Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section.
The 3rd Generation Partnership Project (3GPP) is a globally applicable third generation mobile phone system specification that is a result of collaboration between various groups of telecommunications associations, including the European Telecommunications Standards Institute, the Association of Radio Industries and Businesses/Telecommunication Technology Committee (ARIB/TTC), China Communications Standards Association, and the Alliance for Telecommunications Industry Solutions. 3GPP work is ongoing with Universal Terrestrial Radio Access Network (UTRAN) Long Term Evolution (LTE). Long Term Evolution (LTE) is a next generation broadband communication technology developed by the 3rd Generation Partnership Project (3GPP) in order to meet high-speed requirements. A LTE system may realize high-speed packet-based communication at up to 100 Mbps in the downlink.
In 3GPP technical specification of Rel-8 or Rel-9, two kinds of radio resource measurement need to be performed by a User Equipment (UE), one is Radio Link Monitoring (RLM) measurement, and the other one is Radio Resource Management (RRM) measurement.
A heterogeneous environment is under discussion in LTE-Advanced (LTE-A), in which environment a plurality pico cells operating with relatively low transmission power are distributed in a macro cell operating with relatively high transmission power. For a UE located at the coverage boundary between a Macro cell and a Pico cell, if the received downlink signal from the Macro cell is stronger than that from the Pico cell, the UE is associated with the Macro cell and receive downlink signals from the Macro cell. While for the uplink, since the Pico cell is closer to the UE than the Macro cell, its is better select the Pico cell as the reception point of the UE, in order to reduce the transmit power of the UE and the interference to normal UEs in the Pico cell. Therefore, for this UE, the downlink serving cell is the Macro cell but the uplink serving cell is the Pico cell, which is called uplink and downlink decoupling.
FIG. 1 illustrates a scenario of a typical decoupling handover process. As shown in (A) of FIG. 1, Macro evolved NodeB (eNB) serves UE at both the uplink and downlink at the beginning. The UE moves around in the system. When the UE moves such that Pico eNB becomes closer to the UE than Macro eNB, the UE switches uplink bearers from Macro eNB to Pico eNB first, as shown in (B) of FIG. 1. If both the Macro eNB and the Pico eNB support decoupling, the UE will maintain its downlink carriers to Macro eNB and its uplink carriers to Pico eNB at the area where the signal power from Pico eNB is lower than that from Macro eNB. If the UE moves to be further closer to Pico eNB and that the signal power from Pico eNB is larger than that from Macro eNB, the UE switches its downlink bearers from Macro eNB to Pico eNB, as shown in (C) of FIG. 1.
The same criterion is applicable to the cell change from Pico to Macro. The downlink carriers are switched from Macro eNB to Pico eNB first when the signal power from the Macro eNB is larger than that from Pico eNB. After that, the uplink carriers are then switched from Macro eNB to eNB if needed. That is, when a decoupling handover occurs to the UE, it switches one-direction carriers first, and switches the other direction carriers later.
To activate or deactive uplink and downlink decoupling, the network has to rely on RRM measurement and report mechanism.
The current RRM measurement and report mechanism does not differentiate a decoupling handover case and a normal handover case, i.e., uplink and downlink carriers are switched together. In order to support the decoupling, the UE shall be configured to report the measurement when either the criteria for a normal handover or the criteria for a decoupling handover is satisfied. When a normal handover is to be decided, the measurement reported when the criteria for a decoupling handover is unuseful. Similarly, when a decoupling handover is to be cided, the measurement reported when the criteria for a normal handover is unuseful. Therefore, unnecessary Radio Resource Control (RRC) report is generated, which wastes the bandwidth resource of the network and the processing resource on the UE.