What is CDMA?

CDMA stands for Code Division Multiple Access and is flipped as Code Division Multiple Access. It is a technique used in modern communication technology to realize channel ****enjoyment.

The so-called channel can be a specific frequency region of an electromagnetic signal, called a frequency band, or a specific time segment of a signal, called a frame. The so-called channel *** enjoyment, is the same channel for multiple users at the same time and ensure that there is no interference with each other. Channel ***sharing improves the utilization of channel resources.

There are many different techniques that can be used to achieve channel **** sharing. The channel band is divided into a number of narrower, non-intersecting frequency bands (called sub-bands), each of which is dedicated to a single user (called an address). This technique is called "Frequency Division Multiple Access" (FDMA). This is the basic technology for analog carrier communications, microwave communications, satellite communications, and the first generation of analog mobile communications. Similarly, the channel frame can be divided into a number of non-overlapping time slots, each of which is assigned to a user as a dedicated address. This is called "Time Division Multiple Access", or TDMA (Time Division Multiple Access/Ad dress). This is the basic technology for digital data communications and second-generation mobile communications. If the address of each user is neither a designated signal sub-band nor a time slot, but a set of orthogonal coding structures (code patterns) of the signal, these user signals can also be transmitted on the same channel simultaneously without interfering with each other. This technology is called "code division multiple access", that is, CDMA.

Theory and practice have proved that, compared with the FDMA and TD MA, in addition to other advantages, in the same channel conditions, CDMA has a higher utilization of channel resources, therefore, become the third generation of mobile communications channel **** enjoy the basic The way of the third generation of mobile communication channel *** enjoy.

CDMA is the code division multiple access of the English acronym (Code Division Muitiple Access), it is in the digital technology branch - spread spectrum communication technology on the development of a new and mature wireless communication technology. CDMA technology is based on the principle of spread-spectrum technology, that is to be transmitted with a certain signal bandwidth information data, with a bandwidth much larger than the signal bandwidth, high-speed wireless communication technology. The principle of CDMA technology is based on spread spectrum technology, that is, the information data to be transmitted with a certain signal bandwidth is modulated with a high-speed pseudo-random code whose bandwidth is much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded, and then modulated by the carrier and sent out. The receiving end uses the exact same pseudo-random code, and the received bandwidth signal for correlation processing, the broadband signal into the original information data of the narrow-band signal that is the de-expansion, in order to realize the information communication.

Mobile communication system has a variety of classification methods. For example, according to the nature of the signal, can be divided into analog, digital; modulation mode, can be divided into frequency modulation, phase modulation, amplitude modulation; according to multiple access connection mode, can be divided into frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). The GSM mobile phone network used by China Unicom and China Mobile is a combination of FDMA and TDMA; GSM has great advantages over analog cell phones, but the spectral efficiency is only three times that of analog systems, and the capacity is limited; it is difficult to reach the level of wired telephones in terms of voice quality; the maximum access rate of TDMA terminals can only be 9.6 kbit/s; TDMA systems have no soft-switching; and there is no soft-switching in TDMA systems. The maximum access rate of TDMA terminal can only reach 9.6kbit/s; TDMA system has no soft switching function, so it is easy to drop calls, which affects the service quality. Therefore, TDMA is not the best wireless access to modern cellular mobile communications, and CDMA multiple access technology is fully suitable for modern mobile communications network requirements of high capacity, high quality, integrated services, soft switching, etc., is being more and more operators and users of the favor.

The emergence of CDMA technology stems from mankind's need for higher quality wireless communications. CDMA technology was developed during World War II due to the needs of the war, and its original idea was to prevent the enemy from interfering with their own communications, and was widely used in military anti-jamming communications during the war, and was later updated into a commercial cellular telecommunication technology by the U.S. Qualcomm. 1995, after the first commercial CDMA system was in operation, the theoretical advantages of CDMA technology were tested in practice, and thus the technology was widely used in North America, South America, and the United States. After the operation of the first commercial CDMA system in 1995, many theoretical advantages of CDMA technology have been tested in practice, and thus it has been rapidly popularized and applied in North America, South America and Asia. Many countries and regions around the world, including Hong Kong, China, South Korea, Japan, and the United States have built CDMA commercial networks. In the United States and Japan, CDMA has become the main mobile communication technology in the country. In the U.S., 7 out of 10 mobile communication operating companies have chosen CDMA, and by April this year, 60% of the population in Korea had become CDMA users. In the 28th Olympic Games hosted by Australia, CDMA technology played an important role

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