无线通信基础知识讨论Discussion on basic knowledge of wireless communication文档格式.docx

1、These two types of decline are contradictory and should be considered when designing a system.6, wireless communication books are on the top7, multipath channel modeling requires that multipath should be independent. How should independence be reflected in channel modeling? This should also be the c

2、ase for MIMO channels and multiuser channels.The correlation coefficients of the two paths are as small as possible, or modeled separately according to what is said above.8, MIMO channel modeling, sometimes required to consider the correlation between antennas, and how this correlation should be mod

3、eled?Firstly, the correlation coefficient matrix is constructed, and then the Chol is decomposed. The matrix obtained by the decomposition is multiplied by the signal of each antenna.Biezs was published at 20:53 2006-10-25quote or 2006-10-25 20:42 published by ilucatt0415/i in（but its good against f

4、requency selective fading）./quoteCan you explain why these two types of decline are contradictory?56 2006-10-25The correlation coefficients of the two paths are as small as possible, or modeled separately according to what is said above. /quoteThe relative coefficient of the two paths as small as po

5、ssible is our goal, but Im not sure what the so-called individual modeling means. For example, what does this single modeling mean for the traditional Jakes model?Lucatt0415 was published at 23:39 2006-10-25The reasons are as follows: the coherence bandwidth requirements of signal bandwidth less tha

6、n the channel against frequency selective fading, which requires bandwidth as small as possible, from the time it is symbolic time or chip time as large as possible, but with the increase of symbol or of the chip cycle, and when the channel phase do when a long time, it is difficult to fight against

7、 fast fading so, the design of the system should fully consider the application object system, reasonable design parameters.44 2006-10-25Or in accordance with the MIMO modeling method is better, that is, the use of coefficient correlation matrix for Chol decomposition, and then use the decomposed ma

8、trix multiplied by two signals,Individual modeling does not necessarily guarantee that the two paths are uncorrelated.SWAs was published in 2006-10-26 08:46Large scale fading is mainly path loss, which can be approximated by free space propagation model, but some characteristics are different, such

9、as fading index, and so onWhat are the factors associated with the lognormal variance of shadow fading? How much is the typical value?OFDM system is used to discuss the guiding role of coherent time and coherent bandwidth in practical system design.In addition to the fading characteristics of wirele

10、ss channel, which is different from wired channel, we must consider, such as multi user shared channel, multiple access methods are discussed, the discussion on the basis of the understanding of great help. A good subject. I hope you will have a heated discussion.Lucatt0415 was published in 2006-10-

11、26 08:54The three effects of the wireless channel are missing:Three effects of wireless channelShadow effect, near far effect and Doppler effect（1） shadow effect: when the electric wave is disturbed by undulating terrain, buildings, vegetation and other obstacles on the propagation path, the half bl

12、ind zone of electromagnetic field will be produced（2）: Near far effect due to random mobility receiving users, mobile users and the distance between the base station and then low change, if the mobile users transmit power, then arrive at the base station signal is strong if different from the base s

13、tation near strong signal, far from the base station signal is weak. In which the base station receiver appears strong stronger and the weak weaker and strong weak phenomenon. This is the reason for power control（3） Doppler effect: because of the high speed motion of the mobile user in the receiving

14、 state, the propagation frequency is diffused, and the diffusion degree is directly proportional to the users moving speed.Lcj2212916 was published at 18:23 2006-10-26What are the characteristics of wireless （mobile） channels?Turn from: urlRadio waves in different frequency bands have different prop

15、agation modes and characteristics.The mobile communication system to work in the VHF and UHF bands, radio wave propagation is the main way of space, namely direct wave, refraction wave, wave scattering and their synthesis wave.In the land mobile system, the mobile station is in the city or in the bu

16、ildings in the complex terrain area, the antenna will receive signals from multiple paths came, coupled with the mobile station itself, the wireless channel between the mobile station and the base station is changeable and difficult to control.In analog wired channels, the typical signal-to-noise ra

17、tio is about 46dB, that is, the signal level is 40000 times higher than the noise level, and for the wired channel, the quality of transmission is controllable. By selecting the right materials and careful processing, you can ensure that there is a relatively stable electrical environment in the wir

18、ed transmission system. As a result, the signal-to-noise ratio usually does not exceed 12dB in a wired transmission line. Only when a line has been running for a long period of time, will the loss of the line gradually reach 1015dB, so in this case, the line will need to be updated.In terrestrial mo

19、bile radio channels, a sudden drop in signal intensity, known as fading, is frequent, with a depth of about 30dB.In urban environments, the number of signals received by a mobile station on a fast moving vehicle can decline significantly within a second. This kind of fading seriously deteriorates th

20、e quality of received signals and affects the reliability of communications.In the cellular mobile environment, the same frequency interference is a problem that must be paid attention to. When fading occurs, the signal to be received may be weaker than the interference signal from the same frequenc

21、y cell base station, so the receiver will easily lock on the wrong signal.The analog mobile communication adopts FM signal, and the capture effect of FM mode has a certain inhibitory effect on the same frequency interference. The fading phenomenon will significantly change the characteristics of FM

22、signal and weaken its capture effect. For digital transmission, fading will greatly increase bit error rate （BER）.The fading characteristics of mobile channels depend on the propagation environment of radio waves. Different environments, their propagation characteristics are not the same.A large cit

23、y with many tall buildings, for example, has a very different spread environment compared to a flat open country, and the mobile channel characteristics vary greatly. The communication environment itself is quite complex, which makes the mobile channel characteristics is very complex.It is spread in

24、 different environment, led directly to the multipath delay size have obvious difference, if we want to transmit high-speed data, T symbol period should be as small as possible, but the smaller the T, the ability to resist multipath delay is weak, resulting in a OFDM, it is because the symbol period

25、 in OFDM system because of the parallel transmission of variable length, which can effectively resist the multipath delay.Complex and harsh propagation conditions are the characteristics of mobile channels. In order to maintain acceptable transmission quality under such propagation conditions, a var

26、iety of technical measures must be adopted to counteract the adverse effects of fading. Therefore, a variety of anti fading technologies have been developed, including diversity, spread spectrum / frequency hopping, equalization, interleaving and error correction coding. In addition, the signal tran

27、smission mode, such as modulation mode, will also have a certain adaptability to fading in the channel.i this post was finally edited by sreight at 19:14 2006-10-26 on /iLcj2212916 was published at 20:29 2006-10-26Provide two reference materials, the basic knowledge written in more detail, the Xian electronics division of the big lesson plans!We mainly discuss large scale and small scale fading and general modeling of channel