胡愛群

東南大學(xué)信息科學(xué)與工程學(xué)院,南京210096

物理層安全技術(shù)特別是無線物理層安全技術(shù),利用通信系統(tǒng)物理層的信息為通信提供安全保護(hù),在網(wǎng)絡(luò)安全、電子對(duì)抗中有著廣泛的應(yīng)用.它利設(shè)備指紋對(duì)設(shè)備身份進(jìn)行識(shí)別,進(jìn)而實(shí)施接入控制;利用信道特征為通信雙方建立對(duì)稱密鑰,進(jìn)而保護(hù)傳輸數(shù)據(jù)的安全;或者通過加大合法信道與竊聽信道的差異,使得敵手的竊聽變得更加困難.

近十年來,無線物理層安全技術(shù)的研究主要集中在:(1)無線發(fā)射機(jī)的設(shè)備指紋(又稱射頻指紋,RFF)的提取與識(shí)別方法研究;(2)基于無線信道互易性的密鑰生成方法研究;(3)與認(rèn)知無線電網(wǎng)絡(luò)相結(jié)合時(shí)帶來的用戶服務(wù)質(zhì)量(QoS)問題研究;(4)與波束賦形相結(jié)合的物理層安全技術(shù)研究等.更多的研究集中在前面兩點(diǎn).

在射頻指紋的研究方面,重點(diǎn)需要解決的問題是如何提高射頻指紋提取的穩(wěn)定性.發(fā)射機(jī)發(fā)射的信號(hào)到達(dá)接收機(jī)后,在接收機(jī)中提取發(fā)射機(jī)的射頻指紋.對(duì)射頻指紋穩(wěn)定性影響最大的是無線信道的多徑效應(yīng),尤其對(duì)于寬帶發(fā)射機(jī)而言更是如此.另外,如何增加射頻指紋可區(qū)分性的研究也在積極開展中.

在基于無線信道互易性的密鑰生成方面,如何增強(qiáng)信道互易性、提高密鑰生成速率是研究的重點(diǎn).其中的困難在于存在不同情況的信道,包括靜態(tài)信道、緩慢移動(dòng)信道和移動(dòng)信道.充分研究在不同情況下的信道互易性和隨機(jī)性,有助于改善密鑰生成的性能.目前已有開展主動(dòng)信道研究的報(bào)導(dǎo),即利用發(fā)射機(jī)和接收機(jī)的多天線配置,在靜態(tài)和緩慢移動(dòng)的信道情況下,模仿高速移動(dòng)通信信道,生成快速變化的信道特性.

本專欄組織了4篇論文,包括1篇綜述性論文和3篇不同技術(shù)方向的論文.

第一篇是綜述性論文《基于設(shè)備與信道特征的物理層安全方法》,全面總結(jié)了無線物理層安全技術(shù)的研究進(jìn)展和主要應(yīng)用.闡述了設(shè)備指紋的特點(diǎn)、關(guān)鍵技術(shù)、研究進(jìn)展以及可以進(jìn)一步研究的若干問題;闡述了基于信道特征的密鑰生成方法,保障密鑰的一致性、隨機(jī)性、防竊聽性等關(guān)鍵技術(shù),以及若干難點(diǎn)研究問題等,指出了無線物理層安全技術(shù)的四個(gè)未來應(yīng)用方向.

第二篇論文是《多徑傳輸環(huán)境下的射頻指紋估計(jì)方法》,重點(diǎn)研究了射頻指紋與無線信道特征的分離問題.論文基于多天線和多載波現(xiàn)代通信技術(shù),提出了基于主路徑分解的射頻指紋估計(jì)方法,通過重構(gòu)信號(hào)子空間來獲取主路徑中包含的發(fā)射機(jī)射頻指紋,通過仿真實(shí)驗(yàn)驗(yàn)證了方法的有效性,并給出了多徑環(huán)境下接收機(jī)天線數(shù)量的建議.

第三篇論文是《不同環(huán)境下無線信道密鑰生成性能研究》,呈現(xiàn)了三種無線環(huán)境下信道互易性的實(shí)驗(yàn)結(jié)果和密鑰生成情況,滿足讀者了解無線物理層密鑰生成的實(shí)際性能和可應(yīng)用性.

第四篇論文是《聯(lián)合考慮主用戶QoS和安全約束下認(rèn)知NOMA安全傳輸》,從另一個(gè)角度看待無線物理層安全技術(shù).分析了該技術(shù)運(yùn)用到認(rèn)知無線電網(wǎng)絡(luò)等多用戶環(huán)境時(shí),從功率分配的角度,如何分析主用戶與次用戶之間的服務(wù)質(zhì)量QoS的相互影響,為我們部署無線通信設(shè)施提供了有益的參考.

由于篇幅的原因,本專欄組織的內(nèi)容未能完全覆蓋無線物理層安全的所有方面,歡迎從事本方向研究的學(xué)者更多地向本刊投稿,進(jìn)行更多的學(xué)術(shù)交流.

The physical layer security technology,especially in the wireless field,exploits the inherent physical-layer information of the communication system to provide security protection for communication.It has been widely used in network security and electronic countermeasures.Based on the physical layer security,the device fingerprints are used to identify the device for access control,the channel characteristics are used to establish a pair of symmetric key for both parties to protect the security of transmitted data,or the noise is used to enlarge the channel condition gap to make the eavesdropping more difficult.

In the past ten years,research on wireless physical layer security technologies has mainly focused on the following topics,including

(1)Research on extraction and identification of device fingerprints(also known as radio frequency fingerprints,RFF)of wireless transmitters;

(2)Research on key generation based on the reciprocity of wireless channels;

(3)Research on user quality of service(QoS)issues when combined with cognitive radio networks;

(4)Physical layer security technology research combined with beamforming,etc.

More research has focused on the first two points.

In the research of RF fingerprints,the key problem is how to improve the stability of the extracted RFF features.After the signal transmitted by the transmitter reaches the receiver,the RFF of the transmitter is extracted from the received signal.The major impact on the stability of RF fingerprints is the multipath e ff ect of wireless channels,especially for broadband cases.In addition,some active e ff orts have been made to increase the distinguishability of RFF.

In terms of key generation based on wireless channel reciprocity,the focus of research is how to enhance channel reciprocity and increase key generation rate.The difficulty lies in the existence of different channels,including static channels,slow-moving channels,and mobile channels.Fully studying the channel reciprocity and randomness in different situations will help improve the performance of key generation.At present,there has been some reports of active channel research,which uses the multiple antenna con figurations of the transmitter and receiver to imitate high-speed mobile communication channels under static and slow-moving channel conditions to generate rapidly changing channel characteristics.

This column organizes 4 papers,including 1 review paper and 3 research papers with different technical directions.

In particular,the first one is a review paper“Research on Physical-layer Security Based on Device and Channel Characteristics”,which comprehensively summarizes the research progress and main applications of wireless physical layer security technologies. In the part of device fingerprints,it summarizes key technologies,research progress,and several issues worth studying in the future.For key generation methods based on channel characteristics,it illustrates some key technologies such as guaranteeing key consistency,randomness,and anti-eavesdropping properties,as well as several difficult problems for further study.The authors also point out four future application directions of wireless physical layer security technology.

The second paper is the“Radio Frequency Fingerprint Estimation in Multi-path Transmission Environment”,which focuses on the separation of RF fingerprints from the wireless channel.Based on the multi-antenna and multi-carrier modern communication technology,this paper proposes a method of RF fingerprint estimation based on the decomposition of the main path.The reconstructed signal subspace is used to obtain the RF fingerprint of the transmitter contained in the main path.The validity of the method is verified by simulation experiments and the results provide suggestions for the number of receiver antennas in a multipath environment.

The third paper is“On Key Generation Performance of Wireless Channel in Different Environments”,which presents the experimental results of channel reciprocity and key generation in three wireless environments,which satisfies the reader’s understanding of the performance and applicability of wireless physical layer key generation in real environments.

The fourth paper is“Secure Transmission in Cognitive NOMA Networks under QoS and Security Constraints of Primary User”,which studies wireless physical layer security technology from another perspective.When the technology is applied to multi-user environments such as cognitive radio networks,this paper analyzes the interaction of the quality of service(QoS)between the primary and secondary users from the perspective of power allocation.It provides a useful reference for the deployment of wireless communication facilities.

Due to the space limitation,the content of this column does not fully cover all aspects of wireless physical layer security.Scholars who are engaged in research in this direction are welcome to submit more papers to this journal for more academic exchanges.