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 technique

8. 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 spectrum

11. 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 intervals

12．What are the primary causes of atmospheric attenuation for satellite communications? Answers: The primary causes of atmospheric attenuation are oxygen and water

13．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 capability

15．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 channel