Soft Handover
Thanks to the fact that neighboring cells have the same frequency, the mobile call can be handed over between Base Stations without interrupting the call (figure below). The handover can be done during a longer period of time, depending on how the mobile subscriber is moving.
The soft handover mode means that the mobile is connected to two or three Base Stations at the same time. This gives a tremendous quality enhancement in the handover situation.
The mobile and the network can combine the signals from the different Base Stations and that way get a better signal than in a interfrequency or hard handover situation. This implies a double capacity load on the system for this period.
Hard Handover
The Hard handover (figure above) is done in case we have a hierarchical cell structure, a hot spot or a handover between GSM/UMTS or between UMTS operators. The hard handover is similar to the handover in GSM, where the connection is in fact broken off with the old Base Station before connection to the new can take place.
Thanks to the so-called Compressed mode, the downlink allows the mobile to listen in for other frequencies. The mobile will then inform the network of stringer signals.
