We study the problem of optimal power allocation in a single-hop ad hoc wireless network. In solving this problem, we depart from classical purely model-based approaches and propose a hybrid method that retains key modeling elements in conjunction with data-driven components. More precisely, we put forth a neural network architecture inspired by the algorithmic unfolding of the iterative weighted minimum mean squared error (WMMSE) method, that we denote by unfolded WMMSE (UWMMSE). The learnable weights within UWMMSE are parameterized using graph neural networks (GNNs), where the time-varying underlying graphs are given by the fading interference coefficients in the wireless network. These GNNs are trained through a gradient descent approach based on multiple instances of the power allocation problem. We show that the proposed architecture is permutation equivariant, thus facilitating generalizability across network topologies. Comprehensive numerical experiments illustrate the performance attained by UWMMSE along with its robustness to hyper-parameter selection and generalizability to unseen scenarios such as different network densities and network sizes.Index terms-WMMSE, power allocation, graph neural networks, deep learning, algorithm unfolding.
I. INTRODUCTIONPower and bandwidth are fundamental resources in communication, playing a key role in determining the effective capacity of a wireless channel [1], [2]. In modern wireless communication systems, the scope of resources has been broadened to include beams in a multiple-input-multipleoutput (MIMO) system, time slots in a time-division multiple access system (TDMA), frequency sub-bands in a frequencydivision multiple access (FDMA) system, spreading codes in a code-division multiple access (CDMA) system, among several others [3]. Optimal allocation of these resources under randomly varying channel characteristics and user demands is essential for the smooth operation of wireless systems. In particular, power allocation in a wireless ad hoc network is crucial to mitigate multi-user interference, one of the main performance-limiting factors. In addition, transmission power of a mobile user is in itself a scarce resource. Indeed, careful