CN101888359A - Multi-address access system based on TDS-OFDM (Time-Domain Synchronous Orthogonal Frequency Division Multiplexing) as well as signal frame structure and receiving method thereof - Google Patents

Abstract

The invention relates to a multi-address access system based on TDS-OFDM (Time-Domain Synchronous Orthogonal Frequency Division Multiplexing). A 'time-user two-dimensional frame structure' is designed in a transmitting end, and a receiving end accomplishes multi-user combined circulating feature reconstitution through adding and subtracting operation, thereby the invention can accomplish the orthogonal separation of frequency-domain multi-user signals through DFT (Discrete Fourier Transformation) and simultaneously relatively accomplishes the orthogonal separation of time-domain multi-user channels through one-step circulation; and the channels belonging to respective users are selected by setting user windows, and then the transmitting signal of each user is recovered by adopting a single-tap frequency-domain balancing method, thereby the invention realizes multi-user access and communication. The invention solves the technical problem that superimposed interference between a frame header and a frame body among multiple users is difficult to eliminate when the TDS-OFDM is used for multi-address access, and meanwhile, the system also realizes multi-user access with lower complexity than that of the traditional single-user TDS-OFDM system and acquires better system performance under the moving condition.

Description

Based on the multiple access system of TDS-OFDM and signal frame structure thereof, method of reseptance

Technical field

The present invention relates to multiple access access communications field, be specifically related to a kind of multiple access system and signal frame structure, method of reseptance based on TDS-OFDM.

Background technology

OFDM technology quilt extensively should be with in one-way broadcast systems or single user system, such as DVB and WLAN, and most practical communication system all is to support the multi-user concurrent two-way communication, so be necessary OFDM is done further expansion, forms the OFDM technology of supporting that the multi-user inserts.

In wireless communication system, multi-access mode allows a plurality of mobile subscribers to share limited frequency spectrum resources simultaneously.Frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA) are three kinds of main access technologies sharing effective bandwidth in the wireless communication system.And OFDM (Orthogonal Frequency Division Multiplexing Access OFDMA) technology is a kind of multiple access technology based on OFDM, be also referred to as the multi-user OFDM technology, this technology proposes and is applied to (CATV) in the cable TV network by Sari and Karam at first.OFDMA is divided into the sub-carrier set of quadrature with transmission bandwidth, reaches the purpose that the multi-user inserts to different users different sub-carrier set flexible allocation.In the OFDMA up link, the signal of different user arrives the base station simultaneously and receives, and supposes each with reaching ideal synchronisation per family, and then separate by subcarrier in frequency domain the base station, can separate and recover each user's signal accurately, thereby avoid the multiple access between different user to disturb.OFDMA is the effective means that realizes multiuser multiplexing and access in the ofdm system, therefore also receive much attention in recent years and study, just adopted the OFDMA technology at European Digital Television return path standard DVB-RCT, in the IEEE802.16e standard, OFDMA is applied in the WiMAX system as most crucial physical-layer techniques.OFDMA extensively is considered as the one preferred technique of NGBW communication.

In many OFDMA systems; the OFDM symbol all uses the protection interval of Cyclic Prefix (CyclicPrefix) as the IDFT piece; so that the multipath signal that may exist in the counteracting received signal prevents intersymbol interference, this structure is called Cyclic Prefix in OFDM System (CP-OFDM).CP-OFDM has obtained extensive use at present, and as DAB, DVB-T, IEEE 802.11a, HIPERLAN/2, WLAN, WiMAX etc., CP-OFDM has all been used in most at present B3G/4G motions.The Chinese invention patent of Tsing-Hua University's application " protection fill method at interval in the orthogonal FDM modulation system " (grant number is 01124144.6) has proposed protection at interval the OFDM frame structure of PN sequence as the IDFT piece; and formed based on this Chinese terrestrial DTV standard DTMB core technology TDS-OFDM (TimeDomain Synchronous OFDM, TDS-OFDM).With respect to CP-OFDM; because the PN sequence in the TDS-OFDM system is except the protection at interval as the OFDM piece; can also be used as the purposes such as frame synchronization, carrier wave recovery and automatic frequency tracking, symbol clock recovery, channel estimating of signal frame at receiving terminal; thereby do not need to utilize as CP-OFDM special pilot tone or leading training sequence to assist to finish synchronously and channel estimating, thereby TDS-OFDM can provide the spectrum efficiency than CP-OFDM high about 10% again.In addition, existing document proves that TDS-OFDM can provide than CP-OFDM better system performance.

In OFDMA system based on CP-OFDM; different sole users' signal frame is through after the multipath channel; frame head protection interval and frame OFDM data all can produce shown in shade among Figure 1A " hangover "; but because protection is the Cyclic Prefix of frame OFDM data at interval; so when channel is supposed under the constant prerequisite at same signal frame in the duration; " hangover " that the frame head protection produces at interval is identical with " hangover " that frame OFDM data produce; in receiving end signal, directly intercept the frame part; then be equivalent to " hangover " that frame produces directly is superimposed upon on the frame receiving sequence; like this; the frame receiving sequence just has cycle characteristics, shown in Figure 1A.The CP-OFDM system has cycle characteristics just because of the frame receiving sequence of directly removing after protecting at interval; thereby the linear convolution of frame OFDM data and interchannel is converted into circular convolution; thereby can just can finish the channel equalization of frame OFDM data by simple discrete Fourier transform (DFT) (DFT), and then recover the frame OFDM data of transmitting terminal.In the OFDMA system; the frequency domain data that different user sends is mutually orthogonal; behind too much channel; these signals then are superimposed at the time-domain signal of base station receiving terminal; suppose that each is with reaching ideal synchronisation per family; then according on all four method in single user's ofdm system; protection is directly removed at interval in the base station from received signal; resulting each user data linear superposition received signal together still has cycle characteristics; therefore; this signal is transformed to frequency domain as DFT, then separate, and then can recover the transmission data of different user at the frequency domain subcarrier that each user is mutually orthogonal.

Yet in the OFDMA system based on TDS-OFDM, situation is just more complex.For certain sole user based on the multiple access system of TDS-OFDM; because its frame head protection is not a Cyclic Prefix at interval; but different PN sequence; so the TDS-OFDM signal frame is through after the multipath channel; shown in Figure 1B; " hangover " that frame head PN sequence produces is fully different with " hangover " that frame OFDM data produce; directly the sequence of intercepting frame part gained will no longer have cycle characteristics because " hangover " of frame head PN sequence disturbed in receiving end signal, so can not directly use the DFT conversion to realize channel equalization.Therefore, need adopt the method for continuous iteration to eliminate of the interference of PN sequence, so that recover the cycle characteristics of frame ofdm signal to frame OFDM data at receiving terminal.Document is arranged in the prior art on the basis of above-mentioned iteration interference elimination method, proposed a kind of respectively based on the auxiliary iteration interference elimination method of part judgement with based on the iteration interference elimination method of training sequence reconstruction, to reduce the complexity of iteration interference eliminated.Yet all there is the problem of two aspects in above-mentioned three kinds of methods: at first, the iteration interference elimination method need carry out repeatedly iteration, and algorithm is comparatively complicated, and operand is very big, and implementation complexity is higher, and the power consumption of receiver is also bigger; Secondly, only can obtain under the situation of desirable channel estimating, could eliminate the influence of PN sequence fully, otherwise will have remaining intersymbol interference at receiving terminal, thus the systematic function of having a strong impact on.We can say, the PN sequence is the main difficult point and the deficiency of TDS-OFDM system with mutual interference mutually between the OFDM data block, this problem is particularly outstanding in based on the multi-address system of TDS-OFDM, because the signal that different user sends among Figure 1B is through behind the different channels, the base station receiving terminal must be isolated the signal of different user, and the PN sequence of different user (even different usefulness adopts identical PN sequence per family) is through all producing different interference to the OFDM data division behind the different channels, these interference are superimposed, have only after the base station estimates all subscriber channel impulse responses and just can the interference of these stacks be removed one by one according to above-mentioned iteration interference elimination method, and to obtain all users' channel estimating, must at first eliminate of the interference (suppose channel estimating still by PN sequence obtain) of the data of the different user that is superimposed to the PN sequence, but data are known each user's transmission data and the channel estimating that obtains all users to the prerequisite of the stack interference eliminated of PN sequence, and this is impossible before each user's signal is correctly separated in the base station.Therefore, in multi-user TDS-OFDM, interference between the data of different user and the PN sequence is superimposed, make and originally may not eliminate the interference that a plurality of users are superimposed with regard to the iteration interference elimination method of more complicated, the base station receiving terminal also just can not be isolated the signal of different user.Just because of this reason, at present the document based on the multiple access system of TDS-OFDM is very few.

Summary of the invention

The purpose of this invention is to provide a kind of multiple access system and signal frame structure and method of reseptance based on TDS-OFDM, when solving TDS-OFDM and being used for multiple access and inserting between the multi-user stack between frame head and the frame disturb and be difficult to eliminate this technical barrier, this system has been also having realized multi-user's access than traditional lower complexity of single user TDS-OFDM system simultaneously, and obtained better system performance under mobile condition.

For achieving the above object, the present invention adopts following technical scheme:

The invention provides a kind of signal frame structure of the multiple access system based on TDS-OFDM, signal frame comprises frame head PN sequence, signal frame have time-user's two-dimensional frames structure:

On time shaft, m user is at the m of i+1 frame sequence p _{M, i+1}Be m sequence p by the i frame _{M, i}Through L _tObtain behind the cyclic shift of position, i, m are positive integer;

On user's axle, adjacent m and m+1 the m sequence p that the user is adopted in i signal frame _{M+1, i}And p _{M, i}, p _{M+1, i}Be p _{M, i}Through L _uObtain behind the cyclic shift of position;

M sequence in each signal frame is through L _tObtain the frame head PN sequence of this signal frame after the cyclic extensions of position.

Preferably, L _tThe length that is less than or equal to the m sequence;

L _u〉=l _MaxAnd ML _u≤ N _p, l wherein _MaxBe the maximum multipath time delay of the channel of different user process, N _pBe the length of m sequence, M is the total number of users in the system.

Preferably, obtain the frame head PN sequence of each user in each signal frame after, obtain comprising the complete signal frame of each user data signal according to the signal processing flow of TDS-OFDM modulation system.

The invention allows for a kind of method of reseptance of the multiple access system based on TDS-OFDM, the receiving terminal of this system is finished the reconstruct of multi-user association cycle characteristics by a plus and minus calculation, reconstructs the cycle characteristics of all user's received signals on time domain simultaneously.

Preferably, the receiving terminal of this system will arrive frequency domain through the signal transformation after the reconstruct of multi-user association cycle characteristics on the time domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, thereby the quadrature of having finished all subscriber signals on frequency domain separates.

Preferably, the receiving terminal of this system separates all users' channel quadrature on time domain.

Preferably, receiving terminal according on the frequency domain isolated each user's received signal with on time domain, separate each the subscriber channel information that obtains, adopt single tap frequency-domain equilibrium method to recover each user's transmission data.

Preferably, this method is done circular convolution or the relevant channel estimating that obtains all subscriber channels of time domain with the signal that the multi-user m sequence that receives is superimposed with local m sequence, and selects to belong to each user's channel by mutually orthogonal user window is set on time domain.

Preferably, being used for doing the relevant local m sequence of circular convolution or time domain is the m sequence that any one user of multiple access system is adopted at the current demand signal frame.

The present invention also provides a kind of multiple access system based on TDS-OFDM, in this system multi-user's transmitting terminal have be used to generate have time-the frame production unit of signal frame of user's two-dimensional frames structure;

The receiving terminal of this system has time domain cycle characteristics reconfiguration unit, finishes the reconstruct of multi-user association cycle characteristics by a plus and minus calculation, reconstructs the cycle characteristics of all user's received signals on time domain simultaneously.

The receiving terminal of this system also has:

Subscriber signal quadrature separative element: be used for and arrive frequency domain through the signal transformation after the reconstruct of multi-user association cycle characteristics on the time domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, the quadrature of having finished all subscriber signals on frequency domain separates;

Channel quadrature separative element is used on time domain all users' channel quadrature is separated;

Data recovery unit, be used for according on the frequency domain isolated each user's received signal with on time domain, separate each the subscriber channel information that obtains, adopt single tap frequency-domain equilibrium method to recover each user's transmission data.

Utilize multiple access system and the signal frame structure, method of reseptance based on TDS-OFDM provided by the invention, when solving TDS-OFDM and being used for multiple access and inserting between the multi-user stack between frame head and the frame disturb and be difficult to eliminate this technical barrier, this system has been also having realized multi-user's access than traditional lower complexity of single user TDS-OFDM system simultaneously, and obtained better system performance under mobile condition.

Description of drawings

Figure 1A is based on the frame assumption diagram in the CP-OFDM multiple access system in the prior art;

Figure 1B is based on the frame assumption diagram in the multiple access system of time-domain synchronization OFDM TDS-OFDM in the prior art;

Fig. 2 be the present invention is based on transmitting terminal in the multiple access system of TDS-OFDM time-user's two-dimensional frames structure chart;

Fig. 3 A is the transmission signal frame structure figure that the present invention is based on m user data of transmitting terminal in the multiple access system of TDS-OFDM;

Fig. 3 B is the received signal frame assumption diagram that the present invention is based on m user of receiving terminal in the multiple access system of TDS-OFDM;

With 3C be the reconstruct schematic diagram that the present invention is based on the Cyclic Prefix of m user data of receiving terminal in the multiple access system of TDS-OFDM;

Fig. 4 is the cycle characteristics combined reconstruction process schematic diagram that the present invention is based on receiving terminal all customer data in the multiple access system of TDS-OFDM;

Fig. 5 the present invention is based on that the local m sequence of receiving terminal is p in the multiple access system of TDS-OFDM _{1, i}The position of each user window when (first user's m sequence);

Fig. 6 the present invention is based on that the local m sequence of receiving terminal is p in the multiple access system of TDS-OFDM _{2, i}The position of each user window when (second user's m sequence);

Fig. 7 A～7C is the sub-carrier distribution manner schematic diagram that the present invention is based in the multiple access system of TDS-OFDM;

Fig. 8 A is that to the present invention is based on number of users in the multiple access system of TDS-OFDM be 2 o'clock theory diagram;

Fig. 8 B is that to the present invention is based on number of users in the multiple access system of TDS-OFDM be 3 o'clock theory diagram;

Fig. 8 C is the theory diagram that the present invention is based on when number of users is M in the multiple access system of TDS-OFDM;

Fig. 9 A the present invention is based on different user actual channel figure in the multiple access system of TDS-OFDM;

Fig. 9 B the present invention is based in the multiple access system of TDS-OFDM different user to estimate channel mapping;

Figure 10 is based on the SER performance of different user in the multiple access system of TDS-OFDM in the embodiment of the invention;

Figure 11 be in the embodiment of the invention based in the multiple access system of TDS-OFDM under the time varying channel condition with single SER performance comparison with the positive Frequency Division Multiplexing system of Domain Synchronous.

Embodiment

Multiple access sending, receiving method and device and multiple access system based on TDS-OFDM that the present invention proposes are described as follows in conjunction with the accompanying drawings and embodiments.

These two key issues of channel of disturbing and can't distinguish different user at the stack between the data that can't eliminate different user among the multi-user TDS-OFDM and the PN sequence, the present invention proposes a kind of multiple access system and signal frame structure thereof based on TDS-OFDM, method of reseptance, by frame structure design special in this multiple access system, make multiple access system not only can separate at the frequency domain quadrature by the cycle characteristics of simple all subscriber channels of plus and minus calculation reconstruct once and with each subscriber signal, and can separate by the channel quadrature on time domain of simple related operation once with all users, thereby recover each user's transmission signal at receiving terminal, realized the application in multiple access access field of this core technology of TDS-OFDM, established solid foundation for opening up the more wide application of TDS-OFDM.

Embodiment 1

Multiple access system based on TDS-OFDM of the present invention is also handled this M user's data simultaneously but there be M user to initiate to insert request in the back-up system simultaneously.

In the multiple access system based on time-domain synchronization OFDM of the present invention, signal frame comprises frame head PN sequence, and the frame head PN sequences Design of each user in the unlike signal frame is as follows: on time shaft, m user is at the m of i+1 frame sequence p _{M, i+1}Be m sequence p by the i frame _{M, i}Through L _tObtain behind the cyclic shift of position, i, m are positive integer; On user's axle, adjacent m and m+1 the m sequence p that the user is adopted in i signal frame _{M+1, i}And p _{M, i}, p _{M+1, i}Be p _{M, i}Through L _uObtain behind the cyclic shift of position; M sequence in each signal frame is through L _tObtain the frame head PN sequence of this signal frame after the cyclic extensions of position.

As shown in Figure 2 " time-user's two-dimensional frames structure ", each user's signal frame is N by frame OFDM data block and length _gFrame head PN sequence constitute the PN sequence c of m user's i signal frame _{M, i}=[c _{M, i}(0), c _{M, i}(1) ..., c _{M, i}(N _g-1)] then by m sequence p _{M, i}=[p _{M, i}(0), p _{M, i}(1) ..., p _{M, i}(M _p-1)] and L _tThe position Cyclic Prefix constitutes:

$c_{m,i}\left(n\right)=\left\{\begin{array}{cc}{p}_{m,i}(N_p-L_t+n)& 0\≤n\≤L_t-1\\ p_{m,i}(n-L_t)& L_t\≤n{\≤N}_g-1\end{array}\right.---\left(1\right)$

Obviously following formula is set up:

N _g＝N _p+L _t???????????????????????????????(2)

On the time shaft in " time-user's two-dimensional frames structure ", m the m sequence p of user in i+1 signal frame _{M, i+1}Be m sequence p by the i frame _{M, i}Through L _tThe position obtains behind the cyclic shift forward, on user's axle, and m+1 the m sequence p of user in the i frame _{M+1, i}, then be by the m sequence p of m user in the i frame _{M, i}Through L _uObtain behind the cyclic shift of position:

$\left\{\begin{array}{c}{p}_{m,i+1}=p_{m,i}\·D^{L_t}\\ p_{m+1,i}=p_{m,i}\·D^{L_u}\end{array}\right.---\left(3\right)$

D wherein ^LExpression is to a certain sequence cycles displacement L position.

On time shaft,, can get by (3) for m+1 user

$p_{m+1,i+1}=p_{m+1,i}\·D^{L_t}---\left(4\right)$

I.e. m+1 the m sequence p of user in the i+1 frame _{M+1, i+1}Also be m sequence p by the i frame _{M+1, i}Through L _tObtain behind the cyclic shift of position.

On user's axle, in the i+1 frame, can get by (3)

$p_{m+1,i+1}=p_{m,i+1}\·D^{L_u}---\left(5\right)$

Promptly in the i+1 frame, m+1 user's m sequence p _{M+1, i+1}Also be m sequence p by m user _{M, i+1}Through L _uObtain behind the cyclic shift of position.

Present embodiment is at first analyzed in " time-user's two-dimensional frames structure " characteristics of frame structure on the time shaft.

By (1), (3) as can be known, the PN sequence c of i+1 frame _{M+1, i}M sequence p with the i frame _{M, i}Between the pass be:

$c_{m,i+1}\left(n\right)=\left\{\begin{array}{cc}{p}_{m,i}\left(n\right)& 0\≤n\≤N_p-1\\ p_{m,i}(n-N_p)& N_p\≤n{\≤N}_g-1\end{array}\right.---\left(6\right)$

The PN sequence that obtains is inserted between the frame OFDM data block, obtains complete signal frame as shown in Figure 2.By (1), (6) as can be known, the frame head of m user i signal frame protection sequence c _{M, i}Back N _pThe frame head protection sequence c of individual symbol and i+1 signal frame _{M+1, i}Preceding N _pIndividual symbol is identical, all is the m sequence p of i signal frame _{M, i}, also be the frame OFDM data x of i signal frame _{M, i}Two ends are close to identical m sequence p respectively _{M, i}This characteristic is the m sequence p by next frame in the above-mentioned frame structure design _{M, i+1}Be m sequence p by present frame _{M, i}Through L _tThis method that position rotation bit in-migration obtains guarantees, analysis from behind as can be known, this specific character that receiving terminal utilizes this phase relation to obtain is just come the cycle characteristics of reconstruct frame OFDM data.

After obtaining the frame head PN sequence of each user in each signal frame, obtain comprising the complete signal frame of each user data signal according to the signal processing flow of TDS-OFDM modulation system, details are as follows: suppose that the number of users that inserts based on time in the multiple access system of time-domain synchronization OFDM is M, all can utilize the sets definition of subcarrier to be Γ, Γ _mThe subcarrier table of representing m user, element has wherein been represented the subcarrier label of m CU.Then have:

$\mathrm{\Γ}=\underset{m=1}{\overset{M}{\∪}}{\mathrm{\Γ}}_m---\left(7\right)$

If m user i the L that the OFDM symbol need send _mIndividual frequency-region signal is D _{M, i}=[D _{M, i}(0), D _{M, i}(1) ..., D _{M, i}(L _m-1)], through obtaining the frequency domain vectors x of N dimension after the subcarrier allocation _{M, i}=[X _{M, i}(0), X _{M, i}(1) ..., X _{M, i}(N-1)]:

$X_{m,i}\left(n\right)=\left\{\begin{array}{cc}{D}_{m,i}\left(n\right)& n\&Element;{\mathrm{\&Gamma;}}_{\mathrm{<figure-callout\; id="0"\; label="m"\; filenames="H2009100837922E0000092.png"\; state="\{\{state\}\}">m</figure-callout>}}\\ 0& \mathrm{otherwise}\end{array}\right.---\left(9\right)$

x _{M, i}After the IDFT computing, its time domain signal indication is:

$x_{m,i}\left(n\right)=\mathrm{IDFT}\left[X_{m,i}\right]=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_{m,i}\left(k\right)\exp \left\{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2009100837922E0000052.png,H2009100837922E0000062.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;nk}}{N}\right\}0\&le;n\&le;N-1---\left(10\right)$

Time domain frame volume data x in the IDFT output that obtains _{M, i}(n) (the preceding insertion frame head PN sequence c of 0≤n≤N-1) _{M, i}(n) (0≤n≤N _g-1), then obtained m user i time-domain signal frame s _{M, i}(n) (0≤n≤N _f-1):

$S_{m,i}\left(n\right)=\left\{\begin{array}{cc}{c}_{m,i}\left(n\right)& 0\&le;n\&le;N_g-1\\ x_{m,i}\left(n\right)& N_g\&le;n{\&le;N}_f-1\end{array}\right.$

Obviously, N is arranged here _f=N+N _g

For using existing m sequence commonly used, its length N in the system _pCan choose flexibly according to the maximum multipath time delay of the required antagonism of system, preferably embodiment can be: first kind of execution mode: N _p=127; Second kind of execution mode: N _p=255; The third execution mode: N _p=511.

The phase difference L of the m sequence that is adopted for same user's consecutive frame _t, should satisfy L _t≤ N _p, work as N _p=255 o'clock, preferably its embodiment can be: first kind of execution mode: L _t=211; Second kind of execution mode: L _t=165; The third execution mode: L _t=153; The 4th kind of execution mode: L _t=N _p

The phase difference L of the m sequence that in same signal frame, is adopted for neighboring user _u, should satisfy L _u〉=l _Max, l wherein _MaxThe maximum multipath time delay of the channel of expression different user process should satisfy ML simultaneously _u≤ N _p, work as N _p=255, M=2, l _Max=60 o'clock, preferably its embodiment can be: first kind of execution mode: L _u=60; Second kind of execution mode: L _u=76; The third execution mode: L _u=127.

For available sub-carrier number N, preferably its execution mode can be: first kind of execution mode: N=1000; Second kind of execution mode: N=2000; The third execution mode: N=3780; The 4th kind of execution mode: N=8000.

The distribution of the subcarrier that M different user is taken for transmitting terminal, its execution mode can be: first kind of execution mode: whole bandwidth is distributed into a plurality of continuous sub-carriers groups, the subcarrier that continuous adjacent is arranged in each group, distribute one or more sub carrier group to transmit its signal frame for each user, shown in Fig. 7 A; Second kind of execution mode: adopting the subcarrier that interweaves is M the subcarrier that different user distributes it to take: have one group of subcarrier allocation at interval and give same user, make each user's subcarrier be evenly distributed on the given bandwidth, the carrier wave of different subchannels interweaves in the mode of rule, shown in Fig. 7 B; The third execution mode: the third execution mode is the improvement to second kind of execution mode, adopting pseudorandom interlace assignment is M the subcarrier that different user distributes it to take: one group of subcarrier allocation with unequal interval is given same user, make each user's subcarrier non-uniform Distribution on given bandwidth, the carrier wave of different subchannels interweaves in pseudorandom mode, shown in Fig. 7 C.

Embodiment 2

Present embodiment provides the method for reseptance based on the multiple access system of TDS-OFDM.

According to top formula (11) as can be known, transmitting terminal is at the time domain frame volume data x of the IDFT output that obtains _{M, i}(n) (the preceding insertion frame head PN sequence c of 0≤n≤N-1) _{M, i}(n) (0≤n≤N _g-1), then obtained m user i time-domain signal frame s _{M, i}(n) (0≤n≤N _f-1):

$s_{m,i}\left(n\right)=\left\{\begin{array}{cc}{c}_{m,i}\left(n\right)& 0\&le;n\&le;N_g-1\\ x_{m,i}\left(n\right)& N_g\&le;n{\&le;N}_f-1\end{array}\right.$

Obviously, N is arranged here _f=N+N _g

M user's transmission discrete-time signal can be expressed as:

$s_m^{\left(T\right)}\left(n\right)=\underset{i}{\mathrm{\&Sigma;}}{s}_{m,i}(n-i\&CenterDot;N_f)---\left(12\right)$

Suppose that m user is expressed as h in the impulse response of the channel of i signal frame process _{M, i}=[h _{M, i}(0), h _{M, i}(1) ..., h _{M, i}(l _m)], l wherein _mMaximum multipath time delay and the hypothesis of representing m subscriber channel

Above-mentioned signal frame s _{M, i}(n) through after the multipath channel, the data of different piece all can produce " hangover " because of multipath in the signal frame, thereby cause the interference of frame head to frame, and frame is to the interference of next signal frame frame head, shown in the dash area among Fig. 3 B.

For the ease of analyzing, in the present embodiment i frame signal quadrature on time domain of transmitting terminal is decomposed into three parts as shown in Fig. 3 A: j _{M, i}(n), p _{M, i}(n) and x _{M, i}(n), j wherein _{M, i}(n) be p _{M, i}(n) L _tThe position suffix.By formula (4) as can be known, the PN sequence c of i+1 frame _{M, i+1}(n) front N _pIndividual symbol is p _{M, i}(n), as shown in Figure 3A.A few part transmitting terminal data j among Fig. 3 A _{M, i}(n), p _{M, i}(n) and x _{M, i}(n) be h through channel impulse response _{M, i}=[h _{M, i}(0), h _{M, i}(1) ..., h _{M, i}(l _m)] multipath channel after, produce after " hangover " the receiving terminal data respectively correspondence table be shown the k shown in Fig. 3 B _{M, i}(n), q _{M, i}(n) and y _{M, i}(n) part promptly has:

$k_{m,i}\left(n\right)=j_{m,i}\left(n\right)*h_{m,i}\left(n\right)=\underset{w=0}{\overset{l_m}{\mathrm{\&Sigma;}}}{h}_{m,i}\left(w\right)\&CenterDot;j_{m,i}(n-w),0\&le;n{\&le;L}_t+l_m-1---\left(13\right)$

$q_{m,i}\left(n\right)=p_{m,i}\left(n\right)*h_{m,i}\left(n\right)=\underset{w=0}{\overset{l_m}{\mathrm{\&Sigma;}}}{h}_{m,i}\left(w\right)\&CenterDot;p_{m,i}(n-w),0\&le;n\&le;N_p+l_m-1---\left(14\right)$

$y_{m,i}\left(n\right)=x_{m,i}\left(n\right)*h_{m,i}\left(n\right)=\underset{w=0}{\overset{l_m}{\mathrm{\&Sigma;}}}{h}_{m,i}\left(w\right)\&CenterDot;x_{m,i}(n-w),0\&le;n\&le;N+l_m-1---\left(5\right)$

Top * represents linear convolution.Because j _{M, i}(n) be p _{M, i}(n) L _tThe position suffix is so work as l _m≤ L _tAnd when the variation of channel in the duration of a signal frame can be ignored, the two was through the response k after the multipath channel _{M, i}(n) and q _{M, i}(n) " hangover " With

Also inevitable identical (shown in vertical line dash area among Fig. 3 B) promptly has:

${\left\{k_{m,i}\left(n\right)\right\}}_{n=L_t}^{L_t+l_m-1}={\left\{q_{m,i}\left(n\right)\right\}}_{n=N_p}^{N_p+l_m-1}---\left(16\right)$

Received signal among Fig. 3 B Can be expressed as:

r _m，i(n)＝u _m，i(n)+v _m，i(n)0≤n≤N _f+N _p-1????????(17)

V wherein _{M, i}(n) be gaussian additive noise, u _{M, i}(n) then can receive data by each several part among Fig. 3 B is expressed as:

$u_{m,i}\left(n\right)=\left\{\begin{array}{cc}{k}_{m,l}\left(n\right)+y_{m,i-1}(N_f+n)& 0\&le;n\&le;L_t-1\\ q_{m,i}(n-L_t)+k_{m,i}\left(n\right)& L_t\&le;n{\&le;N}_g-1\\ y_{m,i}(n-N_g)+q_{m,i}(n-N_g+N_p)& N_g\&le;n\&le;N_f-1\\ q_{m,i}(n-N_f)+y_{m,i}(n-N_f+N)& N_f\&le;n{\&le;N}_f+N_p-1\end{array}\right.---\left(18\right)$

When ignoring noise v _{M, i}(n) time, as shown in Fig. 3 C, to receiving sequence

Do the new sequence of reception that following plus and minus calculation obtains frame OFDM data

$y_{m,i}^{\&prime;}\left(n\right)=\left\{\begin{array}{cc}{r}_{m,i}(n+N_g)+r_{m,i}(n+N_f)-r_{m,i}(n+L_t)& 0\&le;n\&le;N_p-1\\ r_{m,i}(n+N_g)& N_p\&le;n\&le;N-1\end{array}\right.---\left(19\right)$

With (16), (17), (18) formula substitution (19), can get:

$y_{m,i}^{\&prime;}\left(n\right)=\left\{\begin{array}{cc}{y}_{m,i}(n+N)+y_{m,i}\left(n\right)& 0\&le;n\&le;l_m-1\\ y_{m,i}\left(n\right)& l_m\&le;n\&le;N-1\end{array}\right.---\left(20\right)$

Sequence

Form and Figure 1A in the form of CP-OFDM received signal in full accord, therefore, the present invention just can reconstruct cycle characteristics based on m user's frame OFDM data in the multiple access system of time domain orthogonal frequency division multiplexing by the simple plus and minus calculation to receiving sequence.

Equally, for based on whole M users in the multiple access system of TDS-OFDM, suppose that receiving terminal reaches ideal synchronisation, M user's signal is superimposed at receiving terminal, as shown in Figure 4:

$r_{\mathrm{total},i}\left(n\right)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}\left(n\right),0\&le;n{\&le;N}_f+N_p-1---\left(21\right)$

According to aforementioned m the on all four plus and minus calculation of subscriber signal handled the signal that receiving terminal is superimposed:

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\left\{\begin{array}{cc}{r}_{\mathrm{total},i}(n+N_g)+r_{\mathrm{total},i}(n+N_f)-r_{\mathrm{total},i}(n+L_t)& 0\&le;n\&le;N_p-1\\ r_{\mathrm{total},i}(n+N_g)& N_p\&le;n\&le;N-1\end{array}\right.---\left(22\right)$

Bring formula (21) into (22), can get:

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\left\{\begin{array}{cc}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}(n+N_g)+r_{m,i}(n+N_f)-r_{m,i}(n+L_t)& 0\&le;n\&le;N_p-1\\ \underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}(n+N_g)& N_p\&le;n\&le;N-1\end{array}\right.---\left(23\right)$

By formula (19) as can be known, in the summation symbol each user's the equal restructural of plus-minus processing is gone out the cycle characteristics of this user's frame OFDM data in the formula (23), in (19) substitution (23), promptly has:

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{y^{\&prime;}}_{m,i}\left(n\right),0\&le;n\&le;N-1---\left(24\right)$

Therefore, the linear superposition signal for M the received signal that obtains after M user data and the channel linearity convolution separately after the plus-minus processing through formula (22), is converted into the linear superposition that M user with cycle characteristics receives data.

This process as shown in Figure 4.Can find, very similar in the TDS-OFDM multiple access system among Fig. 4 through the signal in the CP-OFDM multiple access system among the multiple user signals form after the plus-minus processing and Figure 1A.

The signal y ' with cycle characteristics of the multi-user's time domain linear stack that obtains after above-mentioned plus and minus calculation handled _{Total, i}=[y ' _{Total, i}(0), y ' _{Total, t}(1) ..., y ' _{Total, i}(N-1)] transform to frequency domain as DFT, obtain Y ' _{Total, i}=[Y ' _{Total, i}(0), Y ' _{Total, i}(1) ..., Y ' _{Total, i}(N-1)]:

${Y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\mathrm{DFT}\left\{{y^{\&prime;}}_{\mathrm{total},i}\right\}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{y^{\&prime;}}_{\mathrm{total},i}\left(k\right)\exp \{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2009100837922E0000052.png,H2009100837922E0000062.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;nk}}{N}\},0\&le;n\&le;N-1---\left(25\right)$

According to transmitting terminal sub-carrier distribution manner one to one, choose at frequency domain and to belong to user's signal separately:

${Y^{\&prime;}}_{m,i}\left(n\right)=\left\{\begin{array}{cc}{Y^{\&prime;}}_{\mathrm{total},i}\left(n\right)& n\&Element;{\mathrm{\&Gamma;}}_m\\ 0& n\&NotElement;{\mathrm{\&Gamma;}}_m\end{array}\right.,1\&le;m\&le;M---\left(26\right)$

Wherein, n is the numbering of subcarrier, the user that the m representative is different.Y ' in the formula _{M, i}(n) the signal y ' that obtains for process Cyclic Prefix reconstruct among Fig. 4 _{M, i}(n) frequency domain representation, its vector representation is

${Y^{\&prime;}}_{m,i}=\left[{Y^{\&prime;}}_{m,i}\left(n\right)\right]{|}_{n\&Element;{\mathrm{\&Gamma;}}_m}.$

Because between the subcarrier that different user takies is mutually orthogonal

Therefore, separated by quadrature at frequency domain, thereby the quadrature of having realized multi-address signal separates at the multiple user signals of time domain linear stack.

As seen, receiving terminal at the TDS-OFDM multiple access system, just can reconstruct the cycle characteristics of the frame OFDM data that all users superpose in time domain linear simultaneously by simple plus and minus calculation once, not only avoided in the multiple access system receiving the computing and the error thereof of the high complexity that the cycle characteristics of data may bring, and the cycle characteristics reconstructing method in this multiple access system is much also simpler than the iterative cycles reconstructing method that single user in the traditional TDS-OFDM system receives data for each user of reconstruct respectively.After having the signal process DFT conversion of cycle characteristics, can each user's signal in orthogonal be separated at frequency domain.

Embodiment 3

Present embodiment provide employing and embodiment 2 same procedure at receiving terminal after the quadrature of having finished all subscriber signals on the frequency domain separates, how recover the process of the initial data of making a start by channel estimating.

If l _Max≤ L _t, then have the Y ' of cycle characteristics _{M, i}Can be expressed as:

Y′ _m，i(n)＝H _m，i(n)·X _m，i(n)+W _m，i(n)??0≤n≤N-1??????????????(27)

W wherein _{M, i}(n) be noise, H _{M, i}=[H _{M, i}(0), H _{M, i}(0) ..., H _{M, i}(N-1)] be the channel h of m user in i frame process _{M, i}The DFT conversion:

$H_{m,i}\left(n\right)=\underset{l=0}{\overset{l_m}{\mathrm{\&Sigma;}}}{h}_{m,i}\left(l\right)\&CenterDot;\exp \{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2009100837922E0000052.png,H2009100837922E0000062.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;nl}}{N}\},0\&le;n\&le;N-1---\left(28\right)$

As seen, but at the multi-address signal that the quadrature that frequency domain obtains separates is the signal of transmission signal through obtaining behind each self-channel of different user, therefore, recover each user's transmission signal, also must obtain different user channel estimating separately, thus the initial data that just can obtain making a start after the frequency domain channel equalization by one group of single tap.

In order to obtain each user's channel estimating, present embodiment is analyzed in the multiple access system based on time-domain synchronization OFDM in " time-user's two-dimensional frames structure " characteristics of frame structure on user's axle again.The m sequence p that neighboring user m and m+1 are adopted in same signal frame (such as the i frame) among Fig. 2 _{M+1, i}And p _{M, i}Satisfy the relation in the formula (3), so

$p_{m,i}={\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="H2009100837922E0000021.png,H2009100837922E0000031.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1,i}\&CenterDot;D^{(m-1)\&CenterDot;L_u},1\&le;m\&le;M---\left(29\right)$

Because the m sequence has very good autocorrelation, promptly has:

$\underset{k=0}{\overset{N_p-1}{\mathrm{\&Sigma;}}}{p}_{m,i}\left(k\right)\&CenterDot;p_{m,i}(<k-n{>}_{N_p})=N_p\&CenterDot;\mathrm{\&delta;}\left(n\right)---\left(30\right)$

In the following formula＜N _pN is pressed in expression _pDelivery.(30) formula also can be expressed as:

$p_{m,i}\&CircleTimes;p_{m,i}\&ap;N_p\&CenterDot;\mathrm{\&delta;}\left(n\right),1\&le;m\&le;M---\left(31\right)$

Wherein

The expression circular convolution.

By (30) formula as can be known, p _{M+1, i}And p _{M, i}Between cross-correlation function be:

$\underset{k=0}{\overset{N_p-1}{\mathrm{\&Sigma;}}}{p}_{m+1,i}\left(k\right)\&CenterDot;p_{m,i}(<k-n{>}_{N_p})=\underset{k=0}{\overset{N_p-1}{\mathrm{\&Sigma;}}}{p}_{m,i}\left({<k-{\mathrm{<figure-callout\; id="0"\; label="L"\; filenames="H2009100837922E0000092.png"\; state="\{\{state\}\}">L</figure-callout>}}_0>}_{N_p}\right)\&CenterDot;p_{m,i}\left({<k-n>}_{N_p}\right)=N_p\&CenterDot;\mathrm{\&delta;}(n-L_u)---\left(32\right)$

Promptly have:

$p_{j,i}\&CircleTimes;p_{k,i}\&ap;N_p\&CenterDot;\mathrm{\&delta;}[n-(k-j)\&CenterDot;L_u],1\&le;k,j\&le;M---\left(33\right)$

Suppose total M user in the multiple access system, the channel of process is expressed as h respectively _{M, i}=[h _{M, i}(0), h _{M, i}(1) ..., h _{M, i}(l _m)], 1≤m≤M wherein is because L before in a user the PN sequence _tIndividual symbol is the Cyclic Prefix of m sequence, and has

Therefore the m sequence that receives of receiving terminal itself just has cycle characteristics, so the stack sequence q of M m sequence receiving of i frame _iCan be expressed as:

$q_i=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,i}\&CircleTimes;h_{m,i}+v_i---\left(34\right)$

Vector v wherein _iThe Gaussian noise of representing the i frame.

To receive stack sequence q _iWith one of local m sequence p _{1, i}Make circular convolution, utilize (33) formula, can get:

$q_i\&CircleTimes;{\mathrm{<figure-callout\; id="1"\; label="q"\; filenames="H2009100837922E0000021.png,H2009100837922E0000031.png"\; state="\{\{state\}\}">q</figure-callout>}}_{1,i}\&ap;(\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,i}\&CircleTimes;h_{m,i})\&CircleTimes;{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="H2009100837922E0000021.png,H2009100837922E0000031.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1,i}\&ap;N_p\&CenterDot;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{h}_{m,i}\&CenterDot;\mathrm{\&delta;}[n-(m-1)\&CenterDot;L_u]---\left(35\right)$

By (35) formula as can be known, h _{M, i}On time domain, moved (m-1) L _u, if l _Max≤ L _uAnd ML _u≤ N _p, so by the h after moving _{M, i}(1≤m≤M) and non-overlapping copies on time domain also are M user's channel h _{M, i}(1≤m≤M) on time domain, separated by quadrature, as shown in Figure 5." user window " among Fig. 5 represents that the channel of this user's correspondence will drop in this window, the window function w of user m correspondence _{M, i}For:

$w_{m,i}=\underset{n=1}{\overset{L_u}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}[n-(m-1)\&CenterDot;L_u],1\&le;m\&le;M---\left(36\right)$

Window function w with user m correspondence _{M, i}Multiply each other with (35) formula, can obtain the channel estimating of user m

${\hat{h}}_{m,i}=w_{m,i}\&CenterDot;\frac{1}{N_p}\&CenterDot;(q_i\&CircleTimes;{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="H2009100837922E0000021.png,H2009100837922E0000031.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1,i})$

$\&ap;\left(\underset{n=1}{\overset{L_u}{\mathrm{\&Sigma;}}}\mathrm{\&delta;}\right[n-(m-1)\&CenterDot;L_u\left]\right)\&CenterDot;(\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{h}_{m,i}\&CenterDot;\mathrm{\&delta;}[n-(m-1)\&CenterDot;L_u\left]\right)\&ap;h_{m,i},1\&le;m\&le;M---\left(37\right)$

As seen, originally on time domain, be aliasing in the multiuser channel that can't separate together, through just can separating by disposable quadrature behind the circular convolution of above-mentioned (35) formula, just can select the channel that belongs to each user by " user window " among Fig. 5 corresponding window function simultaneously.

It should be noted that the m sequence p that to be used for local m sequence that quadrature separates multiuser channel can be M any one user of user _{U, i}(1≤u≤M), this be because

$q_i\&CircleTimes;p_{u,i}\&ap;(\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,i}\&CircleTimes;h_{m,i})\&CircleTimes;p_{u,i}\&ap;N_p\&CenterDot;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{h}_{m,i}\&CenterDot;\mathrm{\&delta;}[n-(m-u)\&CenterDot;L_u]---\left(38\right)$

But the position of this moment each " user window " needs corresponding change the, i.e. window function w _{M, i}Also should change accordingly.Therefore, when selecting for use different local m sequences to be used for the separation of multiuser channel time domain orthogonal, receiver is when selecting the channel of each user's correspondence, and corresponding adjustment also should be done in the position of each user window.Fig. 5 and Fig. 6 have provided when local m sequence and have been respectively p _{1, i}And p _{2, i}The time each user window correspondence position.

Each user's who obtains channel estimating will be separated through quadrature on the time domain Be DFT by (28) formula and transform to frequency domain, go balanced each user's received signal that separation obtains through quadrature by simple single tap frequency-domain equalizer then, then can recover transmitting of each user of transmitting terminal:

${\hat{X}}_{m,i}=\frac{{Y^{\&prime;}}_{m,i}}{{\hat{H}}_{m,i}}---\left(39\right)$

Wherein

Be m user i signal frame in the frequency-region signal x that sends _{M, i}Estimation.

So far, we have separated and have recovered each user's that makes a start transmission data.

The multiple access system based on TDS-OFDM in the present embodiment comprises transmitting terminal and receiving terminal, wherein:

In this system multi-user's transmitting terminal have be used to generate have time-the frame production unit of signal frame of user's two-dimensional frames structure;

The receiving terminal of this system has: the time domain reconstruction unit, finish the reconstruct of multi-user association cycle characteristics by a plus and minus calculation, and on time domain, reconstruct the cycle characteristics of all user's received signals simultaneously; Subscriber signal quadrature separative element: be used for and arrive frequency domain through the signal transformation after the reconstruct of multi-user association cycle characteristics on the time domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, the quadrature of having finished all subscriber signals on frequency domain separates; Channel quadrature separative element is used on time domain all users' channel quadrature is separated; Data recovery unit, be used for according on the frequency domain isolated each user's received signal with on time domain, separate each the subscriber channel information that obtains, adopt single tap frequency-domain equilibrium method to recover each user's transmission data.

For based on the maximum number of user M that allows in the multiple access system of time-domain synchronization OFDM to insert simultaneously in the same time slot, can comprehensively choose the most mostly according to concrete application scenarios, power system capacity, up user's maximum data throughput demand, system are opposable through time delay, the number of users that can insert simultaneously that allows with reference to existing GSM standard is 8, for the maximum number of user that the present invention supported can insert simultaneously at same time slot, its preferred implementation can be:

1) first kind of execution mode: M=2

N the subcarrier allocation that system can be used given 2 users, and the method for salary distribution of concrete subcarrier can be any in the above-mentioned three sub-carrier methods of salary distribution, and the system block diagram during M=2 is shown in Fig. 8 A;

2) second kind of execution mode: M=3

N the subcarrier allocation that system can be used given 3 users, and the method for salary distribution of concrete subcarrier can be any in the above-mentioned three sub-carrier methods of salary distribution, and the system block diagram of M=3 correspondence is shown in Fig. 8 B;

3) the third execution mode: M=8

N the subcarrier allocation that system can be used given 8 users, and the method for salary distribution of concrete subcarrier can be any in the above-mentioned three sub-carrier methods of salary distribution;

4) the 4th kind of execution mode: M=12

N the subcarrier allocation that system can be used given 12 users, and the method for salary distribution of concrete subcarrier can be any in the above-mentioned three sub-carrier methods of salary distribution;

5) the 5th kind of execution mode: M gets any positive integer less than system's usable data subcarriers number

N the subcarrier allocation that system can be used given M user, and specifically the method for salary distribution of subcarrier can be any in the above-mentioned three sub-carrier methods of salary distribution;

Usually, when the number of users that inserts simultaneously in the multiple access system is M, based on the transceiver architecture block diagram of the multiple access system of time-domain synchronization OFDM shown in Fig. 8 C.The used signal modulating method of transmitting terminal is existing method commonly used among Fig. 8 A～Fig. 8 C, and just frame structure is different from prior art, no longer describes in detail here about its modulation process of transmitting.

It should be noted that for example when M=12, the number of users ability of system's support is 12/55556 μ s=216 * 10 because the TDS-OFDM signal frame duration is 555.6 μ s ⁴Individual/second.In the VB-RCT in Europe (return path) standard, per second can simultaneously treated short delivery mutual information be 20 * 10 in each sector of each sub-district ⁴

In order to analyze the complexity of method proposed by the invention, table 1 has provided the inventive method and direct iterative method (referring to document [1] J.Wang, Z.Yang, C.Pan, J.Song, and L.Yang, " Iterative padding substruction of the PN sequence for the TDS-OFDMover broadcasting channels; " IEEE Trans.Consumer Electron., vol.51, no.4, pp.1148-1152, Nov.2005), based on the iteration interference elimination method of part decision-feedback (referring to document [2] Shigang Tang, Kewu Peng, Ke Gong, et al., " NovelDecision-Aided Channel Estimation for TDS-OFDM Systems; " in Proc.IEEE International Conference on Communications (ICC ' 08), May.2008, vol.1, pp.946-950), based on the method for training sequence reconstruction (referring to document [3] FangYang, Jintao Wang, Jun Wang, et al., " Channel Estimation for the ChineseDTTB System Based on a Novel Iterative PN Sequence Reconstruction; " in Proc.IEEE International Conference on Communications (ICC ' 08), May.2008 pp.285-289) waits document needed computation complexity contrast when realizing interference eliminated and channel estimating.J in the table represents iterations.

Table 1 is based on the complexity comparative analysis of the multiple access system of time-domain synchronization OFDM

Computing	Document [1]	Document [2]	Document [3]	The inventive method
					??IFFT/FFT?256	??0	??0	??0	??3
??IFFT/FFT?2048	??4(J+1)	??2(J+1)	??3(J+1)	??0

Computing	Document [1]	Document [2]	Document [3]	The inventive method
					??IFFT/FFT?3780	??2	??1	??2	??1
??IFFT/FFT?4200	??0	??5(J+1)	??0	??0
					??IFFT/FFT?8192	??3(J+1)	??0	??0	??0

As can be seen from the table, when iterations J=1, complexity based on the iteration interference elimination method of part decision-feedback is 68% of a direct alternative manner, complexity based on the method for training sequence reconstruction is 24% of a direct iterative method, and proposed by the invention based on time-method of user's two-dimensional frames structure, owing to do not need iteration, and combined cycle reconstruct and combined channel estimation approach are all very simple, so its complexity only is 6% of a direct iterative method.When iterations J increased, the relative complex degree of the method for the invention was then lower.

Based on foregoing description and embodiment, to the multiple access system based on time-domain synchronization OFDM proposed by the invention, with M=2 is example, other major parameters of system are as shown in table 1, present embodiment has carried out Computer Simulation to the feasibility and the performance of this system, in the emulation used channel be 2 kinds of typical radio multipath channel Brazil A shown in the table 2 and Brazil D (referring to document: " Digital Television Systems-Brazilian Tests-FinalReport; " ANATEL SP, May 2000), the channel of user's 1 process is Brazil A, and the channel of user's 2 processes then is Brazil D.As can be seen from Table 2,5 in 6 multipaths of these two kinds of channel models overlap in time, multipath is bigger with respect to the decay in main footpath in the Brazil A channel, and the decay of multipath is all very little in the Brazil D channel, and the energy of indivedual multipaths (such as the 1st footpath) is about the same with main footpath (the 5th footpath), and therefore existing very significantly in this channel, multipath disturbs.In order to contrast multi-user system and single user system, also provided in the traditional TDS-OFDM system single user simultaneously through error sign ratio (Symbol Error Rate, SER) performance behind Brazil A and the Brazil D channel.

The main simulation parameter of table 1

Number of users M	??2
		Subcarrier distribution scheme	Interlace assignment
Available OFDM sub-carrier number sum N	??3780
		The sub-sub-carrier number that each user is assigned to	??1890
The subcarrier planisphere	??QPSK
		Symbol rate	7.56M symbol/second
Subcarrier spacing	??2kHz
		M sequence length N p	??255

Number of users M	??2
		Consecutive frame m sequence phase difference L among the same user t	??153
Neighboring user m sequence phase difference L in the same frame u	??76

The channel impulse response of table 2 channel model

Present embodiment has provided the channel estimation results that the multiuser channel time domain orthogonal separates.Channel among Fig. 9 A is user's 1 pairing Brazil A channel and the user's 2 pairing Brazil D channels in the multi-address system, and Fig. 9 B then is the channel by two users that separate at time domain orthogonal of obtaining after the channel estimating of the present invention.From simulation result as can be seen, the channel of aliasing mutually on two time domains, if with traditional channel estimation methods, the channel estimation results that obtains will be that two channels are aliasing in " composite channel " together, thereby two users' channel can't be separated, and after adopting channel estimation methods of the present invention, user's 2 pairing BrazilD channels " have been moved " L on time domain _u, if L _uGreater than the maximum multipath time delay of user's 1 pairing Brazil A channel, then the channel of two user's correspondences can be separated fully.

Figure 10 has provided the SER performance based on different user in the multiple access system of time-domain synchronization OFDM of the present invention.As a comparison, provided simultaneously among the figure when having only a user in traditional TDS-OFDM system and taking all available subcarriers, through with SER performance based on system behind the identical channel of the multiple access system of time-domain synchronization OFDM.As can be seen, for the multiple access system based on time-domain synchronization OFDM of the present invention, the SER performance that user can reach in the SER performance that each user can reach and the traditional TDS-OFDM single user system is almost consistent from simulation result.Simulation result shows simultaneously, because the multipath of Brazil D channel is more abominable than Brazil A channel, so after this channel of user's process, the SER performance is less better.

Figure 11 has provided when system's maximum doppler frequency is 30Hz, in the multiple access system of time-domain synchronization OFDM and traditional single user TDS-OFDM system, certain user becomes the SER performance comparison after the multipath Rayleigh fading channel when identical.The channel model that emulation is used is a Brazil D channel.As can be seen, under time varying channel, the multiple access system that the present invention proposes can obtain than traditional better SER performance of single user TDS-OFDM system from simulation result.When SER=0.03, the SNR demand in the multiple access system is 20dB, and the SNR demand of traditional single user TDS-OFDM system is 25dB.The reason that the multiple access system that the present invention proposes under situation of movement obtains better system performance is, in the combined cycle characteristic restructuring procedure of multi-user's received signal, do not need channel information, avoided the iteration interference eliminated computing of PN sequence and data division, and traditional single user TDS-OFDM system needs constantly to utilize channel information progressively to eliminate the interference of PN sequence and data division in the iterative reconstruction process of cycle characteristics, the time change condition under, there is certain error in the channel information that obtains by channel estimating, and this error may constantly add up in iterative process, thereby has caused the deterioration of systematic function.

Above-mentioned theory analysis and simulation result all show, multiple access system based on time-domain synchronization OFDM of the present invention, just can reconstruct the cycle characteristics of all user's received signals by simple plus and minus calculation once, and then can on frequency domain, all users' signal in orthogonal be separated, this system just can separate channel quadrature on time domain of all users by a circular correlation simultaneously, thereby can adopt simple single tap frequency-domain equilibrium method to recover each user's transmission signal, whole multiple access access scheme simple possible, and having realized multi-user's access, and under mobile condition, obtained better system performance than traditional lower complexity of single user TDS-OFDM system.

The present invention is based in each user's emitter of multiple access system of time-domain synchronization OFDM, the length that same user's consecutive frame is adopted in its " time-user's two-dimensional frames structure " is N _pThe phase difference of m sequence be L _t, the phase difference of the m sequence that neighboring user is adopted in same signal frame is L _u, the frame head PN sequence of all users' unlike signal frame is by its corresponding m sequence process L _tThe position cyclic extensions obtains.For based on all operable subcarriers in the multiple access system of time-domain synchronization OFDM, each user's transmission signal takies a part of subcarrier wherein, and the subcarrier that different user takies is mutually orthogonal.

In the receiving system of the multiple access system based on time-domain synchronization OFDM of the present invention, at first the multiple user signals that will be superimposed in time domain linear is by the disposable combined cycle characteristic reconstruct of finishing all user's received signals of simple plus and minus calculation, be DFT then and transform to frequency domain, separate thereby finish the quadrature of each user's received signal on frequency domain.Estimate for multiuser channel, then utilize the m sequence that the multi-user is superimposed in local m sequence and the received signal to do time domain relevant (or circular convolution), thus on time domain with the channel quadrature separation of different user.Behind received signal of having separated different user and channel, can recover each user's transmission signal by simple single tap frequency domain equalization, thereby the access that has realized the multi-user with communicate by letter.

Above execution mode only is used to illustrate the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; under the situation that does not break away from the spirit and scope of the present invention; can also make various variations and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.

Claims (11)

1. based on the signal frame structure of the multiple access system of TDS-OFDM, signal frame comprises frame head PN sequence, it is characterized in that, signal frame have time-user's two-dimensional frames structure:

On time shaft, m user is at the m of i+1 frame sequence p _{M, i+1}Be m sequence p by the i frame _{M, i}Through L _tObtain behind the cyclic shift of position, i, m are positive integer;

On user's axle, adjacent m and m+1 the m sequence p that the user is adopted in i signal frame _{M+1, i}And p _{M, i}, p _{M+1, i}Be p _{M, i}Through L _uObtain behind the cyclic shift of position;

Obtain the frame head PN sequence of this signal frame after the m sequence process Lt position cyclic extensions in each signal frame.

2. the signal frame structure of the multiple access system based on TDS-OFDM according to claim 1 is characterized in that,

L _tThe length that is less than or equal to the m sequence;

L _u〉=l _MaxAnd ML _u≤ N _p, l wherein _MaxBe the maximum multipath time delay of the channel of different user process, N _pBe the length of m sequence, M is the total number of users in the system.

3. the signal frame structure of the multiple access system based on TDS-OFDM according to claim 1 and 2 is characterized in that,

After obtaining the frame head PN sequence of each user in each signal frame, obtain comprising the complete signal frame of each user data signal according to the signal processing flow of TDS-OFDM modulation system.

4. based on the method for reseptance of the multiple access system of TDS-OFDM, it is characterized in that the receiving terminal of this system is finished the reconstruct of multi-user association cycle characteristics by a plus and minus calculation, reconstructs the cycle characteristics of all user's received signals on time domain simultaneously.

5. the method for reseptance of multiple access system according to claim 4, it is characterized in that, the receiving terminal of this system will arrive frequency domain through the signal transformation after the reconstruct of multi-user association cycle characteristics on the time domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, thereby the quadrature of having finished all subscriber signals on frequency domain separates.

6. the method for reseptance of multiple access system according to claim 4 is characterized in that, the receiving terminal of this system separates all users' channel quadrature on time domain.

7. the method for reseptance of multiple access system according to claim 6, it is characterized in that, receiving terminal according on the frequency domain isolated each user's received signal with on time domain, separate each the subscriber channel information that obtains, adopt single tap frequency-domain equilibrium method to recover each user's transmission data.

8. the method for reseptance of multiple access system according to claim 6, it is characterized in that, this method is done circular convolution or the relevant channel estimating that obtains all subscriber channels of time domain with the signal that the multi-user m sequence that receives is superimposed with local m sequence, and selects to belong to each user's channel by mutually orthogonal user window is set on time domain.

9. the method for reseptance of multiple access system according to claim 8 is characterized in that, being used for doing the relevant local m sequence of circular convolution or time domain is the m sequence that any one user of multiple access system is adopted at the current demand signal frame.

10. based on the multiple access system of TDS-OFDM, it is characterized in that,

In this system multi-user's transmitting terminal have be used to generate have time-the frame production unit of signal frame of user's two-dimensional frames structure;

The receiving terminal of this system has time domain cycle characteristics reconfiguration unit, finishes the reconstruct of multi-user association cycle characteristics by a plus and minus calculation, reconstructs the cycle characteristics of all user's received signals on time domain simultaneously.

11. system according to claim 10 is characterized in that, receiving terminal also has:

Subscriber signal quadrature separative element: be used for and arrive frequency domain through the signal transformation after the reconstruct of multi-user association cycle characteristics on the time domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, the quadrature of having finished all subscriber signals on frequency domain separates;

Channel quadrature separative element is used on time domain all users' channel quadrature is separated;

Data recovery unit, be used for according on the frequency domain isolated each user's received signal with on time domain, separate each the subscriber channel information that obtains, adopt single tap frequency-domain equilibrium method to recover each user's transmission data.

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