Directional handover control in digital mobile radio systems employing MAHO

An apparatus for selecting handover targets for a communication unit exchanging a communicated signal through a serving base site in a digital cellular system, such apparatus comprising:

• A) means for determining a directionality of the communication unit based upon a first set of measured RSSI values of base sites within a base site frequency list;
• B) means for comparing a timing advance value of the communication unit with a first threshold;
• C) means for modifying the base site frequency list to include base sites non-adjacent the serving base site when the timing advance value exceeds the first threshold based upon the directionality of the communication unit;
• and
• D) means for selecting a handover target providing a highest relative RSSI value to the communication unit based upon a second set of measured RSSI values of base sites within the modified base site frequency list.

A method of selecting handover targets from a communication unit exchanging a communicated signal through a serving base site in a digital cellular system, such method comprising the steps of:

• A) measuring RSSI values of base sites within a base site frequency list for sites adjacent the serving base site;
• B) determining a directionality of the communication unit based upon the measured RSSI values;
• C) comparing a timing advance value of the communication unit with a first threshold;
• D) when the timing advance value exceeds the first threshold, modifying the base site frequency list to include base sites non-adjacent the serving base site based upon the directionality of the communication unit;
• and
• E) measuring RSSI values of base sites of base site frequency list including base sites non-adjacent the serving base site;
• and
• F) selecting a handover target providing a highest relative RSSI value to the communication unit from the modified base site frequency list.