CDMA FAQs, CDMA Phones, GSM vs CDMA

Code Division Multiple Access (CDMA) uses the concept Spread Spectrum technology. In this transmission technique, the frequency spectrum of a data-signal is spread using a code uncorrelated with that signal. As a result the bandwidth occupancy is much higher then required. 

The codes used for spreading have low cross-correlation values and are unique to every user. 

A number of advantages are:

• Low power spectral density. As the signal is spread over a large frequency-band, the Power Spectral Density is getting very small, so other communications systems do not suffer from this kind of communications. However the
• Gaussian Noise level is increasing.
• Interference limited operation. In all situations the whole frequency-spectrum is used.
• Privacy due to unknown random codes. The applied codes are - in principle - unknown to a hostile user. This means that it is hardly possible to detect the message of an other user.
• Applying spread spectrum implies the reduction of multi-path effects.
• Random access possibilities. Users can start their transmission at any arbitrary time.
• Good anti-jam performance. 

Because of the difficulty to jam or detect spread spectrum signals, the first applications were in the military field. However nowadays spread spectrum systems are gaining popularity also in commercial applications like Cell phones