Nowadays satellite communications are undergoing strong development in order to follow explosive increase in requirement for superior data rate, capacity and omnipresent connectivity. On the apex of that, satellite communication industry has to keep promptness with terrestrial communication technology, which has shown strong and fast development. In this view, Multiple Input Multiple Output (MIMO) technology is a promising candidate. Multiple Input Multiple Outputs along with multicarrier modulation technique can be a good solution to mitigate frequency selective fading. Single Carrier Frequency Division Multiple Access (SC-FDMA) has shown robustness to multipath fading and has got the same characteristics as that of Orthogonal Frequency Division Multiplexing (OFDM). The main advantage of Single Carrier Frequency Division Multiple Access is that it has low Peak to Average Power Ratio (PAPR). Due to low Peak to Average Power Ratio, Single Carrier Frequency Division Multiple Access is used in uplink for Land Mobile Satellite (LMS) systems. The link level performance of Land Mobile Satellite systems is diminished by rapid amplitude variations of the received signal due to shadowing. In this paper we have investigated, Single Input Multiple Output (SIMO) Single Carrier Frequency Division Multiple Access performance for Maximal Ratio Combining (MRC) diversity over correlated shadowed Rice Land Mobile Satellite channel, where the Line Of Sight (LOS) follows Nakagami-m distribution.
The electromagnetic spectrum is a scarce resource that needs to be efficiently and effectively reused to allow the provider the necessary conditions to satisfy its customers increasing demands. It is vital that the reuse of the spectrum does not lead to high interference scenarios. The use of heterogeneous networks (HetNets) allows a better spatial reuse of the spectrum. However it also leads to higher interference scenarios. Thus, it is necessary to create tools that help to mitigate the interference, increasing the effectiveness of spectrum reuse. This paper evaluates interference-coordination algorithms based on game theory for scenarios with different access policies. The results are given in terms of user and cell throughputs. They show that although the use of closed access policies can benefit from the use of cell-driven algorithms, open access policy is preferential to use with user-driven algorithms, in particular for the increase of the service capacity.
This paper describes the economic and environmental comparative analysis performed on macro and femtocell deployments and most prevalent results obtained. Four specific scenarios are studied and, for each one, an evaluation is made in terms of network capacity, cost effectiveness and expected carbon emissions on the environmental side. It provides mobile networks operators (MNO) with novel relevant information, enabling them to adapt business models and deployment approaches to current and future trends in a sustainable way, while minimizing capital (CAPEX) and operational expenditure (OPEX). It is verified that the scenario is mandatory to the best option macro-femtocell.
The mobile internet data traffic is growing rapidly in non-uniform peak traffic patterns. Emerging radio access technologies are forcing the backhaul network architectures to undergo a major transition in the direction of heterogeneous architectures. This paper provides a brief overview on the applicable protocols with reference to a futuristic backhaul network model serving a variety of radio access technologies. The data traffic paths in the backhaul network are mapped to the candidate protocols mentioned in the paper. In the attempt of developing flexible network architectures for transporting humongous amounts of data generated from next generation radio access technologies, some challenges in protocol layer are presented.
In the Internet of things (IoT), the activities of daily life are supported by a multitude of heterogeneous, loosely coupled ubiquitous devices. Traditional access control models are not suitable to the nomadic, decentralized and dynamic scenarios in the IoT where identities are not known in advance. This makes the trust management in IoT more promising to address the access control issues. This paper present a Fuzzy approach to the Trust Based Access Control (FTBAC) with the notion of trust levels for identity management. The presented fuzzy approach for trust calculations deals with the linguistic information of devices to address access control in the IoT. The simulation result shows that the fuzzy approach for trust based access control guarantees scalability and it is energy efficient. This paper also proposes FTBAC framework for trust based dynamic access control in distributed IoT. FTBAC framework is a flexible and scalable as increasing number of devices do not affect the functioning and performance.
In this work, we propose a buffer-aided successive opportunistic relaying scheme that aims to improve the average capacity of the network when inter-relay interference arises between relays that are selected for transmission and reception. In order to exploit the benefits of buffering at the relays, we propose a relay-pair selection policy that decouples the receiving relay at the previous time slot from being the transmitting relay at the next slot. Furthermore, we impose an interference cancellation threshold allowing the relay that is selected for reception, to decode and subtract the inter-relay interference. The proposed relaying scheme selects the relaying pair that maximizes the average capacity of the relay network. The performance of the proposed scheme is evaluated via simulation and comparisons with other state-of-the-art half and full-duplex relay selection schemes, in terms of outage probability, average capacity and average delay. The results reveal the need for a tradeoff between improving the outage on the cost of reduced capacity and increased delay, and vice versa. Finally, conclusions are drawn and future directions are discussed, including the need for a hybrid scheme incorporating both half and full-duplex characteristics.
This paper investigates applying Extended Kalman Filter (EKF) to non-coherently estimate the phase of Gaussian Frequency Shift Keying (GFSK) modulation scheme in Bluetooth receivers. The paper examines the performance of Extended Kalman filters for Additive White Gaussian channel noise (AWGN) with IEEE802.11 coexistence. Both technologies operate in the unlicensed 2.4GHz Industrial Scientific Medical (ISM) Band. Experimental results for Extended Kalman Filter for Gaussian channel are provided.
This paper proposes a novel spectrum sensing scheme for cognitive radio (CR) systems in high traffic environments where primary users (PUs) might randomly depart or arrive during the sensing period of a CR user. We first model the spectrum sensing problem in high traffic environments as a binary hypothesis testing problem, and then, derive a test statistic based on the cyclostationarity of the PU signals by applying an estimate of spectral coherence function of the PU signal to the generalized likelihood ratio. Numerical results demonstrate that the proposed scheme provides a better spectrum sensing performance compared with the conventional spectrum sensing scheme using the energy of the PU signals in high traffic environments.
Estimation analysis for rainfall time series can be applied as a technique in improving dynamic rain fade countermeasures. In this study, the nth-powered sine function is considered in analyzing the time series patterns in Durban, South Africa. With an assumed exponent factor, n = 2 and width factor, β = 0.9, the proposed function is seen as an appropriate envelope with Root Mean Square (RMS) error ranging between 13% and 30%. The Fast Fourier Transform (FFT) and Power Spectral Density (PSD) show that the frequency components of the measured rainfall residues compare well with those of the proposed function. At simulated microwave frequencies of 12 GHz, the function is seen to mask and track the fluctuating rainfall specific attenuation patterns at our site.
In this paper, we propose a model for estimating the error floor in a small-time-dispersion environment - typically indoor, where both channel and overall OFDM symbol are represented stochastically. The developed novel model for the error floor prediction involves modified common channel time dispersion parameters as well as the ones characterizing the OFDM signal. The validity of the model was confirmed by the results of the corresponding Monte-Carlo simulations.
Cognitive radio techniques have been introduced to improve the spectrum utilization in the frequency bands already allocated to licensed users. Under spectrum sharing model, secondary users can share spectrum with primary users with the condition that total interference caused by SUs should not be exceeded from a predefined level. Energy efficiency is one of the important metric in cognitive radio networks as it has to work under strict transmit power constraint. In this paper, we explore how better energy efficiency can be achieved in a spectrum sharing environment. Our analysis shows that energy efficiency in cognitive radio network is better when number of secondary users is more than available channels.
Beamspace MIMO (BS-MIMO) systems have been recently proposed as a means to address the two key weaknesses of conventional MIMO systems: the antenna size and the need for multiple RF chains. Based on Electronically Steerable Passive Array Radiators (ESPAR), the research effort on BS-MIMO focuses on the development of functional MIMO transmission schemes with efficient multiplexing and beamforming capabilities with the use of a single RF chain while maintaining extremely small antenna size. Previous studies have shown that for small-sized antenna arrays, BS-MIMO systems clearly outperform conventional systems in terms of system capacity. However, until now research is limited to the ESPAR antenna properties and theoretical results. This paper makes the first step to practical system design and focuses on BS-MIMO channel estimation. Basic estimators are applied in a BS-MIMO system with adaptive pattern reconfiguration. Finally the first, fundamental link level evaluation results are produced from simulation and system performance is compared vs. equivalent conventional MIMO.
This paper proposes a novel direct sequence ultra wideband (DS-UWB) radar system with a reduced correlation processing time. The distance estimator in the proposed DS-UWB radar accumulates the correlator outputs to average out the noise, and thus, reduces the correlation processing time by shortening the required length of the DS-UWB signal. Numerical results confirm that the proposed DS-UWB radar estimates a distance with a reduced correlation processing time while providing a better estimation performance compared with the conventional DS-UWB radar systems with a distance estimator exploiting the correlations individually.
Orthogonal frequency division multiplexing (OFDM) is a bandwidth efficient modulation scheme used widely for high speed data communication. In OFDM system, intersymbol interference (ISI) and intercarrier interference (ICI) occur due to synchronization errors. Fast, simple and robust synchronization algorithms are necessary for OFDM systems. In this paper, a simple and robust algorithm for timing synchronization is proposed. In OFDM downlink transmission, every terminal perform synchronization by exploiting reference symbols called training symbols of received frame. Proposed timing synchronization algorithm is based on use of reference symbol. Performance analysis shows that the proposed timing offset estimator have better performance despite being simple. Performance is studied over AWGN and time-dispersive multipath Rayleigh fading channel with the conclusion that the proposed synchronization technique result in better performance with respect to all the parameters.
The security attacks wireless sensor network (WSN) are increasing. These security attacks degrade the performance of WSN, e.g. energy consumption, throughput, and delay. These are biggest obstacle to make WSN greener. The aim of the paper is to model the behavior of jamming attack and analyze its effect on performance of WSN. Jamming attack jams the traffic in network by blocking the channel. The behavioral modelling and analysis of jamming attack in realistic situations (e.g. sensing in industrial application by following all network rules), gives the clear understanding of jamming attack execution. The paper also presents the possibility of jamming attack in cluster-based WSN, i.e. intelligent cluster head (CH) jamming attack. This degrades the performance of WSN around 30% more than normal reactive jamming attack. The paper finally proposes the requirements for designing the efficient solution against jamming attack.
To save the power and time of total relay processing and to achieve a higher bandwidth efficiency in relay usage, a simple multi-relay switching scheme is proposed and analyzed for cooperative spectrum sensing, where energy detection is employed for the detection of a spectrum hole. In the cooperative spectrum sensing with relay switching, not all available relays are activated and used at all time. A relay is used only if the strength of faded signal-to-noise ratio (SNR) for its reporting channel to the cognitive destination (CD) is larger than a preset threshold. Otherwise, another switched-to relay is considered and tested for its usage. The probabilities of false alarm and correct detection are derived for independent and identically distributed (i.i.d.) Rayleigh fading channels. The average number of active relays is evaluated for the examination of total required relay processing. Various numerical results are presented for performance illustrations. Based on the numerical results, the proposed scheme can enhance the detection performance in many aspects.
This paper presents two efficient adaptive signal processing techniques for co-cancel interference suppression in digital beamforming Quadrature Amplitude Modulation (QAM) receivers. The adaptive techniques are employed at the receiver's baseband in the digital signal processor, and a time-varying weight update is automatically generated at each iteration during the adaptation process. The first method separately updates the real and imaginary parts of the weight vector along their respective gradient directions with distinctive optimum step sizes, while the second method directly updates the weight vector components as complex numbers, aiming at minimizing the error signal in th next iteration. Computer simulations are performed to validate the effectiveness of the proposed techniques. The simulation results confirm that, compared to the classic complex-valued Least Mn Square (LMS) algorithm, both proposed techniques exhibit satisfying interference suppression performance, with th second method performing slightly better than the first one.
This paper evaluated resilience of the reference IMS based network topology in operation through the keys reliability parameters via OPNET. The reliability behaviors of communication within similar and across registered home IMS domains were simulated and compared. Besides, the reliability effects when increasing requested traffics were presented; as well, the results were compared when applying equally load balancing of a 1:1 redundancy of S-CSCF unit into the core registered domain. The results exposed insight reliability behaviors of communication within similar and different registered domains.
The Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) scheme, which offers significant improvement on the performance of the conventional IDMA technique, has been in the forefront of recent mobile communication researches as it is expected to deliver a high quality, flexible and efficient high data-rate mobile transmission. Most papers on OFDM-IDMA scheme assume a system free of carrier frequency offset. However, the scheme is susceptible to synchronization errors and performance degradation because of the presence of OFDM, which is highly sensitive to carrier frequency offset (CFO) especially at the uplink. The effect of CFO on the performance of the scheme, in a slow fading multipath channel scenario, is therefore investigated, and analyzed. In addition, the effect of CFO on the performance of the OFDM-IDMA scheme, in a fast fading multi path channel, which has not been hitherto reported in literature, is investigated and analyzed. Simulation results clearly show that the presence of CFO degrades the performance of the system. Furthermore, results show that system performance degradation due to CFO, increases in a fast fading multi path channel in comparison with slow fading channel scenario.
