What is CDMA (Code Division Multiple Access) technology?

CDMA (Code Division Multiple Access), also known as Code Division Multiple Access, is a technology used in wireless communications. CDMA allows all users to use the entire frequency band (1.2288Mhz) at the same time and treats the signals sent by other users as noise, so that there is no need to consider the collision of signals. CDMA provides voice coding technology, call quality is better than the current GSM, and can reduce the ambient noise of the user's conversation, making the call clearer. In terms of security, CDMA not only has a good authentication system, but also because of its transmission characteristics, the code to distinguish between users, the ability to prevent eavesdropping is greatly enhanced. Wideband CDMA (WCDMA) wideband code division multiple access transmission technology, an important basic technology for IMT-2000, will be one of the third generation of digital wireless communication system standards.

ADVANTAGES OF CDMA:

CDMA mobile communication network is a combination of several technologies such as spread spectrum, multiple access, cellular networking and frequency multiplexing, which contains a collaboration of three-dimensional signal processing in the frequency domain, time domain, and code domain, and therefore it has the attributes of good anti-jamming, anti-multipath fading, high confidentiality and security, the same frequency can be reused in several small areas, and the trade-offs can be made between the capacity and quality. trade-off between capacity and quality. These attributes give CDMA a great advantage over other systems.

1, the system capacity

Theoretically, in the use of the same frequency resources, CDMA mobile network than the analog network capacity 20 times greater than in practice than the analog network 10 times greater than the GSM is 4-5 times greater.

2, flexible configuration of the system capacity

In the CDMA system, the increase in the number of users is equivalent to the increase in background noise, resulting in a decline in voice quality. However, there is no limit to the number of users, the operator can be a compromise between capacity and voice quality. In addition, automatic equalization between multiple cells is possible based on the volume of traffic and interference.

This feature is related to the mechanism of CDMA, which is a self-interference system in which all mobile users occupy the same bandwidth and frequency, for example, imagine the bandwidth is like a big house, and all people will enter the only big house. If they use completely different languages, they can hear their peers clearly with only some interference from other people's conversations. Here, the air in the house can be imagined as a broadband carrier wave, and the different languages are treated as codes that can be added to the users until the whole background noise is limited. If the signal strength of the users can be controlled, more users can be accommodated while maintaining high quality calls.

3. Better call quality

TDMA's channel structure can only support up to 4Kb voice encoder, it can not support more than 8Kb voice encoder. Whereas the structure of CDMA can support 13Kb voice encoder. Thus it can provide better call quality.The vocoder of CDMA system can dynamically adjust the data rate and select different level level transmissions according to the appropriate threshold value. Also the threshold value changes according to the change in background noise so that better call quality can be obtained even in the presence of high background noise. In addition, TDMA adopts a kind of hard handover, users can obviously feel the interruption of the call, in the user-intensive, base station-intensive city, this interruption is especially obvious, because in such areas will occur every minute 2 to 4 times the handover situation. The CDMA system "drop call" phenomenon is significantly reduced, the CDMA system uses soft switching technology, "first connected and then disconnected", which completely overcame the hard switching easy to drop the shortcomings of the call.

4, frequency planning is simple

Subscribers are differentiated by different sequence codes, so different CDMA carriers can be used in neighboring areas, flexible network planning, expansion is simple.

5, low network construction costs

CDMA technology through the use of the same frequency in each part of each cellular, simplifies the planning of the entire system, in the case of not lowering the volume of traffic to reduce the number of sites required to reduce the cost of deployment and operation.CDMA network coverage, high system capacity, the need for fewer stations to reduce the cost of building the network.

CDMA digital mobile technology is different from the now well-known GSM digital mobile system. Analog technology is known as the first generation of mobile telephony technology, GSM is the second generation, CDMA is part of the second generation and a half of mobile communications and is more advanced than GSM.

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