DS - CDMA (Direct Sequence - Code Division Multiple Access)

DS - CDMA (Direct Sequence - Code Division Multiple Access) namely Direct Sequence Code Division Multiple Access (CDMA). In principle, saying, DS - CDMA will carry information is through the relatively narrow-bandwidth signals with high speed and address signals multiplication and obtain the broadband spread spectrum signal. Accept the need to use the same address with inchoation synchronous control input signal to the carrier frequency inverter phase can be realized solution extender. DS - CDMA system can resist narrowband interference, resistance to multipath fading and secrecy good points. DS - CDMA remaining advantages: many users can share the frequency resource, beardless complex frequency distribution and management; With a "soft capacity" character, i.e. within limits subscribers increased, only makes signal-to-noise ratio decreases, and won't terminate communication, i.e. DS - CDMA not absolute storage limit.

problems

Of course, DS - CDMA, there exist some problems, such as multi-access interference problem, this is due to the different address between the non-absolute orthogonality and those who cause, communication process of different user signal will mutual interference. Multi-access interference is DS - CDMA system pretty serious a problem, it still needs to address selection of people through further research to solve. In addition, in the DS - CDMA system exist in "near-far effect", i.e. from base stations near strong signal that users will base on away from the weak signal of network users forming interferences, essentially that is due to the address are not fully orthogonality caused by people, but at this stage in the mobile communication system already through introducing "automatic power control" technical weaken the near-far effect influence.

DS - CDMA technology

The following provisions ITU IMT - 2000 specifications, and with W - CDMA way on the basis of a communication technology. This technology can use 5MHz channel provide up to 2Mbps data rate, and to expand system capacity, improve communication voice quality, reduce the conversation dropped rate, supports IP data services. DS - CDMA technology in addition to provide narrowband service (such as voice business) besides, still can offer a variety of user rate communication, VOD bandwidth ability, as well as provide different according to different business service levels of ability. In the CDMA standards, DS - CDMA technology is one of the important part is the key to realize the wireless multimedia communication. DS - CDMA technology originating in Europe and Japan's third generation wireless research activity, GSM the huge success of the third generation system in Europe the standardization of significant impact. In 1996, Japan launched a set of DS - CDMA experiment system solutions, and obtained when the world's major equipment-makers support. Founded in December 1998 3GPP (third generation partnership project) greatly promoted the DS - CDMA technology development, accelerate the DS - CDMA of standardized process, and finally make DS - CDMA technology to become ITU approved international communications standards. DS - CDMA based on ANSI - 41 core network, it USES new band, using FDD way of working code piece rate for 384 Mbps. DS - CDMA have greater coverage, using adaptive antennas and multi-user detection and other new technologies and can support frequency to switch between them. By DS - CDMA technology composed of communication system usually include wireless base bureau device, wireless network control devices, multimedia signal processing device. DS - CDMA system of air is used to connect the 5MHz, 10MHz or 20MHz wireless channel

DS/CDMA system of anti-jamming

The rapid development of modern electronic technology, space electromagnetic environment increasingly complex, channel relative crowded, in military communications, more faces various kinds of human interference. In order to enhance the reliability of communication system, increasing channel capacity, people USES code division multiple access (cdma) technology to spread spectrum communication. Compared with conventional communication, DS/CDMA system has high processing gain, improved the system of anti-disturbance capacity, processing gain GP can be expressed as: P bigger then system anti-interference ability is stronger, the actual system to withstand interference can be expressed by interference tolerance:

Mj = GP - [Lsys + (S/N) out] (2)

One GP for system treatment for system implementation Lsys gain and loss, including rf filter losses in the related processor frequency mixing loss, amplifier the signal-to-noise ratio of the loss, etc. (S/N) out for related receiving fan-out requirements of the signal-to-noise ratio. In practical application, GP impossible increases indefinitely, and because of the device nonlinear and tracking error code element caused SNR loss, so spread spectrum receiver actually allow input interference and signal power, more than interference tolerance is still lower. And DS/CDMA system itself exists multi-access interference, therefore, must take some to suppress the interference of measures to strengthen the system reliability.