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We study the secret key rate (SKR) of a multiple-input multiple-output (MIMO) continuous variable quantum key distribution (CVQKD) system operating at terahertz (THz) frequencies, accounting for the effects of channel estimation. We propose a practical channel estimation scheme for the THz MIMO CVQKD system which is necessary to realize transmit-receive beamforming between Alice and Bob. We characterize the input-output relation between Alice and Bob during the key generation phase, by incorporating the effects of additional noise terms arising due to the channel estimation error and detector noise. Furthermore, we analyze the SKR of the system and study the effect of channel estimation error and overhead. Our simulation results reveal that the SKR may degrade significantly as compared to the SKR upper bound that assumes perfect channel state information, particularly at large transmission distances., Comment: Submitted to IEEE Transactions on Communications

A receive diversity power line communication (PLC) system subject to correlated multipath channel fading and corrupted by additive Nakagami- $m$ background noise is considered. The optimal receiver employing a 4-ary imbalanced-phase-amplitude modulation (I-PAM) scheme for data transmission is obtained, using which closed form expressions for the symbol error probability (SEP) in the union bound sense and the SEP in the asymptotic sense at high signal-to-noise ratio (SNR) are derived. The diversity order of the system is found to be independent of the shape parameter of the additive noise. Furthermore, the optimal 4-ary I-PAM constellation minimizing the SEP at lower SNR values is computed numerically. The optimal 4-ary I-PAM constellation is found to be elliptical in shape as opposed to the traditional circular QPSK constellation generally employed in wireless communication systems. The effects of the correlation among the multipath channel gains and the shape parameter of the noise on the optimality of the considered constellation are also presented via numerical studies.

The letter proposes a receive diversity PLC system subject to uncorrelated Rayleigh multipath channels and corrupted by Nakagami- $m$ background noise employing $M$ -ary phase-shift keying modulation for data transmission. The estimates of the channel gains are obtained prior to data transmission by the minimum mean square estimation technique utilizing pilot symbol transmission. A suboptimal receiver structure employing the maximum likelihood decision rule is proposed for the PLC system which is further used to obtain the closed form and the asymptotic expressions for the symbol error probability of the system via a characteristic function approach. The improvement of the system performance with the increase in the channel diversity, the effects of the pilot-to-signal strength ratio, and the noise shape parameter $m$ of the background noise on the system performance are studied via numerical results providing various insights into the design of the PLC system with various system parameters.

A single-input single-output visible light communication (VLC) system corrupted by additive white Gaussian noise is considered in this letter. Closed-form expressions for the symbol error probability (SEP) for the system with perfect knowledge of the channel, and with least square estimate of the channel at the receiver, are derived. The dependence of the SEP on the ratio of the vertical and horizontal distances between the transmitter and the receiver, the semi-angle of the LED transmitter, and on the powers of the transmitted data and pilot symbols provide various insights to the design of the VLC system for reliable communication.

The cooperative device-to-device (D2D) network employing non-orthogonal multiple access (NOMA) is expected to play an important role in the next-generation wireless networks. In this work, the authors derive outage probability expressions of a cooperative NOMA D2D network which employs decode-and-forward relaying. A wireless link experiencing Nakagami-m fading is considered which is further assisted in the communication network by a wired link which is a powerline communication link and experiences Rayleigh fading. The outage analysis, shown for both the strong user and the weak user, is derived assuming that at the receiver there is perfect successive interference cancellation. Employing power division NOMA, optimum value for the coefficient of power allocation is obtained corresponding to the minimum probability of outage of the strong user. Furthermore, a range of the NOMA power allocation coefficient is provided for the communication link at the weak user which is between the wireless and the powerline link. Symbol error probability expressions are also derived for the strong and the weak users for the scenario when: i) both the wireless and the wired links are available for communication and ii) only the wireless link is available for communication.

This letter considers a single-input single-output powerline communication (PLC) system employing quadrature phase-shift keying (QPSK) modulation scheme under Rayleigh fading and Nakagami- $m$ noise environment. The series form expression of the symbol error probability (SEP) for the system is derived by considering the QPSK constellation as a combination of two orthogonal binary phase-shift keying constellations. Moreover, the optimal QPSK constellation minimizing the SEP under the constraint of given average transmission power is obtained. It is observed that the optimal solution of the QPSK constellation is elliptical in shape as compared to the traditional circular QPSK constellation. Further studies on the shape of the optimal elliptical QPSK constellation with varying shape parameter of the additive noise are carried out by numerical studies.

An $N$ -branch receive diversity power line communication (PLC) system subject to Rayleigh fading and corrupted by additive Nakagami- $m$ background noise is considered. A suboptimal maximal-ratio-combining (MRC), an optimal diversity combining, and a Gauss-optimal receiver are proposed for the PLC system. A closed form expression for the exact symbol error probability (SEP) and a union bound SEP expression are obtained for the proposed MRC and Gauss-optimal receivers, respectively, using a characteristic function (c.f.) approach for the system employing $M$ -ary phase-shift keying (MPSK) at the transmitter, conditioned to $mN$ being an integer. The asymptotic expression for the SEP obtained for the MRC receiver at high signal-to-noise (SNR) demonstrates that the diversity order of the system is independent of the shape parameter $m$ of the additive noise which is identical to the diversity order of the optimal and the Gauss-optimal receivers. Further, numerical studies justify the advantages of employing receive diversity to achieve superior SEP performance. The effect of increasing the diversity branches on the PLC system performance with varying $m$ and the power efficiency of the PLC system are also presented.

In this paper, we consider a hybrid smart grid communication network consisting of power line communication (PLC) at the transmitter side and the device-to-device (D2D) cellular communication on the receiver side which provides last mile connectivity. The PLC channel is assumed to experience Rayleigh fading and is corrupted by impulsive noise, and the D2D communication being a short range communication system, is assumed to experience Nakagami- $m$ fading with additive Gaussian noise. We propose a maximal-ratio combining (MRC) receiver for the considered hybrid smart grid communication system employing binary phase shift keying (BPSK) modulation at the transmitter and derive a closed-form symbol error probability (SEP) expression for the proposed receiver. The interference between the D2D links is assumed to be negligible for the tractability of the error probability analysis. Numerical results demonstrate the optimality of operating the D2D links at lower signal-to-noise ratio (SNR) values to overcome the effect of the impulsive PLC channel by utilizing diversity branches.

We propose a multiple-input multiple-output (MIMO) quantum key distribution (QKD) scheme for terahertz (THz) frequency applications operating at room temperature. Motivated by classical MIMO communications, a transmit-receive beamforming scheme is proposed that converts the rank-$r$ MIMO channel between Alice and Bob into $r$ parallel lossy quantum channels. Compared with existing single-antenna QKD schemes, we demonstrate that the MIMO QKD scheme leads to performance improvements by increasing the secret key rate and extending the transmission distance. Our simulation results show that multiple antennas are necessary to overcome the high free-space path loss at THz frequencies. We demonstrate a non-monotonic relation between performance and frequency, and reveal that positive key rates are achievable in the $10-30$ THz frequency range. The proposed scheme can be used for both indoor and outdoor QKD applications for beyond fifth-generation ultra-secure wireless communications systems., Comment: Revisions submitted to IEEE Communications Letters

This paper considers a device-to-device (D2D) cellular communication network with the wireless communication link among the devices and the base station (BS) modeled by the Rician fading and the wireless communication link between the devices modeled by Nakagami-m fading distribution. The devices and the BSs are assumed to be placed randomly as independent Poisson point processes with the devices experiencing interference from both D2D users and the cellular users. Using the techniques of stochastic geometry, series form expressions of the coverage probability of the cellular users are derived for the underlying interference-limited D2D cellular network. Furthermore, the optimal coverage values that maximize the energy efficiency of the network are also obtained analytically. The effect of the Rician factor and other system parameters on the performance of the system is studied by numerical results. The study of the variations of the optimal coverage analysis with the system parameters presented in this paper gives an insight into the design of cellular D2D communication networks.

The authors consider a single-channel power line communication (PLC) system in the presence of Middleton Class-A impulsive noise employing multi-level amplitude-shift keying (ASK) modulation at the transmitter and non-coherent detection at the receiver. An asymptotically optimal detector for the PLC system is obtained using a tight approximation of the noise statistics. The magnitude of the received symbol is obtained as the decision variable, whose statistics is utilised to derive a series expression for the symbol error rate (SER). An asymptotic expression for the SER at high signal-to-noise ratio (SNR) is also obtained which is further utilised to find the optimal ASK constellation minimising the SER. It is shown by numerical examples that the optimal solution is extremely close to the equally spaced ASK constellation set at high SNR. It is also observed that the SER variation of the system with the impulsive index of the noise validates the optimality of the proposed detector at high SNR.

Cooperative device-to-device communication with non- orthogonal multiple access (NOMA) employing additional power line communication technology is an effective way to increase the coverage and spectral efficiency of the next generation hybrid networks. In this paper, we present the outage analysis of a cooperative network with NOMA and decode-and-forward relaying assuming a direct link between the base station and the users. We consider a relaying network consisting of a wireless link for the strong user and the weak user having both wireless and a wired link which is assumed as a power line link. The wireless links are subjected to Nakagami-m fading and the power line link experiences Rayleigh fading. The outage probability expressions for both the strong and the weak users are derived assuming power division NOMA and perfect successive interference cancellation at the receivers. We also derive the optimal value of the NOMA power allocation coefficient minimizing the outage probability at the strong user and obtain the range of the power allocation coefficient between the power line and the wireless link at the weak user. Furthermore, numerical results validate the derived analytical results.

A noncoherent quadratic diversity reception system for multilevel amplitude-shift keying (ASK) signals in Rayleigh fading with different cases of the channel covariance matrix is considered. These include the important case of distributed antennas, which exhibit uncorrelated fading with distinct mean-squared channel gains (uncorrelated nonidentical fading) and weighted energy detectors, and the cases of exponentially correlated and uniformly correlated channels with equal mean-squared channel gains. For these cases, closed-form expressions for the symbol error probability (SEP) of the system are derived using the decision statistics obtained from the maximum likelihood receiver. The problem of determining the optimal amplitude levels that minimize the SEP under a total signal energy constraint is formulated and solved analytically for the high signal-to-noise ratio (SNR) configuration and numerically for the general configuration. For the high SNR configuration, it is shown that the optimal ASK levels should follow an approximately geometric progression. It is also observed that an equally spaced ASK constellation is not optimal in terms of achieving the minimum SEP. Numerical results are presented to highlight performance trends for channel gain imbalance and correlation.

This paper proposes a novel optimal receiver for an $N$ -branch receive diversity power line communication (PLC) system subject to Rayleigh fading and perturbed by Nakagami-m background noise. A Gauss-optimal receiver is obtained from the optimal receiver which is further utilized to derive a closed form expression for the symbol error probability (SEP) for binary phase-shift keying (BPSK) modulation using a characteristic function approach under the condition that mN is an integer. An asymptotic expression for the SEP at high signal-to-noise ratio (SNR) shows the diversity order of the PLC system to be independent of the noise shape parameter $m$ . Numerical studies demonstrate that the diversity order of the optimal receiver is preserved with the suboptimal receiver as well. Furthermore, the advantage of using multiple receive branches in terms of achieving better error performance and the effect of the shape parameter $m$ on the SEP of the suboptimal receiver are also presented.