56,511 research outputs found
Quantitative Assessment of TV White Space in India
Licensed but unutilized television (TV) band spectrum is called as TV white
space in the literature. Ultra high frequency (UHF) TV band spectrum has very
good wireless radio propagation characteristics. The amount of TV white space
in the UHF TV band in India is of interest. Comprehensive quantitative
assessment and estimates for the TV white space in the 470-590MHz band for four
zones of India (all except north) are presented in this work. This is the first
effort in India to estimate TV white spaces in a comprehensive manner. The
average available TV white space per unit area in these four zones is
calculated using two methods: (i) the primary (licensed) user and secondary
(unlicensed) user point of view; and, (ii) the regulations of Federal
Communications Commission in the United States. By both methods, the average
available TV white space in the UHF TV band is shown to be more than 100MHz! A
TV transmitter frequency-reassignment algorithm is also described. Based on
spatial-reuse ideas, a TV channel allocation scheme is presented which results
in insignicant interference to the TV receivers while using the least number of
TV channels for transmission across the four zones. Based on this reassignment,
it is found that four TV band channels (or 32MHz) are sufficient to provide the
existing UHF TV band coverage in India
Optimal Quantization of TV White Space Regions for a Broadcast Based Geolocation Database
In the current paradigm, TV white space databases communicate the available
channels over a reliable Internet connection to the secondary devices. For
places where an Internet connection is not available, such as in developing
countries, a broadcast based geolocation database can be considered. This
geolocation database will broadcast the TV white space (or the primary services
protection regions) on rate-constrained digital channel.
In this work, the quantization or digital representation of protection
regions is considered for rate-constrained broadcast geolocation database.
Protection regions should not be declared as white space regions due to the
quantization error. In this work, circular and basis based approximations are
presented for quantizing the protection regions. In circular approximation,
quantization design algorithms are presented to protect the primary from
quantization error while minimizing the white space area declared as protected
region. An efficient quantizer design algorithm is presented in this case. For
basis based approximations, an efficient method to represent the protection
regions by an `envelope' is developed. By design this envelope is a sparse
approximation, i.e., it has lesser number of non-zero coefficients in the basis
when compared to the original protection region. The approximation methods
presented in this work are tested using three experimental data-sets.Comment: 8 pages, 12 figures, submitted to IEEE DySPAN (Technology) 201
Spectrum Sharing for LTE-A Network in TV White Space
Rural areas in the developing countries are predominantly devoid of Internet
access as it is not viable for operators to provide broadband service in these
areas. To solve this problem, we propose a middle mile Long erm Evolution
Advanced (LTE-A) network operating in TV white space to connect villages to an
optical Point of Presence (PoP) located in the vicinity of a rural area. We
study the problem of spectrum sharing for the middle mile networks deployed by
multiple operators. A graph theory based Fairness Constrained Channel
Allocation (FCCA) algorithm is proposed, employing Carrier Aggregation (CA) and
Listen Before Talk (LBT) features of LTE-A. We perform extensive system level
simulations to demonstrate that FCCA not only increases spectral efficiency but
also improves system fairness.Comment: 5 page
HopScotch - a low-power renewable energy base station network for rural broadband access
The provision of adequate broadband access to communities in sparsely populated rural areas has in the past been severely restricted. In this paper, we present a wireless broadband access test bed running in the Scottish Highlands and Islands which is based on a relay network of low-power base stations. Base stations are powered by a combination of renewable sources creating a low cost and scalable solution suitable for community ownership. The use of the 5~GHz bands allows the network to offer large data rates and the testing of ultra high frequency ``white space'' bands allow expansive coverage whilst reducing the number of base stations or required transmission power. We argue that the reliance on renewable power and the intelligent use of frequency bands makes this approach an economic green radio technology which can address the problem of rural broadband access
Resistance to carbapenems in non-typhoidal Salmonella enterica serovars from humans, animals and food
Non-typhoidal serovars of Salmonella enterica (NTS) are a leading cause of food-borne disease in animals and humans worldwide. Like other zoonotic bacteria, NTS have the potential to act as reservoirs and vehicles for the transmission of antimicrobial drug resistance in different settings. Of particular concern is the resistance to critical “last resort” antimicrobials, such as carbapenems. In contrast to other Enterobacteriaceae (e.g., Klebsiella pneumoniae, Escherichia coli, and Enterobacter, which are major nosocomial pathogens affecting debilitated and immunocompromised patients), carbapenem resistance is still very rare in NTS. Nevertheless, it has already been detected in isolates recovered from humans, companion animals, livestock, wild animals, and food. Five carbapenemases with major clinical importance—namely KPC (Klebsiella pneumoniae carbapenemase) (class A), IMP (imipenemase), NDM (New Delhi metallo-β-lactamase), VIM (Verona integron-encoded metallo-β-lactamase) (class B), and OXA-48 (oxacillinase, class D)—have been reported in NTS. Carbapenem resistance due to the production of extended spectrum- or AmpC β-lactamases combined with porin loss has also been detected in NTS. Horizontal gene transfer of carbapenemase-encoding genes (which are frequently located on self-transferable plasmids), together with co- and cross-selective adaptations, could have been involved in the development of carbapenem resistance by NTS. Once acquired by a zoonotic bacterium, resistance can be transmitted from humans to animals and from animals to humans through the food chain. Continuous surveillance of resistance to these “last resort” antibiotics is required to establish possible links between reservoirs and to limit the bidirectional transfer of the encoding genes between S. enterica and other commensal or pathogenic bacteria
Periodicities In The X-Ray Intensity Variations of TV Columbae: An Intermediate Polar
We present results from a temporal analysis of the longest and the most
sensitive X-ray observations of TV Columbae--an intermediate polar. The
observations were carried out with the RXTE PCA, ROSAT PSPC, and ASCA. Data
were analyzed using a 1-dimensional CLEAN and Bayesian algorithms. The presence
of a nearly sinusoidal modulation due to the spin of the white dwarf is seen
clearly in all the data, confirming the previous reports based on the EXOSAT
data. An improved period of 1909.7+/-2.5s is derived for the spin from the RXTE
data.The binary period of 5.5hr is detected unambiguously in X-rays for the
first time. Several side-bands due to the interaction of these periods are
observed in the power spectra, thereby suggesting contributions from both the
disk-fed and the stream-fed accretion for TV Col. The accretion disk could
perhaps be precessing as side-bands due to the influence of 4 day period on the
orbital period are seen. The presence of a significant power at certain
side-bands of the spin frequency indicates that the emission poles are
asymmetrically located. The strong power at the orbital side-bands seen in both
the RXTE and ROSAT data gives an indication for an absorption site fixed in the
orbital frame. Both the spin and the binary modulation are found to be
energy-dependent. Increased hardness ratio during a broad dip in the intensity
at binary phase of 0.75--1.0 confirms the presence of a strong attenuation due
to additional absorbers probably from an impact site of the accretion stream
with the disk or magnetosphere. Hardness ratio variations and the energy
dependent modulation depth during the spin modulation can be explained by
partially covered absorbers in the path of X-ray emission region in the
accretion stream.Comment: 34 pages, including 12 figures, Accepted for publication in
Astronomical Journal, scheduled for January 2004 issue (vol. 127
Mobile Telephony: Economic and Social Impact
The ubiquitous cell phone is often portrayed as the scourge of civilized society: rude callers on streets, in malls and offices, disturbing those around them with loud talking, school kids constantly texting in class, drivers whose attention has wandered during a cell phone conversation causing accidents, “crackberry” addicts who check their e-mail during real-world conversations, the list goes on. Is this an invention whose result has been to make us all worse off, like Internet spam and phishing attacks? In this paper, I informally survey the rise and impact of cellular technology, both in the US and the world. I find that the reach and the speed of its worldwide diffusion has exceeded even that of the Internet, and certainly with far more reach and speed than the personal computer. Mobile’s economic and social impact has been unprecedented, especially in the developing world where it has been a boon to economic development. While many in the US focus on expanding the diffusion of the PC both domestically and worldwide, as well as expanding the availability of broadband connectivity, I argue that while PC-broadband architecture will continue to be important, the terminal device of choice for most people on this planet will be the mobile, accessing information services over a wireless connection. Mobile telephony is, I believe, the highest impact communications technology of the last 50 years, rivaled only by the Internet.
- …