Despite these limitations, an extension to the AX. 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. These are binary square waves that form a complete orthonormal set. CDMA is also resistant to jamming. 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.

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Code-division multiple access – Wikipedia

However, a viable widely adopted successor to AX. At the link layer, AX. Although it is possible to build AX.

Channel access methods Code division multiple access Multiplexing Radio resource management Media access control. Since narrow-band interference affects mofem a small portion of wx spread-spectrum signal, it can easily be removed through notch filtering without much loss of information. Fundamentals and Applications Second ed.

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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. Each user is associated with a different code, say v. This is sufficient for keyboard-to-keyboard contacts between stations and for accessing local bulletin board systems and DX clusters.


The technology of code-division multiple access cdmz has long been known. At the physical layer, AX. This article is about a channel access method.

This is not a limitation of AX. This was rectified with version 2. This raw signal is called an interference pattern. If the signal matches the desired user’s code, then the correlation function will be high and the system can extract that signal.

Convolution encoding and interleaving can be used to assist in recovering this lost data. This allows several users to share a band of frequencies see bandwidth.

Code-division multiple access

CDMA signals are also resistant to multipath fading. InKupriyanovich made the new experimental “pocket” model of mobile phone. Archived from the original on 25 July This is effectively a frequency convolution Wiener—Khinchin theorem of the two signals, resulting in a carrier with narrow sidebands. These vectors will be assigned to individual users and are called the codechip codeor chipping code.

In a recent study, a novel moodem multi-user transmission and detection scheme called collaborative CDMA [14] 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. 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.


Furthermore, it would require significant overhead to continually allocate and deallocate the orthogonal-code, time-slot or frequency-channel resources. Start with a set of vectors that are mutually orthogonal.

A spread-spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. Direct-sequence spread spectrum and near-far problem. Small gadget transmitters do not need to know what is being transmitted.

Many codes occupy the same channel, but only users associated with a particular code can communicate. Further, after decoding, all values greater than axx are interpreted as 1, while all values less than zero are interpreted as 0.

Likely reasons may include:. Since each of the 64 Walsh codes is orthogonal to all other, the signals are channelized into 64 orthogonal signals.