A method of using random antenna switching (RAS) is proposed to guarantee the information security during the physical layer transmission. The method uses multiple antennas at the base station and a single antenna at the mobile terminal. The expected mobile terminal (target user) first transmits a training symbol which is used by the base station to estimate the channel. The base station then randomly selects several antennas to transmit each symbol. The weighting coefficients are obtained according to the estimated channel, which is similar to the distributed beamforming except that the magnitudes are random in this paper. Signals from all the selected antennas are finally superimposed in phase at the target user so that the maximum likelihood demodulation can be directly implemented. The RAS makes the channel for an eavesdropper change fast and randomly to prevent the eavesdropper from demodulating the signals. Simulation results show that the target user's bit error rate of RAS is lower with less transmission power than the traditional method of using random weighting coefficients, while the eavesdropper cannot correctly demodulate and hence the low probability of interception is achieved.
A method of using random antenna switching (RAS) is proposed to guarantee the information security during the physical layer transmission. The method uses multiple antennas at the base station and a single antenna at the mobile terminal. The expected mobile terminal (target user) first transmits a training symbol which is used by the base station to estimate the channel. The base station then randomly selects several antennas to transmit each symbol. The weighting coefficients are obtained according to the estimated channel, which is similar to the distributed beamforming except that the magnitudes are random in this paper. Signals from all the selected antennas are finally superimposed in phase at the target user so that the maximum likelihood demodulation can be directly implemented. The RAS makes the channel for an eavesdropper change fast and randomly to prevent the eavesdropper from demodulating the signals. Simulation results show that the target user's bit error rate of RAS is lower with less transmission power than the traditional method of using random weighting coefficients, while the eavesdropper cannot correctly demodulate and hence the low probability of interception is achieved.
A scheme based on projection operator is proposed to guarantee the information theoretical security in MIMO physical layer transmission.The transmitter has multiple antennas and is able to simultaneously transmit separately information bearing signal to the intended receiver and randomized interference to the eavesdropper in the projection space.An iterative algorithm of power allocation between them is given according to the secret channel capacity criteria.Based on the special statistical distributions of the adversary’s received signal,the indeterminacy of its blind deconvolution is proved.Numerical results indicate that the secret channel capacity of this scheme is enhanced with reduced bit error rate at the target user,while the eavesdropper can not demodulate correctly.
Wireless communication security can be enhanced by leveraging the characteristics of the physical (PHY) layer, where discriminatory scrambling can be employed at the symbol level to either improve the signal quality of the legitimate receiver or degrade that of the eavesdroppers. However, in the presence of multiple passive eavesdroppers with more antennas than the transmitter, the transmitted signals can still be reliably separated from random disturbances. To mitigate this challenge, we propose a two-dimensional vectorized secure transmission scheme. Unlike existing transmission schemes (where the same data symbol is sent over each antenna with a predesigned complex weight at a time), in the proposed scheme, a sequence of data symbols in a predefined order (named symbol vector) is first pre-superposed through pre-coding with a random complex matrix prior to been sent as a vector in parallel over each transmitting antenna at a time. As a result, physical randomness of the legitimate channel is introduced into the received signals at passive eavesdroppers in the pre-coding procedure. Moreover, to ensure that transmitted data symbols can be recovered in the right order, each symbol vector is sent repeatedly, according to the principle of maximum entropy. To ensure the intended receiver can recover the transmitted symbol vector, the random pre-coding matrices are selected such that a linear constraint imposed by the CSI of the legitimate channel is satisfied. In addition, an extended maximum likelihood (ML) detection method is developed for the desired receiver while the random pre-coding matrices are not required to be transmitted. We then analyze its security based on the signal detection theory to demonstrate that the intended receiver can recover the transmitted symbol vectors while the eavesdroppers are not capable of doing so. We also evaluate the performance of the proposed scheme to demonstrate its effectiveness.
The projection of the random multi-antenna weighted vector structured with spatial scrambling is of constant modulus on the main channel, Eavesdropper can take the advantage of multi-antenna to intercept private information. To solve this problem, we design a kind of physical-layer secrecy method based on the joint scrambling with spatial and frequency resource. Based on the parallel transmission nature of OFDM, we construct a random multiple antenna weighted vector in the each subcarrier, the projection of which on the main channel is equal to a dynamic reference variable. The legitimate user can correctly demodulate the receive signal by this reference variable obtained from the estimation of the reference subcarrier. Meanwhile, because of the difference between the main channel and eavesdropper channel, eavesdropper can't obtain the useful information. The simulation results show that, when the legitimate users can correctly demodulate the received signal, the eavesdropper can't intercept the private information using whether blind equalization or MUSIC-like method.
Recently, MIMO (multiple-input-multiple-output) physical layer secure transmission has attracted great attentions. However, current schemes cannot defend against the passive eavesdroppers with arbitrary number of antennas. To address this problem, in this work, we propose a practical physical layer MIMO secure communication scheme (PLSC) to defend against such an eavesdropper with arbitrary number of antennas. In the proposed scheme, the transmitter first independently generates a random binary sequence as the “key bits (KB)” to “encrypt” (XOR) the confidential information. After that, the transmitter sends the “encrypted information” over the wireless channel, along with mapping key bits to the legitimate receiver simultaneously. The key principle lies in that the KB information is coded in the indexes of the activated/non-activated antennas combination of the legitimate user. Then, the legitimate receiver first observes his/her activated antenna indexes to obtain the corresponding key bits. After that, he/she demodulates the “encrypted information” at the activated antennas, and finally “decrypts” (XOR) the confidential information by using the observed key bits. However, due to the uniqueness and independence of MIMO wireless channel, for any other eavesdroppers who suffer an independent channel from legitimate users, we prove that it cannot observe any information about KB from the received signals, regardless of how many antennas it has used. Consequently, without knowledge of KB, it cannot decrypt any information about the confidential information, too. The reliability and security of PLSC are theoretically demonstrated. The simulation and numerical results fully verified the validity and effectiveness of the proposed scheme.
In this paper, we propose a pseudo-random beamforming (PRBF) technique for improving physical-layer security (PLS) in multiple input multiple output (MIMO) downlink cellular networks consisting of a legitimate base station (BS), multiple legitimate mobile stations (MSs) and potential eavesdroppers. The legitimate BS can obtain available potential eavesdroppers’ channel state information (CSI), which is registered in an adjacent cell. In the proposed PRBF technique, the legitimate BS pseudo-randomly generates multiple candidates of the transmit beamforming (BF) matrix, in which each transmit BF matrix consists of multiple orthonormal BF vectors and shares BF information with legitimate MSs before data transmission. Each legitimate MS generates receive BF vectors to maximize the receive signal-to-interference-plus-noise (SINR) for all pseudo-randomly generated transmit beams and calculates the corresponding SINR. Then, each legitimate MS sends a single beam index and the corresponding SINR value of the BF vector that maximizes the received SINR for each BF matrix since a single spatial stream is sent to each legitimate MS. Based on the feedback information from legitimate MSs and the CSI from the legitimate BS to eavesdroppers, the legitimate BS selects the optimal transmit BF matrix and the legitimate MSs that maximizes secrecy sum-rate. We also propose a codebook-based opportunistic feedback (CO-FB) strategy to reduce feedback overhead at legitimate MSs. Based on extensive computer simulations, the proposed PRBF with the proposed CO-FB significantly outperforms the conventional random beamforming (RBF) with the conventional opportunistic feedback (O-FB) strategies in terms of secrecy sum-rate and required feedback bits.
We propose a novel attack that compromises the physical layer security in wireless systems with eavesdropper's channel state information at the transmitter side. This technique is based on the transmission of a slowly-varying random symbol by the eavesdropper during its uplink transmission, so that the equivalent fading channel observed at the base station (BS) has a larger variance. Then, the BS designs the secure downlink transmission under the assumption that the eavesdropper's channel experiences a larger fading severity than in reality. We show that this approach can lead the BS to transmit to Bob at a rate larger than the secrecy capacity, thus compromising the system secure operation. Our analytical results, corroborated by simulations, show that the use of multiple antennas at the BS may partially alleviate but not immunize against these type of attacks.