# Improving the Worst-Case Bidirectional Communication Complexity for Nonconvex Distributed Optimization under Function Similarity

arXiv: https://arxiv.org/abs/2402.06412 · HTML: https://mlsanity.com/paper/2402.06412/

## Key facts

- Cited by 5 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 9 Feb 2024.

## Built on by (most cited first, 5 of 5)

- [Tighter Performance Theory of FedExProx](https://mlsanity.com/paper/2410.15368/) (2024)
- [MARINA-P: Superior Performance in Non-smooth Federated Optimization with Adaptive Stepsizes](https://mlsanity.com/paper/2412.17082/) (2024)
- [BiCoLoR: Communication-Efficient Optimization with Bidirectional Compression and Local Training](https://mlsanity.com/paper/2601.12400/) (2026)
- [Proving the Limited Scalability of Centralized Distributed Optimization via a New Lower Bound Construction](https://mlsanity.com/paper/2506.23836/) (2025)
- [Communication-Efficient Agnostic Federated Learning via Faster Convergence and Compression](https://mlsanity.com/paper/2609.36610/) (2026)

## Abstract (arXiv)

Effective communication between the server and workers plays a key role in distributed optimization. In this paper, we focus on optimizing the server-to-worker communication, uncovering inefficiencies in prevalent downlink compression approaches. Considering first the pure setup where the uplink communication costs are negligible, we introduce MARINA-P, a novel method for downlink compression, employing a collection of correlated compressors. Theoretical analyses demonstrates that MARINA-P with permutation compressors can achieve a server-to-worker communication complexity improving with the number of workers, thus being provably superior to existing algorithms. We further show that MARINA-P can serve as a starting point for extensions such as methods supporting bidirectional compression. We introduce M3, a method combining MARINA-P with uplink compression and a momentum step, achieving bidirectional compression with provable improvements in total communication complexity as the number of workers increases. Theoretical findings align closely with empirical experiments, underscoring the efficiency of the proposed algorithms.