Joint Power Control and Data Size Selection for Over-the-Air Computation Aided Federated Learning

TL;DR

This paper proposes a joint optimization of power control and data size in over-the-air federated learning to minimize mean-squared error, thereby enhancing training performance under channel fading and noise.

Contribution

It introduces a novel bi-level optimization framework for jointly tuning amplification factors and data sizes, improving over existing methods in FL over noisy channels.

Findings

Significant MSE reduction achieved

Enhanced federated learning training performance

Effective joint optimization method demonstrated

Abstract

Federated learning (FL) has emerged as an appealing machine learning approach to deal with massive raw data generated at multiple mobile devices, {which needs to aggregate the training model parameter of every mobile device at one base station (BS) iteratively}. For parameter aggregating in FL, over-the-air computation is a spectrum-efficient solution, which allows all mobile devices to transmit their parameter-mapped signals concurrently to a BS. Due to heterogeneous channel fading and noise, there exists difference between the BS's received signal and its desired signal, measured as the mean-squared error (MSE). To minimize the MSE, we propose to jointly optimize the signal amplification factors at the BS and the mobile devices as well as the data size (the number of data samples involved in local training) at every mobile device. The formulated problem is challenging to solve due to its non-convexity. To find the optimal solution, with some simplification on cost function and variable replacement, which still preserves equivalence, we transform the changed problem to be a bi-level problem equivalently. For the lower-level problem, optimal solution is found by enumerating every candidate solution from the Karush-Kuhn-Tucker (KKT) condition. For the upper-level problem, the optimal solution is found by exploring its piecewise convexity. Numerical results show that our proposed method can greatly reduce the MSE and can help to improve the training performance of FL compared with benchmark methods.