Many people use mobile stations, such as cell phones, personal digital assistants (PDAs), tablet computers, laptop computers, desktop computers, in-car computers, and so on, to communicate with cellular wireless networks. These WCDs and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1×RTT networks” (or “1× networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Mobile stations typically conduct these wireless communications with one or more base transceiver stations (BTSs), each of which send communications to and receive communications from mobile stations over the air interface. Each BTS is in turn communicatively connected with an entity known as a base station controller (BSC), which (a) controls one or more BTSs and (b) acts as a conduit between the BTS(s) and one or more switches or gateways, such as a mobile switching center (MSC) and/or packet data serving node (PDSN), which may in turn interface with one or more signaling and/or transport networks.
As such, mobile stations can typically communicate with one or more endpoints over the one or more signaling and/or transport networks from inside one or more coverage areas (such as cells and/or sectors) of one or more BTSs, via the BTS(s), a BSC, and an MSC and/or PDSN. In typical arrangements, MSCs interface with the public switched telephone network (PSTN), while PDSNs interface with one or more core packet-data networks and/or the Internet.
To meet increasing demand for high-speed data on mobile devices, cellular service providers have begun implementing “4G” networks, which provide service under one or more 4G air interface protocols, such a long-term evolution (LTE) protocol. LTE was developed by the 3rd Generation Partnership Project (3GPP), and is based on GSM/EDGE and UMTS/HSPA network technology.
In the context of LTE, a mobile station is typically referred to as a “user equipment” (UE), and may take various mobile and stationary forms, such as a mobile phone, tablet computer, laptop computer, desktop computer, or any other device configured for wireless communication. Herein, the terms “mobile station,” “wireless communication device” (or WCD), and “user equipment” (or UE) may be used interchangeably. Further, in the context of LTE, a base station is typically referred to as an “eNodeB.” Herein, the terms “base station” and “eNodeB” may be used interchangeably.
In a further aspect of some protocols, such as LTE, reception at cell edges may be problematic for various reasons. For example, the greater distance to a base station at a cell edge may result in lower signal strength. Further, at a cell edge, interference levels from neighboring cells are likely to be higher, as the wireless communication device is generally closer to neighboring cells when at a cell edge.
In an effort to improve the quality of service at cell edges, 3GPP LTE-A Release 11 introduced a number of Coordinated Multipoint (CoMP) schemes. By implementing such CoMP schemes, a group or cluster of base stations may improve service at cell edges by coordinating transmission and/or reception in an effort to avoid inter-cell interference, and in some cases, to convert inter-cell interference into a usable signal that actually improves the quality of service that is provided.
LTE-A Release 11 defines a number of different CoMP schemes or modes for both the uplink (UL) and the downlink (DL). For the downlink, there or two basic types of CoMP modes: coordinated scheduling/beamforming (CSCH or DL-CSCH) and joint processing. When coordinated scheduling/beamforming is implemented for a given UE, data is only sent to the given UE in one cell at a time, but scheduling and beamforming decisions for the given UE are coordinated amongst multiple cells. When a type of joint processing referred to as joint transmission is implemented for a given UE, data is transmitted to the UE in multiple cells concurrently. Other types of CoMP schemes on the uplink and downlink also exist.