A framework for leakage-based autonomous uplink inter-cell interference coordination in OFDMA/LTE heterogeneous networks

The inter-cell interference (ICI) problem in OFDMA wireless systems is a major impediment to attain high rates particularly for cell-edge users in reuse-1 systems. Using centralized resource allocation to combat ICI is not practical, particularly in heterogeneous networks (HetNets), as they require intensive signalling about interference and channel state information that may not always be practically available. The main contribution of this paper is devising efficient autonomous power allocation schemes such that the interference produced by each cell is below a certain limit. We develop two inter-cell interference coordination (ICIC) frameworks; the overall interference limit (OIL), and the interference limit per resource block (ILR). The first framework imposes an overall interference limit on each cell, while the second imposes different interference limits on different resource blocks in each cell. We propose a closed form solution, and an iterative solution for the OIL framework, and a closed form solution for the ILR framework which has an additional advantage of possible autonomous application at each terminal rather than at the base station. We present two semi-autonomous heuristic and optimal adaptive schemes that use the overload indicator (OI) signal in LTE to adjust the values of the interference limits in the ILR scheme. They attempt to alleviate the interference seen by overloaded cells in order to achieve fairness among different cells, which is very important especially in HetNets. A method based on the Kalman filter is introduced to predict the values of the OI in the intervals between the OI exchanges. This estimation can be applied to the adaptive schemes almost autonomously as it requires very infrequent signalling between cells. Simulations show that the proposed schemes exhibit better performance than equal power allocation. Comparison with centralized optimal allocation that uses global information shows good performance with acceptable degradation in the spectral efficiency which decreases as the interference limit increases. Simulations also show that the ILR and the OIL schemes almost have the same performance, and the adaptive schemes achieve fairness among different cells especially in a HetNet environment.