5,134 research outputs found
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
Relaying Strategies for Cooperative Systems
In this thesis, we investigate several relaying strategies for cooperative networks with the aim of finding techniques to improve the performance of such networks. The objective here is to increase the spectral efficiency while achieving full diversity. Therefore, we focus on two-way
relaying and relay assignment since they are both efficient ways in improving the spectral efficiency of cooperative networks. Specifically,we propose efficient relay strategies to cope with the asymmetric data rates in two-way relay channels and address practical issues in relay assignment.
In the first part of the thesis, we consider two decode-and-forward (DF) relaying schemes for two-way relaying channels where the two sources may have different rate requirements.
One scheme combines hierarchical zero padding and network coding (HZPNC) at the relay. The novelty of this scheme lies in the way the two signals (that have different lengths) are network-coded at the relay. The other scheme is referred to as opportunistic user selection (OUS) where the user with a better end-to-end channel quality is given priority for transmission. We analyze both schemes where we derive closed form expressions for the end-to-end(E2E) bit error rate (BER). Since the two schemes offer a trade-off between performance and throughput, we analyze and compare both schemes in terms of channel access probability and average throughput. We show that HZPNC offers better throughput and fairness for both users, whereas OUS offers better performance. We also compare the performance of HZPNC with existing schemes including the original zero padding, nesting constellation modulation and superposition modulation. We demonstrate through examples the superiority of the proposed HZPNC scheme in terms of performance and/or reduced complexity.
In the second part of the thesis, we consider a hybrid relaying scheme for two-way relay channels. As per the proposed scheme, if the E2E signal-to-noise ratio (SNR) of both users is above a specified threshold, both sources transmit over orthogonal channels and the relay node uses hierarchical modulation and network coding to relay the combined signals to both sources in the third time slot. Otherwise, the user with the better E2E SNR transmits, while the other user remains silent. The advantage of the proposed scheme is that it compromises between throughput and reliability. That is, when both users transmit,
the throughput improves. Whereas when the better user transmits, multiuser diversity is achieved. Assuming asymmetric channels, we derive exact closed-form expressions for the E2E BER, access probability and throughput for this scheme and compare its performance to that of existing schemes. We also investigate the asymptotic performance of the proposed scheme at high SNRs where we derive the achievable diversity order of both users. We show
through analytically and simulation results that the proposed scheme improves 1) the overall
system throughput, 2) fairness between the two users, and 3) the transmission reliability. This all comes while achieving diversity two for both users, which is the maximal diversity.
In the third part of the thesis, we study relay assignment with limited feedback. In networks with many multiple source-destination pairs, it is normally diffcult for destinations to acquire the channel state information (CSI) of the entire network without feedback. To this end, we design a practical limited feedback strategy in conjunction with two relay assignment schemes, i.e., fullset selection and subset selection, which are based on maximizing
the minimum E2E SNR among all pairs. In this strategy, each destination acquires its SNR,quantizes it, and feeds it back to the relays. The relays then construct the E2E SNR table
and select the relay assignment permutation from all possible relay assignment permutations or only a subset of these permutations. We analyze the performance of these schemes over independent Rayleigh fading channels in terms of the worst E2E SNR. We derive closed-form
expressions for the E2E BER and investigate the asymptotic performance at high SNR. We show that relay assignment with quantized CSI can achieve the same first-order diversity as
that of the full CSI case, but there is a second-order diversity loss. We also demonstrate that increasing the quantization levels yields performance that is close to that of having full knowledge of the CSI
Splitting algorithm for DMT optimal cooperative MAC protocols in wireless mesh networks
A cooperative protocol for wireless mesh networks is proposed in this paper. The protocol implements both on-demand relaying and a selection of the best relay terminal so only one terminal is relaying the source message when cooperation is needed. Two additional features are also proposed. The best relay is selected with a splitting algorithm. This approach allows fast relay selection within less than three time-slots, on average. Moreover, a pre-selection of relay candidates is performed prior to the splitting algorithm. Only terminals that are able to improve the direct path are pre-selected. So efficient cooperation is now guaranteed. We prove that this approach is optimal in terms of diversity-multiplexing trade-off. The protocol has been designed in the context of Nakagami-mfading channels. Simulation results show that the performance of the splitting algorithm does not depend on channel statistics
On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff
This paper presents access protocols with optimal Diversity-Multiplexing Tradeoff (DMT) performance in the context of IEEE 802.11-based mesh networks. The protocols are characterized by two main features: on-demand cooperation and selection of the best relay terminal. The on-demand characteristic refers to the ability of a destination terminal to ask for cooperation when it fails in decoding the message transmitted by a source terminal. This approach allows maximization of the spatial multiplexing gain. The selection of the best relay terminal allows maximization of the diversity order. Hence, the optimal DMT curve is achieved with these protocols
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
Optimal Cooperative MAC Protocol with Efficient Selection of Relay Terminals
A new cooperative protocol is proposed in the context of wireless mesh networks. The protocol implements ondemand
cooperation, i.e. cooperation between a source terminal
and a destination terminal is activated only when needed. In that case, only the best relay among a set of available terminals is re-transmitting the source message to the destination terminal. This typical approach is improved using three additional features. First, a splitting algorithm is implemented to select the best relay. This ensures a fast selection process. Moreover, the duration of the selection process is now completely characterized.
Second, only terminals that improve the outage probability of the direct link are allowed to participate to the relay selection. By this means, inefficient cooperation is now avoided. Finally, the destination terminal discards the source message when it fails to decode it. This saves processing time since the destination terminal does not need to combine the replicas of the source message: the one from the source terminal and the one from the best relay. We prove that the proposed protocol achieves an optimal performance in terms of Diversity-Multiplexing Tradeoff
(DMT)
Joint Relay Selection and Power Allocation in Large-Scale MIMO Systems with Untrusted Relays and Passive Eavesdroppers
In this paper, a joint relay selection and power allocation (JRP) scheme is
proposed to enhance the physical layer security of a cooperative network, where
a multiple antennas source communicates with a single-antenna destination in
presence of untrusted relays and passive eavesdroppers (Eves). The objective is
to protect the data confidentially while concurrently relying on the untrusted
relays as potential Eves to improve both the security and reliability of the
network. To realize this objective, we consider cooperative jamming performed
by the destination while JRP scheme is implemented. With the aim of maximizing
the instantaneous secrecy rate, we derive a new closed-form solution for the
optimal power allocation and propose a simple relay selection criterion under
two scenarios of non-colluding Eves (NCE) and colluding Eves (CE). For the
proposed scheme, a new closed-form expression is derived for the ergodic
secrecy rate (ESR) and the secrecy outage probability as security metrics, and
a new closed-form expression is presented for the average symbol error rate
(SER) as a reliability measure over Rayleigh fading channels. We further
explicitly characterize the high signal-to-noise ratio slope and power offset
of the ESR to highlight the impacts of system parameters on the ESR. In
addition, we examine the diversity order of the proposed scheme to reveal the
achievable secrecy performance advantage. Finally, the secrecy and reliability
diversity-multiplexing tradeoff of the optimized network are provided.
Numerical results highlight that the ESR performance of the proposed JRP scheme
for NCE and CE cases is increased with respect to the number of untrustworthy
relays.Comment: 18 pages, 10 figures, IEEE Transactions on Information Forensics and
Security (In press
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