1、名词解释1Explain 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 ce
2、ll.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 han
3、doff state until which it is connected to the two base stations.2What 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.3What is attenuation?4What two functions are performed by
4、an antenna?5What 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 g
5、enerations: (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 wire
6、less 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 e
7、qually.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 intervals12What are the primary ca
8、uses of atmospheric attenuation for satellite communications?Answers: The primary causes of atmospheric attenuation are oxygen and water13What 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.14What are
9、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 capability 15In general, physical models include three basic modes of propagation.Answers：（1）Fr
10、ee-space or link-of-signal transmission;（2）Reflection；（3）Diffraction.16In 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
11、 the following。Answers: (1)Adding new channels；(2)Frequency borrowing；(3)Cell splitting；(4)Cell sectoring；(5)Microcells。17Explain 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-lo
12、op power control adjusts signal strength in the reverse channel based on some metric of performance in that reverse channel.18Define 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 cha
13、nnel capacity.填空题1Antenna characteristics are essentially the same whether an antenna is sending or receiving electromagnetic energy.2The basis for analog signaling is acontinuous constant frequency signal known as the carrier signal.3Nikola Tesla invented the wireless telegraph in 1893 .4A transmis
14、sion from earth station to satellite is referred to as uplink in the satellite communication.5The essence of a cellular network is the use of multiple low-power transmitters, on order of 100W or less.6Third generation system generally call WCDMA or UMTS .7Adjacent cells are assigned different freque
15、ncies 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.9The data signaling rate, or just data rate , of a signal is the rate, in bits per
16、 second, that data are transmitted.10The TD-SCDMA is a multiple connect into include the FCDMA/TDMA/CDMA 11 Nikola Tesla invented the wireless telegraph in 1893.12A digital signal is one in which the signal intensity maintains a constant level for some period of time and then changes to another cons
17、tant level.13. Reflection occurs when an electromagnetic signal encounters a surface that is large relative to the wavelength of the signal.14If the size of an obstacle is on the order of the wavelength of the signal or less scattering occurs.15. For a data of , the duration of a bit is seconds and
18、the duration of a signal element is seconds. If is greater then or to , the spreading modulation is referred to as slow-frequency-hop spread spectrum; otherwise it is known as fast-frequency-hop spread spectrum.16A transmission from satellite station to earth is referred to as downlink in the satell
19、ite communication.17The cells sufficiently distant from each other can use the same frequency band18Code division multiple access is a spread spectrum based technique for multiplexing.19The objective of the third generation of wireless communication is to provide fairly high speed wireless communica
20、tions to support multimedia, data, and video in addition to voice.20Power control technique is core in the CDMA .21One purpose of the data-layer is to perform error correction or detection.22The channel provides the physical means for transporting the signal produced by the transmitter and deliverin
21、g it to the receiver .24The key physical resource is the radio spectrum in wireless system.24A 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.25The frequency is the rate at which the signal repeats.26A
22、n antenna that transmits equally in all directions called the isotropic radiatio .27Noise can be defined as unwanted electrical signals interference with the desired signal.28The basic idea with cellular system is to reuse channel in different cell, increasing the capacity29During the period from 18
23、95 to 1901 , Guglielmo Marconi developed an apparatus for transmitting radio waves over longer distances.30An 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.31The spectrum of a signal is the range of
24、frequencies that it contains.1. 32The same frequency assignments cannot be made in adjacent cell because of inter-channel interference.33 Handoff may be network initiated.34That each user occupies a cyclically repeating time slot in the TDMA system.35All users in a CDMA , use the same carrier freque
25、ncy and may transmit simultaneously.36Self-jamming is a problem in CDMA system.37The GSM key technique consist of eight parts 38. Reflection occurs when an electromagnetic signal encounters a surface that is large relative to the wavelength of the signal.判断题1. Thermal noise can be eliminated. ( N )2
26、. 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 distance from the transmitter. ( Y )5. Fast fading is the rapid variation of signal levels when th
27、e 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 finite amount of radio spectrum. ( Y )8.Direct sequence multiple access is also called code division multipl
28、e access (CDMA). ( Y )9. The most popular second generation standards include three TDMA standards and one CDMA standard. ( Y )10. The NS controls handoff between cell in different BSSs, authenticates users and validates their accounts, and includes functions for enabling worldwide roaming of mobile
29、 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 fourt
30、h power of distance. ( Y )15.Slow fading arises from the fact that most of the large reflectors and diffracting objects along 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 s
31、lot 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 validates their accounts, and includes functions for enabling wor
32、ldwide 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 ampli
33、tude, speed, and phase; D. peak amplitude, frequency, and speed.2Transmission media can be classified as ( C ).A. guided; B. unguided; C. guided and unguided; D. wired and wireless.3Fading effects in a mobile environment can be classified as either ( A ).A. fast or slow; B. fast and slow; C. fast; D
34、. slow.4( 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;5The boundaries at Um, Abis, and A refer to interfaces between functional elements that are standardi
35、zed in the ( B ) documents.A. AMPS; B. GSM; C. GPRS; D. CDMA.6Which of the following is not core technique of the CDMA? ( A )A. Power control; B. PN code; C. RAKE; D. transfers.7GSM key technique consist of ( C ) parts.A. 6; B 12; C. 8; D. 10.8The GSM spectral allocation is 25MHz for base transmissi
36、on ( D ) and 25MHz for mobile transmission( 890915MHz).A. 18051880MHz; B. 17101785MHz; C. 890915MHz; D. 935960MHz.9Third 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
37、( B )A. TDMA, FDMA and CDMA; B. BS, NS and MS;CCDMA2000,WCDMA and CDMA; D. FDD, TDD and FHSS.11There 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,
38、 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;12Two techniques for multiplexing in telecommunications network are in common use, they are ( D ). A. CDMA
39、and TDMA; B. FDMA and TDMA; FDMA and CDMA; D. TDM and FDM.13For 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.14The number of subchannels provide within a
40、 satellite channel via FDMA is limited by ( C ) factors.A. Thermal; B. Intermodulation noise; C. Thermal, Intermodulation noise and Crosstalk; D. Crosstalk;15Cellular 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.
41、Open-loop power control and MS; D. closed-loop power and control.16A mobile station communication across the ( C ) interface, also known as the air interface. A. Abis; B. A; C. Um; D. Iu.17Which of the following is not core technique of the WCDMA? ( A )A. Transfers; B. PN code; C. RAKE; D. Power con
42、trol.18 Which of the following is core technique of the TD-SCDMA? ( B ) A. Transfers; B. Smart antennas; C. Encoding; D. Error control.19The GSM spectral allocation is 25MHz for base transmission (935960MHz) and 25MHz for mobile transmission ( D ). A. 935960MHz; B. 18051880MHz; C. 17101785MHz; D. 89
43、0915MHz.20Third 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.21A 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 c
44、ontroller and a radio antenna; D. one or more base transceiver stations.22Fading 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
45、mobile unit moves from one cell to another. A. Transmission; B. change; C. divert; D. Handoff.24Fast 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.25Third generation system mostly comprise the ( A ). A. RAN and CN; B. MS and BS; C. MS and CN; D. RAN
