We propose a new secure transmission scheme for uplink multiple-input single-output (MISO) orthogonal-frequency multiplexing (OFDM) systems in the presence of multiple eavesdroppers. Our proposed scheme utilizes the sub-channels orthogonality of OFDM systems to simultaneously transmit data and secret key symbols. The base station, Bob, shares secret key symbols with the legitimate user, Alice, using wiretap coding over a portion of the sub-channels. Concurrently, Alice uses the accumulated secret keys in her secret-key queue to encrypt data symbols using a one time pad (OTP) cipher and transmits them to Bob over the remaining sub-channels. if Alice did not accumulate sufficient keys in her secret-key queue, she employs wiretap coding to secure her data transmissions. We propose fixed and dynamic sub-channel allocation schemes to divide the sub-channels between data and secret keys. We derive the secrecy outage probability (SOP) and the secure throughput for the proposed scheme. We quantify the system's security under practical non-Gaussian transmissions where discrete signal constellation points are transmitted by the legitimate source nodes. Numerical results validate our theoretical findings and quantify the impact of different system design parameters.
We propose a new secure transmission scheme for uplink multiple-input single-output (MISO) orthogonal-frequency multiplexing (OFDM) systems in the presence of multiple eavesdroppers. Our proposed scheme utilizes the sub-channels orthogonality of OFDM systems to simultaneously transmit data and secret key symbols. The base station, Bob, shares secret key symbols with the legitimate user, Alice, using wiretap coding over a portion of the sub-channels. Concurrently, Alice uses the accumulated secret keys in her secret-key queue to encrypt data symbols using a one time pad (OTP) cipher and transmits them to Bob over the remaining sub-channels. if Alice did not accumulate sufficient keys in her secret-key queue, she employs wiretap coding to secure her data transmissions. We propose fixed and dynamic sub-channel allocation schemes to divide the sub-channels between data and secret keys. We derive the secrecy outage probability (SOP) and the secure throughput for the proposed scheme. We quantify the system's security under practical non-Gaussian transmissions where discrete signal constellation points are transmitted by the legitimate source nodes. Numerical results validate our theoretical findings and quantify the impact of different system design parameters.
Orthogonal frequency division multiplexing (OFDM) has been established as the preferred modulation choice for high-rate data transmission over dispersive channels, as it allows rejection of inter-symbol interference (ISI) and efficient utilization of the available spectrum. We address the issues of determining achievable secrecy rates and secrecy capacity for OFDM transmission in the presence of a generic eavesdropper. In doing so, we refrain from making the restrictive assumption made in previous works that the eavesdropper uses a standard fast Fourier transform (FFT)-based demodulator. First, the high SNR secrecy capacity under a total input power constraint is evaluated for both cyclic prefix and zero-padding suffix OFDM systems. It is shown that in both cases the result is sensibly lower than what we would get if the eavesdropper used an OFDM receiver. Then, optimal power allocation schemes are proposed for both types of OFDM systems and the secrecy rates are compared with results obtained by using existing power allocation methods described in the literature for parallel Gaussian wiretap channels and multiple-input multiple-output (MIMO) Gaussian wiretap channels.
This paper investigates artificial noise injection into the temporal and spatial dimensions of a legitimate wireless communication system to secure its transmissions from potential eavesdropping. We consider a multiple-input single-output (MISO) orthogonal frequency division multiplexing (OFDM) system in the presence of a single-antenna passive eavesdropper and derive both the secrecy rate and average secrecy rate of the legitimate system. It is assumed that the legitimate transmitter knows the full channel information of the legitimate transceivers but does not know the instantaneous channel state information of the passive eavesdropper. Closed-form expressions for the secrecy rate and average secrecy rate are derived for the asymptotic case with a large number of transmit antennas. We also investigate 1) the power allocation between the data and the AN; 2) the power allocation between the spatial and the temporal AN. Computer simulations are carried out to evaluate the performance of our proposed artificial noise scheme.
In this paper, the secure transmission strategy for a multi-input-single-output multi-eavesdropper system with coexistence of a secure user (Bob) and a normal user (NU) is investigated. The NU and Bob require normal and secure data transmissions, respectively, and thus, the stream for the NU can be exploited to confuse the eavesdroppers. To guarantee the security of Bob, artificial noise (AN) is also deliberately injected into the null space of Bob and NU. The power allocation among Bob, NU, and AN, as well as the wiretap code rates, is jointly optimized to maximize the effective secrecy throughput (EST), under the average throughput constraint of the NU and statistical channel state information (CSI) of eavesdroppers. Both non-adaptive and adaptive transmission schemes are proposed, based on the statistical and instantaneous CSI of the legitimate channels, respectively. An alternative optimization algorithm is proposed to obtain the optimal parameters. It is proved that the EST is a quasi-concave function of the secrecy rate and the power allocated to Bob, and for fixed wiretap code rates, the optimal power allocation is derived in a closed-form expression. Numerical results show that the EST increases with the increase in transmitting power and the number of transmit antennas, and decreases with the increasing throughput constraint of the NU. Improved EST can be achieved through injecting AN and concurrent transmission of Bob and NU.
In this paper, the resource allocation for multiuser wiretap Orthogonal Frequency-Division Multiplexing(OFDM) systems is investigated to improve the system power efficiency. In such a multiuser wiretap OFDM system, one legitimate transmitter (Alice), multiple legitimate receivers (Bobs), and one eavesdropper (Eve) are simultaneously considered. The time-domain artificial noise (AN) is firstly involved to guarantee the target secrecy rates of multiple Bobs. Different from the traditional sum secrecy rate maximization problem which may result in the unfair transition for Bobs with bad channel gains and more transmit power consumptions, a non-convex transmit power minimization problem is formulated to jointly optimize the power, subcarrier allocation and AN design, in which a target secrecy rate for each individual Bob is ensured. An iterative algorithm is further proposed to solve this power minimization problem by updating the subcarrier, power allocation and AN design alternatively. Numerical simulation results demonstrate the effectiveness of the proposal, including the improvements of system power efficiency and the fairness of multiple Bobs.
We investigate the physical-layer security of uplink single-carrier frequency-division multiple-access (SC-FDMA) systems. Multiple users, Alices, send confidential messages to a common legitimate base-station, Bob, in the presence of an eavesdropper, Eve. To secure the legitimate transmissions, each user superimposes an artificial noise (AN) signal on the time-domain SC-FDMA data symbol. We reduce the computational and storage requirements at Bob's receiver by assuming simple per-sub-channel detectors. We assume that Eve has global channel knowledge of all links in addition to high computational capabilities, where she adopts high-complexity detectors such as single-user maximum likelihood (ML), multi-user minimum-mean-square-error, and multi-user ML. We analyze the correlation properties of the time-domain AN signal and illustrate how Eve can exploit them to reduce the AN effects. We prove that the number of useful AN streams that can degrade Eve's signal-to-noise ratio is dependent on the channel memories of Alices-Bob and Alices-Eve links. Furthermore, we enhance the system security for the case of partial Alices-Bob channel knowledge at Eve, where Eve only knows the precoding matrices of the data and AN signals instead of knowing the entire Alices-Bob channel matrices, and propose a hybrid security scheme that integrates temporal AN with channel-based secret key extraction.
PHY-layer security is one of promising techniques for enhanced security and privacy protection in 5G communications. In this paper, the joint resource allocation and artificial noise (AN) design problem of multiuser wiretap orthogonal frequency-division multiplexing (OFDM) systems is investigated to improve the system secrecy rate and power efficiency, which can help to provide waveform design references for secure 5G communications. In such a multiuser wiretap OFDM system, one legitimate transmitter (Alice), multiple legitimate receivers (Bobs), and one eavesdropper (Eve) are simultaneously considered. The time-domain artificial noise is firstly involved to guarantee the target secrecy rates of multiple Bobs. Then a sum secrecy rate maximization problem with nonconvex integer nonlinear programming is formulated to jointly optimize the power, subcarrier allocation and AN design. To solve this tough problem with low computational complexity, a heuristical sub-optimal subcarrier allocation method is proposed, followed by the Lagrange dual method based joint power allocation and AN design scheme. Moreover, considering that sum secrecy rate maximization may result in unfairness for Bobs with bad channel gains, the transmit power minimization problem that ensures a target secrecy rate for each individual Bob is further addressed. An iterative algorithm is proposed to solve this power minimization problem by updating the subcarrier, power allocation and AN design alternatively. Numerical results demonstrate the effectiveness of the proposed algorithms.