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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GSM and CDMA – How Cell Phones Work | HowStuffWorks

Fundamentals and Applications Second ed. CDMA can also effectively reject narrow-band interference. This page was last edited on 16 Octoberat The digital modulation method is analogous to those used in simple radio transceivers. This is effectively a frequency convolution Wiener—Khinchin theorem of the two signals, resulting in a carrier with narrow sidebands.


TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are received in the correct time slot and do not cause interference. Spread spectrum in digital communications. Convolution encoding and interleaving can be used to assist in recovering this lost data. Many codes occupy the same channel, but only users associated with a particular code can communicate.


Suppose there are 2 N users that only talk half of the time, then 2 N users can be accommodated with the same average bit error probability as N users that talk all of the time.

For example, binary string is represented by the vector 1, 0, 1, 1. Retrieved from ” https: If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible. These are binary square waves that form a complete orthonormal set. From Wikipedia, the cxma encyclopedia. This is different from hard hand-offs utilized in other cellular systems.

Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. Circuit mode constant bandwidth.

The following table shows the decode at the receiver:. A receiver cannot demodulate this transmission without knowledge of the pseudo-random sequence used to encode the data. One of the initial reasons for doing this was military applications including guidance and communication systems. Tecunology CDMA offers a key advantage in the flexible allocation of resources i.

Code-division multiple access – Wikipedia

An analogy to the problem of multiple access is a room channel in which people wish to talk to each other simultaneously. This article is about a channel access method. All forms of CDMA use spread-spectrum process gain to allow receivers to partially discriminate against unwanted signals. By using this site, you agree to the Terms of Use and Privacy Policy.


In other words, asynchronous CDMA is ideally suited to a mobile network where technoogy numbers of transmitters each generate a relatively small amount of traffic at irregular intervals.

Gold codes are an example of a PN suitable for this purpose, as there is low correlation between the codes.

How Cell Phones Work

The best signal quality is selected until the hand-off is complete. Since each of the 64 Walsh codes is orthogonal to all other, the signals are channelized into 64 orthogonal signals. If the desired user’s code has nothing in common with the signal, the correlation should be as close to zero as possible thus techno,ogy the signal ; this is referred to as cross-correlation.

Start with a set of vectors that are mutually orthogonal. Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. Each user in synchronous CDMA uses a code orthogonal to the others’ codes to modulate their signal. Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource.