Unless otherwise indicated herein, the description in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
A typical wireless communication system includes one or more base stations, each radiating to define one or more coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. Further, each base station of the system may then be coupled or communicatively linked with network infrastructure such as a switch or gateway that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the system may thus engage in air interface communication with a base station and thereby communicate via the base station with various remote network entities or with other UEs served by the system.
In practice, physical base station equipment in such a system may be configured to provide multiple coverage areas, differentiated from each other by direction, carrier frequency, or the like. For simplicity in this description, however, each coverage area may be considered to correspond with a respective base station and each base station may be considered to correspond with a respective coverage area. Thus, an arrangement where physical base station equipment provides multiple coverage areas could be considered to effectively include multiple base stations, each providing a respective one of those coverage areas.
In general, a wireless communication system may operate in accordance with a particular air interface protocol or radio access technology, with communications from a base station to UEs defining a downlink or forward link and communications from the UEs to the base station defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA) (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communication (GSM), WI-FI, and BLUETOOTH. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each of the one or more coverage areas of such a system may operate on one or more carrier frequencies and may define a number of air interface channels for carrying information between the base station and UEs. By way of example, each coverage area may define a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that UEs may detect as an indication of coverage and may measure to evaluate coverage strength. Further, each coverage area may define a downlink control channel for carrying system information, page messages, and other control signaling from the base station to UEs, and an uplink control channel for carrying service requests and other control signaling from UEs to the base station, and each coverage area may define downlink and uplink traffic channels or the like for carrying bearer traffic between the base station and UEs.
When a UE initially enters into coverage of a wireless communication system (e.g., powers on in coverage of the system), the UE may detect the reference signal and read system information broadcast from a base station and may engage in a process to register itself to be served by the base station and generally by the system. For instance, the UE may transmit an attach message on an uplink control channel to the base station, and the base station and/or supporting infrastructure may then responsively authenticate and authorize the UE for service, establish a record indicating where in the system the UE is operating, establish local profile or context records for the UE, and provide an attach accept message to the UE.
When a UE is served in a particular base station coverage area, the UE may also regularly monitor the reference signal strength in that coverage area and in other coverage areas of the system, in an effort to ensure that the UE operates in the best (e.g., strongest) coverage area. If the UE detects threshold weak coverage from its serving coverage area and sufficiently strong coverage from another coverage area, the UE may then engage in a handover process by which the UE transitions to be served by the other coverage area. In the idle mode, the UE may do this autonomously and might re-register in the new coverage area. Whereas, in the connected/active mode, the UE may report signal strengths to its serving base station when certain thresholds are met, and the base station and/or supporting infrastructure may work to hand the UE over to another coverage area. By convention, a UE is said to hand over from a “source” coverage area or base station to a “target” coverage area or base station.