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IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB)

Secure channel estimation method in TDD OFDM systems

Sen‐Hung Wang, Frank Po-Chen Lin, Chih–Peng Li

Published Jun 1, 2016• 2 citations
Publisher

Abstract

Physical layer security in wireless communication deals mainly with unauthorized users, eavesdroppers, and/or jammers. It is crucial for wireless network due to its broadcast nature and the channel state information (CSI) is easily acquired by unauthorized receivers. Thus, eavesdroppers can easily obtain information by utilizing the estimated CSI. In this paper, we propose a secure channel estimation method which includes two components, i.e., the designs of pilot signals and estimator for time division duplex orthogonal frequency division multiplexing systems. According to analyses, the CSI can be estimated successfully at the authorized receiver. Eavesdroppers cannot obtain the CSI even if they are close to the transmitter or the authorized receiver.

DOI
10.1109/bmsb.2016.7521979

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Physical layer security in wireless communication deals mainly with unauthorized users, eavesdroppers, and/or jammers. It is crucial for wireless network due to its broadcast nature and the channel state information (CSI) is easily acquired by unauthorized receivers. Thus, eavesdroppers can easily obtain information by utilizing the estimated CSI. In this paper, we propose a secure channel estimation method which includes two components, i.e., the designs of pilot signals and estimator for time division duplex orthogonal frequency division multiplexing systems. According to analyses, the CSI can be estimated successfully at the authorized receiver. Eavesdroppers cannot obtain the CSI even if they are close to the transmitter or the authorized receiver.
In this paper, we investigate a physical layer security technique in an orthogonal frequency-division multiplexing (OFDM) based wireless communications. In an OFDM system, the legitimate transmitter (Alice) can increase secrecy capacity with proper power allocation and/or bit loading methods for example by maximizing mutual information for own communication, i.e. between Alice and the legitimate receiver (Bob). The reason of increasing secrecy capacity is that the power allocation is suitable for the channel state between Alice and Bob but not suitable for the channel state between Alice and the eavesdropper (Eve). In this paper, we investigate a new approach where dummy data is exploited to achieve further improvement of secrecy capacity. Specifically, real data and dummy data are implemented in transmit OFDM symbols and secure pilot signals are employed to inform the receiver about their respective locations. Two secure pilot signal designs are introduced and in both of them it is designed that Bob can easily detect correct real data locations but not for Eve. One of them uses fake pilot signals that cause Eve to mistakenly select dummy data as real data. Numerical results will show that secrecy capacity performance of the first secure pilot signal based secure communication (not using fake signal) is slightly less than the performance of water filling algorithm. One significant advantage of the first secure pilot signal based secure communication is that the computational cost should be significantly less than the water filling algorithm. In addition, we will show that fake pilot signal based secure communication can provide significant gain in secrecy capacity while the computational cost is still small.
In this work, novel physical layer security (PLS) schemes are proposed for orthogonal frequency-division multiplexing (OFDM) to secure both data and pilots in multiple-input multiple-output (MIMO) systems. The majority of previous studies focus on only securing the data without considering the security of the pilots used for channel estimation. However, the leakage of channel state information (CSI) from a legitimate node to an eavesdropper allows the latter to acquire knowledge about the channel of the legitimate nodes. To this end, we propose adaptive and flexible PLS algorithms which can 1) secure data, 2) secure pilots, and 3) jointly secure both data and pilots. Particularly, minimum-phase all-pass channel decomposition is exploited, where the proposed algorithms use the all-pass component to provide security without harming the performance of the legitimate user. In the analysis for data security, we evaluate the secrecy under correlated and uncorrelated eavesdropping channels via closed-form bit error rate (BER) formulas. For pilot security, we analyze the estimated channel’s normalized mean squared error (NMSE) performance. The simulation results and theoretical analysis demonstrate that the proposed algorithms can effectively enhance the communication secrecy of the overall system.
We present a secure transmission method for orthogonal frequency division multiplexing (OFDM) signaling between legitimate nodes (Alice and Bob) communicating in time-division duplex (TDD) mode under an active attack. An active eavesdropper carries out pilot contamination attack in pilot phase by transmitting the pilot signal of the legitimate user and jamming attack in data phase. In the proposed method, Alice estimates the reciprocal channel between Alice and Bob by employing successive cancellation of the pilot contamination and interference from an active eavesdropper in pilot and data phases, respectively. We estimate reciprocal channels of legitimate users and eavesdropper. The precoder design at Alice from the estimated channels steers information towards Bob and artificial noise towards Eve in order to enhance the secrecy capacity of channel of the legitimate nodes. The simulation results show that the proposed method effectively estimates the channels of legitimate users and eavesdropper by removing the impact of contamination attack. Consequently, legitimate channel achieves higher secrecy capacity.
Wireless communication is highly susceptible to eavesdropping attacks where a malicious user can exploit the broadcast nature of the wireless signals to eavesdrop on confidential information. At the physical layer, there are multiple possible avenues to utilize the inherent randomness of the wireless transmission medium to achieve secure communication. One of the lucrative possibilities is to use the channel state information (CSI) to establish a secure communication link because it is vital in decoding the received signal at the transmitter. This technique is commonly referred to as discriminatory channel estimation (DCE) where the channel estimation performance is intentionally degraded at the eavesdropper as compared to the legitimate nodes to achieve secure communication.In this thesis, we capitalize on full-duplex (FD) transmissions to transmit the pilot signals to obscure the channel estimates from the eavesdropper. FD transmission severely limits the estimation performance at the eavesdropper while the legitimate nodes can acquire robust estimates. The secrecy of channel estimates from the eavesdropper provides a bandwidth-efficient security technique as the channel estimation requires less bandwidth than the data transmission. We have presented the achievable secrecy capacity analysis along with the simulation analysis to illustrate the performance improvements achieved by the proposed novel secure channel estimation. In this thesis, we also study the impact of artificial noise (AN) to improve the secrecy achieved by the use of FD transmission of pilot signals. For a strategically located eavesdropper, we have presented novel DCE techniques where AN signals are transmitted along with pilot signals using FD transmission. The AN signals confuse the nearby eavesdropper to establish a secure and robust communication link. We have also presented novel local adaptive power allocation algorithms, where each legitimate node performs power allocation in the absence of statistical channel characteristics regarding the eavesdropping channel. We have provided an in-depth simulation analysis including a location-based simulation analysis to illustrate that the secrecy performance achieved by the proposed DCE techniques. The simulation results indicate that the proposed DCE techniques achieve robust secure communication against a strategically located eavesdropper: while the other DCE techniques are unable to avoid the leakage of information to the eavesdropper
In recent years, physical layer security (PLS) has emerged as a promising concept to complement cryptography solutions. Many PLS schemes require perfect knowledge of the channel state information (CSI) at the transmitter. However, in practical cases, CSI is often imperfect due to channel estimation errors, noisy feedback channels and outdated CSI. In this paper, we study the impact of imperfect CSI on an adaptive PLS scheme that combines diversity with interleaving to provide security. Particularly, we derive the secrecy capacity expressions for the legitimate receiver and the eavesdropper's channels under imperfect CSI conditions. Numerical and theoretical simulations for secrecy capacity and bit error rate (BER) are carried out for the frequency-selective Rayleigh fading wiretap channel model. The results reveal the negative impact of imperfect CSI on the secrecy and BER performance of the single input single output (SISO) orthogonal frequency division multiplexing (OFDM) system. The analysis is done under both frequency division duplex (FDD) and time division duplex (TDD) modes.
Orthogonal frequency division multiplexing (OFDM) offers a promising solution for emerging high-data-rate services. Moreover, physical layer security was proposed as an alternative way to provide information security in wireless communications. In this work, we focus on improving physical layer security in OFDM systems. Our approach perturbs the effective channels observed at eavesdroppers by nonlinear distortion, while maintaining the same effective channel experienced at the intended receiver. At the transmitter, the perturbation on eavesdropper's effective channel is random and can be changed on a symbol-by-symbol basis based on the known original channel state information (CSI). At the intended receiver, no additional information or information exchange with the transmitter is required for data detection. We derive the results of the proposed scheme for the multiple-input single-output single-antenna-eavesdropper (MISOSE) wiretap channel. According to simulations, the proposed scheme can severely degrade the receiving performance at eavesdroppers and outperform the artificial-noise-based approaches in the performance measure of BER.