CDMA TECHNOLOGY FILETYPE PDF

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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Channel access methods Media access control. In other words, unlike synchronous CDMA, the signals of other users will appear as noise to the signal of interest and interfere slightly with the desired signal in proportion to number of users. Values of exactly 0 means that the sender did not transmit any data, as in the following example:.

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By comparison, asynchronous CDMA transmitters simply send when they have something to say and go off the air when they don’t, keeping the same PN fjletype sequence as long technologt they are connected to the system.

These PN sequences are statistically uncorrelated, and the sum of a large number of PN sequences results in multiple access interference MAI that is approximated by a Gaussian noise process following the central limit theorem in statistics.

Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. 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.

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

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The frequencies used in different cells must be planned carefully to ensure signals from different cells do not interfere with each other.

Code-division multiple access

In a bursty traffic environment like mobile telephony, the advantage afforded by asynchronous CDMA is that the performance bit error rate is allowed to fluctuate randomly, with an average value determined by the number of users times the percentage of utilization. In general, CDMA belongs to two basic categories: From Wikipedia, the free encyclopedia.

Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system.

Furthermore, it would require significant overhead to cxma allocate and deallocate the orthogonal-code, time-slot or frequency-channel resources. Gold codes are an example of a PN suitable for this purpose, as there is low correlation between the codes. Since it is not mathematically possible to create signature sequences that are both orthogonal for arbitrarily random starting points and which make full use of the code space, unique “pseudo-random” or “pseudo-noise” PN sequences are used in asynchronous CDMA systems.

Like the narrow-band interference, this will result in only a small loss of data and can be overcome.

Since adjacent cells use the same frequencies, CDMA systems have the ability to perform soft hand-offs. Retrieved from ” https: Similarly, in radio CDMA, each group of users is given a shared code.

Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.

Since each of the 64 Walsh codes is orthogonal to all other, the signals are channelized into 64 orthogonal signals.

When mobile-to-base links cannot be precisely coordinated, particularly due to the mobility of the handsets, a different approach is required. Since the spread-spectrum signal occupies a large bandwidth, only a small portion of this will undergo fading due to multipath at any given time.

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This allows several users to share a band of frequencies see bandwidth. Some CDMA devices use a rake receiverwhich exploits multipath delay components to improve the performance of the system. Similarly, FDMA systems must use a guard band between adjacent channels, due to the unpredictable Doppler shift of the signal spectrum because of user mobility. The jammer can either spread its energy over the entire bandwidth of the signal or jam only part of the entire signal.

Circuit mode constant bandwidth.

Code-division multiple access – Wikipedia

Code-division multiple access CDMA technoloy a channel access method used by various texhnology communication technologies. CDMA signals are also resistant to multipath fading. The authors show that it is possible to achieve this increase at a low complexity and high bit error rate performance in flat fading channels, which is a major research challenge for overloaded CDMA systems.

One of the initial reasons for doing this was military applications including guidance and communication systems.

GSM and CDMA – How Cell Phones Work | HowStuffWorks

If the dot product is zero, the two vectors are said to be orthogonal to each other. Each user in synchronous CDMA uses a code orthogonal to the others’ codes to modulate their signal. In contrast, CDMA systems use the soft hand-off, which is undetectable and provides a more reliable and higher-quality signal.