Albert A. Lysko

Comparison of MANET routing protocols using a scaled indoor wireless grid

Predicting the performance of ad-hoc networking protocols has typically been performed by making use of software based simulation tools. Experimental study and validation of such predictions is vital to obtaining more realistic results, but may not be possible under the constrained environment of network simulators. This paper presents experimental comparisons of routing protocols using a 7 × 7 grid of closely spaced WiFi nodes. It firstly demonstrates the usefulness of the grid in its ability to emulate a real world multi-hop ad-hoc network. It specifically compares hop count, routing traffic overhead, throughput, delay and packet loss for three protocols which are listed by the Internet Engineering Task Force Mobile Ad-hoc Networks (MANET) working group. These are the Ad-hoc on demand distance vector routing protocol (AODV), the optimized link state routing protocol (OLSR) and the dynamic MANET on demand routing protocol (DYMO).

First large TV white spaces trial in South Africa: A brief overview

The paper overviews African first of the really large scale trials of television (TV) white space (TVWS) technology and white space devices (WSDs) designed to co-use the frequency spectrum allocated to TV broadcasting. The WSD obtains information about availability of the spectrum in a particular area for a particular period of time from a geolocation spectrum database (GLSD). The GLSD bases its estimations about the availability on stored information about primary users/transmitters in the area, propagation prediction algorithms and local spectrum management regulations. As the overall system is fairly complex and new, extensive testing and trials are required to prove its functionality and compatibility with existing users of the spectrum. Some of the experiences, specifically those from the largest in Africa TVWS trial providing Internet to 10 large schools, held in Tygerberg, South Africa, and conclusions on testing of WSD and use of white space are overviewed.

New MoM code incorporating multiple domain basis functions

A new method of moments (MoM) code is discussed. The code supports standard functionality, e.g. fully automatic re-meshing and variables assignment, ground plane and symmetry planes. In addition, the code realizes several new features. These include significant acceleration of the filling-in of the impedance matrix for high accuracy calculations on structures with redundancies, as well as realization of the multiple domain basis functions with a support for various aggregating basis functions profiles, including piecewise linear and piecewise sinusoidal. New profiles may be easily defined. The current realization of the code has been tested on several references and showed an excellent match to the reference results.

Beam steering for circular switched parasitic arrays using a combinational approach

In this paper we present a method of electronic beam steering for circular switched parasitic array (SPA) antennas. In circular SPA antennas, one achieves azimuth beam steering by open-circuiting and short-circuiting different parasitic elements, usually with only one parasitic element open-circuited at a time. For the SPA antenna with few parasitic elements, this results in low azimuth beam steering resolution. In the proposed method, we iterate through different combinations of parasitic elements and the possible switch states of the lumped impedance loads connected to the parasitic elements. Our method aims to increase the azimuth beam steering resolution of the circular SPA antennas. The method is verified using a combination of simulation (using both MATLAB and WIPL-D) and a SPA antenna prototype implementation. The MATLAB code uses the induced EMF method, while the WIPL-D uses the Methods of Moment (MoM) for solving the antenna impedances. The three sets of results (simulations and measurement) match very well at 2.4 GHz. The results indicate the availability of more options (different loading configurations) for electronic beam switching that can be adopted to improve the beam steering resolution of circular SPA antennas.

Using TV White Spaces and e-Learning in South African rural schools

This paper uses the example of the television white space (TVWS) project in Limpopo Province of South Africa to consider benefits of TVWS technology to enable e-Learning environment and introduce pupils and teachers previously unfamiliar with Internet to information and communication technologies (ICT) including Internet. The Limpopo TVWS project uses TVWS to provide broadband Internet to five schools which are up to 10 km away around the University of Limpopo (UL) in the rural Mankweng Township. Each one of the participating five schools was donated 31 tablets, an overhead projector and smart phone to enable e-learning delivery. The paper presents preliminary results on a socio-economic study conducted at the five participating schools, and also discusses various benefits of availability of connectivity and of e-Learning.

Network performance analysis of the Limpopo TV white space (TVWS) trial network

Television white spaces (TVWS) refers to vacant channels in the ultra-high frequency (UHF) band between 470 and 690 MHz assigned for television broadcast and can be used opportunistically by secondary users (SUs). Research has shown that when the spectrum allocation is managed appropriately, SUs can co-exist on the same radio frequency (RF) spectrum band with licensed networks. This paper introduces the Limpopo TVWS trial network, which provides a point-to-point Internet connectivity to five rural secondary schools. A set of 24 hours RF monitoring results of the TVWS trial network are presented which shows the behaviour of white space devices with respect to incumbent TV band services. The network performance results with respect to average throughput, average latency, and jitter are also presented. The performance results show that good throughput for each link which is in the magnitude of 4 to 8 Mbps and latency of less than 10 ms for typical packet sizes ranging from 32 to 1500 bytes are achievable.

The Television White Space Opportunity in Southern Africa: From Field Measurements to Quantifying White Spaces

The lack of sufficient fixed-line communication infrastructure in African rural areas has resulted in wireless communication being the only cost effective alternative solution for broadband connectivity. However, access to valuable spectrum—specifically sub-1 GHz spectrum—is mostly allocated to broadcasting or mobile telephony. The global digital switch over (DSO) of television (TV) broadcasting systems will see more sub-1 GHz TV band spectrum being made available for the digital dividend and also result in more TV white space (TVWS) spectrum. In order to ensure dynamic and efficient utilization of the TV white space spectrum, there is an increasing trend to use cognitive radiosystems that use geo-location spectrum databases and spectrum sensing as an enabling technology. In this paper, we overview the relevant signals and standards and present field measurement results showing the actual usage of TV bands before the DSO in selected urban and rural areas of Southern Africa. Measurements were conducted using low-cost and high-grade radio instruments. The low-cost spectrum analyser was built in-house using the Universal Software Radio Peripheral (USRP-2) and GNU Radio software. A metric to quantify available TV white space, based on the minimum acceptable field strength, is introduced and applied to quantify the availability of TV white space. Our results show medium spectrum usage in urban areas and very low spectrum usage in rural areas, making TVWS an attractive solution for rural broadband connectivity.

Using piecewise sinusoidal basis functions to blanket multiple wire segments

This paper discusses application of the piecewise sinusoidal (PWS) basis function (BF) over a chain of several wire segments, i.e. as a multiple domain basis functions. The usage of PWS BF is compared to results based on the piecewise linear (PWL) basis functions. An example of meander monopole demonstrates the advantages associated with the PWS BF.

VillageLink: A channel allocation technique for wide-area white space networks

White spaces promise to revolutionize the way wireless connectivity is delivered over wide areas. However, large-scale white space networks face the problem of allocating channels to multiple contending users in the wide white space band. To tackle the issue, we first examine wireless propagation in a long-distance outdoor white space testbed and find that a complex combination of free-space loss and antenna effects impacts transmission in white spaces. Thus, a need arises for a strategy that goes beyond simple channel utilization balancing, and uses frequency probing to profile channels according to their propagation properties. We devise VillageLink, a Gibbs sampling-based method that optimizes channel allocation in a distributed manner with a minimum number of channel switching events. Through extensive simulations we demonstrate that VillageLink results in a significant capacity improvement over alternative solutions.

VillageLink: Wide-area wireless coverage

White spaces promise to revolutionize the way wireless connectivity is delivered over wide areas. However, large-scale white space networks face the problem of allocating channels to multiple contending users in the wide white space band. To tackle the issue, we first examine wireless propagation in a long-distance outdoor white space testbed and find that a complex combination of free-space loss and antenna effects impacts transmission in white spaces. Thus, a need arises for a strategy that goes beyond simple channel utilization balancing, and uses frequency probing to profile channels according to their propagation properties. We devise VillageLink, a Gibbs sampling-based method that optimizes channel allocation in a distributed manner with a minimum number of channel switching events. Through extensive simulations we demonstrate that VillageLink results in a significant capacity improvement over alternative solutions.