95 research outputs found
Cooperative underwater acoustic communications
This article presents a contemporary overview of underwater acoustic communication (UWAC) and investigates physical layer aspects on cooperative transmission techniques for future UWAC systems. Taking advantage of the broadcast nature of wireless transmission, cooperative communication realizes spatial diversity advantages in a distributed manner. The current literature on cooperative communication focuses on terrestrial wireless systems at radio frequencies with sporadic results on cooperative UWAC. In this article, we summarize initial results on cooperative UWAC and investigate the performance of a multicarrier cooperative UWAC considering the inherent unique characteristics of the underwater channel. Our simulation results demonstrate the superiority of cooperative UWAC systems over their point-to-point counterparts. © 1979-2012 IEEE
Multi-resampling Doppler compensation in cooperative underwater OFDM systems
We consider a multi-carrier cooperative underwater acoustic communication (UWAC) system and investigate the Doppler scaling problem arising due to the motion of different nodes. Specifically, we assume an orthogonal frequency division multiplexing (OFDM) system with amplify and forward (AF) relaying. Our channel model is built on large-scale path loss along with the short-term frequency-selective fading. For Doppler scaling compensation, we use multi-resampling (MR) receiver designs both at the relay and destination nodes. We present an extensive Monte Carlo simulation study to evaluate the error rate performance of the proposed UWAC system. In simulations, we use the publicly available VirTEX software in conjunction with the ray-tracing based BELLHOP software to precisely reflect the characteristics of an underwater geographical location and the movement of the nodes. © 2013 IEEE
Physical layer network coding based communication systems in frequency selective channels
PhD ThesisThe demand for wireless communications is growing every day which requiresmore
speed and bandwidth. In two way relay networks (TWRN), physical
layer network coding (PLNC) was proposed to double the bandwidth. A
TWRN is a system where two end users exchange data through a middle node
called the relay. The two signals are allowed to be physically added before being
broadcasted back to the end users. This system can work smoothly in flat
fading channels, but can not be applied straightforward in frequency selective
channels. In a multipath multi-tap FIR channel, the inter-symbol interference
(ISI) spreads through several symbols. In this case, the symbols at the relay
are not just an addition of the sent symbols but also some of the previous
symbols from both sides. This not only causes a traditional PLNC to fail but
also a simple one equalizer system will not solve the problem. Three main
methods have been proposed by other researchers. The OFDM based PLNC
is the simplest in terms of implementation and complexity but suffers from
the disadvantages of the OFDMlike cyclic prefix overhead and frequency offset.
The main disadvantage, however is the relatively low BER performance
because it is restricted to linear equalizers in the PLNC system. Another
approach is pre-filtering or pre-equalization. This method also has some disadvantages
like complexity, sensitivity to channel variation and the need of
a feedback channel for both end nodes. Finally, the maximum likelihood
sequence detector was also proposed but is restricted to BPSK modulation
and exponentially rising complexity are major drawbacks. The philosophy in
this work is to avoid these disadvantages by using a time domain based system.
The DFE is the equalizer of choice here because it provides a non-trivial
BER performance improvement with very little increase in complexity. In
this thesis, the problem of frequency selective channels in PLNC systems can
be solved by properly adjusting the design of the system including the DFE.
The other option is to redesign the equalizer to meet that goal. An AF DFE
system is proposed in this work that provides very low complexity especially
at the relay with little sensitivity to channel changes. A multi-antenna DNF
DFE system is also proposed here with an improved performance. Finally, a
new equalizer is designed for very low complexity and cost DNF approach
with little sacrifice of BER performance. Matlab was used for the simulations
with Monte Carlo method to verify the findings of this work through finding
the BER performance of each system. This thesis opens the door for future
improvement on the PLNC system. More research needs to be done like testing
the proposed systems in real practical implementation and also the effect
of adding channel coding to these systems.Iraqi Government, Ministry of
Higher Educatio
Multi-resampling Doppler compensation in cooperative underwater OFDM systems
We consider a multi-carrier cooperative underwater acoustic communication (UWAC) system and investigate the Doppler scaling problem arising due to the motion of different nodes. Specifically, we assume an orthogonal frequency division multiplexing (OFDM) system with amplify and forward (AF) relaying. Our channel model is built on large-scale path loss along with the short-term frequency-selective fading. For Doppler scaling compensation, we use multi-resampling (MR) receiver designs both at the relay and destination nodes. We present an extensive Monte Carlo simulation study to evaluate the error rate performance of the proposed UWAC system. In simulations, we use the publicly available VirTEX software in conjunction with the ray-tracing based BELLHOP software to precisely reflect the characteristics of an underwater geographical location and the movement of the nodes. © 2013 IEEE
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