Title :
Using Lagrangian Relaxation for Radio Resource Allocation in High Altitude Platforms
Author :
Ibrahim, Ahmed ; Alfa, Attahiru S.
Author_Institution :
Dept. of Electr. & Comput. Eng., Univ. of Manitoba, Winnipeg, MB, Canada
Abstract :
In this paper, we study radio resource allocation for multicasting in OFDMA based high altitude platforms (HAPs). We formulate and solve an optimization problem that finds the best allocation of HAP resources such as radio power, sub-channels, and time slots. The problem also finds the best possible frequency reuse across the cells that constitute the service area of the HAP. The objective is to maximize the number of user terminals that receive the requested multicast streams in the HAP service area in a given OFDMA frame. A bounding subroutine in a branch and bound algorithm can be obtained by decomposing it into two easier subproblems, due to its high complexity, and solving them iteratively. Subproblem 1 turns out to be a binary integer linear program of no explicitly noticeable structure and therefore Lagrangian relaxation is used to dualize some constraints to get a structure that is easy to solve. Subproblem 2 turns out to be a linear program with a continuous knapsack problem structure. Hence a greedy algorithm is proposed to solve subproblem 2 to optimality. The subgradient method is used to solve for the dual variables in the dual problem to get the tightest bounds.
Keywords :
OFDM modulation; frequency allocation; gradient methods; greedy algorithms; integer programming; linear programming; HAP resources; Lagrangian relaxation; OFDMA based high altitude platforms; binary integer linear program; bounding subroutine; branch and bound algorithm; continuous knapsack problem; greedy algorithm; optimization problem; radio resource allocation; subgradient method; Interference; OFDM; Optimization; Resource management; Signal to noise ratio; Throughput; Wireless communication; Continuous Knapsack Problem; High Altitude Platforms; High altitude platforms; Lagrangian Relaxation; Multicasting; Radio Resource Allocation; continuous knapsack problem; lagrangian relaxation; multicasting; radio resource allocation;
Journal_Title :
Wireless Communications, IEEE Transactions on
DOI :
10.1109/TWC.2015.2443095