Sharif Digital Repository

For a Rayleigh fading full-duplex decode-and-forward relay channel, we analytically derive optimum power allocation schemes subject to individual power constraints for the source and the relay. The optimization problem is taken over the source power and the relay power. It is proven that the optimization problem is concave for this scenario, and optimum power allocations are derived in a closed-form. Finally, the implications of the theoretical results are discussed through the graphs  

In this letter, array null steering is formulated as a sparse recovery problem. In addition, a novel null steering scheme for large arrays by perturbing only a few elements is presented. To achieve this goal, compressed sensing (CS) is used to exploit the sparsity of the perturbed elements. The advantages of the proposed scheme are a significant reduction in hardware cost and lower power consumption, as well as less aging of the elements and faster response. Simulation results show that the CS-based method could be efficiently used to generate wide nulls using at least two elements. The interference rejection ratio achieved by the proposed method is 10-20 dB better than the existing... 

A new method of spatial filtering in high-order finite volume methods is presented and assessed. The base of this method is to filter face-averaged variables (fluxes) and then the recovery of cell-averaged ones. Two kinds of filtering method are proposed. The first kind is highly dissipative and appropriate for the numerical regions that need high dissipation, e.g. sponge zones. The second kind, on the other hand, is a precise method and hence is suitable for applying the high-order finite difference filters to the finite volume methods. Applying high-order finite difference filters directly to the high-order finite volume methods without using the proposed method causes stability problems... 

In this paper, we investigate the achievable energy efficiency of cognitive radio networks where two main modes are of interest, namely, spectrum sharing (known as underlay paradigm) and spectrum sensing (or interweave paradigm). In order to improve the energy efficiency, we formulate a new multiobjective optimization problem that jointly maximizes the ergodic capacity and minimizes the average transmission power of the secondary user network while limiting the average interference power imposed on the primary user receiver. The multiobjective optimization will be solved by first transferring it into a single objective problem (SOP), namely, a power minimization problem, by using the... 

In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communications reliability with Base Station (BS). For combating Multiple-Access Interference (MAI) as well as transferring complexity and spatial processing from the mobile terminals to the transmitter of BS, multiuser transmitter precoding is considered. In addition to multiuser precoding based on Minimum Mean-Square Error (MMSE) criterion for mitigating MAI, the proper transmission power control strategy under a fixed total power constraint is proposed and analyzed. Compared with... 

In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA), where a set of Mobile Terminals (MT) are cooperating with the purpose of improving their downlink communications reliability with the Base Station (BS). In order to achieve the spatial diversity, a new cooperation scenario is proposed. Afterward, in addition to multiuser precoding, Maximum Ratio Combining (MRC) according to the Maximum Signal to Noise Ratio (MSNR) criterion at the destination is investigated. Then, the optimal transmission power control strategy under a fixed total power constraint is illustrated and analyzed. Compared with equal transmission power assignment where BS... 

In this letter, we surpass the jamming effect and also estimate the jamming channel state information by using Kalman filtering (KF) approach. Furthermore, we design a closed-form beamforming weight for maximizing the achievable rate subject to the condition that the total relays power transmission would be below a predefined threshold level, which is formulated as a Quadratically Constrained Quadratic Program (QCQP). Simulation results show efficient performance of the proposed method for different destruction powers of jammer by achieving the Cramer Rao Lower Bound (CRLB). IEEE  

In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communications reliability with the Base Station (BS). For combating Multiple-Access Interference (MAI) as well as transferring complexity and spatial processing from the mobile terminals to the transmitter of BS, multiuser transmitter precoding is considered. In addition to multiuser precoding based on Minimum Mean-Square Error (MMSE) criterion for mitigating MAI, the proper transmission power control strategy under a fixed total power constraint is proposed and analyzed. Compared with... 

A single cell downlink scenario is considered where a multiple-antenna base station delivers contents to cache-enabled user terminals. Using the ideas from multi-server coded caching (CC) scheme developed for wired networks, a joint design of CC and general multicast beamforming is considered to benefit from spatial multiplexing gain, improved interference management and the global CC gain, simultaneously. The proposed multicast beamforming strategies utilize the multiantenna multicasting opportunities provided by the CC technique and optimally balance the detrimental impact of both noise and inter-stream interference from coded messages transmitted in parallel. The proposed scheme is shown... 

In this letter, we surpass the jamming effect and also estimate the jamming channel state information by using the Kalman filtering approach. Furthermore, we design a closed-form beamforming weight for maximizing the achievable rate subject to the condition that the total relays power transmission would be below a predefined threshold level, which is formulated as a quadratically constrained quadratic program. Simulation results show the efficient performance of the proposed method for different destruction powers of the jammer by achieving the Cramér-Rao lower bound. © 1997-2012 IEEE  

In this paper, an adaptive channel estimation algorithm is proposed for the multi-user robust relay beamforming problem. We propose a norm-bounded channel uncertainty model for all of the channels. We employ the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF) for joint estimation of channel coefficients and beamforming weights, and propose a Markov model for source-relay and relay-destination channels as well as the beamforming weights in the relays. The channel coefficients and bemforming weights are shown to be well-estimated in order to minimize the total relays power transmission subject to worst-case signal to interference and noise ratio (SINR) criterion at each... 

In this paper, we study the secrecy throughput in a massive Multiple-Input-Multiple-Output (MIMO) full-duplex wireless powered communication network (WPCN). The network consists of a massive MIMO base station (BS) and two groups of single- antenna sensor nodes which harvest energy from the BS. The first group, referred to as information transmitters (ITs), use the harvested energy to transmit information back to the BS; the second group, referred to as energy receivers (ERs), use the harvested energy for non- transmission related operations. We consider a two-slot protocol. In the first time slot, all nodes harvest energy from the BS. In the second slot, ITs transmit information to the BS,... 

In the case that phased array systems are not capable of attenuating interferences, Radio Frequency (RF) front-ends and Analog Digital Converters (ADCs) with a large dynamic range are required to avoid saturation of the receiver. This leads to a higher power consumption. In this paper, employing N-path circuits in Mixer-First receivers, a novel method is introduced in which spatial and frequency blockers are eliminated right before entering the system on the antennas input. In fact using this technique, adjustable spatial notch filter and band-pass frequency filter are implemented to suppress spatial and frequency interferences. The proposed method enhances the robustness and effectiveness... 

In this letter, we use G/T as a figure of merit to evaluate the performance of time-modulated arrays (TMA). The noise performance of a receiver, which is periodically switched on and off, is quite different from that of a conventional receiver. We analytically investigate the noise performance of a TMA. Based on this analysis, the figure of merit, G/T, of the TMA structure is investigated, including the details of the receiver hardware. Moreover, the G/T of the TMA is compared with that of a phased array. The comparison indicates that the TMA structure provides the same or even better performance compared to a phased array system, which demonstrates the capability of TMA in providing... 

In this paper, we study the secrecy throughput of a full-duplex wireless powered communication network (WPCN) for Internet of Things (IoT). The WPCN consists of a full-duplex multiantenna base station (BS) and a number of sensor nodes. The BS transmits energy all the time, and each node harvests energy prior to its transmission time slot. The nodes sequentially transmit their confidential information to the BS, and the other nodes are considered as potential eavesdroppers. We first aim to optimize the sum secrecy throughput of the nodes. The optimization variables are the duration of the time slots and the BS beamforming vectors in different time slots. The optimization problem is shown to... 

In this paper, it is shown that an optimum coupling between massive MIMO elements improves the SNR for each user in 5G downlink mode. It is assumed that a massive MIMO base station with 64 compact antennas with sub-wavelength spacing (0.37λ) serves 8 user equipments. With proper design of antennas couplings, the mean received SNR of users improves from 4 to 7 dB. Different coupling values are implemented for a sample patch antenna at 28 GHz with a slot on substrate between adjacent patch elements to control the element coupling. The whole system is simulated in MATLAB, with 5G millimeter-wave channel characteristics and OFDM modulation  

A phase-coherent technique for multiple all-digital phase-locked loops (ADPLLs) is presented and developed in this paper to target a 57-63-GHz multiple-input multiple-output (MIMO) transmitter (TX) with a digital beam-steering capability. The ADPLL TX chains are first fabricated in nanoscale CMOS and then time-synchronized and frequency-phase locked by a field-programmable gate array (FPGA) evaluation board. The calibration approach for phase alignment is carried out using a cancellation method to acquire the out-of-phase state within two ADPLLs. The accuracy of beam steering and phase alignment is investigated and analyzed based on a time-domain model for ADPLL to consider the impact of... 

In this paper, we investigate the secrecy throughput for a full-duplex wireless powered communication network. A multi-antenna base station (BS) transmits energy towards nodes all the time and each node harvests energy prior to its transmission time slot. Nodes sequentially transmit their confidential information to the BS in presence of other nodes which are considered as potential eavesdroppers. We derive the secrecy rate and formulate the sum secrecy throughput optimization of all nodes. The optimization variables are the time slot duration and the BS beamforming during different transmission phases. The problem is non-convex and non-trivial. We propose a suboptimal approach in which the... 

In this paper, an analytical and low cost computational antenna array beamforming method in the presence of mutual coupling has been proposed. Mutual coupling effects is taken under consideration through the induced EMF method and the concept of active element pattern. After establishing the corresponding optimization problem, the desired beamformer is obtained through solving a convex optimization. At the end, the 3D arrays of half-wave dipole elements, of different geometries are compared based on the SIR criterion  

A single cell downlink scenario is considered, where a multiple-antenna base station delivers contents to cache-enabled user terminals. Depending on the available degrees of freedom, several multicast messages are transmitted in parallel to distinct subsets of users. In the multicast beamformer design, we restrict ourselves to linear receiver implementation, which does not require successive interference cancellation unlike in the more optimal baseline scheme. With a small loss in performance, the complexity of both the receiver and transmitter implementation can be significantly reduced. © 2018 IEEE