Inter-cell interference (ICI) may be considered to be interference at a cell due to transmissions originating in another cell. Usually, ICI occurs between adjacent cells of a communications system. As an example, relatively high-powered transmissions to and from a cell edge user (CEU) operating in a first cell may cause more interference to adjacent cells utilizing the same operating frequency than relatively lower-powered transmissions to and from a cell center user (CCU) operating in the first cell to adjacent cells utilizing the same operating frequency due to correspondingly higher power levels of the transmissions to and from the CEU.
FIG. 1 illustrates a prior art communications system 100. Communications system 100 includes a first enhanced NodeB (eNB) 105 and a second eNB 115. An eNB (also commonly referred to as a base station, communications controller, NodeB, and so forth) may control communications of User Equipment (UE) operating within its coverage area. For example, eNB 105 may have a coverage area illustrated in FIG. 1 as hexagon 110, while eNB 115 may have a coverage area illustrated as hexagon 120. Operating within hexagon 110 may be a first UE 125 and a second UE 130. A UE may also be commonly referred to as a mobile station, user, terminal, subscriber, and so on).
Generally, an eNB, a relay node (RN), a low power node (LPN), or so on, may be referred to as a communications controller. Typically, communications controllers may be sectorized into a number of sectors, with each sector being referred to as a cell, to increase utilization, decrease interference, and so forth. Without loss of generality, a cell, as used herein, may refer to a communications controller, a portion of a coverage area of a communications controller, or the coverage area of the communications controller in its entirety.
A coverage area of an eNB (or more generally, a cell) may be categorized based upon a distance to the eNB. For example, coverage area of eNB 105 (i.e., hexagon 110) may be categorized into two regions, with a first region being a cell center region (shown as circle 135) and a cell edge region (portions of hexagon 110 outside of circle 135, shown as region 140). Normally, with downlink fractional frequency reuse ICIC, UEs operating within a cell center region, such as UE 125, may receive transmissions made at a lower power level than UEs operating outside of a cell center region, such as UE 130, due to their closer proximity to an eNB serving the coverage area.
Furthermore, since transmissions made by UEs (i.e., uplink transmissions) operating with a cell edge region, such as UE 130, are usually made at higher power levels and the UEs are also located closer to neighboring (e.g., adjacent) eNBs, the transmissions may cause more interference to the neighboring eNBs. For downlink transmissions, UEs in a first eNB (e.g., a serving eNB) that are located closer to a neighboring eNB (i.e., an adjacent eNB) may experience high interference from transmissions of the neighboring eNB than UEs operating in a cell center region of the first eNB.
One form of ICIC is fractional frequency reuse (FFR) ICIC. In FFR ICIC, available time and/or frequency resources may be divided up into multiple parts, also commonly referred to as a FFR pattern or frequency reuse pattern, which may be allocated to different transmitters. The transmitters may then transmit only during times and/or in frequencies associated with their allocated time and/or frequency part(s) or transmit with different power densities in different time and/or frequency parts according to predefined power density mask. Assignment of the time and/or frequency parts may be made so that adjacent and/or close transmitters cause little or no interference to one another and/or receivers.
It is widely considered that ICI management will be a key technology for enhancing the performance of Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications systems, for example, and overall UE experience Therefore, there is a need for ICI reducing techniques, of which, inter-cell interference coordination (ICIC) is one form. ICIC is a simple and efficient ICI management scheme. Generally, ICIC attempts to reduce and/or control ICI through the use of radio resource management (RRM) methods. Typically, ICIC takes into account information from multiple cells, such as neighboring cells, to control inter-cell interference. A usual ICIC strategy may be to determine resources available at a cell, which may then be scheduled (i.e., allocated) to users. ICIC in Orthogonal Frequency Division Multiple Access (OFDMA) communications systems, such as 3GPP LTE communications systems, have received considerable study.