移动通信试题库

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 cell exceeds that of the current cell, plus a threshold, the mobile station is instructed to switch to a new frequency band that is within the allocation of the new cell. The soft handoff is that a mobile station is temporarily connected to more than one base station simultaneously. A mobile unit may start out assigned to a single cell. If the unit enters a region in which the transmissions from two base stations are comparable, the mobile unit enters the soft handoff state until which it is connected to the two base stations.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 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 two 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 examination technique, SCDMA technique, software wireless 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?Answers:An isotropic antenna is a point in space that radiates power in all direction 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 from frequency to frequency at fixed intervals12．What are the primary 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 a receiver to the total average interference power.14．What are features of CDMA?Answers:(1) High spectrum efficiency(2)Release from frequency management(3)Low mobile 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：（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 enough frequency bands assigned to a cell to handle its calls. A number of approaches have been used to cope with this situation, including the following。

Answers: (1)Adding new channels；(2)Frequency borrowing；(3)Cell splitting；(4)Cell sectoring；(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 no feedback from the BS.Closed-loop power control adjusts signal strength in the reverse channel based on some metric of performance in that reverse channel.18．Define channel capacity.Answers: The maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions is referred to the channelcapacity.填空题1．Antenna characteristics are essentially the same whether an antenna is sendingor receiving electromagnetic energy.2．The basis for analog signaling is a continuous constant frequency signal known as the carrier signal.3．Nikola Tesla invented the wireless telegraph in 1893 .4．A transmission from earth station to satellite is referred to as uplink in the satellite communication.5．The essence of a cellular network is the use of multiple low-power transmitters, on orderof 100W or less.6．Third generation system generally call WCDMA or UMTS .7．Adjacent cells are assigned different frequencies to avoid interference or crosstalk.8.Viewed as a function of, an electromagnetic signal can be either analog 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 , of a signal is the rate, in bits per second, that data are transmitted.10The TD-SCDMA is a multiple connect into include the FCDMA/TDMA/CDMA11． Nikola Tesla invented the wireless telegraph in 1893.12．A digital signal is one in which the signal intensity maintains a constant level for some period of time and then changes to another constant level.13. Reflection occurs when an electromagnetic signal encounters a surface that is large relative to the wavelength of the signal.14．If the size of an obstacle is on the order of the wavelength of the signal orless scattering occurs.15. For a data of R , the duration of a bit is R T 1 seconds and the duration of a signal elementisLTTSseconds. If CTis greater then or to ST, the spreading modulation is referred toas slow-frequency-hop spread spectrum; otherwise it is known as fast-frequency-hop spread spectrum.16．A transmission from satellite station to earth is referred to as downlink in the satellite communication.17．The cells sufficiently distant from each other can use the same frequency band18．Code division multiple access is a spread spectrum based technique for multiplexing.19．The objective of the third generation of wireless communication is to provide fairly high speed wireless communications to support multimedia, data, and video in addition to voice.20．Power control technique is core in the CDMA .21．One purpose of the data-layer is to perform error correction or detection.22．The channel provides the physical means for transporting the signal produced by the transmitter and delivering it to the receiver .24．The key physical resource is the radio spectrum in wireless system.24．A digital signal is one in which the signal intensity maintains a constant level for some period of time and then changes to another constant level.25．The frequency is the rate at which the signal repeats.26．An antenna that transmits equally in all directions called the isotropic radiatio .27．Noise can be defined as unwanted electrical signals interference with the desired signal.28．The basic idea with cellular system is to reuse channel in different cell, increasing the capacity29．During the period from 1895 to 1901 , Guglielmo Marconi developed an apparatus for transmitting radio waves over longer distances.30．An electromagnetic signal can be either analog or digital. An analog signalis one in which the signal intensity varies in a smooth fashion over time.31．The spectrum of a signal is the range of frequencies that it contains.1.32．The same frequency assignments cannot be made in adjacent cell because ofinter-channel interference.33．Handoff may be network initiated.34．That each user occupies a cyclically repeating time slot in the TDMA system.35．All users in a CDMA , use the same carrier frequency and may transmit simultaneously.36．Self-jamming is a problem in CDMA system.37．The GSM key technique consist of eight parts38. Reflection occurs when an electromagnetic signal encounters a surface that is largerelative to the wavelength of the signal.判断题1. Thermal noise can be eliminated. ( N )2. The time-selective channels are time-invariant channels. ( N )3. A high SNR will mean a high-quality signal. ( Y )4. Free-space propagation, in which the received power decreases as the square of the distancefrom the transmitter. ( Y )5. Fast fading is the rapid variation of signal levels when the user terminal moves short distances. ( Y )6. Traffic channels are used to exchange information. ( N )7. Multiple access schemes are used to allow many mobile users to share simultaneously a finiteamount of radio spectrum. ( Y )8.Direct sequence multiple access is also called code division multiple access (CDMA). ( Y )9. The most popular second generation standards include three TDMA standards and one CDMAstandard. ( Y )10. The NS controls handoff between cell in different BSSs, authenticates users and validatestheir accounts, and includes functions for enabling worldwide roaming of mobile users. ( Y )11. Thermal noise cannot be eliminated. ( Y )12. Frequency-Selective Channels is time-invariant channels. ( N )13. The greater the bandwidth, the higher the information-carrying capacity. . ( Y )14.Reflection, wherein, for the plane-Earth model, the received power decreases as the fourthpower of distance. ( Y )15.Slow fading arises from the fact that most of the large reflectors and diffracting objectsalong the transmission path are distant from the terminal. ( Y )16.Control channels are used to exchange information. ( Y )17. That each user occupies a cyclically repeating time slot in the FDMA system. ( N )18.Many users of a CDMA system share the same time-slot. ( N )19. Like TDMA or FDMA, CDMA has a soft capacity limit.. ( N )20. The NS controls handoff between cell in different BSSs, authenticates users and validatestheir accounts, and includes functions for enabling worldwide roaming of mobile users. ( Y )选择题For each sentence there are four choices. Choose the ONE answer that best completes the sentence.1. A general sine wave can be represented by three parameters, they are ( A ).A. peak amplitude, frequency, and phase;B. speed, frequency, and phase;C. peak amplitude, speed, and phase;D. peak amplitude, frequency, and speed.2．Transmission media can be classified as ( C ).A. guided;B. unguided;C. guided and unguided;D. wired and wireless.3．Fading effects in a mobile environment can be classified as either ( A ).A. fast or slow;B. fast and slow;C. fast;D. slow.4．( D ) is the procedure for changing the assignment of a mobile unit from one BS to anotheras the mobile unit moves from one cell to another.A. Transmission;B. change;C. divert;D. Handoff;5．The boundaries at Um, Abis, and A refer to interfaces between functional elements that are standardized in the ( B ) documents.A. AMPS;B. GSM;C. GPRS;D. CDMA.6．Which of the following is not core technique of the CDMA? ( A )A. Power control;B. PN code;C. RAKE;D. transfers.7．GSM key technique consist of ( C ) parts.A. 6; B 12; C. 8; D. 10.8．The GSM spectral allocation is 25MHz for base transmission ( D ) and 25MHz for mobile transmission( 890—915MHz).A. 1805—1880MHz;B. 1710—1785MHz;C. 890—915MHz;D. 935—960MHz.9．Third generation system mostly comprise the ( A ).A. RAN and CN;B. MS and BS;C. MS and CN;D. RAN and BS.10. The cellular mobile communication system consist of three parts, they are ( B )A. TDMA, FDMA and CDMA;B. BS, NS and MS;C．CDMA2000,WCDMA and CDMA; D. FDD, TDD and FHSS.11．There is direct relationship between the information-carrying capacity of a signal and bandwidth: ( B )A. The narrow the bandwidth, the low the information-carrying capacity;B. The greater the bandwidth, the higher the information-carrying capacity;C. The narrow the bandwidth, the low the information-carrying capacity;D. The narrow the bandwidth, the higher the information-carrying capacity;12．Two techniques for multiplexing in telecommunications network are in common use, they are ( D ).A. CDMA and TDMA;B. FDMA and TDMA; FDMA and CDMA; D. TDM and FDM.13．For direct sequence spread spectrum (DSSS), each bit in the original signal is represented by multiple bits in the transmitted signal, using a ( B ).A. code ;B. spreading code;C. FHSS;D. DSSS.14．The number of subchannels provide within a satellite channel via FDMA is limited by ( C ) factors.A. Thermal;B. Intermodulation noise;C. Thermal, Intermodulation noise and Crosstalk;D. Crosstalk;15．Cellular system use the two kinds of power control, they are ( A ).A. Open-loop power control and closed-loop power control;B. MS and BS;C. Open-loop power control and MS;D. closed-loop power and control.16．A mobile station communication across the ( C ) interface, also known as the air interface.A. Abis;B. A;C. Um;D. Iu.17．Which of the following is not core technique of the WCDMA? ( A )A. Transfers;B. PN code;C. RAKE;D. Power control.18． Which of the following is core technique of the TD-SCDMA? ( B )A. Transfers;B. Smart antennas;C. Encoding;D. Error control.19．The GSM spectral allocation is 25MHz for base transmission (935—960MHz) and 25MHz for mobile transmission ( D ).A. 935—960MHz;B. 1805—1880MHz;C. 1710—1785MHz;D. 890—915MHz.20．Third generation system mostly comprise the ( A ).A. UTRAN, CN and UE;B. MS, MSC and BS;C. MS, RAN and CN;D. RAN, CN and BS.21．A base station subsystem (BSS) consists of ( B ).A. a base station;B. a base station controller and one or more base transceiver stations;C. a base station controller and a radio antenna;D. one or more base transceiver stations.22．Fading effects in a mobile environment can be classified as either ( D ).A. fast or slow;B. fast and slow;C. fast;D. slow.23．( D ) is the procedure for changing the assignment of a mobile unit from one BS to another as the mobile unit moves from one cell to another.A. Transmission;B. change;C. divert;D. Handoff.24．Fast fading is due to reflections of local objects and the ( D ) of the terminal relative to those objects.A. multipath;B. environment;C. large reflectors;D. motion.25．Third generation system mostly comprise the ( A ).A. RAN and CN;B. MS and BS;C. MS and CN;D. RAN and BS.26. The cellular mobile communication system consist of three parts, they are ( B ).A. TDMA, FDMA and CDMA;B. BS, NS and MS;C. CDMA2000,WCDMA and CDMA;D. FDD, TDD and FHSS.27．Second generation standards use digital modulation formats and ( A )and CDMA/FDD multiple access techniques. 注意：A和B答案相同A. TDMA/FDD;B. TDMA/FDD；C.SCDMA/FDD；D. TDMA/TDD28．Two techniques for multiplexing in telecommunications network are in common use, they are ( D ).A. CDMA and TDMA;B. FDMA and TDMA;C. FDMA and CDMA;D. TDM and FDM.29．A GSM cell can have a radius of between( B ), depending on the environment.A. 100 m and 5kmB. 100m and 35km;C. 100m and 50km;D. 100m and 100km.30．As a general rule of thumb, we must keep the “( A )Fresnel zone” free of obstructions in order to obtain transmission under free-space conditions.A. first;B. secondly;C. thirdly;D. fourthly.31．Thermal noise is due to thermal agitation of ( B ).A. molecules;B. electrons;C. particles;D. photon.32．Third generation system mostly comprise the ( A ).A. RAN and CN;B. MS and BS;C. MS and CN;D. RAN and BS.33. The same frequency assignments cannot be made in adjacent cell because of ( B ).A. multiple-access interference;B. inter-channel interference;C. cochannel interference;D. coantenna interference..计算题：1.Given a receiver with an effective noise temperature of 249K and a 10MHz bandwidth, thethermal noise level at the receiver ’s output isSolution :)(9.133707.246.22810lg 10294lg 10)(6.2287dBW dBW N -=++-=++-=2. Given a receiver with an effective noise temperature of 300K and a 10MHz bandwidth, thethermal noise level at the receiver ’s output isSolution :)(8.133708.246.22810lg 10300lg 10)(6.2287dBW dBW N -=++-=++-= 3.Let MHz f c 1000=, h T =100m, h R =2m, and d =10km. estimate the path loss for a medium-size city.Solution:dBdBdBf h f h A c R c R 38.188.326.5)8.01000log 56.1(2)7.01000log 1.1()8.0log 56.1()7.0log 1.1()(=-=--⨯-=---= dBdh h A h f L T R T c dB 25.1518.313.164.2784.7855.69log )log 55.69.44()(log 82.13log 16.2655.69=+--+=-+--+=4.Let MHz f c 900=,m h t 40=,m h r 5=, and km d 10=. Estimate the path loss for a medium-size city.Solution:db dbh A r 95.88.375.12)8.0900log 56.1(5)7.0900log 1.1()(=-=---=db L db 14.1504.3495.814.2228.7755.6910log )40log 55.69.44(95.840log 82.13900log 16.2655.69=+--+=-+--+=。