21 research outputs found
Differential Amplify-and-Forward Relaying in Time-Varying Rayleigh Fading Channels
This paper considers the performance of differential amplify-and-forward
(D-AF) relaying over time-varying Rayleigh fading channels. Using the
auto-regressive time-series model to characterize the time-varying nature of
the wireless channels, new weights for the maximum ratio combining (MRC) of the
received signals at the destination are proposed. Expression for the pair-wise
error probability (PEP) is provided and used to obtain an approximation of the
total average bit error probability (BEP). The obtained BEP approximation
clearly shows how the system performance depends on the auto-correlation of the
direct and the cascaded channels and an irreducible error floor exists at high
signal-to-noise ratio (SNR). Simulation results also demonstrate that, for
fast-fading channels, the new MRC weights lead to a better performance when
compared to the classical combining scheme. Our analysis is verified with
simulation results in different fading scenarios
Differential Modulation and Non-Coherent Detection in Wireless Relay Networks
The technique of cooperative communications is finding its way in the next
generations of many wireless communication applications. Due to the distributed
nature of cooperative networks, acquiring fading channels information for
coherent detection is more challenging than in the traditional point-to-point
communications. To bypass the requirement of channel information, differential
modulation together with non-coherent detection can be deployed. This thesis is
concerned with various issues related to differential modulation and
non-coherent detection in cooperative networks. Specifically, the thesis
examines the behaviour and robustness of non-coherent detection in mobile
environments (i.e., time-varying channels). The amount of channel variation is
related to the normalized Doppler shift which is a function of user's mobility.
The Doppler shift is used to distinguish between slow time-varying
(slow-fading) and rapid time-varying (fast-fading) channels. The performance of
several important relay topologies, including single-branch and multi-branch
dual-hop relaying with/without a direct link that employ amplify-and-forward
relaying and two-symbol non-coherent detection, is analyzed. For this purpose,
a time-series model is developed for characterizing the time-varying nature of
the cascaded channel encountered in amplify-and-forward relaying.Comment: PhD Dissertatio
Differential Distributed Space-Time Coding with Imperfect Synchronization
Differential distributed space-time coding (D-DSTC) has been considered to
improve both diversity and data-rate in cooperative communications in the
absence of channel information. However, conventionally, it is assumed that
relays are perfectly synchronized in the symbol level. In practice, this
assumption is easily violated due to the distributed nature of the relay
networks. This paper proposes a new differential encoding and decoding process
for D-DSTC systems with two relays. The proposed method is robust against
synchronization errors and does not require any channel information at the
destination. Moreover, the maximum possible diversity and symbol-by-symbol
decoding are attained. Simulation results are provided to show the performance
of the proposed method for various synchronization errors and the fact that our
algorithm is not sensitive to synchronization error.Comment: to appear in IEEE Globecom, 201