# Reliable Semantic Communication System Enabled by Knowledge Graph
## 1 Introduction  
In recent years, wireless communication technology has developed rapidly, bringing great convenience to human life. Fifth-generation (5G) wireless communication technology has played an important role in smart cities, autonomous driving, telemedicine, and other fields [1]. However, with the gradual increase in the communication rate, the explosive growth of data has created enormous challenges for wireless communication technology [2]. According to the forecast from the International Telecommunication Union (ITU), the annual growth rate of the global mobile data stream will reach up to 55% by 2030 [3]. Moreover, the transmission rate of existing communication technologies has gradually approached the Shannon capacity [4], which cannot meet the continuously growing communication demands in the future 6G era. In the future, the 6G communication system will play an important role in remote holography [5], digital twin [6], and other application fields. Therefore, the sixth-generation wireless communication system needs to provide an ultra-high peak rate, ultra-large user experience rate, and ultra-low network latency, which will consume more limited available spectrum and power and bring huge challenges to communication technology. Semantic communication is one of the effective techniques used to overcome these challenges [7]. Semantic communication, as a revolution against traditional communication, is a new communication paradigm [8]. The concept of semantic communication was first proposed by [PERSON] (1949) [9]. After [PERSON] (1948) put forward the classical information theory [4], [PERSON] proposed that communication should be divided into three different layers, namely the technical layer, semantic layer, and effectiveness layer. The technical layer represents traditional communication, focusing on \"how to accurately transmit communication symbols\". The semantic layer focuses on \"how to accurately convey the meaning of communication symbols\"; the effectiveness layer focuses on \"how the received meaning effectively affects the receiver's behavior\". Compared with traditional communication, semantic communication aims to reduce the uncertainty of message understanding between the transmitter and the receiver. Moreover, semantic communication mainly transmits semantic-relevant information, which greatly reduces the amount of redundant data. Therefore, semantic communication is a suitable technology (against the scenarios) with limited communication bandwidth and a low signal-to-noise ratio (SNR) [10; 11]. However, some fundamental problems of semantic communication have not been effectively solved. One of them is semantic representation, which limits the development of semantic communication [7]. Regarding semantic representation--existing research studies tend to use transmitted content features to represent the semantics. This representation lacks human language logic and cannot be interactive verification with human understanding [12]. To solve this problem, we considered using the knowledge graph instead of features to represent semantics. The knowledge graph can decompose text into multiple semantic units without losing semantics [13], ensuring the accuracy of semantic representation. The basic structure of the knowledge graph is a triplet in the form of an \"entity-relation-entity\" [13]. From the linguistic point of view, a single entity may have multiple types of semantic information. The specific semantic information can be determined after a relationship is formed between entities, so the triplet in the knowledge graph can be regarded as the smallest semantic symbol. There have been some research studies exploring the relationship between the knowledge graph and semantics. [PERSON] et al. (2019) proposed that the knowledge graph was the next-generation infrastructure for semantic scholarly knowledge [14]. [PERSON] (2021) proposed that the knowledge graph could help with semantic category prediction [15]. [PERSON] et al.