Abstract: Spectrum sensing is the main feature of cognitive
radio technology. Spectrum sensing gives an idea of detecting the
presence of the primary users in a licensed spectrum. In this paper we
compare the theoretical results of detection probability of different
fading environments like Rayleigh, Rician, Nakagami-m fading
channels with the simulation results using energy detection based
spectrum sensing. The numerical results are plotted as Pf Vs Pd for
different SNR values, fading parameters. It is observed that
Nakagami fading channel performance is better than other fading
channels by using energy detection in spectrum sensing. A MATLAB
simulation test bench has been implemented to know the performance
of energy detection in different fading channel environment.
Abstract: In order to better understand the performance of
screen channel liquid acquisition devices (LADs) in liquid oxygen (LOX), a computational fluid dynamics (CFD) simulation of LOX passing through a LAD screen channel was conducted. In the
simulation, the screen is taken as a 'porous jump' where the pressure
drop across the screen depends on the incoming velocity and is formulated by Δp = Av + Bv2
. The CFD simulation reveals the importance of the pressure losses due to the flow entering from
across the screen and impacting and merging with the channel flow
and the vortices in the channel to the cumulative flow resistance. In fact, both the flow resistance of flows impact and mergence and the
resistance created by vortices are much larger than the friction and dynamic pressure losses in the channel and are comparable to the
flow resistance across the screen. Therefore, these resistances in the
channel must be considered as part of the evaluation for the LAD
channel performance. For proper operation of a LAD in LOX these resistances must be less than the bubble point pressure for the screen
channel in LOX. The simulation also presents the pressure and velocity distributions within the LAD screen channel, expanding the understanding of the fluid flow characteristics within the channel.
Abstract: Power line channel is proposed as an alternative for broadband data transmission especially in developing countries like Tanzania [1]. However the channel is affected by stochastic attenuation and deep notches which can lead to the limitation of channel capacity and achievable data rate. Various studies have characterized the channel without giving exactly the maximum performance and limitation in data transfer rate may be this is due to complexity of channel modeling being used. In this paper the channel performance of medium voltage, low voltage and indoor power line channel is presented. In the investigations orthogonal frequency division multiplexing (OFDM) with phase shift keying (PSK) as carrier modulation schemes is considered, for indoor, medium and low voltage channels with typical ten branches and also Golay coding is applied for medium voltage channel. From channels, frequency response deep notches are observed in various frequencies which can lead to reduce the achievable data rate. However, is observed that data rate up to 240Mbps is realized for a signal to noise ratio of about 50dB for indoor and low voltage channels, however for medium voltage a typical link with ten branches is affected by strong multipath and coding is required for feasible broadband data transfer.
Abstract: power-line networks are promise infrastructure for
broadband services provision to end users. However, the network
performance is affected by stochastic channel changing which is due
to load impedances, number of branches and branched line lengths. It
has been proposed that multi-carrier modulations techniques such as
orthogonal frequency division multiplexing (OFDM), Multi-Carrier
Spread Spectrum (MC-SS), wavelet OFDM can be used in such
environment. This paper investigates the performance of different
indoor topologies of power-line networks that uses MC-SS
modulation scheme.It is observed that when a branch is added in the
link between sending and receiving end of an indoor channel an
average of 2.5dB power loss is found. In additional, when the branch
is added at a node an average of 1dB power loss is found.
Additionally when the terminal impedances of the branch change
from line characteristic impedance to impedance either higher or
lower values the channel performances were tremendously improved.
For example changing terminal load from characteristic impedance
(85 .) to 5 . the signal to noise ratio (SNR) required to attain the
same performances were decreased from 37dB to 24dB respectively.
Also, changing the terminal load from channel characteristic
impedance (85 .) to very higher impedance (1600 .) the SNR
required to maintain the same performances were decreased from
37dB to 23dB. The result concludes that MC-SS performs better
compared with OFDM techniques in all aspects and especially when
the channel is terminated in either higher or lower impedances.
Abstract: Power-line networks are widely used today for broadband data transmission. However, due to multipaths within the broadband power line communication (BPLC) systems owing to stochastic changes in the network load impedances, branches, etc., network or channel capacity performances are affected. This paper attempts to investigate the performance of typical medium voltage channels that uses Orthogonal Frequency Division Multiplexing (OFDM) techniques with Quadrature Amplitude Modulation (QAM) sub carriers. It has been observed that when the load impedances are different from line characteristic impedance channel performance decreases. Also as the number of branches in the link between the transmitter and receiver increases a loss of 4dB/branch is found in the signal to noise ratio (SNR). The information presented in the paper could be useful for an appropriate design of the BPLC systems.