Md. Zahurul I. Sarkar

Secrecy capacity of Nakagami-m fading wireless channels in the presence of multiple eavesdroppers

This paper is concerned with the transmission of confidential message through Nakagami-m fading wireless channel in the presence of multiple eavesdroppers. The eavesdroppers are mutually independent and the information is secure if it cannot be eavesdropped by any eavesdropper. Considering the problem of secret communications between two nodes over Nakagami-m fading channel where a number of eavesdroppers observes their transmissions through other Nakagami-m fading channels, we characterize the probability of non-zero secrecy capacity and secure outage probability to investigate the secrecy capacity in terms of secure outage probability. We also present a formulation of the ergodic secrecy capacity in the presence of multiple eavesdroppers.

Enhancing Security in Correlated Channel With Maximal Ratio Combining Diversity

In this correspondence, we consider a confidential communication through slow non-selective correlated Rayleigh fading channel, where a single antenna transmitter communicates at a pre-decided constant rate with a legitimate receiver in the presence of an eavesdropper. Both the legitimate receiver and eavesdropper are equipped with multiple antennas and employ maximal ratio combining (MRC) reception scheme. With the presence of channel diversity, we find the closed-form expressions for the probability of non-zero secrecy capacity and the outage probability of secrecy capacity in terms of channel parameters such as correlation coefficient and the ratio of main and eavesdropper channel gains that will be called average channel gain ratio (CGR). The analysis of secure outage performance with the MRC diversity scheme tells how the channel diversity enhances the secrecy capacity. We quantify the effect of antenna correlation on the probability of positive secrecy capacity and the secure outage probability. We also investigate how the target secrecy rate influences the effect of antenna correlation on the secure outage probability. Moreover, as a result of obtaining the closed-form expressions for the probability of positive secrecy capacity and the outage probability, it is insightful to see how the channel parameters affect the secure outage performance of the correlated channels.

On the Secrecy Mutual Information of Nakagami-m Fading SIMO Channel

In this paper, we consider the transmission of confidential message through non-identically and identically independent Nakagami-m fading single-input multiple-output (SIMO) channel in the presence of an eavesdropper. We are interested in protecting this message against eavesdropping i.e. the information is secure if it cannot be eavesdropped by any eavesdropper. Based on the problem of secure communications between transmitter and intended receiver over Nakagami-m fading channel where an eavesdropper observes their transmissions through another Nakagami-m fading channel, we derive the analytical expressions for the probability of non-zero secrecy mutual information, secure outage probability and ergodic secrecy mutual information of SIMO wireless communication systems over non-identically and identically independent Nakagami-m fading subchannels. Numerical results are presented and verified via Monte-Carlo simulation.

Outage Performance of MIMO Multiple Access Interference Channel with Cognitive Relay

In this paper, we consider a cognitive relay assisted multiple-input multiple-output (MIMO) communication scenario through Rayleigh fading channel where multiple primary and secondary users wish to communicate with two different receivers in the presence of a cognitive relay. We assume that secondary users transmit simultaneously with the primary users over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. We consider both the cases when cognitive relay is present or not and derive the expressions for the mutual information received at the primary and secondary receivers. We also present the closed form expressions for the outage probabilities and complementary cumulative distribution functions (CCDFs) of mutual information received at the primary and secondary receivers in the absence of cognitive relay. Our results show that with the help of a cognitive relay, not only both the primary and secondary users are able to communicate with their intended receivers compensating interferences created at their receivers, but also the outage performance of primary and secondary users are improved due to the additional diversity obtained via cognitive relaying.

Secure Communication through Nakagami-m Fading MISO Channel

We consider the problem of secret communication over Nakagami-m fading multiple-input single-output (MISO) broadcast channel, where transmitter sends messages to the destination users following two different transmission protocols. In the first transmission protocol, transmitter sends a confidential message to user 1, and user 2 acts as an eavesdropper. In this protocol, at first, we define the ergodic secrecy capacity for the full channel state information (CSI) case and then we consider the case of only main channel CSI at the transmitter. Finally, we define the secrecy capacity in case of open-loop spatial multiplexing transmission scheme and present the analytical expression for the lower bound of ergodic secrecy capacity. In the second transmission protocol, we consider the transmission of two independent messages to user 1 and user 2 with informationtheoretic secrecy, where each user would like to obtain its own confidential message in a reliable and safe manner. Under this communication scenario, an achievable secrecy capacity region is developed using secret dirty-paper coding scheme.

Secrecy capacity over correlated log-normal fading channel

This paper is concerned with the study of secrecy capacity for the log-normal fading channel in which the main channel is correlated with the eavesdropper channel. Perfect secrecy is achieved when the transmitter and legitimate receiver can communicate at some positive rate, while insuring that the eavesdropper gets zero bits of information. We consider the full channel state information (CSI) case, where the transmitter has access to both the main channel and eavesdropper channel gains. Under this assumption, we define the secrecy capacity of single-input single-output (SISO) log-normal fading channel and find the optimal power allocation at the transmitter that achieves the secrecy capacity. By analyzing the resulting secrecy capacity, we quantify the loss of secrecy capacity due to the correlation. We also find the closed-form analytical expression for the upper bound of secrecy capacity in terms of correlation coefficient which includes the independent case as a special one. The analysis of upper bound tells how the correlation coefficient and the ratio of main and eavesdropper channel gains affect the secrecy capacity.

Combined approach of zero forcing precoding and cooperative jamming: A secrecy tradeoff

We consider the problem of secret communication through cognitive relay assisted interference channels in which secondary user (SU) is allowed to transmit simultaneously with the primary user (PU) over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. We propose two cooperative jamming (CJ) schemes to improve the secrecy rate of cognitive interference channels, where the multiple antenna cognitive relay transmit weighted jamming signals to create additional interferences in the direction of eavesdropper with the purpose of confusing it. !n the first CJ scheme, transmitter has the knowledge of all the channel state information (CSI) including eavesdropper channel while in the second CJ scheme transmitter has no CSI of the eavesdropper channel. The proposed CJ schemes are designed to cancel out jamming interference at both the primary receiver (PR) and the secondary receiver (SR) maintaining interference at the PR under a certain threshold. CJ with full CSI enhances secrecy rate by employing zero forcing (ZF) precoding while CJ with partial CSI also combining with ZF precoding improves the secrecy rate by degrading the signal-to-interference plus noise ratio (SINR) at the eavesdropper. Our results show that a combined approach of ZF precoding with CJ scheme is more significant in improving secrecy rate of cognitive interference channels for both full CSI and partial CSI scenarios.

Error exponents for Rayleigh fading product MIMO channels

Along with the channel capacity, the error exponent is one of the most important information theoretic measures of reliability, as it sets ultimate bounds on the performance of communication systems employing codes of finite complexity. In this paper, we derive the closed-form expressions for the Gallagers random coding and expurgated error exponents for Rayleigh fading product multiple-input multiple-output (MIMO) channels under the assumption that there is no channel-state information (CSI) at the transmitter and perfect CSI at the receiver. From the derived analytical expressions, we get insight into an elementary tradeoff between the communication reliability and information rate for the Rayleigh fading product MIMO channels. Moreover, we can easily compute the necessary codeword length without the extensive Monte-carlo simulation to achieve predefined error probability at a given rate below the channel capacity. In addition, we derive the exact closed-form expressions for the ergodic capacity and cutoff rate based on easily computable Meijer G-function. The closed-form expressions for the error exponents, ergodic capacity and cutoff rate have also been derived for Rayleigh fading keyhole MIMO channels as the example of special case.

Aspect of security in the cognitive relay assisted interference channels

We consider the problem of secret communication through cognitive relay assisted interference channels where the secondary users are allowed to transmit simultaneously with the primary users over the same channel in the presence of an eavesdropper. At first, we investigate the effect of diversity in enhancing security of the cognitive interference channels with multiple relays. Then, the performance of cognitive relay beamforming system is optimized in such a way that the eavesdropper gets zero bits of information maintaining interferences at the primary receiver under a certain threshold. Finally, we characterize secrecy rate at the primary and secondary receivers compensating interferences using zero-forcing (ZF) precoding at the cognitive relay.

Error exponents for Orthogonal STBC in generalized-K fading MIMO channels

In this paper, we study the error exponent of generalized-K fading multiple-input multiple-output (MIMO) channels over Orthogonal Space-Time Block Codes (OSTBC). Error exponent sets ultimate bounds on the performance of communication systems employing codes of finite complexity and has been seen as one of the most significant information theoretic measures of reliability. In this paper, closed-form expressions of Gallagers random coding and expurgated error exponents for generalized-K fading MIMO channels over OSTBC are derived, assuming that there is no channel-state information (CSI) at the transmitter and perfect CSI at the receiver. Based on which, we gain valuable insight into the fundamental tradeoff between the communication reliability and information rate of the channel. The necessary codeword length to achieve predefined error probability at a given rate below the capacity of channel is identified. Moreover, we derive closed-form expressions for the cutoff rate, critical rate and expurgation rate.