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PHYSICS (536 journals)            First | 1 2 3 4 5 6 | Last

physica status solidi (b)     Hybrid Journal   (Followers: 1)
physica status solidi (c)     Hybrid Journal   (Followers: 1)
Physica Status Solidi - Rapid Research Letters     Hybrid Journal  
Physical Communication     Hybrid Journal  
Physical Review C     Full-text available via subscription   (Followers: 16)
Physical Review Special Topics - Physics Education Research     Open Access   (Followers: 5)
Physical Review X     Open Access   (Followers: 5)
Physical Sciences Data     Full-text available via subscription   (Followers: 1)
Physics - spotlighting exceptional research     Full-text available via subscription   (Followers: 1)
Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B     Full-text available via subscription   (Followers: 2)
Physics and Chemistry of Liquids: An International Journal     Hybrid Journal  
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 3)
Physics in Medicine & Biology     Full-text available via subscription   (Followers: 7)
Physics in Perspective     Hybrid Journal   (Followers: 1)
Physics International     Open Access   (Followers: 2)
Physics Letters A     Hybrid Journal   (Followers: 9)
Physics Letters B     Open Access   (Followers: 2)
Physics of Fluids     Hybrid Journal   (Followers: 21)
Physics of Life Reviews     Hybrid Journal   (Followers: 1)
Physics of Plasmas     Hybrid Journal   (Followers: 6)
Physics of the Dark Universe     Open Access  
Physics of the Solid State     Hybrid Journal   (Followers: 3)
Physics of Wave Phenomena     Hybrid Journal   (Followers: 1)
Physics Procedia     Partially Free   (Followers: 1)
Physics Reports     Full-text available via subscription   (Followers: 1)
Physics Research International     Open Access   (Followers: 1)
Physics Today     Hybrid Journal   (Followers: 15)
Physics World     Full-text available via subscription   (Followers: 3)
Physics-Uspekhi     Full-text available via subscription  
Physik in unserer Zeit     Hybrid Journal  
Physik Journal     Hybrid Journal  
Plasma Physics and Controlled Fusion     Hybrid Journal   (Followers: 2)
Plasma Physics Reports     Hybrid Journal   (Followers: 2)
Pramana     Open Access   (Followers: 8)
Preview     Hybrid Journal  
Proceedings of the National Academy of Sciences     Full-text available via subscription   (Followers: 375)
Proceedings of the National Academy of Sciences, India Section A     Hybrid Journal   (Followers: 3)
Progress in Materials Science     Hybrid Journal   (Followers: 18)
Progress in Planning     Hybrid Journal   (Followers: 1)
Progress of Theoretical and Experimental Physics     Open Access  
Quantum Electronics     Full-text available via subscription   (Followers: 2)
Quantum Measurements and Quantum Metrology     Open Access  
Quarterly Journal of Mechanics and Applied Mathematics     Hybrid Journal   (Followers: 3)
Radiation Effects and Defects in Solids     Hybrid Journal   (Followers: 1)
Radiation Measurements     Hybrid Journal   (Followers: 2)
Radiation Physics and Chemistry     Hybrid Journal   (Followers: 1)
Radiation Protection Dosimetry     Hybrid Journal   (Followers: 1)
Radiation Research     Full-text available via subscription   (Followers: 2)
Radio Science     Full-text available via subscription   (Followers: 2)
Radiological Physics and Technology     Hybrid Journal   (Followers: 1)
Reflets de la physique     Full-text available via subscription  
Reports on Mathematical Physics     Full-text available via subscription  
Reports on Progress in Physics     Full-text available via subscription   (Followers: 2)
Research & Reviews : Journal of Physics     Full-text available via subscription  
Research in Drama Education     Hybrid Journal   (Followers: 8)
Research Journal of Physics     Open Access  
Results in Physics     Open Access   (Followers: 1)
Reviews in Mathematical Physics     Hybrid Journal  
Reviews of Accelerator Science and Technology     Hybrid Journal  
Reviews of Geophysics     Full-text available via subscription   (Followers: 17)
Reviews of Modern Physics     Full-text available via subscription   (Followers: 16)
Revista Colombiana de Física     Open Access  
Revista Mexicana de Astronomía y Astrofísica     Open Access  
Revista Mexicana de Física     Open Access  
Revista mexicana de física E     Open Access  
Rheologica Acta     Hybrid Journal   (Followers: 3)
Russian Journal of Mathematical Physics     Hybrid Journal  
Russian Journal of Nondestructive Testing     Hybrid Journal  
Russian Physics Journal     Hybrid Journal  
Samuel Beckett Today/Aujourd'hui     Full-text available via subscription   (Followers: 2)
Science and Technology of Nuclear Installations     Open Access   (Followers: 2)
Science China Physics, Mechanics and Astronomy     Hybrid Journal   (Followers: 1)
Science Foundation in China     Full-text available via subscription   (Followers: 2)
Scientific Journal of Physical Science     Open Access  
Scientific Reports     Open Access   (Followers: 10)
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of     Hybrid Journal   (Followers: 15)
Sensor Letters     Full-text available via subscription   (Followers: 1)
Sensors and Actuators A: Physical     Hybrid Journal   (Followers: 20)
Services Computing, IEEE Transactions on     Hybrid Journal   (Followers: 3)
Shock and Vibration     Hybrid Journal   (Followers: 7)
Shock Waves     Hybrid Journal   (Followers: 4)
Small     Hybrid Journal   (Followers: 7)
Software Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 21)
Solid State Physics     Full-text available via subscription  
Solid-State Circuits Magazine, IEEE     Hybrid Journal   (Followers: 1)
South African Journal for Research in Sport, Physical Education and Recreation     Full-text available via subscription   (Followers: 3)
Space Research Journal     Open Access   (Followers: 2)
Space Weather     Full-text available via subscription   (Followers: 3)
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy     Hybrid Journal   (Followers: 7)
Spectrochimica Acta Part B: Atomic Spectroscopy     Hybrid Journal   (Followers: 4)
Spectroscopy     Hybrid Journal   (Followers: 3)
Spectroscopy Letters: An International Journal for Rapid Communication     Hybrid Journal   (Followers: 3)
Sri Lankan Journal of Physics     Open Access  
Strain     Hybrid Journal   (Followers: 2)
Strength of Materials     Hybrid Journal   (Followers: 3)
Strength, Fracture and Complexity     Hybrid Journal   (Followers: 1)
Structural Dynamics     Open Access  
Studies In Applied Mathematics     Hybrid Journal   (Followers: 1)
Superconductor Science and Technology     Hybrid Journal   (Followers: 1)
Surface Engineering     Hybrid Journal   (Followers: 3)

  First | 1 2 3 4 5 6 | Last

Journal Cover Physical Communication
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1874-4907
     Published by Elsevier Homepage  [2563 journals]   [SJR: 1.326]   [H-I: 13]
  • Terahertz band: Next frontier for wireless communications
    • Abstract: Publication date: September 2014
      Source:Physical Communication, Volume 12
      Author(s): Ian F. Akyildiz , Josep Miquel Jornet , Chong Han
      This paper provides an in-depth view of Terahertz Band (0.1–10 THz) communication, which is envisioned as a key technology to satisfy the increasing demand for higher speed wireless communication. THz Band communication will alleviate the spectrum scarcity and capacity limitations of current wireless systems, and enable new applications both in classical networking domains as well as in novel nanoscale communication paradigms. In this paper, the device design and development challenges for THz Band are surveyed first. The limitations and possible solutions for high-speed transceiver architectures are highlighted. The challenges for the development of new ultra-broadband antennas and very large antenna arrays are explained. When the devices are finally developed, then they need to communicate in the THz band. There exist many novel communication challenges such as propagation modeling, capacity analysis, modulation schemes, and other physical and link layer solutions, in the THz band which can be seen as a new frontier in the communication research. These challenges are treated in depth in this paper explaining the existing plethora of work and what still needs to be tackled.

      PubDate: 2014-04-27T19:25:27Z
  • Radar sensor network for target detection using Chernoff information and
           relative entropy
    • Abstract: Publication date: Available online 25 January 2014
      Source:Physical Communication
      Author(s): Ishrat Maherin , Qilian Liang
      In this paper, we propose to apply information theory to Ultra wide band (UWB) radar sensor network (RSN) to detect target in foliage environment. Information theoretic algorithms such as Maximum entropy method (MEM) and mutual information are proven methods, that can be applied to data collected by various sensors. However, the complexity of the environment poses uncertainty in fusion center. Chernoff information provides the best error exponent of detection in Bayesian environment. In this paper, we consider the target detection as binary hypothesis testing and use Chernoff information as sensor selection criterion, which significantly reduces the processing load. Another strong information theoretic algorithm, method of types, is applicable to our MEM based target detection algorithm as entropy is dependent on the empirical distribution only. Method of types analyzes the probability of a sequence based on empirical distribution. Based on this, we can find the bound on probability of detection. We also propose to use Relative entropy based processing in the fusion center based on method of types and Chernoff Stein Lemma. We study the required quantization level and number of nodes in gaining the best error exponent. The performance of the algorithms were evaluated, based on real world data.

      PubDate: 2014-04-27T19:25:27Z
  • Nested sparse sampling and co-prime sampling in sense-through-foliage
           target detection
    • Abstract: Publication date: Available online 14 February 2014
      Source:Physical Communication
      Author(s): Na Wu , Qilian Liang
      This paper firstly introduces nested sampling and co-prime sampling, which were proposed recently, but have never been applied to real world target detection. We apply nested sampling and co-prime sampling to target detection in UWB radar sensor networks (RSN), based on a differential approach. The non-stationary UWB signal needs to be decomposed into several approximate wide sense stationary (WSS) signals so that nested sampling could be used in this situation. We also compare the performance of nested sampling and co-prime sampling against uniform under-sampling. The results show that in terms of good quality data and poor quality data, both nested sampling and co-prime sampling work better.

      PubDate: 2014-04-27T19:25:27Z
  • Synthetic Aperture Radar image nonlinear enhancement algorithm based on
           NSCT transform
    • Abstract: Publication date: Available online 30 January 2014
      Source:Physical Communication
      Author(s): Ying Tong , Meirong Zhao , Zilong Wei , Leilei Liu
      Due to the imaging mechanism, Synthetic Aperture Radar (SAR) images are susceptible to speckle noise, which affects radar image interpretation. So image denoising and enhancement are important topics of improving SAR image performance. A nonlinear image enhancement algorithm based on nonsubsampled contourlet transform (NSCT) is proposed in this paper. The image is decomposed into coefficients of different scales and directions through nonsubsampled contourlet transform. It is denoised by the threshold method of the multi-scale product of NSCT coefficients. Then thresholds of the nonlinear enhancement function are determined according to the coefficients of each scale. The two parameters of the function, among which one is used to control the range of enhancement and the other can determine the strength of enhancement, are obtained by solving nonlinear equations. The coefficients processed by the enhancement function are used to reconstruct the image. The simulation results on the Matlab platform show that the algorithm has a good effect of enhancing details of images and suppressing noise signals meanwhile.

      PubDate: 2014-04-27T19:25:27Z
  • Optimization for distributed Radar Sensor Network (RSN) and MIMO-RSN in
           flat fading channels
    • Abstract: Publication date: Available online 17 February 2014
      Source:Physical Communication
      Author(s): Yang Liu , Jing Liang
      Investigation in distributed Radar Sensor Network (RSN) and MIMO-RSN are more like two parallel paths other than one research field in current literature. In this paper, we address the comparison between optimal fusion scheme of distributed-RSN and optimal power control of MIMO-RSN for target detection. We first establish the wireless statistic channel model for these two types of RSNs under flat fading channel condition. Using Jake’s model, Rayleigh flat fading channel is obtained. Then we provide optimization for the fusion scheme and the power control. Both amplitude and phase of the received signals are applied to the optimal/suboptimal fusion schemes for the distributed-RSN. Water-filling, the optimal power control scheme is utilized in the MIMO-RSN, where two suboptimal schemes (equal power and channel inversion) are also investigated to provide a comparison. The detection performance is analyzed and compared in terms of probability of detection ( P d ) and probability of false alarm ( P f a ). The simulation results show that the water-filling in MIMO-RSN achieves the best performance, whereas the optimal fusion scheme for distributed-RSN obtains worse performance than the equal power control in MIMO-RSN, and the channel inversion in MIMO-RSN gets the worst performance, which has almost the same performance as the suboptimal fusion scheme in distributed-RSN.

      PubDate: 2014-04-27T19:25:27Z
  • Indoor navigation and tracking
    • Abstract: Publication date: Available online 24 February 2014
      Source:Physical Communication
      Author(s): Kegen Yu , Ian Oppermann , Eryk Dutkiewicz , Ian Sharp , Guenther Retscher

      PubDate: 2014-04-27T19:25:27Z
  • Synthetic aperture radar image de-noising based on Shearlet transform
           using the context-based model
    • Abstract: Publication date: Available online 19 February 2014
      Source:Physical Communication
      Author(s): Shuaiqi Liu , Mingzhu Shi , Shaohai Hu , Yang Xiao
      As the synthetic aperture radar (SAR) has been widely used in agriculture, forestry, hydrology, mining, marine, mapping and other fields, the method to improve the image quality and visual effect of the SAR image has become a hot research issue. The suppression and removal of the speckle of SAR image have become more and more important. This paper analyzes how the noises of the SAR image are generated and the models are appropriate for the characteristics of SAR images. Then based on the advantages of the Shearlet transform, we proposed an SAR image de-noising algorithm which combines the improved Shearlet transform with a cycle spinning de-noising algorithm by using an adaptive threshold method based on the context model. Simulation results show that the proposed algorithm can significantly suppress the speckle noise and improve the peak signal-to-noise ratio (PSNR) of the image; it also holds the characteristics of translational invariance (which can keep the edges of the image detail signal well and inhibit Gibbs phenomenon caused by noise reduction), and it can greatly improve the visual effect.

      PubDate: 2014-04-27T19:25:27Z
  • Design protocol and performance analysis of indoor fingerprinting
           positioning systems
    • Abstract: Publication date: Available online 26 February 2014
      Source:Physical Communication
      Author(s): Vahideh Moghtadaiee , Andrew G. Dempster
      Location fingerprinting is a technique widely suggested for indoor positioning. Given specific positioning requirements, this paper provides methods for setting up the network elements such that those requirements can be met by the location fingerprinting method. In particular, the paper aims to optimize indoor fingerprinting systems such that the positioning performance gets close to the optimal performance indicated by the lower bound of the system. The Weiss–Weinstein bound (WWB) and Extended Ziv–Zakai bound (EZZB) are suggested for indoor environments, as they are shown to have superior predictive performance for this application. The effects of the number and geometry of access points (APs), the number and spatial arrangement of reference points (RPs), and the number of signal strength samples taken per location are presented, both through simulations and analytical lower bound estimates. The impact of the path-loss exponent, the standard deviation of the signal strength measurement, and size of the operating area are also investigated. These theoretical/simulation estimates are also assessed using experimental data. By utilizing these tools, a system designer is able to set appropriate parameters to optimize the compromise between positional accuracy and the costs associated with the setting up of the fingerprinting measurements database.

      PubDate: 2014-04-27T19:25:27Z
  • A history-aware greedy channel restoration scheme for cognitive
           radio-based LTE networks
    • Abstract: Publication date: March 2014
      Source:Physical Communication, Volume 10
      Author(s): Arash Azarfar , Jean-François Frigon , Brunilde Sansò
      Cognitive radio-based Long Term Evolution (LTE) networks benefit from the powerful features of cognitive Radios (CR), such as learning and reconfigurability, enabling them to perform, if required, channel switching to a channel with higher quality. This process of searching and sensing other channels is a restoration (recovery) process where the objective is to find the best channel in the shortest time. We propose in this paper a history-aware greedy restoration scheme triggered not only when the quality of the current operating channel of the user goes below a threshold, but at regular intervals. Based on the state of the current channel, our scheme computes the optimal number of channels to be sensed in this restoration period and this number is dynamically updated after each channel sensing result. Intrinsic features of learning and history-awareness of CRs are used to create the list of channels to be sensed based on the channels’ background and historical information. The sensing order improves the restoration mechanism by providing a shorter restoration time or a restored channel with a higher quality. We show that the proposed combined scheme provides improvements for the CR-based LTE network’s throughput, compared to other restoration schemes which work based on only greediness or history-awareness.

      PubDate: 2014-04-27T19:25:27Z
  • Editorial Board
    • Abstract: Publication date: March 2014
      Source:Physical Communication, Volume 10

      PubDate: 2014-04-27T19:25:27Z
  • No title
    • Abstract: Publication date: March 2014
      Source:Physical Communication, Volume 10
      Author(s): Ian F. Akyildiz

      PubDate: 2014-04-27T19:25:27Z
  • Sum capacity maximization for MIMO–OFDMA based cognitive radio
    • Abstract: Publication date: March 2014
      Source:Physical Communication, Volume 10
      Author(s): H. Shahrokh Shahraki , K. Mohamed-pour , L. Vangelista
      In the opportunistic Cognitive Radio (CR) networks, the secondary users’ (SU) capacity is limited due to the need to avoid the primary users’ (PUs) bands. The combination of the Multiple-Input Multiple-Output (MIMO) structure with the orthogonal frequency division multiplexing (OFDM) structure is a very promising candidate which can compensate for such a shortage of capacity increasing the spectral efficiency. In this paper, a MIMO–OFDMA structure is proposed for the multiple access in multi-user CR networks. Furthermore, in order to achieve the maximum capacity in this structure, the resource allocation problem including proper allocation of sub-carriers to users and proper power allocation is investigated. To this aim, an efficient algorithm for the resource allocation is introduced. Furthermore, an alternative sub-optimal algorithm is obtained with lower complexity and very good performance. The performance of the suggested algorithms is investigated in a realistic scenario using LTE (Long Term Evolution) parameters with Spatial Channel Propagation Model (3GPP SCM). Simulation results verify the enhancement and efficiency of the proposed algorithms compared to the conventional ones applied in CR networks.

      PubDate: 2014-04-27T19:25:27Z
  • Price-bandwidth dynamics for WSPs in heterogeneous wireless networks
    • Abstract: Publication date: Available online 18 April 2014
      Source:Physical Communication
      Author(s): S. Anand , S. Sengupta , R. Chandramouli
      This paper presents a comprehensive approach to spectrum pricing and bandwidth management for wireless service providers (WSPs) in heterogeneous wireless networks. Most approaches to spectrum management focus on revenue maximization for the WSPs. However, the key issue of the competitive edge held by a WSP over the others (i.e., its market share) is hardly addressed. The market shares of the WSPs depend on the prices they advertise and the bandwidths they provide. We develop a three phase game between WSPs. The first phase called the WSP-WSP price game enables WSPs determine the optimal price they must advertise. In the second phase, called the WSP-WSP bandwidth game, the WSPs use the Nash equilibrium of the WSP-WSP price game, to determine the optimal bandwidths they should advertise in order to maximize their market share. Finally, in the third phase, we develop a WSP-WSP trading game model the fact that users that start off with a WSP can not only demand bandwidth from that WSP, but also demand bandwidth from other WSPs in order to make best use of the available bandwidth at all the WSPs.

      PubDate: 2014-04-27T19:25:27Z
  • Energy and delay constrained scheduling of real time traffic over OFDM
           communication system with non-causal channel information
    • Abstract: Publication date: Available online 18 April 2014
      Source:Physical Communication
      Author(s): Ritesh Kumar Kalle , Debabrata Das
      A point to point wireless communication system based on Orthogonal Frequency Division Multiplexing (OFDM) is considered, wherein R bits of information have to be scheduled within a hard delay deadline of T time slots over a frequency selective slow fading channel. The scheduling objective is to minimize the energy expenditure with non-causal knowledge of channel state over a limited time horizon, number of bits to be served and delay constraints. We assume a convex monomial energy-bit cost function and propose novel efficient two stage heuristic algorithm that allocate the R bits on the time slots, followed by greedy optimal bit loading over the OFDM subcarriers. Analytical model is developed and numerical simulations are performed to validate the proposed approach as well as the results show that our algorithms outperform existing approaches in published literature by up to 10dB in power margin on an average in high load conditions while meeting the deadline of T timeslots.

      PubDate: 2014-04-27T19:25:27Z
  • A framework for leakage-based autonomous uplink inter-cell interference
           coordination in OFDMA/LTE heterogeneous networks
    • Abstract: Publication date: Available online 26 April 2014
      Source:Physical Communication
      Author(s): Mai B.S.A. Kafafy , Khaled M.F. Elsayed
      The inter-cell interference (ICI) problem in OFDMA wireless systems is a major impediment to attain high rates particularly for cell-edge users in reuse-1 systems. Using centralized resource allocation to combat ICI is not practical, particularly in heterogeneous networks (HetNets), as they require intensive signalling about interference and channel state information that may not always be practically available. The main contribution of this paper is devising efficient autonomous power allocation schemes such that the interference produced by each cell is below a certain limit. We develop two inter-cell interference coordination (ICIC) frameworks; the overall interference limit (OIL), and the interference limit per resource block (ILR). The first framework imposes an overall interference limit on each cell, while the second imposes different interference limits on different resource blocks in each cell. We propose a closed form solution, and an iterative solution for the OIL framework, and a closed form solution for the ILR framework which has an additional advantage of possible autonomous application at each terminal rather than at the base station. We present two semi-autonomous heuristic and optimal adaptive schemes that use the overload indicator (OI) signal in LTE to adjust the values of the interference limits in the ILR scheme. They attempt to alleviate the interference seen by overloaded cells in order to achieve fairness among different cells, which is very important especially in HetNets. A method based on the Kalman filter is introduced to predict the values of the OI in the intervals between the OI exchanges. This estimation can be applied to the adaptive schemes almost autonomously as it requires very infrequent signalling between cells. Simulations show that the proposed schemes exhibit better performance than equal power allocation. Comparison with centralized optimal allocation that uses global information shows good performance with acceptable degradation in the spectral efficiency which decreases as the interference limit increases. Simulations also show that the ILR and the OIL schemes almost have the same performance, and the adaptive schemes achieve fairness among different cells especially in a HetNet environment.

      PubDate: 2014-04-27T19:25:27Z
  • A model based on poison point process for downlink K tiers fractional
           frequency reuse heterogeneous networks
    • Abstract: Publication date: Available online 26 April 2014
      Source:Physical Communication
      Author(s): He Zhuang , Tomoaki Ohtsuki
      Modern cellular networks are currently transitioning from homogeneous networks to heterogeneous networks (HetNets). Unlike homogeneous networks, HetNets comprise of K tiers of random base stations (BSs), where each tier may differ in terms of transmit power, BSs’ deployment density and target signal to interference plus noise ratio (SINR). Although HetNets significantly increase spatial frequency efficiency and transmit capacity, they also introduce two main problems: introducing cross-tier interference, and increasing the difficulty of modeling and analysis, due to the increase of randomness of BSs’ locations, particularly, user-deployed femto BSs. For the first problem, fractional frequency reuse (FFR), as an interference management technique, can mitigate effectively the impact of interference. Recently, Poisson point process (PPP) is more and more used to model HetNets, because it can naturally capture the randomness of the BSs’ locations. In this work, we develop a general downlink model based on PPP for HetNets utilizing FFR. We derive tractable expressions of coverage probability under both open and closed access schemes, which even can be simplified to a simple closed form for interference-limited HetNets (neglect noise). We also show the impact of the main parameters on the coverage probability.

      PubDate: 2014-04-27T19:25:27Z
  • A Survey of QoS/QoE mechanisms in heterogeneous wireless networks
    • Abstract: Publication date: Available online 26 April 2014
      Source:Physical Communication
      Author(s): Jason B. Ernst , Stefan C. Kremer , Joel J.P.C. Rodrigues
      Heterogeneous Wireless Networks (HWNs) are an important step in making connectivity ubiquitous and pervasive. Leveraging the increasing variety of connectivity options available to devices solves many problems such as capacity, spectrum efficiency, coverage and reliability. Anytime decisions are made for selection, handover, scheduling or routing many performance metrics along with energy efficiency and cost for access must be considered. The increased number of choices in a HWN makes the problem more difficult than traditional homogeneous networks since each Radio Access Technology (RAT) has unique characteristics. For instance, Bluetooth networks have low range and speed but are cheap compared to 4G networks. These types of observations can be factored into decision making in HWNs. Quality of Service and Experience should be considered so that the best possible configuration of connectivity, price and user application is made. All of this should occur autonomously. This paper provides a survey of recent works in HWNs with these ideas in mind. Existing approaches are categorized by function. Limitations and strengths of solutions are highlighted and comparisons between approaches are made to provide a starting point for further research in the area.

      PubDate: 2014-04-27T19:25:27Z
  • Cell selection for open-acces femtocell networks: Learning in changing
    • Abstract: Publication date: Available online 26 April 2014
      Source:Physical Communication
      Author(s): Chaima Dhahri , Tomoaki Ohtsuki
      This paper addresses the problem of cell selection in dynamic open-access femtocell networks. We model this problem as decentralized restless multi-armed bandit (MAB) with unknown dynamics and multiple players. Each channel is modelled as an arbitrary finite-state Markov chain with different state space and statistics. Each user tries to learn the best channel that maximizes its capacity and reduces its number of handovers. This is a classic exploration/exploitation problem, where the reward of each channel is considered to be Markovian. In addition, the reward process is restless because the state of each Markov chain evolves independently of the user action. This leads to a decentralized restless bandit problem. To solve this problem, we refer to the decentralized restless upper confidence bound (RUCB) algorithm that achieves a logarithmic regret over time for MAB problem (proposal 1). Then, we extend this algorithm to cope with dynamic environment by applying a change point detection test based on Page–Hinkley test (PHT) (proposal 2). However, this test would entail some waste of time if the change-point detection was actually a false alarm. To face this problem, we extend our previous proposal by referring to a meta-bandit algorithm (proposal 3) to solve the dilemma between Exploration and Exploitation after the change-point detection occurs. Simulation results show that • our proposal come close to the performance of opportunistic method in terms of capacity, while fewer average number of handovers is required. • The use of a change point test and meta-bandit algorithm allow better performance than RUCB in terms of capacity particularly in a changing environment.

      PubDate: 2014-04-27T19:25:27Z
  • Fuzzy Logic Classifier design for air targets recognition based on HRRP
    • Abstract: Publication date: Available online 26 April 2014
      Source:Physical Communication
      Author(s): Jing Liang , Fangqi Zhu
      The paper describes a Fuzzy Logic Classifier (FLC) to achieve the recognition for air targets. We first acquire the high range resolution profiles (HRRP) of three types of air targets from the measurements. We extract two typical features, namely, the length of the air targets and the difference between adjacent two HRRP based on HRRP from the measurements. Then we design the FLC to synthesize the two characters and identify the type of air targets. Simulation results show that our FLC can achieve the function of target recognition with a high ratio of recognition and also shows a robust performance to some extent.

      PubDate: 2014-04-27T19:25:27Z
  • MAC level Throughput comparison: 802.11ac vs. 802.11n
    • Abstract: Publication date: September 2014
      Source:Physical Communication, Volume 12
      Author(s): Oran Sharon , Yaron Alpert
      We compare between the Throughput performance of IEEE 802.11n and IEEE 802.11ac under the same PHY conditions and in the three aggregation schemes that are possible in the MAC layer of the two protocols. We find that for an error-free channel 802.11ac outperforms 802.11n due to its larger frame sizes, except for the case where there is a limit on the number of aggregated packets. In an error-prone channel the bit error rate sometimes determines the optimal frame sizes. Together with the limit on the number of aggregated packets, these two factors limit the advantage of 802.11ac.

      PubDate: 2014-04-27T19:25:27Z
  • Redundant residue number system based space–time block codes
    • Abstract: Publication date: Available online 22 January 2014
      Source:Physical Communication
      Author(s): Avik Sengupta , Balasubramaniam Natarajan
      In this paper, we propose a novel application of Redundant Residue Number System (RRNS) codes to Space–Time Block Codes (STBCs) design. Based on the so-called “Direct Mapping” and “Indirect Mapping” schemes, the link between residues and complex signal constellations is optimized. We derive upper bounds on the codeword error probability of RRNS–STBC and characterize its achievable diversity gain assuming maximum likelihood decoding (MLD). The knowledge of apriori probabilities of residues is utilized to implement a probability based Distance-Aware Direct Mapping scheme. Using simulation results, we demonstrate that the Distance-Aware Direct Mapping scheme provides performance gain, relative to a traditional direct mapping scheme, that increases with decreasing code rate.

      PubDate: 2014-01-25T03:07:54Z
  • Efficient Coupled PHY and MAC use of Physical Bursts by ARQ-Enabled
           connections in WiMAX/IEEE 802.16e Networks
    • Abstract: Publication date: Available online 9 January 2014
      Source:Physical Communication
      Author(s): Oran Sharon , Amit Liron , Yaron Alpert
      In this paper we address an aspect of the mutual influence between the PHY layer budding blocks (FEC Blocks) and the MAC level allocations in the Uplink and Downlink of IEEE 802.16e/WiMAX networks. In these networks it is possible to transmit MAC level frames, denoted MAC PDUs, such that a PDU contains an integral number of fixed size Data Blocks. PDUs are transmitted over PHY Bursts, which are divided into FEC Blocks. We suggest several algorithms to computes the best way to define PDUs in a Burst in order to maximize several performance criteria. We also give guidelines on how to choose the best Modulation/Coding Scheme (MCS) to use in the Burst, given the SNR of the channel and the performance criteria.

      PubDate: 2014-01-13T04:34:46Z
  • Seamless outdoor/indoor navigation with WIFI/GPS aided low cost Inertial
           Navigation System
    • Abstract: Publication date: Available online 9 January 2014
      Source:Physical Communication
      Author(s): Jiantong Cheng , Ling Yang , Yong Li , Weihua Zhang
      This paper describes an integrated navigation system that can be used for pedestrian navigation in both outdoor and indoor environments. With the aid of Global Positioning System (GPS) positioning solutions, an Inertial Navigation System (INS) can provide stable and continuous outdoor navigation. When moving indoors, WIFI positioning can replace the GPS in order to maintain the integrated system’s long-term reliability and stability. On the other hand, the position from an INS can also provide apriori information to aid WIFI positioning. Signal strength-based WIFI positioning is widely used for indoor navigation. A new fingerprinting method is proposed so as to improve the performance of WIFI stand-alone positioning. For pedestrian navigation applications, a step detection method is implemented to constrain the growth of the INS error using an Extend Kalman Filter (EKF). Experiments have been conducted to test this system and the results have demonstrated the feasibility of this seamless outdoor/indoor navigation system.

      PubDate: 2014-01-13T04:34:46Z
  • Sense-through-wall human detection using UWB radar with sparse SVD
    • Abstract: Publication date: Available online 30 December 2013
      Source:Physical Communication
      Author(s): Xiaoyang Li , Qilian Liang , Francis C.M. Lau
      In this paper, a method for through-wall human detection based on the singular values decomposition of the measurement matrices is presented. After demonstrating the sparsity of the matrices using CLEAN algorithm, an SVD algorithm based on Lanczos process is applied to compute their singular values. We also analyze the singular values of matrices constructed by difference square techniques for different types of walls and compare our algorithm with a 2-D imaging approach proposed by researchers in Time Domain Company. Detection results show that our method performs well in gypsum wall, brick wall, and wooden door.

      PubDate: 2014-01-01T03:02:44Z
  • Macrocell–femtocells resource allocation with hybrid access
           motivational model
    • Abstract: Publication date: Available online 23 December 2013
      Source:Physical Communication
      Author(s): Hanaa Marshoud , Hadi Otrok , Hassan Barada
      Femtocell technology has emerged as an efficient cost-effective solution not only to solve the indoor coverage problem but also to cope with the growing demand requirements. This paper investigates two major design concerns in two tier networks: resource allocation and femtocell access. Base station selection together with dual bandwidth and power allocation among the two tiers are investigated under shared spectrum usage. To achieve fair and efficient resource optimization, our model assumes that hybrid access mode is applied in the femtocells. Hybrid access mode is beneficial for system performance as (1) it lessens interference caused by nearby public users, (2) it allows public users to connect to near femtocells and get better Quality of Service (QoS) and (3) it increases system capacity as it allows the macrocell to serve more users. However, femtocells’ owners can behave selfishly by denying public access to avoid any performance reduction in subscribers’ transmissions. Such a problem needs a motivation scheme to assure the cooperation of femtocells’ owners. In this paper, we propose a game-theoretical hybrid access motivational model. The proposed model encourages femtocells’ owners to share resources with public users, thus, more efficient resource allocation can be obtained. We optimize the resource allocation by means of the Genetic Algorithm (GA). The objective of the formulated optimization problem is the maximization of network throughput that is calculated by means of Shannon’s Capacity Law. Simulations are conducted where a modified version of the Weighted Water Filling (WWF) algorithm is used as a benchmark. Our proposed model, compared to WWF, achieves more efficient resource allocation in terms of system throughput and resources utilization.

      PubDate: 2013-12-28T04:32:38Z
  • Sensor-based dead-reckoning for indoor positioning
    • Abstract: Publication date: Available online 12 December 2013
      Source:Physical Communication
      Author(s): Ian Sharp , Kegen Yu
      This paper presents a method of indoor position determination using an accelerometer, compass and gyroscope which are typically available in devices such as smart phones. The method makes use of measurements from such a device worn on the body, such as attached to a belt. The accelerometer in the device estimates the stride length indirectly from the vertical acceleration associated with walking, while the compass and gyroscope measure the heading angle. The position of the subject is then determined by combining the stride length distance estimates and the heading information, but corrected periodically at known checkpoints within the building. The method was tested with a range of both males and females wearing the device, at different walking speeds and styles. The experimental results demonstrate that the stride length estimation can be accurate to about 7 percent. The measured data agree closely with a theoretical dynamical model of walking. The results also show that the position of the subject can be determined with an accuracy of 0.6 m when walking along an indoor path.

      PubDate: 2013-12-16T12:07:14Z
  • Optimal multisensor integrated navigation through information space
    • Abstract: Publication date: Available online 6 December 2013
      Source:Physical Communication
      Author(s): Yong Li
      Although the centralized Kalman filtering (CKF) solution is widely accepted as providing the globally optimal parameter estimation for multisensor navigation systems, it has inherent defects such as heavy communication and computational load and poor fault-tolerant capability. To address these problems decentralized Kalman filtering (DKF) methods have been proposed. The DKF is configured as a bank of filters instead of the central filter, and aims to achieve the same level accuracy as the CKF. This CKF-based approach however is found too rigorous to limit the further development of DKF algorithms. This paper proposes an alternative framework for resolving the optimal state estimation problem of multisensor integration. The data fusion algorithm is implemented through a series of transformations of vectors from one space into another. In this way, the vectors in the source information spaces are transformed into the estimate information space, where the globally optimal solution is obtained simply by a sum of these transformed vectors. The paper demonstrates how easy to derive the conventional DKF algorithms, such as the federated Kalman filter that has been widely applied in the multisensor navigation community. A new global optimal fusion algorithm is derived from the proposed approach. Simulation results demonstrate that the algorithm has higher accuracy than the CKF.

      PubDate: 2013-12-08T10:55:58Z
  • Receiver structure and estimation of the modulation index for tamed
           frequency modulated (TFM) signals
    • Abstract: Publication date: Available online 7 December 2013
      Source:Physical Communication
      Author(s): Markku Kiviranta , Aarne Mämmelä
      Tamed frequency modulation (TFM) is a spectrally efficient constant amplitude continuous phase modulation (CPM) scheme which can be simply realized by using a frequency modulator (FM). In the implementation the modulation index of TFM is calibrated to have a nominal value of 0.5, but due to temperature variations it can drift causing time varying phase jitter. In this paper we present novel algorithms and performance results to measure and control the modulation index in a coherent receiver based on joint reduced state sequence detector (RSSD) and per-survivor processing (PSP) carrier phase estimation. The modulation index estimator measures phase transitions in the receiver and derives estimates by comparing the result to the coding rule of the TFM signal. The estimator has acquisition and tracking ability, and the current estimate can be used to replace the nominal index value. Our simulation results show that the proposed coherent receiver with the novel modulation index estimator has less than 1 dB performance degradation compared to around 4.5 dB exploiting only the PSP carrier phase estimation.

      PubDate: 2013-12-08T10:55:58Z
  • Detection and countermeasure of interference in slow FH/MFSK systems over
           fading channels
    • Abstract: Publication date: Available online 2 December 2013
      Source:Physical Communication
      Author(s): Aye Aung , Kah Chan Teh , Kwok Hung Li
      In this paper, we present an algorithm to detect unknown interference in slow frequency-hopped M -ary frequency-shift-keying (SFH/MFSK) systems over fading channels. Both partial-band noise interference (PBNI) and multitone interference (MTI) are considered. The proposed algorithm performs the detection process after dehopping by making use of square-law detectors. We first analyze the statistical property of the outputs of the square-law detectors over one hop duration, and an appropriate threshold level is derived for detecting the interference based on a binary hypothesis testing. We also formulate the closed-form expressions for the probabilities of detection of both types of interference experienced in any particular frequency hop. The analytical results are validated by the simulation results and they reveal that the proposed algorithm is able to provide good detection performance for both types of interference and outperforms the conventional ratio-threshold test (RTT) method.

      PubDate: 2013-12-04T04:40:03Z
  • LTE-Advanced and the evolution to beyond 4G (B4G) systems
    • Abstract: Publication date: Available online 20 November 2013
      Source:Physical Communication
      Author(s): Ian F. Akyildiz , David M. Gutierrez-Estevez , Ravikumar Balakrishnan , Elias Chavarria-Reyes
      Cellular networks have been undergoing an extraordinarily fast evolution in the past years. With commercial deployments of Release 8 (Rel-8) Long Term Evolution (LTE) already being carried out worldwide, a significant effort is being put forth by the research and standardization communities on the development and specification of LTE-Advanced. The work started in Rel-10 by the Third Generation Partnership Project (3GPP) had the initial objective of meeting the International Mobile Telecommunications-Advanced (IMT-Advanced) requirements set by the International Telecommunications Union (ITU) which defined fourth generation (4G) systems. However, predictions based on the wireless traffic explosion in recent years indicate a need for more advanced technologies and higher performance. Hence, 3GPP’s efforts have continued through Rel-11 and now Rel-12. This paper provides a state-of-the-art comprehensive view on the key enabling technologies for LTE-Advanced systems. Already consolidated technologies developed for Rel-10 and Rel-11 are reviewed while novel approaches and enhancements currently under consideration for Rel-12 are also discussed. Technical challenges for each of the main areas of study are pointed out as an encouragement for the research community to participate in this collective effort.

      PubDate: 2013-11-22T03:07:43Z
  • Performance evaluation of random linear network coding using Vandermonde
    • Abstract: Publication date: Available online 19 November 2013
      Source:Physical Communication
      Author(s): Pallavi R. Mane , Sudhakar G. Adiga , M. Sathish Kumar
      This paper discusses random linear network coding with and without the use of a Vandermonde matrix to obtain the coding coefficients. Performance comparison of such random linear network coded networks with networks employing traditional store and forward technique are also provided. It is shown that random linear network coding using Vandermonde matrix can improve the network utilization factor by reducing the overhead compared to random linear coding that does not use Vandermonde matrix. Our numerical results show that random linear network coding with Vandermonde matrix provides considerable improvement in throughput and delay when compared to a network employing traditional store and forward strategy. An inherent feature of random linear network coding which makes it possible to employ simple encryption techniques is as well discussed.

      PubDate: 2013-11-22T03:07:43Z
  • A prototype cognitive radio architecture for TVWS exploitation under the
           real time secondary spectrum market policy
    • Abstract: Publication date: Available online 21 November 2013
      Source:Physical Communication
      Author(s): Athina Bourdena , Evangelos Pallis , George Kormentzas , George Mastorakis
      This paper elaborates on the design and implementation of a prototype system architecture enabling for TVWS exploitation by LTE Advanced systems, under the real time secondary spectrum market policy. It describes a centralised infrastructure-based cognitive radio network, where dynamic TVWS allocation among unlicensed systems is administrated by a spectrum broker, carrying out radio-resource management and spectrum trading in real time. For efficient system performance as a matter of both maximum-possible radio resource exploitation and trading revenue, the paper discusses the design and implementation of a prototype mechanism at the spectrum broker side, which exploits backtracking algorithm for obtaining the best-matching solution. Performance evaluation experiments carried-out under controlled conditions (i.e. simulation) verified the validity of the proposed architecture, besides establishing its capacity for maximum spectrum utilisation and minimum fragmentation under a fixed-price trading policy.

      PubDate: 2013-11-22T03:07:43Z
  • Channel interpolation for LTE uplink systems with high mobility using
           Slepian sequences
    • Abstract: Publication date: Available online 14 November 2013
      Source:Physical Communication
      Author(s): Bahattin Karakaya , Hakan A. Çırpan , Hüseyin Arslan
      Single Carrier Frequency Division Multiple Access (SC-FDMA) has been adopted for 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink communication since it combines the low peak to average power ratio feature of single-carrier transmission systems with the multi-path resistance and flexible frequency allocation of orthogonal frequency-division multiple access (OFDMA). Unfortunately, SC-FDMA transmission over time-varying multipath fading channels for very high speed environments the subcarrier orthogonality is destroyed giving rise to inter carrier interference (ICI) due to channel variation within an SC-FDMA symbol. This paper is, therefore, focused on the use of time-domain channel interpolator for LTE uplink systems in large Doppler spread scenarios to improve channel tracking performance. The resulting interpolation algorithm is based on the discrete prolate spheroidal wave functions (DPSWF) which is particularly well suited to represent the rapidly time-varying fading channel due to optimum finite time and frequency support feature. The variations of the channel taps are tracked first by Kalman filter in time domain during training symbols. Then, DPSWF based channel interpolator is applied to recover the time variation of channel taps between training symbols within two consecutive slots in a single subframe. The performance of the proposed interpolator is compared with polynomial interpolator whose order is adjusted adaptively to achieve best fit under particular user mobilities. Moreover, the analytical mean square error (MSE) performance of DPSWF is derived and compared with the simulations. The results show that the DPSWF represents the time-varying fading channel very effectively and the proposed algorithm has excellent channel estimation performance in high SNR even with a very small number of channel interpolation parameters employed in the algorithm.

      PubDate: 2013-11-18T02:46:33Z
  • Cyclostationary signatures for LTE Advanced and beyond
    • Abstract: Publication date: Available online 16 November 2013
      Source:Physical Communication
      Author(s): P.D. Sutton , B. Özgül , L.E. Doyle
      Long Term Evolution (LTE) Advanced is the next generation of the LTE standard, offering peak data rates of up to 1 Gbps using up to 100 MHz of spectrum. A key mechanism in achieving this is carrier aggregation (CA) whereby multiple LTE component carriers (CCs) are combined in a contiguous or non-contiguous fashion. With the introduction of CA comes the challenge of network rendezvous. In order to associate with an LTE Advanced basestation or eNodeB, a (UE) device must be capable of detecting component carriers in use by that eNodeB and establishing communications links. Looking beyond LTE Advanced, the introduction of service and technology neutral approaches to spectrum management is likely to increase the importance of rendezvous, as more diverse spectrum bands become available for use. This paper presents cyclostationary signatures as a powerful tool for overcoming the challenge of network rendezvous in LTE Advanced networks and beyond. A signature detector design, based on the (AF), is presented and a number of mechanisms for embedding signatures in downlink LTE CC waveforms are described. The performance of our signature detector is examined in depth through simulation under conditions of doubly-selective fading. Simulation results highlight the performance advantages which can be achieved through use of the (AF)-based detector over the simpler (TS-CCP)-based detector. Over the air experiments using a software radio based transceiver are described and results are presented.

      PubDate: 2013-11-18T02:46:33Z
  • PHY modulation/rate control for fountain codes in 802.11a/g WLANs
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Xiaomin Chen , Vijay G. Subramanian , Douglas J. Leith
      In this paper we consider the joint performance of fountain codes and 802.11a/g PHY modulation/coding. We consider optimality both in terms of maximizing goodput and minimizing energy, and results are presented for both theoretical and experimental channel models. In contrast to studies in cellular networks, we find that in 802.11a/g WLANs the cross-layer approach of a higher-layer fountain coding with a PHY layer modulation and FEC coding can yield very limited gains, and the PHY modulation/rate that optimizes the uncoded multicast performance is also close to that for fountain-coded multicast traffic over a wide-range of network conditions. This is potentially an important observation as it indicates that in 802.11a/g WLANs cross-layer design for multicast rate control would bring few benefits and PHY layer rate control can be carried out without regard to the use of fountain coding at higher layers.

      PubDate: 2013-11-18T02:46:33Z
  • Editorial Board
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9

      PubDate: 2013-11-18T02:46:33Z
  • Dynamic spectrum access in LTE-advanced networks
    • Abstract: Publication date: Available online 12 November 2013
      Source:Physical Communication
      Author(s): Juan D. Deaton , Ryan E. Irwin , Luiz A. DaSilva
      As early as 2014, mobile network operators’ spectral capacity will be overwhelmed by the demand brought on by new devices and applications. To augment capacity and meet this demand, operators may choose to deploy a Dynamic Spectrum Access (DSA) overlay. The signaling and functionality required by such an overlay have not yet been fully considered in the architecture of the planned Long Term Evolution Advanced (LTE+) networks. This paper presents a Spectrum Accountability framework to be integrated into LTE+ architectures, defining specific element functionality, protocol interfaces, and signaling flow diagrams required to enforce the rights and responsibilities of primary and secondary users. We also quantify, through integer programs, the benefits of using DSA channels to augment capacity under a scenario in which the LTE+ network can opportunistically use TV and GSM spectrum. The framework proposed here may serve as a guide in the development of future LTE+ network standards that account for DSA.

      PubDate: 2013-11-14T03:10:01Z
  • Maximizing capacity with trellis exploration aided limited feedback
           precoder design for multiuser MIMO-MAC
    • Abstract: Publication date: Available online 9 November 2013
      Source:Physical Communication
      Author(s): Sayak Bose , Balasubramaniam Natarajan , Dalin Zhu
      In this paper, a linear trellis based precoding technique is proposed for maximizing multiuser MIMO capacity in a multiple access channel with inter symbol interference (ISI). We use the trellis exploration algorithm to design a precoding matrix that minimizes the interference from other users by allocating power in the appropriate eigen modes. Employing a finite number of phases, the precoder matrix for each user is first custom designed at the receiver. Then a bit sequence indicating the phase indices of the optimized precoding matrix elements for the corresponding user is fed back to the transmitter. We show that under this approach, the sum rate capacity achieved is comparable to the optimal sum-rate capacity employing the well-known water filling solution with complete channel knowledge at the transmitter for spatio-temporal vector coding (STVC). Our simulations for various multiuser MIMO cases, show that the per user precoding with limited feedback and equal power allocation strategy achieves desirable capacity gains relative to eigen beamforming and Grassmannian precoding.

      PubDate: 2013-11-10T04:30:02Z
  • Carrier aggregation in power limited devices over Rayleigh fading channels
    • Abstract: Publication date: Available online 9 November 2013
      Source:Physical Communication
      Author(s): Brage Ellingsæter
      In this paper we analyze, both theoretically and through simulations, the aspect of carrier aggregation in power limited devices over Rayleigh fading for use in future wireless systems. We derive analytical expressions for the probability of transmitting over K carriers, as well as an upper bound on the gain achieved with carrier aggregation and the probability of carrier aggregation yielding a certain gain over single carrier allocation. These analytical expressions are verified through simulations. The analysis gives insight to the average SNR one needs to obtain the desired gain with carrier aggregation. As suspected, carrier aggregation does not increase the spectral efficiency in the uplink of a wireless system and in the low SNR regime one does not achieve any gain with carrier aggregation. However, carrier aggregation can be employed to achieve the 4G bit-rates as stated by 3GPP, given that certain users have very good channel conditions.

      PubDate: 2013-11-10T04:30:02Z
  • A method for the construction of hierarchical generalized space shift
           keying (GSSK) modulation for unequal error protection
    • Abstract: Publication date: Available online 16 September 2013
      Source:Physical Communication
      Author(s): Ronald Y. Chang , Sian-Jheng Lin , Wei-Ho Chung
      In this paper, we propose a systematic method to achieve two-level unequal error protection (UEP) with generalized space shift keying (GSSK) modulation for multiple-input multiple-output (MIMO) systems. GSSK is a modulation scheme that encodes the source information in the antenna indices. To enable the nonuniform arrangement of the spatial constellation of GSSK modulation, new techniques are needed as new features of GSSK modulation as opposed to the conventional modulation are observed. The proposed method is based on first partitioning the GSSK constellation into subsets and then choosing constellation points inside a subset. The high-priority (HP) bits select the subset and the low-priority (LP) bits select constellation points inside a subset. The proposed subset partitioning procedure developed based on a theoretical study on set partitioning in the multidimensional space guarantees optimal or near-optimal HP protection, enables simple and systematic designs for LP protection, and increases the LP capacity. The proposed systematic design approach applies to systems with any numbers of transmit antennas and can create various hierarchical GSSK schemes with different HP/LP protection capabilities.

      PubDate: 2013-09-17T00:39:53Z
  • On spectrum sensing in cognitive radio CDMA networks with beamforming
    • Abstract: Publication date: Available online 4 September 2013
      Source:Physical Communication
      Author(s): Sanjay Dhar Roy , Sumit Kundu , Gianluigi Ferrari , Riccardo Raheli
      In this paper, the performance of Cognitive Radio (CR) Code Division Multiple Access (CDMA) networks is analyzed in the presence of receive beamforming at the Base Stations (BSs). More precisely, we analyze, through simulations, the performance achievable by a CR user, with and without spectrum sensing, in a three-cell scenario. Uplink communications are considered. Three different schemes for spectrum sensing with beamforming are presented, together with a scheme without spectrum sensing. CR users belong to a Cognitive Radio Network (CRN) which is coexisting with a Primary Radio Network (PRN). Both CRN and PRN are CDMA-based. The CRN is assumed to utilize beamforming for its CR users. Soft Hand-Off (HO) and power control are considered in both the CRN and the PRN. The impact of beamforming on the system performance is analyzed considering various metrics. In particular, we evaluate the performance of the proposed systems in terms of outage probability, blocking probability, and average data rate of CR users. The obtained results clearly indicate that significant performance improvements can be obtained by CR users with the help of beamforming. The impact of several system parameters on the performance of the three considered spectrum sensing schemes with beamforming is analyzed. Our results, in terms of probability of outage, show that the relative improvement brought by the use of beamforming is higher in the absence of spectrum sensing (reduction of 80%) than in the presence of spectrum sensing (reduction of 42%).

      PubDate: 2013-09-05T02:09:24Z
  • Special issue on Cognitive radio: The road for its second decade
    • Abstract: Publication date: Available online 29 August 2013
      Source:Physical Communication
      Author(s): Kareem E. Baddour , Yeheskel Bar-Ness , Octavia A. Dobre , Mengüç Öner , Erchin Serpedin , Umberto Spagnolini

      PubDate: 2013-09-01T00:45:13Z
  • On the capacity of the multiple-hop relay channel with linear relaying
    • Abstract: Publication date: Available online 26 August 2013
      Source:Physical Communication
      Author(s): Zhixiang Deng , Bao-Yun Wang
      The relay nodes with linear relaying transmit linear combination of their past received signals. The capacity of the multiple-hop Gaussian relay channel with linear relaying is derived, assuming that each node in the channel only communicates with its nearest neighbor nodes. The capacity is formulated as an optimization problem over the relaying matrices and the covariance matrix of the signals transmitted from the source. It is proved that the solution to this optimization problem is equivalent to a “single-letter” optimization problem when some certain conditions are satisfied. We also show that the solution to the “single-letter” optimization problem has the same form as the expression of the rate achieved by time-sharing amplify-and-forward (TSAF). In order to solve this equivalent problem, we give an iterative algorithm. Simulation results show that the achievable rate with TSAF is close to the capacity, if channel gain of one certain hop is smaller than that of all the other hops relatively.

      PubDate: 2013-08-28T00:35:30Z
  • A tree-structured DFT filter bank based spectrum detector for estimation
           of radio channel edge frequencies in cognitive radios
    • Abstract: Publication date: Available online 19 June 2013
      Source:Physical Communication
      Author(s): M. Narendar , A.P. Vinod , A.S. Madhukumar , Anoop Kumar Krishna
      Cognitive Radio (CR) aims to provide efficient spectrum utilization in spectrum scarce wireless environments. One of the key CR functionalities is the spectrum sensing, which allows CRs to monitor the electromagnetic spectrum and detect unused bands of spectrum. Wideband spectrum sensing needs to be employed for better spectrum opportunity detection and interference avoidance both in the case of commercial and military applications. Accurate sensing needs to be employed for blocker detection in commercial systems such as LTE for the design of transmit/receive path. In military radios, the challenge lies in the robust detection of the location of the center frequencies and bandwidths of individual radio channels in the wideband input signal. In this paper, an energy detector based on tree-structured discrete Fourier transform based filter bank (TDFTFB) is proposed for detecting the edges of the channels in the spectrum. The proposed method is compared with the conventional wavelets based method for complexity and performance. The design example and simulations show that the gate count resource utilization of the proposed detection scheme is 22.9% lesser than the wavelets method at the cost of a slight degradation (0.5%) in detection accuracy. Over-the-air tests performed using Universal Software Radio Peripheral 2 (USRP2) and MATLAB/SIMULINK showed that the present method is not input specific whereas the conventional wavelet based approach depends on the spectral location of the input.

      PubDate: 2013-06-20T14:06:33Z
  • Interference suppression for LTE uplink
    • Abstract: Publication date: Available online 28 May 2013
      Source:Physical Communication
      Author(s): Mehmet Bahadır Çelebi , İsmail Güvenç , Hüseyin Arslan , Khalid A. Qaraqe
      Interference cancellation is expected to have significant importance for next-generation wireless communication systems due to various co-channel deployment scenarios and denser frequency reuse. In this study, an interference cancellation receiver that exploits the unique characteristics of single-carrier frequency-division multiple access based systems is proposed. The proposed receiver suppresses the co-channel dominant interference by blanking the frequency-domain samples where the desired and interfering signals overlap. In order to improve the performance, demodulation and regeneration stages can be introduced and repeated multiple times. Further enhancement is possible by initially accommodating a group of reliable symbols before the iterations. The simulation results indicate that proposed methods work particularly well for low overlap ratios compared to interference coordination and no cancellation schemes.

      PubDate: 2013-05-31T14:04:53Z
  • Cooperation within the Small Cell: The indoor, correlated shadowing case
    • Abstract: Publication date: Available online 10 May 2013
      Source:Physical Communication
      Author(s): Vasileios K. Sakarellos , Dimitrios Skraparlis , Athanasios D. Panagopoulos
      The deployment of Small Cells in fourth generation (4G) communication systems is aimed at providing significant capacity improvements and higher availabilities. However, the design of Small Cell systems in indoor environments is especially challenging due to high shadowing attenuation induced by clutter and human blockage. This paper studies node cooperation and multiple relaying and proposes novel analytical formulas for the outage probability of cooperative Small Cells suffering from shadowing. The channel fading gains are modelled as correlated lognormal random variables, in order to reflect the properties of indoor propagation environments. Various cooperative strategies are considered, taking into account the use of one or two Relays and different receiver combining techniques. In addition, the relative performance of each cooperative configuration and the benefit of cooperation over non-cooperation are investigated. Finally, interesting and useful insights are produced regarding the impact of the correlated lognormal environment parameters on the configuration of cooperative Small Cells.

      PubDate: 2013-05-11T14:02:09Z
  • Enabling next generation small cells through femtorelays
    • Abstract: Publication date: Available online 23 April 2013
      Source:Physical Communication
      Author(s): Ian F. Akyildiz , Elias Chavarria-Reyes , David M. Gutierrez-Estevez , Ravikumar Balakrishnan , John R. Krier
      Today’s society is driven by ever-growing information needs, which cause increased demand for ubiquitous and very high speed wireless communications. In search for the urgent need of improved coverage and capacity, cellular networks are currently undergoing a major transformation from an architecture comprised of thoroughly planned macrocell base stations (MBSs) to a much more heterogeneous architecture where the macrocell network is underlaid by one or several tiers of unevenly deployed small cells. However, this new set of technologies is not exempt of several challenges. Backhaul is still an unresolved issue, i.e. which is the best technology for the small cell to reach the core network. In the case of uncoordinated co-channel deployments where the macrocell and small cell tier share the spectrum (e.g. femtocells or metrocells), the interference is also a major problem. In this paper, a new concept and architecture called femtorelays is introduced as a novel solution for next generation small cell problems. A femtorelay is a small cell access point that enables improved cellular coverage within indoor environments while increasing the overall system capacity through spatial frequency reuse. Working as an open-access small cell, it provides dual-backhaul connectivity to the core network for registered and unregistered users. One of the backhaul connections is the internet-based, and the second one is the relay-based operating on spectrum owned by the wireless carrier. The radio interference between macrocell and small cell is overcome by servicing the macrocell interfering users at the femtorelay. Unlike the traffic from subscribers, this traffic will be forwarded to the network through the relay-based backhaul. The internal architecture, the approach employed to make the technology fit in existing networks, and future evolution of the basic femtorelays for larger scenarios are also presented. Finally, performance results show the potential of this technology to outperform other existing solutions.

      PubDate: 2013-04-25T14:05:03Z
  • New results on performance analysis of opportunistic regenerative relaying
    • Abstract: Available online 3 April 2013
      Publication year: 2013
      Source:Physical Communication

      In this paper, we investigate an opportunistic relaying scheme where the selected relay assists the source-destination (direct) communication. In our study, we consider a regenerative opportunistic relaying scheme in which the direct path may be unusable, and takes into account the effect of the possible erroneously detected and transmitted data at the selected relay. We first derive the signal-to-noise (SNR) statistics for each hop, which are used to determine accurate closed form expressions for end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation and end-to-end outage probability for a transmission rate R over Rayleigh fading channels. Furthermore, we evaluate the asymptotical performance and deduce the diversity order. Finally, we validate our analysis by showing that performance simulation results coincide with our analytical results over linear network architecture.

      PubDate: 2013-04-05T20:05:03Z
  • Rate-lossless PAPR reduction in per-subcarrier antenna selection OFDM
    • Abstract: Available online 22 March 2013
      Publication year: 2013
      Source:Physical Communication

      We propose a generalised rate-lossless technique for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing systems employing antenna selection on a per-subcarrier basis. The proposed technique, which is from the family of the active constellation extension (ACE) approaches to PAPR reduction, exploits the nulled subcarriers (for a given antenna) that arise through the antenna selection process to reduce the PAPR by introducing a controlled level of distortion to these subcarriers. We demonstrate that known PAPR reduction methods are unsuitable for per-subcarrier antenna selection systems, which motivates our modifications. We then show that our proposal achieves a much lower PAPR than traditional ACE methods for the given systems. Moreover, we demonstrate through a detailed theoretical analysis of the bit-error rate and a simulation analysis of the distortion transmitted on the nulled subcarriers, that the interference to the data signal caused by this distortion will not hinder practical system performance. Finally, we show that the efficacy of the proposed technique increases with the number of transmit antennas.

      PubDate: 2013-03-24T15:08:00Z
  • Complexity reduced detection for MIMO–OFDMA uplink with distinct
           frequency offsets from each user
    • Abstract: Available online 16 March 2013
      Publication year: 2013
      Source:Physical Communication

      In this work, we propose a relatively low-complexity iterative algorithm for the detection of transmitted symbols at the uplink of a multiple-input multiple-output (MIMO) orthogonal frequency-division multiple-access (OFDMA) system. The algorithm allows distinct frequency-offsets (FO)s between each user and the base-station (BS). FOs cause inter-carrier-interference (ICI), which degrades the performance of the receiver and increases the computational-complexity to decode the transmitted symbols. In order to decrease the computational-complexity at each receive antenna the proposed algorithm accounts for the interference of subcarrier k onto only ± D nearby subcarriers and ignores the interference on remaining subcarriers. This yields a banded structured ICI matrix, which is exploited to design a low-complexity soft-interference-cancellation minimum mean-squared error (SIC-MMSE) equalizer. The effects of ignoring the subcarriers are compensated for by increasing the number of receive antennas. Simulation results show that for an uncoded system the bit-error-rate (BER) performance of the proposed algorithm outperforms the MMSE equalization and is very much close to the no FO scenario. Moreover, when convolution encoding is incorporated in the proposed algorithm outperforms the coded MMSE equalizer only after first iteration.

      PubDate: 2013-03-16T15:07:31Z
School of Mathematical and Computer Sciences
Heriot-Watt University
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