In a system with reuse factor 1, it may be disastrous for the system if a user is not connected to the best base station. The reason is that the transmit power in the mobile will by set such that the received signal is strong enough in the connected base station. If another connection is "better", the transmit power of the mobile may cause too much interference in that base station, degrading the quality for other users. Soft handover means that the user is connected to more than one base station. The goal is to ensure that the best base station is always connected, even when the conditions are quickly varying. In soft handover, the transmit power of the mobile is controlled by the "best" base station, i.e. the base station to which the attenuation is lowest. Thereby, the power can be kept down and excessive interference can be avoided. 3.8 FDMA/TDMA vs. CDMA Here are some technology comparisons between FDMA/TDMA and CDMA. 3.8.1 Fading resistance Because CDMA systems use a higher bandwidth compared to systems that use FTMA, the systems are less vulnerable to frequency-selective fading. On the other hand, the neartar effect means that fast power control is needed in CDMA systems to ensure that interference is not too large.
3.8.2 Flexibility A FDMA/TDMA system is limited by its choice of channel bandwidth and time slot structure, which typically can not be changed after standardization. In a CDMA system, on the other hand, the resource sharing is accomplished by control the amount of power transmitted for each user, which can be changed in real-time. 3.8.3 Frequency planning Systems based on FDMA require frequency planning, which is difficult and time consuming. This is not necessary with CDMA systems. 3.8.4 Radiation Mobile stations based on TDMA transmit in short pulses, causing strong power peaks and potentially interfering with other devices. CDMA-based mobile stations, on the other hand-