CN1434588A - Time-frequency union spreading method based on OFDM-CDMA for broadband radio communication system - Google Patents
Time-frequency union spreading method based on OFDM-CDMA for broadband radio communication system Download PDFInfo
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Abstract
This invention discloses a new type of time frequency joint expanding modulation way used in radio broadband multicarrier mobile communication system. This invented method makes better use of performance gain brough with time space-apart and frequency space-apart, different from the traditional single time domain or frequency domain frequency expanding modulation method which is compatible with the present multi-carrier frequency domain expanding modulation way favorable to developing working system according to this invention is short time.
Description
Technical field
The present invention relates to a kind of broad band multicarrier wireless communication technology, particularly the band spectrum modulation and the multiple access technology of physical layer in the broad band multicarrier wireless communication system.The band spectrum modulation of physical layer and multiple access technology have very important meaning for the effective frequency spectrum resource of using preciousness.In cell mobile communication systems and wireless communication system (as WLAN) that some is specific, adopted code division multiple access to insert and orthogonal frequency division multiplexi, but then there are a lot of problems in effective fusion of two kinds of technology.The invention discloses a kind of novel band spectrum modulation mode and access mode of being applicable to cell mobile communication systems or wireless communication system, and understand its advantage and implementation in detail based on code division multiple access access and orthogonal frequency division multiplexi
Background technology
Code division multiple access inserts (CDMA) mode because its remarkable advantages is defined as access mode in the 3-G (Generation Three mobile communication system) by International Telecommunication Association.The development of Internet and ecommerce etc. will further promote the development of following mobile communication, and following mobile radio system can provide the peak information bit rate up to tens of million.At this moment, traditional single carrier direct sequency-code division multiple access (DS-CDMA) system can't operate as normal.MC-CDMA (OFDM-CDMA) system based on OFDM (OFDM) technology can overcome complicated multipath situation well, and have the very high availability of frequency spectrum and easy implementation, become the most promising a kind of system schema of following wide-band mobile communication system.For many years, researchers are devoted to seek a kind of method that effectively OFDM technology and CDMA technology is combined always, more effectively utilize the advantage [1] of two kinds of technology.From present domestic and international research, the most methods that proposed can be divided into two big classes [2] [3]: first kind (MC-DS-CDMA) at first utilizes orthogonal code that the information modulation symbol is carried out the spread processing of similar and traditional DS-CDMA system on time domain, and these spread-spectrum signals are sent into the IFFT module and formed ofdm signal then; Second kind (MC-CDMA) utilizes spreading code that it is carried out spread spectrum on frequency domain after original modulation signal is repeated, and reaches the effect of frequency domain Rake receiver like this at receiver end.The former is a kind of method that well the OFDM technology is incorporated in the DS-CDMA system, and particularly for up accurate synchronizing channel, still, if lack effective forward error correction coding and interleaving technology, the method can't realize frequency diversity basically.The latter reaches diversity on the frequency by identical modulation symbol information well in the expansion on the frequency domain, although because the frequency selectivity of channel can destroy the orthogonality of orthogonal code, can be by selecting suitable despreading merging mode to reduce nonorthogonality to Effect on Performance at receiver end; Similarly, the method can't reach the effect of time domain diversity.
Summary of the invention
The present invention proposes a kind of novel OFDM-CDMA modulation system, reached at receiver end and effectively utilized the effect of time diversity and frequency diversity simultaneously, thereby improved the performance of receiver based on time-frequency 2 dimension expansions.
In time-frequency combination spread spectrum mode, each user all need to utilize one group of spread spectrum length for the orthogonal code sequence of N as the frequency expansion sequence group, different users should use the different permutation and combination of this group frequency expansion sequence to form corresponding time-frequency spread spectrum grid chart.This point is different from fully that each user only uses some specific frequency expansion sequences in one group of frequency expansion sequence in simple time domain of tradition or the frequency domain spread spectrum mode.
Corresponding to the time-frequency 2 dimension band spectrum modulation modes that propose among the present invention, can be with N OFDM symbol as a basic frame, no matter be the time-frequency spread processing of transmitter terminal, or the time-frequency despreading of receiver end merge processing, all is with the elementary cell of this basic frame as the processing time.
At transmitter terminal, relation according to different number of sub carrier wave and frequency expansion sequence length, we can select different time-frequency extend web trrellis diagrams, at a basic handling time quantum (promptly in a basic frame), finish the associating extension process of modulation symbol on time domain and frequency domain then.Because in real system, the number of the operable subcarrier of system is not equal to frequency expansion sequence length usually, so we must be at the different different time-frequency extend web trrellis diagrams of situation design.But these design all based on a common principle, are exactly that the information of certain user's same modulation symbol is expanded on each subcarrier of each OFDM symbol, to reach the effect of time diversity and frequency diversity to greatest extent.Simultaneously, consider the temporal correlation that mobile channel exists, in design during frame structure, should make the correlation time of duration of a basic handling time quantum and mobile channel can be comparable, thereby could embody the advantage of time diversity in the time-frequency combination expansion better.On the other hand, because the total bandwidth that occupies of each subcarrier is general all much larger than the correlation bandwidth of mobile channel, so the time-frequency combination expansion can realize the effect of frequency diversity easily.
At receiver end, keep consistent with transmitter terminal, the basic processing time quantum is basic frame, i.e. N OFDM symbol, and the use time-frequency extend web trrellis diagram consistent with transmitter terminal come certain user is carried out the time-frequency despreading and merge to handle, to recover former modulation symbol data stream.Generally consider to use simple equal gain combining mode (EGC) at receiver end.Consider the destruction of mobile channel to the frequency expansion sequence orthogonality, in order to obtain more performance, the square error average that minimizes that can use energy effectively overcoming noise and multiple access to disturb merges mode (MMSEC).
The time-frequency 2 dimension band spectrum modulation modes that the present invention proposes have kept the compatibility with existing frequency domain spread spectrum system based on OFDM well, only need just can finish the transformation of original system easily by the time-frequency de-spread grid chart of time-frequency extend web trrellis diagram in the spread spectrum module of upgrading transmitter terminal and receiver end and some coefficients in the merging module.
The invention will be further described below in conjunction with accompanying drawing.
The main description of accompanying drawing
Fig. 1 describes the block diagram of a digital mobile communication system designed according to this invention.
Fig. 2 has described in the invention when number of sub carrier wave M equates with the frequency expansion sequence length N i.e. M=N, some users' the basic time-frequency extend web trrellis diagram and the realization of spread spectrum.
Fig. 3 has described in the invention when number of sub carrier wave M equates with the frequency expansion sequence length N i.e. M=N, the basic time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.
Fig. 4 has described in the invention as number of sub carrier wave M during greater than the frequency expansion sequence length N, and M=KN, and K is an integer, some users' the time-frequency extend web trrellis diagram and the realization of spread spectrum.
Fig. 5 has described in the invention as number of sub carrier wave M during greater than the frequency expansion sequence length N, and M=KN, and K is an integer, the time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.
Fig. 6 has described in the invention as number of sub carrier wave M during less than the frequency expansion sequence length N, and N=KM, and K is an integer, some users' the time-frequency extend web trrellis diagram and the realization of spread spectrum.
Fig. 7 has described in the invention as number of sub carrier wave M during less than the frequency expansion sequence length N, and N=KM, and K is an integer, the time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.
Describe in detail
Fig. 1 describes the block diagram of a digital mobile communication system designed according to this invention.In the example of Fig. 1, original information bit data are flowed through ovennodulation module 101 (for example QPSK or high-order QAM modulation) afterwards, do string and conversion then at module 102 places.At this moment; identical modulation symbol has been assigned on a plurality of subcarriers by replication module 103; and be implemented in associating spread spectrum effect on the time and frequency zone by time-frequency spread spectrum module 104; data behind the spread spectrum are through IFFT module 105; form ofdm signal after process module 106 is done parallel serial conversion, and add that at module 107 places the protection prefix is to eliminate intersymbol interference.Then, the ofdm signal of band protection prefix arrives receiver end through behind the mobile channel.To take a series of and the corresponding anti-operation of transmitter terminal to recover original information bit data stream at receiver end.At first be will protect prefix to remove to recover ofdm signal at module 109 places, pass through serial to parallel conversion module 110 then after, the signal after the processing enters FFT module 111.At this moment, can finish at module 114 places by the pilot signal of inserting at transmitter terminal and finish channel estimating, for the merging module of back provides required channel information.Enter time-frequency despreading module 112 and merge module 113 through the signal after the FFT resume module, and recover the modulation signal before the spread spectrum.At last, will enter demodulation module 116, recover original data bit flow through the signal after the parallel serial conversion module 115.
Fig. 2 has described in the invention when number of sub carrier wave M equates with the frequency expansion sequence length N i.e. M=N, some users' the time-frequency extend web trrellis diagram and the realization of spread spectrum.The input modulation symbol sequence of supposing the time-frequency spread spectrum module is { a
1, a
2..., a
N, modulation symbol a so
1Will be by No. 1 Walsh sign indicating number sequence { W
1 1, W
2 1..., W
N 1Expanded to the 1st work song carrier wave in the 1st the OFDM symbol, the 2nd work song carrier wave in the 2nd OFDM symbol ... and the N work song carrier wave in N OFDM symbol.In like manner, modulation symbol a
2Will be by No. 2 Walsh sign indicating number sequence { W
1 2, W
2 2..., W
N 2Expanded to the 2nd work song carrier wave in the 1st the OFDM symbol, the 3rd work song carrier wave in the 2nd OFDM symbol ... and the 1st work song carrier wave in N OFDM symbol.By that analogy, modulation symbol sequence { a
1, a
2..., a
NBe that the Walsh orthogonal code of N has expanded on N the subcarrier of N OFDM symbol by a group length.Certain user's concrete time-frequency extend web trrellis diagram as shown in Figure 2, transverse axis is represented the time, represents different OFDM symbols, the longitudinal axis is represented frequency, represents different subcarriers.This N OFDM symbol formed a frame, at receiver end, must could carry out corresponding despreading and merging according to the spreading code compound mode of transmitter terminal after receiving a frame.
Fig. 3 has described in the invention when number of sub carrier wave M equates with the frequency expansion sequence length N i.e. M=N, the time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.What suppose Fig. 2 explanation is basic time-frequency extend web trrellis diagram of the user 1, and user 2 spread spectrum grid chart is to turn right to carry out cyclic shift and once obtain on the basis of user 1 time-frequency extend web trrellis diagram figure so.In like manner, turn right again and carry out the time-frequency extend web trrellis diagram that cyclic shift once obtains user 3 ..., until the time-frequency extend web trrellis diagram that reaches user N.
Fig. 4 has described in the invention as number of sub carrier wave M during greater than the frequency expansion sequence length N, and M=KN, and K is an integer, some users' the time-frequency extend web trrellis diagram and the realization of spread spectrum.M subcarrier is divided into the K group, and each group comprises N subcarrier, and like this, the number of sub carrier wave in each group equals the length N of frequency expansion sequence, so can adopt and identical basic time-frequency extend web trrellis diagram shown in Figure 2 in each group.
Fig. 5 has described in the invention as number of sub carrier wave M during greater than the frequency expansion sequence length N, and M=KN, and K is an integer, the time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.Each user will use all M subcarrier, and so, each user is divided into M subcarrier the K group, uses the basic time-frequency extend web trrellis diagram of this user's correspondence in each group.
Fig. 6 has described in the invention as number of sub carrier wave M during less than the frequency expansion sequence length N, and N=KM, and K is an integer, some users' the time-frequency extend web trrellis diagram and the realization of spread spectrum.(sequence of M＜N) is formed one group of new sequence set and is formed required time-frequency spread spectrum grid chart to select M from the frequency expansion sequence group that N length is N.N chip of each frequency expansion sequence in the new sequence set is divided into the M group, and each group comprises K chip.Say something with the time-frequency extend web trrellis diagram that forms the 1st user's correspondence.Comprise that 1 to K chip is assigned on the 1st subcarrier of the 1st to K OFDM symbol to the 1st group in the 1st frequency expansion sequence, comprise that K+1 is assigned to K+1 to the 2nd subcarrier of 2K OFDM symbol to 2K chip to the 2nd group ..., by that analogy; Comprise that 1 to K chip is assigned to K+1 to the 1st subcarrier of 2K OFDM symbol to the 1st group in the 2nd frequency expansion sequence, comprise that K+1 is assigned to 2K+1 to the 2nd subcarrier of 3K OFDM symbol to 2K chip to the 2nd group ...; So repeat N * M chip up to M frequency expansion sequence to being assigned in the whole time-frequency extend web trrellis diagram.
Fig. 7 has described in the invention as number of sub carrier wave M during less than the frequency expansion sequence length N, and N=KM, and K is an integer, the time-frequency extend web trrellis diagram under multi-user's situation and the realization of spread spectrum.What suppose Fig. 6 explanation is basic time-frequency extend web trrellis diagram of the user 1, and user 2 time-frequency extend web trrellis diagram is to turn right to carry out cyclic shift K position and obtain on the basis of user 1 time-frequency extend web trrellis diagram so.In like manner, turn right again and carry out the spread spectrum grid chart that cyclic shift K position obtains user 3 ..., until the time-frequency extend web trrellis diagram that reaches user M.It is worthy of note, time-frequency extend web trrellis diagram in this case, utilize this M frequency expansion sequence, can allow M user work simultaneously (furthermore at most simultaneously, can use a remaining N-M frequency expansion sequence, these frequency expansion sequences are formed time-frequency extend web trrellis diagram equally, equally also can be used to distinguish the user, so just can increase number of users).
From above being clear that, the present invention proposes a kind of novel time-frequency combination spread spectrum mode and the access mode that is used for based on the wideband digital mobile communication system of multi-carrier spread spectrum technology.Adopt these technology, can overcome the limitation of traditional time domain or frequency domain multi-carrier spread spectrum well, and the performance gain that acquisition adequate time and frequency diversity are brought.Can select different time-frequency combination spread spectrum modes adaptively according to different mobile environment, special in the mobile environment of high translational speed and high data rate.
List of references: [1] R.Prasad, S.Hara, " An Overview of Multicarrier CDMA " IEEE ISSSTA ' 96, vol.1, Sept.1996, pp.107-114[2] S.Hara, R.Prasad, " Design and Performance of Multicarrier CDMA System in Frequency Selective Rayleigh Fading Channels ", IEEE Trans.on Veh.Tech., vol.48, No.5,1999, pp.1584-1594[3] S.Abeta, H.Atarashi, and M.Sawahashi, " Forward link capacity of coherent DS-CDMA and MC-CDMA broadband packet wireless access in a multi-cell environment ", IEEE VTC2000-Fall, Sept.2000.pp.2213-2218
Claims (6)
1. based on novel OFDM code division multiple access (OFDM-CDMA) system of broadband wireless communication of OFDM (OFDM) technology, it is characterized in that time-frequency 2 dimension expansion techniques are applied to have the higher availability of frequency spectrum in the OFDM-CDMA system.
2. system of broadband wireless communication according to claim 1 is characterized in that: for the modulating data of a basic processing unit that comprises a plurality of OFDM symbols, continue to carry out on processing time and each subcarrier 2 dimension expansions at basic processing unit;
3. system of broadband wireless communication according to claim 1 and 2 is characterized in that: different users can distinguish by the different ordering of a plurality of spreading codes on subcarrier in the OFDM-CDMA system based on the time-frequency expansion;
4. system of broadband wireless communication according to claim 1 and 2 is characterized in that: when the number of subcarrier during greater than spreading code length, can use to each subcarrier one group of spreading code cycle assignment;
5. system of broadband wireless communication according to claim 1 and 2 is characterized in that: when the number of subcarrier during less than spreading code length, only need to select the part spreading code from whole spreading code set, and each spreading code segmentation is assigned on each subcarrier;
6. according to claim 1,2,3,4 or 5 system of broadband wireless communication is characterized in that: utilize the 2 dimension time-frequency extend web trrellis diagrams that constitute, form access mode of the present invention.
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| WO2006010327A1 (en) * | 2004-07-27 | 2006-02-02 | Huawei Technologies Co., Ltd. | A distributing method of the time frequency power in communication system |
| WO2006037258A1 (en) * | 2004-10-09 | 2006-04-13 | Zte Corporation | A ofdm and ofdma coexistence system and a cooperation method thereof |
| WO2006037257A1 (en) * | 2004-10-09 | 2006-04-13 | Zte Corporation | A method for assigning frequency spectrum bandwidthe of a ofdm and ofdma coexistence system |
| WO2007137489A1 (en) * | 2006-05-15 | 2007-12-06 | Huawei Technologies Co., Ltd. | Signal receiving and transmitting method in the Orthogonal Frequency Division Multiplexing system and apparatus thereof |
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| CN101390327B (en) * | 2006-01-09 | 2012-04-11 | 新加坡科技研究局 | Method and device for transmitting data between a communication network unit and a plurality of communication devices |
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| WO2007137489A1 (en) * | 2006-05-15 | 2007-12-06 | Huawei Technologies Co., Ltd. | Signal receiving and transmitting method in the Orthogonal Frequency Division Multiplexing system and apparatus thereof |
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| CN101399797B (en) * | 2007-09-27 | 2012-01-04 | 北京信威通信技术股份有限公司 | Time frequency code spreading method and device for resisting time frequency selection by OFDMA system |
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| CN102939722B (en) * | 2010-06-14 | 2015-04-01 | 独立行政法人产业技术综合研究所 | Spectrum spread communication system |
| CN102939722A (en) * | 2010-06-14 | 2013-02-20 | 独立行政法人产业技术综合研究所 | Spectrum spread communication system |
| CN113179107A (en) * | 2021-02-07 | 2021-07-27 | 西安宇飞电子技术有限公司 | Method for dynamically adjusting data link code rate of OFDM system based on subcarrier spread spectrum |
| CN113179107B (en) * | 2021-02-07 | 2022-11-15 | 西安宇飞电子技术有限公司 | Method for dynamically adjusting data link code rate of OFDM system based on subcarrier spread spectrum |
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