Method and apparatus for mobile assisted handoff
First Claim
1. A method of handing off an on-going communication of a mobile unit leaving a serving cell to a neighboring cell of a cellular communication system, wherein the mobile unit has a scanning receiver for measuring received signal strength of a predetermined maximum number of scanned channels in a scanning sequence, the method comprising the steps ofgenerating a measurement list at the serving cell that includes channels of a plurality of designated neighboring cells,requesting the mobile unit to measure a plurality of channels of the plurality of designated neighboring cells;
- reporting by the mobile unit to the base station of the serving cell, the channel quality measurements;
replacing a portion of the plurality of channels with unreported channels of the generated measurement list at times when none of the reporting channels meet a handoff criteria and the total number of cells of the measurement list exceeds a maximum number of channels scannable in a sequence by the mobile unit;
repeating the steps of generating, requesting, reporting, and replacing until all the channels of the measurement list are scanned by the mobile unit or until one of the channels of the measurement list meets the handoff criteria, whichever is first to occur; and
performing handoff to said one of the channels meeting the handoff criteria.
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Accused Products
Abstract
A method and system for selecting the best handoff candidate cell at times when the number of neighboring cells that meet the measurement criteria is greater than twelve a measurement list is generated. The cells are assigned a handoff measurement priority wherein a handoff priority of zero is assigned to 12-N cells where N is between 1 and 6. A priority of 8 is assigned to the worst N cells. A new measurement list is generated using the 12-N cells and other unreported cells having a higher priority than the N worst cells.
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Citations
15 Claims
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1. A method of handing off an on-going communication of a mobile unit leaving a serving cell to a neighboring cell of a cellular communication system, wherein the mobile unit has a scanning receiver for measuring received signal strength of a predetermined maximum number of scanned channels in a scanning sequence, the method comprising the steps of
generating a measurement list at the serving cell that includes channels of a plurality of designated neighboring cells, requesting the mobile unit to measure a plurality of channels of the plurality of designated neighboring cells; -
reporting by the mobile unit to the base station of the serving cell, the channel quality measurements; replacing a portion of the plurality of channels with unreported channels of the generated measurement list at times when none of the reporting channels meet a handoff criteria and the total number of cells of the measurement list exceeds a maximum number of channels scannable in a sequence by the mobile unit; repeating the steps of generating, requesting, reporting, and replacing until all the channels of the measurement list are scanned by the mobile unit or until one of the channels of the measurement list meets the handoff criteria, whichever is first to occur; and performing handoff to said one of the channels meeting the handoff criteria. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for handing off an ongoing communication of a digital mobile unit in a serving cell to one of a plurality of neighboring cells of a cellular communication system wherein the digital mobile unit is limited to scanning in a scanning sequence a predetermined maximum number of neighboring cell channels, the apparatus comprising
means in each cell responsive to a transmission signal threshold of a mobile unit for initiating a mobile assisted handoff; -
means responsive to the initiated handoff for generating a measurement list of channels of identified neighboring cells for transmission to the mobile unit; means for scanning a plurality of the channels at the mobile unit to obtain signal strength measurements; means for reporting by the mobile unit to the serving cell the signal strength measurements of the plurality of channels; means for receiving, at the serving cell, the signal strength measurements reported by the mobile unit; means for replacing a portion of the channels for which measurements were reported by the mobile unit with unreported channels of the generated measurement list at times when none of the plurality of channels meets a handoff criteria and the total number of channels of the measurement list is greater than the maximum number of channels scannable in a scanning sequence by the mobile unit; means coupled to the generating means for causing the generating means to repeat the generation of a new measurement list and coupled to the scanning means for causing the scanning means to repeat scanning from the new measurement list, whereby the reporting means and receiving means repeat reporting and receiving of signal measurements until all channels of the measurement list are scanned by the mobile unit or until one of the channels meets a handoff criteria whichever is first to occur; and means for handing off the mobile unit communication to a cell having said one channel in response to said one channel meeting the handoff criteria. - View Dependent Claims (7, 8, 9, 10)
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11. A method of handing off an on-going communication of a mobile unit leaving a serving cell to a neighboring cell of a cellular communication system, wherein the mobile unit has a scanning receiver for measuring received signal strength of a fixed maximum number of scanned cells concurrently, the method comprising
providing a first measurement list at the serving cell base station that includes a plurality of designated neighboring cells; -
requesting initially that the mobile unit measure the signal strength of a plurality of the cells of the first measurement list; reporting, by the mobile unit, to the base station of the serving cell, the quality measurement of the signals of each of the plurality of cells of the initial requested measurements up to the fixed maximum number of scanned cells; replacing a selected number of the plurality of cells with other cells of the first measurement list at times when the total number of cells in the first measurement list exceeds the fixed maximum number of scanned cells of the mobile unit and none of the scanned cells meets a handoff criteria list; providing a subsequent measurement list for the other cells and a selected number of the said plurality of cells; requesting subsequently that the mobile unit measure the signal strength of the subsequent measurement list; reporting the measured signal strength of the subsequently requested cells; and performing a handoff at times when one reported cell meets the handoff criteria. - View Dependent Claims (12, 13)
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14. Apparatus for handing off an on-going communication of a digital mobile unit in a serving cell to one of a plurality of neighboring cells of a cellular communication system wherein the digital mobile unit is limited to scanning at any one time a fixed number of channels of neighboring cells;
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first means for selecting neighboring cells for inclusion in a measurement list in accordance with a configured measurement class and priority designation within the measurement class of each neighboring cell, signal strength of the mobile unit measured in the serving cell, signal, and strength of the serving cell traffic channel; second means for selecting 12 of the best cells in accordance with the measurement class and priority; third means for transmitting a measurement order to the mobile unit; fourth means for reporting, by the mobile unit, channel quality measurement to the serving cell; fifth means for selecting candidate cells for handoff based on a reporting criteria of the channel quality measurement; sixth means for selecting a new measurement list at times when no candidate cells are selected for handoff, the selecting means including means for replacing with new cells these previous candidate cells with lowest RF signal strength of the list generated by the first selection means; and means for handing off the on-going communication in response to the selected candidate cells by the fifth means. - View Dependent Claims (15)
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Specification