Mobile communication exercises

1. What is mobile communication ? What are the characteristics of mobile communication ?

answer ： Mobile communication is the communication between mobile users , It is the communication between mobile users and fixed users .
Its characteristics are ：① The path of electromagnetic wave propagation is complex
② Mobile communication works in strong interference environment
③ Mobile communication has Doppler effect
④ Users are often on the move

2. What is the difference between simplex communication and duplex communication ? What are the advantages and disadvantages of each ?

answer ：① Simplex communication , It means that the radio stations of both sides of the communication receive and send messages alternately .
② Duplex communication , It refers to the working mode that both communication parties can transmit messages at the same time , Sometimes called full duplex communication

3. What are the advantages of digital mobile communication system ?

answer ： Digital mobile communication , It is easy to use coherent or incoherent demodulation ; Strong anti noise and anti-interference ability ; And suitable for transmission in fading channels .

4. What types of mobile communication systems are commonly used ?

answer ：① According to the object of use, it can be divided into civil equipment and military equipment ;
② It can be divided into land communication according to the use environment 、 Maritime and air communications ;
③ According to the multiple access method, it can be divided into frequency division multiple access (FDMA)、 Time division multiple access (TDMA) And code division multiple access (CDMA) etc. ;

5. What technologies are used in the cellular communication system ? It works with wireless paging 、 Cordless telephone 、 What are the main differences between clustered systems ?

answer ： In cellular communication system , Channel reuse technology is used to improve the frequency utilization of the system

6. What is the basic concept and mode of cluster ? What is the difference between it and common voice communication ?

answer ： The basic technology used in trunked mobile communication system is frequency sharing technology .
The difference ：① Send some to various departments
The decentralized private communication network is centralized , Unified network construction and management , And dynamically utilize the limited channels allocated to them , To accommodate a larger number of users ;
② Improve channel sharing , That is, the mobile user is in the process of communication , It doesn't occupy a certain channel , Instead, press its “ Press the talk switch ”(PTT) when , To occupy a channel ; Once released PTT, The channel will be released , Become an idle channel , And allow other users to occupy the channel .

7. What are the typical mobile satellite communication systems ? What is the difference between it and terrestrial cellular mobile communication ?

answer ：IMARSAT-P. Besides , And American TRITIUM Systems and CELSAT System , And Japan MPT Of COMETS Wait for the plan .

8. What is a packet radio network ?

answer ： Packet radio network (PRN) is a communication network that uses wireless channel for packet switching , That is, the information transmitted in the network should be in the form of “ grouping ” Or called “ Letter packet ”( Sometimes abbreviated to “ package ”) For the basic unit . A packet is an information segment consisting of several bits , Usually contains “ baotou ” and “ Text ” Two parts . The packet header contains the source address of the packet ( Initial address )、 Home address ( Destination address ) And related routing information ; The text is the information that really needs to be transmitted

9. What are the main technologies of mobile communication ? What are the main functions of various technologies ?

answer ： The main technologies of mobile communication are ： Modulation technology 、 Research on radio wave transmission characteristics in mobile channel 、 Multiple access 、 Anti interference measures 、 Networking technology . The main function of modulation technology is to improve the frequency band utilization of the system ; Enhanced anti noise 、 Anti interference capability ; Make the signal suitable for transmission in fading channel ; The study of radio wave transmission characteristics in mobile channel is to clarify the propagation law of mobile channel, the mechanism of various physical phenomena and the adverse effects of these phenomena on signal transmission , And then study the countermeasures to eliminate various adverse effects ; The main function of multiple access is to improve the capacity of communication system ; The function of anti-interference measures is to improve the anti-interference ability of the communication system ; The function of networking technology is to solve the problems in mobile communication networking .

10. What functional entities does the mobile communication system consist of ? Which layers of functions does the wireless interface include ?

answer ：Sm:  Interface between user and network , Also known as man-machine interface ;
Um:  The interface between the mobile station and the base transceiver , Also called wireless interface or air interface ;
A:  The interface between the base station and the mobile switching center ;
Abis:  The interface between the base station controller and the base station transceiver ;
B:  Interface between mobile switching center and access location register ;
C:  Interface between mobile switching center and home location register ;
D:  Interface between home location register and access location register ;
E:  Interface between mobile switching centers ;
F:  Interface between mobile switching center and device flag register ;
G:  Access the interface between location registers .