Measurement management in small-cell systems

Abstract

A system and method for neighbor-cell measurement reporting in a cellular environment supporting multistate cells limits measurement reporting by requiring that state-specific trigger conditions are met. Thus for example, a dormant cell may need to meet more stringent measurement conditions before a report is generated by the user device, since a current primary cell may prefer to hand off to an active cell. In particular, state-specific thresholds, offsets, and hysteresis values may be used to enforce a preference for active cells, for example.

We claim: 
     
       1. A method for measurement reporting in a cellular user device connected to a primary cell and being within receiving range of a second cell, the method comprising:
 measuring a signal from the second cell; 
 determining a measurement quantity based on the measurement; 
 determining a cell state associated with the second cell; 
 evaluating a trigger condition using both the measurement quantity and the cell state; and 
 transmitting a measurement report if the trigger condition is satisfied. 
 
     
     
       2. The method of  claim 1  wherein determining a cell state associated with the second cell comprises determining whether the second cell is in an active state or in a dormant state. 
     
     
       3. The method of  claim 2  wherein the active state is a state wherein the second cell transmits reference signals with a periodicity that is equal to or shorter than 5 ms and the dormant state is a state wherein the second cell transmits reference signals with a periodicity greater than 5 ms. 
     
     
       4. The method of  claim 1  wherein measuring a signal from the second cell comprises measuring one of the following signals corresponding to the second cell: a common reference signal, a primary synchronization signal, a secondary synchronization signal, a small-cell discovery signal, a positioning reference signal, and a channel-state information reference signal. 
     
     
       5. The method of  claim 1  wherein determining a measurement quantity comprises determining one of the following measurement quantities: a reference signal received power and a reference signal received quality. 
     
     
       6. The method of  claim 2  wherein evaluating a trigger condition using both the measurement quantity and the cell state further comprises evaluating the trigger condition using a first cell-specific offset value if the second cell is in active state and evaluating the trigger condition using a second cell-specific offset value if the second cell is in dormant state. 
     
     
       7. The method of  claim 2  wherein evaluating a trigger condition using both the measurement quantity and the cell state further comprises evaluating the trigger condition using a first hysteresis parameter value if the second cell is in active state and evaluating the trigger condition using a second hysteresis parameter value if the second cell is in dormant state. 
     
     
       8. The method of  claim 2  wherein evaluating a trigger condition using both the measurement quantity and the cell state further comprises evaluating the trigger condition by comparing the measurement quantity to a first threshold value if the second cell is in active state and evaluating the trigger condition by comparing the measurement quantity to a second threshold value if the second cell is in dormant state. 
     
     
       9. The method of  claim 8  wherein the second threshold value is greater than the first threshold value. 
     
     
       10. The method of  claim 2  further comprising:
 measuring a second signal from a third cell; 
 determining a second measurement quantity based on the measured second signal; 
 determining if the second measurement quantity is smaller than a third threshold value; and 
 transmitting a measurement report including the second measurement quantity to the primary cell if the second measurement quantity is smaller than the third threshold and the trigger condition is satisfied. 
 
     
     
       11. A method for configuring a cellular user device for measurement reporting, the cellular user device being connected to a primary cell and being within receiving range of a neighboring cell, the method comprising transmitting a configuration from the primary cell to the cellular user device, the configuration including information for determining a trigger condition for reporting a measurement of a characteristic of the neighboring cell, the trigger condition being based upon both the measurement and a state of the neighbor cell. 
     
     
       12. The method of  claim 11  wherein the state of the neighbor cell is one of an active state and a dormant state, wherein in the active state, the neighbor cell transmits reference signals with a periodicity equal to or shorter than 5 ms, and in the dormant state the neighbor cell transmits reference signals with a periodicity greater than 5 ms. 
     
     
       13. The method of  claim 11  wherein the measured characteristic is measured relative to a common reference signal, a primary synchronization signal, a secondary synchronization signal, a small-cell discovery signal, a positioning reference signal, and a channel-state information reference signal. 
     
     
       14. The method of  claim 11  wherein the measured characteristic is one of a reference signal received power and a reference signal received quality. 
     
     
       15. The method of  claim 12  wherein the information used for determining the trigger condition includes a first cell-specific offset value for use if the neighbor cell is in the active state and a second cell-specific offset value for use if the neighbor cell is in the dormant state. 
     
     
       16. The method of  claim 12  wherein the information used for determining the trigger condition includes a first hysteresis parameter value for use if the neighbor cell is in the active state and a second hysteresis parameter value for use if the neighbor cell is in the dormant state. 
     
     
       17. The method of  claim 12  wherein the information used for determining the trigger condition includes a first threshold value for comparison to the measured characteristic of the neighboring cell for use if the second cell is in active state and a second threshold value for comparison to the measured characteristic of the neighboring cell for use if the second cell is in dormant state. 
     
     
       18. The method of  claim 17  wherein the second threshold value is greater than the first threshold value. 
     
     
       19. A cellular user device comprising:
 a processor; and 
 a measurement module run by the processor, the measurement module being configured to measure a characteristic of a neighbor cell while the cellular user device is connected to a primary cell and to determine whether to transmit a measurement report to the primary cell by applying a trigger condition, wherein the trigger condition depends upon both the measured characteristic and a state of the neighbor cell. 
 
     
     
       20. The cellular user device in accordance with  claim 19 , wherein the state of the neighbor cell is one of an active state, wherein the neighbor cell transmits reference signals with a periodicity equal to or shorter than 5 ms, and a dormant state, wherein the neighbor cell transmits reference signals with a periodicity greater than 5 ms.