Mumbai University > Information Technology > Sem 4 > CN

Marks: 5M

Year: May 2016

• Many users of a CDMA system share the same frequency. Either TDD or FDD may be used.

• Unlike TDMA or FDMA, CDMA has a soft capacity limit. Increasing the number of users in a CDMA system raises the noise floor in a linear manner. Thus there is no absolute limit on the number of users in CDMA but the system performance gradually degrades for all users as the number of users is increased.

• CDMA is a interference limited system.

• Multipath fading is substantially reduced because the signal is spread over a large spectrum. If the spread spectrum bandwidth is greater than the coherence bandwidth of the channel, the inherent diversity will reduce the effect of small scale fading.

• Channel data rates are very high in CDMA systems. The symbol duration is very short and usually much less than the channel delay spread. A RAKE receiver can be used to improve reception by collecting time delayed versions of the required signal.

• CDMA uses co-channel cells thus it can use macroscopic spatial diversity to provide soft handoff.

• Self jamming is a problem in CDMA system. Self jamming arises from the fact that the spreading sequences of different users are not exactly orthogonal.

• The near-far problem occurs at a CDMA receiver if an undesired user has a high detected power as compared to the desired powers