- published: 24 Jul 2013
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Code division multiple access (CDMA) is a channel access method used by various radio communication technologies.
CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). To permit this without undue interference between the users, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code).
CDMA is used as the access method in many mobile phone standards such as cdmaOne, CDMA2000 (the 3G evolution of cdmaOne), and WCDMA (the 3G standard used by GSM carriers), which are often referred to as simply CDMA.
In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference, noise and jamming, to prevent detection, and to limit power flux density (e.g. in satellite downlinks).
This is a technique in which a telecommunication signal is transmitted on a bandwidth considerably larger than the frequency content of the original information. Frequency hopping is a basic modulation technique used in spread spectrum signal transmission.
Spread-spectrum telecommunications is a signal structuring technique that employs direct sequence, frequency hopping, or a hybrid of these, which can be used for multiple access and/or multiple functions. This technique decreases the potential interference to other receivers while achieving privacy. Spread spectrum generally makes use of a sequential noise-like signal structure to spread the normally narrowband information signal over a relatively wideband (radio) band of frequencies. The receiver correlates the received signals to retrieve the original information signal. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI).
Example of how the data from three different users is spread (using codes), combined and sent as a single waveform, and then how the data from each user is recovered using each user-specific code.
Multiplexing is the process of combining multiple signals and transmitting them over a common channel and it is implemented on telecommunication using Multiple Access as a Application. Here, Multiple Access is explained with the example of Wi-Fi Hotspot sharing its internet connection among multiple users by providing them a frequency block over which they can transmit and receive data. The greater the size of this block, greater is the throughput. There are several way by which we can use Multiple Access Technique such as TDMA, FDMA, CDMA, W-CDMA, SDMA, OFDMA, SCMA. We have also mentioned, How TDMA and FDMA, CDMA, W-CDMA works and implemented in Earlier Generation system which is AMPS, GSM, GPRS, EDGE, UMTS, HSPA+. To overcome issues faced in earlier generation such as, - Low Through...
Two basic technologies in mobile phones, CDMA and GSM represent a gap you can't cross. They're the reason you can't use AT&T; phones on Verizon's network and vice versa. But what does CDMA vs. GSM really mean for you? For more info, check out our full guide on PCMag: http://www.pcmag.com/article2/0,2817,2407896,00.asp
This video will show working of CDMA technology with the help of animation. In CDMA every user receive a unique code known as chipping sequence. These codes are orthogonal in nature.
Advanced 3G and 4G Wireless Mobile Communications by Prof. Aditya K. Jagannatham, Department of Electronics & Communication Engineering, IIT Kanpur. For more details on NPTEL visit http://nptel.iitm.ac.in
This video is aimed at the average consumer, who is not tech savvy, but interested in learning about the basics of wireless. This information is especially helpful for someone who is looking to change wireless carriers, but continue using the same device. In this video, I talk about the difference between 3 types of cellular networks- GSM, CDMA, and LTE.
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