communication technology

The CDMA cellular mobile communication technology

Since the nineteen seventies at the end of the first generation analog mobile communication system, mobile communication industry has been released,htc flyer with breathtaking speed swift and violent development, has become the lead in the development of the global economy is one of the high-tech industry, and on the human life and social progress produced major effect. Among them, CDMA CDMA mobile communication technology with its large capacity, high utilization of the spectrum, strong confidentiality, green environmental protection and many other advantages, show powerful vitality, caused the people's extensive concern, become the third generation of mobile communication core technology.

CDMA communication technology

CDMA ( CodeDivisionMultipleAccess, code division multiple access) as a multiple access technique has already appeared, at first only in anti-jamming and security performance and other aspects of attention, being used in military anti-jamming system. In 1989, the United States of America Qualcomm ( Qualcomm ) company is the first to launch the CDMA cellular mobile communication system.

CDMA cellular mobile communication technology actually contains two basic techniques, namely the CDMA technology and the technology of spread spectrum communication. The so-called spread spectrum, simply speaking is a technology will signal to extend the spectrum, commonly used in engineering direct sequence of the signal spectrum, which uses a high speed code sequence code to modulation speed of original data information. Code division multiple access ( CDMA ) and frequency division multiple access ( FDMA ), time division multiple access ( TDMA ), is a kind of multiple access technology.

CDMA system in every signal is assigned an orthogonal sequence or PN ( PseudoNoise, pseudo random noise ) sequence is used as the spreading sequence for spread spectrum,HTC flyer p512 different signal energy are assigned to different orthogonal sequence or PN sequences. In the receiver, by using the correlator to accept only the selected orthogonal sequence or PN sequences and compression of the frequency spectrum, which do not meet the user orthogonal sequence signal will not be compressed bandwidth, only the specified signal can be extracted.

We will be CDMA and FDMA, TDMA three multiple access modes are compared. FDMA uses frequency modulation multiple access technique, in different frequency band for traffic channels are allocated to different users; TDMA is using time division multiple access technology,toshiba tablet business channel in different time are assigned to different users; CDMA using spread spectrum CDMA technology, all users at the same time, the same frequency band, but according to the different coding gain business channel. In technology, is to use the code to the different modulation and demodulation of different users.