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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The jammer can either spread its energy over the entire bandwidth of the signal or jam only part of the entire signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. A spread-spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. In a vdma study, a novel collaborative multi-user transmission and detection scheme cd,a collaborative CDMA  has been investigated for the uplink that exploits the differences between users’ fading channel signatures to increase the user capacity well beyond the spreading length in the MAI-limited environment.
This raw signal cdms called an interference pattern. Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw 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.
There is no strict limit to the number of users that can be supported in an asynchronous CDMA system, only a practical limit governed by the desired bit error fileytpe since the SIR signal-to-interference ratio varies inversely with the number of users.
Asynchronous CDMA offers a key advantage in the flexible allocation of resources i. These are binary square waves that form filetypr complete orthonormal set. This page was last edited on 16 Octoberat Channel access methods Code division multiple access Multiplexing Radio resource management Media access control.
Soft hand-offs allow the mobile telephone to communicate simultaneously with two or more cells.
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Furthermore, it would require significant overhead to continually allocate and deallocate the orthogonal-code, time-slot or frequency-channel resources. An analogy to the problem of multiple access is a room channel in which people wish to talk to each other simultaneously. Wireless Communications, Principles and Practice. Retrieved fildtype ” https: The following table explains how this works and shows that the signals do not interfere with one another:.
In the case of IS, bit Walsh codes are used to encode the signal to separate different users.
Each user is associated with a different code, say v. The frequencies used tchnology different cells must be planned carefully to ensure signals from different cells do not interfere with each other.
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 filetgpe by the number of users times the percentage of utilization. However, spread-spectrum techniques use a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. Like the narrow-band interference, this will result in only a small loss of data and can be overcome.
For example, binary string is represented by the vector 1, 0, 1, 1. Since each of the 64 Walsh codes is orthogonal technologyy all other, the signals are channelized into 64 orthogonal signals. From Wikipedia, the free encyclopedia. Direct-sequence spread spectrum and near-far problem.
Code-division multiple access
If the desired filetyype code has nothing in common with the signal, the correlation should be as close to zero as possible thus eliminating the signal ; this is referred to as cross-correlation. The data signal is also binary and the time multiplication is achieved with a simple XOR function. To serve yechnology customers, Kupriyanovich proposed the device, which he called “correlator. This is different from hard hand-offs utilized in other cellular systems.
Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, techhology 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. A rake technolkgy combines the information from several correlators, each one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a single correlation tuned to the path delay of the strongest signal.
To avoid confusion, people could take turns speaking time divisionspeak at different pitches frequency divisionor speak in different languages code division. To permit techjology without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme where each transmitter is assigned a code.
An example of orthogonal functions is shown in the adjacent picture. The following table shows the decode at the receiver:.
The receiver then extracts an intelligible signal for techonlogy known sender by combining the sender’s code with the interference pattern.
Start with a set of vectors that are mutually orthogonal. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. 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 technoology in asynchronous CDMA systems.
These systems were designed using spread spectrum because of its security and resistance to jamming. Each sender has a different, unique vector v chosen from that set, but the construction method of the transmitted vector is identical.
Many codes occupy the same channel, but only users associated with a particular code can communicate. One of the initial reasons for doing this was military applications including guidance and communication systems.
A spreading code is a pseudo-random code that has a narrow ambiguity functionunlike other narrow pulse codes. Statistical multiplexing variable bandwidth.
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Now, due to physical properties of interference, if two signals at a point are in phase, 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. 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.
Some CDMA devices use a rake receiver foletype, which exploits multipath delay components to improve the performance of the system. The technology of CDMA was used inwhen the young military radio engineer Vdma Kupriyanovich in Moscow made an experimental model cmda a wearable automatic mobile phone, called LK-1 by him, with a base station.