FedCompressIEEE ICASSP · 2024

Communication-Efficient Federated Learning through Adaptive Weight Clustering and Server-Side Distillation

Compress both directions of federated training.

Vasileios Tsouvalas Aaqib Saeed Tanir Ozcelebi Nirvana Meratnia

At a glance

Compress both directions of federated training. Clustering makes client uploads compact, but averaging can undo that structure. FedCompress restores it with server-side distillation and adjusts cluster capacity using an unlabeled representation score.

Cluster · Distill · Adapt
ServerGlobal model
Client ALocal model
Client B · Other clients
ON EACH CLIENT

Many weights · Few shared values

Warm-upTask + Clustering
After warm-up
01−1.202−0.8030.8041.2
↓ Shared centroids
Clustered client A
01−1
02−1
031
041
Two learned values
0−111
4 weights
2 values
Warm-up → Task learning + Weight clustering
ServerGlobal model
Client ALocal model
Client B · Other clients
CLIENTS → SERVER

Compact client models → Server

Client A
01−102−1031041
Centers
0−111
+
Position indices
010020031041
Client B
010022030042
Centers
0012
+
Position indices
010021030041
Compressed modelsServer
Centers + Position indices → Compressed client uploads
ServerGlobal model
Client ALocal model
Client B · Other clients
ON THE SERVER

Averaging breaks the shared values

Client A
01−102−1031041
Client B
010022030042
FedAvgEqual data shares
Global weights
01−0.5020.5030.5041.5
2 values / client3 global values
Position-wise FedAvg · 2 values per client → 3 global values
ServerGlobal model
Client ALocal model
Client B · Other clients
ON THE SERVER

Global teacher → Clustered student

Unlabeled OOD dataServer auxiliary data
Global teacher
Aggregated weights
01−0.5020.5030.5041.5
Soft predictions
Match
Clustered student
Shared values
010.1020.1030.1041.2
Matching predictions
KL matching+Weight clustering
Unlabeled server data → Prediction matching + Weight clustering
ServerGlobal model
Client ALocal model
Client B · Other clients
CLIENTS → SERVER

Stalled score → More capacity

Local unlabeled dataEmbeddings → Effective rank
↑ Client scores
Data-weighted scoreMoving average
Window · 3 roundsPatience · 3 rounds
Plateau
+
Increase capacityNext clustering · Within budget
Local embeddings → Effective rank → Server trend → Cluster budget
ServerGlobal model
Client ALocal model
Client B · Other clients
SERVER → CLIENTS

Compact model → Next round

Compressed global student
010.1020.1030.1041.2
↓ Compress + Broadcast
Shared values
00.111.2
+
Position indices
010020030041
Client A
Restored model
010.1020.1030.1041.2
Client B
Restored model
010.1020.1030.1041.2
Next roundLocal training · Updated cluster budget
Compressed global student → Clients · Updated cluster budget
Method diagram

Swipe across the diagram

What this adds

  • 01

    Dual compression: clustered local training plus server self-compression after aggregation.

  • 02

    Adaptive capacity: use embedding effective rank to guide the number of shared weight values.

  • 03

    Vision and audio evidence: report communication, model size and device inference separately.

Abstract

Federated Learning (FL) is a promising technique for the collaborative training of deep neural networks across multiple devices while preserving data privacy. Despite its potential benefits, FL is hindered by excessive communication costs due to repeated server-client communication during training. To address this challenge, model compression techniques, such as sparsification and weight clustering are applied, which often require modifying the underlying model aggregation schemes or involve cumbersome hyperparameter tuning, with the latter not only adjusts the model's compression rate but also limits model's potential for continuous improvement over growing data. In this paper, we propose FedCompress, a novel approach that combines dynamic weight clustering and server-side knowledge distillation to reduce communication costs while learning highly generalizable models. Through a comprehensive evaluation on diverse public datasets, we demonstrate the efficacy of our approach compared to baselines in terms of communication costs and inference speed.

Read more ↗
How it works

FedCompress

01

Learn task and compression together

Each client minimizes cross-entropy plus a weight-clustering penalty. The local warm-up uses β=0 before enabling clustering with β=1.

Lk=Lce+βLwc(θk,μ,C)

Equation 1, PDF page 3. μ denotes learnable centroids; C is their count.

02

Restore clusters after aggregation

Keep the underlying aggregation rule. Then optimize a clustered student to match the temperature-scaled teacher outputs on unlabeled auxiliary data held by the server.

Ls=LKL(pT∥p)+βLwc

Equation 2, PDF page 4, with model arguments abbreviated. The KL term includes the paper’s temperature scaling.

03

Measure representation diversity

Normalize the singular values of local embeddings and compute their effective rank. This is an unlabeled proxy for representation quality, not a generalization guarantee.

E=exp(−∑jrjlogrj)

Dynamic weight-clustering section, PDF page 4. r is the normalized singular-value spectrum; the implementation description adds a small stability constant.

04

Use the score to adjust capacity

Start with a small cluster count and increase it when score progress stalls. The prose uses a three-round window and patience, with an optional maximum cluster budget.

PDF page 4. This describes the intended schedule; Appendix A contains notation differences and is not an independently verified implementation.

Method details in the paper ↗

Original paper figures & sources
FedCompress diagram showing local training with clustered weights, server aggregation, self-compression through teacher-student distillation on out-of-distribution data, and dynamic adjustment of cluster counts.Enlarge
Weight clustering compresses client uploads. After aggregation, server-side distillation restores a clustered global model for the return trip, while a representation-quality score adjusts the number of clusters. Figure 1 in the public preprint
Evaluation

Results

Recompress after aggregation

CIFAR-100 · ResNet-20 · 20 clients · 20 rounds · reduction relative to FedAvg

Communication reduction (×) ↑ Higher is better

FedZip
Communication reduction (×): 1.94
FedCompress without server self-compression
Communication reduction (×): 1.02
FedCompress
Communication reduction (×): 3.80

Server recompression lifts communication reduction from 1.02× to 3.80×; CIFAR-100 accuracy loss is 1.88 pp.

Paper ↗

Savings across five tasks

20 clients · 20 rounds · accuracy mean of 2 trials

Communication savings and accuracy cost. 20 clients, 20 rounds, ten client epochs and ten server self-compression epochs per round. Accuracy is averaged over two trials. Δ accuracy is percentage points relative to FedAvg; CCR and MCR are reduction factors, higher is better.
DatasetFedCompress Δ accuracy (pp)Communication reduction (×)
CIFAR-10−1.834.53
CIFAR-100−1.883.80
PathMNIST−1.724.79
SpeechCommands−0.425.04
VoxForge−0.315.41

3.80–5.41× less communication accompanies 0.31–1.88 pp accuracy loss; audio tasks have the smallest losses.

Paper ↗
Reference

Cite this work

BibTeX
@inproceedings{tsouvalas2024fedcompress,
  title = {Communication-Efficient Federated Learning through Adaptive Weight Clustering and Server-Side Distillation},
  author = {Vasileios Tsouvalas and Aaqib Saeed and Tanir Ozcelebi and Nirvana Meratnia},
  booktitle = {ICASSP 2024 - 2024 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP)},
  year = {2024},
  pages = {5805--5809},
  doi = {10.1109/ICASSP48485.2024.10447174},
  url = {https://arxiv.org/abs/2401.14211},
  eprint = {2401.14211},
  archivePrefix = {arXiv}
}

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