| 1. |
- Hamid, Mohamed, 1983-, et al.
(författare)
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On Spectrum Sharing and Dynamic Spectrum Allocation : MAC Layer Spectrum Sensing in Cognitive Radio Networks
- 2010
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Konferensbidrag (refereegranskat)abstract
- One of the most critical issues regarding wireless networks regulation agencies is how to manage the available electromagnetic radio spectrum in a way that satisfies the needs of the huge growing in wireless systems both economically and technically, especially with the recent crowding in the available spectrum. Hence, building cognitive radio systems supporting dynamic access to the available spectrum has appeared recently as a novel solution for the wireless system huge expansion. In this paper we investigate the MAC layer sensing schemes in cognitive radio networks, where both reactive and proactive sensing are considered. In proactive sensing the adapted and non-adapted sensing periods schemes are also assessed. The assessment of these sensing schemes has been held via two performance metrics: available spectrum utilization and idle channel search delay. Simulation results show that with proactive sensing adapted periods we achieve the best performance but with an observable overhead computational tasks to be done by the network nodes.
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| 2. |
- Hult, Tommy, et al.
(författare)
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Application of Space-Time Signal Processing and Active Control Algorithms for the Suppression of Electromagnetic Fields
- 2011
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Ingår i: Applied Signal and Image Processing. - Hershey : IGI Global. - 9781609604776 ; , s. 45-60
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Bokkapitel (refereegranskat)abstract
- Several studies have been conducted on the effects of radiation on the human body. This has been especially important in the case of radiation from hand held mobile phones. The amount of radiation emitted from most mobile phones is very small, but given the close proximity of the phone to the head it might be possible for the radiation to cause harm. The suggested approach involves the use of adaptive active control algorithms and a full space-time processing system setup (i.e. multiple antennas at both the transmitter and receiver side or MIMO), with the objective of reducing the possibly harmful electromagnetic radiation emitted by hand held mobile phones. Simulation results show the possibility of using the adaptive control algorithms and MIMO antenna system to attenuate the electromagnetic field power density.
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| 3. |
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| 4. |
- Hult, Tommy, et al.
(författare)
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Performance of a multiple HAP system employing multiple polarization
- 2010
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Ingår i: Wireless Personal Communications. - : Springer. - 0929-6212 .- 1572-834X. ; , s. 105-117
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Konferensbidrag (refereegranskat)abstract
- In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. In addition, we evaluate the performance of the system for different separation angles between HAPs, and determine the optimal separation angle that maximizes the total capacity of the system. © 2008 Springer Science+Business Media, LLC.
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| 5. |
- Hult, Tommy, et al.
(författare)
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The Effect of Mutual Coupling on a High Altitude Platform Diversity System Using Compact Antenna Arrays
- 2010
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Ingår i: International Journal of Antennas and Propagation. - : Hindawi Publishing Corporation. - 1687-5869 .- 1687-5877. ; 2010
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the destructive effects of mutual coupling and spatial correlation between the separate antenna elements on a combined diversity system consisting of multiple HAPs (High-Altitude Platforms) employing various compact MIMO (Multiple-Input Multiple-Output) antenna array configurations, in order to enhance the mutual information in HAP communication links. In addition, we assess the influence of the separation angle between HAPs on system performance, and determine the optimal separation angles that maximize the total mutual information of the system for various compact MIMO antennas. Simulation results show that although the mutual information is degraded by mutual coupling and spatial correlation, the proposed HAP diversity system still provides better performance compared to a nondiversity system for all tested scenarios.
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| 6. |
- Kamal, Hany, et al.
(författare)
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Game Theory for Cognitive Radio
- 2013
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Ingår i: Cognitive Radio and Interference Management. - : IGI Global. - 9781466620056 ; , s. 115-126
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Bokkapitel (refereegranskat)abstract
- Demands on high data rate applications are increasing and consequently demands on spectral resources are increasing as well. Although electromagnetic spectrum is recently said to be in a scarcity situation, several studies have shown that this scarcity is mainly due to the legacy command-and-control regulation rather than due to physical scarcity of spectrum. For this reason, researchers have started investigating techniques to better manage the usage of spectrum. Among these techniques there exist the methods allowing the primary/secondary usage of spectrum, or secondary market. Secondary market techniques mainly manage sensing, accessing, and aborting the spectrum usage by the secondary users. Techniques developed for secondary market context are also referred to as algorithms for Cognitive Radio (CR) networks. Regulators worldwide took measures to promote the deployment of primary/secondary context. In this chapter, the authors give an illustrative discussion on CR and on the application of game theory to overcome the spectrum scarcity problem. Game theory is a field of applied mathematics that describes and analyzes scenarios with interactive decisions. In recent years, there has been considerable interest in adopting game theoretic approaches to model many communications and networking problems such as radio resource management and routing. Nowadays, game theory is also used to model interactive situations for CR terminals.
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| 7. |
- Khan, Zaheer Abbas, et al.
(författare)
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Optical thin film filters of colloidal gold and silica nanoparticles prepared by a layer-by-layer self-assembly method
- 2011
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Ingår i: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 46:21, s. 6877-6882
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Tidskriftsartikel (refereegranskat)abstract
- A novel fabrication method for optical thin film filters based on the self-organization of alternating layers of colloidal gold and silica nanoparticles (NP) is reported. The filter is designed to work in the deep-UV to visible spectral range. The spectral absorption peaks are tuned by three parameters: the organic capping ligand of the gold NPs (citrate, chitosan, poly (diallyl-dimethylammonium)- chloride or PDDA); the capping environment (bare, chitosan, or PDDA) of the silica NPs and the thickness of the film. Precise control of the transmission color (less than 1% color distance per layer), is achieved by changing the film thickness. Exploitation of the self-assembly process should lead to the facile production of highly reliable large area thin film optical filters at considerably lower costs.
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| 8. |
- Mohammed, Abbas, et al.
(författare)
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Application of Novel Signal Processing Algorithms for the Detection and Minimization of Skywave Interfering Signals in Loran Receivers
- 2011
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Ingår i: Applied Signal and Image Processing. - Hershey : IGI Global. - 9781609604776 ; , s. 28-44
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Bokkapitel (refereegranskat)abstract
- Skywave interference commonly affects Loran receivers’ performance. Traditional skywave rejectionmethods that use fixed, worst-case, sample timing are far from optimal. This chapter reports on novel signal processing techniques for measuring in real-time the delay and strength of the varying skywave components of a Loran signal relative to the groundwave pulse. The merits and limitations of these techniques will be discussed. Their effectiveness will be assessed by theoretical analysis, computer simulations under a range of realistic conditions, and by testing using off-air signals. A prototype Loran system employing the proposed techniques is also presented. This work establishes a basis on which to design a Loran receiver capable of adjusting its sampling point adaptively to the optimal value in a constantly-changing skywave environment. Such receivers promise to improve significantly the accuracy and reliability of positioning under adverse operational conditions.
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| 9. |
- Mohammed, Abbas, et al.
(författare)
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Next Generation Broadband Services from High Altitude Platforms
- 2010
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Ingår i: Fourth-Generation Wireless Networks. - : IGI Global. - 9781615206742
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Bokkapitel (refereegranskat)abstract
- In this chapter the authors investigate the possibility and performance of delivering broadband services from High Altitude Platforms (HAPs). In particular, the performance and coexistence techniques of providing worldwide interoperability for microwave access (WiMAX) from HAPs and terrestrial systems in the shard frequency band are investigated. The WiMAX standard is based on orthogonal frequency-division multiplexing (OFDM) and multiple-input and multiple-output (MIMO) technologies and has been regarded as one of the most promising 4G standards to lead 4G market and deliver broadband services globally. The authors show that it is possible to provide WiMAX services from an individual HAP system. The coexistence capability with the terrestrial WiMAX system is also examined. The simulation results show that it is effective to deliver WiMAX via HAPs and share the spectrum with terrestrial systems.
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| 10. |
- Mohammed, Abbas, et al.
(författare)
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OFDM-MIMO Applications for High Altitude Platform Communications
- 2010
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Ingår i: Orthogonal Frequency Division Multiple Access Fundamentals and Applications. - : Auerbach Publications, CRC Press. - 9781420088243
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Bokkapitel (refereegranskat)abstract
- In this chapter we propose a combined Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO), i.e. OFDM-MIMO system, in order to increase the capacity of High Altitude Platform (HAP) communication links. In the proposed system, the OFDM parameters and various compact MIMO antenna array configurations are investigated and their performance, in term of capacity, is analysed. In addition, since these special compact MIMO antenna array configurations depend on the array elements being positioned very closely together, the effect of mutual coupling and spatial correlation will also be analysed and taken into account when performing the simulation for this combined diversity system. Further, we will investigate the influence of the separation angle between the multiple relaying platforms on system performance, and determine the optimal separation angles that maximize the total capacity of the system.
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| 11. |
- Mohammed, Abbas, et al.
(författare)
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Overview of Wireless Channel Models for UMTS and LTE
- 2010
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Ingår i: Evolved Cellular Network Planning and Optimization for UMTS and LTE. - : Auerbach Publications, CRC Press. - 9781439806494 ; , s. 43-86
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Bokkapitel (refereegranskat)
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| 12. |
- Mohammed, Abbas, et al.
(författare)
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The Role of High-Altitude Platforms (HAPs) in the Global Wireless Connectivity
- 2011
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Ingår i: Proceedings of the IEEE. - : IEEE (The Institution of Electrical & Electronics Engineering). - 0018-9219 .- 1558-2256. ; 99:11, s. 1939-1953
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Tidskriftsartikel (refereegranskat)abstract
- Since 1990s, the investigations of aerospace communication segment have not only been concerned with satellites, but increasingly with lower altitude repeaters flying in the stratosphere. They are the so-called high-altitude platforms (HAPs) with important advantages with respect to satellites in terms of reduced cost of implementation, deployment, and launch. However, HAPs are characterized by a reduced coverage, as compared with satellites. Nevertheless, in recent literature, HAPs are not regarded as competitors of the satellite technology. On the contrary, the emphasis is on the effective and seamless integration among heterogeneous aerospace segments (GEO, LEO, and HAP) and aerospace segments with terrestrial wireless networks in order to globally extend the broadband wireless connectivity. This paper is focused on the role of HAPs in providing global connectivity in future communication systems and services. Potentialities, enabling technologies, and challenges are presented from the perspective of the integrated terrestrial/HAPs/satellite communications infrastructure.
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| 13. |
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| 14. |
- Muhammad, Bilal, et al.
(författare)
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Uplink closed loop power control for LTE system
- 2010
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Konferensbidrag (refereegranskat)abstract
- The role of uplink power control is to suppress interference. Power control refers to set output power levels of transmitters, base stations in the downlink and User Equipment (UE) in the uplink. In this paper the performance of 3GPP Long Term Evolution (LTE) closed loop power control combined with fractional path loss compensation factor is evaluated by simulating the effects of open loop error, Transmit Power Control (TPC) command delay and power headroom reporting. Simulation results show that the closed loop power control with fractional path loss compensation factor is advantageous compared to closed loop power control with full path loss compensation. The closed loop power control with fractional path loss compensation factor is found to improve the system performance in terms of mean bit rate by 63%.
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| 15. |
- Mustafa, Wail, et al.
(författare)
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Fuzzy-based Opportunistic Power Control Strategy in Cognitive Radio Networks
- 2010
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Konferensbidrag (refereegranskat)abstract
- This paper considers the spectrum sharing network consisting of a pair of primary users (PUs) and a pair of cognitive users (CRs) in a fading channel. The pair of PUs establishes a wireless link as the PU link. The pair of CRs establishes a wireless link as the CR link. The PU link and CR link utilize spectrum simultaneously with different priorities. The PU link has a higher priority to utilize spectrum with respect to the CR link. When the PU link utilizes spectrum, a desired quality of service (QoS) is given to be assured and the CR utilizes spectrum with an opportunistic power scale under this constraint, assuring the desired QoS on the PU link. To compute an optimal opportunistic power scale for the CR link, a fuzzy-based opportunistic power control strategy is proposed based on the Mamdani fuzzy control model using two input variables: the PU’s SNR and PU’s interference channel gain. By the proposed fuzzy-based power control strategy, the desired QoS could be assured on the PU link and the bit error rate (BER) is also reduced compared with the spectrum sharing network without power control strategy.
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| 16. |
- Salih, Sami, et al.
(författare)
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A novel spectrum sensing scheduler algorithm for Cognitive Radio Networks
- 2013
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Konferensbidrag (refereegranskat)abstract
- Cognitive Radios' is recognized as a novel approach to improve the utilization of a precious wireless communication natural resource; the radio frequency spectrum. Historically, telecom regulators assigned fixed spectrum bands to the licensee wireless network operators, this spectrum management approach is guarantee interference free environment, except of some configurations faults or illegal usage. However, with the increasing demand for more bandwidth in the finite radio spectrum, the concept of secondary operator's was emerged, but with emphases to not influence licensed operators. Consequently, Cognitive Radio Networks (CRN) architecture enters the market as an intelligent solution to these issues, with concentration on the spectrum sensing procedures to achieve the regulatory constraint. The most successful sensing algorithms is those applying cooperation and scheduling to have better scanning information, however those algorithms are developed base on the primary network activities which is good in terms of reducing the expected interference, but it lay more computational loads on the CRN. In this paper, a novel sensing scheduler algorithm is proposed, the idea is to utilize the CRN by fairly distribute the sensing task among the sensors, then utilizing the radio spectrum shared with the primary networks.
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| 17. |
- Salih, Sami H O, et al.
(författare)
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A Novel Spectrum Sensing Scheduling Algorithm for Cognitive Radio Networks
- 2012
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Ingår i: Self-Organization and Green Applications in Cognitive Radio Networks. - : IGI Global. ; , s. 136-153
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Cognitive Radios are recognized as a novel approach to improve the utilization of a precious natural resource of wireless communications: the radio frequency spectrum. Historically, telecom regulators assigned fixed spectrum bands to the licensed wireless network operators. This spectrum management approach guarantees an interference free environment, except for some configuration faults or illegal usage. However, with the increasing demand for more bandwidth in the finite radio spectrum, the spectrum becomes underutilized. Hence, the concept of secondary operators have emerged, but with emphasis not to influence licensed operators. Consequently, the Cognitive Radio Network (CRN) architecture enters the market as an intelligent solution to these issues, with concentration on spectrum sensing procedures to achieve the regulatory constraint. The most successful sensing algorithms are those applying cooperation and scheduling to have better scanning information; however, those algorithms are developed based on the primary network activities, which are good in terms of reducing expected interference, albeit with more computational load on the CRN. In this chapter, a novel sensing scheduler algorithm is proposed. The idea is to utilize the CRN by fairly distributing the sensing task among the sensors and afterwards utilizing the radio spectrum shared with the primary networks.
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| 18. |
- Salih, Sami, et al.
(författare)
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Implementation of adaptive modulation for broadband wireless access networks using cognitive radio approaches
- 2013
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Konferensbidrag (refereegranskat)abstract
- Broadband Wireless Access (BWA) has become the best way to meet escalating business demand for rapid Internet connection and integrated 'triple play' services. In addition, not only for topographic but also for technological limitations, alternative wireless solutions have been found. These systems are designed based on Cognitive Radio (CR) approaches, which can adjust its operation according to the environment and technical variations. This tracking feature allows the communication system to deliver the Best Ever, compare to Best Effort, services to the users. In this paper, an implementation of a cognitive engine for adaptive modulation and coding (AMC) is presented. This engine will track the radio channel variations in terms of SNR and be able to select a suitable modulation order among predefined Modulation and Coding Schemes (MCS) to maintain the specified BER by the user requirements.
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| 19. |
- Yang, Zhe, et al.
(författare)
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Deployment and Capacity of Mobile WiMAX from High Altitude Platform
- 2011
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the deployment and capacity of delivering mobile WiMAX based on IEEE 802.16e-2005 from aerial platform such as High Altitude Platforms (HAPs). A urban scenario and an suburban scenario with mobile broadband usages as complement or substitute to the fixed Internet connection are developed to compare the delivery of broadband services from terrestrial and aerial platforms. A deployment strategy is based on maximizing and meeting the networking traffic demand and coverage area. In the end, a comparison based on cell radii and capacities between services from aerial platforms and existing terrestrial based solutions, such as universal mobile telecommunications system (UMTS) and high speed packet access (HSPA) is proposed. Currently, most research has been done to develop advanced technologies to enhance standards to support a higher data rate in a cost-effective way for wireless communication systems. From analysis and investigation, aerial platform can provide a cost-effective solution for a large area with a medium to high traffic demand.
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| 20. |
- Yang, Zhe, et al.
(författare)
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Wireless communications from high altitude platforms : Applications, deployment and development
- 2010
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Konferensbidrag (refereegranskat)abstract
- In this paper, an overview of the HAP concept development and HAP trails is introduced to show the worldwide interest and development in the emerging novel technology. A comparison of the HAP, terrestrial and satellite system characteristics is given. Main advantages of HAPs for wireless communication applications are large coverage area, high capacity and cost-effective deployment. Three applicable scenarios of HAP communication are shown.
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