Timeliness-Aware Joint Source and Channel Coding for Adaptive Image Transmission

Accurate and timely image transmission is critical for emerging time-sensitive applications such as remote sensing in satellite-assisted Internet of Things. However, the bandwidth limitation poses a significant challenge in existing wireless systems, making it difficult to fulfill the requirements of both high-fidelity and low-latency image transmission. Semantic communication is expected to break through the performance bottleneck by focusing on the transmission of goal-oriented semantic information rather than raw data. In this paper, we employ a new timeliness metric named the value of information (VoI) and propose an adaptive joint source and channel coding (JSCC) method for image transmission that simultaneously considers both reconstruction quality and timeliness. Specifically, we first design a JSCC framework for image transmission with adaptive code length. Next, we formulate a VoI maximization problem by optimizing the transmission code length of the adaptive JSCC under the reconstruction quality constraint. Then, a deep reinforcement learning-based algorithm is proposed to solve the optimization problem efficiently. Experimental results show that the proposed method significantly outperforms baseline schemes in terms of reconstruction quality and timeliness, particularly in low signal-to-noise ratio conditions, offering a promising solution for efficient and robust image transmission in time-sensitive wireless networks.