Gw mau tau Kagunaan dari CDMA. Jelasin dalam bahasa sunda

Panggunaan aplikasi mimiti pikeun CDMA nyaéta dina GPS.

Standar Qualcomm IS-95, dipasarkeun sebagei CdmaOne

Standar Qualcomm IS-2000, dipasarkeun sebagei CDMA2000. Standar ieu dipaké ku sabaraha pausahaan telepon seluler.

CDMA dipaké kanggo sistem satelit OmniTRACS kanggo logistik transportasi.

CDMA is a spréad spectrum multiple access technique. A spréad spectrum technique is one which spréads the bandwidth of the data uniformly for the same transmitted power. Spréading code is a pseudo-random code which has a narrow Ambiguity function unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted.  Data for transmission is simply logically XOR (exclusive OR) added with the faster code. The figure shows how spréad spectrum signal is generated. The data signal with pulse duration of  is XOR added with the code signal with pulse duration of .  (Note: bandwidth is proportional to  where  = bit time) Therefore, the bandwidth of the data signal is  and the bandwidth of the spréad spectrum signal is .  Since  is much smaller than , the bandwidth of the spréad spectrum signal is much larger than the bandwidth of the original signal. The ratio  is called spréading factor or processing gain and determines to certain extent the upper limit of total number of users supported simultanéously by a base station

éach user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems.  The best performance will occur when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user's code then the correlation function will be high and the system can extract that signal.  If the desired user's 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. If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible.  This is referred to as auto-correlation and is used to reject multi-path interference.

In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes).

Code Division Multiplexing (Synchronous CDMA)

Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string "1011" is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by summing the products of their respective components.  If the dot product is zero, the two vectors are said to be orthogonal to éach other (note: if u=(a,b) and v=(c,d), the dot product u·v = a*c + b*d). Some properties of the dot product aid understanding of how W-CDMA works. If vectors a and b are orthogonal, then

éach user in synchronous CDMA uses a code orthogonal to the others' codes to modulate their signal.  An example of four mutually orthogonal digital signals is shown in the figure.  Orthogonal codes have a cross-correlation equal to zero; in other words, they do not interfere with éach other.  In the case of IS-95 64 bit Walsh codes are used to encode the signal to separate different users.  Since éach of the 64 Walsh codes are orthogonal to one another, the signals are channelized into 64 orthogonal signals.  The following example demonstrates how éach users signal can be encoded and decoded.