The first job
1. What is the mobile communication? What are the main features of mobile communication have?
Mobile communication refers to communication parties at least one party is in motion (or temporarily stop moving) communication of the state.
Features: (1) the complexity of radio wave propagation (2) of the mobile station subject to severe interference (3) limited radio spectrum resources (4) high requirements on the mobile device (5) complexity of the system
2, a mobile communication system composed of several parts? Briefly its main role.
A mobile switching subsystem, operation and maintenance management subsystem, a base station subsystem
1, information exchange is completed, the user information management, call connection, number of management functions.
2, BSS system is a certain radio coverage area controlled by the MSC, a system device in communication with the MS, the channel assignment is completed, the user access and paging, transmitting information and other functions.
3, MS is a mobile user equipment of the GSM system, which consists of two parts, the mobile terminal and a subscriber identity card (SIM card). The mobile terminal is the "machine", it can complete speech encoding, channel encoding, encryption, modulation and demodulation of the information, the information transmission and reception. SIM card is a "person", which is similar to the IC card we used, and therefore also known as smart cards, there all the information needed to authenticate the identity of customers, and can perform some important information related to security and confidentiality, in order to prevent illegal clients into the network. SIM card also stores data and network management and customer-related, after only a SIM card into a mobile terminal to access the net.
3, the conventional mobile communication system includes several types which?
(1) a cellular public land mobile communication system (cellular system)
(2) trunked mobile communication system
(3) cordless telephone system
(4) radio paging system
(5) mobile satellite communications system
(6) wireless LAN
4. What FDD and TDD concepts and their respective strengths?
Frequency division duplex (FDD): fast, full use of spectrum.
Time division duplex (TDD): configuration flexibility frequency bands using FDD systems less fragmented use; by adjusting the uplink-downlink switching point, to improve downlink slot ratio, better support asymmetric services; consistent with uplink and downlink channels reception and transmission of the base station may be part of the common radio frequency unit, reducing the equipment cost; uplink and downlink data is received, the transceiver does not require an isolator, a switch only can reduce the complexity of the apparatus; a downlink channel reciprocity , can be employed better transmission pre-processing techniques, such as pre-RAKE technology, joint transmission technology, smart antenna technology, can effectively reduce the processing complexity of the mobile terminal.
