1,720,985 research outputs found
Handover Management In Mobile Satellite Systems
No full textTwo handover management strategies have been proposed to efficiently manage the channel resource of a cell in a mobile satellite system (MSS) and to improve its service quality by reducing the handover failure rate and drop call rate caused by insufficient number of communication channels
A spectrum sharing model that counters eavesdropping
No full textCybersecurity has become a major concern in the modern world. A serious threat to wireless networks is eavesdropping. On the other hand, usable spectrum is diminishing due to the presence of various wireless services. To address the problem, highly spectral efficient methods have been introduced e.g. spectrum sharing. Cognitive radio networks could sense unused spectrum and make use of it. In this paper, the cognitive radio is to perform a second task, i.e. jamming the eavesdropper. This paper is significant in revealing the cognitive radio’s energy efficiency in this setting, where a cognitive transmitter (CT) can transmit its own data when it senses the absence of primary transmitter (PT). If PT is present, CT is to jam an eavesdropper (EA) by transmitting artificial noise. Our main contribution is finding the CT’s optimal energy efficiency. Through the proposed formulas, we have determined the fractions of time and power required by CT to achieve the optimal energy efficiency, subject to constraints like minimum required secrecy rate Rs, etc. Our major findings are: (1) only a small portion of a time frame (66 μs in our setting) is required for sensing. CT can utilize the remaining time for sending its data or jamming EA. (2) To achieve a target energy efficiency of 0.5 bps/Hz/J, PT should not be actively transmitting more than 35% of the time, and Rs should not be larger than 1.2 bps/Hz
Wireless power transferable from unmanned aerial vehicle
No full textUnmanned aerial vehicle (UAV) could wirelessly transfer power to the devices on ground, thus recharging their batteries conveniently. Nevertheless, the efficiency of this wireless power transfer from UAV to ground remains unclear. This paper aims to answer this question from the theoretical perspective. We need two models for this purpose: an energy harnessing model and a UAV-to-ground wireless channel model. In the literature, a model of harnessing radio frequency (RF) energy and turning it into DC power is available. Our goal is to quantify the theoretical efficiency of RF-to-DC power conversion, and the amount of DC power gained as a result. Following this nonlinear energy harvesting circuit model, the signal level fluctuations caused by channel fading actually enhance the power conversion. To model the wireless channel gain from the UAV to the ground, we use the modified Loo’s channel model. Connecting it to the RF-to-DC power conversion model, we can determine the theoretical amount of DC power attainable from UAV’s transmission, in addition to its power conversion efficiency. Our finding shows that a heavy shadowing condition can enhance the RF-to-DC power conversion of a nonlinear energy harvesting circuit. For example, certain heavy shadowing condition may yield a conversion efficiency that is 7 dB higher than when shadowing is absent. This concurs with the previous finding that signal attenuation and fluctuation actually made the energy easier to be captured and harnessed by the nonlinear rectenna circuitry. Our finding confirms that high RF-to-DC conversion efficiency is attainable even under shadowing conditions
Harmonious Coexistence of IEEE 802.11af Wireless LAN and Digital TV
No full textCongested Industrial, Scientific, and Medical (ISM) band stifles the growth of Wireless Local Area Network (WLAN). The recent switchover from analog to digital TV (DTV) broadcast frees from the conventional TV bands a sizeable amount of spectrum, which is commonly called TV white space (TVWS). TVWS is very attractive to many wireless technologies, including WLAN. IEEE came up with 802.11af, the standard for the WLAN technology that operates in TVWS. Nevertheless, it is unsure how best to guarantee its operation not causing harmful interference to DTV. In this paper, we present the conditions required for harmless coexistence of IEEE 802.11af WLAN and DTV. We make use of the standard prediction method based on radio propagation characteristics, i.e. the ITU-R P.1411-9 method which has been adopted in communication system planning. Based on our findings, we suggest the followings: (1) Operate IEEE 802.11af WLAN at any adjacent channel other than the first (i.e. except the closest neighbour channel). (2) The height of IEEE 802.11af installation does play a part when there is a relatively large separation distance between the WLAN and DTV (e.g. 50 m). (3) For outdoor operation, IEEE 802.11af WLAN should be installed at the second, third, or fourth channels adjacent to the DTV’s; fifth or sixth adjacent channel for indoor operation
Deployment of wireless regional area network and its impact on DTV service coverage
No full textPrediction of digital TV (DTV) coverage has not considered the potential interference originating in the IEEE 802.22 Wireless Regional Area Network (WRAN), which operates in the same TV bands. WRAN interference could affect DTV reception, resulting in DTV service outage in some areas. Spectrum sensing is a means of minimizing the interference by not operating WRAN in the TV band where DTV signal is detected to be present. However, limited sensing accuracy could lead to erroneous decision. This paper investigates the extent of which DTV service quality is affected by the operation of WRAN with limited sensing accuracy. One of the main factors that limit sensing accuracy is the variability in radio propagation channel. Depending on the characteristics of the statistical variation, radio channels are modeled as Gaussian, Rayleigh, Nakagami, and Rician channels in this paper. The probability of DTV service outage is analyzed and expressed as a function of sensing accuracy. The theoretical results presented here have been validated by the Monte Carlo simulations
Dominant Interferers in Cognitive Radio Network
No full textWireless Personal Communications is an archival, peer reviewed, scientific and technical journal addressing mobile communications and computing. It investigates theoretical, engineering, and experimental aspects of radio communications, voice, data, images, and multimedia.
A partial list of topics includes propagation, system models, speech and image coding, multiple access techniques, protocols performance evaluation, radio local area networks, and networking and architectures.
The journal features five principal types of papers: full technical papers, short papers, technical aspects of policy and standardization, letters offering new research thoughts and experimental ideas, and invited papers on important and emerging topics authored by renowned experts
Operating white space devices in the DTV service area
No full textWhite space devices (WSDs) that operate in the underutilized TV bands (TV white space) must not interfere with the incumbent digital TV (DTV) reception. We identify the conditions for harmonious coexistence between WSD and three different DTV services: Advanced Television Systems Committee, Integrated Services Digital Broadcasting - Terrestrial, and Digital Video Broadcasting - Terrestrial. We find that a WSD can operate within all three regions provided that (1) its radiated power is smaller than 13 dBm, (2) it keeps a minimum distance of 50 m from a DTV receiver, (3) it operates in the adjacent channels except the closest one
Energy Efficiency of Cooperative Relay and Spectrum Sharing
No full textUnderutilization of spectrum causes wastage.
Harmful jamming disrupts the reception of data. How to
overcome the two problems with one solution? Based on a
physical layer security measure, we propose a spectrum
sharing model that defends against jamming. When a channel
is unused by its primary user, it can be shared with others.
Being capable of sensing the state of channel occupancy,
cognitive radio is introduced to share the channel. When the
channel is unoccupied, cognitive radio accesses the channel for
its own data transmission. When primary user is sensed to be
actively transmitting, cognitive radio helps relaying the
primary message. Information redundancy certainly benefits
the primary user, but to what extent this model benefits the
cognitive radio? The main concern is its energy efficiency, i.e.
the ratio of throughput to energy consumption. We investigate
the relationships between energy efficiency and (1) the
percentage of frame duration cognitive radio allocates for
sensing, (2) power allocated for relaying the primary data, and
(3) detectable level of primary signal. In a typical setting, we
find that allocating 5% to 30% of a time frame for sensing
(and the remaining for relaying the primary data) yields good
energy efficiency
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