Derivation of optimal antenna weights during soft handover

A method in a mobile terminal of a wireless communication system for use during a soft handover between base stations using closed loop transmit diversity, comprising the steps of:

• receiving, by a mobile terminal, a common pilot channel (CPICH) and a dedicated physical channel (DPCH) on the downlink from a base station involved in a soft handover;
• calculating, by the mobile terminal, optimal antenna weights;
• estimating, by the mobile terminal, the channel responses from the CPICH and the DPCH;
• using, by the mobile terminal, the estimated channel responses, and the optimal antenna weights calculated in a previous time slot, to verify whether the antenna weights applied to the channels by the base station match the optimal antenna weights from the previous time slot;
• determining, by the mobile terminal, a set of scale factors based on estimated weight factors and based on whether those weight factors indicate reliable feedback information at the base station;
• calculating, by the mobile terminal, a set of optimal antenna weights for the current time slot from the scale factors and the channel responses from the CPICH;
• and
• sending, by the mobile terminal, the optimal antenna weights to the base station on the up link in the form of feedback information.

A method to implement closed loop transmit diversity in a mobile terminal, comprising the steps of:

• receiving, by a mobile terminal, a signal from a plurality of an active set of base stations involved in a soft handover;
• performing, by the mobile terminal, antenna verification;
• updating, by the mobile terminal, a feedback information detection error rate for all the links using the antenna verifications;
• choosing, by the mobile terminal, scale factors, based on a feedback information detection error rate;
• scaling, by the mobile terminal, channel response estimates using the scale factors;
• using, by the mobile terminal, the scaled channel response estimates to determine the optimal antenna weights;
• mapping the optimal antenna weights to the feedback information;
• and
• sending to the feedback information to the plurality of base stations.

A method to implement closed loop transmit diversity in a mobile terminal;

• comprising the steps of:
• receiving, by a mobile terminal, a signal from a plurality of an active set of base stations involved in a soft handover;
• detecting the transmit power commands for the links of a plurality of active base stations;
• computing, by the mobile terminal, an Up/Down ratio of the transmit power commands for each link;
• choosing, by the mobile terminal, based on the Up/Down ratio, appropriate scale factors;
• scaling, by the mobile terminal, channel response estimates using the scale factors;
• using, by the mobile terminal, the scaled channel response estimates to determine the optimal antenna weights;
• mapping the optimal antenna weights to the feedback information;
• and
• sending to the feedback information to the plurality of base stations.

A mobile terminal of a wireless communication system adapted to estimate antenna weights for use during a soft handover between base stations using closed loop transmit diversity, comprising:

• means for estimating a reliability of feedback information detection at each base station;
• means for obtaining scale factors for channel responses of downlinks from each base station, said scale factors determined based on said reliability of said feedback information detection at each base station;
• means for applying said scale factors to said channel responses;
• means for calculating antenna weights based on said channel responses having said scale factors applied thereto;
• and
• means sending said antenna weights as feedback information on uplinks to all base stations involved in said soft handover.

A mobile terminal of a wireless communication system for use during a soft handover between base stations using closed loop transmit diversity, comprising:

• means for receiving a common pilot channel (CPICH) and a dedicated physical channel (DPCH) on the downlink from a base station involved in a soft handover;
• means for calculating optimal antenna weights;
• means for estimating the channel responses from the CPICH and the DPCH;
• means for using the estimated channel responses, and the optimal antenna weights calculated in a previous time slot, to verify whether the antenna weights applied to the channels by the base station match the optimal antenna weights from the previous time slot;
• means for determining a set of scale factors based on estimated weight factors and based on whether those weight factors indicate reliable feedback information at the base station;
• means for calculating a set of optimal antenna weights for the current time slot from the scale factors and the channel responses from the CPICH;
• and
• means for sending the optimal antenna weights to the base station on the uplink in the form of feedback information.

A mobile terminal for use in a wireless system, comprising:

• means for receiving, by a mobile terminal, a signal from a plurality of an active set of base stations involved in a soft handover;
• means for performing antenna verification;
• means for updating a feedback information detection error rate for all the links using the antenna verifications;
• means for choosing scale factors, based on a feedback information detection error rate;
• means for scaling channel response estimates using the scale factors;
• means for determining the optimal antenna weights using the scaled channel response estimates;
• means for mapping the optimal antenna weights to the feedback information;
• and
• means for sending to the feedback information to the plurality of base stations.

A mobile terminal, comprising:

• means for receiving a signal from a plurality of base stations involved in a soft handover;
• means for detecting the transmit power commands for the links of a plurality of involved base stations;
• means for computing an Up/Down ratio of the transmit power commands for each link;
• means for choosing, based on the Up/Down ratio, appropriate scale factors;
• means for scaling channel response estimates using the scale factors;
• means for using the scaled channel response estimates to determine the optimal antenna weights;
• means for mapping the optimal antenna weights to the feedback information;
• and
• means for sending to the feedback information to the plurality of base stations.