移动通信试题库

1、1 / 11名词解释1 Explain the difference between hard and soft handoff.Answers：The hard handoff is that when the signal strength of a neighboring cellexceeds that of the current cell, plus a threshold, the mobile station is instructed toswitch to a new frequency band that is within the allocation of the n

2、ew cell.The soft handoff is that a mobile station is temporarily connected to more than onebase station simultaneously. A mobile unit may start out assigned to a single cell. If theunit enters a region in which the transmissions from two base stations are comparable,the mobile unit enters the soft h

3、andoff state until which it is connected to the two basestations.2 What are the cores techniques of WCDMA?Answers: The WCDMA key techniques mostly consist of the power control technique,PN code technique, RSKE, Soft Handoff, and Speech coding.3 What is attenuation?4 What two functions are performed

4、by an antenna?5 What are the advantages of using CDMA for a cellular network?Answers: (1)Frequency diversity; (2) Multipath resistance; (3) Privacy; (4) Gracefue degradation.6. What are the key differences between first and second generation cellular system?Answers: The key differences between the t

5、wo generations:(1). Digital traffic channels; (2). Encryption; (3). Error detection correction;(4). Channel access.7. What are the cores techniques of TD-SCDMA?Answers: The cores techniques of TD-SCDMA are smart antenna (intelligent antenna), joint examinationtechnique, SCDMA technique, software wir

6、eless technique, and dynamic channel allocation technique8. What is direct broadcast satellite (DBS)?Answers: The satellite video signals are transmission directly to the home user.9. What is an isotropic antenna?2 / 11Answers: An isotropic antenna is a point in space that radiates power in all dire

7、ction equally.10. What is CDMA?Answers: CDMA is a multiplexing technique used with spread spectrum11. What is frequency hopping spread spectrum?Answers: The signal is broadcast over a seemingly random series of radio frequency, hopping fromfrequency to frequency at fixed intervals12 What are the pri

8、mary causes of atmospheric attenuation for satellite communications?Answers: The primary causes of atmospheric attenuation are oxygen and water13 What is a SIR?Answers: This ratio is defined to be the ratio of the desired average signal power at areceiver to the total average interference power.14 W

9、hat are features of CDMA?Answers:(1) High spectrum efficiency(2)Release from frequency management (3)Lowmobile station transmit power (4)Soft-handover (5)Path Diversity (RAKE Fingers)(6)Security (7)Anti-jamming capability15 In general, physical models include three basic modes of propagation.Answers

10、：( 1)Free-space or link-of-signal transmission(;2)Reflection ；(3)Diffraction.16 In time, as more customers use the the system, traffic may build up so that there are not enoughfrequency bands assigned to a cell to handle its calls. A number of approaches have been used to copewith this situation, in

11、cluding the following 。Answers: (1)Adding new channels；(2)Frequency borrowing；(3)Cell splitting；(4)Cellsectoring；(5)Microcells。17 Explain the difference between open-loop and closed-loop power control.Answers: Open-loop power control depends solely on the mobile unit, with nofeedback from the BS.Clo

12、sed-loop power control adjusts signal strength in the reverse channel based onsome metric of performance in that reverse channel.18. Define channel capacity.3 / 11Answers: The maximum rate at which data can be transmitted over a given com municati on path, or cha nn el, un der give n con diti ons is

13、 referred to the cha nnel capacity.填空题1.Antenna characteristics are essentially the same whether an antenna is sendingor receivi ngelectromag netic en ergy.2.The basis for analog signaling isaeontinuousconstantfrequency signal known as thecarrier sig nal.3.Nikola Tesla inven ted the wireless telegra

14、ph in 18934.A transmission from earth station to satellite is referred to as uplink in the satellite com muni catio n.5.The essence of a cellular network is the use of multiple low-power transmitters, on orderof 100W or less.6.Third gen eration system gen erally call WCDMA or UMTS7.Adjace nt cells a

15、re assig ned different freque ncies to avoid in terfere nce or crosstalk.8. Viewed as a fun ctio n of, an electromag netic sig nal can be either an alog or digital.An analog signal is one in which the signal intensity varies in a smooth fashion over time.9.The data signaling rate, or just data rate

16、, of a signal is the rate, in bits per second, that data are transmitted.10The TD-SCDMA is a multiple conn ect i nto i nclude theFCDMA/TDMA/CDMA11.Nikola Tesla inven ted the wireless telegraph in 1893.12.A digital signalis one in which the signal intensity maintains a constant levelfor some period o

17、f time and then changes to another constant level.13.Reflect ion occurs whe n an electromag netic sig nal encoun ters a surface that is large relative tothe wavele ngth of the sig nal.14. If the size of an obstacle is on the order of the wavelength of the signal orless scattering occurs.15. For a da

18、ta ofR, the durati on of a bit isTsec on ds a nd the durati on of a sig nal eleme nt4 / 11isTSLTsec on ds. IfTCis greater the n or toTS, the spreadi ng modulati on is referred to asslow-frequency-hopspread spectrum; otherwise it is known as fast-frequency-hop spreadspectrum.16. A transmission from s

19、atellite station to earth is referred to as downlink in the satellite com muni cation.17. The cells sufficie ntly dista nt from each other can use the same freque ncy ba nd18.Code division multiple access is aspread spectrumbased technique for multiplexing.19. The objective of the third gen erati on

20、 of wireless com muni cati on is to provide fairly high speedwireless com muni cati ons to supportmultimedia, data, and video_ in additi on to voice.20. Power control technique is core in the CDMA .21.One purpose of the data-layer is to performerrorcorrect ionor detect ion.22. The channel provides t

21、he physical means for transporting the signal produced by thetran smitterand deliveri ng it to thereceiver.24. The key physical resource is theradio spectrumin wireless system.24. Adigital signalis one in which the signal intensity maintains a constant level for some period oftime and then changes t

22、o another constant level.25. Thefrequencyis the rate at which the signal repeats.26. An antenna that tran smits equally in all direct ions called theisotropic radiatio.27. Noise can be defi ned asunwan tedelectrical sig nals in terfere nee with the desired sig nal.28. The basic idea with cellular sy

23、stem is toreusechannel in different cell, increasing the capacity29. During the period from1895 to 1901, Guglielmo Marconi developed an apparatus fortran smitt ing radio waves over Ion ger dista nces.30.An electromagnetic signal can beeither analog or digital. Ananalog signalis one in which the sign

24、al intensity varies in a smooth fashion over time.5 / 1131. Thespectrumof a sig nal is the range of freque ncies that it con tai ns.1.32 . The same freque ncy assig nments cannot be made in adjace nt cell because ofinter-channel interferenee .33.Handoffmay be network ini tiated.34. That each user oc

25、cupies a cyclically repeatingtime slotin the TDMA system.35. All users in aCDMA, use the same carrier frequency and may transmit simultaneously.36. Self-jamming is a problem inCDMAsystem.37.The GSM key technique consist ofeight parts38. Reflectio n occurs whe n an electromag netic sig nal encoun ter

26、s a surface that is large relativeto the wavele ngth of the sig nal.判断题1. Thermal no ise can be elim in ated.( N )2. The time-selective cha nn els are time-i nvaria nt cha nn els.( N )3. A high SNR will mea n a high-quality sig nal.( Y )4. Free-space propagation, in which the received power decreases as the square of the distaneefrom the tran smitter.( Y )5. Fast fading is the rapid variation of signal levels when the user terminal moves short distances.(Y )6. Traffic cha nn els are used to excha nge in formati on.( N )7. Multiple access schemes are used to