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  Subjects -> PHYSICS (Total: 736 journals)
    - ELECTRICITY (2 journals)
    - MECHANICS (5 journals)
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    - OPTICS (53 journals)
    - PHYSICS (623 journals)
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PHYSICS (623 journals)            First | 1 2 3 4 5 6 7 | Last

Meccanica     Hybrid Journal   (1 follower)
Mechanics of Advanced Materials and Structures     Hybrid Journal   (3 followers)
Mechanics of Materials     Hybrid Journal   (11 followers)
Mechanics of Solids     Hybrid Journal   (1 follower)
Mechanics of Time-Dependent Materials     Hybrid Journal   (1 follower)
Mechanics Research Communications     Hybrid Journal   (2 followers)
Metal Science and Heat Treatment     Hybrid Journal   (8 followers)
Metamaterials     Hybrid Journal   (2 followers)
Micro and Nano Systems Letters     Open Access   (1 follower)
Microfluidics and Nanofluidics     Hybrid Journal   (9 followers)
Microporous and Mesoporous Materials     Hybrid Journal   (3 followers)
Modern Instrumentation     Open Access   (2 followers)
Modern Physics Letters A     Hybrid Journal   (1 follower)
Modern Physics Letters B     Hybrid Journal  
Molecular Diversity     Hybrid Journal  
Moscow University Mechanics Bulletin     Hybrid Journal  
Moscow University Physics Bulletin     Hybrid Journal   (1 follower)
Multibody System Dynamics     Hybrid Journal  
NANO     Hybrid Journal   (6 followers)
Nano Letters     Full-text available via subscription   (37 followers)
Nano Reviews     Open Access   (15 followers)
Nanoscale and Microscale Thermophysical Engineering     Hybrid Journal   (3 followers)
Nanoscale Research Letters     Open Access   (4 followers)
Nanotechnology Magazine, IEEE     Full-text available via subscription   (12 followers)
Natural Science     Open Access   (9 followers)
Nature Communications     Hybrid Journal   (35 followers)
Nature Materials     Full-text available via subscription   (33 followers)
Nature Photonics     Full-text available via subscription   (13 followers)
Nature Physics     Full-text available via subscription   (22 followers)
NDT & E International     Hybrid Journal   (10 followers)
NEUTRINO     Open Access  
Neutron News     Hybrid Journal  
New Journal of Physics     Open Access   (7 followers)
Niels Bohr Collected Works     Full-text available via subscription  
Noise & Vibration Worldwide     Full-text available via subscription   (5 followers)
Noise Notes     Full-text available via subscription   (3 followers)
Nondestructive Testing And Evaluation     Hybrid Journal   (3 followers)
Nonlinear Dynamics     Hybrid Journal   (5 followers)
NTM Zeitschrift für Geschichte der Wissenschaften, Technik und Medizin     Hybrid Journal   (4 followers)
Nuclear Engineering and Design     Hybrid Journal   (11 followers)
Nuclear Fusion     Full-text available via subscription   (1 follower)
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment     Hybrid Journal   (5 followers)
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms     Hybrid Journal   (6 followers)
Nuclear Medicine and Biology     Hybrid Journal   (1 follower)
Nuclear Physics A     Hybrid Journal   (2 followers)
Nuclear Physics B     Open Access   (1 follower)
Nuclear Physics B - Proceedings Supplements     Hybrid Journal  
Nuclear Physics News     Hybrid Journal  
Nuclear Receptor     Full-text available via subscription   (1 follower)
Open Journal of Biophysics     Open Access   (1 follower)
Open Journal of Fluid Dynamics     Open Access   (3 followers)
Open Journal of Microphysics     Open Access  
Optical Communications and Networking, IEEE/OSA Journal of     Hybrid Journal   (3 followers)
Optical Engineering     Full-text available via subscription   (6 followers)
Optics and Photonics Letters     Open Access   (3 followers)
Optics Express     Open Access   (12 followers)
Optics Letters     Full-text available via subscription   (4 followers)
Optoelectronics Letters     Hybrid Journal  
Organic Electronics     Hybrid Journal   (3 followers)
PAJ: A Journal of Performance and Art     Hybrid Journal   (10 followers)
Particle Physics Insights     Open Access   (1 follower)
Particuology     Hybrid Journal  
Pattern Recognition in Physics     Open Access   (1 follower)
Pergamon Materials Series     Full-text available via subscription  
Phase Transitions and Critical Phenomena     Full-text available via subscription   (1 follower)
Philosophical Magazine     Hybrid Journal   (2 followers)
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences     Full-text available via subscription   (7 followers)
Philosophy and Foundations of Physics     Full-text available via subscription  
Photonics and Optoelectronics     Open Access   (1 follower)
Photonics Journal, IEEE     Full-text available via subscription   (5 followers)
Photonics Letters of Poland     Open Access  
Physica A: Statistical Mechanics and its Applications     Hybrid Journal   (6 followers)
Physica B: Condensed Matter     Hybrid Journal   (4 followers)
physica status solidi (a)     Hybrid Journal   (1 follower)
physica status solidi (b)     Hybrid Journal   (1 follower)
physica status solidi (c)     Hybrid Journal   (1 follower)
Physica Status Solidi - Rapid Research Letters     Hybrid Journal  
Physical Acoustics     Full-text available via subscription   (1 follower)
Physical Communication     Hybrid Journal  
Physical Mesomechanics     Hybrid Journal  
Physical Review C     Full-text available via subscription   (15 followers)
Physical Review Special Topics - Physics Education Research     Open Access   (5 followers)
Physical Review X     Open Access   (5 followers)
Physical Sciences Data     Full-text available via subscription   (1 follower)
Physics - spotlighting exceptional research     Full-text available via subscription  
Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B     Full-text available via subscription   (2 followers)
Physics and Chemistry of Liquids: An International Journal     Hybrid Journal  
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (3 followers)
Physics in Medicine & Biology     Full-text available via subscription   (7 followers)
Physics in Perspective     Hybrid Journal   (1 follower)
Physics International     Open Access   (2 followers)
Physics Letters A     Hybrid Journal   (9 followers)
Physics Letters B     Open Access   (2 followers)
Physics of Atomic Nuclei     Hybrid Journal  
Physics of Fluids     Hybrid Journal   (18 followers)
Physics of Life Reviews     Hybrid Journal   (1 follower)
Physics of Particles and Nuclei     Hybrid Journal   (1 follower)
Physics of Particles and Nuclei Letters     Hybrid Journal   (1 follower)
Physics of Plasmas     Hybrid Journal   (6 followers)
Physics of the Dark Universe     Open Access  

  First | 1 2 3 4 5 6 7 | Last

Physical Communication    Follow    
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1874-4907
     Published by Elsevier Homepage  [2556 journals]   [SJR: 1.326]   [H-I: 13]
  • 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
           approach
    • 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
       
  • Single frequency network based mobile tracking in NLOS environments
    • Abstract: Publication date: Available online 26 November 2013
      Source:Physical Communication
      Author(s): Jun Yan , Kegen Yu , Lenan Wu
      In single frequency network (SFN) positioning, base station (BS) identification is inevitable and non-line-of-sight (NLOS) propagation is usually dominant especially for indoor scenarios. BS identification and NLOS mitigation are two challenging problems which have significant impact on the SFN positioning performance. In this paper, a mobile tracking scheme is proposed to deal with these challenging issues. Specifically, BS identification is first formulated as a data validation problem. Each time-of-arrival (TOA) measurement is tentatively associated with a specific BS so that a number of TOA-BS relationship sets are produced. The gate technique is adapted to evaluate all the TOA-BS relationship sets and the set with the smallest gate parameter value is selected. This identification technique is suited for both line-of-sight (LOS) and NLOS propagation scenarios. The interacting multiple model (IMM) smoother is then utilized to smooth the identified TOA measurements at each BS to reduce the NLOS errors. In addition, the position determination and BS identification are jointly considered to enhance position estimation accuracy. Simulation results demonstrate that the proposed SFN positioning approach can perform satisfactorily in different propagation scenarios and has better performance than other SFN positioning algorithms.


      PubDate: 2013-11-30T03:07:00Z
       
  • 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
           matrix
    • 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
       
  • Propagation characteristics and modeling in indoor multi-floor environment
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Jianhua Zhang , Liang Xin , Fenghua Zhang
      In this paper, the wideband propagation characteristic for an indoor multi-floor scenario is investigated based on wideband multi-frequency channel measurements in two typical indoor environments. Based on the measurement results, the log-distance (LD) model is used to analyze path loss (PL) in different floors. We find that the total penetration loss does not increase linearly in dB with the number of floors traversed, and the propagation condition in same floor, that is line of sight (LOS) or non-LOS (NLOS), can affect the penetration loss significantly. Besides, additional loss caused by traversing floor upwards is 1–2 dB larger than that introduced by traversing floor downwards. Then, we adopt a small error-prediction attenuation factor (AF) model for PL prediction. The modeling process and rationality of the AF model are presented. Finally, delay spread of wideband indoor channel is analyzed. Statistics of time dispersion parameters are compared among floors and frequencies. It is found that the delay spread on the middle floors is the largest, the delay spread on higher floors is relatively small due to lack of power source, and its relation with frequency is not obvious.


      PubDate: 2013-11-18T02:46:33Z
       
  • Rule-based dynamic TV white space spectrum sharing services composition
           framework
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): B. Ye , M. Nekovee , A. Pervez , J.L. Chen
      When developing a TV White Space (TVWS) system with the available TV spectrum after digital switchover, the smooth introduction of new technologies and components has to be supported because the requirements of users change frequently in a new system. We need to provide a modular, extensible and easy to implement framework rather than building highly integrated systems. According to environment, rules, polices and users’ requirements, advanced intelligent management functionalities that can guarantee the proper configuration of devices in TVWS networks and proper load balance, have to be developed. According to different requests from users, different algorithms and components have to be used to meet the needs of the users. How, when and which algorithms and components should be combined in order to meet the requests from the users become essential problems. Based on Service Oriented Architecture, all things in the proposed system including algorithms and components can be defined as services. This paper presents a framework of rule-based dynamic TVWS services composition that can meet the above needs and combine different TVWS services to fulfil users’ requirements dynamically.


      PubDate: 2013-11-18T02:46:33Z
       
  • Joint transmitter adaptation and power control for cognitive radio
           networks with target SIR requirements
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Shiny Abraham , Dimitrie C. Popescu
      In this paper we study joint transmitter adaptation and power control in the uplink of Cognitive Radio (CR) networks with target values imposed on the signal-to-interference +noise-ratios (SINR) at the CR receiver. We use a framework based on block transmissions and linear precoders to formulate this as a constrained optimization problem for which we discuss the conditions that must be satisfied by the optimal solution. We also present an algorithm which adapts the transmit precoder and power values incrementally until a fixed point is reached where the specified target SINRs are achieved with minimum transmitted power. Convergence of the proposed algorithm is discussed and is illustrated with numerical examples obtained from simulations.


      PubDate: 2013-11-18T02:46:33Z
       
  • Analysis of mobility impact on interference in cognitive radio networks
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Ali Rıza Ekti , Serhan Yarkan , Khalid A. Qaraqe , Erchin Serpedin , Octavia A. Dobre
      Cognitive radio (CR) technology seems to be a promising candidate for solving the radio frequency (RF) spectrum occupancy problem. CRs strive to utilize the white holes in the RF spectrum in an opportunistic manner. Because interference is an inherent and a very critical design parameter for all sorts of wireless communication systems, many of the recently emerging wireless technologies prefer smaller size coverage with reduced transmit power in order to decrease interference. Prominent examples of short-range communication systems trying to achieve low interference power levels are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). It is clear that a comprehensive interference model including mobility is essential especially in elaborating the performance of such short-range communication scenarios. Therefore, in this study, a physical layer interference model in a mobile radio communication environment is investigated by taking into account all of the basic propagation mechanisms such as large- and small-scale fading under a generic single primary user (PU) and single secondary user (SU) scenario. Both one-dimensional (1D) and two-dimensional (2D) random walk models are incorporated into the physical layer signal model. The analysis and corresponding numerical results are given along with the relevant discussions.


      PubDate: 2013-11-18T02:46:33Z
       
  • HF spectrum activity prediction model based on HMM for cognitive radio
           applications
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): L. Melián-Gutiérrez , S. Zazo , J.L. Blanco-Murillo , I. Pérez-Álvarez , A. García-Rodríguez , B. Pérez-Díaz
      Although most of the research on Cognitive Radio is focused on communication bands above the HF upper limit (30 MHz), Cognitive Radio principles can also be applied to HF communications to make use of the extremely scarce spectrum more efficiently. In this work we consider legacy users as primary users since these users transmit without resorting to any smart procedure, and our stations using the HFDVL (HF Data+Voice Link) architecture as secondary users. Our goal is to enhance an efficient use of the HF band by detecting the presence of uncoordinated primary users and avoiding collisions with them while transmitting in different HF channels using our broad-band HF transceiver. A model of the primary user activity dynamics in the HF band is developed in this work to make short-term predictions of the sojourn time of a primary user in the band and avoid collisions. It is based on Hidden Markov Models (HMM) which are a powerful tool for modelling stochastic random processes and are trained with real measurements of the 14 MHz band. By using the proposed HMM based model, the prediction model achieves an average 10.3% prediction error rate with one minute-long channel knowledge but it can be reduced when this knowledge is extended: with the previous 8 min knowledge, an average 5.8% prediction error rate is achieved. These results suggest that the resulting activity model for the HF band could actually be used to predict primary users activity and included in a future HF cognitive radio based station.


      PubDate: 2013-11-18T02:46:33Z
       
  • A comparative study of spectrum awareness techniques for cognitive radio
           oriented wireless networks
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Raza Umar , Asrar U.H. Sheikh
      Spectrum scarcity is impeding practical implementations of emerging wireless multimedia applications requiring significantly more frequency spectrum. Cognitive radio (CR) has emerged as a promising solution to the current spectral congestion problem by imparting intelligence to the conventional software defined radio that allows spectrum sharing through opportunistic spectrum access. The principal objective of CR is to optimize the use of under-utilized spectrum through robust and efficient spectrum sensing (SS). This paper introduces cognitive functionality and provides an in-depth comparative survey of various spectrum awareness techniques in terms of their sensing accuracy and computational complexities along with their merits and demerits. Specifically, key challenges in SS are highlighted and possible solutions are discussed. A classification of SS is presented to address the sensing method selection criterion. Both non-cooperative and cooperative sensing schemes are reviewed and open research problems are highlighted to identify future research directions.


      PubDate: 2013-11-18T02:46:33Z
       
  • Spectrum sensing in cognitive radio networks: Performance evaluation and
           optimization
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Gang Xiong , Shalinee Kishore , Aylin Yener
      This paper studies cooperative spectrum sensing in cognitive radio networks where secondary users collect local energy statistics and report their findings to a secondary base station, i.e., a fusion center. First, the average error probability is quantitively analyzed to capture the dynamic nature of both observation and fusion channels, assuming fixed amplifier gains for relaying local statistics to the fusion center. Second, the system level overhead of cooperative spectrum sensing is addressed by considering both the local processing cost and the transmission cost. Local processing cost incorporates the overhead of sample collection and energy calculation that must be conducted by each secondary user; the transmission cost accounts for the overhead of forwarding the energy statistic computed at each secondary user to the fusion center. Results show that when jointly designing the number of collected energy samples and transmission amplifier gains, only one secondary user needs to be actively engaged in spectrum sensing. Furthermore, when the number of energy samples or amplifier gains are fixed, closed form expressions for optimal solutions are derived and a generalized water-filling algorithm is provided.


      PubDate: 2013-11-18T02:46:33Z
       
  • Multiple transmitter localization and communication footprint
           identification using energy measurements
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Venugopalakrishna Y.R. , Chandra R. Murthy , D. Narayana Dutt
      Whitespace identification is a crucial first-step in the implementation of cognitive radios, where the problem is to determine the communication footprint of active primary transmitters in a given geographical area. To do this, a number of sensors are deployed at known locations chosen uniformly at random within the given area. The sensors’ decisions regarding the presence or absence of a signal at their location is transmitted to a fusion center, which then combines the received information to construct the spatial spectral usage map. Under this model, several innovations are presented in this work to enable fast identification of the available whitespace. First, using the fact that a typical communication footprint is a sparse image, two novel compressed sensing based reconstruction methods are proposed to reduce the number of transmissions required from the sensors compared to a round-robin querying scheme. Second, a new method based on a combination of the K -means algorithm and a circular fitting technique is proposed for determining the number of primary transmitters. Third, a design procedure to determine the power thresholds for signal detection at sensors is discussed. The proposed schemes are experimentally compared with the round-robin scheme in terms of the average error in footprint identification relative to the area under consideration. Simulation results illustrate the improved performance of the proposed schemes relative to the round-robin scheme.


      PubDate: 2013-11-18T02:46:33Z
       
  • Optimization of hard fusion based spectrum sensing for energy-constrained
           cognitive radio networks
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Sina Maleki , Sundeep Prabhakar Chepuri , Geert Leus
      The detection reliability of a cognitive radio network improves by employing a cooperative spectrum sensing scheme. However, increasing the number of cognitive radios entails a growth in the cooperation overhead of the system. Such an overhead leads to a throughput degradation of the cognitive radio network. Since current cognitive radio networks consist of low-power radios, the energy consumption is another critical issue. In this paper, throughput optimization of the hard fusion based sensing using the k -out-of- N rule is considered. We maximize the throughput of the cognitive radio network subject to a constraint on the probability of detection and energy consumption per cognitive radio in order to derive the optimal number of users, the optimal k and the best probability of false alarm. The simulation results based on the IEEE 802.15.4/ZigBee standard, show that the majority rule is either optimal or almost optimal in terms of the network throughput.


      PubDate: 2013-11-18T02:46:33Z
       
  • 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
       
  • Interference mitigation for cognitive radio MIMO systems based on
           practical precoding
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Zengmao Chen , Cheng-Xiang Wang , Xuemin Hong , John Thompson , Sergiy A. Vorobyov , Feng Zhao , Xiaohu Ge
      In this paper, we propose two subspace-projection-based precoding schemes, namely, full-projection (FP)- and partial-projection (PP)-based precoding, for a cognitive radio multiple-input multiple-output (CR-MIMO) network to mitigate its interference to a primary time-division-duplexing (TDD) system. The proposed precoding schemes are capable of estimating interference channels between CR and primary networks, and incorporating the interference from the primary to the CR system into CR precoding via a novel sensing approach. Then, the CR performance and resulting interference of the proposed precoding schemes are analyzed and evaluated. By fully projecting the CR transmission onto a null space of the interference channels, the FP-based precoding scheme can effectively avoid interfering the primary system with boosted CR throughput. While, the PP-based scheme is able to further improve the CR throughput by partially projecting its transmission onto the null space.


      PubDate: 2013-11-18T02:46:33Z
       
  • Joint utility-based uplink power and rate allocation in wireless networks:
           A non-cooperative game theoretic framework
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Eirini Eleni Tsiropoulou , Panagiotis Vamvakas , Symeon Papavassiliou
      In this paper a novel utility-based game theoretic framework is proposed to address the problem of joint transmission power and rate allocation in the uplink of a cellular wireless network. Initially, each user is associated with a generic utility function, capable of properly expressing and representing mobile user’s degree of satisfaction, in relation to the allocated system’s resources for heterogeneous services with various transmission rates. Then, a Joint Utility-based uplink Power and Rate Allocation (JUPRA) game is formulated, where each user aims selfishly at maximizing his utility-based performance under the imposed physical limitations, and its unique Nash equilibrium is determined with respect to both variables, i.e. uplink transmission power and rate. The JUPRA game’s convergence to its unique Nash equilibrium is proven and a distributed, iterative and low complexity algorithm for computing JUPRA game’s equilibrium is introduced. The performance of the proposed approach is evaluated in detail and its superiority compared to various state of the art approaches is illustrated, while the contribution of each component of the proposed framework in its performance is quantified and analyzed.


      PubDate: 2013-11-18T02:46:33Z
       
  • Performance analysis of dual-cell HSDPA plus MIMO and LTE along with
           adaptive MIMO switching at the cellular level
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Muhammad Usman Sheikh , Jukka Lempiäinen
      The main target of this research work is to present the performance analysis of Dual-Cell High Speed Downlink Packet Access (DC-HSDPA) plus Multiple Input Multiple Output (MIMO) supported by sophisticated Power Control (PC) with Long Term Evolution (LTE) integrated with Adaptive MIMO Switching (AMS). A simple approach of power allocation for DC-HSDPA in the downlink direction is presented in this paper, in which power resources are dynamically allocated to the users, irrespective of the number of code utilizations. This paper also highlights the impact of efficient power allocation in DC-HSDPA compared to conventional DC-HSDPA without any PC. In addition to different Intersite Distance (ISD), the impact of serving variable numbers of users per Transmission Time Interval (TTI) was also analyzed in terms of average cell throughput, relative throughput gain, and user’s probability of no data transfer in a macrocellular environment. Simulation results revealed that at 500 m ISD LTE exhibits better performance with AMS compared to spatial multiplexing, and it offered an average cell throughput of around 47 Mbps with nearly 5.5% user’s probability of no data transfer. It was learned that DC-HSDPA performance improves by adopting a PC scheme in the Downlink (DL) direction. At small ISD, DC-HSDPA with MIMO provides an average cell throughput of around 19.5 and 13.7 Mbps with and without PC, respectively.


      PubDate: 2013-11-18T02:46:33Z
       
  • A novel hybrid simulation methodology for capacity estimation in mobile
           networks
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): S.E. Elayoubi , M.K. Karray , Y. Khan , S. Jeux
      Radio capacity simulation tools are gaining a large importance with the development of mobile networks. System radio simulators that are currently used in standardization bodies are becoming increasingly complex as they have to work on two time scales: the scale of “milliseconds” for modeling the behavior of schedulers and the scale of “tens of seconds” for modeling the dynamic behavior of arrivals and departures of users. In this paper, we propose a hybrid system simulation methodology that combines the advantages of system simulators in accurately modeling the physical/MAC interfaces, with the robustness of queuing theory analysis that catches the flow dynamics. We validate our simulation methodology versus complete system level simulators in representative scenarios and show an excellent match between both methodologies. We then show how to extend our simulation methodology for including a mix of services and how to incorporate network measurement results within the proposed methodology.


      PubDate: 2013-11-18T02:46:33Z
       
  • Multiuser scheduling on the LTE downlink with meta-heuristic approaches
    • Abstract: Publication date: December 2013
      Source:Physical Communication, Volume 9
      Author(s): Mehmet E. Aydin , Raymond Kwan , Joyce Wu
      In this paper, the issue of multi-user radio resource scheduling on the downlink of a Long Term Evolution (LTE) cellular communication system is addressed. An optimization model has been proposed earlier, where radio resources for multiple users are jointly allocated at the air-interface. It has been shown that an optimal solution to such a problem may provide reasonable gain over a simply greedy approach. However, the complexity of such an optimal approach could be prohibitively high. By exploiting meta-heuristic methods such as Genetic Algorithm (GA) and Simulated Annealing (SA), the results in this paper show that significant reduction in complexity can be obtained while achieving near-optimal solutions.


      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
       
  • Uplink CFO compensation for FBMC multiple access and OFDMA in a high
           mobility scenario
    • Abstract: Publication date: Available online 31 October 2013
      Source:Physical Communication
      Author(s): Gustavo J. González , Fernando H. Gregorio , Juan Cousseau , Risto Wichman , Stefan Werner
      We study in this work CFO compensation methods for two multicarrier multiple access techniques in a high mobility scenario. In particular, we consider orthogonal frequency division multiple access (OFDMA) and filter bank multicarrier multiple access (FBMC-MA). The main motivation for this study is not only the different sensitivity these multicarrier techniques have to CFO but also the different methods they use to reduce CFO effect. In a high mobility scenario the CFO is re-estimated to follow its variation. We show that the frequency at which the CFO is re-estimated has a strong influence in the performance and the complexity of the proposed compensation methods. Additionally, we present a low-complexity CFO compensation method for OFDMA that employs a better approximation of the intercarrier interference than previous approaches. Regarding FBMC-MA, we introduce an extension of a CFO-compensation method that allows to consider a multitap channel equalizer. Finally, using simulations, we compare the performance of the compensation methods over several channel and time-varying CFO conditions.


      PubDate: 2013-11-02T04:33:20Z
       
  • Resource block filtered-OFDM for future spectrally agile and power
           efficient systems
    • Abstract: Publication date: Available online 17 October 2013
      Source:Physical Communication
      Author(s): Jialing Li , Erdem Bala , Rui Yang
      Spectrum sharing is a common paradigm in future communication systems and a spectrally agile baseband waveform with minimal out-of-band emissions is a critical component. In this paper, we propose a new multicarrier modulation technique, called resource block Filtered-OFDM (RB-F-OFDM) and present the transceiver design. This waveform can be used over channels with non-contiguous spectrum fragments and exhibits very low adjacent channel interference, which is required for cognitive radio systems with multi channel carrier aggregation capabilities. As such, regulatory based very stringent adjacent channel leakage ratio (ACLR) and adjacent channel selectivity (ACS) requirements can be met. We show that the transceiver complexity may be reduced by utilizing an efficient polyphase implementation that is commonly used in the filter bank multicarrier (FBMC) modulation. In addition, some efficient peak-to-average power ratio (PAPR) reduction techniques can be naturally applied. The new design is backwards compatible with legacy OFDM based systems. Simulation results to evaluate the performance, including measured bit error rate (BER) in multipath channels, are provided.


      PubDate: 2013-10-21T02:00:08Z
       
  • 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
       
  • Planning and optimization of wireless communication networks
    • Abstract: Publication date: Available online 29 August 2013
      Source:Physical Communication
      Author(s): Lingyang Song , Jie Zhang , Yan Zhang , Nirwan Ansari , Shaohui Suni



      PubDate: 2013-09-01T00:45:13Z
       
  • 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
       
  • An extended 3-dimensional channel model for polarized antenna array
    • Abstract: Publication date: Available online 23 April 2013
      Source:Physical Communication
      Author(s): Mei-fang Jing , Rui-ping Wei , Xin Su , Shao-hui Sun , Rakesh Tamrakar
      Based on existing 3-Dimensional (3-D) channel model developed by WINNER II/+, we propose an extended 3-D channel model, which takes the vertical velocity component and polarized array structure into account. The distributions of several channel parameters are verified through simulation. Furthermore, initial system-level simulation results for 3D-MIMO transmission scheme are presented in this paper.


      PubDate: 2013-04-25T14:05:03Z
       
  • Inter-cell spectrum efficiency improvement technology
    • Abstract: Publication date: Available online 23 April 2013
      Source:Physical Communication
      Author(s): Zhaohua Lu , Xiaodan Zhang , Huahua Xiao , Dengkui Zhu , Kun Liu
      Improvement of inter-cell spectrum efficiency is a valuable research topic in mobile communication system, which impact cell edge user experience especially. According to current research results, three methods to deal with inter-cell interference to improve inter-cell spectrum efficiency, including inter-cell interference randomization, inter-cell interference cancellation and inter-cell interference co-ordination. This paper analyses three important inter-cell spectrum efficiency improvement technologies: soft frequency reuse (SFR), uplink power control, downlink coordinated multi-point transmission/reception (CoMP), and relative research progress.


      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
           systems
    • 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
       
 
 
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