Search

Resource sharing and management can significantly improve the performance and spectral efficiency of wireless systems. In power domain non-orthogonal multiple access (NOMA) systems, users share a common bandwidth for simultaneous data transmission and therfore, the spectral efficiency of the system will be improved at the expense of increased complexity. Provided proper power allocation, it is possible to detect symbols at receivers. In this paper, the downlink of a cellular system is considered where a base station (BS) communicates with two users using NOMA with the assistance of a decode-and-forward (DF) relay. In the proposed scheme, receivers combine received signals from direct and cooperative links, and decode symbols by employing successive interference cancellation (SIC). The bit error rate (BER) performance of the proposed scheme is analyzed and the optimal power allocation is also derived through a Min-Max optimization, and a closed form approximation solution is proposed for BPSK modulation. Furthermore, it is proved that the proposed receiver achieves full diversity order for all users for proper choice of power allocation. Simulation results also corroborate BER and diversity analysis.

In this paper, we theoretically investigate the impact of power allocation for subcarriers on the bit error rate (BER)performance of a non-orthogonal variable multi-band carrier-less amplitude and phase modulation (m-CAP)scheme within the contest of visible light communications. We consider subcarriers with different bandwidth as well as sub-carrier with overlapping in order to efficiently utilize the passband region of the system frequency response for data transmission. We show that, for the proposed scheme the average BER performance is improved by up to 20% compared to the conventional m-CAP system.

In this study a novel biodegradable edible film based on Alyssum homolocarpum seed gum (AHSG) was fabricated and characterized. Glycerol at three levels (25, 35, and 45% based on dried AHSG) as plasticizer were added. The microstructure and barrier, electromagnetic, mechanical, and thermal properties of the film were characterized. Results showed that permeability to both oxygen and water vapor, increased as the plasticizer content increased from 25 to 45%. The mechanical properties of AHSG films were comparable to those of polysaccharide films. Results showed that the glycerol content significantly decreased the glass-transition temperature of the film. The color measurement indicated that increasing the plasticizer content augmented the b* and L* values. Results of the field emission scanning electron microscopy revealed a uniform and smooth surface morphology and an absence of phase separation among the film compositions. The findings demonstrated that AHSG has the potential to fabricate edible films with enhanced quality characteristics.

Multiple Accesses Broadcasting (MABC) is a spectral efficient protocol in two-way relay channel (TWRC). The drawback of this protocol in decode-and-forward (DF) mode is decoding complexity at the relay's side. Erroneous decoding at the relay can bring about error propagation that leads to performance degradation in all of the relay networks operating in the DF mode. In this paper, we propose ML detection at the multiple antenna relay. With analytical investigation, we prove that this decoding rule can achieve full diversity order at the MAC phase of the MABC protocol. Then, we propose a new beamforming algorithm named as “Channel Alignment” and show that the proposed algorithm will result in better performance compared with the well-known MAX-MIN antenna selection method while it has full diversity order at the BC phase of the MABC protocol. The analytical results are verified through simulations and the performance of our proposed method is also compared with another method.

Transmission in frequency selective channels has some challenges due to the generated ISI which significantly deteriorates the performance of the system; hence, most of the proposed methods in literature for flat fading cannot be established in frequency selective conditions. Filter and forward strategy was proposed in AF protocol for combating the ISI in frequency selective channels. In this paper, we have proposed filter and forward strategy in DF relay networks which consists of a multi-antenna relay and destination, and with considering MMSE criterion, we have calculated the optimum filter coefficients at relay and destination. We also have verified our proposed method with simulation and compared it with some other works in literature.

In this paper, we consider adaptive quadratic amplitude modulation (QAM) for a cooperative network consists of a source, one decode-and-forward (DF) relay and a destination which are single antenna systems. For increasing the spectral efficiency of the system, we use adaptive modulation method for data transmission. We propose a new adaptive modulation scheme which has less complexity than available schemes. Then, we analyze average spectral efficiency (ASE), average bit error performance (ABEP) and outage probability of the proposed scheme. Computer simulation results corroborate our theoretical relations; furthermore, it shows that our proposed scheme has the same performance as maximum spectral efficiency scheme (MSES) with much lower complexity and has better performance than some other schemes.

This paper considers joint power and subcarrier allocation on the uplink OFDMA-based cooperative cognitive networks. We propose three schemes to maximize sum-capacity of Primary Users (Ups) in a situation that Secondary Users (SUs) relay the data of PUs and achieve subcarrier from PUs. We investigate the optimization problem under PUs peak power constraint to avoid interference with other cells with lower complexity compared to other works. The greedy algorithm is also modified to improve active PUs in the network. Our simulation results show preference of cooperative mode than non-cooperative mode in many parameters.

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, specifically when the source-relay channel state information (CSI) is not available at the destination. In this paper, we investigate the SNR-based selection relaying scheme and present a closed-form expression for the end-to-end symbol error probability (SEP) of the system for M-PSK modulation. The optimal threshold which minimizes the end-to-end SEP and provides full diversity order is also presented in closed-form. In our analysis, we examine the error propagation scenario in detail and derive a closed-form expression for the SEP under this scenario. Numerical results demonstrate that the SNR-based selection relaying scheme by employing the optimal threshold, without using error detection codes that reduce the bandwidth efficiency, effectively mitigates the error propagation and significantly improves the diversity order.

We introduce an algorithm for blind adaptive multiuser detection of synchronous direct sequence code division multiple access (DS-CDMA) signals. This algorithm is based on the affine projection algorithm (APA). We first derive the algorithm for a single antenna at the receiver and then generalize it to the multiple antenna case at the receiver. Simulation results show that the proposed algorithm has lower misadjustment, an improved convergence rate, and superior bit error rate performance compared to existing conventional methods.

The importance of localization task has drawn much attention to location estimation and object tracking systems in wireless sensor networks. Many methods have been proposed to improve the location accuracy in which received signal strength (RSS) values of sensor nodes are used as an indicator of the distance between sensor node and the source node. Some of the previously proposed tracking algorithms are based on Kalman Filtering (KF) which makes us capable of tracking the location of a mobile node (MN). In this paper, the implementation and enhancement of a tracking system based on RSS indicator with the aid of an Extended Kalman Filter (EKF) is described and an adaptive filter is derived. The dynamic characteristic of channel requires considering the variations of path loss exponent of the space. Fast variations in the movement path of the source node can explicitly interrupt the performance of the localization because of inappropriate initial conditions. This imperfect behavior of the initially modelled EKF is improved and the simulation results are provided to assess the achieved enhancement. It is shown that MSE of the proposed algorithm is considerably lower than other modelled EKFs and that in presence of high measurement noise or with fewer sensor nodes this method clearly outperforms the conventional approach.

In this paper a multistatic radar system with n transmitters and one receiver is considered and several constant false alarm rate (CFAR) algorithms for detection are introduced. The decision statistics of the proposed detectors are the sum of the n largest returning signals in an array of N+n range cells. It is shown that the proposed decision statistic satisfies the CFAR condition and it is justified that the sum of the largest returning signals is the optimal statistic. The proposed CFAR detectors are simulated both in homogenous and non-homogenous backgrounds and their performances are compared with the performance of a monostatic radar of higher power. It is shown that a multistatic radar outperforms a monostatic radar under equal transmit power condition.