due to the powerful dynamic channel selection and allocation and seamless handover capabilities of dect, portables can escape from an interfered radio connection by establishing a second radio link - on a newly selected channel - to either the same (intercell handover as shown in figure 6) or to another base station. the two radio links are temporarily maintained in parallel with identical speech information being carried across while the quality of the links is being analyzed. after some time the base station determines which radio link has the best quality and releases the other link.
if the dect portable is moving from one cell area into another, the received signal strength - as measured by the portable’s dynamic channel selection and allocation functions - of the base station will reduce gradually. the signal strength of the base station serving the cell towards which the portable is moving will gradually increase. at the moment the new base station’s signal becomes stronger than the signal from the old base station, a seamless handover (as described above) will be performed to the new base station (see figure 7.). the seamless handover is a fully autonomous initiative from the dect portable part, which the user will not notice.
although a handover is always initiated by the dect portable part, it may also be the uplink (from pp to fp) that suffers from poor quality. for this case, dect has signaling protocols that enable the fixed part to signal the perceived link quality to the pp, which can subsequently initiate the handover.
handover in dect is a mechanism to escape from interfered or channels with low signal level. handover is however not sufficiently fast to counteract fast fading situations. for this purpose the dect base station can be equipped with antenna diversity (see figure 8). a signalling protocol is available in the standard to control fp antenna diversity from the portable. due to the tdd nature (symmetry) of the radio link between the fp and pp, the fp antenna diversity not only improves the uplink quality but also the downlink quality, at slow speed.
