The present invention relates to a basestation for use in a cellular mobile communications network, and to a method for controlling uplink transmit power for a plurality of basestations in a mobile communications network.
Small cell basestations are known and used in many cellular networks. A small cell basestation forms an access point that provides mobile coverage in areas where such coverage is problematic. Small cell basestations may for example be deployed indoors in residential, public access, or business premises, or in hot-spot or rural outdoor locations. The small cell basestation connects to the core network of a cellular network operator and provides cellular network coverage for subscribers within a coverage area of the small cell. Small cell basestations are intended to complement existing macro layer network coverage such that user equipment devices may attach to and use either a macro layer basestation or a small cell basestation, depending on their location.
Small cell basestations may be deployed co channel with a macro layer carrier, or may operate on a partially overlapping carrier, which may for example be straddled between two macro layer carriers. Engineering the radio frequency coexistence of the small cell basestations and the macro layer basestations is an important design consideration in the deployment of small cell basestations. While both uplink and downlink channels have to be considered, the present specification addresses coexistence issues concerned with uplink channels, that is wireless transmission of signals from user equipment devices (UEs) to a basestation.
In systems supporting time and/or frequency domain multiple access techniques, resources may be partitioned to enforce isolation between the macro and small cell layers. However, it is often the case that better resource efficiency can be achieved by ensuring that uplink power controlled by the small cell layer remains below the macro noise floor while maintaining full flexibility on time and frequency resource allocation. Existing procedures typically achieve this by limiting the maximum uplink transmit power for basestations in the small cell layer to a fixed amount, known as the uplink noise margin, below the macro noise floor. The uplink noise margin is established based on the expected macro noise rise contribution of user equipment devices (UEs) connected to the small cell layer. This noise margin is used by all basestations operating on the small cell layer. In establishing an appropriate uplink noise rise margin, the aim of protecting macro layer basestations has to be balanced against potential adverse impact on uplink performance of the small cell layer.
The coexistence issues described above are experienced in WCDMA and other 3G technologies, as well as in many heterogeneous and other multilayered network technologies and systems, including for example LTE.