26-11-2012, 06:13 PM
Overview of CDMA 2000 1X & EVDO
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System Architecture
The CDMA cellular mobile communication system consists of four independent
subsystems: Mobile Station (MS), Base Transceiver Subsystem (BSS), Mobile
Switching Subsystem (MSS) and Operation & Maintenance Subsystem (OMM). MS
and BSS can communicate directly, while the communication between BSS and MSS
is implemented through the standard A interface. Other interfaces, such as B, C, D, E,
H, M, N, O and P represents the interfaces among the functional entities. When
different functional entities are configured in each physical unit, some interfaces will
become internal interfaces that may not follow the unified interface standard. Ai, Di
and Pi are the system’s interfaces to interconnect with other communication networks.
Fig. 2.2-1 shows the architecture and interfaces of the CDMA system.
An Introduction to Network Entities
BTS Subsystem
The BTS Subsystem (BSS) is the assembly of radio equipment and radio channel
control equipment, serving one or more cellular cells. In certain radio coverage, it is
controlled by the Mobile Switching Center (MSC) to implement channel assignment,
user access and paging, and information transfer. Normally, the BSS consists of one or
more BSCs and BTSs. The BTS is responsible for radio transmission and BSC for
control and management.
Base Transceiver
The Base Transceiver (BTS) belongs to the radio part of a basestation system.
Controlled by BSC, it serves the radio transceiving equipment of a certain cell,
implements the conversion between BSC and radio channels, radio transmission
through air interface between BTS and MS and related control, and communicates
with BSC through the Abis interface.
Base Station Controller
One end of the Base Station Controller (BSC) can be connected with one or more
BTSs, while its other end can be connected with MSC and OMC. Oriented to radio
network, BSC implements radio network management, radio resource management
and radio BTS monitoring and management. It also controls the establishment,
connection and disconnection of radio connection between MS and BTS, controls the
positioning, handoff and paging of MS, provides voice coding and rate adjustment
and carries out operation and maintenance of the BSS.
Mobile Switching Subsystem
The Mobile Switching Subsystem (MSS) implements the main switching functions of
the CDMA network. Meanwhile it manages the database for user data and mobility.
Mobile Switching Center
MSC is the core of the CDMA network. It controls and implements voice channel
connection for MSs within its coverage, namely serving as an interface between
CDMA and other networks. The functions MSC carries out include call connection,
charging, BSS-MSC handoff, assist radio resource management and mobility
management. Besides, each MSC also implements the GMSC function for call route
establishment to the MS, namely, to query the location information of each MS. MSC
gets all data required for call request processing from three databases, VLR, HLR and
AUC.
Visitor Location Register
The Visitor Location Register (VLR) is a dynamic user database, storing the related
user data of all MSs (visitors) within the MSC’s management range, including user
ID, MS’s location area information, user status and services available for the user.
VLR gets and stores all necessary data from the HLR of a mobile subscriber. Once the
mobile subscriber leaves the control area of the VLR, it will be registered in another
VLR, and the previous VLR will delete its data log.
Authentication Center
The Authentication Center (AUC), a functional entity managing the authentication
information related with mobile stations (MSs). It implements MS authentication,
stores the MS authentication parameters, generates and sends the corresponding
authentication parameters according to the requests of MSC or VLR, including AKEY
, SSD, ESN, MIN and AAV, and then calculates all random numbers to get the
authentication result.
Short Message Center
The Short Message Center (SC) is responsible for receiving, storing and forwarding
short messages between the CDMA mobile subscribers and fixed line users or
between mobile subscribers. It serves as a postal office, receiving mails from every
place, sorts them out and then distribute them to the corresponding users. Through
SC, the messages can be sent to destination more reliably.The short message services
include point-to-point server and cell broadcast service.