The present invention relates to cellular telecommunication systems. More particularly, and not by way of limitation, particular embodiments of the present invention are directed to an apparatus and method for determining the severity of interference in different areas of a cellular radio network and for coordinating Radio Resource Management (RRM) features in response.
Inter-cell interference (ICI) is one of the most dominant sources for performance impairment in a wireless cellular network. To alleviate the impact on the performance impairment, the 3rd Generation Partnership Project (3GPP) has specified in 3GPP Technical Specification 36.331, signaling over an X2 interface between the eNodeBs (eNBs) to exchange load information. Various inter-cell interference coordination (ICIC) solutions for multi-cell wireless systems have also been proposed, as described in G. Fodor et al, “Intercell Interference Coordination in OFDMA Networks and in the 3GPP Long Term Evolution Systems”, Journal of Communications, Vol. 4, No. 7, August 2009.
The ICI problem in a one-reuse system, such as the Long Term Evolution (LTE) radio access network, can be illustrated in a simplified example. Two serving cells, cell A and Cell B, operating in a frequency band, allocate a number of Physical Resource Blocks (PRBs), or subbands, to their users. Users who are allocated to transmit at the same time and in the same subbands will interfere with each other, causing a conflict or collision. A collision may cause a lower Signal-to-Interference-and-Noise-Ratio (SINR) and Hybrid Automatic Repeat Request (HARQ) retransmission may needed to decode the transmitted bits. The retransmissions reduce the user throughput.
The load indication procedure for ICIC, as specified in 3GPP TS 36.331, includes two load indicators:                Uplink Interference Overload Indicator (UL IOI). The UL IOI indicates the interference level experienced by the indicated cell on all resource blocks. The message is enumerated per PRB with high, medium, or low interference.        UL High Interference Indicator (UL HII). The UL HII indicates the occurrence of high interference sensitivity, as seen from the sending eNB. The message is a bit map of high or low interference per PRB.        
In a simple example, a UL IOI and a UL HII may be transmitted from Cell A to Cell B. In an example scenario, the UL IOI may indicate High (interference) on PRBs in the upper third of the frequency bandwidth while indicating Low (interference) on the remaining two-thirds of the PRBs. Having received the UL IOI message, the receiving cell, Cell B in this example, may take the UL IOI into account and select cell-center User Equipments (UEs) to be scheduled on highly interfered PRBs to reduce interference to the indicated cell.
Likewise, Cell A may transmit a UL HII indicator to Cell B. The UL HII may indicate High (interference) on PRBs in the lower two-thirds of the frequency bandwidth while indicating Low (interference) on the remaining third of the PRBs. Having received the UL HII message, the receiving cell may take the UL HII into account and avoid scheduling cell-edge UEs on the concerned PRBs.
Besides the load information messages transferred between eNBs for coordinating the interference between neighboring cells, there are also messages and processes specified between each UE and neighboring cells to request and report Reference Signal Received Power (RSRP) measurements.
LTE, as well as High Speed Packet Access (HSPA) networks, are designed for a frequency reuse of one, which means that every base station uses the entire system bandwidth for transmission and there is no frequency planning among cells to cope with interference from neighboring cells. In homogeneous networks with uniformly distributed macro base stations, the inter-cell interference is mostly likely to occur at the boundaries of the cells. The traditional approach to identify the interference area is to divide cells into cell-center and cell-edge portions based on path loss and geometry measurements. However, real networks are not always homogeneous. Areas with interference problems depend on how macro base stations are deployed in each operator's network. Furthermore, the problem is complicated by the recent evolution of a multi-layer heterogeneous network (HetNet), where a layer of high-power macro base stations is overlaid with layers of lower powered pico or micro cells. There are new interference scenarios in HetNet deployments due to the large imbalance between the transmission power of macro and pico BSs and the serving cell selection specified by the standard. The traditional approach does not identify the actual interference situation since interference depends not only on the path loss or geometry but also the transmission power.
ICIC has been identified to play a vital role in a variety of deployments in the radio networks. Many ICIC schemes are proposed to improve the performance of ICIC for the Fourth Generation (4G) LTE system. Existing ICIC techniques mainly fall into two categories: static ICIC and dynamic ICIC. The static ICIC provides gains only in some scenarios and no gain and even loses in many others. Dynamic coordination may be necessary to improve ICIC schemes; however, dynamic ICIC can be very computationally complex.