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.
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.
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.
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.
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.
In this paper, secure transmission of information over fading broadcast channels is studied in the presence of statistical queueing constraints. Effective capacity is employed as a performance metric to identify the secure throughput of the system, i.e., effective secure throughput. It is assumed that perfect channel side information (CSI) is available at both the transmitter and the receivers. Initially, the scenario in which the transmitter sends common messages to two receivers and confidential messages to one receiver is considered. For this case, the effective secure throughput region, which is the region of constant arrival rates of common and confidential messages that can be supported by the buffer-constrained transmitter and fading broadcast channel, is defined. It is proven that this effective throughput region is convex implying that time-sharing between any two viable transmission and power control strategies results in effective throughput values inside the region. Then, the optimal power control policies that achieve the boundary points of the effective secure throughput region are investigated and an algorithm for the numerical computation of the optimal power adaptation schemes is provided. Additionally, the throughput region achieved by time-division multiplexing of common and confidential messages is explored. Subsequently, the special case in which the transmitter sends only confidential messages to one receiver is addressed in more detail. For this case, effective secure throughput is formulated and two different power adaptation policies are studied. These power adaptation policies are compared with the opportunistic ones that are optimal in the absence of quality of service (QoS) constraints. It is shown that opportunistic schemes, in which data transmission with high rates and high power occurs only when the main channel is much better than the eavesdropper channel, are no longer optimal under buffer constraints, and the transmitter should send the data at a certain moderate rate and power even when the main channel strength is comparable to that of the eavesdropper channel to avoid buffer overflows.
We introduce opportunistic power control (OPC) as a physical-layer security technique to enable wireless communications with secrecy in fading channels, enabling secure communication in the presence of an eavesdropper. OPC is a scheme where the transmitter only transmits when the channel gain is above a certain threshold, and a larger modulation alphabet than necessary is employed to maintain a target spectral efficiency. When the transmitter does transmit, it transmits with less power due to the higher channel gain. This effect reduces the signal power received by the eavesdropper, inducing decoding errors for the eavesdropper and enhancing the secrecy. Hence, the secrecy improves as the threshold increases. However, since the transmitter does not always transmit, buffers are necessary at the transmitter and receiver to smooth out gaps in the transmission, introducing delay. A higher threshold results in a longer delay before that threshold is met. Due to the direct relationship between the threshold and the delay, there exists a tradeoff between secrecy and delay. We obtain a closed-form expression for the average achievable secrecy rate with OPC under Rayleigh fading and optimize over the target SNR to obtain the maximum average achievable secrecy rate. We then present numerical results to quantify the incurred delay. We find that with OPC, the secrecy improves with increasing delay, reaching the aforementioned maximum, beyond which, there is no benefit in secrecy nor in delay. We also find that communication with a positive average achievable secrecy rate is possible even when the eavesdropper channel is better than the main channel on average, and that for the maximum average achievable secrecy rate, there is an inverse relationship between the target spectral efficiency and the secrecy, and a direct relationship between the target spectral efficiency and the delay.