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    Publication date: Available online 29 May 2018
    Source:Physical Communication
    Author(s): Muhammad Basit Shahab, Soo Young Shin
    This paper comprehensively investigates the dynamics of user pairing and power allocation (UPPA) in non-orthogonal multiple access (NOMA). The focal point of this work is to explore the effects of UPPA on capacity and bit error rate (BER) of NOMA users, thereby understanding the tradeoffs involved when UPPA is performed. These tradeoffs facilitate the design of UPPA strategies to maximize system capacity and satisfy individual target data rates of users without exceeding their allowed BER upper bounds to meet the strict data reliability constraints. Data reliability is critical in NOMA and serves as bottleneck to its manifold capacity gains, as NOMA users are prone to significant interference. The existing UPPA strategies focusing on capacity maximization or user fairness completely neglect this extremely critical tradeoff. This paper provides extensive analysis and results of UPPA considering individual/sum capacity and BER of users. Results are summarized in the form of look-up tables, which facilitate swift selection of user pairs and power allocation factors. The process of performing UPPA by using the developed look up tables, such that both capacity and data reliability goals can be simultaneously achieved, is comprehensively explained in the end.


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    Publication date: Available online 4 June 2018
    Source:Physical Communication
    Author(s): Inam Ullah, Edward Mutafungwa, Jyri Hämäläinen, David González González
    The benefits of Decode and Forward (DF) relaying span from deployment flexibility to coverage extension and improved capacity distribution in the network. Accordingly, relaying has become an integral part of the modern radio access network standards. Besides the evident benefits of DF relaying, the fact is that it uses part of the valuable radio access resources for the communication between network elements. Thus, the amount of radio resources allocated to the Relay Link (RL) between serving Donor Base Station (DBS) and the Relay Node (RN) should be minimized. This easily makes the RL a bottleneck in conventional two-hop infrastructure relaying. Furthermore, current mobile systems apply universal frequency reuse in macrocell deployments where macrocell BS’s serve RN’s as well. As a result, RL’s may suffer from severe interference. We propose a practical limited feedback approach that can be used to simultaneously improve the signal strength and to suppress the interference in the RL. To that end, we deduce analytical formulas for the distribution of the Signal to Interference and Noise Ratio (SINR) in the RL by assuming Rice and Rayleigh fading combinations in desired and interfering links. Furthermore, we compute two-hop end-to-end (e2e) outage probabilities for different interference and limited feedback scenarios. Results show that especially in Rice fading environment, large performance gains can be obtained with only few bits feedback in case where RL has scarce radio resources and suffers from dominant interferer. This makes the proposed method very feasible for the infrastructure relaying where RN’s can be placed either in the rooftop level or other locations that provide a line of sight towards macro BS’s.


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    Publication date: Available online 4 June 2018
    Source:Physical Communication
    Author(s): Ravinder Singh, Timothy O’Farrell, Mauro Biagi, John P. David
    The adaptive tri-chromatic color shift keying (CSK) modulation standardised in IEEE 802.15.7 and the advanced quad-chromatic CSK are unable to utilize their entire spectral efficiency range over dispersive indoor VLC channels and incur large power penalties without the use of channel equalization and forward error correction. This degrades the energy efficiency and limits the throughput capability of CSK schemes to approximately half of the data-rates specified in the IEEE standard for multimedia services in wireless personal area networks. To comply with the desire for low latency and minimal implementation complexity in the CSK standardisation framework, we consider an industry standard binary convolutional code and frequency domain equalization (FDE) which provide one-shot data packet processing. Our results show that when operating over hybrid indoor visible light communication (VLC) links, the FDE based rate-adaptive coded modulation CSK scheme achieves a significant 11 dB SNR gain over an uncoded, unequalized system.


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    Publication date: Available online 5 June 2018
    Source:Physical Communication
    Author(s): Arghyadip Roy, Rajarshi Roy
    Network coding (NC) can reduce the number of packet retransmissions and improve the network reliability in lossy networks. Reliability gain of NC over traditional error control mechanisms has been investigated in recent works. In this paper, we study reliable broadcast in a real-world topology where link loss probabilities are different from each other. We derive approximate closed-form expressions and analyse asymptotic behaviour for expected number of transmissions employing stop-and-wait automatic repeat request (ARQ) and NC as error control mechanisms. In physical layer cooperative communication, multiple nodes can transmit collectively to take advantage of spatial diversity. We incorporate the idea of physical layer cooperative communication with ARQ and NC separately, to obtain further reliability. Numerical results based on our asymptotic analysis indicate that NC offers more reliability than stop-and-wait ARQ. However, as the size of the cooperating set increases, both the schemes offer the same reliability. Approximate closed-form expressions for the reliability metric of these schemes and their asymptotic results match well with simulation results. Furthermore, simulation results establish that the proposed NC scheme outperforms existing schemes in literature.


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    Publication date: Available online 6 June 2018
    Source:Physical Communication
    Author(s): Feifei Zhao, Wenping Ma, Momiao Zhou, Chengli Zhang
    Heterogeneous Network (HetNet) has been viewed as an effective way to meet the tremendous growth of mobile traffic, in which the cross-tier and co-tier interference are the key limitations. Most of the traditional interference management strategies only focus on addressing either cross-tier interference or co-tier interference. We in this paper propose a resource allocation scheme to systematically cope with both of them in Orthogonal Frequency Division Multiple Access (OFDMA)-based HetNets. Specifically, the proposed scheme combines the dynamic enhanced inter-cell interference coordination (eICIC) and orthogonal resource allocation (ORA), to eliminate the cross-tier and co-tier interference respectively. Furthermore, with tracking the real-time variations of the user information (e.g., locations or service requirements), the proposed scheme is separated into two timescales. At the large timescale, a centralized strategy is performed to roughly allocate resource blocks (RBs) to cells; at the small timescale, a distributed strategy is performed to further schedule RBs among users. Also, we formulate two optimization problems to maximize the minimum of users’ throughput satisfaction rate (TSR) for our proposed scheme, followed by two graph-based algorithms to solve them with low complexity. Simulation results manifest the superiority of our proposed scheme in guaranteeing the fairness of users’ TSR.


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    Publication date: Available online 15 June 2018
    Source:Physical Communication
    Author(s): Ruining Zhang, Xuemei Jiang, Ruifang Li
    The allocation of spectrum resources efficiently and equitably in dynamic cognitive vehicular networks is more challenging than static cognitive networks. Currently, most spectrum allocation algorithms are on the basis of a fixed network topology, thereby ignoring the mobility of cognitive vehicular users (CVUs ), timeliness of licensed channels, and uncertainty of spectrum sensing in complex environments. In this paper, a cognitive vehicular network spectrum allocation model for maximizing the network throughput and fairness is established considering these factors. A rapid convergence, improved performance algorithm for solving this multi-objective problem is necessary to adapt to a dynamic network environment. Therefore, an improved decomposition-based multi-objective cuckoo search (MOICS/D) algorithm is proposed. This algorithm integrates a decomposition-based multi-objective optimization framework and an improved CS algorithm. The multi-objective problem is decomposed into multiple scalar sub-problems with different weight coefficients, and the cuckoo algorithm with adaptive steps is used to optimize these sub-problems simultaneously. Simulation results show that the MOICS/D algorithm has faster and more stable convergence than the MOEA/D and NSGA-II algorithms and can improve the throughput and fairness of the network.


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    Publication date: Available online 19 June 2018
    Source:Physical Communication
    Author(s): Mubbashar Altaf Khan, Mohsin M. Jamali
    Cognitive Radios (CR) propose for an opportunistic access to new Secondary Users (SUs) in the white spaces existing in the already licensed radio spectrum on a non-interfering basis with the current Primary Users (PUs). The Secondary Spectrum Markets (SSMs) have lower operating costs as compared to those for the Primary Licensed Operators (PLOs) as they do not require to license dedicated spectrum bands for their operation. This naturally makes CR a disruptive technology and its emergence is inevitably subject to economic viability challenges and technological hijack threats by the PLOs. The existing literature does not address the possible use of economic malpractices by the PLOs to raise the spectrum reuse costs to be no longer affordable by their direct competitors. This research proposes a secondary spectrum trade model based on a carrot and stick rule to keep the business in the SSMs competitive and fair using monetary incentives and penalties based on participation behaviors. A methodology for QoS optimization using Genetic Algorithms (GAs) with respect to those requested by the SUs is implemented. The simulation results indicate that the overall revenues of the participating PLOs with unfair bidding behaviors are lowered due to the incurrence of penalty costs.


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    Publication date: August 2018
    Source:Physical Communication, Volume 29
    Author(s): Ming Zhao, Dan Deng, Wuyang Zhou, Lisheng Fan
    In this paper, we consider a scenario where the source node powered by the conventional power grid transmits data with the assistance of some energy harvesting (EH) decode-and-forward (DF) relay nodes. Unlike EH providing renewable energy, most power grids are supported by the non-renewable fossil fuels. So our goal is to maximize the non-renewable energy efficiency (EE) of the non-EH source throughout multiple timeslots. To deal with the randomness of energy arrivals and non-ideal circuit power, we formulate the EE optimization problem of the relaying system by combining the power allocation and the sleep mode in both the source and the relay. We firstly deal with this problem in a special case with just one timeslot and then solve it in a multi-timeslot scenario with dynamic programming (DP) approach. We also propose a heuristic algorithm with a complexity lower than the DP algorithm. We compare the performance of the two algorithms with a baseline scheme. Simulation results show that the heuristic algorithm provides close EE with the DP algorithm, and a significant EE gain over the baseline scheme.


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    Publication date: Available online 26 June 2018
    Source:Physical Communication
    Author(s): Jessica Khoriaty, Hassan Artail, Youssef Nasser
    One of the goals of Heterogeneous Networks (HetNets) is to offload traffic from the macrocell BS to the microcell base stations (BSs). It has been proposed that in order for the microcell to acquire more users and offload increasing amounts of traffic, its region of coverage must be expanded. This however causes significant cross-tier interference, which can be remedied by utilizing coordinated multipoint (CoMP) within the microcell expanded region (ER). Our methodology considers the effect of overlapping ERs, and proposes the cooperation of concerned microcell BSs with the macro cell BS to further reduce the outage probability and improve throughput. Another important consideration in our analysis is the effect of having non-ideal backhaul on the system’s performance. That is, CoMP increases the strain on the backhaul network, since additional data that is proportional to the number of cooperating BSs needs to travel on the backhaul links. Furthermore, the delay should be minimal and less than one subframe duration in order for reported channel state information to remain valid. With this in mind, our proposed system considers the effect of having non-ideal backhaul in a cellular network with CoMP, while taking into account overlaps in the microcell ERs.


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    Publication date: Available online 28 June 2018
    Source:Physical Communication
    Author(s): Sarwesh P., N. Shekar V. Shet, K. Chandrasekaran
    Internet of Things network is managed by battery operated devices and low power radio links since they are referred to low power networks. In present communication era, many research works are concentrating on low power wireless network. Cross layer design is one of the acclaimed technique that decidedly improves the network performance. In this article, we come up with the cross-layer model that satisfies distinct network requirements and prolongs network lifetime. It integrates physical layer, data link layer (Media Access Control) and network layer in the protocol stack. In our model, a threshold value called ETRT (Expected Transmission Range Threshold) is introduced, which is computed with the help of routing information. Later, MAC based power control technique utilizes the ETRT value and assigns optimum transmission range for every node. The idea at the heels of proposed cross layer model is estimating the capability (ETRT value) of the particular node and assigning the suitable transmission power for every node, based on its capability (ETRT value). Hence, assigning optimum transmission power based on ETRT information prolongs the network lifetime with better reliability and Quality of Service(QoS). From our results, it is noticed that the ETRT based cross layer model performs twice better than the standard model.


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    Publication date: Available online 28 June 2018
    Source:Physical Communication
    Author(s): Mahua Rakshit, Subhankar Bhattacharjee, Sanjib Sil, Amlan Chakrabarti
    Partial Transmit Sequence (PTS) currently can be regarded as an extremely attractive and popular method which allows the achievement of very good Peak to Average Power Ratio (PAPR) reduction for signals that have undergone Orthogonal Frequency Division Multiplexing (OFDM), while also is being a technique which does not distort the signals being processed. In this method, a comprehensive search is conducted taking into account all possible combinations of phase-factors that can occur, leading to an increasing complexity of computation with respect to increasing in sub-blocks. The current paper outlines a novel low complexity sub-optimal PTS technique with its basis in an altered implementation of Differential Evolution (DE) algorithm shortly MBLX-DE which significantly diminishes the PAPR of OFDM signals. More specifically SWDE_Sucess_MBLX (Switched parameter Differential Evolution with success based mutation and modified blending crossover) algorithm (Ghosh et al., 0000) is modified in an efficient way and has been implemented for the PTS scheme. The proposed algorithm introduces modifications in three stages of SWDE_Sucess_MBLX like population central tendency based mutation scheme is incorporated along with the success based mutation, a random selection between two cross-over strategies with blending rate concept and threshold-based selection. A theoretical performance study with general formulas of the proposed scheme is presented and a comparative analysis is done with existing algorithms. Extensive simulation results demonstrate that our proposed method can substantially outperform against the currently best-known algorithms in the context of reduction of PAPR as well as performance in terms of complexity of the computations to be performed.


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    Publication date: Available online 30 June 2018
    Source:Physical Communication
    Author(s): Vivek Rajpoot, Vijay Shanker Tripathi
    Internet of things (IoT) is a technology which facilitates passive devices to participate in active communication. In the presented work the radio frequency identification (RFID) system is used to access information from passive primary receiver (PURx). This inspires to develop a novel sensing algorithm along with PURx protection from harmful transmissions of cognitive radio (CR) nodes in CR network. The novelty in the sensing and protection lies in the approach of accessing information from primary users. Here a CR node can detect occupancy of primary channel from both, primary transmitter (PUTx) end as well as from PURx end on the basis of relative distance. For protection of PURx a novel power control algorithm is proposed and implemented. The results indicate less energy is needed to run the network along with a notable improvement in average throughput and reduction in delay for increasing amount of CR traffic.


older | 1 | .... | 32 | 33 | (Page 34)