The optimal locations of transmitters in a building, that best meet the bandwidth requirements of all users, was studied in the past by a small number of authors. They used empirical path loss models ...to constrain an optimization cost function. This paper concentrates on using a signal-to-interference ratio cost function with realistic field parameters obtained using a fast ray-tracing algorithm. The solution obtained is shown to perform well in realistic scenarios, meeting a large proportion of user bandwidth requirements. However, it does not perform well in an oversaturated environment.
This paper describes a point-to-multipoint 3-D convex space-based ray-tracing technique. This visibility list is calculated and stored and can be reused as needed. What distinguishes our method is ...that the visibility list is transmitter location-independent, is a 3-D implementation, and is highly computationally efficient. The division of the building into free and filled convex spaces leads to an efficient Method of Images reflection and diffraction path generation algorithm. This technique can be used to optimize the locations of base transceivers in a highly efficient manner. The first step in producing this tool is the generation of efficient ray-tracing algorithms. The ray-tracing algorithm was specifically designed for later incorporation into a transmitter optimization algorithm. This requires a fast ray-tracing method because of its computationally intensive needs-running multiple times over a point-to-multipoint grid. Our algorithm is executed for sample building environments and then for a real building and compared with measurements to confirm its validity. It is clear that the results are in good agreement but do indicate that a highly accurate spatial modeling of the building is required.
In this paper, we show that the cumulative and probability distribution functions (cdf and pdf, respectively) of small-scale wideband signal envelope fading in microcells can be very closely ...approximated by both the Rice and Nakagami distributions, which are already known to describe the cdfs and pdfs of small-scale narrowband signal envelope fading. Our results are obtained by means of an extensive Monte Carlo-based study of a wideband propagation model by Yan and Kozono, which is itself supported by extensive measurements. Over a comprehensive range of microcell propagation parameters, the average maximum error in the approximation is 1.65% and 1.78% for the Rice and Nakagami cdfs, respectively. The error in the approximation is 3.58% and 3.87% for the 95th percentile and does not exceed 7.61% and 7.80%, respectively, in the worst case. We propose an expression that maps the significant wideband small-scale signal envelope fading parameters to their narrowband counterparts for different standards like Dedicated Short Range Communication, WiMAX, Universal Mobile Telecommunications Service, and the family of the IEEE 802.11 standards. This mapping enables narrowband small-scale signal envelope fading statistical distributions, which are currently used, e.g., in fading simulators, link quality determination algorithms, and outage probability calculators, to be readily adapted to deal with small-scale wideband signal envelope fading. As an application example of this proposed mapping, we derive the appropriate sample spacing and averaging interval (window size) that ought to be used to estimate the large-scale fading signal in an IEEE 802.11 receiver.
In this paper it is envisaged that cognitive radios (CRs) consult a supporting network infrastructure for permission to transmit. The network server either grants or rejects these requests by ...estimating, from the CRs geo-location and antenna features, the likely impact its transmission would have on incumbents and other CR devices. This decision would be based on a real-time radio environment map which would be kept up to date with readings from CRs, sensors and dynamic radio propagation prediction. By this means coexistence with incumbents and other CRs can be satisfied. It is maintained here that integral-equation (IE)-based algorithms are suitable candidates for the propagation engine given their 'automatic' nature and that they can be implemented to give results arbitrarily close to the exact numerical solution. IE methods based on the Fast Multipole Method are examined as a likely route to achieve the accuracy and speed necessary for real-time propagation mapping. It is concluded that the results obtained using one of the most recent of these, the Field Extrapolation Method (FEXM), are promising for rural/suburban profiles and could serve to enable coexistence, for example, in IEEE802.22 networks. It is also explained how dynamic propagation prediction can address some fundamental security threats to CR networks.
This paper introduces a new P2P Electronic Cash system called Netcoin. The purpose of Net coin is to facilitate inexpensive peer-to-peer monetary transactions on the Web. Its salient features are ...that it is a traceable system with an efficient mechanism for verifying transactions. Net coins are reusable and can be easily passed from one user to another. The issuing of virtual currency and verification of transactions are performed by trusted mints, which act as the gateway between the fiat and virtual currency worlds. There is no need to maintain a public ledger, which would inhibit use on a global scale because of rapidly increasing memory and bandwidth requirements. The system is neither inflationary nor deflationary in nature and does not purport a new economic model. As a fiat-backed currency it should not suffer the volatility issues associated with Bit coin. In this paper the two most prominent electronic payment systems of the last forty years, namely Ecash and Bit coin, are examined. Net coin is then introduced in detail and is designed to address the shortcomings of these payment systems.
P2P live video streaming in WebRTC Rhinow, Florian; Veloso, Pablo Porto; Puyelo, Carlos ...
2014 World Congress on Computer Applications and Information Systems (WCCAIS),
01/2014
Conference Proceeding, Journal Article
In this paper, we analyse the feasibility of implementing live video streaming protocols into web applications with the use of WebRTC. As a result of demand the distribution of video content requires ...ever increasing bandwidth. Although, specialised programs exist to distribute video content efficiently, web pages have up until recently not been able to leverage these technologies. WebRTC could serve as a solution by enabling peer-to-peer communication directly between browsers without any need for a server as an intermediary. The feasibility analysisis accompanied by a practical implementation of a peer-to-peer streaming protocol in WebRTC that runs natively in all browsers and an identification of optimal settings for such a protocol. Our work highlights current limitations and future challenges when implementing sophisticated peer-to-peer solutions using a technology that is still in its infancy. Finally, we provide preliminary experimental data on WebRTC which measures the performance of such a system in a laboratory environment.
In this paper it is proposed that cognitive radios consult with a supporting network infrastructure to provide the means by which Quality of Service and coexistence and can be acheived. The network ...server would either grant or reject transmission requests by estimating, from the cognitive radio's geo-location, the likely impact its transmission would have on incumbents and other cognitive radio devices. This decision must be based on an accurate real-time Radio Environment Map which is kept up to date by readings from cognitive radios, sensors and dynamic radio propagation prediction. It is concluded that real-time Radio Environment Mapping of signal strength in space, time and frequency will address the most fundamental of cognitive radio's challanges.
The paper presents an improved fast and accurate integral equation (IE) method to evaluate the slow fading signal over a two dimensional terrain profile. The local variation of the induced surface ...current with distance is modelled as a constant amplitude sinusoid (O'Nuallain, E., 2001). This model can be used to eliminate the computational overhead associated with modelling localised electromagnetic (EM) interactions and give accurate results. A significant reduction in the order of complexity of the problem and memory requirements ensues.
In this lecture the proposal that cognitive radios consult with a supporting network infrastructure to enable coexistence in the signal strength domain is examined. The network server would either ...grant or reject transmission requests by estimating, from the cognitive radio's geo-location, the likely impact its transmission would have on incumbents and other cognitive radio devices. This decision must be based on an accurate real-time radio environment map (REM) 1 which is kept up to date by readings from cognitive radios, sensors and dynamic radio propagation prediction. By this means the imperative of coexistence in the signal strength domain of cognitive radio technology can be satisfied. It is also shown that this approach also offers a means with which to detect physical-layer attacks.
It is explained that Integral Equation-based propagation prediction algorithms are appropriate candidates for the dynamic propagation engine necessary for the purposes outlined above given their 'automatic' nature and that they can give results arbitrarily close to the exact numerical solution.
The humanitarian relevance of cognitive radio is that where operated as infrastructureless networks they will provide telecommunications services to deprived areas and could prove vital in disaster recovery. Where there is network support cognitive radios will become cheaper as a result.
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