We consider a single-user, single-hop wireless communication system, in which data packets arrive at a data queue to be transmitted to a receiver over a block fading channel, privately from an eavesdropper. We assume that the eavesdropper listens to the transmitter over another independently fading channel and that the transmitter only has knowledge of the distribution of the eavesdropper's channel. We propose a joint secrecy rate, transmission, and admission controller based on a simple index policy that only relies on the distribution of the eavesdropper's channel rate. Given any arrival sample path, we show that our controller achieves the maximum possible data admission rate, while keeping the data queue stable as well as meeting an upper bound on the rate of secrecy outage, i.e., the fraction of data packets that are in part or fully decodable by the eavesdropper. While the solution is not unique, i.e., there are other schemes that can achieve the aforementioned performance, we show that our scheme also achieves a low queuing delay for the data packets enqueued at the data queue by striking the correct balance between direct secrecy encoding for data bits and secret key generation and utilization. To obtain this result, our transmission controller makes use of the secret key queue to smooth out the variations in the achievable secrecy rate of the associated fading wiretap channel.
We consider a single-user, single-hop wireless communication system, in which data packets arrive at a data queue to be transmitted to a receiver over a block fading channel, privately from an eavesdropper. We assume that the eavesdropper listens to the transmitter over another independently fading channel and that the transmitter only has knowledge of the distribution of the eavesdropper's channel. We propose a joint secrecy rate, transmission, and admission controller based on a simple index policy that only relies on the distribution of the eavesdropper's channel rate. Given any arrival sample path, we show that our controller achieves the maximum possible data admission rate, while keeping the data queue stable as well as meeting an upper bound on the rate of secrecy outage, i.e., the fraction of data packets that are in part or fully decodable by the eavesdropper. While the solution is not unique, i.e., there are other schemes that can achieve the aforementioned performance, we show that our scheme also achieves a low queuing delay for the data packets enqueued at the data queue by striking the correct balance between direct secrecy encoding for data bits and secret key generation and utilization. To obtain this result, our transmission controller makes use of the secret key queue to smooth out the variations in the achievable secrecy rate of the associated fading wiretap channel.
We consider a single-user secure data communication system. Data packets arriving at the transmitter are enqueued at a data queue to be transmitted to the receiver over a block fading channel, securely from an eavesdropper that listens to the transmitter over another independent block fading channel. Part of the data is secured by the available secrecy rate while the other part is encrypted by the key bits, enqueued at both the transmitter and the receiver. We first address two separate problems in this paper: (1) with an average power constraint, given any sample path of arrivals, how to admit the arrivals and allocate power such that the long term average secrecy rate is maximized and the maximum admission rate is achieved while the data queue is kept stable; (2) with infinite queue backlog, given any sample path of secrecy rate, how to control the data transmission rate and key generation such that a smooth transmission rate and then a small queueing delay are achieved. We propose a power controller, transmission controller and an admission controller based on simple index policies that do not rely on any prior statistical information on the data arrival process and channel conditions. We show that our controllers have a provably efficient performance and solve the above two problems simultaneously. Furthermore, for any given secrecy rate sample path and correspondingly admissible arrival, we provide a rate allocation policy which is sample-path queueing-delay optimal.
In this paper, we consider a single-user secure data communication system. Data packets arriving at the transmitter are enqueued at a data queue to be transmitted to the receiver over a block fading channel, securely from an eavesdropper that listens to the transmitter over another independent block fading channel. We address two separate problems, both of which involve the maximization of a long-term average utility, defined as a function of the number of secure packets transmitted in each time slot. We propose a transmission controller and an admission controller based on simple index policies that do not rely on any prior statistical information on the data arrival process. The former chooses a random key generation (and transmission) rate as well as the secure data transmission rate in each time slot. Part of the data is secured by the available secrecy rate while the other part is encrypted by the key bits, enqueued at both the transmitter and the receiver. The latter chooses the amount of data admitted by the transmitter to be enqueued in the data queue. We show that our controller pair has a provably efficient performance. Also, we illustrate via simulations that the use of a key queue reduces the queuing delay for the data packets, while serving packets that are admitted at the maximum admissible rate. To our best knowledge, this is the first work that addresses the queuing delay in the context of secrecy.
In recent years, the famous wiretap channel has been revisited by many researchers and information theoretic secrecy has become an active area of research in this setting. In this paper, we design a wireless communication system that achieves constant bit rate data transmission over a block fading channel, securely from an eavesdropper that listens to the transmitter over another independent block fading channel. It is well known that, the method of sending secure information using the binning techniques inspired by the wiretap channel fails to secure the information at times when the eavesdropper channel has favorable conditions over the main channel. This phenomenon is called secrecy outage. In our system, however, we exploit the times at which the main channel is favorable over the eavesdropper channel for us to be able to transmit some random secret key bits along with the data bits. These key bits are stored in a separate key queue at the transmitter as well as the receiver, and are utilized to secure data bits, whenever the channel conditions favor the eavesdropper. We show that, our system achieves a high performance at any given desired outage probability by jointly controlling the key queue and the transmit power. We show that the optimal power control involves a time sharing between secure waterfilling and channel inversion strategies and the key queue operates in the heavy traffic regime to achieve the maximum delay limited rate possible, under a small outage constraint. This work can be viewed as a first step in providing a framework that combines both information theory and queueing analysis for the study of information theoretic security.
In applications of wireless packet-oriented data networks, a special coding scheme, the hybrid automatic retransmission request (HARQ) exhibits high throughput efficiency by adapting its error correcting code redundancy to channel conditions. Motivated by the increasing importance of secure communication over wireless networks, we investigate secure packet communication based on HARQ over block-fading (BF) channels. More specifically, we consider two legitimate users communicating over a BF channel in the presence of a passive eavesdropper who intercepts the transmission through another independent BF channel. We assume that the transmitter can obtain a 1-bit ACK/NACK feedback from the receiver via a reliable public channel. Under this setting, we consider incremental redundancy (IR) and repetition time diversity (RTD) HARQ schemes based on rate-compatible Wyner secrecy codes from an information theoretic point of view. We study a good Wyner code sequence, with which the legitimate receiver can decode the message and the eavesdropper can be perfectly confused. For a given pair of reliability/secrecy outage probabilities, we derive an achievable secrecy throughput of HARQ protocols for block-fading channels. Finally, we illustrate numerically that HARQ can benefit both throughput and secrecy.
Due to the dynamic arrival of data packets and time-varying channel states, secure transmission opportunities will be wasted when there is no confidential message to transmit, and data packet transmission can be delayed while waiting for the next available secure transmission opportunity. In order to seize every precious secure transmission opportunity and reduce the data packet waiting time, we propose a secure transmission protocol in which the under-utilized secure transmission opportunities can be exploited to transmit key packets, and these key packets will encrypt the confidential messages in the subsequent transmissions. Following the above-mentioned principle, we first apply this protocol to a single-input single-output network, and optimally allocate the secure transmission opportunities for the key and data transmissions, such that the secrecy rate is maximized under the constraints of the minimum energy efficiency and queue stability requirements. In addition, the packet delay for the proposed protocol is investigated using a generating function approach and a closed-form expression of the packet delay is derived. Then, we extend our work to the multiple-input single-output network and utilize the key queue as well as the artificial noise to protect the confidential messages. Similarly, we also optimally allocate the transmission opportunities for the key and data transmissions to maximize the secrecy rate and study the data packet delay performance. Since all secrecy transmission opportunities are utilized in the proposed protocol, the full secrecy rate is achieved. Numerical results are demonstrated to verify the performance superiority of the proposed protocols when compared with the other key encrypted schemes in terms of the data packet delay and the secrecy rate.
Wireless systems are susceptible to eavesdropping as an unwelcome result of the broadcast nature of the wireless medium. Fortunately, the wireless medium also provides endowments including the temporal dispersion, the capability of signal superposition and other properties, to facilitate defending against eavesdropping. The focus of the thesis is to provide schemes for utilizing these properties at the physical layer and their performance analysis from an information-theoretic secrecy perspective. The work is based on Wyner's results on the wire-tap channel, in which the transmission between two legitimate users (Alice and Bob) is eavesdropped upon by Eve. The secrecy level is measured by the equivocation rate at Eve. The system performance is measured by the secrecy capacity. This is the maximum rate at which a message can be sent from Alice to Bob, while constraining the equivocation rate at Eve equal to the communication rate, and thus ensuring that Eve cannot deduce any useful information asymptotically. First, the scenario where a secret message needs to be delivered to the intended receiver within a given delay constraint and without the knowledge of the channel state information (CSI) at the transmitter is considered. In particular, hybrid automatic retransmission request (HARQ) protocols are revisited for a block-fading wire-tap channel via a joint consideration of channel coding, secrecy coding, and retransmission protocols. Two secure HARQ protocols: a repetition time diversity (RTD) scheme with maximal-ratio combining, and an incremental redundancy (INR) scheme based on ratecompatible Wyner secrecy codes are analyzed via an outage-based formulation. The throughput of RTD and INR protocols under probabilistic outage requirements is derived. Asymptotic analysis and numerical computations are given to demonstrate both the benefits of HARQ protocols and the tradeoff between reliability and confidentiality in delay-constrained communications. Second, the effects of interference on information-theoretic secret communication is considered. More specifically, the wiretap channel with a helping interferer (WT-HI) is proposed and studied. Here, an interferer, which does not know the confidential message, helps in ensuring the secrecy of the message by sending independent signals. Achievable secrecy rates and upper bounds on the secrecy capacity are given for both discrete memoryless and Gaussian channels. Interference has conventionally been regarded as a harmful phenomenon that leads to decreasing the rate and the reliability performance of wireless systems. In this work, it is shown that interference can be exploited to assist wireless secrecy. Lastly, the problem of secret key generation over fading channels, in which there exists an additional authenticated, public and error-free feedback channel from Bob to Alice, is considered. A key generation scheme consisting of a communication phase and a key-generation phase is presented. The communication phase is based on layered broadcast coding, which adapts the decoded rate at Bob to the actual channel state without requiring CSI available at Alice. The key-generation phase is based on the messages decoded by Bob after the communication phase and the public feedback. The achievable secrecy key rate and the optimal power distribution over coded layers for maximizing the secrecy key rate are characterized. Theoretical and numerical results show that the broadcast approach outperforms the single-level-coding based approach significantly, and hence demonstrate the role of introducing self-interference in facilitating secret-key generation over slowly fading channels when transmit CSI is not available.