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 gave some significant advantages when compared to the technologies used for previous in terms of overall performance and specifically in terms of spectrum efficiency.
It is found that the larger the spreading gain of the CDMA spread spectrum signal, the more effective the performance of the system is. 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.
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.
CDMA Spread Spectrum Basics ::
Each bit in the spreading sequence is called a chip, and this is much shorter than each information bit. Broadcast technology Embedded Design principles Distribution Formulae. Its development lead on to the CDMA series of standards. This is because the wanted signal becomes larger.
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.
Take as an example that the data to be transmitted isand the chip fieltype spreading code is 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. CDMA is based around the use of direct sequence spread spectrum techniques.
In the example shown above, the spreading gain is four, as seen by the fact that four “1”s are fileetype for each required data bit.
CDMA has been a particularly successful technology. The bandwidth of the CDMA spread spectrum signal will be much wider than the original data stream. CDMA uses spread spectrum technology with the use of different codes to separate between different stations or users rather than different frequencies of time slots as in the case of previous access technologies. 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 on the same carrier and then reconstitute them at the receiver without mutual interference.
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 this way a base station can communicate with several mobiles on a single channel.
However once received and processed with the correct descrambling codes, it is possible to extract the required data. The spreading code used in this example was only four bits long.
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.
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. This is multiplied with the spreading code to regenerate the original data. Broadcast technology Embedded Design principles Distribution Formulae.
The baseband data stream is then modulated onto a carrier and in this way the overall the overall signal is spread over a much wider bandwidth than if the data had been simply modulated onto the carrier. Power management RF technology Test Wireless. 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, signals with high data rates occupy wider signal bandwidths than those with low data rates. This was only one cellular telecommunications system, although it was the first. The first part of cdna process is to bascis 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.
Build More-Effective Smart Devices: 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. Data produced by other dispreading codes would appear as noise and can be discarded as it would be fioetype in value.
The CDMA history can be directly linked back to the s when this form of transmission was first envisaged. When transmitting a CDMA spread spectrum signal, the required data signal is multiplied with what is known as a spreading or chip code data stream.
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 fiiletype. The resulting data stream has a higher data rate than the data itself. Similarly several mobiles can communicate with a single base station, provided that in each case an independent spreading code is used. As electronics technology improved, it started to be used for covert military transmissions in view of the facts that the transmissions look like noise, it is difficult to decipher without the knowledge of the right codes, and furthermore it is difficult to jam.
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.
Build More-Effective Smart Devices: To quantify the increase in bandwidth, a term known as the spreading gain is used.
CDMA technology basics tutorial
It has a number of distinguishing features that are key to spread spectrum transmission technologies:. CDMA is a form of spread spectrum transmission technology. By using CDMA spread spectrum technology, many users are able to use the same channel and gain access to the system without causing undue interference to each other.
The spreading sequence or chip sequence has the same data rate as the final output from the spreading multiplier.
CDMA Tutorial | Code Division Multiple Access Basics |
This enabled the process to be visualised more easily. As a result this it was possible to start writing a specification for CDMA in The principle behind CDMA spread spectrum communications is relatively straightforward. 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.
Power management RF technology Test Wireless. In this way, CDMA is different to the previous schemes used to provide different cellular users with access to the radio network. 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.