CN101807954A - Time domain synchronous frequency division multiple access method for uplink multi-users - Google Patents

Abstract

The invention discloses a time domain synchronous frequency division multiple access method for uplink multi-users, which comprises the following steps of: forming signal frames at a sending terminal by taking a superframe as a basic unit, wherein a framing way comprises that a leader sequence is inserted in front of L signal subframes; the signal subframes comprise a time domain data block and a post-guard interval; the leader sequence comprises a training sequence, a pre-guard interval and the post-guard interval; the pre-guard interval is the same as the post-guard interval; and the training sequence consists of a m sequence in which time-domain circulating displacement exists between the adjacent users; and sending the formed signal frames. The time domain synchronous frequency division multiple access method solves the problem that superimposed interference is difficult to eliminate between frame headers and frame bodies among the multi-users when TDS-OFDM is used for uplink multiple access, so that a multi-carrier OFDMA and a single-carrier SC-FDMA can perform the transmission of the uplink multi-users by adopting a uniform structure of the signal frames; and multi-user access is realized by the complexity lower than that of the conventional single-user TDS-OFDM system, and the system performance is higher under the condition of movement and particularly low-speed movement.

Description

Time domain synchronous frequency division multiple access method for uplink multi-users

Technical field

The present invention relates to the multiple access technique in the radio communication, be specifically related to a kind of time domain synchronous frequency division multiple access method for uplink multi-users that adopts single carrier or multi-carrier signal.

Background technology

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 orthogonal frequency division multiplexing multiple access (Orthogonal Frequency Division MultiplexingAccess, 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, different sub-carrier set is distributed to different users neatly reach the purpose that the multi-user inserts.OFDMA is the effective and efficient manner 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 IEEE 802.16e 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 using widely at present, and as DAB, DVB-T, IEEE802.11a, HIPERLAN/2, WLAN, WiMAX etc., CP-OFDM has all been used in most at present B3G/4G motions.Application number is that 01124144.6 Chinese invention patent application " protection fill method at interval in the orthogonal FDM modulation system " 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 (Time DomainSynchronous 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 IDFT data block all can produce shown in shade among Fig. 1 (a) " hangover "; but because protection is the Cyclic Prefix of frame IDFT data block at interval; the frame receiving sequence of directly removing behind the CP just has cycle characteristics; thereby the linear convolution of frame IDFT data block and interchannel is converted into circular convolution; and can finish the channel equalization of frame IDFT data block, and then recover the frame data of transmitting terminal by simple discrete Fourier transform (DFT) (DFT).In the CP-OFDMA system; the frequency domain data that different user sends is mutually orthogonal; 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 Fig. 1 (b); " 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 based on auxiliary iteration interference elimination method and a kind of iteration interference elimination method of part judgement, to reduce the complexity of iteration interference eliminated based on training sequence reconstruction.Yet all there is the problem of two aspects in above-mentioned two kinds of methods: at first, the iteration interference elimination method need carry out repeatedly iteration, and algorithm is comparatively complicated, operand is very big, implementation complexity is higher, the power consumption of receiver is 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 Fig. 1 (b) 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 to the prerequisite of the stack interference eliminated of PN sequence, and obtaining all users' channel estimating, this was impossible correctly separate each user's signal in the base station before.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

(1) technical problem that will solve

The technical problem to be solved in the present invention is: when how to solve TDS-OFDM and being used for uplink multi-address and inserting between the multi-user stack between frame head and the frame disturb the problem that is difficult to eliminate; How to make multi-carrier OFDM A and single carrier SC-FDMA can adopt unified signal frame structure to carry out the uplink multi-users transmission; And as how realize that than the lower complexity of traditional single user TDS-OFDM system the multi-user inserts, and obtain better system performance when particularly low speed moves under mobile condition.

(2) technical scheme

In order to solve the problems of the technologies described above, the invention provides a kind of time domain synchronous frequency division multiple access method for uplink multi-users, may further comprise the steps:

The framing step is that elementary cell is formed signal frame with the superframe at transmitting terminal, and the mode of forming described superframe is: inserted targeting sequencing before L signal subframe; Wherein, described signal subframe comprises time-domain data blocks and back protection at interval, described targeting sequencing comprise training sequence, preceding protection at interval and the protection of described back at interval, described before protection identical at interval with the back protection at interval;

The signal forwarding step will send according to the signal frame that the mode of described framing step is formed.

Wherein, according to wireless channel coherence time size or the pace of change of wireless channel determine the number L of described signal subframe.

Wherein, Doppler's spread bandwidth of described wireless channel is big more, and the value of the number L of then described signal subframe is more little; Doppler's spread bandwidth of described wireless channel is more little, and the value of the number L of then described signal subframe is big more.

Wherein, described preceding protection is protected last K the symbol that is at interval in the described training sequence with the back at interval, and K is more than or equal to the maximum delay expansion of wireless channel.

Wherein, described training sequence is the time domain m sequence of single carrier form, and wherein, the time domain sequences that adjacent two users m, m+1 are adopted is p _mAnd p _M+1, p _M+1Be p _mThrough L _sThe sequence that obtains behind the cyclic shift of position;

Wherein, described training sequence is the frequency domain sequence of multicarrier form, and the training sequence of different user takies subcarrier mutually orthogonal on the frequency domain, obtains training sequence in its corresponding time domain by inverse Fourier transform then.

Wherein, described time-domain data blocks is the IDFT time-domain data blocks.

Wherein, described IDFT time-domain data blocks is the multi-carrier signal of orthogonal frequency division multiplexing multiple access form, perhaps the single-carrier signal of single-carrier frequency division multiple access form.

Wherein, if described training sequence is the frequency domain sequence of multicarrier form, different user all takies mutually orthogonal subcarrier corresponding in described training sequence and the IDFT time-domain data blocks respectively according to mode one to one.

Wherein, also comprise multi-user's cycle characteristics reconstruction step after described signal forwarding step, described multi-user's cycle characteristics reconstruction step comprises step S1: by the back protection in the described signal subframe at interval and the plus and minus calculation between the back protection at interval of described targeting sequencing described IDFT data block is carried out multi-user's cycle characteristics reconstruct on the time domain.

Wherein, described multi-user's cycle characteristics reconstruction step also comprises step S2: receiving terminal with time domain on through the signal transformation after the reconstruct of multi-user cycle characteristics to frequency domain, and select each user's frequency-region signal in the set of subcarriers of each user's correspondence, thereby the quadrature of finishing all subscriber signals on frequency domain separates.

Wherein, also comprise channel estimation steps after described multi-user's cycle characteristics reconstruction step: signal and local training sequence that the training sequence by each user that will receive is superimposed are done the channel estimation results that circular correlation obtains all subscriber channels, select each user's channel estimation results by mutually orthogonal user window is set then on time domain.

Wherein, after described channel estimation steps, also comprise the signal recovering step, according in isolated each user's received signal and the channel estimation results that on time domain, separates each user who obtains on the frequency domain, adopt single tap frequency-domain equilibrium method to recover each user's that transmitting terminal sends single-carrier signal or multi-carrier signal at receiving terminal.

(3) beneficial effect

The present invention can be used for the frame structure that uplink multi-users inserts by design, when having solved TDS-OFDM and being used for uplink multi-address and inserting between the multi-user stack between frame head and the frame disturb and be difficult to eliminate this technical barrier; Simultaneously,, also be applicable to the SC-FDMA single-carrier signal, thereby make multi-carrier OFDM A and single carrier SC-FDMA can adopt unified signal frame structure to carry out the uplink multi-users transmission because this frame structure both had been applicable to the OFDMA multi-carrier signal; The 3rd, because the new frame structure of the present invention's design, when realizing interference eliminated and channel estimating, do not need interative computation, therefore adopt the uplink multi-users time domain synchronous frequency division multiple access of frame structure of the present invention to insert (TDS-FDMA) method, and can obtain better system performance when particularly low speed moves under mobile condition also having realized multi-user's access than traditional lower complexity of single user TDS-OFDM system.

Description of drawings

Fig. 1 be based on the multiple access system of CP-OFDM with based on the contrast of the frame structure in the multiple access system of TDS-OFDM (a) with (b);

Fig. 2 is a frame structure designed in the multiple access method of the embodiment of the invention;

Fig. 3 is the schematic diagram of the cycle characteristics restructuring procedure of all users' of receiving terminal IDFT data block in the multiple access method of the embodiment of the invention;

Fig. 4 is the system architecture diagram based on the up multi-carrier signal of multiple access method transmission OFDM A of the embodiment of the invention and transmission SC-FDMA single-carrier signal;

Fig. 5 is the performance comparison result of iterative channel estimation method aspect mean square error (MSE) in multiuser channel method of estimation in the multiple access method of the embodiment of the invention and the traditional TDS-OFDM single user system;

Fig. 6 is the multiple access method of the embodiment of the invention and traditional bit error rate (BER) the performance comparison result of TDS-OFDM single user system in four kinds of typical multipath channels;

Fig. 7 is the multiple access method of the embodiment of the invention and the traditional BER performance comparison result of TDS-OFDM system under rayleigh fading channel.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used to illustrate the present invention, but are not used for limiting the scope of the invention.

Embodiment 1

The time domain synchronous frequency division multiple access method for uplink multi-users of the embodiment of the invention, but there be M user to initiate the situation that inserts the request and handle this M user's data simultaneously in the back-up system simultaneously.

In time domain synchronous frequency division multiple access method for uplink multi-users of the present invention, the elementary cell of each user's signal frame structure is a superframe, and as shown in Figure 2, superframe is made of targeting sequencing and L signal subframe.

Signal number of sub-frames L in the superframe can dynamically adjust according to size coherence time of wireless channel, generally, the translational speed of user terminal fast more (perhaps the Doppler of channel expansion is big more), then the value of L is more little; Otherwise, the translational speed of user terminal slow more (perhaps the Doppler of channel expansion is more little), then the value of L is big more.Particularly, the execution mode of the signal number of sub-frames L in the superframe can be:

L=1 promptly has only a signal subframe behind the targeting sequencing in the superframe, what this moment, channel estimation results upgraded is fastest, is suitable for the very fast situation of channel variation;

L=3 promptly has 3 signal subframes behind the targeting sequencing in the superframe, similar every 1 frequency pilot sign of 3 symbols appearance with uplink frame structure among the LTE, the speed ratio that this moment, channel estimation results upgraded is very fast, is suitable for channel variation ratio situation faster;

L=12 promptly has 12 signal subframes behind the targeting sequencing in the superframe, the speed that this moment, channel estimation results upgraded is slow, is suitable for the slow situation of channel variation; Perhaps

L gets other any big or small positive integers, and speed and L that channel estimation results upgrades are inversely proportional to, and when L is bigger, can pass through interpolation, and modes such as filtering improve performance for estimating channel to a certain extent.

Length in the superframe is N _gTargeting sequencing be N by length _pThe m sequence constitute and preceding protection at interval and the back protection at interval, preceding protection at interval and the back protect the interval identical, form by K symbol, all be equal to last K symbol of m sequence in the targeting sequencing, promptly have

N _g＝N _p+2K.????????????????????(1)

M sequence in the targeting sequencing (one of execution mode of training sequence) useable linear feedback shift register (LFSR) generates, the length N of required m sequence _pThe institute of depending on the number of users M that can support simultaneously in the uplink multi-users time domain synchronous frequency division multi-address accessing system and each user experiences the maximum delay of channel and expands l _Max, the length of m sequence should satisfy N _p〉=Ml _MaxParticularly, the execution mode of the m sequence length in the targeting sequencing can be: N _p=255; N _p=511; N _p=1023; Or N _p=2047.

Preceding protection in the targeting sequencing is in order under the multipath situation m sequence to be protected with the back protection at interval at interval; be used for the cycle characteristics reconstruct of superframe IDFT data block simultaneously, preceding protection at interval should be more than or equal to the maximum delay expansion l of each subscriber channel with back protection length K at interval _Max, be less than or equal to the length N of m sequence simultaneously _p, i.e. l _Max≤ K≤N _pParticularly, the execution mode of preceding protection interval in the targeting sequencing and back protection length K at interval: K=l _Max Wherein

Expression rounds up; K=N _pPerhaps K gets and satisfies l _Max≤ K≤N _pAny positive integer.

For the m sequence of targeting sequencing, adjacent two user m and user m+1 m sequence p that is adopted _{M, 0}And p _M+1,0, p _M+1,0Be p _{M, 0}Through L _sObtain behind the cyclic shift of position, promptly

$p_{m+\mathrm{1,0}}=p_{m,0}^{{\mathrm{\Ξ}}_{L_s}},---\left(2\right)$

Wherein

Expression is to sequence

Carry out L _sThe position cyclic shift:

$p_m^{{\mathrm{\Ξ}}_{L_s}}=[p_m\left(L_s\right),p_m(L_s+1),...,p_m(N_p-1),p_m\left(0\right),p_m\left(1\right),...,p_m(L_s-1)].---\left(3\right)$

The figure place L of m sequence cycles displacement _sDepend on depend on the number of users M that can support simultaneously in the uplink multi-users time domain synchronous frequency multiple access system, each user experience the maximum delay expansion l of channel _Max, the m sequence length N _pParticularly, the figure place L of m sequence cycles displacement _sExecution mode: L _s=l _Max, l wherein _MaxBy each user the maximum delay expansion of experience channel; Preferably, get

Wherein

Expression rounds up.

Signal subframe in the superframe is made of at interval IDFT time-domain data blocks and back protection.IDFT data block in the signal subframe both can be the multi-carrier signal of orthogonal frequency division multiplexing multiple access (OFDMA) form, also can be the single-carrier signal of single-carrier frequency division multiple access (SC-FDMA) form.Particularly, the signal subframe is by the generation execution mode of IDFT time-domain data blocks:

Execution mode one: the IDFT time-domain data blocks is the multi-carrier signal of OFDMA form, the frequency-region signal that is each user at first transforms to time domain through carrying out IDFT again after the subcarrier allocation, the concrete grammar that its signal produces is as follows: at first, user m is i signal subframe frequency domain signal transmitted

Through after the subcarrier allocation expansion being obtained the frequency domain vectors of N dimension

$X_{m,i}\left(n\right)=\left\{\begin{array}{cc}{D}_{m,i}\left(n\right)& n\∈{\mathrm{\Γ}}_m\\ 0& n\∉{\mathrm{\Γ}}_m\end{array}\right.,---\left(4\right)$

Γ wherein _mRepresent m user's subcarrier set, for keeping the orthogonality of a user data, each user's subcarrier set { Γ _m} _M=1 ^MShould keep quadrature, promptly

(i ≠ j); Then, with frequency-region signal

Through obtaining the IDFT time-domain data blocks of multicarrier form after the N point IDFT conversion

$x_{m,i}\left(n\right)=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_{m,i}\left(k\right)\exp \left\{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000061962100061.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;nk}}{N}\right\}---\left(5\right)$

Execution mode two: the IDFT time-domain data blocks is the single-carrier signal of SC-FDMA form, each user's time-domain signal at first transforms to frequency domain through DFT, return time domain through carrying out the IDFT conversion after the subcarrier allocation then, the concrete grammar that its signal produces is as follows: at first, user m is at the time-domain signal of i signal subframe transmission

Through L _mObtain its frequency-region signal after the some DFT conversion

$D_{m,i}\left(n\right)=\frac{1}{\sqrt{L_m}}\underset{k=0}{\overset{L_m-1}{\mathrm{\&Sigma;}}}{d}_{m,i}\left(k\right)\exp \left\{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HSA00000061962100061.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;nk}}{L_m}\right\}.---\left(6\right)$

Secondly, frequency-region signal

Through similarly after the subcarrier allocation expansion being obtained the frequency domain vectors that N ties up with (4)

At last, with frequency-region signal

Through obtaining the IDFT time-domain data blocks of single carrier form after the N point IDFT conversion

The selection of the embodiment of the generation of above-mentioned IDFT time-domain data blocks can be controlled by the single multi-carrier signal selector switch in each user transmitter of Fig. 4.

For the IDFT time-domain data blocks in the signal subframe, no matter it is the multi-carrier signal of OFDMA form, or the single-carrier signal of SC-FDMA form, its generative process all relates to orthogonal sub-carriers and distributes.For subcarrier distribution scheme, its concrete execution mode:

Execution mode one: continuous subcarrier allocation, be about to whole bandwidth and be distributed into a plurality of continuous sub-carriers groups, the subcarrier of continuous adjacent is arranged in each group, distribute one or more sub carrier group to transmit its signal frame for each user;

Execution mode two: subcarrier allocation interweaves, promptly 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;

Execution mode three: subcarrier allocation immediately, promptly adopting pseudorandom mode 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.

Embodiment 2

Present embodiment provide time domain synchronous frequency division multiple access method for uplink multi-users in multi-user's cycle characteristics reconstructing method.

Among Fig. 3, (a) being M user's received signal schematic diagram, (b) is m user's cycle characteristics reconstruct schematic diagram, (c) is M user's combined cycle characteristic reconstruct schematic diagram.As shown in Figure 3, for whole M users in the uplink multi-users time domain synchronous frequency division multi-address accessing system, M user's signal will be superimposed at receiving terminal.The received signal of targeting sequencing correspondence

Received signal with signal subframe i correspondence

Can be expressed as respectively:

$\left\{\begin{array}{cc}{r}_{\mathrm{total},0}\left(n\right)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,0}\left(n\right)& 0\&le;n\&le;N_p+2K-1\\ r_{\mathrm{total},i}\left(n\right)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}\left(n\right)& 0\&le;n\&le;N+K-1\end{array}\right.---\left(7\right)$

For the cycle characteristics of IDFT data block among the reconstruction signal subframe i, with the received signal { r of this subframe IDFT data block correspondence _{Total, i}(n) } _N=0 ^N-1Protect pairing received signal { r at interval after at first adding this frame IDFT data block _{Total, i}(n) } _N=N ^N+K-1, deduct the pairing receiving sequence in back protection interval in the targeting sequencing then

Thereby obtain a new sequence ${y^{\&prime;}}_{\mathrm{total},i}={\left\{{y^{\&prime;}}_{\mathrm{total},i}\left(n\right)\right\}}_{n=0}^{N-1}:$

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\left\{\begin{array}{cc}{r}_{\mathrm{total},i}\left(n\right)+r_{\mathrm{total},i}(n+N)-r_{\mathrm{total},o}(n+N_p+K)& 0\&le;n\&le;K-1\\ r_{\mathrm{total},i}\left(n\right)& K\&le;n\&le;N-1\end{array}\right.---\left(8\right)$

With formula (8) substitution formula (7), can get:

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\left\{\begin{array}{cc}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}\left(n\right)+r_{m,i}(n+N)-r_{m,o}(n+N_p+K)& 0\&le;n\&le;K-1\\ \underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{r}_{m,i}\left(n\right)& K\&le;n\&le;N-1\end{array}\right.---\left(9\right)$

Suppose that channel is constant substantially in a superframe, then the m sequence in the targeting sequencing, back protection all produce identical hangover at interval and after the back protection interval process multipath channel in each signal subframe, represent with identical shade in Fig. 3 (a).Therefore, we can obtain:

$\left\{\begin{array}{cc}{r}_{m,i}(n+N)-r_{m,o}(n+N_p+K)=y_{m,i}(n+N)-g_{m,o}(n+N_p)& 0\&le;n<l_m-1\\ r_{m,i}\left(n\right)=y_{m,i}\left(n\right)+g_{m,o}(n+N_p)& 0\&le;n<l_m-1\end{array},-,-,-,\left(10\right)\right.$

Wherein,

With

It is respectively the m sequence in the targeting sequencing

With the IDFT data block among the signal subframe i

Through channel After response, l _mThe channel h that is experienced for user m _{M, i}Maximum delay expansion.With (10) substitution (9), can get:

${y^{\&prime;}}_{\mathrm{total},i}\left(n\right)=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{y^{\&prime;}}_{m,i}\left(n\right),0\&le;n\&le;N-1---\left(11\right)$

Wherein

${y^{\&prime;}}_{m,i}\left(n\right)=\left\{\begin{array}{cc}{y}_{m,i}(n+N)+y_{m,i}\left(n\right)& 0\&le;n<l_m-1\\ y_{m,i}\left(n\right)& l_m-1\&le;n\&le;N-1\end{array}\right.---\left(12\right)$

Obtain sequence

Process can be by shown in Fig. 3 (b), from (12) and Fig. 3 (b) as can be seen, new sequences y ' _{M, i}Form and the IDFT received signal in the CP-OFDM system in full accord.Therefore, new sequences y ' _{M, i}Finished the cycle characteristics reconstruct in the IDFT of i subframe data block to user m.According to identical mode, Fig. 3 (b) has also provided the cycle characteristics restructuring procedure of the IDFT data block of other subframes in the superframe.

Obtain new sequences y ' _{Total, i}Process can be by shown in Fig. 3 (c).Obviously, because y ' _{Total, i}Be the arrangement set of having finished cycle characteristics reconstruct y ' _{M, i}} _M=1 ^MLinear combination, so y ' among formula (11) and Fig. 3 (c) _{Total, i}Also have cycle characteristics, the form of received signal is in full accord in this and the CP-OFDMA system shown in Figure 1.So far, the frame structure that utilizes the present invention to propose has just been finished the combined cycle characteristic reconstruct that receives the IDFT data block in the uplink multi-users time domain synchronous frequency division multi-address accessing system by the simple plus and minus calculation of receiving terminal.

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}Do the DFT conversion and obtain its frequency-region signal

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

${Y^{\&prime;}}_{m,i}\left(n\right)=\left\{\begin{array}{cc}{Y^{\&prime;}}_{\mathrm{total},i}\left(n\right)& n\&Element;{\mathrm{\&Gamma;}}_m\\ 0& n\&NotElement;{\mathrm{\&Gamma;}}_m\end{array}\right.,1\&le;m\&le;M---\left(13\right)$

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 reconstruct through Cyclic Prefix _{M, i}(n) frequency domain representation, its vector representation is ${Y^{\&prime;}}_{m,i}=\left[{Y^{\&prime;}}_{m,i}\left(n\right)\right]{|}_{n\&Element;{\mathrm{\&Gamma;}}_m}.$

Since between the subcarrier that takies of different user be mutually orthogonal (

(i ≠ j)), therefore, separated by quadrature at frequency domain, thereby the frequency domain quadrature of having realized multi-address signal separates at the multiple user signals of time domain linear stack.

As seen, receiving terminal at uplink multi-users time domain synchronous frequency division multi-address accessing system, just can reconstruct the cycle characteristics of the frame IDFT data block that all users superpose in time domain linear simultaneously by simple plus and minus calculation once, this has not only been avoided in the multiple access system receiving for each user of reconstruct respectively 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.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, recover the process of the initial data of making a start by channel estimating.

Subscriber signal Y ' through cycle characteristics reconstruct and quadrature separation on frequency domain _{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????(14)

W wherein _{M, i}(n) be noise,

Be the channel h of m user in i frame process _{M, i}The DFT conversion.

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, then initial data by just recovering to make a start after the frequency domain channel equalization.

Each user's channel estimating can be done circular correlation by the m sequence that receives in local m sequence and the targeting sequencing and obtain.Because the m sequence p that neighboring user m and m+1 are adopted in targeting sequencing in the design of frame structure _M+1,0And p _{M, 0}Satisfy the L shown in the formula (2) _sPosition cyclic shift relation, so

$p_{m,0}={\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HSA00000061962100041.png,HSA00000061962100051.png"\; state="\{\{state\}\}">\; <figure-callout\; id="0"\; label="p"\; filenames="HSA00000061962100031.png"\; state="\{\{state\}\}">p</figure-callout>\; </figure-callout>}}_{\mathrm{1,0}}^{{\mathrm{\&Xi;}}_{(m-1)L_s}},1\&le;m\&le;M---\left(15\right)$

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

$p_{m,0}\&CircleTimes;p_{m,0}\&ap;N_p\&CenterDot;\mathrm{\&delta;}\left(n\right),1\&le;m\&le;M---\left(16\right)$

Wherein

Expression circular correlation.So, p _{J, 0}And p _{K, 0}Between cross-correlation function then be:

$p_{j,0}\&CircleTimes;p_{k,0}\&ap;N_p\&CenterDot;\mathrm{\&delta;}[n-(k-j)\&CenterDot;L_s],1\&le;k,j\&le;M---\left(17\right)$

Owing to all comprised length in each user's the targeting sequencing is the preceding protection interval of the m sequence of K, when

The time, the stack sequence of the M that receiving terminal receives a m sequence

Itself just satisfies cycle characteristics, q _mCan be expressed as:

$q_m=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,0}\&CircleTimes;h_{m,i}+v_m---\left(18\right)$

Vector v wherein _mGaussian noise in the reception m sequence of expression user m.

To receive stack sequence q _mWith one of local m sequence p _1,0Doing circular correlation can get:

$q_m\&CircleTimes;{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HSA00000061962100041.png,HSA00000061962100051.png"\; state="\{\{state\}\}">\; <figure-callout\; id="0"\; label="p"\; filenames="HSA00000061962100031.png"\; state="\{\{state\}\}">p</figure-callout>\; </figure-callout>}}_{\mathrm{1,0}}\&ap;(\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,0}\&CircleTimes;h_{m,i})\&CircleTimes;{\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="HSA00000061962100041.png,HSA00000061962100051.png"\; state="\{\{state\}\}">\; <figure-callout\; id="0"\; label="p"\; filenames="HSA00000061962100031.png"\; state="\{\{state\}\}">p</figure-callout>\; </figure-callout>}}_{\mathrm{1,0}}\&ap;N_p\&CenterDot;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{h}_{m,i}\&CenterDot;\mathrm{\&delta;}[n-(m-1)\&CenterDot;L_s]---\left(19\right)$

By formula (19) as can be known, h _{M, i}On time domain, moved (m-1) L _s, if l _Max≤ L _sAnd ML _s≤ 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, thus the channel estimating of user m can be obtained

As seen, on time domain, be aliasing in the multiuser channel that can't separate together originally, after the m sequence that receives in above-mentioned local m sequence of process and the targeting sequencing is done a circular correlation, just can on time domain, finish quadrature and separate.

It should be noted that the local m sequence that is used for above-mentioned multi-user association channel estimating can be M any one user's of user the m sequence p that targeting sequencing adopted _{U, 0}(1≤u≤M), this be because

$q_m\&CircleTimes;p_{u,0}\&ap;(\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{p}_{m,0}\&CircleTimes;h_{m,i})\&CircleTimes;p_{u,0}\&ap;N_p\&CenterDot;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{h}_{m,i}\&CenterDot;\mathrm{\&delta;}[n-(m-u)\&CenterDot;L_s]---\left(20\right)$

Each user's who obtains channel estimating will be separated through quadrature on the time domain Being DFT transforms to frequency domain and obtains

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:

${\hat{X}}_{m,i}=\frac{{Y^{\&prime;}}_{m,i}}{{\hat{H}}_{m,i}}---\left(21\right)$

Wherein Be m user i signal subframe in the frequency domain signal X that sends _{M, i}Estimation.To the frequency-region signal behind the frequency domain equalization

Adjudicate, its embodiment can be: if the employing of transmitting terminal IDFT data block is the multi-carrier signal of OFDMA form, then right

Directly adjudicate; If what transmitting terminal IDFT data block adopted is the single-carrier signal of SC-FDMA form, it is right then to need

Obtain time-domain signal after doing the IDFT conversion

And then adjudicate.

The selection of the embodiment of above-mentioned judgement mode can be controlled by the single multi-carrier signal selector switch in Fig. 4 receiver.

So far, we have separated and have recovered each user's that makes a start in the uplink multi-users time domain synchronous frequency division multi-address accessing system transmission data.Fig. 4 has provided the system block diagram based on the up multi-carrier signal of transmission OFDM A of invention uplink multi-users time domain synchronous frequency division multi-address accessing system and transmission SC-FDMA uplink single-carrier signal.

In order to analyze the complexity of time domain synchronous frequency division multiple access method for uplink multi-users proposed by the invention, table 1 has provided multiple access method of the present invention and direct iterative method (referring to document [1] J.Wang, Z.Yang, C.Pan, J.Song, and L.Yang, " Iterativepadding substruction of the PN sequence for the TDS-OFDM overbroadcasting 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 theChinese DTTB System Based on a Novel Iterative PN SequenceReconstruction; " in Proc.IEEE International Conference onCommunications (ICC ' 08), May.2008 pp.285-289) waits method needed computation complexity contrast when realizing interference eliminated and channel estimating of putting down in writing in the document.J in the table represents iterations.

Table 1

Computing	Document [1]	Document [2]	Document [3]	The present invention
					256 IFFT/FFT	??0	??0	??0	??3
2048 IFFT/FFT	??4(J+1)	??2(J+1)	??3(J+1)	??0
					3780 IFFT/FFT	??2	??1	??2	??1
4200 IFFT/FFT	??0	??5(J+1)	??0	??0
					8192 IFFT/FFT	??3(J+1)	??0	??0	??0

As can be seen from Table 1, 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 the present invention is based on new superframe 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 time domain synchronous frequency division multiple access method for uplink multi-users proposed by the invention, support simultaneously that with system 4 users (M=4) are example, the major parameter of system is as shown in table 2, present embodiment has carried out Computer Simulation to the feasibility and the performance of this system, in the emulation used channel be 4 kinds of typical radio multipath channel Brazil A shown in the table 3 and Brazil D (referring to document: " Digital Television Systems-BrazilianTests-Final Report; " ANATEL SP, May 2000), and the channel model Indoor B and Vehicular A that recommends of ITU is (referring to document: Recommendation ITU-RM.1225, " Guideline for Evaluation of Radio Transmission Technologyfor IMT-2000, " 1997).User 1 in the uplink multi-users system, user 2, user 3 and user 4 pass through multipath channel Brazil A, Indoor B, Vehicular A and Brazil D respectively.

Table 2

Number of users M	??4
		System bandwidth	??8MHz
Available OFDM sub-carrier number sum N	??3780
		Subcarrier spacing	??2kHz
Subcarrier distribution scheme	Interlace assignment
		The sub-carrier number that each user is assigned to	??945
Modulation system	??QPSK
		Symbol rate	??7.56MHz
M sequence length N p	??255
		Number of sub-frames L in the superframe	??4
Protection interval, back protection gap length K before in the targeting sequencing	??64

Table 3

Present embodiment has provided the performance comparison simulation result of iterative channel estimation method (list of references [1]) aspect mean square error (MSE) in multiuser channel method of estimation in the uplink multi-users time domain synchronous frequency division multi-address accessing system that the present invention proposes and the traditional TDS-OFDM system.Provide in the simulation result at Fig. 5, Iter represents iterations.Document [1] is pointed out, when Iter=2, the MSE of channel estimating can reach the performance upper bound that iterative method can obtain substantially, but the simulation result among Fig. 8 shows, this moment the iterative method performance for estimating channel still not have to utilize among the present invention targeting sequencing to carry out the method performance of multi-user association channel estimating good.This is that the IDFT data block will influence the performance of iterative channel algorithm for estimating to the interference of PN because in traditional TDS-OFDM system, though the method that can reduce by the interference eliminated of iteration comes this clock to disturb, disturbs and can not eliminate fully.On the contrary; be used for the m sequence of channel estimating in the present invention owing to protected preceding protection at interval in the frame structure design; therefore there be not of the interference of IDFT data block to the m sequence; even therefore channel estimating is to carry out simultaneously at all users in the uplink multi-users system, also can obtain more precise channels estimated result.

Fig. 6 has provided the uplink multi-users time domain synchronous frequency division multi-address accessing system of proposition and traditional bit error rate (BER) the performance comparison result of TDS-OFDM single user system in four kinds of typical multipath channels.The sub-carrier distribution manner that emulation is adopted is an interlace assignment, and 4 users in the multi-user system take 1/4 of available subcarrier sum respectively, have only a user in traditional TDS-OFDM single user system and take all available subcarriers.Simulation result shows, the BER performance that user can reach in the BER performance that each user can reach in the uplink multi-users of the present invention system and the traditional TDS-OFDM single user system is very approaching, and slightly is better than traditional single user system.This is because on the one hand, can obtain more precise channels estimated result based on the channel estimating of m sequence in the targeting sequencing of the present invention; On the other hand, different with traditional TDS-OFDM single user system is, the present invention without any need for channel information (CSI), thereby can obtain more accurate reconstruction result when the cycle characteristics of reconstruct IDFT data block.

Fig. 7 has provided the uplink multi-users TDS-FDMA system of the present invention's proposition and the traditional BER performance comparison of TDS-OFDM system under rayleigh fading channel, the channel model that adopts is VehicularA, the maximum Doppler expansion of channel is respectively 10Hz, 30Hz and 100Hz, respectively counterpart terminal user's low speed, middling speed and high-speed mobile scene.From simulation result, as can be seen, be 5 * 10 for BER ^-3, when maximum Doppler expansion was respectively 10Hz, required SNR was about 25dB in the traditional single user TDS-OFDM system, and the required SNR of multi-user TDS-FDMA system then is about 22dB, so SNR has promoted about 3dB; When the maximum Doppler expansion was respectively 30Hz, SNR had promoted about 4dB; When the maximum Doppler expansion was respectively 100Hz, the room for promotion of SNR significantly reduced, and the BER performance of the two is very approaching.As can be seen, can obtain better BER performance than the single user TDS-OFDM of tradition system in the low speed uplink multi-users TDS-FDMA system that particularly the present invention proposes under the middling speed time varying channel, this be because, frame structure of the present invention in the combined cycle characteristic restructuring procedure of multi-user IDFT data without any need for channel information, avoided the iteration interference eliminated 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; Under the high-speed mobile situation, because shorten the coherence time of channel, and channel estimating of the present invention obtains by targeting sequencing, therefore renewal speed slows down relatively, therefore just become big owing to become the channel estimation errors that causes fast the time, thereby lost the gain that loop restructuring does not need channel information to bring.This problem can solve by the number L of signal subframe in the dynamic adjustment frame structure, yet less L just means the loss of this bigger transmission availability, but this is the cost that need pay for the reliability that obtains to transmit under high-speed mobile condition.

Above-mentioned theory analysis and simulation result all show; the back protection of time domain synchronous frequency division multiple access method for uplink multi-users of the present invention by IDFT data block in the frame structure at interval and between the back protection at interval of targeting sequencing once simply plus and minus calculation just can finish the combined cycle characteristic reconstruct that all users receive the DFT data block; a circular correlation by m sequence in local m sequence and the targeting sequencing just can be finished all users' channel estimating; the whole proposal simple possible; and having realized multi-user's access, and under low speed and middling speed mobile condition, obtained better system performance than traditional lower complexity of single user TDS-OFDM system.Simultaneously, the present invention also provides a kind of unification uplink multi-address frame structure flexibly for multi-carrier OFDM a-signal and single carrier SC-FDMA signal.

The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the technology of the present invention principle; can also make some improvement and modification, these improve and modification also should be considered as protection scope of the present invention.

Claims (9)

1. a time domain synchronous frequency division multiple access method for uplink multi-users is characterized in that, may further comprise the steps:

The framing step is that elementary cell is formed signal frame with the superframe at transmitting terminal, and the mode of forming described superframe is: inserted targeting sequencing before L signal subframe; Wherein, described signal subframe comprises time-domain data blocks and back protection at interval, described targeting sequencing comprise training sequence, preceding protection at interval and the protection of described back at interval, described before protection identical at interval with the back protection at interval;

The signal forwarding step will send according to the signal frame that the mode of described framing step is formed.

2. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 1 is characterized in that, according to wireless channel coherence time size or the pace of change of wireless channel determine the number L of described signal subframe.

3. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 2 is characterized in that, Doppler's spread bandwidth of described wireless channel is big more, and the value of the number L of then described signal subframe is more little; Doppler's spread bandwidth of described wireless channel is more little, and the value of the number L of then described signal subframe is big more.

4. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 1; it is characterized in that; protection interval and back protection are last K symbol in the described training sequence at interval before described, and K expands more than or equal to the maximum delay of wireless channel.

5. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 1 is characterized in that, described training sequence is the time domain m sequence of single carrier form, and wherein, the time domain sequences that adjacent two users m, m+1 are adopted is p _mAnd p _M+1, p _M+1Be p _mThrough L _sThe sequence that obtains behind the cyclic shift of position.

6. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 1, it is characterized in that, described training sequence is the frequency domain sequence of multicarrier form, the training sequence of different user takies subcarrier mutually orthogonal on the frequency domain, obtains training sequence in its corresponding time domain by inverse Fourier transform then.

7. as each described time domain synchronous frequency division multiple access method for uplink multi-users of claim 1～6, it is characterized in that described time-domain data blocks is the IDFT time-domain data blocks.

8. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 7 is characterized in that, described IDFT time-domain data blocks is the multi-carrier signal of orthogonal frequency division multiplexing multiple access form, perhaps the single-carrier signal of single-carrier frequency division multiple access form.

9. time domain synchronous frequency division multiple access method for uplink multi-users as claimed in claim 6, it is characterized in that, if described training sequence is the frequency domain sequence of multicarrier form, different user all takies mutually orthogonal subcarrier corresponding in described training sequence and the IDFT time-domain data blocks respectively according to mode one to one.

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