Water-Filling Algorithm for System Power and Subcarrier Allocation - A Classical Approach

In communication systems, the water-filling algorithm serves as a widely adopted method for optimizing system power and subcarrier allocation. As a classical algorithm, it dynamically adjusts power distribution and subcarrier assignment to maximize total system throughput. The algorithm operates by allocating power and subcarriers during each time slot while maintaining user requirements, thereby achieving optimal spectral efficiency. A typical implementation involves sorting subcarriers by channel gain, calculating the water-level threshold, and distributing power inversely proportional to channel conditions. Key computational steps include: 1) Initializing channel state information matrices, 2) Iteratively determining the optimal power allocation using Lagrange multipliers, and 3) Applying convergence criteria to ensure solution stability. This algorithm finds extensive applications in modern communication systems like OFDM and massive MIMO due to its proven optimality in capacity-achieving power distribution.