Code division multiple access

What is code division multiple access?
Code Division Multiple Access (CDMA) is a digital cellular network standard that uses spread spectrum technology. This technology does not limit the digital signals or frequencies of the bandwidth, but distributes them over a fully available spectrum or over several channels via the partition. Thus there is an improved voice and data communication capability and a more secure private line.

The CDMA digital standard is a leading communications network standard in North America and parts of Asia. Qualcomm, a US-based wireless communications company, patented and commercialized CDMA.

CDMA technology was originally used in World War II military operations to thwart enemy attempts to access radio communication signals. In the early 1990s, Qualcomm introduced the ability to use the same concept with publicly available cellular network technology. During this time, an alternative digital standard for mobile networks was gaining traction and proving to be a challenge for CDMA advocates. Despite relentless negativity and discouragement from prominent industry insiders, CDMA supporters successfully convinced these leaders to consider, use, and ultimately accept the newly introduced CDMA standard.

In essence, CDMA provides more airspace capacity than the Time Division Multiple Access (TDMA) based Global System for Mobile Communications (GSM) standard. In addition, CDMA also uses less power. Another benefit of CDMA technology is that it enables soft handoffs between base stations, that is, less likelihood of shutdown calls.

The usual analogy given when comparing CDMA to other channel access methods such as FDMA or TDMA is that of people talking to a friend in a crowded room. In this case, the space represents a channel (also called a carrier frequency).

TDMA is compared to the method of communicating by speaking one by one (hence the name 'time division'). FDMA, on the other hand, is compared to the method in which communication occurs by speaking at different pitches (hence frequency division). After all, CDMA is compared to people who speak at the same time but in different languages. Since only those who speak the same language can understand each other, it is possible for several conversations to take place in the room at the same time.

The basic concept in CDMA is that users who want to communicate through them are given a common code. While multiple codes can occupy the same channel, only users with the same code can communicate with each other.

Since CDMA and GSM standards each have distinct advantages and disadvantages, the preferred technology standard is now in the hands of potential subscribers. The final choice, however, depends heavily on the availability of these standards in the localities of the participants.

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