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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Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. 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.
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 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.
This is referred to as auto-correlation and is used to reject multi-path interference. The frequencies used in different cells must be planned carefully to ensure signals from different cells do not interfere with each other.
Qualcomm CDMA Technologies MSM Windows driver
tcehnology These vectors will be assigned to individual fietype and are called the codechip codeor chipping code. Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal. Although mutual orthogonality is the only condition, these vectors are usually constructed for ease of decoding, for example columns or rows from Walsh matrices.
Each user in synchronous CDMA uses a code orthogonal to the others’ codes to modulate their signal. Now, due to physical properties of interference, if two signals at a point are in filetupe, they add to give twice the amplitude of each signal, but if they are out of phase, they subtract and give a signal that is the difference of the amplitudes.
Code-division multiple access – Wikipedia
Asynchronous CDMA has some level of filstype built in because the signal is spread using a pseudo-random code; this code makes the spread-spectrum signals appear random or have noise-like properties.
A PN code is a binary sequence that appears random but can be reproduced in a deterministic manner by intended receivers. Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. From Wikipedia, the free encyclopedia.
The guard bands will reduce the probability that adjacent channels will interfere, but decrease the utilization of the spectrum. This raw signal is called an interference pattern. CDMA signals are also resistant to multipath fading.
If the signal matches the desired user’s code, then the correlation function will be high and the system can extract that signal.
The following table shows the decode at the receiver:. CDMA is a spread-spectrum multiple-access  technique. To serve more customers, Kupriyanovich proposed the device, which he called “correlator. In the digital case, the sinusoidal carrier is replaced by Walsh functions. The following table explains how this works and shows that the signals do not interfere with one another:.
Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.
A spread-spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. Channel access methods Media access control. The data signal is also binary and the time multiplication is achieved with a simple XOR function.
Some CDMA devices use a rake receiverwhich exploits multipath filstype components to improve the performance of the system.
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. When the receiver attempts to decode the signal using sender1’s code, the data is all zeros, therefore the cross-correlation is equal to zero and it is clear that sender1 did not transmit any data.
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.
Since this cannot be perfectly controlled in a mobile environment, each time slot must have a guard time, which reduces the probability that users will interfere, but decreases the spectral efficiency. In general, CDMA belongs to two basic categories: It was placed in the trunk of the vehicles of high-ranking officials and used a standard handset in the passenger compartment.
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. This phone weighed 0. Spread spectrum in digital communications. In other projects Wikimedia Commons. 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.
CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Each user in a CDMA system uses a different code to modulate their signal. See also Digital communication Modulation Statistical multiplexing Waveform.
A spreading code is a pseudo-random code that has a narrow ambiguity functionunlike other narrow pulse codes. 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 signature sequence as long as they are connected to the system.