Cellular Network Basics Frequency Division Multiple Access (FDMA); Time Division Multiple Access (TDMA); Code Division Multiple Access (CDMA). 3G CDMA – WCDMA and cdma Rodger E. Ziemer. IEEE Communications Society. Distinguished Lecturer Program. May June1, 2. Rules for. Preface Code division multiple access (CDMA) has proven itself to be a viable technique for enabling the simultaneous transmission and reception of data over .
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CDMA technology basics tutorial
When this is done, then only the data with that was generated with the same spreading code is regenerated, all the other data that is generated from different spreading code streams is ignored. This enabled the process to be visualised more easily.
To decode the signal and receive the original data, the CDMA signal is first demodulated from the carrier to reconstitute the high speed data stream. The spreading code used in this example was only four bits long. CDMA or Code Division Multiple Access is a form of access scheme that has been widely used within 3G cellular telecommunications systems as well as being used in a number of other technologies as well.
In this way it can be seen that the original data is recovered exactly by using the same spreading or chip code. Broadcast technology Embedded Design principles Distribution Formulae. Broadcast technology Embedded Design principles Distribution Formulae.
Data produced by other dispreading codes would appear as noise and can be discarded as it would be lower in value.
However once received and processed with the correct descrambling codes, it is possible to extract the required data. In this way, CDMA is different to the previous schemes used to baxics different cellular users with access to the radio network. Each bit in the spreading sequence is called a chip, and this is much shorter than each information bit. Power management RF technology Test Wireless.
CDMA Tutorial | Code Division Multiple Access Basics |
Direct sequence spread spectrum is a form of transmission that looks very similar to white noise over the bandwidth of the transmission. The bandwidth of the CDMA spread spectrum signal will be much wider than the original data stream. The first part of the process is to generate the CDMA spread spectrum signal.
Had another code been used to regenerate the CDMA spread spectrum signal, then it would have resulted in a random sequence after de-spreading. It is found that the larger the spreading gain of the CDMA spread spectrum signal, the more effective the performance of the system is.
Although as the number of users increases care has to be taken to ensure that interference levels do not rise to the extent that performance falls, it is still possible to provide access to a large number of different users and allow them access.
CDMA spread spectrum basics
The CDMA history can be directly linked back to the s when this form of transmission was first envisaged. Latest news LoRa technology integrated in utility metering solution Four-in-one environmental sensor saves space and power MACOM debuts new ultra low phase noise amplifier Ericsson and Panasonic Avionics bringing connectivity to the skies Beeline chooses Broadpeak Solutions for TV Everywhere service.
This is because the wanted signal becomes larger. Essentially CDMA is a form of spread spectrum transmission which uses spreading codes to spread the signal out over a wider bandwidth then would normally be required.
Power management RF technology Test Wireless. In this way a base station can communicate with several mobiles on a single channel. CDMA is a form of spread spectrum transmission technology. The use of a different code in transmission and reception results in a signal similar in character to noise being generated and this can be discarded.
In order to visualise how the CDMA spread spectrum process operates, the easiest method is to show an example of how the system actually operates in terms of data bits, and how the data is recovered from the CDMA spread spectrum signal. To quantify the increase in bandwidth, a term known as the spreading gain is used. Build More-Effective Smart Devices: CDMA technology has been used in all the 3G cellular telecommunications systems in one form or another and has enabled significant improvements to be gained over previously technologies used in 2G systems, for example.
The spreading sequence or chip sequence has the same data rate as the final output from the spreading multiplier. For each data bit, the complete spreading code is used to multiple the data, and in this way, for each data bits, the spread or expanded signal consists of four bits. Take as an example that the data to be transmitted isand the chip or spreading code is CDMA has been a particularly successful technology. Build More-Effective Smart Devices: The principle behind CDMA spread spectrum communications is relatively straightforward.
The same code must be sued within generation and decoding of the CDMA spread spectrum signal to enable the data to pass unchanged through the system.
Fileype has a number of distinguishing features that are key to riletype spectrum transmission technologies:. This is because, signals with high data rates occupy wider signal bandwidths than those with low data rates. Commonly spreading codes may be 64 bits, or even bits long to provide the required performance. This is multiplied with the spreading code to regenerate the original data. CDMA is based around the use of direct sequence spread spectrum techniques.
CDMA technology gave some significant advantages when compared to the technologies used for previous in terms of overall performance and specifically in terms of spectrum efficiency. The use of CDMA spread spectrum is a powerful principle and using this CDMA technique, it is possible to transmit several sets of data independently flietype the same carrier and then reconstitute them at the receiver without mutual interference. Basids news LoRa technology integrated in utility metering solution Four-in-one environmental sensor saves space and power MACOM debuts new ultra low phase noise amplifier Ericsson and Panasonic Avionics bringing connectivity to the skies Beeline chooses Broadpeak Solutions for TV Everywhere service.
Its development lead on to the CDMA series of standards. With the revolution in cellular telecommunications that occurred in the s a then little know company named Qualcomm working on DSSS transmissions started to look at this as the basis for a cellular telecommunications multiple access scheme – CDMA – code division multiple access.
In the example shown above, the spreading gain is four, as seen by the fact that four “1”s are generated for each required data bit. CDMA uses spread spectrum technology with the use of different codes to separate between different stations or users rather than different frequencies of bssics slots as in the case of previous access technologies. This would have appeared as noise in the system.