due to the powerful dynamic channel selection andallocation and seamless handover capabilities of dect, portables can escapefrom an interfered radio connection by establishing a second radio link - on anewly selected channel - to either the same (intercell handover as shown infigure 6) or to another base station. the two radio links are temporarilymaintained in parallel with identical speech information being carried acrosswhile the quality of the links is being analyzed. after some time the basestation determines which radio link has the best quality and releases the otherlink.
if the dect portable is moving from one cell area intoanother, the received signal strength - as measured by the portable’s dynamicchannel selection and allocation functions - of the base station will reducegradually. the signal strength of the base station serving the cell towardswhich the portable is moving will gradually increase. at the moment the newbase station’s signal becomes stronger than the signal from the old basestation, a seamless handover (as described above) will be performed to the newbase station (see figure 7.). the seamless handover is a fully autonomousinitiative from the dect portable part, which the user will not notice.
although a handover is always initiated by the dectportable part, it may also be the uplink (from pp to fp) that suffers from poorquality. for this case, dect has signaling protocols that enable the fixed partto signal the perceived link quality to the pp, which can subsequently initiatethe handover.
handover in dect is a mechanism to escape from interferedor channels with low signal level. handover is however not sufficiently fast tocounteract fast fading situations. for this purpose the dect base station canbe equipped with antenna diversity (see figure 8). a signalling protocol isavailable 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, thefp antenna diversity not only improves the uplink quality but also the downlinkquality, at slow speed.
