History-Aware and Dynamic Client Contribution in Federated Learning
This work addresses fair incentive allocation in federated learning for diverse clients, but it is incremental as it builds on existing Shapley value methods by adapting them to dynamic settings.
The paper tackles the problem of fairly assessing client contributions in federated learning under dynamic participation, proposing FLContrib, a history-aware framework that efficiently computes contributions using Shapley values and applies them to detect dishonest clients, achieving consistent accuracy across utility functions.
Federated Learning (FL) is a collaborative machine learning (ML) approach, where multiple clients participate in training an ML model without exposing their private data. Fair and accurate assessment of client contributions facilitates incentive allocation in FL and encourages diverse clients to participate in a unified model training. Existing methods for contribution assessment adopts a co-operative game-theoretic concept, called Shapley value, but under restricted assumptions, e.g., all clients' participating in all epochs or at least in one epoch of FL. We propose a history-aware client contribution assessment framework, called FLContrib, where client-participation is dynamic, i.e., a subset of clients participates in each epoch. The theoretical underpinning of FLContrib is based on the Markovian training process of FL. Under this setting, we directly apply the linearity property of Shapley value and compute a historical timeline of client contributions. Considering the possibility of a limited computational budget, we propose a two-sided fairness criteria to schedule Shapley value computation in a subset of epochs. Empirically, FLContrib is efficient and consistently accurate in estimating contribution across multiple utility functions. As a practical application, we apply FLContrib to detect dishonest clients in FL based on historical Shaplee values.