Mobile Communication | CDMA (Code-Division Multiple Access) | Architecture | Advantages

Code-Division Multiple Access

CDMA (Code-Division Multiple Access) refers to any of several protocols used in second-generation (2G) and third-generation 3G wireless communications. CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes, which enhances privacy and makes cloning difficult.

CDMA Architecture elements

Mobile Station (MS):

The MS is the mobile subscriber equipment, which can originate and receive calls and communicate with the BTS.

Base Transceiver Station (BTS):

The BTS transmits and receives radio signals, realizing communication between the radio system and the mobile station

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Base Station Controller (BSC):

The BSC implements the following functions:

• Base Transceiver Station (BTS) control and management 
• call connection and disconnection 
• mobility management 
• stable and reliable radio link provision for the upper-layer services by soft/hard handoff 
• power control
•  radio resource management.

Packet Control Function (PCF):

The PCF implements the R-P connection management. Because of the shortage of radio resources, some radio channels should be released when subscribers do not send or receive data, but the PPP connection is maintained continuously. The PCF can shield radio mobility for the upper-layer services via handoff.

Packet Data Service Node (PDSN):

The PDSN implements the switching of packet data services of mobile subscribers. One PDSN can be connected to multiple PCFs. It provides the interface between the radio network and the packet data network

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Home Agent (HA):

The agent locates at the place where the Mobile Node opens its account; receive the registration information from MN, Similar as HLR in mobile network. Broadcast the accessible information of MN. Setup the tunnel between FA&HA. Transfer the data from other computer to the MN via the tunnel.

Mobile Switching Center (MSC): 

The MSC implements the service switching between the calling and called subscribers. One MSC is connected with multiple BSCs. The MSC can also be connected to the PSTN, ISDN or other MSCs. It provides the interface between the radio network and PSTN.

Visitor Location Register (VLR):

It is a dynamic database, stores the temporary information (all data necessary to set up call connections) of the roaming subscribers in the local MSC area.

VLR is used to store the subscriber information of all the MSs in its local area, which can be used to establish the incoming/outgoing call connections, to support basic services, supplementary services and mobility management.

Home Location Register (HLR):

It is a database for mobile subscriber management, the HLR (Home Location Register) is responsible for storing subscription information (telecom service subscription information and subscriber status), MS location information, MDN, IMSI (MIN), etc. The AC (Authentication Center) is physically combined with the HLR. It is a functional entity of the HLR, specially dedicated to the security management of the CDMA system. It stores the authentication information. It also prevents unauthorized subscribers from accessing the system and prevents the radio interface data from being stolen.

Advantages

• Frequency  reuse
• Large coverage
• High spectrum capacity
• High privacy
• Soft handoff
• Good voice quality
• Perfect power control