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  .  “ 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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If the dot product is zero, the two vectors are said to be orthogonal to each other. Each user is associated with a different code, say v.
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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 the case of IS, bit Walsh codes are used to encode the signal to separate different users.
These are binary square waves that form a complete orthonormal set. InKupriyanovich made the new experimental “pocket” model of mobile phone. If the signal matches the desired user’s code, then the correlation function will be high and the system can extract that signal. See also Digital communication Modulation Statistical multiplexing Waveform. If all of the users are received with the same power level, then the variance e. The receiver then extracts an intelligible signal for any known sender by combining the sender’s code with the interference pattern.
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.
In other projects Wikimedia Commons. Views Read Edit View history. Further, after decoding, all values greater than 0 are interpreted as 1, while all values less than zero are interpreted as 0. A spread-spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. This is different technoloty hard hand-offs utilized in other cellular systems.
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. For example, binary string is represented by the vector 1, 0, 1, 1. CDMA is also resistant to jamming.
Channel access methods Media access control. CDMA is used as the access method in many mobile phone standards.
To serve more customers, Kupriyanovich proposed the device, which technollgy called “correlator. There are a fixed number of orthogonal codes, time slots or frequency bands that can be allocated for CDM, TDMA, and FDMA systems, which remain underutilized due to the bursty nature of telephony and packetized data transmissions.
In a CDMA system, the same frequency can be used in every cell, because channelization is done using the pseudo-random codes. Although mutual orthogonality is the only condition, these vectors are usually constructed for ease of decoding, for example columns or rows from Walsh matrices.
Furthermore, it would require significant overhead to continually allocate and deallocate the orthogonal-code, time-slot or frequency-channel resources. Since adjacent cells use the same frequencies, CDMA systems have the ability to perform soft hand-offs.
The guard bands will reduce the probability that adjacent channels will interfere, but decrease the utilization of the spectrum. In other words, as long as the multipath channel induces at least one chip of delay, the multipath signals will arrive at the receiver such that they are shifted in time by at least one chip from the intended signal.
Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.
Similarly, in radio CDMA, each group of users is given a shared code. The new collaborative multi-user receiver consists of two stages: Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, planning of the different pseudo-random sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a nearby cell.
The correlation properties of the pseudo-random codes are such that this slight delay causes the multipath to appear uncorrelated with the intended signal, and it is thus ignored.
Start with a set of vectors that are mutually orthogonal. One of the initial reasons for doing this was military applications including guidance and communication systems.
This allows several users to share a band of frequencies see bandwidth. In contrast, CDMA systems use the soft hand-off, which is undetectable and provides a more reliable and higher-quality signal. The technology of code-division multiple access channels has long been known. The following table shows the decode at the receiver:.
The technology of CDMA was used inwhen the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a wearable automatic mobile phone, called LK-1 by him, with techology base station. A jamming signal only has a finite amount of power available to jam the signal. The key difference here is that the bit error probability for N users talking all of the time is constant, whereas it is a random quantity with the same mean for 2 N users talking half of the time.
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.
Code-division multiple access
CDMA is an example of multiple accesswhere several transmitters can send cda simultaneously over a single communication channel. Now, due to physical properties of interference, if two signals at a point are in phase, they add to give twice the amplitude fdma each signal, but if they tecnology out of phase, they subtract and give a signal that is the difference of the amplitudes.
An example of orthogonal functions is shown in the adjacent picture. Since narrow-band interference affects only a small portion of the spread-spectrum signal, it can easily be removed through notch filtering without much loss of information. Channel access methods and media access control. Proceedings of the Leningrad Experimental Institute of Communication: Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system.