CN101827050B

CN101827050B - Novel CDMA downlink communication method and system

Info

Publication number: CN101827050B
Application number: CN 201010143165
Authority: CN
Inventors: 毛兴鹏; 马会肖; 殷作亮
Original assignee: Harbin Institute of Technology Weihai
Current assignee: Harbin Institute of Technology Weihai
Priority date: 2010-04-11
Filing date: 2010-04-11
Publication date: 2012-11-28
Anticipated expiration: 2030-04-11
Also published as: CN101827050A

Abstract

The invention relates to the technical field of communication and signal processing, in particular to a Group-CDMA communication method and a system. The method is characterized in that all users are divided into G groups, and a code division multiple access way is used for distinguishing between the groups; an interleave division multiple access way is used for distinguishing between users in a group, and the dispreading operation is used for eliminating set-up interference and the stepwise iteration is used for eliminating multiple access interference between the users at a receiving end; and the structural complexity and calculation complexity of a receiver are linear with the number of users in groups. The simulation study shows that the invention can effectively improve the communication capacity and spectral utilization rate and strongly promote the application of MUD in MS, and has remarkable advantages of low complexity, high reliability and the like.

Description

A kind of Novel CDMA downlink communication method and system

Technical field

The present invention relates to communication and signal processing technology field thereof, is the Novel CDMA downlink communication method and the system of a kind of Group-CDMA of can be described as system specifically.

Background technology

The continuous growth of As market; GSM has obtained fast development in these decades; From the first generation GSM based on analog signal processing technology at initial stage, experienced less than the semicentennial time to the second generation GSM of obtaining huge business success based on Digital Signal Processing.According in February, 2010, the research expression of tame affiliated institutions of the United Nations one, the mobile phone use amount increases sharply, so B3G, and the 4G technology is to speed, capacity, the availability of frequency spectrums etc. are had higher requirement.At present, the TD-SCDMA system of the included China of 3G (Third Generation) Moblie (3G) system, the WCDMA in Europe, and the CDMA2000 of North America beginning commercialization on Chinese market.

Traditional cdma communication system carries out elementary modulation through orthogonal PSK (QPSK) or similar mode to the initial data that will transmit; And rely on the spreading code as PN sign indicating number (pseudo noise code) that elementary modulation signal is carried out secondary modulation; With spread bandwidth, the information that will pass through secondary modulation then sends out.In this system, each user uses same frequency band to communicate, and identified through unique spreading code; Because spreading code is limited, therefore intrasystem number of users is restricted, and is difficult to tackle the demand that communication user quantity increases substantially; Simultaneously owing to exist certain correlation between the user; Frequency expansion sequence between different user can not carry out complete quadrature, and promptly cross-correlation coefficient is non-vanishing, causes producing multiple access and disturbs (MAI); Along with increasing of number of users, multiple access disturbs (MAI) to become one of key factor that influences systematic function.

Disturb (MAI) problem in order to solve multiple access; The researcher has proposed multiuser detection (MUD), but the MUD technical sophistication degree of having studied moulding at present is very high, for example; The complexity of estimating the optimum multiuser detection of ML and maximum a posteriori probability MAP based on maximum likelihood is o (2^K); Because relate to matrix operation, complexity is o (K^2) based on the suboptimum multiuser detection of MMSE, even study the burning hot IDMA technology that is celebrated with the low complex degree receiver recently; Its complexity by the chip iterative receiver also is o (K), and wherein K is a number of users.When imagination K was very big, this complexity still can't bear the heavy load for slight travelling carriage (MS), and this point causes the MUD technology still to can not get using, especially in down channel.

Yet in the present 3G system, because multimedia is downloaded, asymmetric traffics such as video request program make the performance of down link become the development bottleneck of restriction 3G system to the requirement of down link.Therefore be badly in need of the communication system of a kind of low complex degree, high reliability, when effectively improving the message capacity and the availability of frequency spectrum, promote the application of MUD in MS.

Summary of the invention

The present invention is directed to the deficiency in the traditional C DMA communication system, propose that a kind of complexity is low, reliability is high, and can effectively improve the Group-CDMA communication means and the system of the message capacity and the availability of frequency spectrum.

A kind of Novel CDMA downlink communication method; It is characterized in that all users are divided into the G group; Adopt the mode of code division multiple access to distinguish between group and the group, one group of interior user adopts the mode of the branch multiple access that interweaves to distinguish, at receiving terminal; Adopt de-spreading operation to eliminate and set up interference; Adopt the multiple access of eliminating between the user by chip iteraction multiple users detection mode (CBC-IMUD) to disturb, the number of users in the complex structure degree of receiver and computational complexity and the group is linear, specifically comprises the steps:

Steps A: chnnel coding, the targeted customer sends initial data to channel encoder, carries out chnnel coding,

Step B: interleaving treatment, elementary modulation signal is sent into interleaver corresponding with it carry out interleaving treatment, the code stream after obtaining to handle,

Step C: baseband modulation is handled, and the above-mentioned information processed of process is carried out baseband modulation,

Step D: spread processing; To pass through that other code streams merge in code stream and this group after the above-mentioned processing; And send into this and organize and utilize spreading code to carry out spread processing in the corresponding frequency multiplier; Produce chip stream; Be designated as

Figure 2010101431656100002DEST_PATH_IMAGE002

Step e: transmission information, the information after the spread processing is modulated to high frequency delivers to transmitter, send,

Step F: despreading is handled, and receiving terminal is sent into and carried out the despreading processing in the despreader after the information via modulation that receives is dropped to zero-frequency, obtains the estimation of every group of interior user profile superposition,

Step G: iterative processing, despreading to be handled the estimated value of gained and sent into by carrying out iterative processing in the chip iteraction multiple users detection module (CBC-IMUD), the multiple access of eliminating between the user disturbs the back acquired information,

Step H: judgement, the user who obtains after the iteration end is sent the information estimated value send in the decision device, carry out decision process, obtain the binary signal of the information of sending.

In the grouping of system user described in the present invention, can be expressed as K=(G-1) * M+M ' between total number of users K and the group number G in number of users in the average group and the system, wherein M is the number of users in preceding each group of G-1 group, and M ' is the number of users of G group.

Chnnel coding can adopt duplication code described in the steps A of the present invention, convolution code, Trubo sign indicating number, coded systems such as LDPC sign indicating number.

The said modulation treatment of step C can adopt modulation systems such as BPSK, QPSK, QAM among the present invention.

The spread processing described in the step D is meant and utilizes spreading code to distinguish grouping among the present invention, the frequency expansion sequence s that is adopted _gCan also can be the WALSH sign indicating number for the PN sign indicating number.

A kind of Novel CDMA downlink communication system comprises emitter and receiving system, it is characterized in that emitter comprises

Channel encoder is used for user's raw information is carried out chnnel coding,

Interleaver is used for code stream is carried out interleaving treatment,

Modulator is used for information is modulated,

Frequency multiplier is used for code stream is carried out spread processing,

Transmitter is used for transmission information,

Receiving system comprises

Receiver is used for reception information,

Despreader is used for that information is carried out despreading and handles,

By chip iteraction multiple users detection module (CBC-IMUD), the multiple access that is used to the information of eliminating disturbs,

Decision device is used to recover binary 0, the 1 value form of the information of sending.

The quantity G of the quantity M of the interleaver pi that is provided with in the emitter among the present invention and frequency multiplier spreader has following relationship with respect to system user quantity K: K=(G-1) * M+M ', and wherein M is the number of users in preceding each group of G-1 group, M ' is the number of users of G group.

Constituting by baseband signal detection module ESE (elementary signal estimator) and decoder module DECs (decoders) among the present invention in the receiving system by chip iteraction multiple users detection module (CBC-IMUD).

The present invention proves that through analysis and emulation cdma system more traditional on performance and capacity improves a lot, has remarkable advantages such as complexity is low, reliability height.

Description of drawings:

Accompanying drawing 1 is a system architecture diagram of the present invention.

Accompanying drawing 2 is a transmitter architecture block diagram of the present invention.

Accompanying drawing 3 is a receiver structure block diagram of the present invention.

Accompanying drawing 4 is Group-CDMA-PN system packet count and BER property relationship analogous diagram.

Accompanying drawing 5 is number of users M and a BER property relationship analogous diagram in the Group-CDMA-WALSH set of systems.

Accompanying drawing 6 is the performance comparison diagram of GCDMA system and TrCDMA system.

Accompanying drawing 7 is the comparison diagram of GCDMA-WALSH system and TrCDMA systematic function.

Accompanying drawing 8 is GCDMA_PN system and TrCDMA system, and the BER performance of CDMA-MMSE system under the different user said conditions relatively.

Accompanying drawing 9 is a relatively analogous diagram of GCDMA_WALSH system and the IDMA system BER performance under the different user number.

Accompanying drawing 10 is CDMA-MMSE, IDMA, the computation complexity comparison diagram of GCDMA system.

Accompanying drawing 11 is the performance comparison diagram of GCDMA system and cdma system under the multipath conditions.

Embodiment:

Step D: spread processing; To pass through that other code streams merge in code stream and this group after the above-mentioned processing; And send into this and organize and utilize spreading code to carry out spread processing in the corresponding frequency multiplier; Produce chip stream, be designated as

Channel encoder is used for user's raw information is carried out chnnel coding, and interleaver is used for code stream is carried out interleaving treatment, modulator; Be used for information is modulated, frequency multiplier is used for code stream is carried out spread processing, transmitter; Be used for transmission information, receiving system comprises receiver, is used for reception information, despreader; Be used for that information is carried out despreading and handle, by chip iteraction multiple users detection module (CBC-IMUD), the multiple access that is used to the information of eliminating disturbs

Be further described below in conjunction with embodiment:

When system adopts the BPSK modulation system, and system is fully synchronous, establishes

The targeted customer kBe positioned at gThe of group mIndividual problem then has

Figure 2010101431656100002DEST_PATH_IMAGE004

（1）

As shown in Figure 2; Behind m the interleaver

Figure 2010101431656100002DEST_PATH_IMAGE008

in the bit stream that the targeted customer sends is organized through g through the code stream of exporting after the chnnel coding ; With other users in this group through coding and the merging of the code stream of interleaving treatment; Be designated as

Figure 2010101431656100002DEST_PATH_IMAGE010

Pass through the frequency multiplier spreader of this group again _g, by frequency expansion sequence

Figure 2010101431656100002DEST_PATH_IMAGE012

Spread spectrum (length of frequency expansion sequence is designated as L) produces chip stream, is designated as

, then have

Figure 2010101431656100002DEST_PATH_IMAGE014

（2）

Figure 2010101431656100002DEST_PATH_IMAGE016

（3）

Wherein

Figure 2010101431656100002DEST_PATH_IMAGE018

is designated as the spread spectrum computing,

Figure 2010101431656100002DEST_PATH_IMAGE020

represent m interlace operation.And

Figure 2010101431656100002DEST_PATH_IMAGE022

,

Figure 2010101431656100002DEST_PATH_IMAGE024

,

Figure 2010101431656100002DEST_PATH_IMAGE026

, IBe the length of chip sequence, JBe the length of coding back sequence, LBe the length of frequency expansion sequence, and have

Figure 2010101431656100002DEST_PATH_IMAGE028

In said system; If frequency expansion sequence

adopts the PN sign indicating number, the GCDMA system is designated as the GCDMA_PN system.If frequency expansion sequence

adopts the WALSH sign indicating number; The GCDMA system is designated as the GCDMA_WALSH system; In follow-up discussion; If there is not specified otherwise, the GCDMA system just representes the GCDMA_PN system.

The receiver of user k as shown in Figure 3 comprises a frequency multiplier despreader g and a CBC-IMUD module.

Suppose that channel is single footpath fading channel; Channel coefficients is , and then the information

Figure 2010101431656100002DEST_PATH_IMAGE032

that receives of user k can be expressed as

Figure 2010101431656100002DEST_PATH_IMAGE034

（4）

Wherein I is a frame length; is that average is 0, and variance is the Gaussian noise of

Figure 2010101431656100002DEST_PATH_IMAGE038

.

By formula (1), (2) and (3), (4) formula can be expressed as

（5）

Wherein

;

,

.

At receiving terminal; The effect of first order de-spreading operation is to disturb (inter-group-interference IGI) to obtain the estimation of the superposition of all user profile in every group between the elimination group; Be designated as

Figure 2010101431656100002DEST_PATH_IMAGE042

, can be expressed as

Figure 2010101431656100002DEST_PATH_IMAGE044

（6）

Wherein

Figure 2010101431656100002DEST_PATH_IMAGE046

expression despreading computing,

Figure 2010101431656100002DEST_PATH_IMAGE048

is through the expression after the despreading processing.(6) second portion in the formula is the IGI that mentions in the above-mentioned material.

In addition; If is under the situation of WALSH sign indicating number

Figure 2010101431656100002DEST_PATH_IMAGE052

（7）

Then, IGI=0.

The estimated value

that process despreading processing obtains is as the input of CBC-IMUD module; Through the interative computation of CBC-IMUD, obtain the estimated value of targeted customer's transmission information.

CBC-IMUD detector among Fig. 3 comprises 1 ESE module and M is individual based on a PosterioriThe decoder DECs of probability (APP) criterion.Its working method is consistent with the working method of traditional I DMA system.

The performance evaluation of Group-CDMA:

1, the relation of packet count and error rate of system (BER):

Above-mentioned (6) formula has provided the estimation of every group of user profile superposition, and hypothetical target user K is positioned at m position of g group, with (2)-(5) formula substitutions (6) formula, can obtain

Figure 2010101431656100002DEST_PATH_IMAGE054

（8）

In the following formula, part A is targeted customer's a information;

Part B comes from the interference that the targeted customer uses the user of identical interleaver;

Part C is other users' in the g group interference;

Part D is other users' interference.

Wherein, Part B is that the increase along with packet count G increases very much, and Part C is along with the increase of packet count G reduces, and Part D does not change with packet count G; Disturb minimum so make, the optimal selection of G is certain value between maximum and minimum value.

For the Group-CDMA-WALSH system, then have

（9）

Wherein Part A is targeted customer's a information, and Part B is an interference sections, and is obvious, and Part B is along with the increase of user's average M in the group increases, i.e. increase along with packet count G reduces.So want to make the Group-CDMA-WALSH best performance, packet count G will get maximum.

Accompanying drawing 4,5 has provided number of users M and BER property relationship analogous diagram in Group-CDMA-PN system packet count and BER property relationship analogous diagram and the Group-CDMA-WALSH set of systems respectively.

As can be seen from Figure 4, the BER performance of system not only has relation with signal to noise ratio (snr), and is also relevant with packet count G, and the dotted line group is that the spread spectrum code length adopts 7 among the figure, and number of users is the analogous diagram under 12 conditions, can find out when G=3, and minimum all appears in 4 dotted lines.And adopt 15 at the spread spectrum code length, and when number of users is 24 (the solid line group among the figure), when G=6, minimum all appears in 4 solid lines, so the optimal selection of G, is not a fixed value, and it changes along with the variation of system parameters.

Fig. 5 has provided the packet count of Group-CDMA-WALSH system and the analogous diagram of BER property relationship, and simulated conditions is that number of users is 30, and the spread spectrum code length is 32. can find out that from analogous diagram systematic function is optimum during M=1.The optimal selection that is G is that G gets maximum.

Can find out that from above-mentioned analysis and emulation when spreading code adopts PN and WALSH, can draw different conclusions, when adopting the PN sign indicating number, the optimal selection of G is the some values between maximum and minimum value, when adopting the WALSH sign indicating number, the optimal selection of G is a maximum.This is because the PN sign indicating number can not be accomplished complete quadrature, and through behind the despreader, IGI can not eliminate fully.

In traditional cdma system, when number of users surpassed certain value, iff was eliminated multiple access through de-spreading operation and is disturbed; Systematic function can violently descend; Equally, according to the group of the GCDMA of CDMA mode work, when the G value of choosing is too big; IGI only handles through de-spreading operation still can be greatly remaining, so also can have a strong impact on the performance of GCDMA.In traditional I DMA system, chnnel coding one timing, when number of users was too big, systematic function also can acutely descend.And in the GCDMA system, one group of interior user works according to the IDMA mode, so the M value can not be excessive.In sum, in the GCDMA-PN system, the optimal value of G should be one between maximum and minimum value.

2, the simulation performance of the BER of system:

Simulated conditions: system adopts bpsk signal, and Monte Carlo (Monte Carlo) simulation times is 10000.All bit code, interleaver are generation at random.Chnnel coding adopts duplication code.All systems are complete synchro system.To the Group-CDMA system, KThe expression number of users, GBe packet count, Iter=3The iterations of expression CBC-IMUD detector, spread spectrum length adopts 7, and bit length is 125, and interleaver working depth (also being frame length) is 5250.For the TrCDMA system, the spread spectrum code length is 7, and bit length is 125, and the working depth of interleaver is 5250.

Accompanying drawing 6 has provided the BER performance simulation figure of GCDMA-PN and traditional cdma system (TrCDMA), and wherein realization group is the BER performance of GCDMA system, and the dotted line group is represented the analogous diagram of TrCDMA system; Can find out by Fig. 6; Number of users is that single user performance is still approached by 3 GCDMA system, than the performance boost of 3 users' TrCDMA system 2 dB, the TrCDMA system; Number of users was above 3 o'clock; Systematic function will seriously descend, and will be all poorer than 16 users' of GCDMA system performance like the BER performance simulation figure (dotted line of zone circle) of TrCDMA system of figure K=6, than the GCDMA systematic function difference of K=6 nearly 7 dB.

We know that traditional C DMA system relies on spreading code to distinguish the user, and different users uses different spreading codes, so the impossible length that surpasses spreading code of number of users, so when the spread spectrum code length is 7, number of users KShould satisfy,

Figure 2010101431656100002DEST_PATH_IMAGE058

, and in the GCDMA system, during K=16, systematic function still is superior to the TrCDMA system of K=6, the BER of the GCDMA system performance of K=8 (solid line of band triangle) is superior to the TrCDMA systematic function (dotted line of band stain) of K=3.So under identical bandwidth, the GCDMA system compares with cdma system, on systematic function and capacity, all is greatly improved.

Accompanying drawing 7 has provided the performance comparison diagram of GCDMA-WALSH system and TrCDMA system, draws from Fig. 7, and under the same band condition (L=8), number of users is the systematic function that the systematic function of 8 GCDMA_WALSH is still approached single user.Number of users is that 16,24 o'clock systematic functions also remain on merchandiser user performance one one magnitude.Number of users is the performance that 32 o'clock system BER performance still is superior to the TrCDMAPN of K=3.

Because adopt the GCDMA system of WALSH sign indicating number, handle through the despreading of the first order, IGI can eliminate fully.And because the reason of CBC-IMUD, MAI also can eliminate preferably.So adopt the GCDMA system of WALSH, adopt the GCDMA system of PN sign indicating number, the lifting of on performance and capacity, having got back.

Accompanying drawing 8 has provided GCDMA_PN system and TrCDMA system; The BER performance of CDMA-MMSE system under the different user said conditions relatively (M (M ') is 3 or 4); As can beappreciated from fig. 8; The bit error rate performance of the GCDMA-PN system during K=3 has promoted nearly 4 dB than the GCDMA systematic function, has improved nearly 6dB during K=6.For the CDMA_MMSE system, at number of users during less than spreading code length, its BER performance and GCDMA ten minutes are approaching.

Accompanying drawing 9 has provided relatively analogous diagram of GCDMA_WALSH system and the IDMA system BER performance under the different user number.In above-mentioned emulation, the total bandwidth resource of system is certain, and promptly the product of the code length of duplication code and spreading code is certain.Can get by Fig. 9, the slightly better point of the performance of GCDMA_WALSH and IDMA system, and also very approaching.

3, the computation complexity analysis of receiver algorithm

1) CDMA-MMSE: because relate to matrix operation in the MMSE algorithm, its complexity can be expressed as o (U*K^2);

2) the CBC-IMUD receiver of IDMA:IDMA, the computing of each chip has nothing to do with number of users in each iteration, but will upgrade all users' information in the iterative process, makes o (U*K*I) so its complexity can be remembered;

3) GCDMA: because in the GCDMA system number of users is divided into the G group, therefore can carry out Multiuser Detection (we are referred to as the part Multiuser Detection), make o (U*M*J) so its complexity can be remembered to M user of targeted customer place group;

Wherein K representes number of users, and U representes the bar number of multipath, and I, J represent the iterations of IDMA system and GCDMA system respectively, and K=G*M is arranged, J < I.

Accompanying drawing 10 has provided GCDMA system and CDMA-MMSE, the analogous diagram of the receiver computation complexity of IDMA system, and as can be seen from the figure, the complexity of GCDMA system and CDMA-MMSE, IDMA compare and have reduced a lot.

Accompanying drawing 11 is the performance comparison diagram of GCDMA system and cdma system under the multipath conditions, wherein (M=2; K=2, the GCDMA system under 4,6,8 conditions, It=3; L=15; Repeating code length is 6, and CDMA-RAKE is the cdma system that adopts RAKE receiver.

As can beappreciated from fig. 11; Under multipath conditions; The GCDMA system still promotes a lot on performance and capacity than traditional cdma system, for example, and among Figure 11; 2 users' the GCDMA system solid line of stain (band) has promoted nearly 4 dB than 2 users' GCDMA system (solid line of band triangle), and 8 users' GCDMA system is more approaching with the performance of 2 users' cdma system.

From Figure 11, can also obtain one draws a conclusion: under relay-fading channel condition, suppose that bandwidth resources are certain, the capacity of GCDMA can improve at least 4 times.

In sum, show that through simulation study the present invention can effectively improve the message capacity and the availability of frequency spectrum, the strong application of promotion MUD in MS has significant advantage such as low complex degree, high reliability, makes a concrete analysis of as follows:

(1) compare with traditional C DMA system: because the second level receiver of the receiving terminal of GCDMA system adopts CBC-IMUD to detect, CBC-IMUD is superior to other detectors with its lower complexity and preferable performance.The detection complexity of each chip of each user is 8 multiplication in wherein each iteration; 7 sub-additions and a tanh computing, if we limit every group number of users, then Group-CDMA compares with CDMA; Complexity increases few, but obtains very big lifting on performance and the capacity.

(2) compare with CDMA-MMSE: can be found out that by Fig. 8 and Figure 10 during less than spreading code length, GCDMA systematic function and CDMA-MMSE systematic function are similar at number of users, capacity has improved a lot, and complexity has reduced a lot.

(3) compare with IDMA:, can find out that GCDMA compares with IDMA by Fig. 9 and Figure 10, property retention remains unchanged basically, but complexity has obtained the decline of part.

Claims

1.. a CDMA downlink communication method is characterized in that all users are divided into the G group, adopt the mode of code division multiple access to distinguish between group and the group; The user adopts the mode of the branch multiple access that interweaves to distinguish in one group; At receiving terminal, adopt de-spreading operation to eliminate between group and disturb, adopt the multiple access of eliminating between the user by chip iteraction multiple users detection mode CBC-IMUD to disturb; Number of users in the complex structure degree of receiver and computational complexity and the group is linear, specifically comprises the steps:

Step D: spread processing, will pass through that other code streams merge in code stream and this group after the above-mentioned processing, and send into this and organize and utilize spreading code to carry out spread processing in the corresponding frequency multiplier, produce chip stream, be designated as,

Step G: iterative processing, despreading to be handled the estimated value of gained and sent into by carrying out iterative processing among the chip iteraction multiple users detection module CBC-IMUD, the multiple access of eliminating between the user disturbs the back acquired information,

Step H: judgement, the user who obtains after the iteration end is sent the information estimated value send in the decision device, carry out decision process, obtain the binary signal of the information of sending,

In the grouping of system user, can be expressed as K=(G-1) * M+M ' between total number of users K and the group number G in the number of users M in the average group or M ' and the system, wherein M is the number of users in preceding each group of G-1 group, and M ' is the number of users of G group.

2. a kind of CDMA downlink communication method according to claim 1 is characterized in that the said baseband modulation processing of step C employing BPSK modulation system.

3. a kind of CDMA downlink communication method according to claim 1 is characterized in that the frequency expansion sequence s that the spread processing described in the step D adopts _gBe the PN sign indicating number.

4. a kind of CDMA downlink communication method according to claim 1 is characterized in that the frequency expansion sequence s that the spread processing described in the step D adopts _gBe the WALSH sign indicating number.