Hybrid Bit and Semantic Communications

TL;DR

HybridBSC addresses the deployment challenge of semantic communications by embedding semantic information into conventional bit transmissions within existing digital architectures. The approach uses a semantic encoder to produce $\mathbf S = T(\mathbf M_s; \boldsymbol{\alpha})$ and forms a hybrid data unit $\mathbf I = E(\mathbf S, \mathbf M_b)$ that is transmitted through standard bit pipelines, with semantic extraction at the receiver via $\hat{\mathbf S}$ and reconstruction $\hat{\mathbf M_s} = R(\hat{\mathbf S}; \boldsymbol{\gamma})$; channel equalization is incorporated as $\hat{\mathbf x} = (\mathbf h^H \mathbf h)^{-1} \mathbf h^H \mathbf y$. The semantic insertion/extraction algorithms rely on color-space transformation (RGB to YCbCr) and a DWT/ DCT/ SVD embedding scheme that modifies singular values with an insertion factor $\alpha$, enabling robust recovery under source coding and fading, with a 4-bit quantization $q=4$. Evaluations on MNIST/ USC-SIPI and real Pluto SDR experiments show that bit transmission remains competitive with JPEG-LDPC baselines while semantic transmission achieves high perceptual quality (PSNR/SSIM), even in real channels, demonstrating practical coexistence of semantic and bit information in standard OFDM transceivers. This work suggests a viable path to gradual adoption of semantic communications without disrupting current network protocols.

Abstract

Semantic communication technology is regarded as a method surpassing the Shannon limit of bit transmission, capable of effectively enhancing transmission efficiency. However, current approaches that directly map content to transmission symbols are challenging to deploy in practice, imposing significant limitations on the development of semantic communication. To address this challenge, we propose a hybrid bit and semantic communication system, named HybridBSC, in which encoded semantic information is inserted into bit information for transmission via conventional digital communication systems utilizing same spectrum resources. The system can be easily deployed using existing communication architecture to achieve bit and semantic information transmission. Particularly, we design a semantic insertion and extraction scheme to implement this strategy. Furthermore, we conduct experimental validation based on the pluto-based software defined radio (SDR) platform in a real wireless channel, demonstrating that the proposed strategy can simultaneously transmit semantic and bit information.

Figures (7)

• Figure 1: The structure of the proposed HybridBSC.
• Figure 2: The PSNR score versus SNR in AWGN channel.
• Figure 3: The PSNR score versus SNR in Rayleigh channel.
• Figure 4: The SSIM score versus SNR in AWGN channel.
• Figure 5: The SSIM score versus SNR in Rayleigh channel.