CDMA abbreviates Code Division Multiple Access which is a 3G Technology. CDMA refers to Code Division Multiple Access. It’s fair to say that CDMA has emerged as the dominant technology for providing 3G services to subscribers worldwide.
Initially, uses for CDMA for point-to-point military communications, but over the years, it has developed as a significant cellular technology. CDMA uses a very different approach when compared to Global Systems for Mobile Communications (GSM), as it assigns a unique code to each user, enabling multiple devices to utilize the same wideband channel simultaneously.
CDMA uses Code Division Multiplexing:
As the name suggests, CDMA uses code division multiplexing. CDMA uses ADC (Analog to Digital Converter) in combination with spread spectrum technology. Here, the same frequency is made available to many users.
Availability of the full spectrum to every channel ensures that every channel enjoys all of the available bandwidth. To distinguish calls and data transfers, then encode each conversation with a pseudo-random digital sequence.
How Does CDMA Work?
By using ADC, the audio input digitizes into binary elements. Now, the frequency of the transmitted signal is changed using a frequency sequencing code, and this rate can be intercepted only by a receiver whose frequency response is associated with the same data code.
As a result of the presence of the almost unlimited number of these frequency codes, it is virtually impossible to clone a receiver.
CDMA Architecture – Base Station Subsystem:
Like its counterpart GSM, CDMA also uses the basic structures required for mobile telephony. A BSS or Base Station Subsystem serves as the fixed end of radio interface providing control and radio coverage functions for one or more cells and their associated mobile stations. Again, a BSS comprises of a BSC (Base Station Controller) and a BTS (Base Station Transceiver Subsystem).
A BTS performs various functions such as general control of BTS, CDMA signal processing, BTS Interconnection, low noise-high power amplification, signal filtering and frequency conversion. A BSC comprises of CDMA Interconnection networks providing transmission paths among units. Various functions such as noise coding, allocating selectors, assembling/unassembling of packets, power control, and call a BSC performs control processing.
CDMA Mobile Exchange:
For CDMA mobile switching system design, must consider both the traffic and call processing characteristics. In CDMA, a mobile exchange requires greater processor capability. A portable cell phone mobile transaction implements vital functions of mobile switching and visitor location registration.
Other notable functions include providing call and data paths, call and telephony control, call processing, mobility management, call routing and switching, location registration of subscribers and authentication.
CDMA – Home Location Register and Authentication Center:
A Home Location Register or HLR is a location register; in general terms, a database, for storing temporary and permanent subscriber information such as current location, home location, supplementary services that a subscriber has asked for and other such useful information.
An Authentication Center (AC) is implemented along with HLR to ensure subscriber security and to prevent fraud.
Advantages of CDMA:
CDMA significant advantage is that it provides higher bandwidth for voice and data transmissions. The bandwidth results in better voice quality and faster data transfer. The 3G technology was first implemented on CDMA and users are more because of the availability of larger bandwidth.