz.
By claim 1 based on embedding the multi-user OFDM modulation method of training sequence with the LDPC coding, it is characterized in that: said length C as protection Cyclic Prefix at interval be FFT coded data block length K big or small 1/2,1/4,1/8,1/16 and 1/32 in one.
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| WO2011137589A1 (en) * | 2010-05-06 | 2011-11-10 | 华为技术有限公司 | Method, device and communication system for modulation transmission |
| CN102255857B (en) * | 2011-08-22 | 2013-07-24 | 宁波大学 | Multimedia broadcast single-frequency network anti-fading mobile signal framing modulation method |
| CN102255858B (en) * | 2011-08-22 | 2013-07-24 | 宁波大学 | Multimedia broadcast single-frequency robust mobile signal framing modulation method |
| CN102255863B (en) * | 2011-08-22 | 2013-07-24 | 宁波大学 | Anti-noise digital mobile broadcast signal transmitting method |
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| CN101064700A (en) * | 2006-04-26 | 2007-10-31 | 电子科技大学 | Method for synchronization of multi-input multi-output OFDM system |
| CN101141168A (en) * | 2007-10-18 | 2008-03-12 | 郑紫微 | Orthogonal time-domain training sequence based multi-user MIMO-OFDM modulation method |
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| CN101141168A (en) * | 2007-10-18 | 2008-03-12 | 郑紫微 | Orthogonal time-domain training sequence based multi-user MIMO-OFDM modulation method |
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