In this paper, the performance of limited feedback precoded spatial multiplexing multiple-input multiple-output orthogonal frequency division multiplexing (MIMO - OFDM) systems is investigated in time varying fading channels. Most studies into limited feedback precoded (MIMO - OFDM) systems are based on the notion of time invariant channels throughout transmission. Therefore, the precoding matrix for each subcarrier can be designed at the receiver in terms of the current channel state, fed back to the transmitter, and used for the subsequent block of data symbols. However, in time varying channels, the feedback information becomes outdated, which results in significant system performance degradation. To mitigate this system performance degradation caused by outdated information due to a delay in the feedback channel, this paper considers a more practical system, where the channel varies from one block

Conventional precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback are mainly based on the notion of time invariant channels throughout transmission. Consequently, the precoding matrix can be found during the training symbols and used over the subsequent data symbols. In this study, the authors consider a more practical system where the channel varies from one block of symbols to another. In such a scenario, the precoding matrix designed at the receiver based on the previous training symbols becomes outdated, which results in significant system performance degradation. In order to avoid this problem and reduce performance degradation, the authors propose the use of a Kalman filter linear predictor at the receiver to provide the transmitter with the precoding matrix for the next block of symbols. The performance of this method is assessed using computer …

Laser technologies have made distinguished contribution in modern industry. These have principally been realised through the important role played by lasers in advancement of manufacturing technology in areas such as welding. Laser welding has now become a very important joining technique in a wide variety of applications in the oil gas, aerospace, aircraft , medical and electronic industries.

This study presents investigations relating to the production of high quality laser welds that blend closely with surface of the welded materials, (welds termed 'net shaped'). It has not been possible to produce such welds in the past using conventional welding technology.Net shaped welds not only look attractive, but afford functional and economic benefit because no secondary machining and polishing is required.

Mild steel plates and bead-on-plate welding with a 1 kW fiber laser are usd for this investigation. Design of experiments and statistical modeling are used in the experimental study to understand parameter interactions. The independent process variables studied are power and welding speed. Experimental methods and results are detailed and results are discussed. The work shows that the laser and our work to date have made production of net shaped welds possible. The work could lead to new applications for very high geometry accuracy welding  

The sorghum chafer, Pachnoda interrupta Olivier

(Coleoptera: Scarabaeidae: Cetoniinae), is a key pest on

sorghum, Sorghum bicolor (L.) Moench (Poaceae), in

Ethiopia. At present there is a lack of efficient control

methods. Trapping shows promise for reduction of the pest

population, but would benefit from the development of

attractive lures. To find attractants that could be used for

control of P. interrupta, either by mass trapping or by

monitoring as part of integrated pest management, we

screened headspace collections of sorghum and the highly

attractive weed Abutilon figarianum Webb (Malvaceae) for

antennal activity using gas chromatograph-coupled electroantennographic

detection (GC-EAD). Compounds active in

GC-EAD were identified by combined gas chromatography

and mass spectrometry (GC-MS).

Abstract: Own cars are the most common mode of transport in Tripoli, Libya. About 66% of

Tripoli’s residents prefer to use their own cars and only 34% resort to depend on public transports

namely taxi, coaches and microbuses for their transportation activities in the city centre area. Rapid

increase in own cars’ usage, coupled with no public transport system have caused problems such as

acute traffic congestion, an increase in road accidents, deterioration in environmental well being and

unbalanced land use characteristics. A questionnaire survey was carried out in Tripoli to address the

first two of these problems. About 900 respondents were analysed where their needs were observed

and expectations explored. The study has found that the variables to support the use of public

transport system are the reductions in travel time, distance travelled and reasonable fares. The study

also identifies some factors that prevent the users of private cars, taxi, coaches and microbuses from

using the public transportation system, in order to enable the researcher to suggest and formulate

logical policies to support better use of public transportation system.

Key words: Own car, public transport, public transport system, Descriptive and analytical

Precoded spatial multiplexing multiple-input multiple-output (MIMO) systems using limited feedback are mainly based on the notion of delay-free feedback channels. In this paper, we take into account the time varying nature of the channel, and consider the feedback delay problem. In order to reduce performance degradation of spatial multiplexing systems in the presence of feedback delay, we propose the use of a Kalman filter linear predictor at the receiver to provide the transmitter with the predicted channel state information, and hence, mitigate the effect of feedback delay. The performance of this method is assessed using computer simulation, and the obtained results for the proposed channel prediction scheme demonstrate improved bit error rate performance for time varying Rayleigh fading channels.

Information Communication Technologies (ICTs) provide an opportunity to meet the growing needs of rural areas. Many of the key features of ICT can be used to provide information and the requirements of people in rural areas. The digital divide considered is an important problem that countries face and it is much more complex than simply building out telecommunication networks and infrastructure. The divide is the result of a wide range of social factors, including but not limited to economy factors, education, literacy. Telecommunication infrastructure alone will not guarantee that users will be able to access and take advantage of services on the network. The paper begins with an introduction to the digital divide, and thus to highlight several successful initiatives provided by educational institutions and governmental organizations in Libya in the adoption of ICT. Finally, the paper provides some of the solutions proposed to reduce this divide.