2,708 research outputs found
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
Relay-Induced Error Propagation Reduction for Decode-and-Forward Cooperative Communications
An attractive hybrid method of mitigating the effects of error propagation that may be imposed by the relay node (RN) on the destination node (DN) is proposed. We selected the most appropriate relay location for achieving a specific target Bit Error Ratio (BER) at the relay and signalled the RN-BER to the DN. The knowledge of this BER was then exploited by the decoder at the destination. Our simulation results show that when the BER at the RN is low, we do not have to activate the RN-BER aided decoder at the DN. However, when the RN-BER is high, significant system performance improvements may be achieved by activating the proposed RN-BER based decoding technique at the DN. For example, a power-reduction of up to about 19dB was recorded at a DN BER of 10-4
Cooperative Transmission Techniques in Wireless Communication Networks
Cooperative communication networks have received significant interests from both
academia and industry in the past decade due to its ability to provide spatial diversity
without the need of implementing multiple transmit and/or receive antennas at the
end-user terminals. These new communication networks have inspired novel ideas
and approaches to find out what and how performance improvement can be provided
with cooperative communications. The objective of this thesis is to design and analyze
various cooperative transmission techniques under the two common relaying signal
processing methods, namely decode-and-forward (DF) and amplify-and-forward
(AF).
For the DF method, the thesis focuses on providing performance improvement
by mitigating detection errors at the relay(s). In particular, the relaying action is
implemented adaptively to reduce the phenomenon of error propagation: whether or
not a relay’s decision to retransmit depends on its decision variable and a predefined
threshold. First, under the scenario that unequal error protection is employed to
transmit different information classes at the source, a relaying protocol in a singlerelay
network is proposed and its error performance is evaluated. It is shown that
by setting the optimal signal-to-noise ratio (SNR) thresholds at the relay for different
information classes, the overall error performance can be significantly improved.
Second, for multiple-relay networks, a relay selection protocol, also based on SNR
thresholds, is proposed and the optimal thresholds are also provided. Third, an
adaptive relaying protocol and a low-complexity receiver are proposed when binary
frequency-shift-keying (FSK) modulation is employed and neither the receiver nor the
transmitter knows the fading coefficients. It is demonstrated that large performance
improvements are possible when the optimal thresholds are implemented at the relays
and destination. Finally, under the scenario that there is information feedback
from the destination to the relays, a novel protocol is developed to achieve the maximum
transmission throughput over a multiple-relay network while the bit-error rate
satisfies a given constraint.
With the AF method, the thesis examines a fixed-gain multiple-relay network
in which the channels are temporally-correlated Rayleigh flat fading. Developed is
a general framework for maximum-ratio-combining detection when M-FSK modulation
is used and no channel state information is available at the destination. In
particular, an upper-bound expression on the system’s error performance is derived
and used to verify that the system achieves the maximal diversity order. Simulation
results demonstrate that the proposed scheme outperforms the existing schemes for
the multiple-relay network under consideration
Self-concatenated code design and its application in power-efficient cooperative communications
In this tutorial, we have focused on the design of binary self-concatenated coding schemes with the help of EXtrinsic Information Transfer (EXIT) charts and Union bound analysis. The design methodology of future iteratively decoded self-concatenated aided cooperative communication schemes is presented. In doing so, we will identify the most important milestones in the area of channel coding, concatenated coding schemes and cooperative communication systems till date and suggest future research directions
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