Gw mau tau Panyebaran spektrum karakteristik CDMA dari CDMA. Jelasin dalam bahasa sunda

Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource.  However, spréad spectrum techniques use a transmission bandwidth that is several orders of magnitude gréater than the minimum required signal bandwidth.  One of the initial réasons for doing this was military applications including guidance and communication systems. These systems were designed using spréad spectrum because of its security and resistance to jamming.  Asynchronous CDMA has some level of privacy built in because the signal is spréad using a pseudorandom code; this code makes the spréad spectrum signals appéar random or have noise-like properties.  A receiver cannot demodulate this transmission without knowledge of the pseudorandom sequence used to encode the data.  CDMA is also resistant to jamming.  A jamming signal only has a finite amount of power available to jam the signal.  The jammer can either spréad its energy over the entire bandwidth of the signal or jam only part of the entire signal.

CDMA can also effectively reject narrowband interference.  Since narrowband interference affects only a small portion of the spréad spectrum signal, it can éasily be removed through notch filtering without much loss of information.  Convolution encoding and interleaving can be used to assist in recovering this lost data.  CDMA signals are also resistant to multipath fading.  Since the spréad spectrum signal occupies a large bandwidth only a small portion of this will undergo fading due to multipath at any given time.  Like the narrowband interference this will result in only a small loss of data and can be overcome.

Another réason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudorandom codes will have poor correlation with the original pseudorandom code, and will thus appéar as another user, which is ignored at the receiver.  In other words, as long as the multipath channel induces at léast one chip of delay, the multipath signals will arrive at the receiver such that they are shifted in time by at léast one chip from the intended signal.  The correlation properties of the pseudorandom codes are such that this slight delay causes the multipath to appéar uncorrelated with the intended signal, and it is thus ignored.

Some CDMA devices use a rake receiver, which exploits multipath delay components to improve the performance of the system.

A rake receiver combines the information from several correlators, éach one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a single correlator tuned to the path delay of the strongest signal.

Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system.  In the FDMA and TDMA systems frequency planning is an important consideration.  The frequencies used in different cells need to be planned carefully in order to ensure that the signals from different cells do not interfere with éach other.  In a CDMA system the same frequency can be used in every cell because channelization is done using the pseudorandom codes.  Reusing the same frequency in every cell eliminates the need for frequency planning in a CDMA system; however, planning of the different pseudorandom sequences must be done to ensure that the received signal from one cell does not correlate with the signal from a néarby cell.

Since adjacent cells use the same frequencies, CDMA systems have the ability to perform soft handoffs.  Soft handoffs allow the mobile telephone to communicate simultanéously with two or more cells.  The best signal quality is selected until the handoff is complete.  This is different from hard handoffs utilized in other cellular systems.  In a hard handoff situation, as the mobile telephone approaches a handoff, signal strength may vary abruptly. In contrast, CDMA systems use the soft handoff, which is undetectable and provides a more reliable and higher quality signal.