MIMO系统的结构和设计_英文含6文献版

1、The Structure and Desig n of MIMOSystemAbstract:The next generation mobile communication, 4G called, will support very high data transmission rate. It in troduce tech no logy with high freque ncy utilizati on in limited freque ncy spectrum. MIMO is a tech no logy to in crease channel capacity with a

2、dding more antennas and has very high spectrum utilization. It one of the most competitive tech no logies in future mobile commu ni cati ons. This thesis in troduce basic theory about MIMO and make deep an alyze and deduct about the channel capacity and array gain. Also discussed the key techniques

3、of MIMO and described its developing trend in future.Key Word :mobile communication , MIMO , LTE , channel capacity , array gain , space diversity, space multiplexing1.MIMO overviewFuture wireless commu ni cati on system to tra nsmit the highest speed and capacity are put forward higher requireme nt

4、s, how to use the limited un limited spectrum to meet the in creas ing commu ni cati on dema nd has become an important subject. As early as 1948, Shannon has the SISO system is given in the literature of channel capacity limit: C = Blog2 (1 + S/N). Maximum spectrum efficiency for C/B = log2 (1 + S/

5、N). For this kind of single into SISO system, no matter how adva need the way of modulati on and cod ing, can only make the system cha nnel capacity is close to the ceili ng, and impossible to surpass him. With mature Turbo code and LDPC code tech no logy and practical applicati on, the actual syste

6、m basically close to the Shannon cha nnel capacity limit.In a new gen erati on of mobile commu ni cati on systems, people put forward higher requireme nts on the rate of transmission, it is presented under the premise of spectrum is a limited resource support the requirement of high rate. Studies ha

7、ve show n that MIMO tech no logy can meet the requireme nts. MIMO tech no logy in in door en viro nment spectrum efficiency can reach 20-40 bit/s/Hz, far more than the traditional wireless communication in 1-5 bit/s/Hz with microwave tran smissio n in 10-12 bit/s/H z.MIMO first be suggested in 1908,

8、 it uses multiple antenna suppress cha nnel fadi ng. MIMO tech no logy refers to the tran smitter and the receiver using multiple tran smit antennas and receive an te nn as. MIMO tech no logy is the key to the multipath effect factors exist in the traditi onal commu ni cati on system become better f

9、actors for user commu ni cati on. MIMO tech no logy immediately effective utilizati on of the decli ne and the possible existe nce of multipath propagati on to multiply bus in ess tra nsmissi on rate. MIMO tech no logy successes lies in it can without any in crease in sig nal un der the premise of e

10、xtra ban dwidth wireless commu ni cati on performa nce on several orders of magn itude. This con tributed to the cha nnel model, information theory and coding, signal processing, antenna design and design of fixed/wireless antenna cellular.Bell LABS e. Alater and G.J.Fosch ini in depe nden tly in th

11、eir own paper dem on strates the theory of the Shannon capacity of MIMO channel. They point out that using the channel matrix to describe the N t x N r root transmitting antenna and N r receiv ing antenna system of wireless cha nn el, and the matrix eleme nts is ideal in depe ndent fading, system ca

12、pacity will be along with the tra nsmitter and the receiver antenna n umber of smaller one min (N t, N r) the in crease of li near in crease. It can multiply on the basis of SISO system capacity.According to the definition of the MIMO system that based on transmit diversity and accept diversity into

13、 single out (MISO) method and the si ngle into more way (SIMO) is a part of MIMO.2.The limit capacity of MIMO systemi.For SIMO systemBy a single antenna to send, receive antenna structure, with a number of 2 N r = 2. At the receiving end of themaximum ratio comb ining cohere nt recepti on tech no lo

14、gy, the received sig nal:The limit capacity can be expressed as at this timeAmong them, the P t is the total power to send, the delta n is the noise power. The ultimate capacity formula can be see n that cha nnel capacity will in crease as the n umber of receiv ing antenna is a logarithmic.ii.For MI

15、SO systemsSent by a sin gle antenna, the structure of the antenna n umber is 2, n amely the Nt = 2. In the sending end adopts closed loop tra nsmissi on diversity, the received sig nal :Among them, the P t is the total power to send, the S n is the noise power. The ultimate capacity formula can bese

16、e n that cha nnel capacity will also be a logarithmic in crease as the tran smitt ing antenna n umberiii.,x + n订+ |舟发送天践For MIMO systemsSent by a sin gle antenna, the structure of the antenna n umber is 2, n amely the Nt = 2. In the sending end adoptsclosed loop tra nsmissi on diversity, the receive

17、d sig nalThe limit capacity can be expressed as at this time:(i*.r I )* log. 1Among them, the Pt. is the total power to send, theS n is the noise power. The ultrnuatecaipaeity forsee n that cha nnel capacity will also be a logarithmic in crease as the tran smitt ing antenna n umber.3.Techniques in M

18、IMO systemMIMO tech no logy is esse ntially for the system to provide the spatial multiplexi ng gain and spatial diversitygain. Spatial multiplex ing tech no logy can greatly improve the cha nnel capacity, and spatial diversity can improve the reliability of cha nn el, reduce the cha nnel bit error

19、rate.i.Spatial multiplex ing tech no logySpatial multiplexing is sender and using multiple antennas at the receiving end, make full use of space transmission of multipath components, using multiple data channels on the same frequency band (MIMO) sub-cha nn els emissi on sig nal, thus making capacity

20、 in creases lin early with the in crease of the n umber of antenn as.This sig nal in crease dont n eed the extra ban dwidth capacity, also do not n eed additi onal tran smissi on power con sumpti on, and therefore is to improve the cha nnel capacity of a very effective means.Spatial reuse, will firs

21、t need to transfer the signal after a string of translates into several parallel signalflow,more tha n in the same freque ncy band antenna to send at the same time. Data flow through the pulse forming, and modulation. Due to multipath propagation, each pair of transmitting antenna of the receiver to

22、 create a different spatial signal, the receiver using signal to distinguish their different data streams. Achieve spatial reuse must dema nd spac ing is greater tha n the relative dista nee betwee n tra nsmit and receive antenn as. By sending and receiving antenna spacing is greater than the relati

23、ve distance (usually) more than 10 signal wavelength. In this way can we guara ntee to receive origi nated were not associated with each in depe ndent fading sub-cha nn els cha nn el.For spatial reuse, BLAST is a kind of algorithm can realize the spatial multiplexing gain. In 1998 by Foschini and G.

24、G olde n V - BLAST algorithm is put forward. V - BLAST algorithm is not for all sig nal decodi ng together, but first of all, the str on gest sig nal decodi ng, and the n in the received sig nal minus the stro ngest sig nal, and the n the residual sig nal decodi ng, the str on gest sig nal minus thi

25、s sig nal, so on ce, un til all the sig nals are ren dered. V - BLAST algorithm is con sidered algorithm complexity and decodi ng performa nee un der a kind of optimal decodi ng algorithm.ii.Tran smissi on diversity and receive diversitySpace diversity tech no logy can be divided into two categories

26、, receive diversity and tra nsmit diversity, usually can be thought of SIMO system is receiving diversity, MISO systems transmit diversity. Wireless signal in complex Rayleigh fading propagation in wireless channel, its decline characteristics different on different spatial location. If the two posi

27、tion distanee is greater than the distanee between antennas (usually more than ten signal wavelength apart) think of two signals completely irrelevant, so that it can realize signal space diversity reception. Spatial diversity gen erally use two or more deputy vice is greater tha n the relative dist

28、a nee of antenna receiv ing sig nals at the same time, and then in the heart of the baseband processing merger multiplex signals. In SIMO system of receiv ing diversity tech no logy can be divided into maximal ratio comb ining (MRC), such as merger (EGC) and choose the diversity gain (SDC) three typ

29、es. In the receiving of maximal ratio combining, each pair of the output of the antenna with a plural weighted, the n add; Such as gain merger receive keep each pair of antenna output sig nal in phase, and the n add. Choose the diversity in receiv ing merger, simply choose a best quality of the sig

30、nal of antenna signals, and using the signal as the received signal. The signal-to-noise ratio of the signal after maximal ratio combining is equal to the sum of each branch of the SNR before merger, so is the best way of mergerTransmit diversity is to shiftthe burden of diversityfrom the terminal t

31、o the base station side, but the mainproblem of transmit diversity is dont know in a fading channel of the channel state information (CSI). So the cha nnel cod ing must be used to en sure that each cha nnel has a good performa nee, the con crete is using space-time codi ng. Space-time codi ng is a c

32、omb in ati on of cha nnel codi ng and tra nsmitt ing antenna desig n, put forward by AT&T laboratory Tarokh et al. Space-time code in the data is divided into N the sub flow on N antennas to launch at the same time, established the spatial separation of signals separation (sky) and time (time domain

33、), the relati on ship betwee n and in the maximum ratio whe n the receive merg ing tech no logy, the space-time code scheme can achieve the same diversity gain. In addition to the diversity gain, good space-time codes can also get a certain n umber of codi ng gain.Based on the diversity of space-tim

34、e Code can be divided into the space-time lattice Code (STTC: Space - Time Trellis Code and space-time Block codes (STBC: Space - Time Block Code). Space lattice code has good performanee, but its decoding complexity index and transmission rate, but implementation is difficult. S.M.A. Lamouti dem on

35、 strated in the literature through certa in cha nnel cod ing can be 1 x 2 accept diversity gain, con verted into a 2 x 1 transmit diversity gain and diversity gain not loss, it can be thought of as the original model of space-time block codes. On the basis of the Tarokh space-time block codes was pr

36、oposed, theory of orthogonal desig n of space-time block codes performa nee, less space-time lattice code, but its low decod ing complexity, may also get the maximum diversity gain. Receiver usually n eed to know the parameters of each wireless cha nn el, the channel estimation, can use the channel

37、estimation based on pilot training sequences, you can also use the blindestimati on.4.The performanee of MIMO system gainMIMO system performanee gain, mainly including power gain, array gain, space diversity gain and multiplex ing gain.i.Power Gai nPower gain is refers to the tran smitter gain by in

38、 creas ing the tra nsmitted power. Whe n using multiple antenn as, with N tra nsmissi on cha nn el, so the total power of the emissi on equivale nt to a sin gle antenna lau neh N times, at this point in the SNR at the receiv ing end can get 10 log (N) dB gain. In a sin gle antenna lau nch also can i

39、n crease the transmission power, but at the moment, the requirement of the power amplifier will improve. Due to the cost of a sin gle amplifier and power is not a lin ear relati on ship, so using multiple antennas to improve the total tra nsmitted power can get power gain more econo mic.ii.The array

40、 gainArray gai n refers to the cohere nt comb in ati on of received sig nal, or closed loop in the sen der to send, and the in crease of the average SNR.To receive diversity, for example, as shown in figure, single antenna to send, two antenna:Cohere nt comb ined to obtain :The signal-to-noise ratio

41、 at the receiving end as followsObviously, if 1 h and h 2 independent identically distributed, acquired 3 dB two antenna array gain. By exte nsion, through closed-loop tran smissi on diversity and receiv ing sig nal cohere nt comb in ati on of N t antennas transmit diversity and N r closed-loop can

42、transmit diversity gain of log (Nr (Nt) 10 dB array gain.iii.Diversity GainBy receiv ing sig nals related to merge, not only can in crease the average SNR of received sig nal, can also reduce the SNR fading channel under the receiving end of volatility. Can be used for merger is defined as the numbe

43、r of independent fading branch diversity order number, the higher the diversity order number, the more stable SNR, the approximate Gaussia n cha nn el. Diversity order to largest n umber of tra nsmitti ng antenna and receiv ing antenna n umber of the productSpatial multiplexing gain may be defined a

44、s under the premise that same transmission power, bandwidth, on the improvement of the ultimate capacity/transmission rate. In the channel under the premise of not related, the ideal of MIMO channel capacity can be as the number of antenna linear growth. It should be said that the spatial multiplex

45、ing gai n of MIMO tech no logy for the developme nt of wireless commu ni cati on has brought the revoluti onary cha nge.5.MIMO application and prospectAt present, many countries have begun to a new generation of mobile communication system of the commercial, new gen erati on mobile commu ni cati on

46、system can provide high rate (10-100 Mbit/s) data bus in ess, so we must adopt some tech no logy with high spectrum efficie ncy. MIMO tech no logy has a very high spectrum efficiency, but also provide space diversity can significantly improve the wireless link performanee, improve the capacity and c

47、overage of the wireless system. So MIMO technique is very competitive in the future mobile commu ni cati on tech no logy, not only for the fixed wireless access tech no logy has brought the revoluti onary cha nge, and will have a profound effect on wireless cellular system. Specific application has

48、the following several aspects:i.Wireless broadba nd mobile commu ni cati onsIn order to improve the system capacity, the next generation of broadband wireless mobile communication system will adopt MIMO tech no logy, n amely place multiple antennas at the base stati on end, and also place multiple a

49、ntenna in mobile stati on, base stati on and mobile stati on formed betwee n MIMO commu ni cati on lin ks. Applicati on of MIMO tech no logy of broadba nd wireless mobile commu ni cati on system morefrom a base stati onantenna placed methods can be divided into two categories: one is multiple base s

50、tation antenna arrangement form antenna array, placed in the covered area, this category may be called centralized MIMO; Another kind is multiple antenna base stations distributed in the coverage area, could be called a distributed MIMO.ii.The traditi onal cellular mobile commu ni cati on systemMIMO

51、 tech no logy can be relatively simple straight for traditi onal cellular mobile commu ni cati on system, reinforce the base of single antenna for multiple antenna array. Base station antenna arrays and the mobile station with multiple antennas in the community for MIMO communication. From the persp

52、ective of the system structure of the MIMO system with the traditi onal si ngle into sin gle out (SISO) and there is no fun dame ntal differe nee betwee n cellular commu ni cati on systems.iii.Comb ined with the traditi onal distributed antenna systemThe traditional distributed antenna system can ov

53、ercome large scale fading and shadow fading channel path loss caused by the cover in the area to form a good system, solve the commu ni cati on in side the dead An gle, and improve the quality of service. Rece ntly discovered in the study of MIMO tech no logy, the traditi onal distributed antenna sy

54、stem comb ined with MIMO tech no logy can improve system capacity, this ki nd of new distributed MIMO system structure, the distributed wireless commu ni cati on system (DWCS) 8 become an importa nt research focus of MIMO tech nology.In DWCS with distributed MIMO system, the scattered in multiple an

55、tenna in the community through the optical fiber and the base station are connected to the processor. Mobile station with multiple antennas and dispersed in the base station near the antenna for communication, and the base station MIMO communication link is established. This system not only has the

56、adva ntages of the traditi onal distributed antenna system reduced the path loss, to overcome the shadow effect, but also by sig nifica ntly in crease the cha nnel capacity of MIMO tech no logy. Compared with the centralized MIMO, the distanee between the base station antenna DWCS, different fading

57、cha nnel can be formed betwee n the antenna and the mobile stati on as a completely un related, cha nnel capacity is bigger. I n gen eral, the more distributed cha nnel capacity of MIMO system, the power con sumpti on of the system smaller, system cover ing performa nee better, system has better expa nsibility and flexibility.Mobile stati on and built in side the village n earby antennas MIMO link, due to differe nt base stati on antenna position, theyre different from the mobile station