5 research outputs found
Performance analysis of wireless relay systems
There has been phenomenal interest in applying space-time coding techniques in wireless communications in the last two decades. In general, the benefit of applying space-time codes in multiple-input, multiple-output (MIMO) wireless channels is an increase in transmission reliability or system throughput (capacity). However, such a benefit cannot be obtained in some wireless systems where size or other constraints preclude the use of multiple antennas. As such, wireless relay communications has recently been proposed as a means to provide spatial diversity in the face of this limitation. In this approach, some users or relay nodes assist the transmission of other users’ information. This dissertation contributes to the advancement of wireless relay communications by investigating the performance of various relaying signal processing methods under different practical fading environments. In particular, it examines two main relaying methods, namely decode-and-forward (DF) and amplify-and-forward (AF).
For DF, the focus is on the diversity analysis of relaying systems under various practical protocols when detection error at relays is taken into account. In order to effectively mitigate the phenomenon of error propagation, the smart relaying technique proposed by Wang et al. in [R1] is adopted. First, diversity analysis of a single-relay system under the scenario that only the relay is allowed to transmit in the second
time slot (called Protocol II) is carried out. For Nakagami and Hoyt generalized fading
channels, analytical and numerical results are provided to demonstrate that the system always obtains the maximal diversity when binary phase shift keying (BPSK) modulation is used. Second, a novel and low-complexity relaying system is proposed when smart relaying and equal gain combing (EGC) techniques are combined. In
the proposed system, the destination requires only the phases of the channel state
information in order to detect the transmitted signals. For the single-relay system with M-ary PSK modulation, it is shown that the system can achieve the maximal diversity under Nakagami and Hoyt fading channels. For the K-relay system, simulation results suggest that the maximal diversity can also be achieved. Finally, the diversity analysis for a smart relaying system under the scenario when both the source
and relay are permitted to transmit in the second time slot (referred to as Protocol I) is presented. It is shown that Protocol I can achieve the same diversity order as Protocol II for the case of 1 relay. In addition, the diversity is very robust to the quality of the feedback channel as well as the accuracy of the quantization of the power scaling implemented at the relay.
For AF, the dissertation considers a fixed-gain multiple-relay system with maximal ratio combining (MRC) detection at the destination under Nakagami fading channels. Different from the smart relaying for DF, all the channel state information is assumed to be available at the destination in order to perform MRC for any number of antennas. Upperbound and lowerbound on the system performance are then derived.
Based on the bounds, it is shown that the system can achieve the maximal diversity. Furthermore, the tightness of the upperbound is demonstrated via simulation results. With only the statistics of all the channels available at the destination, a novel power allocation (PA) is then proposed. The proposed PA shows significant performance
gain over the conventional equal PA
Selective Combining for Hybrid Cooperative Networks
In this study, we consider the selective combining in hybrid cooperative
networks (SCHCNs scheme) with one source node, one destination node and
relay nodes. In the SCHCN scheme, each relay first adaptively chooses between
amplify-and-forward protocol and decode-and-forward protocol on a per frame
basis by examining the error-detecting code result, and () relays will be selected to forward their received signals to the
destination. We first develop a signal-to-noise ratio (SNR) threshold-based
frame error rate (FER) approximation model. Then, the theoretical FER
expressions for the SCHCN scheme are derived by utilizing the proposed SNR
threshold-based FER approximation model. The analytical FER expressions are
validated through simulation results.Comment: 27 pages, 8 figures, IET Communications, 201
Performance Analysis of Hybrid Relay Selection in Cooperative Wireless Systems
The hybrid relay selection (HRS) scheme, which adaptively chooses
amplify-and-forward (AF) and decode-and-forward (DF) protocols, is very
effective to achieve robust performance in wireless networks. This paper
analyzes the frame error rate (FER) of the HRS scheme in general cooperative
wireless networks without and with utilizing error control coding at the source
node. We first develop an improved signal-to-noise ratio (SNR) threshold-based
FER approximation model. Then, we derive an analytical average FER expression
as well as an asymptotic expression at high SNR for the HRS scheme and
generalize to other relaying schemes. Simulation results are in excellent
agreement with the theoretical analysis, which validates the derived FER
expressions.Comment: IEEE Transactions on Communications, 201
Signal space cooperative communication with partial relay selection.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.Exploiting the available diversity from various sources in wireless networks is an easy way
to improve performance at the expense of additional hardware, space, complexity and/or
bandwidth. Signal space diversity (SSD) and cooperative communication are two promising
techniques that exploit the available signal space and space diversity respectively. This study
first presents symbol error rate (SER) analysis of an SSD system containing a single transmit
antenna and N receive antennas with maximal-ratio combining (MRC) reception; thereafter
it presents a simplified maximum-likelihood (ML) detection scheme for SSD systems, and
finally presents the incorporation of SSD into a distributed switch and stay combining with
partial relay selection (DSSC-PRS) system.
Performance analysis of an SSD system containing a single transmit antenna and multiple
receive antennas with MRC reception has been presented previously in the literature using the
nearest neighbour (NN) approximation to the union bound, however results were not presented
in closed form. Hence, closed form expressions are presented in this work. A new lower bound
for the SER of an SSD system is also presented which is simpler to evaluate than the union
bound/NN approximation and also simpler to use with other systems. The new lower bound is
based on the minimum Euclidean distance of a rotated constellation and is termed the minimum
distance lower bound (MDLB); it is also presented here in closed form. The presented bounds
have been validated with simulation and found to be tight under certain conditions.
The SSD scheme offers error performance and diversity benefits with the only penalty being an
increase in detector complexity. Detection is performed in the ML sense and conventionally,
all points in an M-ary quadrature amplitude modulation (M-QAM) constellation are searched
to find the transmitted symbol. Hence, a simplified detection scheme is proposed that only
searches m symbols from M after performing initial signal conditioning. The simplified
detection scheme is able to provide SER performance close to that of optimal ML detection in
systems with multiple receive antennas.
Cooperative communication systems can benefit from the error performance and diversity
gains of the spectrally efficient SSD scheme since it requires no additional hardware,
bandwidth or transmit power. Integrating SSD into a DSSC-PRS system has shown an
improvement of approximately 5dB at an SER of 10-4 with a slight decrease in spectral
efficiency at low SNR. Analysis has been performed using the newly derived MDLB and
confirmed with simulation