Generalizing and Optimizing Fractional Frequency Reuse in Broadband Cellular Radio Access Networks

For broadband cellular access based on orthogonal frequency divisionmultiple access (OFDMA), fractional frequency reuse (FFR) is one ofthe key concepts for mitigating inter-cell interference and therebyoptimizing cell-edge performance. In standard FFR, the number of OFDMAsub-bands and the reuse factor are both fixed. Whereas this works wellfor an idealized cell pattern, it is neither directly applicable noradequate for real-life networks with very irregular cell layouts. Inthis paper, we generalize the standard FFR to allow for flexibilities inthe total number of sub-bands as well as the number of sub-bands ineach cell-edge zone, enabling network-adaptive FFR. Two powerassignment strategies that use fixed power per sub-band prior tosub-band allocation and apply cell-specific power derived from thenumber of sub-bands allocated to each cell-edge zone, respectively,are investigated. Optimization algorithms based on local search aredeveloped for sub-band allocation to maximize the cell-edgethroughput. Evaluations using networks with realistic radiopropagation conditions demonstrate the applicability of the generalizedand optimized FFR in performance engineering of OFDMA networks