Communication-Efficient Hybrid Language Model via Uncertainty-Aware Opportunistic and Compressed Transmission

TL;DR

This paper introduces CU-HLM, a communication-efficient hybrid language model that reduces transmission overhead by transmitting only uncertain tokens, achieving significant throughput gains while maintaining high accuracy.

Contribution

The paper proposes a novel uncertainty-aware transmission strategy for hybrid language models, optimizing communication and computation efficiency with theoretical analysis and empirical validation.

Findings

Achieves up to 206× higher token throughput.

Skips 74.8% of transmissions with 97.4% vocabulary compression.

Maintains 97.4% accuracy despite compression.

Abstract

To support emerging language-based applications using dispersed and heterogeneous computing resources, the hybrid language model (HLM) offers a promising architecture, where an on-device small language model (SLM) generates draft tokens that are validated and corrected by a remote large language model (LLM). However, the original HLM suffers from substantial communication overhead, as the LLM requires the SLM to upload the full vocabulary distribution for each token. Moreover, both communication and computation resources are wasted when the LLM validates tokens that are highly likely to be accepted. To overcome these limitations, we propose communication-efficient and uncertainty-aware HLM (CU-HLM). In CU-HLM, the SLM transmits truncated vocabulary distributions only when its output uncertainty is high. We validate the feasibility of this opportunistic transmission by discovering a strong correlation between SLM's uncertainty and LLM's rejection probability. Furthermore, we theoretically derive optimal uncertainty thresholds and optimal vocabulary truncation strategies. Simulation results show that, compared to standard HLM, CU-HLM achieves up to 206$\times$ higher token throughput by skipping 74.8% transmissions with 97.4% vocabulary compression, while maintaining 97.4% accuracy.