Wide band CDMA technology is selected for UTRAN air interface. WCDMA; TD- SCDMA. Base stations are referred to as Node-B and control equipment for. 3G CDMA – WCDMA and cdma W-CDMA Versus cdma [2] . [4] “ CDMA Evolution from IS, IS, to 1XTREME,” Technology Transfer Training. GSM Technology. GSM is now a worldwide standard. GSM uses Time Division Multiple Access or TDMA technology as their air interface standard. TDMA has.

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Some CDMA devices use a rake receiverwhich exploits multipath delay components to improve the performance of the system.

The separation of the signals is made by correlating the technollogy signal with the locally generated code of the desired user. Digitally, this behaviour can be modelled by the addition of the transmission vectors, component by component. Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. Channel access methods Media access control.

In contrast, CDMA systems use the soft hand-off, which is undetectable and provides a more reliable and higher-quality signal. Since it is not mathematically possible to create signature sequences that are both orthogonal for arbitrarily random starting points tedhnology which make full use of the code space, unique “pseudo-random” or “pseudo-noise” PN sequences are used in asynchronous CDMA systems.

In tecchnology hard-hand-off situation, as the mobile telephone approaches a hand-off, signal strength may vary abruptly. In general, CDMA belongs to two basic categories: The correlation properties of the pseudo-random codes are such that this slight delay causes the multipath to appear uncorrelated with the intended signal, and it is thus ignored. Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.


The guard bands will reduce the probability that adjacent channels will interfere, but decrease the utilization of the spectrum. Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string is represented by the ttechnology 1, 0, 1, 1. Filetjpe serve more customers, Kupriyanovich proposed the device, which he called “correlator. If all of the users are received with cdmx same power level, then the variance e.

CDMA signals are also resistant to multipath fading. Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal. Like the narrow-band interference, this will result in only a small loss of data and can be overcome.

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Code-division multiple access CDMA is a channel access method used by various radio communication technologies. CDMA is a spread-spectrum multiple-access [8] technique. A spreading code is a pseudo-random code that has a narrow ambiguity functionunlike other narrow pulse codes. Start with a set of vectors that are mutually orthogonal. In techno,ogy digital case, the sinusoidal carrier is replaced by Walsh functions.

Code-division multiple access

Further, after decoding, all values greater than 0 are interpreted as 1, while all values less than zero are interpreted as 0. These are binary square waves that form a complete orthonormal set.

The best signal quality is selected until the hand-off is complete. Each user in a CDMA system uses a different code to modulate their signal. The technology of code-division multiple access channels has long been known. If the desired user’s code has nothing in common with the signal, cdka correlation should be as close to zero as possible thus eliminating the signal ; this is referred to as technoogy. Convolution cma and interleaving can be used to assist in recovering this lost data.

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This raw signal is called an interference pattern.

How Cell Phones Work

Channel access methods and media access control. For instance, if there are N time slots in a TDMA system and 2 N users that talk half of the time, then half of the time there will be more than N users needing to use more than N time slots.

Direct-sequence spread spectrum and near-far problem. Channel access methods Code division multiple access Multiplexing Radio resource management Media access control. This allows several users to share a band of frequencies see bandwidth. In this approach, instead of using one sequence per user as in conventional CDMA, the authors group a small number of users to share the same spreading sequence and enable group spreading and despreading operations.

Asynchronous CDMA has some level of privacy built in because the signal is spread using a pseudo-random code; this technoloty makes the spread-spectrum signals appear random or have noise-like properties.

These systems were designed using spread spectrum because of its security and resistance to jamming. Since narrow-band interference affects only a small portion of the spread-spectrum signal, it can easily be removed through notch filtering without much loss of information. In other words, asynchronous CDMA is ideally suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals.